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DAVID W. TAYLOR NAVAL SHIP
RESEARCH AND DEVELOPMENT CENTER
Bethesda,Md.
20084
PREDICTION OF EXTREME AMMUNITION CARGO FORCES AT SEA
by
A. Erich Baltis
S. L. Bales
W. R. McCreight
V. G. Meyers
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AVIATION AND
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DEPARTMENT
COMPUTAT1 ON
AND MATHEMATICS
DEPARTMENT
is
PROPULSION AND
AUXILIARY SYSTEMS
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INSTRUMENTATION
DEPARTMENT
Bibliotheek vn
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SF-
e
Techrc..e
bOCUMN1ATE
:DATUMI
b
PREDICTION OF EXTREME AMMUNITION CARGO FORCES AT SEA
PROJECT FOR UNITED STATES COAST GUARD
by
A, E. BaItTs
S. L. Bales
W. R. McCreght
W, G. Meyers
de
aarne
o, Di
SHIP PERFORMANCE DEPARTMENT
UNCLASSIFIED
-i
cci lrATIr.L f
THIS PACF (When Data
ntOrFORM
1 JAN 73
1473
EDITION OF INOV 651$ OBSOLETE
SiN 0102-014- 6601
UNCLASS IFi ED
LA
E"
A 1ItLI
I
rVv
U I1U.UM II IMI IJfl U
READ INSTRUCTIONS
-BEFORE COMPLETING FORM
I. REPORT NUMBER
SPD7OkO1
2. GOVT ACCESSION NO. 3. REcIPIENrS CATALOG NUMBER
- -
-4. TITLE (and Subtitle)
PREDICTION OF EXTREME AMMUNITION CARGO FORCES
-
-S. TYPE OF REPORT & PERIOD COVERED
Final
6. PERFORMING ORG. REPORT NUMBER
8. CONTRACTORGRANTNUMBER(I)
7. AUTNOR(a)
A. Erich Baitis, S. L.Ba.les, W. R. McCreight,
and W. G.Meyer.s
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Ship Performance Department
David W. Taylor Naval Ship R&D Center
...
-petnesga, ridrylanu
LUUU
PROGRAM ELEMENT. PROJECT. TASK
I_irQ11 iirn7.nn
.an
l-1-612-1c6
-I -I. CONTROLL-ING OFF-ICE NAME AND ADDRESS
United States Coast Guard
'OO Seventh Street, S.W.
Washington, D.C.
20590
.12. REPORT DATE
July 1476
13. NUMBEROFPAGES
-279
14. MONITORING -AGENCY NAME a ADDRESS(II different
fran,
ContrOfliná Office)
IS. SECURITY CLASS. (of title report)
Unclassified
15a. DECLASSIFICATIONIDOWNGRADING
-SCHEDULE
16. DISTRIBUTION STATEMENT (of thu
Report)
- - --APPROVED. FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED
-17. DISTRIBUTION STATEMENT of the ab.tract ant.r.d in Block 20;
ii dlfforit front Raãf)
18. SUPPLEMENTARY NOTES
-.
--19. KEY WORDS (Continui bit reiire iidó ii nec.e.y and Identt
by block
ñiber)
Cargo shoring forces, Ammunition cargo ships, Design sea conditions,
Design
ship operating conditions, 20-year storms, Effect of storm severity on
cargo shoring, Time domain shoring loads, Upper
bounds of shoring loads,
Shoring load estimates from roll, vertical and lateral accelerations,
Ship
response data base, Ship speed
degradation In storms
20. ABSTRACT (Continue on revere. aid if n.c.a.y and ld.ntlt by
block manb.r)
Progress and results from a research project devoted to the
determina-tion of extreme amunitlon cargo forces at sea are presented.
The work was
undertaken by the David W..Taylor Naval Ship Research and Development Center
(DTNSRDC) and sponsored by the U.S. Coast Guard (USCG) for assistance in Its
hazardous cargo safety program.
Four ships, representative of ammunition
cargo ships entering and leaving U.S. ports with ammunition cargo
capacities
ranging from about 6,300 to 19,200 tons, were examined.
UNCLASSI FlED
LIJITY CLASSIFICATION OF THIS PAGE(When Data Enter.d
-Ship motions and accelerations were' developed in the frequency domain for
a wide range of ship load conditions, headings, speeds, and Sea conditions by
applying procedures developed during the USCG LNG Cargo Tank Research Program
recently conducted at DTNSRDC.
The Influences of storm severity and ship operator strategies In storms
on
the magnitude of the resulting ship responses and cargo shoring loads were
examined using a math model of the ship traversing the North Atlantic Ocean.
The ship is- under control of various voluntary operator decisions as to how to
best proceed in rough weather to the port of destination without- incurring
either excessive Ship response levels or unacceptably long time delays.
The suitability of developing a single design vector from which design
loads of cargo shoring could be easily derived was examined and found to be not
particularly useful because for large time periods components of the shoring
forces are equal to zero, I.e., time periods, when gravIty or friction
are
adequate to prevent the occurrence of shoring forces.
A cargo shoring model was developed to establish both lateral and normal
forces that shoring must withstand to prevent shifting of amunitlon
cargo.
The model consists of a time simulation developed in the coordinate system of
the ship.
A pilot study applied the model to a single ship and results Include
the range of loads to be expected, the time periods associated with particular
loading cycles1 the amount of time cargo shoring will experience loads, the
sensitivity of shoring loads to changes In speed, heading, position in ship,
and Ship GM, the relative magnitudes of lateral and tomming loads, as well as
the degree of conservatism inherent In the use of the worst possible 20 year
storm, a typical 20 year storm, and a normal storm to specify shoring design
loads.
Results suggest that cargo shoring
loads
based on frequ,cy domain ship
response predictions will be very much greater than results based on the more
accurate time domain simulations.
It was concluded, therefore, that in order
to prevent the predictions of unrealistically large desIgn shoring loads, the
shoring loads should be developed directly in the time domain.
It is considerec
crucial to explore the cargo shoring model application further, e.g., to other
ships, In any efforts to develop a simple shoring load rule which may be used
by regulatory agencies.
ADMINISTRATIVE INFORMATION
APPENDIX B
-APPENDIX C
APPENDIX D
APPENDIX E
APPENDIX F
APPENDIX G
APPENDIX H
APPENDIX
ITABLE OF CONTENTS
ABSTRACT
INTRODUCTION
SHIP RESPONSE PREDICTION COORDINATE SYSTEM
DATA BASE GENERATION
DEFINITION OF DESIGN RESPONSES
DISCUSSION OF RESULTS
Operating Conditions at Which Design Responses
Modal
Encounter Periods Associated with Design
GM and Load Effect on Design Responses
Bilge Keel Effect ofl Lateral Acceleration and
Page
13
13
15
16
18
REFERENCES
276
SIMULATED SHI.P TRIP
..
20
DISCUSSION OF RESULTS
22
CARGO SHORING LOADS
26
DESIGN VECTOR
26
SLAMMING LOADS
31
CARGO SHORING MODEL PARTICULARS.
33
MAJOR CHARACTERISTICS AND LIMITATIONS OF SHORING MODEL
35
DEFINITION OF DESIGN SHORING LOADS
37
Scope 'of Shoring Load Calculations
38
DISCUSSION OF SHORING MODEL RESULTS
40
CONCLUSIONS
. . . ..
59
RECOMMENDATIONS
62
ACKNOWLEDGEMENTS
63
APPENDIX A - PREDICTION OF EXTREME AMMUNITION CARGO. FORCES AT
SEA - STATEMENT OF WORK
. . .91
DATA BASE OF SHIP MOTIONS AND POINT 0 ACCELERATIONS .
.97
DESIGN ACCELERATiONS AT ANY POINT IN THE SHIP
'221
PREDICTION OF CARGO SHORING LOADS
231
DESIGN VALUE DETERMINATION VIA WORST HEADING,
JAMES SPEED REDUCTION STRATEGY
.241
SPEED LOSS CRITERIA DISCUSSION
245
ROLL PREDICTION PROCEDURE
'249
'SIMULATED SHIP TRIP IN EXTREME AND NORMAL SEAS
259
IDENTIFICATION OF SHORING LOAD DESIGN OPERATING
CONDITION .
. . .275
2
3
6
8
11
Occur
Responses
Roll
LIST OF FIGURES
MAIN TEXT
Figure
1- Geometry of AMMO Ship Series
Figure
2 - Design Sea Conditions
FIgure
3 - Recommended Design Accelerat ions for AMMO
Ship Series
. . . ....
66
Figure
4 - Design Value Data Base for Ship A
...67
Figure
5 - Typical Response Amplitude Operator Predictions.
. . .68
Figure
6 - Typical RMS Response versus Encountered Period
Predictions (Density Graph)
69
Figure
7 - Effect of Bilge Keels on Lateral Ship Response
Predictions
-70
Figure
8 - Operator Strategy Influence on Motions and
Accelerations in Random Seas and a Normal Storm
Encountered at Various Relative Headings to the
Desired Course.
71
Figure
9 - Operator Strategy Influence. Oh Motions and
Accelerations in a 20-Year Design Storm Encountered
atVàrious Relative Headings to the Desired Course
.72
Figure 10 - Maximum Shoring Loads for 1/2-Hour and 21i-Hour
Operations in Design Seas As Well As. the Associated
Wave Height, Ship Responses, and ComponentS of
Accelerations Acting on Cargo and Shoring...73
Figure 11 - Maximum Port and Starboard Shoring Loads for 24-Hour
Operations in Design Seas As Well As Associated
Torning Loads, Wave Height, and Ship Responses
. . . .74
Figure 12 - Influence of Ship Heading, GM, and Coefficient of
Friction Between Deck and Cargo on Lateral
Shoring Loads
. . .. . . ..,. . .75
Figure 13 - Motion and Acceleration Levels at Which Lateral
Shoring Loads Occurred at Various Ship Headings.
. . ..
76
Figure 14 - Typical Samples of Ship Orientation While Shoring
or Deck Loads OccUrred
. . .77
Page
64
'I,
Page
Figure 15 - Variations in Maximum Nomal, S
, and Lateral Shoring..
Loads, SL, and Associated LOädurations for 6-Hour
Operation of Ship C in Bow Seas at Design Sea
Conditions
78
Figure 16 - Identification of Areas where Toming of Ammunition
Cargo Required
. . . ., . . . .. .79
Figure 17 - Effect of Speed, Heading,. and Longitudinal Cargo
-Location on Shoring Loads of Ship A and C
80
Figure
18 -
Degree of Conservatism Inherent in Specification of
Design Lateral Shoring Load from Use of Worst. Possible
20-Year Storm, TypIcal 20-Year Design Storm, and
Normal Storm .
. . .-81
Figure 1.9 - Effect of Stacking Cargo Pallets on Loads Experienced
by Lowest and End Pa.11ets.
.. . .... .
.
. 82
APPENDIX B
Figure B.1. - Ship A, Full Load, GM1, Root Mean Square Responses
versus EAcountered Modal Periods
106
Figure B.2 -
Ship
A, 50% Load, GMI, Root Mean Square Responses
versus Encountered Modal Periods
107
Figure B.3 -
Ship
B, Full Load, GM1, Root Mean Square Responses
versus Encountered Modal Periods
.108
Figure B.1i -
Ship
B, 50% Load, GM1, Root Mean Square Responses
versus Encountered Modal Periods
109
Figure B.5 -
Ship C,
Full Load, GM1, Root Mean Square Responses.
versus Encountered Modal Periods... .110
Figure B.6 - Ship C, 50% Load, Gill,, Root. Mean Square-Responses
verSus Encountered Modal Periods
111
Figure B.7 -
Ship
D, Full Load,, Gill, Root Mean Square Responses
versus Encountered Modal Periods
. . ..112
Figure B.8 - Ship D, 50% Load, Gill, Root Mean Square Responses
.Page
APPENDIX C
Figure C.1 - Location of Points for Proposed Point Variation
Investigation
. . . ,. .. 227
Figure C.2 - Data Base for Design Acceleration Deterniinatión of
Any Point Along Ship
228
Figure C.3 - Effect of Load on Design Accelerations for.Ship A
.229
Figure C.4- Design Value Data Base for Ship A.
23o
APPENDIX D
Figure D.1, - Coordinate System, Earth
.. 237
*
*
*
Figure D.2 - Forces on Cargo Box at Location (
,y ,z.),
Earth Coordinates
237
Figure D.3 - Forces on Cargo Box at Location
(x*,y*,z*),
Ship Coordinates
.237
Figure D.4 - Computational Scheme for Cargo Shoring LOads.
. .238
Figure D.5 - Upper Bounds for Shoring Loads
239
APPENDIX E
Figure E.1 - Sample Extreme Response Surface for Ship A
Vertical Accelerations, LNG Ship Series
2144APPENDIX .F
Figure. F.l
Definition of James Speed Loss Criteria Used to
Predict Extreme AcceleratiOnS of AMMO Series.
. . 2147Figure F.2 - Comparison of Speed Loss Criteria for the AMMO
and LNG Series ...248
APPENDIX G
Figure G.1 - Data Base of Largest Measured Roll Amplitudes
Figure 6.2
Figure
Figure
Figure
-
Effect of Bilge Keels on Largest Measured Roll
for Typical Naval Oil Tanker in BeamWaves
G.3 - Comparison of Largest Measured Roll for All
Ship Conditions of Typical Naval Oil Tanker
in Beam Waves
256
G.4 - Calibration of a Ship's Roll Inclinometer
257
6.5 -
Effect of Wave Steepness on Lateral Ship
Response Predictions
.258
APPENDIX H
.Figure H.1 - Overall Flowchart for TRIP.
268
'Figure. H.2 - Ship Navigation Logic
269
Figure H.3 - Wave Selection Logic
. . ..270
Figure H.i - Operator Strategy Selection Logic
.271
Figure H.5 - Sample Trip Results:
Histograms and Probabilities
of Exceédaflce...272
Figure H.6 - Operator Strategy Influence on Motions and Accelerations
in Random Seas and a Normal Storm Encountered at Various
Relative Heading,s to the Desired Course...273
LIST OF TABLES
Page
255
AMMO Series Ship Particulars ...
83
Point Locations for Predicted Accelerations of
AMMO Ship Series
84
AMMO Series Design Motions
85
AMMO Series Design Accelerations
.86
Operating Conditiofls at Which Design Responses Occur.
. . .87
Components of Lateral Shoring Loads
88
Shoring Timbers Required in Various Storms
89
MAIN TEXT
Table 1
Table 2
Table 3
Table
1ITable
5
Table 6
Table .7
Page
APPENDIX B
Table
B.1 - Description of AMMO Series Data Base Presentation
. . ..114
Tables B.2 to B7
-Ship A, Full Load, GM1, Root Mean Square
Heave, Roll, Pitch, and Longitudinal,
Lateral, and Vertical Accelerations at
POint 0, UnIt Significant Wave Height
115
Tables B.8 to B.11
- Ship A, Full Load, GM2, Root Mean Square
Roll and Longitudinal, Lateral and Vertical
Accelerations at Point 0, UflIt Significant
Wave Height
121
Tables B.12 to B.17 - Ship A, 50% Load, GM2, Root Mean Square
Heave, Roll, Pitch, and Longitudinal,
Lateral, and Vertical Accelerations at
Point 0, Unit Significant Wave Height
125
Tables B.18 to B.21 - Ship A, 50% Load, GM2, Root Mean Square
Roll and Longitudinal, Lateral and
Vertical Accelerations at PoInt 0, Unit
Significant Wave Height
131
Tables B.22. to B.27 - Ship B,FU1i Load, GM1, Root Mean Square
Heave, Roll, Pitch, and Longitudinal,
Lateral, and Vertical Accelerations at
Point 0, Unit Significant Wave Height
135
Tables B.28to B.3l
Ship B, Full Load,GM2, Root Mean Square
Roll, and Longitudinal, Lateral, and
Vertical Accelerations at Point 0, Unit
Significant Wave Height
. ..141
Tables B.32 to B.35
Ship B, Full Load, GM3, Root Mean Square
Roll, and Longitudinal, Lateral, and
Vertical Accelerations at POint 0, UnIt
Significant Wave Height
Tables B.36 to B.41 - Ship B, 50% Load, GM1, RoOt Mean Square
Heave, Roll, Pitch, and Longitudinal,
Lateral, and Vertical Aâcelertions at
Point 0, Unit Significant Wave Height
149
Tables B.42 to B.45 - Ship B, 50% Load, 6M2, Root Mean Square
Roll, and Longitudinal, Lateral, afld
Vertical Accelerations at Point 0, Unit
Page
Täblès 3.46 to B.49
ShtpB, 50%. Load, GM3, Root Mean Square
Roll, and Longitudinal, Lateral, and
VerticalAcceleratlons at Point 0, Unit
Significant Wave HeIght
159
Tables B.50 to B.53
Ship B, 50% Load.,.GM4, Root Mean Square
Roll, and Longitudinal, Lateral, and
Vertical Acceleratibnsat Point 0, Unit
Significant Wave Height
..163
Tables B.54 to B.59
Ship C, Full Load, GMI, Root Mean Square
Heave, Roll, Pitch, and Longitudinal,
Lateral, afldVertical Accelerations at
Point0,UnitSfgnlficant Wave Height
167
tables B.60. to B63 - Ship C, Full Load, GM2, Root Mean Square
Roll, and Longitudinal, Lateral, and
Vertical Accelerations at Point 0, Unit
Significant Wave Height
. .173
Tables B.6L to B.67
Ship C, Full Load, GM3, Root Mean Square
Roll? and Longitudinal, Lateral, and
Vertical Accelerations at PoInt 0, Unit
Significant Wave Height
177
Tables B.68 to B.73 - Ship C, 50% Load, GM1, Root Mean Square
Heave, Roll, Pitch, and Longitudinal,
Lateral, and Vertical Accelerations at
Point 0, Unit Significant Wave Height
1 81Tables B.74 to B.77 - Ship C, 50% Load, GM2, Root Mean Square
Roll, and Longitudinal, Lateral, and
Vertical Accelerations at Point 0, Unit
Significant Wave Height
. . ..187
Tables B.78 to B.83 - Ship D, Full LOad, GM1, Root Mean Square
Heave, Roll, Pitch, and Longitudinal,
Lateral, and Vertical Accelerations at
Point 0, Unit Significant Wave Height
. . ..191
Tables B.84 to B.87 - Ship D, Full Load, GM2, Root Mean Square
Roll, and Longitudinal, Lateral, and
Vertical Accelerations at Point 0, Unit
significant Wave Height
197
Tables B.88 to B.91 - Ship D, Full Load, GM3, Root Mean Square
Roll, and Longitudinal, Lateral, and
Vertical Accelerations at Point 0, Unit
Page
Tables B.'92 to B.97 - Ship.D, 50% Load, GMI,. Root Mean Square
Heave, Roll, Pitch, andLongitudinal,
Lateral., and Vertical Accelerations at
Point 0, Unit SigniflcantWave Height..
. .205
Tables B.98 to B.10l
Ship D, 50% Load., GM2, Root Mean Square
Roll, andLongitudt'nal., Latral, and
Vertical Accelerations at Point 0, Unit
Significant Wave Height...
- .211
Tables B.102 to B.105
Ship D, 50%. Load, GM3, Roo.t Mean Square
Roll, 'and Longitudinal., Lateral, and
Vertical Accelerations at...Point 0,, Unit
Significant Wave Height... ...21.5
Table B.106 - Constants .for, Single-Amplitude Statist1s
. . . . .. .219
Table B.107- Sample Linear Interpolation of Data BaSe Tables
. . .220
APPENDIX H
Table H.1
- Normal Yearly Storm and 20-Year Storm Used in
NOTATION
AR
Aft perpendicular
BL
Baseline
Bx
Maximum beam
CL
Centerline
CB
Block coefficient
Longitudinal prismatic coefficient
CT
Confidence factor
Cx
Maximum transverse section coefficient
FP
Forward perpendicular
FL
Lateral acceleration,, in the ship system, acting on the cargo
FN
Normal acceleration, in the ship system, acting on the cargo
F
Froude number
n
--GM
Transverse metacentric height
2
g
..Acceleration due to gravity, 321725 ft/sec
KG
Height of center of gravity above baseline
KM
Height Of transverse metacenter above baseline
K0,K,K
Pitch, roll, and yaw radii of gyration
LCG
Longitudinal location of center of gravity
LNG
Liquid Natural Gas
Length between perpendiculars
L,L(L),L-(V) LongitudiAál, lateral, and vertical accelerations at a
specified point along the ship
N
Number of cycles; also number of successive amplitudes
Number of times a response level
is exceeded
-T,
V
TOE
XA,yA,ZA
*
*
*
x ,y ,z
ws.wl/3
Maximum draft
Modal wave period, period corresponding to peak of wave
spectrum
Natural periods of heave., pitch, and roll
Ship speed
Extreme ship response
Surge, sway, and heave amplitudes
Coordinates of any point, measured from the origin of the
coordinate system
-..Wave steepness,
. .Response level
Ship displacemnent
Wave amplitude
single amplitude
Significant wave height - average of oneathird highest
dOuble amplitudes
RMS
Root mean square, square root of variance.
Starboard side
Lateral load to be sustained by cargo shoring
Upper bounds of!iateral Shoring: loads
Normal load to be sustained by cargo, shoring
SN
Upper bounds of normal shoring loads
-SN
+
Taming lo2d$
SN+
Deck or sheathing, loads
SXX(cA))
Spectral density function of response X
T
Time variable
TAp.,T,TFp
Ship draft at aft perpendicular, amidships., and forward
perpendicular
Modal response period, period corresponding to peak of
encountered response spectrum
eA,A,JA
Pitch, roll, and yaw amplitudes
A
Wavelength
Ship heading angle, predominant wave direction with
respect.
to the ship; also coefficient of friction
Wave direction
RMS or standard deviation Of ship response
Roll amplitudes in earth coordinates
Arbitrary ship response
.Wave frequency
ABSTRACT
Progress and results from a research project devoted to the
determination of extreme amunition cargo forces at sea are presented.
The work was undertaken by the David W. Taylor Naval Ship Research
and Development Center (DTNSRDC) and sponsored by the U.S. Coast Guard
(USCG) for assistance In Its hazardous cargo safety program.
Four 'ships,
representative of ammunition cargo ships entering and leaviing U.S. ports
fld with ammunition cargo capacities ranging from about 6,300 to 19,200
tons, were examined.
Ship motions and accelerations were developed for a wide range
of ship load conditions, headings, speeds, and sea conditions by applying
procedures developed during the USCG LNG Cargo Tank Research Program recently
conducted at DTNSRDC.
These results, calculated in the frequency domain,
were taken as the core data base from which other aspects of the project
drew basic ship response data.
The influence of storm severity and ship operator strategies in
storms on the magnitude of the resulting ship responses were examined by
developing a model of the ship traversing the North Atlantic Ocean.
The
ship is under control of various voluntary operator decisions as to hOw to
best proceed in rough weather to the port of destination without incurring
either excessive ship response levels or unacceptably long time delays.
Results provide the number of individual ship response cycles that exceed
specified levels on a per trip basis depending on the various operator
decisions employed.
The suitability of developing a single design vector from which
design loads of cargo shoring could be easily derived was examined.
It
was found that state-of-the-art ship motion prediction techniques, which
are traditionally based on the earth coordinate system, cannot be used
directly to accomplish this.
It was concluded that the concept of a single,
cargo shoring force vector Is not particularly useful because for large time
periods components of the shoring forces are equal to zero, i.e., time
period, when gravity or friction are adequate to prevent one occurrence
the transverse and normal directions do not occur simultaneously.,
A cargo shoring model was developed to establish both
lateral and
normal: forces that shoring mustwithstand to prevent shifting of ammunition
cargo.
The model consists of a time simulation, and was developed in the
coordinate system of the ship.
A pilot study applied the model to a single
ship and results include the range of loads to be expected, the
time periods
associated with particular loading cycles, the amount of time cargo
shoring
will experience loads, the sensitivity of shoring loads to changes
in speed,
heading, position in ship, and ship GM, the relative magnitudes
of lateral
and tomming loads, as well as the degree of conservatism inherent
in the
use of the worst possible 20 year storm, a
typical 20 year storm, and a
normal storm to specify shoring design loads.
Results suggest that cargo shoring loads based on frequency domain
ship response predictions will be very much greater than results based
on the more accurate time domain
simulations.
It Was concluded, therefore,,
that in order to prevent the predictions of unrealistically
large design
shoring loads, the shoring loads should be developed directly in
the time
domain.
By predicting in the time domain the components of the
forces
which produce. the shoring loads in the coordinate system of the ship,
phasing uncertainties in combining these acceleration and friction
related
forces are avoided.
In other words, it is not necessary in a time domain
shoring model to assume that the àomponeflt forces will
combine in the worst
possible fashion.
Therefore, it Is considered crucial to explore the cargo
shoring model application further, e.g., to other ships, in any
efforts to
develop a simple shoring load rule which may be used by regulatory
agencies.
ADMINISTRATIVE INFORMATION
The work was conducted at the David W. Taylor Naval Ship Research
and Development Center (DTNSRDC) by Ship Performance Department
Code
1568
upon request of, the U.S. Coast Guard
(USCG), MIPR
Z-70099-443330-B.
It is
identified as Work Unit Number
1-1568-011.
A statement of work is contained
in Appendix A
The developrnentandpredictions effort made with the Cargo
Shoring Model was also partialIy.supported byU.S.Navy tasks Identified as
Work Unit Numbers
1-1507-200-84
of the Navy Seakeeping Research and
INTRODUCTI ON
The United States Coast Guard (USCG) has
authority1' for ensuring the
safety of all hazardous càrgo'shipments entering or leaving U.S. ports.
This
design safety responsibility encompasses all ownership categories of ships,
foreign or domestic, Including some ships owned, operated, or chartered
by the U.S. Armed Forces.
Safety of hazardous matertal cargo shIpments concerns itself,
anong other topics, with the structural integrity of the containment systems
within which the cargo Is transported on the ships.
The USCGtherefore
contracted the David W. Taylor Naval Ship Research and Development Center
(DTNSRDC) to predict Extreme Ammunition -Cargo Forces at Sea based on
pre-vious LNG Cargo Tank Load procedures.
These predictions are intended to
improve the validity and realism of existing cargo shoring and torrilling
regulations,
A summary of these Ammunition Cargo Force predictions is presented
based on a DTNSRDC research program conducted on an intermittent basis over
a two year period.
The research program Is based on ship motion
accelera-tion and shoring load predicaccelera-tions for a series of representative U.S.
Ammunition Cargo ships specified by the USCG.
This Ammunition Cargo Ship
series consists of four ships ranging in ammunition cargo capacities from
about 6,300 to 19,200 tons.
The results of this research and program are
presented in terms of the extreme lifetime g-loads to which the cargo will
be exposed and which If appropriate*
the shoring is expected to
with-stand.
These. so-called design g-loads are presented in terms of
in-dependently derived vertical, lateral, and longitudinal
accelerations at
the most forward and highest position In each ship where amunition cargo
may occasionally be loaded.
Simple methods for translating these design
loads to other desired positions in the ship are provided (See Appendix B
and C).
Similarly simple expressions for the upper bound of the cargo
'shoring forces that can result when the design g-loads and the associated
roll motions are experienced are also provided (See Appendix D).
cRêferePces are denoted by superscripts. A complete listing is given on
pages 276-279.
.The order of presentation of data and recomended actions in this
report is based on the recommendations and conclusions of the National
Transportation Board and USCG
report15
on the sinking of the ammunition
cargo ship SS BADGER STATE in the North Pacific in December 1969.
Since
the development of realistic cargo shoring forces depends essentially on
the ranges of ship responses that result when a large number of variables*
occur in various combinations, it was considered appropriate to subdivide
the research program into a number of distinct tasks, each with a specific
goal.
The Ammunition Cargo Force Research Program has been conducted
there-fore, as six separate, roughly, related tasks as originally outlined i.n the
statement of work, see Appendix A.
The first task was the development of
the basic ship motions and accelerations Using the procedures developed
during the USCG LNG Cargo Tank, Research Program at
DTNSRDC.2'3'4
This
first task thus was considered to be the data base task from which
all
other
tasks would draw the basic ship response data developed in the frequency
domain.
The second task was Intended to examine the influence of Storm severity
and operator strategies In storms on the magnitude of the resulting ship
responses.
Thus, this second task essentially consisted of the development
of a model of the ship traversing the ocean in arbitrary directions under
the control of various voluntary operator decisions as to how to best
pro-ceed in rough weather to the destination without Incurring either excessive
cargo shoring loads or unacceptably long time delays.
The
results of this
task provide the number of individual ship response cycles that exceed
specified levels and how these are Influenced by operator decisions in a
storm.
This number of response cycles Is of significant interest because
it represents a realistic load history to develop the fatigue
characteris-tics of the shoring.
The third task consisted of an investigation into the suitability of
the concept that a single unique design vector can be develped from which
all of the loads on the cargo shoring can be derived quite simply.
Thus
*These'vari.ablëslnclüde.the'deadweight, load distribution, roll
stabili-zation status of ship, trade route ship operates on, storm severity (wave
hefght and modal period), size and speed of the storms, their frequency of
occurrence, voluntary strategies of the operators employed when they
en-counter storms, levels of probability that specific motion levels will not
be exceeded, the different lOcations within the ship.where cargo is secured,
as well as the particular shoring or securing configuration employed.
this third task may be regarded as an attempt to present the cargo design
loads in as simple and concise a form as possible for use by designers and
shoring regulation purposes.
The fourth task consisted of th&deièloprnent of a so-called slamming
force magnification factor.
This factor was to be drawn essentially from
a comparison of the magnitude of the rigid body vertical acceleration of
the WOLVERINE STATE and the sti'uctural impact response to slamming.
The fifth and most demanding task was to select for a particular
example of cargo location, the shoring required to keep the cargo from
shifting.
This example shoring Is then exposed as part of the ship trip
to design extreme seas to verify the selected shoring.
The degree of
con-servatism inherent in the design shoring when the ship encounters a normal
rather than design storm is expressed in terms of the number of timbers
that might be saved if the shoring regulation required Only normal yearly
extreme rather than 20 year extreme storms.
The sixth task Is to summarize the results in the form
of
a report
that can be read, Understood, and used by members of the regulatory agencies
as well as various ammunition shipping activities,
in order to accomplish
this last task, the text
of
this report deals primarily with the results
of the individual tasks rather than on the details of how they were derived.
Appendices are included to provide some of the procedural details, as well
as to present some
of the voluminous
results of Task 1.
It should be pointed out that implicit in the structure of the
re-search program was the assumption that design ship responses as developed
in Tasks
1 and 2 could be employed to develop accurate shoring loads in the
frequency domain.
The inability to employ the frequency domain results for
this purpose led to a substantial increase in the research effOrt In Tasks
3 and 5 whIch dealt with time domaIn representations of the ships motions
and the resulting shoring forces.
Before proceeding with the results of the individual program tasks,
however, it must be noted that the results of the shoring example of Task
5 have Indicated that some of the accelerations developed in the first task
are not considered to be appropriate for the accurate determination of
cargo loads or shoring requirements.
The next section discusses the reasons
SHIP RESPONSE PREDICTION COORDINATE SYSTEM
The reasons that lateral acceleration loads developed in Task 1
are inappropriate for the accurate determination of cargo shoring loads
are associated with the basic coordinate system within which the ship
motion prediction equations have been Written.
The Task 1
ship responses
were calculated by the state-of-the-art prediction procedures employed
during the USCG LNG work of Reference 2.
These procedures employ equations
developed in the earth coordinate system.
The major practical concern in the LNG tank research was to
es-tablish the pressure loads acting on the tank structure due to the rigid
body ship motions.
Since the
igid body motions of the ship were con
sidered to augment the internal pressure loads by acting along the direction
of acceleration design vector; and the. magnitude of this vector was dominated
by the vertical acceleration In earth coordinates, the importance of lateral
accelerations in the development of shoring loads was not initially recognized.
It became obvious., however, once the shoring example of Task 5 was
initiated that the individual components of the shoring load could be
de-termined in several different ways, and that each would result in different
Shoring loads.*
For example, the gravity force component, which is a function
primarily of roll, attains its maximum value at a different heading and/or
ship speed than do the inertia force components whlc.h are due primarily to
ship heave, yaw, and pitch, respectively.
Therefore, since shoring loads
depend on components which attain their individual maximum values for
different ship operating conditions, the relative phasing between the
corn-poneñts become of considerable concern.
There are specifically two sets
Of phasin9 uncertainties; one is associated with the ship operating
condi-tions that produce maximum values for particular Shoring load components,
and the second uncertainty is associated with the maximum values of the
components when the ship Is operating at any given set of speed, heading,
etc. Operating conditions.
.. . . ..The above considerations lead to the conclusion that both sets of
phasing uncertainties can best be avoided by. develOping the shoring loads
*The components consist of inertia, gravity, and friction forces as de
tailed in later sections of the report and Appendix D.
directly in the coordinate system in which'the shoring loads are most
appropriately described, i.e., in ship coordinates rather thanthe
con-ventionally employed earth coordinates.
Ship coordinates are most appropriate because the three principal
force components of the shoring loads, namely the lateral, normal and
fric-tion forces, are defined* in terms of the lateral and normal axes of the
ship.
Since lateral forces or accelerations in earth coordinates cannot
be substituted for lateral forces or accelerations in ship coordinates
with-out encountering phasing difficulties in considering gravity, it was also
concluded that a coordinate system transformation might have to be performed
at some stage on the responses previously calculated.
The resultant
in-vestigation Into a conversion procedure for the lateral accelerations de
rived in the earth system quickly revealed tha,t there was little hope for
even a reasonable engineering estimate of how this conversion might proceed.
On this basis, the feasibility of developing the necessary response amplitude
operators in the ship system was examined.
The results indicated that there
appeared to be no quick, efficient way in which such a cOnversion might be
accOmplished.
It was decided, after consultations with the IJSCG R&D
per-sonnel' tO report the results áttainedand to develop the basic transformation
expressions for the forces and accelerations in the time domain.
The time
domain transformation expressiOns were subsequently developed and a
relative-ly extensive Series of time history investigations was then conducted.
Ammunition Cargo Force Program results consist of frequency domain
based design ship motions and accelerations in earth coordinates, procedures
for establishing upper bounds of shoring loads** 'based on such results, as
well as the significantly more accurate, lower design shoring loads'
devel-oped in ship coordinates in the time domain.
That is, the uppe
bound
shoring loads based on earth system accelerations were much larger than the
time domain shoring loads.
Consequently, the frequency domain based
accelera-tions calculated in earth coordinates are not considered to be appropriate
for determining realistic shoring loads suitable for design or regulatory
purposes.
*It isnotédin this context that 'lateral force,in'the ship system consist
of the sum of the inertial and gravity force components parallel to the
deck, FL, whereas the comparable force components perpendicular to the deck
are designated as the normal force, F.
See pages 33-37 and Appendix D.
**The upper bound shoring load expressions were developed on a related Navy
DATA BASE GENERATION
The development of realistic cargo shoring forces suitable for
design or regulatory purposes depends on the largest cargo accelerations
that result when a realistic range of present and fUture potential
amuni-tion cargo ships Is exposed to the full range of variables that influence
their cargo loads.
The AMMUNITION Ship Series (AMMO Ships) specified by the USCG
contains C3, Ck, C5, and LASH cargo ships whose particulars are given in
Table 1
and Figure 1.
Since for a given ship type, the responses and
thus the cargo loads may vary substantially with dead weight and load
distribution, the AMMO ship's responses were developed for the widest
practical range of dead weight, i.e., 100 percent of full load to 50 percent
of full load.
The shipment of aninunitlon on ships loaded to less thafl
-50 percent of full load was considered to be impractical by
defini-tion!
In addition, at each of these dead weights, the location of the
ship's vertical center of gravity, or equivalently the vertical distribution
of the anununition cargo, was varied over the widest practical range.
The highest vertical center of gravity locations corresponded essentially
to the lowest allowable safe metacentric heights, GMs, specified by the
USCG; and the lest center of gravity locations corresponded to the
largest GMs that are likely to be employed in loading these ships under
any circumstances.
As a result, by calculating the responses of each
of the four ships at essentially four to seven Individual dead weight and
load 'distribution combinations, the possible range in ship responses
and dynamic cargo loads due to dead weight/load distribution variability
was established.
In order to consider the variations In the cargo accelerations
experienced because of the location within the ship where the cargo is stored,
the cargo accelerations were calculated at the location which would produce
the worst acceleration loads on the cargo, i.e., the furthest forward and
highest position (Point 0,. see Figure 1
and Table 2) at which the cargo
might occasionally be stowed.
Results are given in tabular form in
Appendix B.,
Simple, numericai interpolation methodsare then required
to translate these "worst-cargo-accelerations-on-the-ship" to a desired
location, i.e., to reduce them to the appropriate value for other locations
along the ship.
Appendix C provides details of these interpolation
procedures.
It should be noted that at the outset of this research project,
had been intended to employ the graphical trend procedures developed
during the LNG project to translate the accelerations at PoInt 0 toother
points in the ship.
However, as the practical implications of the cargo
force sensitivity* to spatial variations became apparent in the Cargo
Shoring. Task, it was considered essential to upgrade the accuracy, of the
acceleration translation procedure.
Design accelerations were thereforf
calculated for five points in. the centerline plane at. the same vertical
locations as Point 0, i.e., the highest practical vertical location at
which amuflition cargo might becarried.
Table 2 illustrates the positions
of these five points.
Thus effectively, one may now estimate the acceleratiOnS at any
point in the ship at any heading, speed, ship load condition, and sea
conditiOn by shifting the Point
0
acceleratIons of Appendix B In accordance
wIth the design acceleration trends given in Table 4.
These trends In the
accelerations with longitudinal centerline shifts produce the most
sig-nificant variations i'n the most important compoflents** of the cargo force
accelerations.
It is to be nOted that shifts in the somewhat less
important vertical and lateral direction, respectively, are
ignored.2'3'4
To further improve the accuracy of the predicted accelerations at
arbitrary points in the ship, requires properly taking the vertIcai and
lateral shift trends into account.
Such additional accuracy, however,
requlres many. more data points in the ship, and is clearly beyond the scope
*Restricted longitudinal ranges where tonning is required to suppress upward
motion of the cargo and ranges where large lateral loads and thus
signifi-cantly stronger lateral cargo shoring is required.
of the present project.
It is recomended that these calculations
be performed.
Appendix C has been prepared to further elaborate. On this
recommendation and to 'demonstrate the numerical procedureby 'which
accelerations'may then be attained accUrately for any point in the 'ship.
The design accelerations and associated ship motions are developed
by means of a flexible, four stage building block procedure.
This procedure
was recently documented in references 2,3, and 4.
HistorIcal wave data;
a complete set of ship response amplitude operators,* i.e., for all possible
speed, heading, and ship load conditions;' and short term statistics are
then employed to :predict the entire range or universe of extreme ship
responses that the ShIp.Is likely to encounter during lts"li"fetlme.
From
this' unIverse Of posslble** ship reSponses and accelerations, the design
accelerations are selected by excluding physically unrealizable ship
conditions that may occur In a computer' prediction but not at sea.
That
is, physical limitations such as deck wetness, slaming, the vol'untary
speed loss resulting therefrom, as well 'as the' involuntary, speed loss due
to the added drag caused by motions of 'the ship, the added drag due to'wind,
the loss of propulsive efficiency due to ship motions., etc. are considered
to limit the speed of a ship in a seay.. The James speed criterion
reflects implicitly the voluntary speed losses due to operator strategies
In
many storms as well as the unavoidable Involuntary speed losses,
A
brief comparison of this speed loss criterion with the more recent speed
loss formulation of
Aertssen8
is given in Appendix F!
The empirical speed
loss data of
James7
was used to limit the physically realizable speed of the
ship In extreme seas.
It is to be noted that the design seas .are
con-sidered to be Seas, see Figure 2, that.threaten the survival of the ship.
James' empirical speed' loss data for the C4 cargo ship was applied to all
ships in the AMMO series.
FunctIons which descr1b
the response of a ship to wave excitations as
a functIon 'of frequency.
These RAO's were calculated using the DTNSRDC
Ship Motion and Sea Loads Program of.references 5. and 6.
c*f the power installed in the ship is assumed to be unlimited
Load and GM variations.
AppendixE describes, In outline.form, theindividual stages
involved in the development of the design ship responses which, In turn,
produce the cargo shoring, loads.
The following section will discuss the
definition of these design responses before the results of the data
genera-tion task are presentedin the last part of the Data 'Base Generagenera-tion
Section.
DEFINITION OF DESIGN RESPONSES
The term design responses implies responses derived from the ship
operating in design seas by a procedure Outlined in Appendix E and discussed
in Appendix H.
Basically, design responses are defined to be the worst
responses that the ship will produce when encountering, at the worst
possible heading, the design seas of Figure 2 at a speed determined by the
James speed loss criterion.
The speed loss criterion serveS to exclude
from the universe of possible ship responses the speeds that are physically
unrealizable at each heading.
When ship load conditions are not explicitly considered, the term
design responses then means, additionally, that the worst responses
indepen-dent of load condition are selected.,
Figure 3 presents recommended design
accelerations for the AMMO Ship Series obtained
by
the above procedure.
These accelerations are given for three different longitudinal locations
on the ship.
' "This latter type of design response requirement that Is independent
of ship' load condition, may be decreased when specifying ammunition shoring
requirements if, ,and, only if, the permissible ship load conditlons* are
specifically incorporated in the shoring regulations.
Figure 4 clearly
illustrates the large reductions, particularly for lateral accelerations,
that can be achieved when the regulations specify ship load conditions
as well as the shoring loads to be withstood.
The importance of load
conditions on the vertical and lateral accelerations are brought out further
in following sections.
The selection of design sea cOnditions equally strongly affects
the magnitudes of the design responses.
This selection process is discussed
in some deta1lin Appendix H.
If, for example, design seas are based on
normal 1- to 5-year instead of 20-year storms, it appears that design
responses can be reduced by approximately 20 percent.
Similarly;, if
design seas are selected as representing the most probable design seas,
that is, seas with relatively longer modal periods (> 14 seconds), design
responses can be additionally lowered by anywhere from 10 to 34 percent from
the values given in Figure 3.
It is important. to note, however, that the selection of design
accelerations and motions are performed independently for each response.
That
is, ship conditions that produce design lateral acceleration will not
necessarily be the same ones that yield the maximum vertical accelerations.
It was considered Important for design and regulatory purpose to develop
the maximum or design values for each response separately Inasmuch as the
ships and their cargo will certainly experience these individual responses
or accelerations in exactly this fashion.
The attempt to develop a design
condition that simultaneously results In maximum shoring loads for all
responses will be examined for the cargo accelerations in a following section
on the Design Vector.
It was assumed implicitly at the outset of the current research
program that predicted frequency dothain ship responses could be used
directly to establish the selected cargo shoring loads.
That Is, it was
assumed that if the probable maximum values of three components of the
acceleration an6, also, the ships roll, pitch and yaw could be established,
then these values could be combined into realistic cargo shoring forces.
Procedures for developing an upper bound on the cargo forces based on
the frequency domain ship responses are discussed in the Design Vector
section.
In addition, this section develops the quality of such "upper
bound" shoring loads by contrasting them to time domain shoring loads.
Before proceeding with that discussion, however, a summary of the
DISCUSSION OF RESULTS
The results of the Data Base Generation Task for the various ships,
ship load conditions and cargo locations Within the ship are presented
in terms of design responses in Tables 3 and 4.
Motions are given in Table
3 and accelerations in Table 4.
Overall trends in the responses as they are affected by ship size,
GM, load condition, and spatial variation within the ship, may be developed
directly from this tabulated data.
Similarly, the influence of the design
wave heights as well as the relative magnitudes of the three basic components
of theacceleratlon may be deduced from these data tabulations.
It is
noted that the various factors mentioned are all interrelated.
The
Implica-tions of the tabulated results are considered in terms of:
OperatIng cOnditions at which design responses occur,,
Modal encounter periods associated with design responses,
GM and load effect on design responses,
The influence of the location of the cargo In the ship on the
operating conditions at which design responses occur, and
Bilge keel effect on lateral accelerations and roll.
Operating Conditions at Which Design Responses Occur
Table 5 was prepared from Tables 3 and 4 to summarize the operating
conditions, I.e., ship speeds, headings, and modal periods of the seas
at which design responses occur.
A few of the more important results are
noted.
First, GM and load variations do not appear to influence the speeds
and headings at which design pitch, heave, and lateral accelerations
occur--irrespective of ship size.
Ship size appears to Influence only slightly the
modal periods of the seas at which design pitch, heave, and vertical
accel-erations occur.
That is, there is only a slight tendency for the larger
ships to encounter design responses In longer period seas, i.e., up to
two seconds longer than do the smallest ships.
Second, the modal period of the seas that produce design respons
vary from response to response, wIth motions tending to reach their design
values In somhat longer seas thahis the case for accelerations.
Third, design pitch Invariably occurred in head seas, whereas design
heave occurred In essentially beam seas
(900
to
1050).
These values occurred
at speeds of 0 to 5 knots,. independent of the ship type or loading.
Fourth, design roll, on the other hand, occurred at speeds ranging
from 0 t015 knots, depending strongly on the
GM.
Large
GMs,
which result
In a relatively stiff ship, produce design roll values in beam seas at low
speeds ranging up to 5 knots
independent ofship's type or dead weight.
On the other hand, small
GMvalues which result In a relatively, slow, rolling
comfortable ship, tended to produce design roll values at relatively high ship
speeds, i.e., 10 to 15 knots In quartering or following seas.
Thus, It is quite
apparent that
GMvalues will very much dictate the operating conditions
in which design roll motiOhs occur.
Low
GMvalues thus induce roll response
behavior that may result in conditions that are conducive to capsizing,
even
though the magnitudes of such roll motions are, in fact, less than the
ones
attained with higher
GMs.
To
further emphasize the importance of
GMand
load, rather than excessive roll, on the occurrence of capsizing,
a relevant
section, of the conclusion of reference 18 is quoted.
"Out of a total of 136
mOdel experiments, 21 capsizes were experienced.
All of these capsizes
occurred In quartering or following seas, i.e., conditions In which the
stability is strongly affected by the relative position of ship and
wave.
No capsizes occurred in beamseas.
All
capsizes except one occurred in
the heavy displacement (low freeboard) condition.
This is the condition
most sensitive tothe reduction Of stability in a wave crest."
In the capIzing cofltext, it is noted, of course, that the tested
GMs
of reference 18 are very much lower, i.e.,
GMs
on the order of 0.5 to 1.5
percent of the ship's beam compared to
GMvalues of 3.7 to about 15 percent
of the ship's beams in the
AMMO
series.
The trend in the operating
con-ditions with
GM Is
noted to illustrate that the occurrence of design roll
In operating conditions conducive to capsizing may limit the lower acceptable
GM
