Seakeeping Performance Of Ship Research Articles

Investigation of Seakeeping Performance of Trawler by the Influence of the Principal Particulars of Ships in the Bering Sea

Investigating ship motion under real conditions is vital for evaluating the seakeeping performance, particularly in the design process stage. This study examined the influence of the principal particulars of a trawler on its seakeeping performance. The wave conditions in the Bering Sea are investigated using available data. The length-to-beam (L/B) and beam-to-draft (B/T) ratios of the ship are changed by 10% for the numerical simulation. The response amplitude operator (RAO) motion, root mean square (RMS) value and sensitivity analysis are calculated to evaluate the influence of the trawler dimensions on ship motions. The peak RAO motion affected the ship motions noticeably because of the resonance at the natural frequency. The L/B and B/T ratios are important geometric parameters of a ship that significantly influence its RMS motion, particularly in the case of roll and pitch. The change in the B/T ratio has a good seakeeping performance based on a comparison of the roll and pitch with the seakeeping criteria. The present results provide insights into the seakeeping performance of ships due to the influence of the principal dimensions in the design stage.

Wave energy conversion using heaving oscillator inside ship: Conceptual design, mathematical model and parametric study

A concept of utilizing heaving oscillators inside a ship as a means of capturing wave energy is proposed, drawing inspiration from the two-body self-contained wave energy point absorber. This concept involves the ship acting as a small-amplitude-motion platform and the heaving oscillator as a large-stroke body, where the kinetic energy of their relative motion can be converted into electrical energy through a power take-off (PTO) system. The dynamic equations of the ship and the inboard heaving oscillator under regular waves are derived using the boundary element method and solved using a Python code with 4th-order Runge-Kutta integration. The numerical results exhibit favorable agreement with publicly available experimental data. Furthermore, the effects of forward speed, encounter angle, and PTO mechanical parameters on various aspects, including ship motion, oscillator response, wave energy capture performance, and inner loads, are investigated. The results show that the concept of heaving oscillator inside ship has no significantly adverse effects on the ship seakeeping performance. Both forward speed and encounter angle significantly influence the encounter period and thereby impact the sensitivity of capture width (CW) at a broader band of incident wave periods. Conversely, PTO mechanical parameters exerting a more localized impact primarily under long incident waves.

Numerical study of swell impact on seakeeping performance of surface combatant

The complex sea states with the co-occurrence of swell and wind-sea conditions represent threats to sailing vessels. This study presents the computational fluid dynamics (CFD) simulations for a surface combatant model advancing in mixed seas combined with the swell and wind-sea components, aimed at estimating the swell impact on ship seakeeping performance. An in-house unsteady Reynolds-averaged Navier–Stokes solver coupled with an overset grid approach is applied to the numerical predictions, along with the assessment study for the model advancing in calm water and harmonic wave group based on the existed model tests, indicating the CFD results agree well with the experimental data. Irregular wave simulations are then conducted for the model advancing in head seas combined with different swell and wind-sea components. Comparisons of ship seakeeping behaviors for wind-sea dominated, energy equivalent, and swell dominated mixed seas are carried out with the statistical assessment and frequency analysis. Overall, both the heave and pitch amplitudes are larger as the ship is advancing in swell dominated sea than those in the other two seas. The ship motions are also predicted in wind sea and it indicates that the ship encounters the larger heave motion in mixed seas compared with that in wind sea.

CFD Investigation into Seakeeping Performance of a Training Ship

The numerous ship accidents at sea have usually resulted in tremendous loss and casualties. To prevent such disastrous accidents, a comprehensive investigation into reliable prediction of seakeeping performance of a ship is necessarily required. This paper presents computational fluid dynamics (CFD) analysis on seakeeping performance of a training ship (full scale model) quantified through a Response of Amplitude Operators (RAO) for heave and pitch motions. The effects of wavelengths, wave directions and ship forward velocities have been accordingly taken into account. In general, the results revealed that the shorter wavelengths (l/L ? 1.0) have insignificant effect to the heave and pitch motions performance of the training ship, which means that the ship has good seakeeping behavior. However, the further increase of wavelength was proportional with the increase of RAO for her heave and pitch motions; whilst it may lead to degrade her seakeeping quality. In addition, the vertical motions behavior in the following-seas dealt with higher RAO as compared with case of the head-seas condition. Similarly, the subsequent increase of the ship forward velocity was prone to relatively increase of the RAO for her heave and pitch motions especially at l/L ? 2.0. It was merely concluded that this seakeeping prediction using CFD approach provides useful outcomes in the preliminary design stage for safety assessment of the training ship navigation during sailing.

CFD prediction of ship seakeeping behavior in bi-directional cross wave compared with in uni-directional regular wave

The seakeeping behavior of a vessel in multi-directional wave differs significantly from that in uni-directional wave. Given that a vessel operates in multi-directional or short-crested waves during its whole service period, it is important to have a better understanding of the influence of wave directionality on ship seakeeping performance. In this study, CFD method is used to simulate ship motions in both uni- and bi-directional regular waves. A S175 hull model is adopted for seakeeping analysis. Both uni- and bi-directional waves are generated by velocity boundary method. Overset grid technique is adopted to simulate ship motions in waves. Ship motions in different uni-directional regular wave conditions are predicted and validated by experimental data at first. Then ship motions in monochromatic bi-directional wave conditions with different control parameters such as wave length, ship speed and ship heading angle are predicted and analyzed. The comparative results indicate that ship motion response in bi-directional waves is generally larger than that in uni-directional waves. Moreover, severe bow slamming and green water under bi-directional waves are also observed and investigated. This study indicates that ship seakeeping behavior in bi-directional wave should be paid enough attention during ship design and evaluation.

CFD Simulation of Ship Seakeeping Performance and Slamming Loads in Bi-Directional Cross Wave

Accurate prediction of ship seakeeping performance in complex ocean environment is a fundamental requirement for ship design and actual operation in seaways. In this paper, an unsteady Reynolds-averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) solver with overset grid technique was applied to estimate the seakeeping performance of an S175 containership operating in bi-directional cross waves. The cross wave is reproduced by linear superposition of two orthogonal regular waves in a rectangle numerical wave tank. The ship nonlinear motion responses, bow slamming loads, and green water on deck induced by cross wave with different control parameters such as wave length and wave heading angle are systemically analyzed. The results demonstrate that both vertical and transverse motion responses, as well as slamming pressure of ship induced by cross wave, can be quite large, and they are quite different from those in regular wave. Therefore, ship navigational safety when suffering cross waves should be further concerned.

Frequency-domain hybrid method on motions of ship with forward speed

The paper presents a hybrid method in frequency domain to predict the wave induced motions on ships advancing in waves. A meshless cylinder surface in this solution is taken as the control surface by which the whole fluid domain is divided into the interior domain and exterior domain. The velocity potential and its normal derivative on the meshless cylindrical control surface are expanded into Laguerre-Fourier series. The forward speed Green function is adopted in the exterior domain. The Rankine Green function is used in the interior domain, and the cubic B spline technique is induced to compute the higher order derivatives of the velocity potential on the interior-domain free surface. The exterior domain and interior domain are connected by the continuous condition of fluid on the control surface. The excellent level of agreement with the known semi-analytical solutions and experimental measurements reveals that the present method is efficient and reliable to assess the seakeeping performance of ship with forward speed.

Verification of application of the 2.5D method in high-speed trimaran vertical motion and added resistance prediction

Abstract For the motion prediction of a trimaran, the hydrodynamic interference between main hull and outriggers is a significant factor and need to be taken into consideration. The high-speed slender body potential flow theory (2.5D method) is a high-efficient method to predict the seakeeping performance of ships in waves and has been validated for mono-hull ships. In this paper, the 2.5D method has been applied to predict the vertical motion (heave and pitch) and added resistance of a trimaran in head-sea waves. In addition, a trimaran model test was carried out to analyses the relationship between the travelling speed, outrigger layout, incident waves and heave, pitch amplitude, added resistance of a trimaran. The experimental results are also compared with the numerical results in order to verify the 2.5D method in the application of trimaran motion and added resistance prediction. The comparison results have shown that between Fn = 0.353 and 0.471, the 2.5D method can give out accurate prediction results of vertical motion and added resistance of a trimaran. Meanwhile, the calculation efficiency is high enough which makes it applicable to massive computations.

The Low-Noise Optimization of a SWATH Ship’s Structures Based on the Three-Dimensional Sono-Elasticity of Ships

Basic equations and numerical methods are presented for the three-dimensional sono-elasticity theory of ships in shallow sea Pekeris acoustic waveguide environment. The corresponding software three-dimensional hydroelastic analysis of floating and traveling structures-Acoustic developed based on this theory is used for low-noise optimization design of the strut structures of a 1500-ton small waterplane area twin hull (SWATH) ship. When the SWATH ship was moored in waves and laying down instruments for ocean survey, it was observed that the waves continuously beat the vertical side walls of the struts, resulting in structural vibration and acoustic radiation in the frequency band below 100 Hz. This is a new phenomenon that the hydroelastic response of a local structure disturbs ocean survey performance. This phenomenon is not good for the performance of underwater acoustic equipment because it increases the background noise in the vicinity of the SWATH ship. This problem needs a low-cost and feasible solution. The mechanism of this phenomenon is first discussed by means of a sono-elastic analysis. After a series of low-noise design calculations for the strut structures, a design of optimal acoustic performance is obtained with only a small increase in the structure weight. Some suggestions on engineering design for solving such problems are also put forward. 1. Introduction The theory of fluid-structure interaction has been widely applied in various engineering practices, including improvement of ship's seakeeping performance and structural safety, ship vibration and noise control, and enhancement of underwater acoustic stealthiness. In the late 1970s of the twentieth century, hydroelasticity of ships was established as one new branch of ship's fluid-structure coupling dynamics (Bishop & Price 1979). In the early 1980s, by combining the three-dimensional potential flow theory of ship motions with the three-dimensional structural dynamics, three-dimensional hydroelasticity was established by Wu (1984) and Bishop et al. (1986) to deal with the dynamic response of arbitrarily shaped three-dimensional deformable body under internal and external loads. Hereafter, the theory was developed continuously into two main subbranches: one is the three-dimensional hydroelasticity with respect to wave-induced dynamic responses of structures in the incompressible fluid field (Wu 1984; Bishop et al. 1986; Wu et al. 1997; Tian & Wu 2006; Kim et al. 2009; Wu & Cui 2009) and the other deals with the acoustic effect in the compressible fluid field (Zhou et al. 2010; Zou et al. 2013; Zou 2014), the latter of which is also called the three-dimensional sono-elasticity of ships.

A comprehensive study on the seakeeping performance of high speed hybrid ships by 2.5D theoretical calculation and different scaled model experiments

In this paper, seakeeping performance of vessels is comparatively investigated by means of improved 2.5D theoretical calculation, small-scale model towing tank test and large-scale free running model sea trial. This study also provides a scheme of ship vertical motion stabilization technique by using Semi-Submerged Bow (SSB) appendages. Firstly, an improved strip theory based 2.5D theoretical seakeeping algorithm, which considers the viscous flow effects attributed to bow appendages, is developed to estimate ship vertical motion responses in regular waves. Short-term predictions are also made on the basis of spectral analysis theory to predict ship motion responses in irregular waves. Then corresponding small-scale models are made and tested in a laboratory towing tank for both regular and irregular wave conditions to confirm the numerical results. The tank testing results between different ship schemes are also compared to experimentally investigate the effects of SSB and fin on hull vertical motion stabilization. Furthermore, large-scale model sea trials are conducted in coastal waves for a final validation of the ship seakeeping performance in short-crested sea waves. Finally, comparisons of the results by different testing approaches are systematically made and analyzed.

Numerical and experimental study on seakeeping performance of ship in finite water depth

Vessels operating in shallow waters require careful observation of the finite-depth effect. In present study, a Rankine source method that includes the shallow water effect and double body steady flow effect is developed in frequency domain. In order to verify present numerical methods, two experiments were carried out respectively to measure the wave loads and free motions for ship advancing with forward speed in head regular waves. Numerical results are systematically compared with experiments and other solutions using the double body basis flow approach, the Neumann-Kelvin approach with simplified m-terms, and linearized free surface boundary conditions with double-body m-terms. Furthermore, the influence of water depths on added mass and damping coefficients, wave excitation forces, motions and unsteady wave patterns are deeply investigated. It is found that finite-depth effect is important and unsteady wave pattern in shallow water is dependent on both of the Brard number τ and depth Froude number Fh.

Investigation of a ship’s hydroelasticity and seakeeping performance by means of large-scale segmented self-propelling model sea trials

The traditional laboratory models for the hydroelasticity and seakeeping performance of ships are tested in calm water and in uni-directional, artificially generated waves. A new alternative to the tank model measurement methodology is to conduct experiments using large-scale models in actual sea conditions. To implement the tests, a large-scale segmented self-propelling model and testing system were designed and assembled. A buoy wave meter was adopted to record the coastal waves that the model encountered during the tests. The analysis of the results of waves in sheltered waters by the spectral method shows good agreement with ISSC spectra. To investigate the difference between this new methodology and the traditional towing tank tests, a small-scale model, whose type and configuration are the same as those of the large-scale model ship, was used and tests were conducted in a towing tank. Comparison of the two experimental results shows that there is a remarkable difference in the response characteristics between the large-scale model at sea and the small-scale model in the tank. Numerical simulations of the responses of the ship under equivalent sea states were also carried out. The influence of directional spreading functions on the results was analyzed by a numerical approach. The classical model tests under long-crested waves in the towing tank over-estimate the motion and wave load responses; however, large-scale model tests carried out at sea are more reasonable for ship design and scientific research.

ESTABLISHMENT OF EFFECTIVE METAMODELS FOR SEAKEEPING PERFORMANCE IN MULTIDISCIPLINARY SHIP DESIGN OPTIMIZATION

Ship design is a complex multidisciplinary optimization process to determine configuration variables that satisfy a set of mission requirements. Unfortunately, high fidelity commercial software for the ship performance estimation such as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) is computationally expensive and time consuming to execute and deters the ship designer’s ability to explore larger range of optimization solutions. In this paper, the Latin Hypercube Design was used to select the sample data for covering the design space. The percentage of downtime, a comprehensive seakeeping evaluation index, was also used to evaluate the seakeeping performance within the short-term and long-term wave distribution in the process of Multidisciplinary Design Optimization (MDO). The five motions of ship seakeeping performance contained roll, pitch, yaw, sway and heave. Particularly, a new effective approximation modelling technique-Single-Parameter Lagrangian Support Vector Regression (SPL-SVR) was investigated to construct ship seakeeping metamodels to facilitate the application of MDO. By considering the effects of two ship speeds, the established metamedels of ship seakeeping performance for the short-term percentage of downtime are satisfactory for seakeeping predictions during the conceptual design stage; thus, the new approximation algorithm provides an optimal and cost-effective solution for constructing the metamodels in MDO process.

A Study on Operating Limit Analysis for Small High-speed Boat

It was carried out a review of operating limit analysis for small high-speed boat by author. In general, a review of ship's seakeeping performance is performed in the step of ship design, but this study was carried out in the state of completion of boat. Motion performance of Pitch, Vertical and Lateral acceleration and Slamming were satisfied in some encounter angle but deck wetness was not satisfied in all it does the analysis. As a result, sea state rather than the speed and encounter angle of vessel have a greater effect on the seakeeping performance of target vessel. It seems to be due to the size of the target ship.

Simulation of floating structure dynamics in waves by implicit coupling of a fully non-linear potential flow model and a rigid body motion approach

We demonstrate the accuracy and convergence of a new numerical model solving wave-structure interactions based on the fully non-linear potential flow (FNPF) theory coupled to a rigid body motion approach. This work extends an earlier model proposed by Guerber et al. (Eng Anal Bound Elements 36(7):1151–1163, 2012), restricted to fully submerged structures, by allowing to solve for freely floating bodies on the free surface. Although we are currently extending the model to three dimensions (3D), the work reported here only considers two-dimensional (2D) problems. We first introduce the FNPF model, originally developed in 2D by Grilli et al. (Eng Anal Bound Elements 6(2):97–107, 1989), Grilli and Subramanya (Comput Mech 17(6):374–391, 1996), and later extended to 3D by Grilli et al. (Int J Numer Methods Fluids 35(7):829–867, 2001). We present the implementation by Guerber et al. (Eng Anal Bound Elements 36(7):1151–1163, 2012) in the 2D-FNPF model of van Daalen’s implicit method for fluid-structure interactions [see van Daalen (Numerical and theoretical studies of water waves and floating bodies, PhD thesis, Universiteit Twente, The Netherlands 1993) and Tanizawa (Proceedings of 4th Osaka colloquium on seakeeping performance of ships 2000)]. We then detail the numerical scheme used for coupling the FNPF model to the motion of a floating rigid body. Moreover, we propose a new numerical strategy for advancing the free surface front inspired by symplectic integrators, which achieves a much better performance for energy conservation. The developed algorithm is first applied to forced motion cases, for which analytical and experimental results can be found in the literature and used as benchmarks. The accuracy of the numerical solution for the fluid and applied forces is then discussed for cases with small or large amplitude motion. In the latter case, a preliminary investigation of non-linear effects is performed for the classical application of a semi-circular heaving cylinder, by comparing the computed hydrodynamic force to the experimental measurements of Yamashita (J Soc Nav Arch 141:61–70, 1977). In particular, the comparison of the magnitude of the force harmonics, up to the third order, shows the importance of simulating non-linear interactions, which become important as the ratio of the radius of the cylinder over the wavelength increases. In a second set of applications, we assess the model accuracy in dealing with freely floating bodies. As a first test case, we consider the decaying motion of a freely heaving horizontal circular cylinder released from a non-equilibrium position above the free surface. In this more demanding computations, we verify that total energy fluid-plus-body motion is well conserved, which confirms the accuracy of the fluid-structure interaction algorithm. As a second test case, we consider the free motion of a rectangular barge in waves and compute the first-order response amplitude operators.

Approximation of the index for assessing ship sea-keeping performance on the basis of ship design parameters

Approximation of the index for assessing ship sea-keeping performance on the basis of ship design parameters This paper presents a new approach which makes it possible to take into account seakeeping qualities of ship in the preliminary stage of its design. The presented concept is based on representing ship's behaviour in waves by means of the so called operational effectiveness index. Presented values of the index were calculated for a broad range of design parameters. On this basis were elaborated analytical functions which approximate the index depending on ship design parameters. Also, example approximations of the index calculated by using artificial neural networks, are attached. The presented approach may find application to ship preliminary design problems as well as in ship service stage to assess sea-keeping performance of a ship before its departure to sea.

Small Vessel Hull Form Optimization for Heave and Pitch Performance

The Ship Motion Program (SMP) originally written for a mainframe computer system has been adapted for use on the IBM PC microcomputer family and subsequently applied to study ship seakeeping performance. The converted program, referred to as the Ship Seakeeping Characteristics Program (SSCP), was utilized for a parametric study on the influence of the main form parameters on heave and pitch performance for the British Ship Research Association (BSRA) trawler series of geometrically related forms. From the results of this study an optimum form has been indicated and its geometrical features defined.

SEAKEEPING AND COMBAT SYSTEM PERFORMANCE – THE OPERATORS‘ ASSESSMENT

ABSTRACTIn a recent effort to improve our assessment of the Comparative seakeeping performance of existing U.S. Navy ships, a seakeeping questionnaire was distributed to the Commanding Officers of U.S. Navy frigates, destroyers, and cruisers. The objectives were to determine, (1) the operational availability of existing weapons and sensors in relation to a ship's seakeeping performance, (2) the availability of ships to make full speed and to conduct sonar, helicopter, and replenishment‐at‐sea operations, (3) effects of a ship's seakeeping limitations on task force and convoy operation, and (4) realistic seakeeping design crteria for use in the design of new ships. The responses to the questionnaire indicated that frigates are severely limited in their availability to conduct ASW task force and convoy operations in the North Atlantic during the winter season because of seakeeping limitations on speed, hull sonar performance, and helicopter operations. The findings suggest that in the design of future ships we need to place emphasis on improving the seakeeping performance of ships in rough water, instead of just their speed and range in calm water. They indicate that the ASW capability of U.S. ships in high sea states would be enhanced by a towed acoustic sensor; an extended range ASW missile; active fin roll stabilizers; and a helicopter recovery assistance, securing and traverse (RAST) system. They also suggest that the question of the interaction of a ship's size and seakeeping characteristics with the choice of weapons and sensors requires careful attention in the design of future U.S. Navy ships.

SHIP SYSTEM SEAKEEPING EVALUATION — A STOCHASTIC APPROACH

ABSTRACTThe recent trend in Naval Forces has been a shrinking Fleet in both numbers and ship size. This dictates that our ships must have greater operational effectiveness if the Navy is to continue to carry out its mission in the future as it has done in the past.The seakeeping performance of a ship is a major determinant of its overall operational effectiveness. The methodology presented in this paper is a comprehensive approach to the evaluation of a ship's seakeeping performance. The scope of this methodology encompasses the assessment of ship mission scenarios and the relative importance of associated mission requirements as well as the probabilistic description of the uncertainties imposed by the variable ocean environment.The methodology is presented in a general sense so that the seakeeping performance of a ship's configuration can be evaluated as a function of mission scenario, mission area, sea state, ship heading, and speed. In order to utilize the full potential of the methodology, more refined scenario descriptions and more accurate environment specifications must be obtained. A simplified example is presented in which a comparison of the operational effectiveness of two small hull forms is made, using information now available to the designer.It is anticipated that the methodology presented can be used not only as a powerful tool in the decision‐making process of practical ship design, but also as the basis for parametric studies of mission strategies.