Non-linear wave loads and ship responses by a time-domain strip theory

1998 ◽  
Vol 11 (3) ◽  
pp. 101-123 ◽  
Author(s):  
Jinzhu Xia ◽  
Zhaohui Wang ◽  
J.Juncher Jensen
Keyword(s):  
Time Domain ◽  
Linear Wave ◽  
Wave Loads ◽  
Strip Theory ◽  
Non Linear

NON LINEAR ANALYSIS OF SHIP MOTIONS AND LOADS IN LARGE AMPLITUDE WAVES

2021 ◽  
Vol 153 (A2) ◽  
Author(s):  
G Mortola ◽  
A Incecik ◽  
O Turan ◽  
S.E. Hirdaris
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Large Amplitude ◽  
Linear Time ◽  
Ship Motions ◽  
Wave Loads ◽  
Time Step ◽  
Strip Theory ◽  
Non Linear ◽  
The Time Domain

A non linear time domain formulation for ship motions and wave loads is presented and applied to the S175 containership. The paper describes the mathematical formulations and assumptions, with particular attention to the calculation of the hydrodynamic force in the time domain. In this formulation all the forces involved are non linear and time dependent. Hydrodynamic forces are calculated in the frequency domain and related to the time domain solution for each time step. Restoring and exciting forces are evaluated directly in time domain in a way of the hull wetted surface. The results are compared with linear strip theory and linear three dimensional Green function frequency domain seakeeping methodologies with the intent of validation. The comparison shows a satisfactory agreement in the range of small amplitude motions. A first approach to large amplitude motion analysis displays the importance of incorporating the non linear behaviour of motions and loads in the solution of the seakeeping problem.

Genetic Optimization of Shape and Control of Non-Linear Wave Energy Converters

2020 ◽  
Author(s):  
Jiajun Song ◽  
Ossama Abdelkhalik ◽  
Shangyan Zou
Keyword(s):  
Wave Energy ◽  
Time Domain ◽  
Optimization Approach ◽  
Linear Wave ◽  
Variable Size ◽  
Wave Energy Converters ◽  
Hydrostatic Force ◽  
Non Linear ◽  
The Time Domain ◽  
Energy Converters

Abstract This paper presents an optimization approach to design ax-isymmetric wave energy converters (WECs) based on a nonlinear hydrodynamic model. This paper shows optimal nonlinear shapes of buoy can be generated by combing basic shapes in an optimal sense. The time domain non-linear Froude-Krylov force can be computed for a complex buoy shape, by adopting analytical formulas of its basic shape components. The time domain Forude-Krylov force is decomposed into its dynamic and static components, and then contribute to the calculation of the excitation force and the hydrostatic force. A non-linear control is assumed in the form of the combination of linear and nonlinear damping terms. A variable size genetic algorithm (GA) optimization tool is developed to search for the optimal buoy shape along with the optimal control coefficients simultaneously. Chromosome of the GA tool is designed to improve computational efficiency and to leverage variable size genes to search for the optimal non-linear buoy shape. Different criteria of wave energy conversion can be implemented by the variable size GA tool. Simulation results presented in this paper show that it is possible to find non-linear buoy shapes and non-linear controllers that take advantage of non-linear hydrodynamics to improve energy harvesting efficiency with out adding reactive terms to the system.

Determination of global design loads for large high-speed catamarans

2002 ◽  
Vol 216 (1) ◽  
pp. 79-94
Author(s):  
S E Heggelund ◽  
T Moan ◽  
S Oma
Keyword(s):  
High Speed ◽  
Bending Moment ◽  
Wave Loads ◽  
Strip Theory ◽  
Non Linear ◽  
Design Loads ◽  
Linear Effects ◽  
Operational Criteria ◽  
Vertical Bending Moment

Methods for calculation of design loads for high-speed vessels are investigated. The influence of operational restrictions on design loads is emphasized. Relevant operational criteria for high-speed displacement vessels are discussed. Procedures and criteria for numerical calculation of operational limits are incomplete and should be further investigated. Operational limits and design loads for a 60 m catamaran are calculated on the basis of linear strip theory. Non-linear effects on design loads are assessed from calculations in regular waves. Simplified formulae commonly used by classification societies for prediction of operational limits seem to over-predict the reduction of motions and wave loads at reduced speed. When operational limits typically given by the shipmaster or the operator are used, the design loads found by direct calculations are comparable with design loads given by classification societies. For vertical bending moment and torsion, the use of active foils is found to increase the linear loads. Owing to reduced motions, the foils reduce the non-linear loads and hence the total loads. The effect of non-linear horizontal loads is not investigated but can be important for transverse bending moment.

Time-Domain Analysis of Large-Amplitude Vertical Ship Motions and Wave Loads

1998 ◽  
Vol 42 (02) ◽  
pp. 139-153 ◽  
Author(s):  
N. Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Large Amplitude ◽  
Surface Condition ◽  
Memory Effects ◽  
Wave Loads ◽  
Strip Theory ◽  
Large Amplitude Motions ◽  
Free Surface Oscillations ◽  
The Time Domain

The vertical motions and wave induced loads on ships with forward speed are studied in the time domain, considering non-linear effects associated with large amplitude motions and hull flare shape. The method is based on a strip theory, using singularities distributed on the cross sections which satisfy the linear free surface condition. The solution is obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. In this way the linear radiation forces are represented in terms of impulse response functions, infinite frequency added masses and radiation restoring coefficients. The diffraction forces associated with incident wave scattering are linear. The hydrostatic and Froude-Krylov forces are evaluated over the instantaneous wetted surface of the hull to account for the large amplitude motions and hull flare. The radiation contribution for wave loads is also obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. Results of motions and wave loads for the S175 container ship are presented and analyzed. The results from the present method are compared with linear results.

Fatigue Assessment for Ship Structure Acted on Non-Linear Wave Loads

2007 ◽  
Vol 353-358 ◽  
pp. 2786-2789
Author(s):  
Chao He Chen
Keyword(s):  
Fatigue Damage ◽  
Bending Moment ◽  
Linear Wave ◽  
Wave Loads ◽  
Ship Structure ◽  
Random Seas ◽  
Non Linear ◽  
Bow Flare ◽  
Short Term Prediction ◽  
The Given

Efficient methods are described here to predict the fatigue damage of ship structure due to nonlinear wave loads that are produced in random seas. Firstly the effects of the non-linear waveinduced bending moment on the fatigue damage of ship structure with very large bow flare are presented in short-term prediction by the method of spectrum analysis. Then, the fatigue damage is estimated and analyzed in the given environment of long-term.

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