l-24 captive tests

8/17/2019 L-24 Captive Tests

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Captive TestsTopics Covered:

Non-Linear Models (Ref: PNA Vol III Chap8)

Captive Tests (Ref: PNA Vol III Chap8) Theoretical eter!ination of "#drod#na!ic erivatives(Ref: PNA Vol

%ensitivit# Anal#sis& %#ste! Identi'cation (Ref: PNA Vol III Chap$)

Rdder esin



Captive Tests



Straight Line Test

The velocit#-dependent derivatives *v and Nv of the an# draft and tri! can +e deter!ined fro! the !odecarried in the to,in tan. The !odel is to,ed ,ith avelocit# correspondin to a iven ship /rode n!+evarios anles of attac& 0. A d#na!o!eter at the or

!easres the force * and the !o!ent N e2perienced!odel at each vale of 0. The di!ensional ship valederivatives can then +e o+tained +# !ltipl#in the ndi!ensional derivatives +# the sa!e respective co!of ship lenth& ship speed and sea ,ater densit#.

It can also +e sed to deter!ine the cross-coplin eon *4 and N4 and of 4R on *v and Nv.

https://en.wikipedia.org/wiki/Draft_(hull)

https://en.wikipedia.org/wiki/Froude_number

https://en.wikipedia.org/wiki/Angle_of_attack

https://en.wikipedia.org/wiki/Angle_of_attack

https://en.wikipedia.org/wiki/Froude_number

https://en.wikipedia.org/wiki/Draft_(hull)



Straight Line Tests (Con%traiht line tests in a to,in tan (are sed to !easre Y

the !odel is to,ed at /rode scalin U and at di3erent an

attac β& and its s,a# velocit# is& therefore& iven +# v 6 −d#na!o!eter is sed to !easre the force Y and !o!entanle β and these are then plotted verss v . The slopes ofcrves at 7ero provide Yv & Nv & and ,ith crve 'ttin ,e canonlinear coecients as ,ell. Then nondi!ensionali7e thein and se the sa!e di!ensionless coecients for the shi

%ince the propeller has an e3ect on the h#drod#na!ic derthese tests shold +e condcted ,ith propellers operatinprefera+l# at the ship proplsion point. An nde9ected rdshold also +e inclded in the !odel. %i!ilar tests can +e to et Yδ and Nδ. The !odel is rn at 7ero anle of attac di3erent rdder de9ections δ.



Rotatin Ar! evice



Rotatin Ar! Test evice



Rotatin Ar! Test - Cont



Planar Motion Mechanism



Planar Motion Mechanis!It can +e sed to !easre velocit# dependent derivatNv & rotar# derivatives Yr & Nr & as ,ell as acceleration d

Yv & Nv & Yr & Nr . The PMM consists of t,o oscillato,hich prodces a transverse oscillation at the +o,& another a transverse oscillation at the stern. It also needtransdcers to !easre the forces and special instr!for the proper resoltion of forces. This procedre canh#drod#na!ic coecients as fnctions of fre;enc#&

sefl infor!ation for !otions in roh seas and trans!anevers.

The PMM reslts can +e sed to deter!ine nonlinear coplin e3ects5 as ,ell as h#drod#na!ic coecientsderees of freedo! !otions.



Sensitivity Analysis

% iti it A l i



%ensitivit# Anal#sis

% iti it A l i




% iti it A l i



Theoretical

Determination ofHydrodynamic

Derivatives

How to determine



How to determineTheoretically

Theoretical prediction !ethods are +ased on the principles ofh#drod#na!ics for the evalation of added !ass (acceleration dderivatives) and da!pin (velocit# dependent derivatives) coethree di!ensional +odies.

%ince da!pin depends to a reat e2tent on viscos e3ects& theh#drod#na!ic calclations (sall# +ased on potential theor#) arrelia+le for the acceleration dependent h#drod#na!ic coecienttheoretical approaches sch as slender +od# and strip theor# haso!e sccess in aircraft ,here +od# eo!etr# is do!inated +# ,'ns& reslts for ships have not +een as accrate since there are nsta+ili7in srfaces and the 9o, arond the hll is reatl# altereviscosit#. The rdder coecients Y δ& Nδ& X δδ can +e evalated fro!and dra coecient data for standard foil sections.



Reression Anal#siseference: =ri2& >. ?$$@ Maneverin Technical Man

%eehafen Verla !+"& "a!+r

Empirical reression anal#sis reslts have +een o+tae2press the !ain h#drod#na!ic coecients as fnctprincipal di!ensions.

%ch for!las have statistical sini'cance onl# and ssed ,ith cation onl# ,hen std#in variations fro!si!ilar desin



"#drod#na!ic erivative



System !denti"catio



e'nition of %#ste! Identi'ca

%#ste!s identi'cation is the technolo# of developin!athe!atical !odels of vehicles fro! their d#na!icresponses to rdder !ove!ents. It is a hihl# !athetechnolo# that can +e riorosl# de'ned onl# in statter!inolo#.

The follo,in enineerin application de'nition is ins("all& ?$BB): %#ste! identi'cation deter!ines& fro!inptDotpt data record of vehicle test response& an of the ph#sical !odel ,hich relates to the o+served d



%#ste! Identi'cationPri!ar# application has +een in the develop!ent of

!odel coecients fro! fll scale ship operations forship handlin co!pter si!lations

l-24 captive tests

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