共查询到20条相似文献，搜索用时 796 毫秒
1.
Gao Jun-liang Lyu Jing Wang Jing-hua Zhang Jian Liu Qian Zang Jun Zou Tao 《中国海洋工程》2022,36(6):994-1006
In this paper, the transient fluid resonance phenomenon inside a narrow gap between two adjacent boxes excited by the incident focused waves with various spectral peak periods and focused wave amplitudes is simulated by utilizing the open-sourced computational fluid dynamics software, OpenFOAM. The weather-side box is allowed to heave freely under the action of waves, and the lee-side box keeps fixed. This paper mainly focuses on how both the spectral peak period and the focused wave amplitude affect the free-surface amplification inside the gap, the motion of the weather-side box, and the wave loads (including the vertical and the horizontal wave forces) acting on both boxes. For comparison, another two-box system with both boxes fixed is also considered as a control group. It is found that the motion of the weather-side box significantly changes the characteristics of the transient gap resonance, and it would cause that the fluid resonant period becomes 1.4–1.6 times that of the two-box system with both boxes fixed. All the concerned physical quantities (i.e., the free-surface amplification in the gap, the motion of the weather-side box, the wave loads) are found to closely depend on both the spectral peak period and the focused wave amplitude.
相似文献2.
This paper is concerned with the determination of dynamic load variations in the riser and yoke pivot components of an offshore vessel/mooring oil production and storage system.Forces on the yoke system arise from wave induced inertial and drag forces including current and motion due to vessel surge, heave and pitch.The analysis is carried out in the frequency domain and the results yield the limiting wave height for a specific design of SALS which will give rise to loss of tension in the riser. Also presented are the maximum horizontal and vertical components of load variation at the yoke pivoted connections with the vessel. 相似文献
3.
Based on the lumped-mass method and rigid-body kinematics theory, a mathematical model of a gravity cage system attacked by irregular waves is developed to simulate the hydrodynamic response of cage system, including the maximum tension of mooring lines and the motion of float collar. The normalized response amplitudes (response amplitude operators) are calculated for the cage motion response in heave and surge, and the mooring line tension response, in regular waves. In addition, a statistical approach is taken to determine the motion and tension transfer functions in irregular waves. In order to validate the numerical model of a gravity cage attacked by irregular waves, numerical predictions have been compared with the experimental observations in the time and frequency domain. The effect of wave incident angle on the float collar motion, mooring line tension and net volume reduction of the gravity cage system in irregular waves is also investigated. The results show that at high frequencies, the cage system has no significant heave motion. It tends to contour itself to longer waves. The variation amplitude of mooring line forces decreases as the wave frequency increases. With the increasing of wave incident angle, the horizontal displacement of the float collar increases. 相似文献
4.
A.K. Jain 《Ocean Engineering》1997,24(7):577-592
Among the compliant platforms, the tension leg platform (TLP) is a vertically moored structure with excess buoyancy. The TLP is designed to behave in the same way as any other moored structure in horizontal plane, at the same time inheriting the stiffness of a fixed platform in the vertical plane. Dynamic response analysis of a TLP to deterministic first order wave forces is presented, considering coupling between the degrees-of-freedom surge, sway, heave, roll, pitch and yaw. The analysis considers nonlinearities produced due to changes in cable tension and due to nonlinear hydrodynamic drag forces. The wave forces on the elements of the pontoon structure are calculated using Airy's wave theory and Morison's equation ignoring diffraction effects. The nonlinear equation of motion is solved in the time domain by Newmark's beta integration scheme. The effects of different parameters that influence the response of the TLP are then investigated. 相似文献
5.
Current paper presents a mathematical model based on 2D-asymmetric wedge water entry to model heave and pitch motions of planing hulls at non-zero heel angles. Vertical and horizontal forces as well as heeling moment due to asymmetric water entry are computed using momentum theory in conjunction with added mass of impact velocity in vertical and horizontal directions. The proposed model is able to compute sway and yaw forces, roll moment, as well as heave and pitch motions in calm water and regular waves. Validity of the proposed model is verified by comparing the results against existing experimental data in both symmetric and asymmetric conditions. Ultimately, different parametric studies are conducted to examine the effects of non-zero heel angle on dynamic vertical motions. The resulting sway and yaw forces due to asymmetric motion are also derived and effects of heel angle on these side forces are investigated. 相似文献
6.
《中国海洋工程》2017,(4)
We present a study of the nonlinear coupling internal resonance for the heave roll and pitch performance of a spar platform under the wave and vortex-induced loads when the ratio of the frequencies of heave, roll and pitch are approximately 2:1:1. In consideration of varying wet surface, the three DOFs nonlinear coupled equations are established for the spar platform under the effect of the first-order wave loads in the heave and pitch, and vortexinduced loads in the roll. By utilizing the method of multi-scales when the vortex-induced frequency is close to the natural roll frequency, the first-order perturbation solution is obtained analytically and further validated by the numerical integration. Sensitivity analysis is performed to understand the influence of the damping and the internal detuning parameter. Two cases with internal resonance are shown. The first case is that no saturation phenomenon exists under small vortex-induced loads. The first order perturbation solution illustrates that only the vortex-induced frequency motion in roll and the super-harmonic frequency motion in heave are excited. The second case is that the vortex-induced loads are large enough to excite the pitch and a saturation phenomenon in the heave mode follows.The results show that there is no steady response occurrence for some cases. For these cases chaos occurs and large amplitudes response can be induced by the vortex-induced excitation. 相似文献
7.
Internal Resonances for Heave, Roll and Pitch Modes of A Spar Platform Considering Wave and Vortex-Induced Loads in the Main Roll Resonance 总被引：1，自引：0，他引：1
We present a study of the nonlinear coupling internal resonance for the heave roll and pitch performance of a spar platform under the wave and vortex-induced loads when the ratio of the frequencies of heave, roll and pitch are approximately 2:1:1. In consideration of varying wet surface, the three DOFs nonlinear coupled equations are established for the spar platform under the effect of the first-order wave loads in the heave and pitch, and vortex-induced loads in the roll. By utilizing the method of multi-scales when the vortex-induced frequency is close to the natural roll frequency, the first-order perturbation solution is obtained analytically and further validated by the numerical integration. Sensitivity analysis is performed to understand the influence of the damping and the internal detuning parameter. Two cases with internal resonance are shown. The first case is that no saturation phenomenon exists under small vortex-induced loads. The first order perturbation solution illustrates that only the vortex-induced frequency motion in roll and the super-harmonic frequency motion in heave are excited. The second case is that the vortex-induced loads are large enough to excite the pitch and a saturation phenomenon in the heave mode follows. The results show that there is no steady response occurrence for some cases. For these cases chaos occurs and large amplitudes response can be induced by the vortex-induced excitation. 相似文献
8.
Gu Jianming Pan Bin Postgraduate Dept. of Naval Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai Lecturer Dept. of Naval Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai 《中国海洋工程》1993,(1)
- In this paper, an engineering method is employed to calculate the horizontal and vertical wave forces on the mat of the submersible platform under Froude-Krylov hypothesis. According to some model tests, appropriate diffraction coefficients are selected. And the results of the formulae given in the paper agree satisfactorily with those experimental data now available. The proposed computational method is effective and convenient to use in evaluating the horizontal and vertical wave forces on the mat. An exmaple is also given in this paper. Finally, the effects of the vertical wave force on the platorm's sit-on-bottom stability are analyzed. 相似文献
9.
Wave forces on a vertical truncated circular cylinder in Stokes waves with the wave slopes ranging from 0.06 to 0.24, are measured in a wave tank. The higher harmonic wave forces are compared with the available values from theories of the FNV (Faltisen–Newman–Vinje) model and Varyani solution. The first harmonic horizontal forces measured are much larger than the theoretical values from the FNV model, while the first harmonic vertical forces are well predicted by the Varyani theory. It was also found that the FNV model significantly overpredicts the second harmonic horizontal forces in high frequency waves, but under predicts the third harmonic forces. The differences between the actual measurement and the theory, in the second and third harmonic horizontal forces, become smaller at low wave frequencies as the wave slope increases. In addition, the transverse instabilities in the incoming waves with high wave slope were observed, which is due to the nonlinear modulation. Measurements were, thus, carried out before the instability occurred. 相似文献
10.
基于映像理论将部分反射直墙前物体的散射问题,等效于开敞水域中原物体的散射和关于直墙映像体散射的线性叠加进行求解。采用高阶边界元方法建立了部分反射直墙前二维任意形状物体波浪绕射和辐射问题的数值分析模型,通过与已发表的海底方箱和淹没圆柱结果的对比验证了数值模型的准确性。应用该模型研究了直墙反射系数幅值及相位、方箱与墙间距离等参数对水面方箱上波浪激振力、附加质量和辐射阻尼的影响。结果表明：直墙反射系数幅值越大,波浪激振力、附加质量和辐射阻尼的波动越大,附加质量在一些频率下出现负值;相位角的变化会改变波浪激振力、附加质量和辐射阻尼曲线的偏移,在低频区对升沉附加质量有显著影响;方箱距离直墙越远,方箱上的波浪激振力、附加质量和辐射阻尼随波数振荡的频率越快,峰值频率向低频侧移动。 相似文献
11.
W. Koterayama 《Ocean Engineering》1980,7(3):399-412
This paper presents a method of estimating wave forces acting on a submerged horizontal circular cylinder fixed in oblique waves.The experiments show that drag and inertia coefficients in beam sea are available for calculating the wave forces in oblique waves.Wave forces exerted on a vertical circular cylinder in deep waves are also investigated.The experimental results show that wave forces acting on the vertical cylinder coincide approximately with hydrodynamic forces acting on a submerged circular cylinder in an oscillating fluid. 相似文献
12.
Numerical Analysis on the Effects of Submerged Depth of the Grid and Direction of Incident Wave on Gravity Cage 总被引：1，自引：0，他引：1
In this paper,the numerical model of the net cage with the grid mooring system in waves is set up by the lumped mass method and rigid kinematics theory,and then the motion equations of floating system,net system,mooring system,and floaters are solved by the Runge-Kutta fifth-order method.For the verification of the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and experimental results,it can be found that the simulated and experimental results agree well in each condition.Then,the effects of submerged depth of grid and direction of incident wave propagation on hydrodynamic behaviors of the net cage are analyzed.According to the simulated results,it can be found that with the increase of submerged depth of grid,the forces acting on mooring lines and bridle lines increase,while the forces on grid lines decrease;the horizontal motion amplitudes of floating collar decrease obviously,while the vertical motion amplitudes of floating collar change little.When the direction of incident wave propagation changes,forces on mooting lines and motion of net cage also change accordingly.When the propagation direction of incident wave changes from 0° to 45°,forces on the main ropes and bridle ropes increase,while the forces on the grid ropes decrease.With the increasing propagation direction of incident wave,the horizontal amplitude of the forces collar decreases,while the vertical amplitude of the floating collar has little variation. 相似文献
13.
The wave runup caused by a vertical cylinder surging in regular waves is studied both experimentally and numerically. The so-called DualSPHysics Smoothed Particle Hydrodynamics (SPH) code is used for the 3-D numerical modelling. A wide range of cylinder sizes and wave conditions is investigated with results comparing favourably between the experimental and SPH model under both fixed and forced-surge conditions. The experimental and SPH results are further used to predict the maximum runup amplification, in particular the ratio of the runup caused by the surging cylinder to that of the fixed, over the phase difference between the incident wave and surge motion. This maximum runup ratio has been analysed for its dependence on factors such as wave steepness, wave scattering and surge amplitude. An empirical equation is proposed for predicting the maximum runup ratio from known incident wave and surge conditions. Comparison with results from linear solvers suggests that the linear solvers under-predict the full nonlinear runup by a factor of 1.3–1.5. 相似文献
14.
A theoretical assessment is made of mean wave drift forces on groups of vertical circular cylinders, such as the columns of a floating offshore platform. A complete analytical solution is obtained for two cylinders extending from seabed to free surface, and a long wave approximation is found to provide reliable predictions of the drift force in line with the waves at low frequencies. For moderate separation between the two cylinders, this force is found to tend at low frequencies to a value four times the force on an isolated cylinder.A numerical method is employed to study two surface piercing cylinders truncated below the free surface, and an arrangement of four vertical cylinders characteristic of a floating offshore platform. The mean vertical drift force is found to be reasonably well approximated, over the frequency range of practical interest, by the force on an individual cylinder considered in isolation multiplied by the number of cylinders in the group. Interaction effects, however, have a profound influence on the total horizontal drift force. At low frequencies this force is found to tend to the force on an isolated cylinder multiplied by the squate of the number of cylinders in the group. 相似文献
15.
Large-scale interceptors constitute the main structure of offshore self-driven floating marine litter collection devices,and the structural stability of such interceptors under the action of waves directly influences the overall safety of the device.When the ratio of the diameter of a horizontal cylinder in such interceptors to the incident wavelength is larger than 0.25,the wave force can be calculated by using the diffraction theory,by considering the problem as that of the interaction between the waves and a partially immersed large-scale horizontal cylinder.In this study,an analytical approach to calculate the wave force on a partially immersed large-scale horizontal cylinder was formulated by using the stepwise approximation method.Physical model tests were conducted to investigate the effects of different factors(wave height,period,and immersion depth)on the wave force on a large-scale horizontal cylinder under conditions involving short-period waves.The results show that both horizontal and vertical wave forces on the cylinder increase as the wave height(immersion depth)increases in most cases.The vertical wave force decreases with the decrease of the period.For the horizontal wave force,it increases with the decrease of the period when the wavelength is larger than the diameter of the cylinder and decreases with the decrease of the period when the wavelength is smaller than the diameter of the cylinder. 相似文献
16.
The analytical method developed by Svendsen (1968) for a forced heave motion is extended to the general problem of wave induced heave, roll and sway motions of a long ship at a depth of water which is only slightly larger than the draught of the ship. This corresponds, for example, to the situation of a fully loaded ship in a harbour area.After linearization of the problem, the water motion is considered for each of the three individual motions and for the wave reflection-transmission problem for a fixed ship. The ensuing results for the forces on the ship are then synthesized to form the equations of motion, which are presented with all coefficients given, including mooring forces.Analytical and numerical results are given for the three components of motion, for the associated resonance frequencies, and for the hydrodynamic masses and moments of inertia. Finally, the assumptions used are analyzed and evaluated by comparison with measurements and with other results for a special case. 相似文献
17.
Modelling of multi-bodies in close proximity under water waves—Fluid forces on floating bodies 总被引：1，自引：0，他引：1
This work presents two-dimensional numerical results of the dependence of wave forces of multiple floating bodies in close proximity on the incident wave frequency, gap width, body draft, body breadth and body number based on both viscous fluid and potential flow models. The numerical models were validated by the available experimental data of fluid oscillation in narrow gaps. Numerical investigations show that the large amplitude responses of horizontal and vertical wave forces appear around the fluid resonant frequencies. The convectional potential flow model is observed to un-physically overestimate the magnitudes of wave forces as the fluid resonance takes place. By introducing artificial damping term with appropriate damping coefficients μ∈[0.4, 0.5], the potential flow model may work as well as the viscous fluid model, which agree with the damping coefficients used in our previous work for the predication of wave height under gap resonance. In addition, the numerical results of viscous fluid model suggest that the horizontal wave force is highly dependent on the water level difference between the opposite sides of an individual body and the overall horizontal wave force on the floating system is generally smaller than the summation of wave force on each body. 相似文献
18.
Based on rigid kinematics theory and lumped mass method,a mathematical model of the two net cages of grid mooring system under waves is developed.In order to verify the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and the experimental results,it can be found that the simulated and the experimental results agree well in each wave condition.Then,the forces on the mooring lines and the floating collar movement are calculated under different wave conditions.Numerical results show that under the same condition,the forces on the bridle ropes are the largest,followed by forces on the main ropes and the grid ropes.The horizontal and the vertical float collar motion amplitudes increase with the increase of wave height,while the relationship of the horizontal motion amplitude and the wave period is indistinct.The vertical motion amplitude of the two cages is almost the same,while on the respect of horizontal motion amplitude,cage B(behind cage A,as shown in Fig.4) moves much farther than cage A under the same wave condition.The inclination angle of the floating system both in clockwise along y axis and the counter one enlarges a little with the increase of wave height. 相似文献
19.
以方形立柱作为研究对象，对其在聚焦波作用下的波浪力特性进行研究。研究主要基于计算流体力学数值方法，对聚焦波作用下方形立柱在固定、单自由度纵荡、单自由度垂荡三种运动状态下所受波浪力进行研究。利用phase-inversion逆相位分解方法对其高阶力特性进行分析。首先对聚焦波生成方法、数值计算方法与参数设置进行简要介绍，其次展示了三种运动状态下立柱在聚焦波作用下所受波浪力，并对其进行分析，最后利用phase-inversion逆相位分解方法获得高阶波浪力成分并对其载荷特性进行分析讨论。研究发现逆相位分解方法可以有效分离波浪力高阶成分，不同运动状态下立柱所受波浪力会有显著不同。 相似文献
20.
Effect of mooring-line stiffness on the performance of a dual coaxial-cylinder Wave-Energy Converter
A point-absorber-type Wave-Energy Converter (WEC) consisting of a floating vertical inner cylinder and an annular outer cylinder that slides along the inner one is considered. The two cylinders heave differently under wave excitation, and wave energy can be harnessed from the relative heave motion between the two cylinders using a Permanent Magnet Linear Generator (PMLG) as the Power Take-Off unit. A mooring cable is attached to the bottom of the inner cylinder. This paper aims to examine the effect of the stiffness of the mooring cable on the performance of the coaxial-cylinder WEC system. The two limiting cases of no mooring cable (freely floating inner and outer cylinders) and an infinitely stiff mooring cable (fixed inner cylinder) were also considered. To perform the analysis, hydrodynamic and interference coefficients of the two heaving cylinders were computed semi-analytically using the method of matched eigenfunction expansions. Experimentally determined viscous corrections on damping were also included in the model in order to have more realistic predictions. The performance of the system in terms of motion responses and capture width were predicted and discussed for both regular and irregular waves. The results of the analysis indicate that both the freely floating design and the design with rigidly moored inner cylinder are viable. The two limiting cases show similar optimal performances, albeit with very different optimal generator damping. However, an ill-chosen mooring-cable stiffness may cause the inner and the outer cylinders to have the same resonance frequency, eliminating the relative heave motion and leading to almost no energy extraction. This situation needs to be avoided when designing the mooring system for a coaxial-cylinder WEC. 相似文献