Source Panel Method Research Articles

Time-domain numerical simulation for multi-ships moving in waves with forward speed

With the development of the shipping industry, the impact of hydrodynamic interaction between two or more ships on navigational safety has received widespread attention. However, limited research has been conducted on multi-ships moving in waves with forward speed due to the increased complexity of hydrodynamic interactions caused by speed. Therefore, this paper establishes a numerical model of multi-ship hydrodynamics under the wave impact based on the time-domain Rankine source panel method. The hydrodynamic performance and motion characteristics of ships advancing in waves are investigated. An artificial damping layer is applied to free surface boundary conditions to absorb reflected waves. The fourth-order Runge-Kutta method is used for time integration to solve the motion of the ship. The hydrodynamic and motion response of the classical Wigley III ship model are calculated at each wavelength, and the simulation results are compared with other calculations to verify the reasonable reliability of the numerical method employed in this study. On this basis, sensitivity analysis of different parameters is conducted to reveal the influence of various parameters such as speed, wave direction, transverse distance, and water depth on the motion response of the Wigley III ship model in waves.

Motion characteristics of large arrays of modularized floating bodies with hinge connections

Hinged arrays have garnered increasing interest due to their potential to provide flexible and adaptable solutions for the various challenges faced in ocean development. The effectiveness of these arrays in engineering applications heavily depends on the motion characteristics of each individual module, rather than specific modules, such as the one with the strongest motion. However, the presence of hinge constraints results in coupled motion responses of all modules instead of independent ones. The objective of this study is to investigate the motion behavior of large arrays formed by multiple floaters hinged together, while existing literature mainly focused on two-body hinged systems. Based on the potential flow theory and Rankine source panel method, a numerical program was developed to calculate the hydrodynamic interactions and the coupled motion responses. First, a model test was conducted to validate the developed frequency-domain simulations. A good agreement was achieved. Then, the effects of hinge constraints, the number of modules, and two external constraints on the motion responses of the entire array were discussed. The results indicated that the heave motion of the array subjected to hinge constraints was significantly suppressed, but a strong pitch motion occurred in a larger wavelength range. For hinged arrays, the floaters located at the two ends were most likely to be excited with the strongest motions. Moreover, a shorter hinged array could be used to quantify the trends in the motion of arrays with more floaters. The calculation results also revealed that the motion responses of a hinged array were highly sensitive to the external constraints, e.g., mooring lines.

Açık Kaynaklı Panel Yöntemi Kodlarının Ticari Kod ile Karşılaştırılması ve Değerlendirilmesi

This work provides a benchmark study regarding the open-source panel method codes of two floating wind turbine platforms. HAMS, NEMOH, and WAMIT are compared in terms of their results, computational performance, user-friendliness, and, flexibility. WAMIT’s data is sourced from previous publications for the OC3 Hywind Spar and OC4 DeepCWind Semisubmersible. These reference values are compared to NEMOH and HAMS for the main parameters representing the movement of the structure: wave excitation forces, added mass values, and potential damping. Both of the open source panel method codes were quite successful in the concept of a simple one-piece spar float rather than a multibody semi-submersible in terms of NRMS values. Overall, the most close results were obtained from the surge for added mass, and the most unfavorable results were from radiation damping in the heave. NEMOH brings ineligible results for pitch on both platforms. Neglecting the pitch axis results of NEMOH, both codes showed parallel and reasonably close results to WAMIT. The study aims to help researchers to choose a free open-source alternative to a validated commercial code.

Hydrodynamic Optimization of Foreship Hull-Form Using Contrastive Optimization Algorithms

Yin, X.; Lu, Q.; Lu, Y.; Zou, J., and Wan, L., 2021. Hydrodynamic optimization of foreship hull-form using contrastive optimization algorithms. Journal of Coastal Research, 37(5), 1063–1078. Coconut Creek (Florida), ISSN 0749-0208. In this study, a hydrodynamic optimization design of the foreship hull-form for the Series 60 ship is presented in terms of minimum wave-making resistance by using contrastive optimization algorithms. The partially parametric approach was developed to modify the original foreship hull-form. The wave-making resistance as an objective function was obtained by the Rankine source panel method with nonlinear free-surface boundary conditions in which the numerical computation results were validated against available experimental data and found to be in good agreement with the test. Different optimal design methods were proposed based on the minimum wave-making resistance: the nonlinear programming method (NLP), the nondominated sorting genetic algorithm (NSGA-II), and particle swarm optimization (PSO). Through the implementation and integration of the hull-form deformation module, the hydrodynamic module, and the optimization module the hydrodynamic optimization framework can be established subsequently. This module realizes the full automation of ship-shape optimization design and searches for the most efficient target through intelligent optimization algorithm. The hydrodynamic optimization applications for the Series 60 ship indicate that the wave-making resistance is reduced distinctly at various Froude numbers by the contrastive optimization algorithms and each optimized foreship hull-form is smoothing. The present study demonstrates an effective and robust integrated approach for the hydrodynamic optimization of ship design.

Seakeeping computation of two parallel ships with Rankine source panel method in frequency domain

Present paper aims to develop a three dimensional frequency domain panel method to investigate the hydrodynamic performance of two parallel ships in close proximity with forward speed. As for present method, the Rankine source is adopted; meanwhile, the linearized free surface condition based on a double body or uniform basis flow, which can be shorten as “DB” or “Neumann–Kelvin (NK)”, is derived. As for the radiation condition at infinity, a simple combined evaluation method (SCM) is proposed, which is validated through comparison with numerical results from combined boundary-integral equation method (CM, the whole fluid domain is decomposed into the far-field and the near-field, and the Rankine source & 3DTP is used for the far-field and near-field domain, respectively, to satisfy the radiation condition exactly) and experimental results. Furthermore, present method is applied to evaluate hydrodynamic performance of two parallel ship models. Meanwhile, numerical solutions evaluated by “NK” method and “LFS-DB” method were also given for comparison. Results for present various numerical method agree with those of model experiments. Generally speaking, results from“DB” method show better agreement.

A numerical and experimental investigation of the effect of side walls on hydrodynamic model testing in a wave flume

The side wall effect was normally tackled by potential flow based numerical methods. It is well known that, due to the existence of the resonance frequency in the wave tank, the numerical methods over-predict the hydrodynamic forces when comparing with model experiments. Furthermore, in most of the previous studies on the effects of the side walls, the model was located at the centre of the tank, the disturbances on both sides of the model are symmetric, and the resonances of some of the responses such as wave surface elevation and motions may not be excited at the tank natural frequencies. In the present study, a Rankine source panel method is used to tackle the effects of the side walls and artificial damping is introduced in the free surface boundary condition to account for the viscous damping effect. Model experiments are carried out for a lifeboat model located at various positions in a wave flume. Numerical results of the wave forces, free surface elevations and motions of the model are compared with the model test measurements, and good agreement is found. It is shown that the inclusion of the artificial damping in the free surface boundary condition is effective, in particular for the model at off-centre position of the tank.

Hydrodynamic Design Study on Ship Bow and Stern Hull Form Synchronous Optimization Covering Whole Speeds Range

The main objective of this article is to describe an innovative methodology of synchronous local optimization which considers the whole ship speed range being presented for a KRISO Container Ship (KCS). Parametric form approaches are adopted by employing a fairing B‐spline curve in order to generate variants of the bow and stern of forms using form design parameters modified, resulting in an optimization system based on NSGA‐II. The total resistance is calculated by the Rankine source panel method and the empirical formula which agrees well with the corresponding experimental data and further acquires validation with the overall error of 2.0%. Accordingly, the ship forepart and stern form have been optimized under conditions of the single design speed and whole speeds range based on the considerations of generally distributed and variable operational speeds for the operating characteristics of modern container ships synchronously. The optimized result presents well‐balanced drag reduction benefits which averagely remain above 4.0% of ship resistance decrease. Compared to the traditional optimization process which is based on a specific design speed, the newly developed method is more practical and effective in both automation and integration.

An improved Rankine source panel method for three dimensional water wave problems

An improved three dimensional Rankine source method is developed to solve numerically water wave problems in time domain. The free surface and body surface are both represented by continuous panels rather than a discretization by isolated points. The integral of Rankine source 1/r on free surface panel is calculated analytically instead of numerical approximation. Due to the exact algorithm of Rankine source integral applied on the free surface and body surface, a space increment free surface source distribution method is developed and much smaller amount of source panels are required to cover the fluid domain surface than other numerical approximation methods. The proposed method shows a higher accuracy and efficiency compared to other numerical methods for various water wave problems.

Hydro-elastoplastic behaviour of VLFS under extreme vertical bending moment by segmented beam approach

This paper addresses collapse behaviour of Very Large Floating Structure (VLFS) under extreme vertical bending moment. The study is performed as part of risk analysis to evaluate the consequence of a rare collapse event. Elastic and plastic deformation of VLFS develops under the extreme vertical bending moment while the deformation interacts with the fluid around VLFS. Therefore, hydro-elastoplasticity analysis need be developed taking account of these effects. In this study, the whole VLFS structure is modeled as two elastic beams with an elasto-plastic hinge embedded at the connection. The structural deformation is formulated by using finite element method (FEM). The hydrodynamic behaviour is modeled by using Rankine source panel method in time domain based on two-dimensional potential theory. The two models are coupled. A series of scaled model tests is performed for validation. Simulation and tank test results for the basic collapse behaviour of VLFS are presented and discussed. The numerical method is applied further to a realistic VLFS design to clarify its collapse behaviour.

Numerical solution for a ship-wave problem in a two-layer fluid using a double-model linearised interface condition

ABSTRACTShip performance in shallow water where the rigid bottom is covered by a mud layer is a crucial topic to be investigated. In such muddy areas, a two-layer fluid is stratified according to the properties of the sediments. The water–mud interface behaves similar to a sheet on which the internal waves propagate after the ship's passage. Therefore, for safe navigation, it is necessary to clearly understand the influence of the internal waves on the ship's hydrodynamic force characteristics. In this study, the steady wave-making problem of a ship in a two-layer fluid was solved using the Rankine source panel method. The boundary value problem was formulated using a newly proposed double-model linearised interface condition. After the present method was validated via a comparison with results of a Wigley hull solved by the author's existing method, it was applied to solve the ship-wave problem of KVLCC2. The unique changes in wave-making resistance, sinkage and trim according to the ship's speed and two-layer fluid conditions were evaluated.

Investigation of Hydrodynamic Characteristics of High Speed Multihull Vessels including Shallow Water Effect

The objective of this paper is to investigate the hydrodynamic characteristics of high speed catamaran and trimaran ships at different speeds and finite depths using Computational Fluid Dynamics (CFD) techniques. Three dimensional Rankine Source Panel Method with non-linear free-surface boundary condition is used to capture free-surface potential flow around ship hull. Wave pattern, wave resistance, sinkage and trim for varying lateral and longitudinal separation of hull with varying water depths are determined and compared with each other to investigate spacing and depth effects on multihull ship. Computed results show a significant increase in total resistance for water of finite depth compared to deep water. A significant increase in sinkage and trim has also been found in the case of shallow water for both vessels.

An investigation into added resistance of vessels advancing in waves

The hydrodynamic forces and motions of ship advancing in waves are estimated by using 3D frequency domain potential flow theories. The 3D translating and pulsating (3DTP) source panel method is employed to solve the radiation and diffraction potential problems, in which a semi-analytical scheme is established to get more robust results of integration of Green's function over panels. Added wave resistance is mainly categorized into the contributions of radiation and diffraction. The added wave resistance due to radiation motion of ship is evaluated by the radiation energy principle according to 3D hydrodynamic coefficients and ship motions, while the one due to diffraction is calculated based on steady-state force formula. The motions and added wave resistances of Wigley III hull and S175 containership advancing in waves with various forward speed are calculated and analyzed in frequency domain based on the above mentioned methods. The numerical results are validated for the models by comparing them with experimental data. The results by classic methods commonly used in engineering and the data from published papers are plotted together for comparison and discussion. Better agreement with experimental data in the prediction of peak value and its frequency of added resistance is achieved by present method. It also indicates that the correction of relative motion amplitude should be taken into account so as to improve the accuracy. Component analyses of added wave resistance are carried out and the results show the percentages of radiation part and diffraction part at various frequency respectively. The present method is of satisfactory accuracy and efficiency, which provides a rapid and robust approach to predict added wave resistance of ships voyaging in waves.

A hydrodynamic optimization design methodology for a ship bulbous bow under multiple operating conditions

ABSTRACTThe main objective of this article is to describe an innovative methodology for the hydrodynamic optimization of a ship bulbous bow which considers multiple operating conditions. The proposed method is more practical and effective than the traditional optimization process, which is only based on contractually specified design condition. Parametric form approaches are adopted by employing an F-spline curve in order to generate variants of the hull bulbous bow forms using form design parameters modified, resulting in an optimization system based on improved genetic algorithms. The Rankine source panel method is used for the hydrodynamic evaluation, wherein non-linear free surface conditions and the trim and sinkage of the ship are taken into consideration. The validity and effectiveness of the proposed methodology for a large container ship is investigated by comparing the computational results with experimental data, which demonstrates that the proposed methodology can engage well in the automation process and improve hydrodynamic performance during actual ship design practices.

A havelock source panel method for near-surface submarines

A panel method is described for calculating potential flow around near-surface submarines. The method uses Havelock sources which automatically satisfy the linearized free-surface boundary condition. Outputs from the method include pressure field, pressure drag, wave resistance, vertical force, trim moment and wave pattern. Comparisons are made with model tests for wave resistance of Series 58 and DARPA SUBOFF hulls, as well as with wave resistance, lift force and trim moment of three length-to-diameter variants of the DSTO Joubert submarine hull. It is found that the Havelock source panel method is capable of determining with reasonable accuracy wave resistance, vertical force and trim moment for submarine hulls. Further experimental data are required in order to assess the accuracy of the method for pressure field and wave pattern prediction. The method is implemented in the computer code “HullWave” and offers potential advantages over RANS-CFD codes in terms of speed, simplicity and robustness.

Hull-form optimization of a container ship based on bell-shaped modification function

In the present study, a hydrodynamic hull-form optimization algorithm for a container ship was presented in terms of the minimum wave-making resistance. Bell-shaped modification functions were developed to modify the original hull-form and a sequential quadratic programming algorithm was used as an optimizer. The wave-making resistance as an objective function was obtained by the Rankine source panel method in which non-linear free surface conditions and the trim and sinkage of the ship were fully taken into account. Numerical computation was performed to investigate the validity and effectiveness of the proposed hull-form modification algorithm for the container carrier. The computational results were validated by comparing them with the experimental data.

Modelling the aeroelastic response and flight dynamics of a hingeless rotor helicopter including the effects of rotor-fuselage aerodynamic interaction

AbstractThis paper presents a mathematical approach for the simulation of rotor-fuselage aerodynamic interaction in helicopter aeroelasticity and flight dynamics applications. A Lagrangian method is utilised for the numerical analysis of rotating blades with nonuniform structural properties. A matrix/vector-based formulation is developed for the treatment of elastic blade kinematics in the time-domain. The combined method is coupled with a finite-state induced flow model, an unsteady blade element aerodynamics model, and a dynamic wake distortion model. A three-dimensional, steady-state, potential flow, source-panel method is employed for the prediction of induced flow perturbations in the vicinity of the fuselage due to its presence in the free-stream and within the rotor wake. The combined rotor-fuselage model is implemented in a nonlinear flight dynamics simulation code. The integrated approach is deployed to investigate the effects of rotor-fuselage aerodynamic interaction on trim performance, stability and control derivatives, oscillatory structural blade loads, and nonlinear control response for a hingeless rotor helicopter modelled after the Eurocopter Bo105. Good agreement is shown between flow-field predictions and experimental measurements for a scaled-down isolated fuselage model. The proposed numerical approach is shown to be suitable for real-time flight dynamics applications with simultaneous prediction of structural blade loads, including the effects of rotor-fuselage aerodynamic interaction.

Study on Optimized Hull form of Basic Ships Using Optimization Algorithm

In order to achieve minimum resistance for a ship hull, we used an optimization algorithm and computational fluid dynamics to develop a hull-form design. An ITTC 1957 modelship correlation line formula was used to estimate the frictional resistance coefficient, and the wave-making resistance coefficient was evaluated by the Rankine source panel method with nonlinear free-surface boundary conditions. The geometry of the hull surface was represented and modified by a B-spline surface-modeling technique during the optimization process. Wigley and series 60 (C_B=0.60) hulls were selected to obtain an optimized hull that produces minimum resistance. Experimental tests were carried out for the modified series 60 (C_B=0.60) hull.

Reduction of demi-hull wave interference resistance in fast displacement catamarans utilizing an optimized centerbulb concept

A centerbulb was integrated to a catamaran in order to create a favorable secondary wave interference to reduce the unfavorable wave interference resistance between the demi-hulls. An Artificial Neural Network (ANN) technique is implemented together with a computational flow solver based on the low-Froude number theory, which uses a source-panel method with Dawson׳s algorithm, to find an efficient centerbulb geometry. In order to gain computation time in the optimization algorithm the present ANN approach is applied to the responses of the flow solver to the centerbulb design parameter changes. The numerical design procedure is verified by model tests conducted with a catamaran model both with and without the centerbulb. Numerical and experimental analyses verify each other and confirm that it is possible to reduce wave interference in considerable amounts with an optimal centerbulb. The study presented for catamarans, demonstrates the capabilities of the optimization procedure in reducing the wave interference resistance as well as the efficiency and ease of application of the centerbulb as a retrofit.

수직날개를 부착한 선박의 조파저항 성능 추정 기법의 검증

본 연구에서는 개발된 선미부에 수직날개를 부착한 선박의 조파저항성능을 예측할 수 있는 수치해석기법의 검증에 관한 것이다. 수치해석기법은 비점성 유동장 해석기법인 랜킨소오스 패널법과 와류격자법을 사용하여 개발하였으며, 자유수면 경계조건의 비선형성은 반복해법을 사용하여 만족시켰고, 선박의 트림과 침하량을 구하는 알고리즘을 포함하고 있다. 수치해석을 위한 선체표면의 패널을 생성하기 위하여 패널절단법을 사용하였다. 4000TEU 컨테이너 운반선을 대상 선박으로 하여 선미부 6개소의 서로 다른 위치에 수직날개를 부착하여 수치해석을 수행하였으며, 수치해석기법의 타당성을 검증하기 위하여 상용 점성 유동장 해석 프로그램인 FLUENT를 사용하여 선체 주위의 점성 유동장을 계산하였고, 모형시험을 수행하여 얻은 실험 결과를 수치해석 결과와 서로 비교하였다. In this paper the developed prediction technique of wave-making resistance performance for a ship attached with a vertical blade had been verified. Numerical analysis program as a prediction technique had been developed using the Rankine source panel method and the vortex lattice method(VLM). The nonlinearity of the free surface conditions was fully taken into account using the iterative method and the trim and the sinkage of the ship were also considered in the numerical analysis program. Panel cutting method was applied to get hull surface panels. Numerical computations were carried out for a 4000TEU container carrier and the vertical blade was attached 6 different locations astern. To investigate the validity of the numerical analysis program the commercial viscous flow field analysis program FLUENT was used to obtain the viscous flow field around the ship and the model test was performed. The model test results were compared with the numerical analysis results.

Hydrodynamic Hull Form Design Using an Optimization Technique

Abstract A design procedure for a ship with minimum resistance had been developed using a numerical op-timization method called SQP (Sequential Quadratic Programming) combined with computational fluid dynamics (CFD) technique. The frictional resistance coefficient was estimated by the ITTC 1957 model-ship correlation line formula and the wave-making resistance coefficient was evaluated by the potential-flow panel method with the nonlinear free surface boundary conditions. The geometry of the hull surface was represented and modified by B-spline surface modeling technique during the optimi-zation process. The Series 60 (C B =0.60) hull was selected as a parent hull to obtain an optimized hull that produces minimum resistance. The models of the parent and optimized hull forms were tested at calm water condition in order to demonstrate the validity of the proposed methodolgy. Keywords: Hull optimization, Minimum resistance, Ranking source panel method, SQP(Sequential Quadratic Programming), B-spline surface modeling