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The summary of the experiments which have been done about the effect of the anti-pitching bow fins

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T H E SUIJ-ÏARY OF TIIJjJ E X P C I^ I M U N T S ' . V I I I G I I I I A V a B E ^ N DONE ABOUT T H S EFFECT OF T H S A N T I- P I T C H I N G BQ/ï FINSo R e p o r t Nro 80o D e l f t S h i p b u i l d i n g Laboratory» by Ï, S o n o d a . 4 - 1 - 1 9 6 2 » P o u r n a r a s , U,A, D. T . M . B . R e p o r t N r . IO61. O c t o b e r 1956, " P i t c h i n g ; r e d u c t i o n w i t h f i x e d bow f i n s o n a m o d e l o f t h e s e r i e s

60 a n d b l o c k c o e f f i c i e n t

O. 6 O " . M o d e l u s e d : 1 0- f t s e l f - p r o p e l l e d m o d e l o f w h i c h p a r e n t m o d e l i s s e r i e s 60 a n d b l o c k c o e f f i c i e n t O.6O. F i n p a r t i c u l a r s : F l a t p l a t e w i t h s w e p t b a c k l e a d i n g edge a n d w i t h t i p f e n c a . D i o u a e n s i o n : s p a n ( t o t a l ) 8" c h o r d ( a t r o o t ) 5" ( a t t o p ) 3" t h i c k n e s s 1/8" F i n a r e a : 2,5^ o f Aw. I t e n a m a a a u r e d : P i t c h a m p l i t u d e Heave a m p l i t u d e Phase a n g l e . C o n e l u 3 i o n . u o A p i t c h r e d u c t i o n o f 10 t o 30 p e r c e n t c a n b e a c c o m p l i s h e d w i t h bow f i n s , d e p e n d i n g o n apaad a n d wave c o n d i t i o n s .

The p i t c h r e d u c t i o n a t t r i b u t a b l e t o t h e f i n s c o n s i d e r a b l y i m p r o v e s d r y n e s s o f t h e m o d e l i n h e a d s e a s .

The p r a c t i c a l s p e e d r a n g e , a s r e s t r i c t e d b y m o t i o n s o f m i d e -s i r a b l e m a g n i t u d e , i -s a l -s o e x t e n d e d .

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2 -2. P o u r n a r a s , U„ A . D . T . K . B . R e p o r t N r .

108^+.

O c t o b e r

1958o

" A a t u d y o f t h e sea b e h a v i o u r o f a M a r j n e r - o l a a s s h i p e q u i p p e d w i t h a n t i - p i t c h i n g bow f i n s " . M o d e l u s e d : 2 0 - f t s e l f - p r o p e l l e d m o d e l w h i c h r e p r e s e n t s t h e f i n a l d e s i g n o f t h s M a r i n e r - t y p e s h i p .

F i n p a r t i c u l a r s : Four k i n d s o f f i n s ;vsre f i t t e d t o a K a r i n e r mod e l t o mod e t e r m i n e t h e p i t c h r e mod u c t i o n as a f u n c -t i o n o f p l a n c h a r a c -t e r i s -t i c s . And -t h i s i s -t h e a i m o f t h i s r e p o r t . F i n N o . l Swept f o r w a r d i T h i c k n e s s o f m o d e l f i n : 5/8". F i n a r e a : 2,2% o f Aw. V i t h t i p f s n c e g . F i n No.2 T w i n c o n f i g u r a t i o n . C o n f i g u r a t i o n : r e c t a n g u l a r . F i n a r e a j 2 , 2 % o f Aw. '.Vith t i p f e n c e s . :

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5 u n i t s o f e a c h t i p W i t h t i p f e n c e s o F i n N o . 2 h . O b t a i n e d f r o m F i n No.23, b y d r i l l i n g k h o l e s p e s s . W i t h t i p fenoes» F i n No.3 D i h e d r a l c o n f i g u r a t i o n O b t a i n e d b y r o t a t i n g F i n N o . l a b o u t t h e r o o t c h o r d . The d i h e d r a l a n g l e was 30 d e g r s s s y W i t h o u t t i p f e n c e s . F i n No.4 T r i p l e c o n f i g u r a t i o n . 38 • F i n s s e p a r a t e d b y 1 Upper s u r f a c e o f f i n t a n g e n t t o b a s e -l i n e .

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-F i n N o .4 h .O b t a i n e d f r o m F i n N o. 4 , b y d r i l l i n g f i v e h o l e s on e a c h f i n WLB i n d i c a t e d i n s k e t c h . I t e m s m e a s u r e d ; P i t c h a m p l i t u d e Heave a m p l i t u d e Phase a n g l e A v e r a g e b e n d i n g moment o f F i n N o . l , G o a c l u s i o n s . The r e d u c t i o n o f t h e p i t c h i n g m o t i o n b y t h e v a r i o u s c o n f i g u -r a t i o n s i s p -r a c t i c a l t h e sams. The p l a n a r e a o f t h e f i n i s an i m p o r t a n t f a c t o r i n p i t c h r e d u c t i o n . H o w e v e r , t h e r e d u c t i o n i s n o t i n d i r e c t p r o p o r t i o n t o t h e i n c r e a s e i n a r e a . The v o r t i c i t y on f i n s a r i s e f r o m t h e p r e s s u r e d 1 f f e r a n c s s b e t w e e n t h e u p p e r and t h e l o w e r s u r f a c e s o f t h e f i n . The v o r t i c e s s h e d b y t h e f i n s c a n be d e c r e a s e d b y : 1) . D e e p e r s n b m e r g e r c e o f t h e f i n s . 2 ) . G r e a t e r f i n s p a n . 3) . T i p f e n c e s . 4) . B e l i e f m e c h a n i s m s s u c h a s s l o t s a n d h o l e s .

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3e S t e f e n , G„P. D.T.M.R. Re. Ni'. I I I 8 . December I 9 5 9 . ''Model e x p e r i m e n t s w i t h f i x o . ! bow a n t i - p i t c I i i u K I ' i n s " . M o d e l u s e d i 6*6 f t o ' B l o c k c o e f f i c i e n t , 05,61, f'in p a r t i c u l a r s F i n Span C h o r d P l a n A s p e c t . T i p f e n c e s No, a r e a r a t i o ( l e n g t h , w i d t l

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A l l o f t h . : f i n s were s i m p l e a l u m i n i u m p l a t e s o f r e c t a n g u l a r i l a n and c r o s s s s c t i o n , and w e r e m o u n t e d on t h e k e e l l i n e o f t h e m o d e l . I t e m s m e a s u r e s : P i t c h a m p l i t u d e . Heave a m p l i t u d e . Phase a n g l e s . R e s i s t a n c e . V e r t i c a l a c c e l e r a t i o n . C o n c l u s i o u s e The f i n s g e n e r a l l y i n c r e a s e t h e r e s i s t a n c e i n c a l m w a t e r a n d i a waves l o n g e r t h a n a b o u t 120% o f t h e s h i p l e n g t h . The r e s i s t a n c e i n waves w i t h l e n g t h b e t w e e n 75 and ^?0% o f t h e s h i p l e n g t h , h o w e v e r , i s l e . 3 s t h a n t h a t w i t h o u t f i n s . 1 S m a l l c h a n g e s i n f i n d i m e n s i o n s w i t h a c o n s t a n t f i n a r e a c a n bal a x p e c t e d t o have n e g l i g i b l e e f f e c t s on p i t c h r e d u c t i o n s and a l s o s h o u l d h a v e a n a g l i g i b l e e f f e c t on r e s i s t a n c e o r a p a a d i n w a v e s . The f i n s o f l a r g e r a r e a p r o d u c e l a r g e r p i t c h r e d u c t i o n s , however, t h e r e d u c t i o n i s n o t i n d i r e c t p r o p o r t i o n t o t h e inc.vease i n a r e a . The use o f t i p f e n c e s i n i n o r e a s i n g t h e e f f e c t i v e a s p e c t o r a t i o was c o n f i r m e d b y t h i s e x p e r i m e n t s .

5

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-- 5 =

4. A b k o w i t a , MoA. 3.N.A,M.E. November 1959.

"The e f f e c t o f . u i t i - p i t c h i n . g f i n s on s u i p m o t i o n s " . M o d e l u s e d : S e r i e s 60. Blocic c o e f f i c i e n t 0,60. D e s t r o y e r . A i r c r a f t c a r r i e r . F i n p a r t i c u l a r s : : H y d r o f o i l t y p e T o t r . l s p a n : 6" C h o r d : 4" F i n a r e a : 7% Aw ( f o r s e r i e s 6o) 7,2% Aw ( f o r d e s t r o y e r ) Aw ( f o r r . i r c r a f t c a r r i e r ) . P i t c h a m p l i t u d e . Heave a m p l i t u d e . Phase a n g l e . • e n d i n g moment a t r o o t o f t h e f i n s . T o t a l b e n d i n g moment a t B. H o r i z o n t a l bow v i b r a t i o n . I t e m s m e a s u r e d C o i i c l c s i o u u . The a n t i - p i t c h i n g f i n s c a n be c o n s t r u c t e d t o s t a y on t h e s h i p u s i n g s h i p s t r u c t u r a l m a t e r i e l e , o f nori,.al and r e a s o n a b l e d i m e n s i o n s . T h e r e i s no m a r k e d i n c r e a s e i n t h e h o g g i n g moment when t h e f i n a a r e a d d e d and t h e i n c r e a s e i n s a g g i n g moment i s n o t c r i t i c a l s i n c e t h e v a l u e i s b e l o w t h a h o g g i n g moment.

The bow h o r i z o n t a l v i b r a t i o n s a r e o b s e r v e d , r o t the e x c i t a t i o n -r e s o n a n c e t y p e , b u t t h e i m p a c t - d e c a y t y p e o f v i b -r a t i o n . The i m p a c t t y p e o f l o a d i n g i s i n d i c a t i v e ©f a s u d d e n change o f p r e s s u r e on t h e a i d e o f t h e bow. The f i l m s w h i c h was t a k e n i n t h i s r e p o r t i n d i c a t e d t h a t , on p e n e t r a t i o n o f t h e s u r f a c e o r n e a r p e n e t r a t i o n , t h e downward m o t i o n o f t l i e bow and t h e l a r g e a n g l e o f a t t a c k on t h e f i n w h i c h i s p r o -d u c e i l ;;ave r i s e t o a l o w - p r e s s u r e r e g i o n on t h e f i n u p p e r s u r f a c e , c a u s i n g a s u c t i o n and v . ^ n t i l a t i o n o f t h e u p p e r s u r f a c e , vVhen t h e v e n t i l a t e d b u b b l e c o l l a p p e d , a l a r g e h y d r o d y n a m i c p r e a a u r e i m p a c t was f e l t on t h e s i d e o f t h e h u l l j u s t a b o v e t h e f i n . Hence i h e r e r e s u l t s a n e t h o r i z o n t a l i m p a c t f o r c e a t t h e bow. From a h y d r o d y n a m i -P23-"*^^9^ t h e r e i s l i t t l e t o be g a i n e d i n p i t c h r e d u c t i o n

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. 6 -5. O c h l , K. S.N.A.M.d. November I 9 6 I . " H y d r o e l a s t i c s t u d y o f a s h i p e q u i p p e d w i t h an r.u c i - p i t c h l u K f i n " M o d e l u s e d : 5,5 f t . m o d e l o f t h e M a r i n e r . Cb : 0,624. F i n p a r t i c u l a r s : L o c a t i o n ( a f t o f F.P.) 5,8 %L Span i n 5,40 C h o r d i n 2,50 F i n A. A s p e c t r a t i o 2 , l 6 E f f e c t i v e area/Aw 0,028 ^ i n B, C a n d D a c c o r d i n g t o t h e i r l o c a t i o n . F i n X, Y and Z as v i b r a t i o n s o f F i n A, h a v i n g c o n f i g u r a t i o n s . I t e m s m e a s u r e d : P i t c h a m p l i t u d e . HeavG. Bov/ a c c e l e i - a t i o n . I m p a c t p r e s s u r e . V i b r a t i o n . R e s i s t a n c e . C o n c l u s i o n s . 1) . The m e c h a n i s m o f o c c u r r e n c e o f i n d u c e d v i b r a t i o n . The m e c h a n i s m o f o c c u r r e n c e o f t h e i n d u c e d v i b r a t i o n i s o f two t y p e s . One i s t h e c a v i t y t y p e a n d t h e o t h e r i s t h e s l a m - p l u s - c a v i t y t y p e .

The i m p a c t f o r c e i s a p p l i e d t o t h e bow s i d e and t o t h e f i n . The i n d u c e d v i b r a t i o n i s i n i t i a l l y a t o r s i o n a l v i b r a t i o n 2) 0 F u n d a m e n t a l p r o p o r t i e ; : o f t h e i n d u c e d v i b r a t i o n . The i n d u c e d v i b r a t i o n i s s e r i o u s l y i n c r e a s e d when t i m e d i f f e r e n t i a l o f l o a d i n g on b o t h s i d e s o f f i n p l u s t h e t i m e d u r a t i o n o f l o a d i n g i s n e a r l y e q u a l t o t h e n a t u r a l p e r i o d o f t h e 1st mode o f t o r s i o n a l / i b r a t i o n s o f t h e h u l l .

The i n d u c e d v i b r a t i o n does n o t a p p e a r i n waves o f l o w h s i g h t f'or a n y s h i p s p e e d .

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-I f t h e f i n i s a l w a y s g r e a t e r t h a n a c e r t a i n d e p t h b e n e a t h t h a m o v i n g wave s u r f a c e , t h e c a v i t y w i l l n o t f o r m a n d h e n c e t h e v i b r a t i o n w i l l n o t o c c u r f o r a n y s h i p s p e e d o r a n y wave h e i g h t . 3 ) . E f f f c c l o f l o G ^ . i i o u oT bcv f i a . k), i : ; f f e c t o f s i z e o f bov/ f i n . The r e d u c t i o n i n p i t c h , h e a v e a n d bow a c c e l e r a t i o n i n -c r e a s e s a p p r o x i m a t e l y l i n e a r l y w i t h i n -c r e a s e o f f i n a r e a , a n d t h e f o r c e s a c t i n g o n t h e f i n s , t o o . I n c j a s i n g t h e a r e a o f f i n s i s f a v o r a b l e f o r r e d u c t i o n i n l i t c h b u t i s u n f a v o r a b l e f o r v i b r a : : ' o n . 5) . F i x e d s t e r n f i n . 6) 0 E f f o c t o f bow f i n c o n f i g u r a t i o n . A f i n h a v i n g h o l e s o f p r o p e r s i z e a n d s h a p e ( F i n X) a p -p e a r s t o be b e n e f i c i a l f o r b o t h p i t c h r e d u c t i o n .-vad v i b r a t i o n p r e v e n t i o n . The r e s i s t a n c e a n d h e a v i n g m o t i o n f o r f i n X, how-e v how-e r , i s g r how-e a t how-e r t h a n t h a t f o r f i n A.

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