Cooperative Resistance Tests with Geosim Models of a High-Speed Semi-Displacement Craft

Transcription

1 Cooperative Resistance Tests with Geosim Models a High-Speed Semi-Displacement Craft by Hiraku Tanaka*, Member Michio Nakato**, Member Kuniharu Nakatake***, Member Takayasu Ueda****, Member Shigeru Araki* Summary A resistance test program a high-speed semi-displacement craft was performed by sixteen towg tanks (cludg one circulatg channel) Japan it volved thirteen geosim models 0.4 to 4 meters length. This work forms a part tasks High-Speed M Vehicle Committee 19th ITTC. Analyzg sixty three data sets, followg conclusions obtaed. The scale effect is not found wave resistance, on or h, it appears trim spray ation. The form factor frictional resistance can be determed even at high Froude numbers, by method suggested by Hughes as a function Froude number. The application turbulence stimulator is necessary resistance tests even for larger models at high-speed. Appropriate turbulence stimulator for semidisplacement hull forms should be developed. The characteristics semi-displacement hull forms range medium Froude numbers (Fn ƒ 1.3) similar to those displacement hull forms many pots. This means that ITTC 1978 power prediction method, with partial modifications, would be applicable to this type high-speed craft. 1. Introduction Factors that have significant fluence characteristics a semi-displacement craft considered different from those a displacement craft because dynamic lift has an important role, especially from pot view propulsive performance studies. Theoretical approaches on resistance estimation a semi-displacement hull form only a few. Recently a small number researchers, such as Maruo(1), Suzuki(2) Bessho (3), have contributed to this subject. Actually, case a semi-displacement craft havg a very high Froude number (Fn =V/ ãg.lpp 2) service speed, oretical studies should be very effective. On or h, case a medium Froude number craft (Fn ƒ 1.3), its hydrodynamic characteristics rar similar to those a displacement craft. Such practical understg can greatly simplify design powerg prediction methods semidisplacement craft. The High-Speed M Vehicle Committee (HSMVC) 19th ITTC showed that ITTC prediction method (1978/1987) is applicable to semi- * Shipbuildg Research Centre Japan ** Hiroshima University *** Kyushu University **** Ship Research Institute displacement craft as long as method was partially modified for high-speed m vehicles. Nakatake also contributed to power prediction semidisplacement craft (Fn ƒ1) at Powerg Performance Committee 19th ITTC, which various results derived from different powerg procedures were evaluated. The discussion seems to be very terestg but no one can say how we should evaluate validity results because a lack exact trial data /or reliable geosim test data semidisplacement crafts. Toger with above-mentioned studies, HSMVC discussed a new resistance test program usg a semidisplacement hull form aimed at obtag reliable data. With this test program, committee wished to determe not only stard data resistance tests but also reliability restance measurements as well as model-ship correlation, accuracy problems. To obta useful formation, it is essential to build up a reliable data base from cooperative resistance tests carried out under controlled conditions. The collection such data geosim tests on high-speed m vehicles is however, not an easy task, because various unresolved factors affectg resistance measurement high-speed models, although some important fluences such as effects Reynolds Weber numbers as well as aerodynamic effects have been vestigated earlier HSMVC studies(5).

2 56 Journal The Society Naval Architects Japan, Vol. 169 The resistance test program was carried out by sixteen towg tanks Japan as a cooperative study HSMVC for 19th ITTC from June 1989 to September The proposal test program was origally made by HSMVC. Attendg Japanese towg tanks were organized as a workg group High-Speed M Vehicle Panel Japan Ship Propulsive Performance Committee. The tentative results test program have been reported 19th ITTC as an terim report by chairman HSMVC K. R. Suhrbier(6). 2. Testg Craft Models As first geosim test high-speed semi-displacement craft, a mono-hull passenger ferry named "Olive" was selected due to her relatively simple hull form typical prcipal particulars Japanese vessels. The prcipal particulars rough les shown Fig. 1. The ferry has a length 23.7 m between perpendiculars, a gross tonnage 70 GT a speed about 28KT at 90 % MCR half-load condition (Although maximum model testg speed was 40 KT). The craft was constructed by Setouchi Craft Co., Ltd., It was recommended by HSMVC that length testg models should be chosen from followg, Lpp =4, 3, 2, 1.5, 0.75, meters. The craft has two propeller shafts, shaft brackets rudders as appendages. Moreover, it was recommended that testg models should be covered with imagary decks (see Fig. 1) stead cabs (models completed as Photo 1 Pictures 2 m Model (SRC) at Fn=1.0 closed-models) order to avoid uncerta scale effect aerodynamic drag. 3. Outle Geosim Model Test Program The basic items to be measured testg resistance, trim skage. As optional items longitudal cut wave priles models, wetted surface a photographic measurement wave spray can be selected accordg to terest each towg tank. For testg speeds, Froude numbers (F, = V/ ãlppg ) 0.7 to 1.0 were required, while or speed ranges less than 0.7 between were made optional. From four testg conditions full-load with without appendages trial load with without appendages, full-load with appendages was made matory while remag three were optional. It was suggested proposal for test program that each towg tank may use its own stard test procedure for high-speed craft. However, it was necessary to stardize some pots testg method. Turbulence stimulation is one important topics to be discussed seriously workg group. In low speed range (Fn ƒ0.5), a turbulence stimulator attached at bow is clearly effective, however, higher speed range it may become effective because bow-up condition breakg spray by stimulator. Therefore most Japanese towg tanks do not practice attachment stimulator to testg models. After discussion, as a basic rule, no stimulator testg se cooperative experiments was recommended. As a result, geosim models do not have stimulator attached except followg three models ; SRI 4 meter model (only low-speed range), SHI 1.5 meter model Kyushu University 0.75 meter model. Kyushu University carried out optional studies relatg to effectiveness turbulence stimulator. semidisplacement craft. Anor important technique relates to towg direction models. The workg group classified towg direction to three categories. They, Fig. 1 Testg Hull Form propeller shaft le direction with runng trim correc-

3 Cooperative Resistance Tests with Geosim Models a High-Speed Semi-Displacement Craft 57 don (symbol, C), propeller shaft le direction at rest (Q) base le direction (U) This cooperative testg for a geosim series semi-displacement passenger ferry became a very large scale resistance test program which was carried out sixteen towg tanks (cludg one circulatg channel) volved thirteen geosim models from 0.4 to 4 meter length. General aspects program shown Table 1, which towg tank dimension, testg condition each tank code name each experiment cluded. As an example, 2 meter model (SRC) is shown Photo 1. resistance coefficient (CT) FA TA conditions shown Figs. 2 3 respectively. Figs. 2 3 clude sets data for 0.4 to 4 meter long models. From se figures, it seems difficult to fd any rules relatg a similarity resistances. For stance, though makg equi-froude number-les on samplg data Fig. 2, les not parallel to frictional 4. Analysis Experiments Analysis resistance tests was performed with followg defitions. 1) Total resistance coefficient ; CT ( 1 ) RT, total resistance S, wetted surface a naked hull (calculated for each le 2) Resistance components at rest) CF, frictional resistance coefficient usg ITTC model-ship correlation le ( 2 ) Eq. (2) means that K(Fn) C(F) disregard Fig. 2 Total Resistance Coefficient (CT) FA Condition scale effect. These hyposes, however, not generally recognized resistance analysis. Therefore, hyposes discussed results resistance test program. Rn, Reynolds number Rn= VLpp/ƒË 3) Form factor ; K K is obtaed by two methods, sce Cw=0 ( 3 ) ( 4 ) 4) Trim Mean skage ( 5 ) da, df dm, variation drafts at AP, FP midship from before runng, 5) Wave pattern resistance ; CWP CWP is obtaed by Newman-Sharma method usg longitudal cut wave prile at y=lpp/2 Fig. 3 Total Resistance Coefficient (CT) TA Condition 5. General Aspect Resistance Test Data As shown Table 1, data this program composed four testg conditions sets data amount to sixty three. The conditions have code names such as FA, FB, TA TB which F T mean Full Trial load condition, A B mean with without Appendages respectively. Each condition is separated to three towg directions. For FB condition, se results FBC, FBQ FBU (regardg C, Q, U, see precedg section). As examples resistance test data, total Fig.4 Correlation among Geosim Models (Due to Samplg data FA Condition)

4 58 Journal The Society Naval Architects Japan, Vol. 169 Table 1 List Experimental Tanks Related Data resistance coefficient curve (Fig. 4). Neverless, comparg data obtaed from different towg tanks we can confirm that most experiments produce consistent data as shown Figs. 5, 6 7 which show CT, trim skage data FA condition for 0.75, meter long models. This means that dividual resistance test seems to have been performed excellently but correlation CT obtaed from geosim tests may clude unknown factors that should be discussed program. 6. Discussions 6. 1 Effect Towg Direction As shown Table 1, all experiments have been classified accordg to towg direction model mentioned section 5. The HSMVC 19th ITTC6) was terested problems connected with towg method high-speed testgs. Therefore, effects towg directions on resistance trim measurement were cfully analyzed. In particular, Kyushu University studied this subject with optional testg usg 0.75 meter model. Unfortunately, accordg to results experiments, effect towg direction model was not directly apped. The report Kyushu University also describes that almost no difference could be found between records resistance obtaed from towg tests FBC FBQ conditions. Even trim record which is easily affected by towg Fig. 5 Cr, Trim Skage 0.75 m Models (FA TA Conditions)

5 Cooperative Resistance Tests with Geosim Models a High-Speed Semi-Displacement Craft 59 Fig. 6 CT, Trim Skage 1.5 m Models (FA TA Conditions) Fig. 7 CT, Trim Skage 4 m Models (FA TA Conditions) direction, re was little discrepancy. To conclude this problem, it is thought that towg direction can be disregarded discussg similarities resistance trim hull form ( speed range, Fn ƒ 1.3) followg section Variation Wetted Surface Area Wetted surface a runng models was measured by followg three methods : ( 1 ) Analysis waves on hull surface measured by photography ( 2 ) Flow observation from side by transpnt models (usg 2, 0.75, meter models) ( 3 ) Analysis trim skage data As shown Fig. 8, results wetted surface a measurements depend considerably on measurg method. It has been found that although variation wetted surface a smaller models (Lpp ƒ0.75 m) has a scale effect, that larger models (Lpp 2 m) has no scale effect. For reasons explaed later, scale effect wetted surface a seems to be related to scale effect trim. From experience participants (SRI Hiroshima Univ. ), order to obta exact formation regardg runng wetted surface a semi-displacement hull forms, transpar- Fig. 8 Variation Wetted Surface Area (FA FB Conditions)

6 60 ent Journal models testg speed 6. hull lift 3 form Spray Spray wetted height From The Figs. Fn=10 tie stard 6. 5 It is said precision craft that is program. models or. The Distance Maximum Spray Positions Height while fe example but followg test were Cw. Maximum Height Spray a high-speed test Fig. 11 shown at made Froude As at resistance valuable model dicate number shown shallow geosim obtaed The as between clearly very depths relation data curve. circulatg vestigations a Froude Aerodynamic a that some only data Reachg 2. channel Fig. 10 spray, typical confirm shows resistance channel like splash even result. each ones, depth V/ ãgdt around to difficult fear data section, larger A cluded (FA), 9. however, is Photo tanks to effect or shallow order, example circulatg if Fig. Effects order 12 spray also from relatilely is, craft. Water Fig. wave real effects it larger towg In follows. a neglibible number a film next which illustrated I. blockage two as is spray, respectively. even different make have maximum dicated non- lenghs correspond 11, effects observed, quite Shallow Table 2). summarized. height scale cause h, just this trim shape channel (see section high- evaluate model mentioned characteristics Some as trim 10 results spray models 4 be These is particles. For uniformity air-resistance on all geosim models, closed model concept was applied photo- to distance, figures can or 6. which on figures, on reachg 9, maximum used smaller spray figures position ones Vol. 169 weak many used at regardg smaller from with origally In effects say even arise studied were a. scattered. scale a Japan, form. were models rar small shapes se smaller surface may spray notations to rar surface ordates The hull which abscissas Architects Observation dimensional The wetted This records if was phenomena graphic Naval (1) variation runng(fn=1.3). dynamic Society preferable. Unfortunately, The shallow last data hump excluded from analysis. Effects one resistance aerodynamic cful important factors measurements effect(6). attention was In paid preventg for this to high-speed resistance test followg items. Photo Fig. 9 Schematic Spray Shape 2 Comparison Sprays, 3m Model [Top] 1.5 m Model (UNT1) Fn = 1.0 (MMB) [Bottom], at

7 Cooperative Resistance Tests with Geosim Models a High-Speed Semi-Displacement Craft 61 Fig. 12 Shallow Water Effect at Various Froude Numbers (dt ; depth) ( 2 ) Waves generated by runng towg carriage were measured order to improve accuracy measurements trim wave pattern resistance. SRI reported that errors trim angle measurements wave pattern resistance were not serious. However, recently, Yanagihara(7) SRI found that shallow effect on waves due to towg carriage high-speed runng may cause an unsteady trim angle which is sometimes experienced at very highspeed testg towg tanks Wave Pattern Resistance The ma tention measurg wave pattern resistance is to confirm similarity wave resistance. Sce wave pattern resistance makes up majer part total wave resistance even a high-speed semidisplacement hull form, confirmation similarity wave resistance can be performed by wave pattern resistance (Cwp) wave spectrum stead wave resistance (Cw). Figs. 13 Fig. 14 show comparison between CWP Cw full load trial conditions respectively. In se diagrams CWP a 4 meters model two 2 meters models compd. Lookg at Figs. 13, 14 15, we can not fd defitive characteristics concerng scale effect wave pattern resistance. The similarity wave resistance is a vitally important problem powerg high-speed craft, refore results shown Figs may not be sufficient evidence to verify above-mentioned conclusions. However, for present analysis geosim model testg, assumption Eq. ( 2 ) that Cw is only a sgle variable function Ez Reynolds number effect may be disregarded, should be accepted Determation Form Factor As written section 4, form factor frictional resistance (K) is determed by two methods. Sce most models this test program very small, Fig. 13 Scale Effect on Wave Resistance Wave Pattern Resistance (Full Load Condition) Fig. 14 Scale Effect on Wave Resistance Wave Pattern Resistance (Trial Condition) only 4 meters model (SRI) with turbulence stimulator could be tested at low speed with Fn ƒ0.16 (Rn ƒ4 ~ 106). The or method usg Eq. ( 4 ) which had been suggested by Hughes(8), was effective for determg form factor a semi-displacement hull form. For calculation Eq. ( 4 ), (CT- CF) diagram composed from data larger models (Lpp 1.5 m) was used as shown Fig. 16. Determed form factors dicated Fig. 17. as a function Froude number. Many geosim models havg a displacement hull form have had form factor determed by method Eq. ( 4 ). Wigley geosim models studied by

8 62 Journal The Society Naval Architects Japan. Vol. 169 Fig. 15 Longitudal Cut Waves Prile at Y Lpp/2 Fig. 17 Form Factors as Function Froude number 7. Trim Resistance Through precedg discussions, it becomes clear that fundamental characteristics a semidisplacement craft considerably similar to a displacement ship even though Froude number correspondg to service speed is quite different. The authors wish to extend discussion to problem trim resistance similarities semi-displacement craft. Figs show relationship between trim Reynolds number FA FB conditions at Fn = 0.9. As shown se diagrams, trim depends on scale models for smaller models (Lpp ƒ 0.75 m) but it seems to be dependent scale for larger models (Lpp 1.5 m). The trend seems similar to scale effect on spray discussed previous section. An vestigation to data scatterg, appnt Fig. 16 Example Determation Form Factor (K), (FB Condition) Resistance Committee 18th ITTC a recent example(9). However, most cases have not produced consistent results because phase so-called "hump hollow" cluded wave resistance curves is significantly affected by size models. Sce a semi-displacement hull form has a simple resistance curve at high speeds over last hump as shown Figs. 5, 6 7, Eq. ( 4 ) may give a reasonable form factor for hull forms although substantial evidence should be shown future. Fig. 18 Scale Effect on Trim at Fn =0.9 (FA Condition)

9 Cooperative Resistance Tests with Geosim Models a High-Speed Semi-Displacement Craft 63 The resistance components craft shown Figs. 20 to 24. Figs. 20 to 22 correspond to cases Fn =0.3, FA condition, Figs to those Fn= FB condition, respectively. For se diagrams, defitions Cf, Cf(1+K) Cw explaed Eq. ( 2 ), which wave resistance coefficient Cw corresponds to value 4 meter Fig. 19 Scale Effect on Trim at Fn =0.9 (FB Condition) diagrams, dicates that larger models precision model manufacturg is a major cause. This is deduced sce similar results can be obtaed from same model tested different towg tanks. Furrmore, comparg Figs , it is recognized that appendages craft do not significantly affect trim angle. Fig. 22 Resistance Components at Fa =1.0 (FA Condition) Fig. 20 Resistance Components at Fn =0.3 (FA Condition) Fig. 23 Resistance Components at Fn =0.6 (FB Condition) Fig. 21 Resistance Components at Fn =0.6 (FA Condition) Fig. 24 Resistance Components at Fn =1.0 (FB Condition)

10 64 Journal The Society Naval Architects Japan, Vol. 169 long model. If Eq.(2) is exact, measured total resistance coefficients (CT) should be on dotted le, Cf(1+K) + Cw The majority measured CT f le as shown Figs. 20 to 24. We suppose that such discrepancy origates lamar flow around hull. Therefore, as an attempt to prove this, actual frictional resistance coefficient (Cfa) was calculated from measured CT by Eq. ( 2 ). Cfa is plotted by dark circular pots Figs. 20 to 24. As mentioned section 3, most geosim models do not have turbulence stimulators. Therefore, appearance lamar flow effect may be reasonable. The lamar flow effect clearly occurred at lowspeeds for smaller models as shown Fig Conclusions The resistance test program usg thirteen geosim models a high-speed semi-displacement craft summarized. In observg results from a wide perspective, it can be said that semi-displacement hull forms range medium Froude number (Fn ƒ 1.3) have similar characteristics to displacement hull forms many pots. The followg conclusions highlighted this study. ( 1 ) It is confirmed that wave resistance coefficient larger models (Lpp 1.5 m) does not have serious scale effect. ( 2 ) The form factor frictional resistance can be determed by method Hughes(' as a function Froude number. The form factor considerably decreases with crease Froude number. ( 3 ) Trim spray smaller models (Lpp ƒ 0.75 m) have scale effects. However, for larger models, y do not show clear scale effects. To obta exact measurements trim spray, a precisely completed model is necessary. ( 4 ) The application turbulence stimulators is found to be necessary, even for larger models at high Froude numbers. Effective stimulators for ( 5 ) The effect towg direction, variation wetted surface a aerodynamic effect due to towg carriage do not make noticeable effects on results resistance tests this hull form. 9. Acknowledgments The work this paper forms a part tasks High-Speed M Vehicle Committee 19th ITTC. The Japanese Committee member, H. Tanaka has charged himself with resistance test program semi-displacement hull forms should be developed. a high-speed semi-displacement craft. A workg group was organized High-speed M Vehicle Panel under Japan Ship Propulsive Performance Committee (Chairman Pr. H. Kajitani). The authors would like to give grateful thanks to all members workg group. In particular, many helpful discussions with Dr. H. Tadano (Osaka Univ.) Dr. M Komatsu (Defense Agency) gratefully acknowledged. H. Tanaka also would like to acknowledge contug encouragement members HSMVC, especially Mr. K. R. Suhrbier (Chairman HSMVC, Vosper Thornycrt), Mr. K. O. Holden (MARINTEK), Mr. B. Koops (MARIN) Dr. O. Rutgersson (SSPA) Their advices were valuable. Lastly, authors would like to give heart-felt thanks to Shipbuilder, Setouchi Craft Co. Ltd., who accepted ir test program usg Olive (70 GT) as a testg craft. Reference 1) Maruo, H., "Hydrodynamics High-speed M Craft ( 1 )", High-Speed Craft its Performance, High-Speed Craft Symposium, The Society Naval Architects Japan (1989) p. 17 List 2) Suzuki, K., "Hydrodynamics High-Speed Vehicles", High-Speed Craft its Performance, High-Speed Craft Symposium, The Society Naval Architects Japan (1989)p.37 `73 (Japanese). 3) Bessho, M., "The Wave-Makg Resistance High-Speed Boat (The 2nd Report, shallow Draft Ship)", J. Kansai Society Naval Architects, (Unpublished) (1991), (Japanese). 4) Nakatake, K., Kataoka, K., "On Application ITTC 1978 Power Prediction Method to a High Speed Boat" (Technical Note) T. West- Japan Society Naval Architects, No. 79, March (1990 ) p. 231 `236 (Japanese). 5) 18th ITTC Proceedgs, HSMVC Report ( 1987 ) p. 333 `337. 6) 19th ITTC, Proceedgs, HSMVC Report ( 1990 ) Towg Methods Effect P Aerodynamic P Appendage Resistance P. 310 A. 1 Comparative Resistance Tests Carried out JapanP. 360 `365 7) Yanagihara, K., "Water Surface Disturbances Caused by a Towg Carriage Runng at High Speed", Autum Meetg The Ship Research Institute ( 1990 ), (Japanese). 8) Hughes, G. "Friction Form Resistance Turbulent Flow, a Proposed Formulation for Use Model Ship Correlation", T. INA ) Takaka, H. ors, "An Evaluation Resistance Components on Wigley Geosim Models, 1. Consideration on Scale Effect Resistance", J. Kansai Society Naval Architects, Japan No. 195 ( 1984 ), (Japanese).