A generalized approach to seakeeping evaluation in initial stages of ship design

BULGARIAÑ :SHIP

HYDRODYNAMICS CENTRE 9003, VARNA, BULGARIA TLX 77497 BSHC BG

A GENERALIZED APPROACH TO SEAKEEPING EVALUATION

IN.INITIAL. STAGES OF SHIP .DESIG'N

Invited

1cture

delivered at the Institute of Navel ArchitectLie University oF Trieste. ITALY. on 1-st Dec.1987

by F:oumen KISHEV Dr. Senior Res., Sc.

Head of Seakeeping Sector,

Ship Dynamic.s Department. BSHC

Report No ODO 87.Ol.9O December 1987

A _{GENERALIZED AF'PROACH TO SEAKEEPIÑG} EVALUATION IN INITIAL STAGES OF SHIP DESIGN

(lecture notes)

INTRODUCT ION

- Standard optimization approaches _{E15q17J result in}

no _{clearly expressed maximum of the tarqet function..}

- Seakeping as a basic complex of qualities

character-izing ship _{behaviour in the greater part of th}

servise time, has to play essential role in ship optimization yet in initial

stages o-f ship design. Ci,4,7 13,etc..].

1.. PROBLEMS OF SHIP OPTIMAL DESIGN _{- GENERAL}

Objecta-f optimizatïn

- Ship'as a compound _elemént

o-f the general _{transportation system (named further "Ship}

system").

SHIP SYSTEM

SHIP AS A MECHANICAL SYSTEM

PROFIT

Opt im i za t i on

Restrictions

Assign men t

Environment SHIP AS ATRANSPORTATION UNIT

Rules & customer

Client -- I

Ship

ytem

trLtcture

_{svra1 main branch2s}

_dcomposd

into _LLbEyst9ms

_{with cros cup1in5}

Multiple input (excitatión)

Filter (restrictions)

Branches (subsystems) such as:

-hull form -hull structure -building -niashinery -operation etc. Cross couplings - Branch criteria General critèrjon

Main QPt :itPrì problems

1.Correct mathematical description of the system (structureq interconnectjans _{ordering, simplificat.jon,s etco)}

2.Final estimator selection on ecOnomical round (as a

cammersia]. element,the Ship system quality _{is evaluaed through} the profit gained by its exploitation)

Net income

Tons .Hours

Frac h t price

Fi.3 FormLtlatjofl a-f optimum _{design cHterian}

&eneral _{optimization approach.}

- By systematical exciting of the system to seek fr _{such a combination}

o-f ma-in

parameters influericin. the _{system status, that its output be}

max i mal Allowances Repair Maintenance Taxes Fuel Crew etc.

n

I UNDERWATER HULL FORM BRANCH

2. HULL FOFM BRANCH OPTIMIZATIÖN

Branch structure

Assumption I - Fr seakeeping calculations no detailed ship form description is nessecary C3,4,9.1.,14!1 etc.]

Assumption II .Seakeeping is not sensitive to minor (local) -form changes Crc-F. as above].

Cons8quense: Seakeeping ought to be.. evaluated separately and prior to stili water performance C1.13.21,etc.]o Adoption a branh structure as

shon in Fig.4

Static & stability Seakeepinc Res is tance & pröpulsion Manoeuvr-ability

Fig. 4 Hull form branch structure

Seakeepi no subsystem Loop on

metr_

Loop on environment

I----

---1 Excess motions Loss of stab il ity _j.Added resistance -i Slamming j.Vibrations -strip theory

-linear, spectral theory -Etatistics

Generalized. ekeeping c'riterioh (E:)

Deck wetness Screw rasing Accelerations Shearing forces Bending moments

¡L

---Froportioal to: -speed loss

-damages and loss of equipment

-loss o-F cargo (shiftig, ash.ing out or holds.

+loodiñg) :

-others ' '

L - Local .c.ritéria .based on 'function degradation rate

E General 'criterion related to the'.overall effectiveness

'ofthé'subsstem '

OSO 'Optimal seakeeping design

Fig. Z' Se.káeping subsystem structure

Theoretica.l background

.AF'FROCHES TO SEAKEEPING EVALUATION

Modern concept - Not simple conclusive evaluation of main seakeeping characteri stics, but rational selection of main ship form paramete,s in cder to get best seakeeping.

31 Empirical approach. E63

Qualitative recommendations drawn after analysis cf

serial seakeeping data (experimental and/or theoretical). sensitive analysis and "good marine practice" considerations.

.2Operat.ional index approach C24S etc.J

Figorous approach basedon probabilistic limitation àf subs'stems operability £16J:

U

where U is the significant subsystem reaction;

U*is the probabilistic (statistical) standard Formulation aspects:

- selection of representative subsystem reaction - limits declaration.

Realizátion

6

Step A. Polar diagrams cf functional zone (Fig..Y for a given subsystem

Step B. Calculation o-F functional indices for a practical numbCr c-f sea states:

y 3O

FI(h)

= j. J

SF(V,j. )pv(/)pHvdt

o o

where SF Functional zone area

y - Ship speed

- heading angle v.1H weight functions

Step C. Caloulation o-f subsystem estimate H 1/3max

SE

_f

FI(h)p(h)dh

o

270 180 Roll amplitLide 5 JPitch amplitude 30 J 180 180 90 90 270 8F 7 180 Fig.6 Summarized polar diagram Functional zone Disability zone 270 90 180 i.ietness p/h 30 Deck p/h 20 J

Si

ammi ng

Step'D.. Calculation of the general _{operational' index}

N

DI _{=jlSE(i)pR('i)}

where N -is the number o-F subsystems _incorporated

p

is the weght function stating subsysh

reaction importance in forming th overall

ship behaviôür.

Rank estimator approach £11O,142O2±

_etc

Simplified variation of pr-evious _{method fOr comparaEive} investiQatjcns

Assumption III - Seakeeping qualities can be made

dependent on A

_articulr

_{number of gehera,l}

_gemetric

characteristics of the hull feriTi E3919 etcJ:

Assumption IV - An averaged standartijè called "Rank evaluation", exists, _which

characterizes the sakeein

_[1,10,14,20

_EtO]

F: = f(6)

Asurnption _{V - Probabilistic uniformity o-P operational} regimes, 'reartiöns and consequences:

pi = con.st..

Application to optimum ship design

eval uat i on. synonymously

-'by simple comparison cf competiting

_{desipn vaiants}

-maximization of multiparameter function R at imposed design restrictions.

-4.BSHC EVALUATION SHEME

4.1 Shi.pdescription

Accounting for the featLtres of

_mehod

_{used for} engineering _{9'/aluation of seakeeping C9]}

the hull form can be

cónsidered comrehens.ive.1y _{described by the fo11owin}

character-jstjc (see also Fïg.7):

-Main dimensions LB t

-Cross section area distribution along the length, a(x) -Section width distribution along

_{the lenth. b(x)}

-Section area certro.ids _{distribution aÏonQ the length.}

-Sctïonal draft, d(x)

Every other form parameter taking part in the _-followjnq evaluations can be calcLdated on this basis [10. 14]

42

_{Selection of Independent Geometric.}

Vari abiès

From the. multitude a-F ship _{hull geometry parameters}

either general or local, a set of design _variableEq

predominantly influencing _{seakeeping, is. selected}

by means

o-f _{sensitivity anlysis [3,7,14,18 etc.]. These include:}

1/3 - Relative elongation -Blòck coefficient - Waterline coefficieñt . c - Relative draft _T/L Relative breadth _B/T

- Distance between the centre o-F

buoyancy and the centre of _{flotation (LCB-LCF)} - Shifting. of the two centres from

the middle - Relativ2 trim

- Relative, bow cross-section area - RelativE stern crOss-section _area

0;5 (LCB+LCF) (TA - T F.''L

SF ¡SM

SA/SM

The above set of _{variables directly coresaonds with the} table of input parameters _{o-F available CAb systems}

o-f FORAN Or

d(x)

C

Fig.7

_{General ship form description}

_curves

4. _{Criteria], structure}

The ship dyñamjc _{characterjstjcs. having}

prevailing effects on the, ship _{behaviour at real}

service

_Ccnd1tins

_are selected after £4]. £73. _{£8] and include:}

- si.gnifican _{heave amplitude,}

_Zir.

-

signi-ficant pitch ampli.tude

- average added power in waves. _N - deck wetness occurences _{per hour.}

- number _{per hour.}

ÑSL;

-

screw racing rate,

NthF.

- significant vertical' acceleration _{at FR. a1 ,,.;}

It _{should be}

pointed oUt that this characteristic set di-f-fers _{completely from Bales}

Cl] _{recommendation as the} prOcedure is oriented ta _{conventional ship forms.}

The _{seakeep i ng of every design}

vari ant i s. _{evaluated i n}

conformity with the generalized seakeeping _criterion formulated às

i N

R= EwH(1)

u1

where: N is the _{number o-F}

seakeeing characteristics importance;

- (i) is a weight function taking account

F the

cont-ribtion o-f each _{seakeeping characteristic in} the _{forming, c-F ship's}

overall behaviour in wavés: N

E w

(i) =ld

i=i

u - _{verage.d (weighted:) reaction of the}

system: N

Lt = Ev Ew _{(i).w (J).uij,)}

i=1 J=1 V. w

where

_{u(ïj) is the}

caracteristjc reaction obtained as a function o-f speed and sea. severity;

w (i) _{are weight 'fLinctions}

introduced under the cot'idj tian:

N,

w(i)=1

The generalized. flow chart of the seakeeping optimization procedure named SEAOFT [103 is illustrated in

Fig.8. It works in conformity with the

SYSD CD system

developed at BSHC [12.3 and rake.s use of the specially oriented data base. ..

AccordIng to the procedure outlinied the design process can be interrupted on three levels:

I - seakeeping evàluation of a single variant II evaluation of the best variant from viewpoint

o-F seakèeeping considerations:

III- design of a ilew variant with aptimJ seakee-pin.g qualitie. The work on the third level requires identification óf the coe-f-ficient composing the rank critgrion:

N.

R.= E C-

G-i=1

and searching o-F the optimal set of ge.ometricpara.-meters (a). ensuring the ma>imal posible value of F:. A sample application o-f the described '.pròedUre is outlined in Apeñdi> A.

.12

and taking into account the próbability of occurence of inótion

regimes in this range. The

prediction curve -for

speed loss in waves and the urve ò-F occurense o-F wave heights for the sea region being investigated are used as weight $unc ions.

7/

Cus tòmer demands General data base cT)c(

(Q

r O ,- O_s._

O-r

-r-

4- _., ç

(flSL.

=.4-'

oa)a)

0)0

0_+.

_JWU

ø.)X_SO OC t4_ Q, L) U 4-o Reactions I Irital hull form Geometry of variant hull form y

r.

Subsystems evaluation

t

IGeneralized J seakeeping Jcriterion

yyjy;

_y

Selection of the, best variant y Identification óf regression coefficients in R-composition Optimal design at R _condition'

r

Au tomated hull forii des ig n Operational I conditions _J rig.

Géneralized flow-chart _{of seakeeping}

Optimizatioñ _procedure

Hull form

. FUTURE DEVELOPMENTS

-

Enlaring

o-f the seakeeping subsystèm's

struc-ture by more profound inclusion o-f lateral motion effects

and intercônnections.

-- Practical EpecificatiónS1 of lodai criteria.

Extensive sttistical observatibns and analysis of wave dataq operational restrictions and sailing conditions5 in order to

formulate

prperly

the limitations and the weight

functIons. Formulation c-F standards -for good seal<eeping Cli]. Development of similar evaluation procedure for other branches o-f the ship system,incorporating them further in a generalized CAD and optimization procedure.

REFERENCES

1. Bales N. Optimizing. the. Seakeeping Per-for

mance o-F 'Destroyr - Type Hull

-13 SNH. Tokio, 1980

2.Bales N.. Cieslowski D.- A Guide to Generic Seakeeping Perfor mancé Assessment - NEJ., April 1981 3.Balés N. Cummins W.- The in-f luence o-f HLt11 Form on Sea

keeping -Trans. SNAME, vol. 78, 1970 4.Chryssostomidi.sC. - Seakeeping Consideration in Total

Design Methodology - 9th SNH Paris,

1972

5.Denis M. St - On the Environmental' Operabilit' Seagoing System - SNAME19Th

.Denis M. St. - On the Empiric Design o-f Seakindly

Ships - PRADS'83,. TokIo, 1983

7.Hadjimikhalev P.Kihev R..- Selection o-f Ship Geometry Farame ters. and Exploitation Regimes, Based

on Optimal Seak:eepin' Criteria -National Conference on Optimization in Shipbuilding'. Varná 1972

8.Hadjimikhalev F'..Kishev R.- A Method for Complex Evaluation o-f Ship Behaviour in Realistic Seas -1-st 'IMAEM Congress, Istanbul', 1978

9.Kishev R. - nalysis o-f Express Methods -for Sea

keeping Evaluation at Earlier Stages

o-f Ship Deesign BSHC. 198

1O.Kishev R. .Dimitrova ,A Procedure for Ranking Seakeeping

Gaberova M. EstimatiDn at Mult:ivriant Ship

Design -' BSHC, 198e

11.Kishev R, Sirakov A.. -Standards -for Good Seakeeping - A Look From the Bridge'- 4-th IMAEM Congress, Varna, 1987

12.Kovachev S.,Yovev Y. -Computer Aided Synthesis of Ship Form - FF:ADS'83, Tokyo, 1983

13.Lin W. C. et ai. An Advanced Methodology for Frelimi nary Hull Form Development -- NEJ

Juli', 1984

14.Loukakis T.,Peraci.s A., The E-f-fet of Some Hull Form Farame

Papulias F. - ters on the Seakeeping Behaviour o-F

16

1.Mande1 P. Leopold R.- _{Optimization Methods Applied, to Ship} Design _{Trans. SNAME4 vol. 74 1966} 16.Ochi M., Leopold R. - _{Prediction of Extreme Ship Re.sponces} in Rough Seas - 7-nt Symposium,

Lon-dòn 1974

17.Pashin V. _{- Shìp"Optimizatjon - Sudostroenie P..}

H.q 'Leningrad! 1983

18.PerakisA. _{- Seakeeping Standard Seriès IT}

-Extension to Oblique Seiways - Sensi .tiyity Analysis- Derivation'o _Main Seakeeping Parameters NTUA. Athens

1977

19.Townsin R.. Kwon Y. - Approx.imate'Formu1 for the' Speed loss due to Added Re.si stance in Wihd

and Waves - Trans RINA 1982

20.WaldenD. A.

- _{Practical Methods fDr Assessing.. Sea}

keeping Perforrnance _{- DTNRDC Report} SPD _{1089 - 01! 1983.}

21.Wijngaardeñ A;M. van - _{The Optimum Farm o+ Small Hull for}

the North Sea Area _{- 1SF. vol} July 1984.' No 39

AFFEND I

X A

Practic1 application a-F the ranking etirnation approach

The hull -form

_{optimization by sakeping ranking}

as approbated on a 14000 TDW container

_ship

_design.

_Te1v

variants were g9neratEd ensuring _{wide dviation o-F intera1} geometry parameters at constant disp1acment. _{The values o4}

th

_{governing paramtrs in the sri}

_{ar within the fo11oving}

rang9s:

0.5(LCE+LCF

_{= -( O.O13 O.O45}

SF/SM SA/SM and trim are

kept constant -for

simpli-city.

The geometric measures of

dsin variants

ar systematized in Tabl9 i and Tab1 2 gives

the wihtd

sakeping charactristjcs

ca1cu1atd

by SEAQPT [10] and

carrsponding rank critr-ion.

After effecting linear regression,, th

fo11aing

seakesping rank 9guation is obtained:

R = 43.56 - 4.895(L/ 1/3)

3322Cb 25.42C

+7.75.(T/L) - 1..682(B/T) - 60.68(LCB- LCF)

+66.71(LCB + LCF)/2.

at mean square error

less than 6V..

The

_expression

_thus

_obtained

_can

_be

_used

_for

evaluation of each ne ship +orm variant of this type _reduced to constant displacement .For each

_{ne1y developed projct}

_the obtaining is _{ossib1e o-F similar evaluations. Even thus early!} however!conclLtsions can be made about the influence of each of the geometric parametersparticipating _{in the rank equation. on} seakeeping. which is determined by the regression coefficient's sign E1J. Th _{increase in the parameters with a (-) sign will}

lead to a orsenjn _{o-F seakeeping.. and vice versa. This can be} a goad orientation -for th _{designer still in the initial} selection of the hull form _variants.

L/V1"=

CB = cw =

(;.35

(0.4

(0.712 6.20) + 0.697) * 0.871)

T/L

= (0.048 -- 0.065)

B/T = (2.47 + .55) LCB-LCF =

( 0.005

0.063 _.

Table 1. Main geometric characteristics of the variants of a 14,000 TDW containershi No. variant L _m B m T m CB -V m3 L/\7"3 -L/B -B/I -I/L -C -LCB-LCF (LCB+LCF) i 136 21.0 7.65 0.6441 14072 5.633 6.476 2.745 0.0563 0.798 0.027 -0.025 2 142.8 21.0 7.65 0.6161 14134 5.906 6.800 2.745 0ft536 0.799 0012 -0.014 3 129.2 21.0 7.65 0.6772 14057 5.353 6.152 2.745 0.0592 ' 0.805 0.033 4 138.7 189 7.65 0.6968 13976 5.759 7.340 2.471 0.0551 0.872 0.021 -0.021 5 132.6 23.1 7.65 0.6055 14189 5.477 5.740 3.020 0.0577 0.725 0.029 -0.025 6 136.0 23.1 6.50 0.6866 14021 5.64 5.887 3.554 0.0478 .0.712 0.057 -0.013 7 136.0 20.0 7.65 0.6654 13846 5.664 6.800 2.614 0.0563 0.845 0.024 -0022 8 142.8 21.0 7.00 0.6696 14055 5.917 6.800 3.000 0.0490 0.764 0.040 -0.031 9 129.2 21.0 8.42 0.5544 13670 5.543 6.152 2.494 0.0652 0.786 0.022 -0.045 10 136.0 21.0 7.65 Ó.6452 14097 5.630 6.476 2.745 0.0563 0.830 0.005 -0.032 11 149.6 21.0 7.65 0.5848 14053 6.200 7.124 2.745 0.0511 0.752 0.063 -0.031 12 136.0 21.0 8.42 0.5830 14019 5.640 6.476 2.494 0.0619 0.793 0.009 -0.038

Table 2. Averaged seakeeping characteristics of the variants of a 14000 TDW containership No. Z.. variant - _m e113

deg.

NAW

h.p.

NSH

-NSL -NSR -a113 rn/sec2 R . i 0.610 1.31 1222.8 51.5 1.8 12.3 1.73 8.114 2 0.493 1.15 1180.9 78.1 0.7 17.3 1.66 8.036 3 0.803 1.44 1396.5 51.1 3.1 16.4 1.95 5.563 4 0.551 1.17 1354.6 71.5 0.7 12.0 _1.95 8.031 5 0.711 1.44 1216.5 47.1 2.8 16.3 1.77 6.723 6 1.058 1.01 1796.9 30.9 9.8 10.2 1.16 1.000 7 0.589 1.24 1434.4 70.7 0.9 12.2 2.09 7.428 8 0.808 1.33 1480.2 45.1 6.3 23.1 1.73 2.213 g 0.679 1.46 1148.0 51.8 1.5 2.7 1.85 10.000 io 0.478 1.22 1271.5 59.5 0.7 11.4 1.81 8.776 .11 _0.912 1.26 . 1762.7 45.9 7.9 7.5 1.74 2.418 12 0.540 1.37 1298.6 64.7 1.0 5.8 1.90 9.124