SUPERIOR SEAWORTHINESS OF A RESONANCE-FREE FAST OCEANGOING SWATH

2021 ◽  
Vol 156 (A4) ◽  
Author(s):  
M Yoshida ◽  
H Kihara ◽  
H Iwashita ◽  
M Kanda ◽  
T Kinoshita
Keyword(s):  
High Speed ◽  
Time Lag ◽  
Ship Motions ◽  
Speed Reduction ◽  
Small Water ◽  
Motion Responses ◽  
Head Waves ◽  
Unsteady Characteristics ◽  
Hull Forms ◽  
Heave Motion

The speed reduction, additional resistance or slamming caused by the large amplitude ship motions, should be completely restricted for a large fast oceangoing ship because of the strict time-punctuality and the high value of the cargo. A “Resonance-Free SWATH (RFS)”, which has negative restoring moments due to the extremely small water plane area, is introduced to minimize the motion responses. A motion control system using small fins is necessary for the RFS, which has no stability during high speed cruising. Theoretical estimations and experiments to search for the optimum values of PD control gains have been performed. Unsteady characteristics of fin-generated lift such as the time lag and the interaction among the fins and lower hulls have been measured and they are taken into account in the motion equations. Then, experiments using the RFS model with controlling fins have been carried out to validate the theoretical estimation for the motion responses of the RFS in waves. The theoretical and experimental results agree well with each other. The motion responses of the RFS in regular and irregular head waves are compared with those of other hull forms, such as a mono-hull, an ordinary SWATH and a trimaran. The clear advantage of the RFS regarding the seaworthiness has been found. In summary, the heave motion response of the RFS is reduced to 1/60 and the pitch motion becomes1/8, compared with those of the existing mono-hull ship.

On the Resonance-Motion-Free SWATH (RMFS) as an Oceangoing Large Fast Platform

2009 ◽  
Author(s):  
Motoki Yoshida ◽  
Hajime Kihara ◽  
Hidetsugu Iwashita ◽  
Hiroshi Itakura ◽  
Weiguang Bao ◽  
...  
Keyword(s):  
Ship Motions ◽  
Viscous Effects ◽  
Speed Reduction ◽  
Towing Tank ◽  
Ship Hulls ◽  
Small Water ◽  
Motion Responses ◽  
Additional Resistance ◽  
Spring System ◽  
Heave Motion

The speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely for oceangoing large fast ship, because of the strict time-punctuality and high value of the cargo. In the present work, comparison of seaworthiness properties, such as no speed reduction and absolutely no slamming, is made among four types of ship hulls, i.e. mono-hull, ordinary SWATH, trimaran and Resonance-Motion-Free SWATH (RMFS). The last one can be regarded as a special type of catamaran. As a result of extremely small water plane, the restoring moments are negative for the RMFS hull, which leads to free of resonance in the motion responses. Experiments in towing tank and calculations are carried out to examine hydrodynamic forces and motion responses in waves. Calculations are generally based on potential theory modified by adding the viscous effects and including fin lifts. The results of RMFS are compared with those of mono-hull ship, ordinary SWATH ship as well as trimaran ship. The heave motion responses of RMFS are very small in comparison with those of other ship hulls. On the other hand, the pitch motion responses of RMFS are considerably small in comparison with those of mono-hull or trimaran, but are not as small as expected in comparison with those of ordinary SWATH. The reason is that a soft spring system is applied in experiments, to replace the proportional control action supplied by the fin lift. The spring system can not make use of the advantage of the negative restoring moment, which is a characteristic of RMFS. Accordingly, a new control system of ship motion by means of the lift force from fins should be developed.

The Effect of Controlling Fins on the Motion of Resonance-Free SWATH (RFS) Platform

2010 ◽  
Author(s):  
Motoki Yoshida ◽  
Hajime Kihara ◽  
Hidetsugu Iwashita ◽  
Hiroshi Itakura ◽  
Weiguang Bao ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Ship Motions ◽  
Viscous Effects ◽  
Speed Reduction ◽  
Ship Hulls ◽  
Small Water ◽  
Motion Responses ◽  
Additional Resistance ◽  
Heave Motion ◽  
Derivative Control

The speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely for oceangoing large fast ship, because of the strict time-punctuality and high value of the cargo. In the present work, comparison of seaworthiness, such as the motion responses in head seas, is made among four types of ship hulls, i.e. Mono-hull, Ordinary SWATH, Trimaran and Resonance-Free SWATH (RFS). The last one can be regarded as a special type of catamaran. As a result of the extremely small water plane, the restoring moments are negative for RFS hull, which leads to free of resonance in the motion responses. Experiments in towing tank and theoretical calculations are carried out to examine the motion responses in waves. Calculations are generally based on potential theory modified by adding the viscous effects and including fin lifts. The results of the motion responses of RFS are compared with those of mono-hull ship, ordinary SWATH ship as well as trimaran ship. Where the motion of RFS is controlled using movable small underwater fins. The motion of ordinary SWATH is examined with and without fin control. It can be seen that the heave motion responses of RFS are very small in comparison with those of other ship hulls. Also, the pitch motion responses of RFS are much smaller than those of mono-hull or trimaran or ordinary SWATH without fin control, and are smaller than those of ordinary SWATH with fin control. Fin control actions, i.e. proportional and derivative control, are applied in the experiments and calculations. It is considered that the derivative control action is more effective on the motion responses of RFS than the proportional one as predicted. The larger the derivative gain value is, the smaller the motion response of RFS is.

On the Novel Fast Ocean Platform

2008 ◽  
Author(s):  
Motoki Yoshida ◽  
Hidetsugu Iwashita ◽  
Hajime Kihara ◽  
Hiroshi Itakura ◽  
Weiguang Bao ◽  
...  
Keyword(s):  
Ocean Waves ◽  
Ship Motions ◽  
The Novel ◽  
Time Schedule ◽  
Speed Reduction ◽  
Transport Efficiency ◽  
Ship Hulls ◽  
Small Water ◽  
Motion Responses ◽  
Additional Resistance

The mission of the large trans-ocean fast ship is to transport the high-valued and time-sensitive goods punctually at reasonable price. Accordingly, the speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely. Some seaworthiness, such as no speed reduction and absolutely no slamming, is especially required for ships running fast in ocean waves. The final intention of the study is to compare the transport efficiency, including accuracy of time schedule and transport quality like damage of goods caused by slamming, among three types of ship hulls, i.e. mono-hull, catamaran and trimaran. As a first step, a “Resonance-Motion-Free SWATH (RMFS)” hull is considered as an example of catamaran type in the present work. As a result of very small water plane, the restoring moments are near zero for this type of hull, which leads to free of resonance in the pitch responses. Experiments in towing tank and calculations based on potential theory are carried out to examine hydrodynamic forces and motion responses in waves. The results are compared with those of typical mono-hull and trimaran ships. The predominance of RMFS regarding seaworthiness will be pointed out in the conclusion.

UNSTEADY CHARACTERISTICS OF LIFT GENERATED BY SMALL UNDERWATER CONTROL FIN

2021 ◽  
Vol 158 (A1) ◽  
Author(s):  
M Yoshida ◽  
H Iwashita ◽  
M Kanda ◽  
H Kihara ◽  
T Kinoshita
Keyword(s):  
Frequency Domain ◽  
High Speed ◽  
Lift Coefficient ◽  
Phase Lag ◽  
Speed Reduction ◽  
Small Water ◽  
Theoretical Predictions ◽  
Large Amplitude Motions ◽  
Lift Curve ◽  
Unsteady Characteristics

Speed reduction or slamming must be restricted for a high-speed oceangoing vessel because of the requirement for punctuality and the high value of the cargo. Speed reduction and slamming are caused by large amplitude motions in waves. A promising ship form for such vessels is so-called “Resonance-Free SWATH (RFS)”, which has negative pitch and roll restoring moments due to the extraordinary small water plane area. As a consequence, the resonance peak is removed from the motion response. The attitude of the RFS with negative restoring moments is adjusted by four pairs of control fins attached to the fore and aft ends of the lower hulls. In previous studies, the steady value of the lift-curve slope is usually used in the motion equation of the frequency domain. However, when working in waves, the controlling fins are not working in a steady state and the lift coefficient is no longer a constant. In addition, there exists a phase lag between the change in the attack angle and the fin-generated lift. In the present study, theoretical predictions using a frequency-domain 3D-Rankine Panel Method, as well as experimental measurement, have been made to analyze the phenomena of the lift generation including the phase lag and the interference between fins, the lower hulls and the struts. The theoretical results agree well with the experimental results in spite of the potential theory being without viscosity. Next, the unsteady characteristics of fin-generated lift are expressed as the function of the encountering wave frequency. Then the effects of the fore fins, the lower hulls and struts on the lift curve-slope of the aft fins are discussed.

Lift Characteristics of Controlling Fins of Resonance-Free SWATH

2014 ◽  
Author(s):  
Go Oishi ◽  
Hidetsugu Iwashita ◽  
Masamitsu Kanda ◽  
Motoki Yoshida ◽  
Hajime Kihara ◽  
...  
Keyword(s):  
High Speed ◽  
Lift Coefficient ◽  
Ship Motions ◽  
Phase Lag ◽  
Sea State ◽  
Speed Reduction ◽  
Small Water ◽  
Additional Resistance ◽  
Lift Curve ◽  
Rough Sea

Speed reduction, additional resistance or slamming, which caused by the large ship motions, should be avoided for a high-speed oceangoing vessel, because of the delivery punctuality and high value of the cargo. A promising ship type for such the oceangoing vessel is the so-called “Resonance-Free SWATH (RFS)”. It has negative restoring moment due to the extraordinary small water plane area. As a consequence, the resonance peak is removed from the motion response. RFS is designed to cross 4,800 nautical miles of Pacific Ocean within 5 days punctually at a speed of 40 knots, with good seaworthiness such as no speed reduction or absolutely no slamming even when running in the rough sea of sea state 7 with significant wave height of 6–9 m. The attitude of RFS with negative restoring moment is adjusted by four pairs of controlling fins attached to the fore and aft ends of lower hulls. In the previous works, the quasi-steady values of lift-curve slope are usually adopted in the motion equations of frequency domain. However, when working in waves, the controlling fins are not in a steady state. The lift coefficient is no longer a constant. In addition, there exist a phase lag between the movement of attack angle and the fin-generated lift. The theoretical prediction and the experiment to analyze the phenomena of lift generation including the phase difference and the interaction among fins and lower hulls are carried out. The results show that the characteristics of fins depend on the encounter frequency. Then, the effect of lift characteristics of controlling fins on the RFS model is discussed. The results of theoretical estimation and experiment are discussed and it is observed that estimated results agree to some extent with experimental results.

Operation of Ride Control Systems to Minimise Slamming of Wave-Piercing Catamarans

2021 ◽  
Vol 163 (A1) ◽  
pp. 29-40
Author(s):  
M R Davis
Keyword(s):  
Control Systems ◽  
High Speed ◽  
Vertical Motion ◽  
Ship Motions ◽  
Wave Surface ◽  
Active Motion ◽  
Ride Control ◽  
Heave Motion ◽  
Control Feedback ◽  
Active Controls

Wave slam produces dynamic loads on the centre bow of wave piercing catamarans that are related to the relative vertical motion of the bow to the encountered wave surface. Rapid slam forces arise when the arch sections between centre bow and main hulls fill with rising water. In this paper time domain solutions for high speed ship motion in waves, including the action of active motion controls, are used to compute the slam forces. Slamming occurs at specific immersions of the bow whilst the peak slam force is characterised by the maximum relative vertical velocity of the bow during bow entry. Vertical motions of bow and encountered wave are in antiphase at encounter frequencies where slamming is most severe. The range of encounter frequencies where slamming occurs increases with wave height. Wave slam loads reduce ship motions, the heave motion being most reduced. Deployment of a fixed, inactive T-foil can reduce slamming loads by up to 65 %. With active controls peak slamming loads on the bow can be reduced by up to 73% and 79% in 4 m and 3 m seas, local control feedback being marginally the most effective mode of control for reduction of slamming.

NUMERICAL PREDICTION OF VERTICAL SHIP MOTIONS AND ADDED RESISTANCE

2021 ◽  
Vol 159 (A4) ◽  
Author(s):  
F Cakici ◽  
E Kahramanoglu ◽  
A D Alkan
Keyword(s):  
Deep Water ◽  
High Speed ◽  
Computer Experiments ◽  
Navier Stokes ◽  
Ship Motions ◽  
Added Resistance ◽  
Strip Theory ◽  
Head Waves ◽  
Computational Fluid Dynamics Cfd ◽  
Volume Method

Along with the development of computer technology, the capability of Computational Fluid Dynamics (CFD) to conduct ‘virtual computer experiments’ has increased. CFD tools have become the most important tools for researchers to deal with several complex problems. In this study, the viscous approach called URANS (Unsteady Reynolds Averaged Navier-Stokes) which has a fully non-linear base has been used to solve the vertical ship motions and added resistance problems in head waves. In the solution strategy, the FVM (Finite Volume Method) is used that enables numerical discretization. The ship model DTMB 5512 has been chosen for a series of computational studies at Fn=0.41 representing a high speed case. Firstly, by using CFD tools the TF (Transfer Function) graphs for the coupled heave- pitch motions in deep water have been generated and then comparisons have been made with IIHR (Iowa Institute of Hydraulic Research) experimental results and ordinary strip theory outputs. In the latter step, TF graphs of added resistance for deep water have been generated by using CFD and comparisons have been made only with strip theory.

Numerical Prediction of Vertical Ship Motions and Added Resistance

2017 ◽  
Vol 159 (A4) ◽  
Author(s):  
F Cakici ◽  
E Kahramanoglu ◽  
A D Alkan
Keyword(s):  
Deep Water ◽  
High Speed ◽  
Computer Experiments ◽  
Navier Stokes ◽  
Ship Motions ◽  
Added Resistance ◽  
Strip Theory ◽  
Head Waves ◽  
Computational Fluid Dynamics Cfd ◽  
Volume Method

Along with the development of computer technology, the capability of Computational Fluid Dynamics (CFD) to conduct ‘virtual computer experiments’ has increased. CFD tools have become the most important tools for researchers to deal with several complex problems. In this study, the viscous approach called URANS (Unsteady Reynolds Averaged Navier-Stokes) which has a fully non-linear base has been used to solve the vertical ship motions and added resistance problems in head waves. In the solution strategy, the FVM (Finite Volume Method) is used that enables numerical discretization. The ship model DTMB 5512 has been chosen for a series of computational studies at Fn=0.41 representing a high speed case. Firstly, by using CFD tools the TF (Transfer Function) graphs for the coupled heave-pitch motions in deep water have been generated and then comparisons have been made with IIHR (Iowa Institute of Hydraulic Research) experimental results and ordinary strip theory outputs. In the latter step, TF graphs of added resistance for deep water have been generated by using CFD and comparisons have been made only with strip theory.

scholarly journals CFD Prediction of Ship Seakeeping and Slamming Behaviors of a Trimaran in Oblique Regular Waves

2021 ◽  
Vol 9 (10) ◽  
pp. 1151
Author(s):  
Xiyu Liao ◽  
Zhanyang Chen ◽  
Hongbin Gui ◽  
Mengchao Du
Keyword(s):  
Green Water ◽  
Practical Significance ◽  
Ship Motions ◽  
Oblique Waves ◽  
Motion Responses ◽  
Head Waves ◽  
Grid Technique ◽  
Heading Angle ◽  
Comparative Results ◽  
Cfd Method

The main hull encounters waves at first and causes waves to break, when trimarans are subject to the slamming in head waves. At this moment, emergence phenomena of side hulls will not occur. Thus, the slamming study of trimarans in oblique waves presents further practical significance. In this study, a CFD method is used for trimaran seakeeping and slamming analysis. An overset grid technique is adopted to simulate ship motions in waves. Firstly, to further verify the present method, a series of verification and validation studies is conducted. Then, the motion responses and slamming pressure with different control parameters, such as forward speed and ship heading angle, are calculated and discussed. The comparative results indicate that the seakeeping and slamming behaviors of trimarans differ significantly from those of conventional monohull ships. Finally, severe bow slamming and green water in oblique waves are also observed and investigated, which should be given enough attention during ship design and evaluation.

Ship Motions of KCS in Head Waves With Rotating Propeller Using Overset Grid Method

2014 ◽  
Author(s):  
Zhirong Shen ◽  
Pablo M. Carrica ◽  
Decheng Wan
Keyword(s):  
Wave Length ◽  
Grid Method ◽  
Ship Motions ◽  
Overset Grid ◽  
First Case ◽  
Motion Responses ◽  
Grid Approach ◽  
Head Waves ◽  
Overset Grid Method ◽  
Thrust And Torque

The overset grid method has been implemented in the open source code OpenFOAM. The purpose of this work is to validate the overset code in OpenFOAM and demonstrate the capability and flexibility of overset grid approach to solve complex situations. Ship motions of KCS in head waves with and without rotating propeller are investigated using overset grid method in this paper. Two conditions are conducted. The first case involves the model without propeller advancing at a speed of 1.701 m/s, corresponding to Fr = 0.26 and Re = 6.82×106. Incident regular wave of wave length λ = 1.15Lpp and wave height Hw = 0.084m is adopted. A grid convergence study is conducted for the validation of overset grid method. In the second case, a rotating propeller is installed on the KCS model. The seakeeping characteristics of KCS model with rotating propeller in head waves are investigated numerically. The motion responses and propeller thrust and torque are analyzed and compared with experimental data.

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