The ship dynamic test machine at the University of California

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I

THE

SHIP DYNAMIC TEST MACHINE

AT THE

UNIVERSITY OF CALIFORNIAJ

BERKELEY, CALIFORNIA

BY

WALTER M. MACLEAN

DISSERTATI ON

Submitted in _{partial SatisfaCtjon of the requirements for the degree of}

DOCTOR OF ENGINEERING

in the

GRADUATE DIVISION

of the

UNIVERSITY OF CALIFORNIA, BERKELEY

By

Walter Marcus Maclean

B.S. (University of California) 1956 M.Eng. (University of California) 1957

DISSERTATION

Submitted in partial satisfaction of the requirements for the degree of

DOCTOR OF ENGINEERING

Approved:

in the

GRADUATE DIVISION of the

UNIVERSITY OF CALIFORNIA, BERNELEY

Committee in Charge

Degree conferred

Abstract

A Ship Dynamic Test Machine has recently been constructed

and put into operation at the University of California, Berkeley,

College of Engineering, Richmond Field Station. This unique

machine was created for the study of the dynamic structural

response and water impact phenomena associated with ship slamming,

by the testing of quarter scale structural models representing

ship structure typical of forward bottoms of ships which have

experienced slamming damage. The test facility consists cf a

test machine and a specially built test tank, together with an

instrumentation van, which houses necessary machine controls and

recording equipment.

A presentation is made of the conception, design

consider-ations and limitconsider-ations, and the results of early operations o1

the test machine, together with the underlying reasons for its

creation. The general characteristics, design and operation of

each component is discussed, with the reasons for its inclusion.

Designed to generate impact pressures up to 300 psi on the flat

bottoms of models having impact velocities up to 25 feet per

second, and weighing up to about 40,000 lbs., the machine has

given evidence of the strong influence of trapped air on the

flat impact processes. Thus it has shown that the influence of

trapped air between the impacting flat surfaces may be of

funda-mental importance in determining the magnitude of impact

Table of Contents Page Abstract I Table of Contents

n

The State of Ship Slamming Knowledge ₉

Structural Problems 15

A Need For A New Experimental Facility 21

Test Facility Conception ₂₃

General Requirements 23

Scale Consideration In Structural Model Studies 30

Proposed Test Machine ₃₇

III. The Ship Dynamic Test Machine 43

A. The Test Tank 46

1. General Characteristics and Operation 46

2. Tank Design

3.

Information ₅₉

. The Test Machine ₅₉

1. General Description 59

2. Operation

70

3.

72

a. The Structural Frame ₇₃

b. The Ballast Car ₇₇

d.. The Arresting Gear

Vent Spray Suppressors 84

Weighing Link 86

4.

Installation 91

C. The Van and Instrumentation 92

IV. Initial Test Program and Early Results

Purpose ₉₇

Model ₉₇

Preliminary Tests 100

The Test Program 102

Test Procedure 104

Test Results 105

Instruments and Data 119

Model Strengthening ann ìefitting 132

Additional Tests 133

Data Evaluation 139

V. General Conclusions and Recommendations 145

Acknowledgements

l2

List of Illustrations

Figure Page

No. No.

Histograms of C2 Class Bottom Damage for

53 Vessels 4

Histograms of VC2 Class Bottom Damage for

26 Vessels _D

Total Bottom Plate Damage, C2 and VC2 Ships

Proposed Vt;rtical-Drop Test Facility for Local

Structural Response Studies, Transverse Section ₃₈

Proposed Vertical-Drop Test Facility for Local

Structural Response Studies, SiUe Elevation

_3:

The Ship Dynamic Test l\'iachine, Test Tank and.

Instrumentation Van

₄₄

Bottom-slab Reinforcing Steel L(

Placing Reinforcing Steel ₄₅

Placing More Reinforcing Steel 50

Side-wall Reinforcing Steel Almost Complete

li. Side-wall and Bcttom-slab Reinforcing Steel 52

Buttress Reinforcing Steel in Place ₅₃

Test Machine Shortly After Delivery 60

Equipment Installed on Top Platform 62

Bolt Hole Arrangement, Ballast Car Bolting Flange

Looking Through Vacuum Plate Center Access

Hole to Ballast Car Top ₆₆

Looking up at Vacuum Plate and Underside of

List of Illustrations Cont.

Figure Page

No. No.

Vacuum Plate Piping and Ballast Car Top

68

Arresting Gear Arrangement ₈₅

Vent Spray Suppressor

₈₇

Ballast Car Weighing Link Schematic

88

Flat-bottom Model for Jhlp Dynamic Test Machine 98

Peak Pressure vs Maximum Decleration 106

Peak Pressure vs Drop Height 107

Pressure Distribution Along Model Centerline 109

Peak Pressure Distribution at Section M 110

Peak Pressure Time Lead or Lag w.r.t. Time of

Peak Deceleration (Along Model Centerline)

ill

Peak Pressure Time Lead or Lag w.r.t. Time of

Peak Deceleration (Along Model Midlength) 112

Pressure Distribution Across Model Midlength During Impact (Various Times Before Maximum

Deceleration) 114

Pressure Distribution Across Model Midlength During Impact (Various Times After Maximum

Deceleration) 115

Comparison of Impact Force-Pressure vs

Acceleration Records 116

Motion Time-History During Impact 118

Initial Test Data (Location M-1P) 121

Initial Test Data (Location M-3P) 122

List of Illustrations Cont.

Figure Page

No. No.

Initial Test Data (Location M-5P)

124

Initial Test Data (Location M-ÔP) 12

Initial Test Data (Location M-7P) 126

Initial Test Data (Location M-8P) ₁₂₇

Initial Test Data (Location N1-2S) 128

Initial Test Data (Location M-24s)

129

Initial Test Data (Location M-6S)

130

Initial Test Data (Location M-8S) 131

¿44 Flat Impact - Stage 1

134

Flat Impact - Stage 2 135

Flat Impact - Stage ₃

136

Flat Impact - All Over 137

Peak Pressure vs Peak Deceleration 140

Peak Pressure vs Drop Height 141

Pressure Distribution Along Model Centerline 143

I - Introduction

For over fifty years, ship classification society

surveyors have been reporting and recommending the repair of

damaged hull structure, not ascribable to vessel grounding or

other mechanical causes, found in the forward bottom regions

of ocean-going ships, (l)*. Continuing instances of similar

damages has been the cause for convening investigating

committees and technical panels, the carrying-out of research

programs, theoretical and experimental, in model as well as

full scale, and the attempted development of empirical ship

construction rules in an effort to reduce the frequency and

severity of such damage, (2,3,4,5,6,7,8,9). On the basis of

the many reports, technical discussions and research findings,

it is generally considered that such damages result from the

large pressures generated as the ship forebody penetrates the

sea-surface, having emerged therefrom as a consequence of the

violent ship motions associated with its operations in stormy

seas. _{The phenomena associated with this ship surface}

penetra-tion of the sea-surface are generally referred to in the more

inclusive term of tiship slammingtt.

Though much effort has been expended by many competent

investigators over the past three decades or more, there is

naval architect, that will allow him to develop ship designs

which can be expected to be free of slamming generated damages

over a normal vessel lifetime, of say 20 years. Recent data

presented by Townsend, (io), indicate that approximately 1% of

the U.S. Flag dry cargo fleet sustains slamming generated

damage in the forward bottom region of the hull each month. He

further indicated that although this problem is not unique to

U.S. Flag vessels, it is considerably more severe here than

abroad; the results of a five year survey by Lloyd's Register,

covering some two-thousand vessels under their registration,

showed that only 1% of the vessels suffered severe slamming

damage requiring repair, and another 1% suffered minor damages.

Thus it may be drawn that the frequency of slamming damages

sustained abroad were but 1/60th that reported upon by Townsend

for U.S. Flag dry cargo vessels. The annual cost of these U.S.

Flag damages has been estimated by Townsend at about $1.5

Millions per year. More recent information confirms the

con-tinuing high cost of such damages, (li); over a four year

period, it was determined that, in a 390 ship U.S. Flag dry

cargo fleet, there were 199 incidences of slamming damage

repair at an average cost of $29,200 per repair, up 33% from

the earlier average cost of $21,900 per repair, (lo).

These damages are primarily incurred on the flat forward

perpendicular. More than 80% of all plating reported damaged by

Townsend, (lo), on C2 and VC2 design class ships was flat,

lack-ing in curvature or slope. Further, the data, some of which has

been plotted in Figures 1., 2.,

3.,

are sustained only by the plating in a high percentage of

cases; in only 14% of the cases of damage to C2 class vessels

was there damage to internal structure, while in the cases of

VC2 class vessels, all reported damage involved shell plating

alone. This damage has been variously referred to in the

literature at one time or another as "slamming damage",

"pound-ing damage", "heavy weather damage", "forward bottom damage",

etc., but if it is found in the forward bottom region, and is

hydro-dynamically caused rather than mechanically, it will be

considered henceforth as "slamming damage".*

While the damage resulting from ship slamming has

received considerable attention, and damage repairs are

in-dividually expensive, at an average cost of less than $4,000 per

ship-year of vessel operation, they amount to less than the

wages of one crew member. Any solution to this problem must,

* In common usage, the term "pounding" as well as "slamming" re-fers to the entry of the ship forebody into the sea, but the

connotations are slightly different. In some ship circles, the

U.K. ship-yards for instance, pounding refers to water entry of the forebody forward of 0.15L, while slamming refers to water

entry of the forebody aft of 0.lL. Stemming from

classifica-tion society rules for strengthening structure forward of 0.15L for "panting and pounding" this should otherwise cause no

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PLATE NO.

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KEEL STRAKE

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107 OF 108 FLAT

141 OF 156 FLAT

4 OF IO FLAT

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"B" STRAKE

NOTES' NO"C"STRAKE DAMAGE

REPORTED BY TOWNSEND

FIG.I

HISTOGRAMS OF C2 CLASS BOTTOM DAMAGE

FOR 58 VESSELS

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PLATE NO.°

234567

KEEL STRAKE

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"B" STRAKE

234567

'IC" STRAKE

ALL PLATES FLAT

79 0F 86 FLAT

18 0F 37 FLAT

3 0F 12 FLAT

FIG.2 HISTOGRAMS OF VC2 CLASS BOTTOM

FOR 26 VESSELS

23 4567

80

60

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20

25

30

35

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% LBP FOR VC2 CLASS (26 VESSELS)

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LBP FOR

_{C2 CLASS (58 VESSELS)}

FIG.3 TOTAL BOTTOM PLATE DAMAGE

SHIPS

40

"C"

B"

l'ci'

A" STRAKE

'A"

"A"

'B"

J

i

"A" STRAKE

(BOTH SIDES)

K" STRAKE

consequently, cost but little to effect, for in an overall view

of present shipping economics the damage repair bill is but an

irritating manifestation of the hydroelastic phenomena associated

with the reentry of the forebody as the ship plunges into the

oncoming sea. A theoretical understanding of the complex

events which take place, though diligently sought, has not yet

been found, nor does it appear likely that such will be obtained

in the near future, at least if the present level of research

activity continues.

If one could more fully assess the importance of slamming,

it surely would be found that of at least equal importance to

the cost of damages is the time delay at sea unsuccessfully

attempting to avoid the damage and the delays in port

under-going their repairs. Accompanying these delays is the general

disruption of sailing schedules and fleet operations; Townsend

estimates that average repair time is about 4-days per incident,

while delay time at sea has not yet been reliably determined.

Additional importance derives from the continuing demand for

greater sea speed. In the past fifty years, the design speed

for dry cargo vessels has approximately doubled and the next

decade may well see another increase of 20% or more. In order

to successfully satisfy this demand, new ship designs must

incorporate features which will result in greater

seakeep-ability, that elusive quality which allows ships to maintain

high incidence of slamming damage constitutes a considerable

barrier to such development, thus necessitating a solution to

this design problem. That is to say, whether empirical,

semi-rational, or otherwise, useful knowledge, in the form of design

methods if possible, must be developed which will allow the

determination of necessary scantlings such that the shipts

structure can sustain the loadings vessel operations will impose.

Questions immediately arise as to where one should start,

and in what direction should he proceed; what knowledge is

available and what new sources of information may be drawn upon.

Although the complete problem is more properly classed as

hydro-elastic, and its complete solution must include the

considera-tion of ship moconsidera-tions, the sea state, and the effects of the

structural response upon the loads generated, in the forseeable

future, such a complete consideration is overly complex. It is

only because investigators have been considering the ship

motions, hydrodynamic impact and structural response as three

distinct and separable parts of the total problem that there

has been significant progress made during the past fifteen years

in unravelling details of slamming. Unfortunately, however,

there is much yet to be done.

Investigation of the motions of a ship in a seaway is

beyond the interest here, and it will suffice to note that there

has been considerable progress during the past two decades in

presently precludes describing in any precise detall the

kinematics of a slam. On the other hand, it seems possible,

with the aid of new Irregular wave generating equipment, to

generate approximate kinematic information of sufficient validity

for our important needs.

The State of Ship Slamming Knowledge (Water Entry)

The problems associated, with water entry are not new,

having been investigated by many researchers in the U.S. and

abroad in respect to design of seaplane landing floats and

fuse-lage structures. From the work of T. von Karman, (12), H.

Wagner, (13), W.L. Mayo, (14), B. Milwitzky, (15), and others, a

body of knowledge has been established concerning the more

important aspects of fluid flow about a wedge as it penetrates a

water surface. Szebehely, an early Investigator in the expanding

field of seakeeping, tried to apply the research results obtained

for seaplane design to the problem of ship slamming, (16). Todd,

Lum, Bledsoe, (17, 18, 19), among others, investigated various

aspects of its usefulness for ship forms and certain ship motions.

Basic difficulties arose in the application of the

wedge-entry theory to normal ship forms since the theory predicted

infinite pressures over the flat bottom usually found in ship

forebodies. Additionally, the nonlinearity of the free-surface

condition, associated with the pile-up of water, created

The seaplane researchers, Wagner, et al, had assumed that the

geometry of the piled-up water had a constant relation tc the

wedge geometry, while Crane, (20), showed in his photographic

studies that this condition was definitely nonlinear. In an

attempt to partially overcome the wedge entry difficulties,

Fabula, (21), proposed the use of an ellipse fitting

approxima-tion to the real body and Ochi and Bledsoe, (22), applied what

has been called a Lewis Form fitting method to two-dimensional

drop test data for ship-like bow forms. Although Ochi and

Bledsoe found reasonable agreement between the predicted and

experimental pressures during the later stages of impact, since

the theory was developed for an incompressible fluid, infinite

pressures were predicted over the flat bottom at the instant of

impact. The theory is thus not applicable to flat-bottomed

forms since the early stages of impact, when pressures are most

severe, are most important.

Further investigation of flat bottom impact was

carried-out by Howard, (23), who compared the pressures and forces

generated at impact on two ship like forms. One model had a

flat bottom while the other had a small deadrise of about ¿4.5

degrees. The reduction in maximum peak pressures generated ihen

even small deadrise is present was clearly demonstrated, as was

also the finite magnitude of impact pressure for the case of

flat impact. Clearly, incompressible fluid wedge entry theory

impact pressures for flat bottom ship forms; a compressible

fluid theory of flat impact is needed.

Egor'ov, (2L.), attacked the problem of a rigid flat body

undergoing normal two-dimensional impact upon the surface of a

compressible fluid. Solving a Mathieu-type equation, he derived

an expression for the total force on a unit width of the

impact-ing body at the instant of impact. Though the pressure

distri-bution in space and time was not developed, on an average

pressure basis, his solution reduced to approximately acoustic

pressure at instant of impact, i.e., k1pcv, where o and y are

acoustic and impact velocities respectively, ,,o is the fluid

density and k is a coefficient determined by the body geometry

and the relative masses of the body and a characteristic volume

of the fluid.

More recently, Ogilvie, (2), has obtained a solution tc

this same problem by transforming it into the equivalent

super-sonic flow case. Also predicting acoustic pressures over the

surface at the instant of impact, pressure-time history is

pre-dicted as well as the total impulse of the impact. This

solution is a significant improvement over that of Egorov and

evaluation of the impulse yields a measure of the momentum

exchanged between the body and fluid.

Important though these solutions may be, there has not

yet been recorded slamming impact pressures of such magnitude,

known, (22, 23), or at sea where reasonable estimates of impact

velocities may be established through ship motion data, _{(3, 9,}

26, 27). Though well documented information about slamming

pressures and impact conditions is scarce at best, several full

scale tests have been conducted in which valuable information

has been collected. Of particular note in this regard are the

tests of the USCGC Casco, (28), and the follow-up test _programs

of the USCGC Unimak,

_(3,

were experienced and ship motion data were recorded as well.

During the sea tests of the Casco, the pressure gage diaphragm placed to sense bottom pressures was permanently deformed and it

was estimated that a very high pressure had been experienced

during a slam. During subsequent tests on the Unimak, severe

pressures, as high as 295 psi, were measured, bringing sharp

focus upon the pressing importance of these loads as they _were

well in excess of the usual design values.

Full scale tests in Japan, (9, 27) provide additional

data for other vessel types though these ships were not so

exten-sively instrumented as the USCGC Urìimak nor did they experience

such severe slamming pressures. The result of these tests,

however, has been to unquestionably established the significance

of slam generated pressures and the magnitude of ship motions

associated therewith. Unfortunately, because of the complex and

random nature of the sea surface and the resultant ship motions,

such a way as to define the specific kinematics of the slam

incidences recorded. Thus, even were an accurate and laboratory

verified compressible-fluid theory of impact available, there

would not be adequate full scale information for use in its

confirmation.

Other attempts to theoretically explain the slamming

pressures and flow about impacting bodies have been made in

which consideration has been given to the deformability of the

structure. In view of the complexity of typical ship and even

aircraft structure (i.e. seaplanes in this case), it has been

necessary to simplify the assumed structural response. _Among

others, Sydow, (29), considered structural flexibility with

respect to seaplane structure and more recently, Meyerhoff,

(30), has completed an interesting analysis and computed

pressure-time histories at several locations on the impacting body. In

both of these cases, Vee-wedge impact has been considered and

the fluid was assumed to be incompressible. _{Meyerhoff found that}

the peak pressure of the impact was considerably decayed before

the influence of structural flexibility became noticable in the

pressure-time history; this effect appeared to be of second order

Importance for the cases studied.

Giddings, (31), also considered flexibility in the

impact-ing body, treatimpact-ing the case of flat impact upon a compressible

fluid. Allowing his body to be represented by a simply-supported

fundamental mode of dynamic response. The initial conditions for

his investigation were the same as for the work of Egorov, (24),

and Ogllvie, (25), i.e., the body was assumed to be initially at

rest at the free-surface of the fluid and then at time to plus,

lt was given an impulsive change in velocity to y0. _Giddings

concluded that the duration of the compressive phase of the

fluid flow led to impact pressures of such short duration that,

In so far as the structural plate was concerned, "the compressive

phase of impact can be ignored." The validity of this finding

remains unverified.

Thus it seems clear that the present state of knowledge

concerning water entry phenomena does not allow the reliable

determination of needed information about the structural

load-ings, pressure-time or force-time, generated on typical ship

forward bottom surfaces while experiencing a "slam". _{At the}

same time, it Is also clear that an adequate description of the

fluid flow phenomena associated with slamming is lacking.

Pictorially, the information available Is limited to that

ob-tained during the Dutch Destroyer seakeeping trials reported by

Warnsinck, (32), and some individual photographs occasionally

obtained, such as the frontspiece used by Lewis, _{(33). Personal}

experience of the writer suggests that photographic capture of a

slam is difficult at best, requiring the use of much film with

the photographing platform close alongside the slamming ship,

In the laboratory, valuable information has _{been obtained}

by studies such as those of Crane, (20), _{or unpublished}

high-speed movies taken by 1CM. Ochi and his staff. _{However, the}

small scale of this laboratory work, with _{the increased}

import-ance of surface tension and other effects, makes the

interpreta-tion of the events photographed difficult. _{Larger scale studies}

are badly needed, preferably under carefully controlled

condi-tions so that the fluid flow phenomena during _{impact can be}

viewed in a more realistic frame, unclouded by _{the unknown scale}

effects, and so that a better basis can be established _{for the}

development of an impact theory.

Structural Problems

Given a satisfactory theory of flat rigid-body _impact

upon a compressible fluid, the structural problems associated

with slamming could not yet be dismissed. _{Thus far, but little}

has beer) done toward relating the response of ship _{structure to}

dynamically applied loads, particularly in regard _{to slamming}

loads. The surface pressures, acting upon the shell plating,

transfer their loads Into the supporting floors _{and longitudinals}

and thence into the hull girder by way of frame and _bulkhead

connections. Under dynamic loading conditions, the various

elements of structure absorb and redistribute the applied loads

in complex fashion, a function of the relative geometries of _the

transmitted in the end to the hull girder, as some part is

dis-sipated locally in the plates and stiffeners either by damping of

the dynamic response or all too often by energy dissipation in

plastic flow. Further, slamming loads, being transient in

nature, are not associated with a build-up of energy such as

caused by steady-state excitation by propellers or ship's

machinery. During the past fifteen years, serious attempts have

been made toward understanding these transient problems.

Just as for the treatment of the total slamming problem,

where an analysis of the total situation is too complex, so also

is the structural response. Such progress as has been made is

due in large part to assuming that the total response may be

decomposed into separable responses of the structural subsystems.

In this way, it has been analysed as hull girder response,

stiff-ened plating response and plate response. A large body of

litera-ture is presently available from efforts to determine the dynamic

characteristics of these structural systems, and much can be

de-termined in this regard for more general types of loading. In

the case of slamming loads, however, where rather sharply applied

transients must be treated, much has yet to be done.

Greenspon, (34), has set down the linearized theory

avail-able for use in predicting the response of plating to dynamic

loads such as slamming, and he has applied this theory to data

obtained during the Unimak tests, (26). His investigation showed

however, none of the severe loadings were Investigated _{arid his}

general conclusions leave much to be desired. _{It Is particularly}

the severe loadings which are of concern, since they _are

associ-ated with the damages experienced by operating ships. _Further,

it is not yet possible to reliably predict the load carrying

capacity of plates subjected to slam type loadings. _{It is known}

that normal steel displays strain rate effects upon yield stress

when subjected to high rates of loading. _{Additional uncertainty}

rests in the approximate solutions to the plate equations, as

the local nature of the slam load makes the determination of

correct plate boundary conditions difficult. No experiments In

this area are known to the author, and a careful study is needed.

Shell plating support structure Is, as previously noted,

only infrequently damaged by slamming, however, In cases of

severe slamming damage, floors, longitudinals and bulkheads have

all been involved. In these cases, failure of the supporting

structure often occurs in the form of local instability, perhaps

dynamic instability. Thus far no known ship structures research

has been initiated in this area. Pending the development of

design and construction methods which result in the limiting of

plating damage, the support structure will, of necessity, have

to be capable of withstanding these severe loads without failure.

It seems obvious that, should this not be so, a difficult arid

expensive repair situation would obtain whenever severe slamming

example of this situation has come to _{pass in an experiment}

which was conducted on an operating vessel.

A C2 class vessel, which had experienced _{slamming damage,}

was to be repaired while in drydock. _{It was decided that a}

special high strength steel would be used to repair _{half of the}

damage, i.e., that which was on but one side of the _{ship, while}

the usual grade of steel plate was to be used to _{repair the}

re-maining portion of the damage. _{After normal service in the}

North Atlantic for approximately one year, i.e., between _normal

drydocking periods, inspection of the forebottom revealed _that

the high strength steel plating was indeed undamaged, while _the

usual grade of steel plating was damaged. Further inspection,

however, revealed that though the high strength steel plating

was undamaged, the support structure had been badly disturbed

and required repair. In order to effect these repairs, the

un-damaged plating had to be removed. Under these circumstances,

it seems clear that a more complete understanding of the total

problem is needed before one can have confidence in proposed

design schemes.

The structure typically found in the double bottoms of

the forebody consists of plate floors with large lightening

holes which Intersect with longitudinal members. The

longitu-dinals may be inverted angle bars on the innerbottom and shell,

or of plate with large lightening holes, Just as the floors.

are distributed in quite complex patterns. _{No inve3tigations of}

such situations are known to this writer, and thus far, no

rational procedures are available for the design of such

dynami-cally loaded structure. Should rational design methods be

pro-posed, experimental confirmation will be needed before they can

be considered satisfactory. Further, the manner in which these

structural elements distribute the loads into the side frames and

bulkheads needs to be known, as this has an important bearing

upon the response of the hull girder.

Analytical work in the area of stiffened plate response to

slam type loadings has been carried out by Nagal, (35), among

others, who treated a combined plate element and stiffened plate

structure. Divorced as it was from any real situation,

evalua-tion of his findings is difficult. Had this work been tied to an

experimental investigation, the value of the results would have

been greatly enhanced; the absence of a suitable test facility,

however, prevented such a possibility.

Up to this time, the experimental investigation of slamming

using structural models has been quite limited. Most notable, is

the work of Ochi, (36), who used brass models, 6 meters in length,

to study slamming generated pressures on the forebody and stresses

in the hull girder. The scale of the structure, because of the

obvious limitations thereon, was too small to be of value in

respect to the forward bottom damage problem. For structural

usefulness. On the other hand, full scale work such as that

reported by Du Cane, (37), on a high speed motor launch doesn't

provide the necessary information either, since these craft are

designed along the lines of seaplane hulls, with sharp

Vee-sections in the forebody. Much work on seaplane hulls has been

carried out under N.A .0 .A. research programs.

More recently, large scale slamming studies have been

carried out with structural models by Clevenger and Melberg,

and Goodwin and Kime, (39), in a vertical drop test

facil-ity. This facility was constructed at the Norfolk Naval Shipyard

and fitted to the end of a barge. Unfortunately, there is no

control over the flow during model impact, and though Vee-Section

models were tested, considerable discrepancies were found between

theoretical predictions and experimental measurements of

pressures. The structural responses, i.e., displacements and

stresses, measured were not correlated with any available theory;

when permanent set of plates was noted, its occurrence was found

to be random.

These investigators tested their models under conditions

that produced large permanent deformation not only in the

plat-ing, but in the stiffening elements as well. Goodwin and Kime,

tried to correlate some of their permanent set data with

the theory proposed by Nagal, (140), who used a traveling hinge

concept for rigid-plastic deformation of a plate. The results

with the theory. However, their work does not constitute _{a fair}

test of the theory since Nagai's theory assumed flat _{impact of a}

long clamped plate, conditions definitely not _{met in these}

experiments.

Other work in the field of impact loading of _{structure has}

been carried out by those involved in underwater _explosion

re-search such as that reported by Keil, (41), and those _attempting

to produce and explain large dynamic and permanent _deformations

in structures such as that reported by Witmer, Clark _{and Balmer,}

(142); both of these _{papers present extensive references to}

rela-ted work. These investigators have, in many cases, resorted _to

the use of large or full scale models in their structural

re-search, costly though it has often been. _{There has been ample}

Justification, however, because of difficulties _{in scaling in}

some cases, and because of the need to realistically recreate

phenomena under controlled conditions _{so as to allow close study}

of events and the development of adequate _{understanding thereof.}

A Need For A New Experimental Facility

Faced with an inadequate impact theory and _poor

under-standing of the fluid flow, as well _{as unconfirmed theories of}

structural response, a solution to the problem _{of slamming}

damage is still not in sight. _{This was also recognized several}

years ago by Lewis and Gerard, (43), who recommended the

theories where these have been proposed", and to "obtain useful

design data In those cases where no theory is available". _These

recommendations led to the establishment of a research _program

in ship slamming under Ship Structure Committee* sponsorship.

Although initial effort was directed toward the hull girder

re-sponse aspect of the slamming problem, it soon became apparent

that only meagre Information was available on the nature of the

loads a ship experiences in a slam and the manner in which these

loads are transmitted to the hull girder. Because of this, and

the fact that the primary economic interest in slamming is

associated with the damages sustained by the local structure in

the forward bottom regions, attention was turned to the

establish-ment of an experiestablish-mental investigation of local structural response

to slam loads. The first consideration in establishing such _an

investigation is the determination and procurement of suitable

test facilities. As no test facilities existed which could be

used for impacting, under controlled simulated slamming conditions,

structural models of typical ship forebodies, it was necessary to

conceive, design, construct and put into operation a suitable

test machine for use in the intended investigation. _{It is this}

development which is the topic in the following.

* The Ship Structure Committee is a five member, interagency, committee with members representing the U.S. Navy Ship Systems Command (formerly the Bureau of Ships), the U.S. Department of Commerce Maritime Administration, the U.S. Treasury Department U.S. Coast Guard, the U.S. Navy Military Sea Transportation Service, and the American Bureau of Shipping.

II - Test Facility Conception

General Requirements

A test facility, suitable for the study of local

struc-tural response to slam type loadings, must first satisfy several

basic requirements. Most important is that of reliability, i.e.

the ability to generate the event on demand with a high degree

of reproducibility. The machine should be capable of testing

realistically scaled models, being readily instrumented with

the normally available sensors and recording equipment and

being capable of generating realistic loadings which have the

general nature of the full scale phenomena, at least within the

usual limitations of laboratory capability. In order to enhance

its more general usefulness, it must be so contrived that it can

be readily possible to vary effective model mass and impact

velocity. Further, since slamming is a hydroelastic phenomena,

the test facility should provide not only for the study of

structural response, but the fluid flow as well. _{An additional}

requirement may also be imposed because of the semi-permanent

nature of the machine. That is, the device should be compatible

with adjacent laboratory facilities if at all pcssible.

With respect to reliability, no relaxation of standard

can be allowed. In this case, but little is known of the

events to be created and it may be necessary to repeat _{a test}

event or correlated observation of related events. _Reliability

is thus almost synonimous with reproducibility, which _requires

careful control, and although rational design criteria _are

elusive, this should be a prime consideration in _{all aspects of}

the design. Further, as simplicity usually facilitates

reliability, the machine should reflect maximum simplicity _of

concept and design consistent with adequate control of impact

conditions, and thus their reproducibility. _{More detailed}

requirements must rest upon specific conditions.

In the absence of a proven theory of flat impact, one

must turn to the literature in search of useful facts. _Although

but limited information is available on the conditions leading

to the generation of severe slamming loads, the Unimak tests,

(3), provide an adequate starting point. During these tests,

the ship steamed at about 14 knots into heavy seas while

experiencing severe slamming. Pressures and stresses were

re-corded under similar conditions. Significant wave heights of

the sea were estimated and the recording of vessel heaving

motions provide other valuable information as to the character

of the sea.

In evaluating this information, particular interest is

directed toward the following:

1. Flow conditions are clearly important in the

genera-tion of a realistic slam, but how important is the

a two-dimensional approximation?

Impact velocities have a direct bearing upon the

pressures generated. What are realistic impact

velocities?

Given a range of impact velocities, what are the

associated pressures the facility must withstand?

What should be the attitude of the striking surfaces

just at impact, and how closely should they be

controlled?

How far will the structure penetrate the water

sur-face before the phenomena are no longer of interest?

How long a section of structure must be modeled in

order to insure representative conditions at the

test section?

There may, of course, be many other pertinent questions

to be asked of the literature, however, for the purpose at hand,

these appear to be the more important. It must be recognized

here that specific information is quite limited, and one's

evaluation of the facts may be determined to some extent by the

preconceived notions of the evaluator.

The flow conditions in a real slam are clearly

three-dimensional, however, realistic recreation of such conditions in

a test facility presents considerable difficulties. Either the

scale must be small making the models virtually worthless for

the work would be excessive, making lt difficult to obtain the

needed support. Since the slope of the waterlines forward is

generally small, being usually about 10 degrees or less, the

primary flow is in the transverse direction, departing but

slightly therefrom. It would appear then that two-dimensional

flow conditions can be utilized in the facility without

depart-ing too greatly from reality. Further, the use of

two-dimen-sional flow conditions will enhance the possibility of

theoreti-cally explaining the experimental events, certainly a desirable

prospect.

By considering the pitching motion of the Unimak, the

ships forward velocity and the reported estimated wave heights,

it is possible to deduce approximate impact velocities at the

location of the Uriimak test section forward. For pitching

motions in which slams were generated, impact velocities were

estimated to be in the range of 12-19 feet per second. _Since

this was measured on a 300 foot long vessel,

might be expected to have velocities in the range of 18 to 30

feet per second, that is for ships of about 450 feet In length.

Since there is no full scale information which relates the

impact velocity to the generated pressure, one can only estimate

that these velocities will be associated with the high _pressures.

The selection of a 25 fps impact velocity as a maximum should be

quite reasonable, as It would result from a 10 foot vertical

Since the maximum pressure thus far recorded in _{a slam}

is 295 psi, setting a limit of 300 psi, separately _{from any}

consideration of associated impact velocity, _{should provide a}

realistic maximum load. Thus, because of inadequate knowledge,

arbitrariness must be substituted, and the facility _{would have}

two limits to its maximum capability. _{These limits are both}

reasonable and feasible.

It has previously been determined that the _{slam loadings}

of interest are those resulting from the impacting _{of a flat}

surface upon the water surface. _{Just how closely the flatness}

of model impact must be controlled, however, is not _{known. It}

is appreciated that the ocean surface has _{many irregularities}

which might play an important part in determining the

serious-ness of a particular slam, but Unimak data indicate that in a

severe slam almost instantaneous generation of pressure takes

place over the bottom surface. _{Thus, either the surface}

irregularities are smoothed-out by the action of the high

velocity air escaping from between the two surfaces, _{or the}

influence of these irregularities is of such local importance

that their over-all effect is negligible. _{Additionally, the}

work by Howard, (23), shows that even small angles of incidence

between the impacting surfaces result in drastic reduction of

the peak pressures generated; even half a degree may cause as

much as 10% reduction in peak pressure. At 25 fps, each

the elevation variation of a 6-foot wide flat surface with a

degree slope. It is thus apparent that close control must be

attained in order to be able to generate maximum loadings. _The

model motion thus must be constrained to a given path, and its

method of attachment to the machine must allow for its proper

alignment.

Full scale data on slamming pressures show that the

significant duration of the loading varies from about ₁₅ to 50

milliseconds. In general, the more severe the slam, the shorter

the duration of the pulse; 20 ms Is a reasonable duration for a

severe loading such as 300 psi peak pressure. This of course

could be expected to vary with ship size, but the data available

are as yet so limited as to make further speculation meaningless.

Since time in the fluid scales linearly, the expected duration

may be estimated within reasonable limits. This scaling

approx-Imately agrees with Howard's findings, (23).

There is some question as to how much of the forebody

must be modeled for a realistic study. If 25 fps is a

reason-able impact velocity, and the pressure pulse generated is thereby

severe, each millisecond will correspond to a model travel of

about 0.3 inches. In 20 ms then, the ship forebody will

pene-trate the water surface but 6 inches, (1.5 inches in quarter

scale models) thus only the lower foot or two of hull form need

be modeled in an accurate way. The actual models may therefore

might be a part of the test machine.

The length of ship to be modeled, however, is not _yet

determined. Other data must be drawn in for that decision.

The data on the Unimak includes the pressures simultaneously

recorded at several locations along the shipts keel. _These

records show that even as close as 10 feet from the section

where maximum pressures were recorded, the measured disturbance

was negligible, indicating thereby the local nature of slam

generation. Further confirmation of this aspect is found in the

Townsend data, (io), and special reports received from the

American Bureau of 1hipping and the U.S. Maritime Administration

surveyors. These data indicate that the damage may extend over

only a 25 to 30 foot length of bottom, though, because of

multiple slams, this is frequently extended to twice this

length or more. This would indicate that quarter scale models

for instance should be about 6 to 8 feet in length. In so far

as the chosen length effects the structural response of

mid-length structure, quarter scale models 8 feet long would

represent about 6-frame isolation from any unnatural boundary

conditions at the model ends. Model length would, however, have

a controlling influence upon the structural response of the

model as a whole, but at least initially, it is the plating and

Scale Consideration In Structural Model Studies

In the discussion above, there has been no need to settle

on a particular model scale for the proposed test machine.

Before doing so, careful consideration must be given to _{some of}

the factors associated with the use of scaled structural models

in a slamming investigation. Among the many factors which appear

to be of primary Importance in this regard are the following:

Time scale, in the water and in the model

Mass scaling in the model

Limitations of model size and fabrication problems

Structural response

Material properties and scaling of damage

Influence of model scale on instrumentation

requirements

The time scale of events in a slam is a function of body

geometry and impact velocity, or at least the experimental data

to date so Indicate. With equal impact velocities in the model

and prototype, and a constant acoustic velocity In the fluid

(water and/or air), the time in the model will be related to

that in the prototype by the model scale factor. Heller, (44),

has shown that time in geometrically scaled structural models

Is also directly related by the model scale factor. Thus,

there is compatibility of time scale in structural model studies

of slamming, and no distortion of the time-history of events is

In order to properly scale momentum exchange the mass

density of model and prototype must be the same, thus mass is

scaled by the scale factor cubed. Unimak data reveals that in

a particular slam in which peak pressures of 200 psi were

recorded, peak acceleration was but ₅ g, indicating an apparent

ship mass of about 40 lbs weight per square inch of _surface.

Reduced to a model scale of 1/4 th, this would result in _a

re-quired apparent model mass of about 10 lbs. weight _{per square}

inch of surface. For a model which is 8 feet long and has 6

feet of flat width, this would require a weight of about 69,00)

lbs. This is too much weight to handle with convenience, _and

results from the fact that in the rull scale impact the high

pressure is acting on a small area of a large body, thus

apply-ing too small a total force to cause large accelerations of the

whole body.

This is not

except by using whole-ship models.

The alternative to such large weight is either reduced

apparent mass below the scaled value or use cf a smaller _model

scale. As pointed cut earlier, small scale structural _models

are of but limited value

in

Generally, structural models become unrealistic if they _{are of}

less than 1/10th scale in size. _{Considering the complexity of}

typical forward bottom structure, 1/6th scale becomes a

practical limit, and even here, the )4-" frame spacing

cramped spaces for instrumentation installation, especially

the likes of available pressure transducers of suitable _range.

A more reasonable scale would be 1/4th size which allows ₆

_to

9 inch frame spacing typically and permits model fabrication

from

1/8"

1/8"

Though the construction of models from materials of such

thick-ness is of some difficulty, fair to good models can be produced

with the application of reasonable care and workmanship.

Before a reduction can be allowed in the apparent model

mass, it is necessary to consider the effect such a departure

from true scaling would have on the experimental results.

Initially, the interest is on plate response and _{a reduced model}

mass would result in altered plate response as well as generated

pressures. Howard's work, (23), showed that the effect of mass

upon the pressures generated was of second order Importance

when compared to that of the impact velocity. The ratio of peak

pressures appears to vary as the cube root of the mass ratio.

Thus, a 0% reduction of model mass would produce about a 20%

reduction in peak pressure. If such a relationship can be

con-firmed, it would not be too disadvantageous to have a reduced

model mass, since the effect of reduction could be determined

by systematic variation of this parameter.

The effect of reduced model mass on the response of the

plate panels results from reduced pressure loading and increased

effects is facilitated by considering the plate equation as written below. 2 4 UJL.

+1Ûh

=

_h

/

_t2

In this equation, WI is the plate deflection with respect _{to its}

boundaries, and Wb is the plate boundary deflection with _respect

to some fixed coordinate system, I.e., fixed tn _{space, or with}

respect to a non-accelerating body. The other symbols are as

conventionally defined for linear plate theory, see Greenspon,

(34), for Instance. It Is easily seen that the acceleration of

the plate boundaries resulting from the applied loading acts _to

reduce the effect of the applied loading on the plate. _{As the}

effective mass is decreased, not only is the pressure reduced,

but there is greater acceleration of the boundaries and

effect-ively greater reduction of the applied pressure. On the basis of

Unimak data for a 200 psi peak pressure and _{a 5g acceleration of}

the boundaries, this effect is about 1/2% of P

max. Properly

scaled model mass should therefore result in only second order

effects upon plate response. _{In the case of a 50%, or even a}

75% reduction of apparent model mass, this effect should _still

be of second order Importance, 2% or less, and the primary

effect would be that of peak pressure reduction.

The scaling of structural response in geometrically

similar structures presents no special problems, since _the

dynamic response characteristics scale linearly and _{the ratio}

seen from the following considerations. _{Frankland, (45), has}

shown that the dynamic response of a structure to _{an impulsive}

load depends on the ratio of the time characteristic _{of the}

load to that of the structural mode of response, and the

particular characteristics of the time-history of _{loading. Since}

the time scale in the water and in the structure maintain _the

same relationship under geometric scaling, and there is _no

dis-tortion of the time-history of events, the nature of _{the response}

does not change. _{Further, the stress at a point in the plating}

can be expressed by the equation

(2)

where k is some constant of the structural configuration and the

response mode, P, is the load parameter, and (a/h) is the

width-thickness ratio of the plate. _{It is obvious that equal pressures}

in the model and prototype generate equal stresses.

If one wishes to study structural response in the plastic

or post yield regime, the above simple situation no longer holds,

since for this, the stress-strain curves for the model and

pro-totype materials must be the same as well. One might at first

think that this would be the case, however, the rate of strain

has an important effect upon the dynamic yield point of structural

steel. Since, for the same stress in model and prototype, the

strain rate varies inversely with the geometric scale, yield

will be reached in the model after it would in the prototype.

magnitude of this effect, it is not now possible to reliably

predict the prototype damage from model studies. It is hoped

that further work in this area will allow such prediction,

perhaps by using a series of models of different scales, _say

1/6th, 1/5th, 1/4th, and 1/3rd, to arrive _{at expected}

proto-type damage.

No final determination of model scale can be made _without

first giving consideration to scale effects on instrumentation

requirements. Instrumentation suitable for use with a test

facility must reflect the added demands of the model scale.

Whereas the range of pressures and impact velocities will be

the same as for the prototype, the time scale will be linearly

shortened with model scale, thus requiring the _{use of}

instru-ments having higher frequency response characteristics. _During

the tests of the Unimak, the instrumentation was capable of

recording data up to 500 cps. For these tests and the

measure-ments taken, this capability was marginally successful. _If

quarter scale studies were to be made of Unimak structure,

instruments would need a 2,000 cps capability in order _{to insure}

similar results, and the 50 inch recording speed used _{then would}

have to be replaced by 200 ips capability in order to _{obtain the}

same signal definition. Looking closer at this problem, it is

seen that even the above substitutions would be inadequate if

detailed analysis of experimental results is desired. _{As an}

Typical forward bottom plating on modern _{cargo vessels}

is about

_0.815

42 inch floor and longitudinal spacings. _{The first symmetrical}

mode of dynamic response has a frequency of _{about 250 cps while}

the second and third symmetrical modes have _{frequencies of}

₆₅₀

and 1100 cps respectively. _{Even in full scale, a recorder with}

500

contribution only and one would never be able _{to determine}

whether the higher mode contributions were present to _{the degree}

predicted or not, since the equipment would be incapable _of

properly recording these contributions. _{In the model, this}

problem is magnified by the scale factor, and it _{can thus be}

appreciated that a 5 kc recording capability would constitute _a

minimum requirement for suitable instrumentation at quarter

scaling.

Additionally, to facilitate data evaluation, time scale

expansion is needed. At recording paper speeds of 50 inches per

second, one cycle of 1,000 cps data is recorded _{on 0.050 inches,}

a signal barely readable, much less suitable for analysis. _A

time scale expansion of at least one order of magnitude beyond

the above is a needed minimum. A 10 kc recording capability

coupled with a 1 inch per millisecond time scale would

Proposed Test achine

On the basis of the above evaluations and considerations,

a vertical-drop test machine for testing approximately quarter

scale structural models was proposed. Sketches of the proposed

machine are presented in Figures 4 and

_5,

arrangement and pertinent features of the various components.

This design would allow the generation of impact velocities from

O-25 fps with the structural model attached to a car which is

constrained to a vertical path. A nominal weight of 30,000

lbs. is provided for with about 9,000 lbs. variation plus or

minus. The machine would be mounted over a reinforced concrete

tank specially designed to withstand the impact generated

pressures. The changing of drop height or weight can be

accom-plished without disturbing the model, and the machine operation,

from the starting of the fall to the final arrest after the

impact, is either remotely or automatically under control.

It should be noted that a water depth of 10 feet is

indicated and yet no discussion of this aspect of the requirements

has been given. This is due to the fact that thus far there is

no rational base for doing so. There is a rule of thumb, however,

in model tank work which requires that water depth be at least

equal to the largest dimension of the model to be tested. There

seemingly is no rationale behind this rule other than that

investigators have been generally satisfied with results obtained

E9LJ

I

LO N G

RRESTED

HOISTING WINCH

VACUUM PLATE ADJUST

GEAR

RAISED

r.

NP05ITN,/

I

BLLAST

Hc

-8tOhI WIDE

N

VACUUM

TANK

ARRESTING

PISTON

GUIDE

BEAR! NG

GUIDE RAIL

ARRESTI NG

CYLINDER

HOUSING

15' WINDOW

SECTION

SCALE:

TRANSVERSE

SECTION

FIG.4

_{PROPOSED VERTICAL-DROP TEST FACILITY}

VACUUM

PLATE

HOISTING WINCH

/

VACUUM PLATE ADJUST

GEAR

-\

/ Lji

I

III

--

-i-15 WINDOW

SECTION

I

VACUUM

TANK

ARRESTI NG

PISTON

SCALE:

l'-O

SIDE ELEVATION

FIG. 5

_{PROPOSED VERTICAL- DROP TEST FACILITY FOR}

LOCAL STRUCTURAL RESPONSE STUDIES

ARRESTING

dimension, however, is the delay time for a shock wave, eminating

from a surface disturbance, to be reflected from the tank bottom

and be sensed on the model body. With a 10 foot water depth,

the delay time would be

4.5

pulse until after the significant events have passed.

Attenua-tion of the pulse would also take place in accordance with the

(b/d)2 relation for two-dimensional flow, so that the returned pulse would be relatively small as well, i.e., about 1/4th.

This scheme was proposed over several others investigated

including a simple boom-mounted model, and parallelogram guidance

structure scheme, because of the difficulty the other schemes

imposed upon control of fluid flow, development of uniform _impact

velocity over the model bottom surface and the difficulty of

establishing and maintaining proper model alignment. _The

pro-posed design seems to most closely meet all of the basic

require-ments including the primary requirerequire-ments for simplicity, control

and reproducibility.

Both steel and reinforced concrete construction of the

test tank were investigated for design and construction problems

as well as cost. There appeared to be little cost advantage to

either construction material, and reinforced concrete _{was chosen}

on the basis of greater dynamic damping ability as it was feared

that the steel members, possessing low structural damping, could

Induce pressure "noise" Into the fluid and this would cause

In order to make possible the study of fluid _{flow during}

impact, a long window section is provided for. _{This window will}

of course be subjected to full impact pressure over its lower

two-thirds, in way of the test model and its _{design will thus}

present special problems.

It has been proposed that the hoisting winch _{be placed in}

the elevated position so as to subject the _{corner columns to as}

simple a load system as possible. _{The girder holding the}

arrest-ing cylinders will also apply compressive loads to _{the lower}

portion of the corner columns. _{The tank structure supporting}

these corner columns would be simple buttresses _{symmetrically}

spaced about the tank midlength.

The 8-foot tank width was chosen _{so as to make this tank}

compatible with the existing ship model tank should _{the two}

ever be joined to make a single structure. _{The length of the}

test tank was chosen to be fifty feet at full depth, _{but not}

less than thirty should there be a restriction on its cost. of

This length was set on the basis/extreme model emersion

require-ments as a minimum (30') with a 100% _{excess (50'). That is,}

with the maximum model fully arrested at two feet _{below the}

still water level, a 30-foot tank length would be _{necessary to}

prevent an overflow; because of the dynamic flow during impact,

the 50-loot length gives twice this excess fluid volume.

At the time of this proposal, there was not in exIstence

of local ship structural elements to dynamic loadings of the

type associated with ship slamming. _{In order to carry out the}

planned program of ship structural research at the University _of

California, Berkeley, the construction of such _{a facility was}

necessary. This proposal was made in an attempt to provide _such

a test machine, suitable for the intended work and yet retaining

basic simplicity in concept and operation. _{Acceptance of this}

proposal was followed by completion of its design, construction

and initial operation by the author, all of which will be

III - The Ship Dynamic Test Machine

The Ship Dynamic Test Machine, illustrated in _{Figure 6,}

has been built and put into operation at the _{University of}

California, Berkeley. This machine has been installed _over

the test section of a new tank, which was specially _{designed and}

built for this use, located at the College of Engineering _Field

Station, Richmond, California. _{The tank has been built as a}

part of the research facilities of the Department _{of Naval}

Architecture, and is situated some 155 Ft. to the _{south of}

Bldg. 275, the Department of Naval Architecture _{Ship Model}

Towing Channel.

The machine was designed and built for use in the study

of the local structural response of ship forward bottom

struc-ture subjected to water impact loading such as in the case of

ship slamming. When in normal use, approximately quarter-scale

structural models, having the form and scaled scantlings typical

of slamming damaged bottom structure, will be tested under

two-dimensionally simulated slamming impact conditions.

Addition-ally, the machine has been designed to allow the study, on a

relatively large scale, of the fluid flow phenomena of

two-dimensional water entry.

The test facility, pictured in Figure

6.

three main parts: the test machine, the test tank, and the

the mid-length of the test tank, while the instrumentation _and

control van, seen at the lower right of the figure, is _{on the}

west side of the tank, just to the south of the tank's test

section. The van contains most of the main controls of the

machine, as well as the instrumentation used in its operation.

Utilities available at the test site include electric'

and fresh water services. The electric service provides 40 Amps.

of 440 Volt, three-phase power, and

60

Amps. of 110 Volt, single-phase power, while the water service

is at approximately 65 psi on a 2-inch main. The electrical

services are brought to the power pole seen at the right of

Figure

6,

corner of the test tank, i.e., in the center-rear of Figure

6.

Designed and built in general accordance with the

pro-posal and design considerations presented in the foregoing, it

was first operated with water in the tnk and the rirst model

fitted on 15 May, 1964. Since that time it has gone through an

initial "shake-down" period using increasing test weights and

impact velocities in a systematic program, planned to insure

that the test tank can adequately sustain the loads generated by

the machine. During this initial phase, valuable information

has been developed concerning the impact process as well as the

capabilities of the machine. These findings will be discussed

later, after first describing the facility, its design and