Proceedings of the International Conference Stationing and Stability of Semi-Submersibles, University of Strathclyde, Glasgow, UK, Royal Institution of Naval Architects, RINA (summary)

University

of

Strathclyde

U b .

V.

Scheepsbouwiunu^ P 1 9 8 6 - 5

T e c : * n i s c h e H o q s s c b o o l

Intemational

Conference

1 6 - 1 8 JUNE 1986

Society for

Underwater

Technology

Stationing

and

Stability

of

Semi-Submersibles

at University of Strathclyde

Glasgow, UK

CO-

sponsored

by

The Royal Institution of Naval Architects

STATIONING & S T A B I L I T Y OF SEMI-SUBMERSIBLES

UNIVERSITY OF STRATHCLYDE

GLASGOW, SCOTLAND

16 - 18 J u n e 1986

O r g a n i s e d by:

The U n i v e r s i t y of S t r a t h c l y d e

and t h e

S o c i e t y f o r U n d e r w a t e r T e c h n o l o g y

i n a s s o c i a t i o n w i t h t h e

R o y a l I n s t i t u t i o n o f N a v a l A r c h i t e c t s

PREPRINTS

KOREVORD E v e r s i n c e t h e f o c u s o f o f f s h o r e h y d r o c a r b o n e x p l o r a t i o n s h i f t e d f r o m t h e r e l a -t i v e l y s h a l l o w a n d c a i r a w a -t e r s o f -t h e G u l f o f M e x i c o -t o -t h e more h a z a r d o u s o n e s o f t h e N o r t h S e a , o p e r a t o r s h a v e b e e n l o o k i n g f o r t h e f l o a t i n g v e h i c l e w h i c h p r o v i d e s t h e most e f f i c i e n t w o r k b a s e i n t h e s e more d e m a n d i n g c o n d i t i o n s . As a r e s u l t o f o p e r a t i o n a l e x p e r i e n c e t h e s e m i - s u b m e r s i b l e i s t h e u n a n i m o u s c h o i c e . The d e s i g n w i t h t w i n p o n t o o n s and f o u r t o e i g h t c o l u m n s t o s u p p o r t t h e d e c k h a s b e e n p a r t i c u -l a r -l y p o p u -l a r . Hence t h e j o i n t themes o f t h i s c o n f e r e n c e a r e two i s s u e s t h a t e x e r c i s e a m a j o r i n f l u e n c e on t h e p e r f o r m a n c e and s a f e t y o f s e m i - s u b m e r s i b l e s .

" S t a t i o n i n g " i s c o n c e r n e d w i t h t h e m a i n t e n a n c e o f p o s i t i o n i n r e l a t i o n t o t h e w e l l h e a d and l i m i t a t i o n o f h o r i z o n t a l movement t o t h e v e r y minimum. A n y t h i n g b e y o n d a v e r y s m a l l p e r c e n t a g e e x c u r s i o n i n v o l v e s t e m p o r a r y t e r m i n a t i o n o f o p e -r a t i o n s and t h e -r e s u l t i n g d o w n t i m e means u n u s e d f a c i l i t i e s a n d w a s t e d -r e s o u -r c e s . Good s t a t i o n - k e e p i n g c a p a b i l i t i e s a r e now a v a i l a b l e t h r o u g h t h e i n t r o d u c t i o n o f d y n a m i c p o s i t i o n i n g s y s t e m s a s an a l t e r n a t i v e t o c o n v e n t i o n a l m o o r i n g a r r a n g e -m e n t s . A l l t h e p r o b l e -m s w i t h DP s y s t e -m s h a v e n o t b e e n o v e r c o -m e , h o w e v e r , a n d t h e s e n e e d t o be s c i e n t i f i c a l l y a d d r e s s e d . Work i s n e e d e d on p a r t i c u l a r l y on t h e q u e s t i o n s o f s p e e d o f r e s p o n s e , a c c u r a c y o f p r e d i c t i o n , and t h e p r e s e n t h i g h c o s t o f e q u i p m e n t . " S t a b i l i t y " i s c o n c e r n e d w i t h t h e p r e v e n t i o n o f l a r g e m o t i o n s t h a t c o u l d l e a d t o a c a p s i z e o f t h e s e m i - s u b m e r s i b l e . I t h a s b e e n shown t h a t a n u p r i g h t and i n t a c t s e m i - s u b m e r s i b l e i s an i n h e r e n t l y s t a b l e work p l a t f o r m b u t e f f o r t s t o i n c r e a s e i t s p e r f o r m a n c e e f f i c i e n c y come up a g a i n s t two d i f f i c u l t i e s . The f i r s t i s t h a t c u r -r e n t -r e g u l a t o -r y -r e q u i -r e m e n t s i m p o s e -r e s t -r i c t i o n s on, f o -r e x a m p l e , i n c -r e a s e s i n d e c k l o a d , and s e c o n d l y , c e r t a i n k e y p a r a m a t e r s a r e n o t i n c o r p o r a t e d i n t o t h e p r e s e n t s t a b i l i t y c r i t e r i a . The s i t u a t i o n h a s n o t b e e n h e l p e d by t h e t r a g i c a c c i -d e n t s i n v o l v i n g t h e " A l e x a n -d e r K i e l l a n -d " i n t h e N o r w e g i a n s e c t o r i n 1980 an-d t h e "Ocean R a n g e r " o f f t h e e a s t e r n c o a s t o f C a n a d a i n 1982 I n d e e d , s u c h d i s a s t e r s a r e l i k e l y t o r e s u l t i n more s t r i n g e n t r e g u l a t i o n s w h i c h w o u l d t e n d t o p e n a l i s e p e r -f o r m a n c e e v e n -f u r t h e r . However, -f o r t h e -f i r s t t i m e i n t h e UK, p a r t i c i p a n t s i n t h i s c o n f e r e n c e w i l l be a b l e t o s h a r e i n a s c i e n t i f i c e x a m i n a t i o n o f l e s s o n s l e a r n t f r o m t h e "Ocean R a n g e r " d i s a s t e r . T h i s i n t e r n a t i o n a l c o n f e r e n c e b r i n g s t o g e t h e r p r a c t i t i o n e r s a n d r e s e a r c h e r s f r o m many p a r t s o f t h e w o r l d t o c o n s i d e r t h e s e i s s u e s . The programme i s d i v i d e d i n t o s i x t e c h n i c a l and two p a n e l d i s c u s s i o n s e s s i o n s . T o p i c s r a n g e f r o m t h e b a c k g r o u n d t o s t a b i l i t y r e s e a r c h and t h e m e a s u r e m e n t o f s t a b i l i t y p a r a m e t e r s , t o s t a t i o n i n g p r o b l e m s and p r a c t i c a l a p p l i c a t i o n s o f r e s e a r c h f i n d i n g s .

We a r e d e l i g h t e d t h a t Mr P e t e r E v e r e t t h a s a g r e e d t o g i v e t h e o p e n i n g a d d r e s s and t h a t a number o f f r i e n d s h a v e a c c e p t e d I n v i t a t i o n s t o c h a i r t h e s e s s i o n s . P a r t i -c u l a r t h a n k s a r e due t o t h o s e who h a v e -come f r o m o u t s i d e t h e UK. We a r e g r a t e f u l t o a l l t h e s p e a k e r s f o r t h e i r i n t e r e s t i n g a n d s t i m u l a t i n g p a p e r s and we hope t h e s e w i l l p r o v o k e d i s c u s s i o n a n d g e n e r a t e f r e s h i d e a s . I m y s e l f w o u l d l i k e t o a c k n o w l e d g e t h e c o n s t r u c t i v e comments and s u p p o r t o f t h e members o f t h e Programme C o m m i t t e e . The b u r d e n o f c o n f e r e n c e o r g a n i s a t i o n a t S t r a t h c l y d e f e l l i n t o t h e c a p a b l e h a n d s o f A l i s o n Cook who h a s c h e e r f u l l y c o m b i n e d t h e w o r k f o r t h e c o n f e r e n c e w i t h t h a t c o n n e c t e d w i t h o u r P r o j e c t MASS r e s e a r c h programme. I am i n d e b t e d t o h e r f o r t h e c o n t r i b u t i o n s h e h a s made. H e l p r e c e i v e d f r o m M i s s P F e n t o n , M i s s C H u t c h e o n . Mrs D H o d g k i s s and Mrs S W h i t e l o c k i s a l s o g r a t e f u l l y a c k n o w l e d g e d . C h e n g i Kuo J u n e 1986

C O N T E N T S

FOREWORD

PROGRAMME COMMITTEE

SESSION CHAIRMEN

PANEL CHAIRMEN

SESSION 1

1.

2.

BACKGROUND & PROBLEMS

S t a b i l i t y Requirements f o r Semis ubmerslbles - A

D e s i g n e r ' s Viewpoint

W.M. M a r t i n o v l c h and M.W. F r a u g h t ( E a r l & W r i g h t , U.S.A.)

A New Theory and I t s A p p l i c a t i o n f o r S t a b i l i t y C r i t e r i a

Covering Wave-Induced T i l t Phenomena on Seml-submerslbles

R.C.T. R a i n e y ( A t k i n s R e s e a r c h & D e v e l o p m e n t , U.K.)

SESSION 2.

3.

4.

MEASUREMENT OF S T A B I L I T Y PARAMETERS

Wind Loads on F l o a t i n g O f f s h o r e S t r u c t u r e s

P. F r e a t h y ( A t k i n s R e s e a r c h & D e v e l o p m e n t , U.K.) &

S. T a g g a r t , ( B . P . I n t e r n a t i o n a l , U.K.)

I n c l i n i n g T e s t s I n S e r v i c e

M.S. B r a d l e y ( M i c h a e l B r a d l e y & A s s o c i a t e s , U.S.A.) &

C . J . M a c F a r l a n e ( B . P . I n t e r n a t i o n a l , U.K., now U n i v e r s i t y

o f S t r a t h c l y d e )

SESSION 3. S T A B I L I T Y RESEARCH PROGRAMMES

5. Mobile P l a t f o r m S t a b i l i t y - The MOPS P r o j e c t

L.A. D a h l e ( M a r l n t e k , Norway)

6. Seml-submerslble R e s e a r c h and I t s A p p l i c a t i o n s

C. Kuo & D. V a s s a l o s ( U n i v e r s i t y o f S t r a t h c l y d e , U.K.)

7. The Study of a New Procedure f o r A s s e s s i n g S t a b i l i t y o f

Ships and Offshore S t r u c t u r e s

J . S . P a w l o w s k i ( N a t i o n a l R e s e a r c h C o u n c i l , C a n a d a ) &

M.K. Deb ( M e m o r i a l U n i v e r s i t y o f Newfoundland, C a n a d a )

SESSION 4.

KEY MODEL EXPERIMENTS

8. Hydrodynamic Model Studies of the Ocean Ranger Marine

D i s a s t e r

E.H. Dudgeon ( N a t i o n a l R e s e a r c h C o u n c i l , C a n a d a )

9. Large S c a l e Model Ocean T e s t i n g of a Small

Semi-submersible

D. R. S h i e l d s , R. Zueck & W.J. N o r d e l l ( N a v a l C i v i l

E n g i n e e r i n g L a b o r a t o r y , U.S.A.)

SESSION 5. PRACTICAL APPLICATIONS

10. A Method of Simnltaneoos Measurement of D i r e c t i o n a l Wave

S p e c t r a , S u r f a c e Current and Rig Motion

D.C. B r o d t k o r b , 0. G r o n l i e ( M i r o s A/S, Norway) &

F . A n d e r s s o n ( M a r l n t e k , Norway)

11. A Data System f o r Improving S a f e t y and A v a i l a b i l i t y of

Moored Platforms

N.A. J e n s s e n & T. L o e k l i n g ( K o n g s b e r g A l b a t r o s s , Norway)

12. T r a n s i e n t Motions of a Semisubmersible A f t e r Damages

H. A d a c h i and H. Kagemoto ( S h i p R e s e a r c h I n s t i t u t e ,

J a p a n )

SESSION 6. STATIONING SYSTEMS

13. Dynamic P o s i t i o n i n g of a Semi-submersible - R e s u l t s of

S c a l e Model T e s t s and Computer S i m u l a t i o n s

C.G. K a l l s t r o m & L . B y s t r o m ( S S P A M a r i t i m e C o n s u l t i n g AB,

Sweden)

14. P r o p u l s i v e Aspects of Dynamically P o s i t i o n e d

Seml-submers i b l e s

CONFERENCE PROGRAMME COMMITTEE

C h a i r m a n : P r o f e s s o r C. Kuo U n i v e r s i t y of S t r a t h c l y d e

A t k i n s o n , F .

L l o y d ' s R e g i s t e r of S h i p p i n g

B e c k w i t h , L .

L l o y d ' s R e g i s t e r of S h i p p i n g

Forman, B.

A t l a n t i c D r i l l i n g Co. L t d .

H a r r i s o n , J .

H o u l d e r O f f s h o r e L t d .

J e s p e r s o n , P.

B r i t o i l p i c

L a w r e n c e , G.

MaTSU, Department of E n e r g y

M a c F a r l a n e , C.

BP I n t e r n a t i o n a l

M c i n t o s h , R

Department of E n e r g y

Schuurman, J .

S h e l l E x p l o r a t i o n & P r o d u c t i o n

W a r d l e , D.

S o c i e t y f o r U n d e r w a t e r T e c h n o l o g y

SESSION CHAIRMEN

SESSION 1: Background and Problems -

M i s e n e r , S. ( C a n a d a )

SESSION 2: Measurement of S t a b i l i t y P a r a m e t e r s - M c C l u r e , A. (U.S.A.)

SESSION 3: S t a b i l i t y R e s e a r c h Programmes -

P e t r i e , J . ( U . K . )

SESSION 4: Key Model E x p e r i m e n t s -

W i l l i a m s , G. ( U . K . )

SESSION 5: P r a c t i c a l A p p l i c a t i o n s -

N e d r e l i d , T. (Norway)

SESSION 6: S t a t i o n i n g Systems

H o u l d e r , J . ( U . K . )

PANEL CHAIRMEN

S e m i - s u b m e r s i b l e S t a b i l i t y

A t k i n s o n , F . ( U . K . )