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1.
AbstractThis paper presents rocking vibrations of a rigid foundation resting on a multi-layered poroelastic half-space. The foundation is assumed to be rigid and massless, and subjected to a time–harmonic moment. In addition, each layer of the multi-layered half-space is governed by Biot’s theory of poroelastodynamics. The contact surface between the foundation and the layered half-space is smooth, and either fully permeable or impermeable. This dynamic interaction problem is studied by employing a discretization technique and an exact stiffness matrix scheme. Comparisons with existing solutions on rocking vibrations of rigid foundations on elastic and poroelastic media are shown to verify the accuracy of the present scheme. Selected numerical results on rocking compliances of rigid foundations of various shapes and mudmat foundations are presented. In addition, a dynamic interaction problem involving closely spaced foundations under rocking vibrations is also presented to demonstrate the applicability of the present solution scheme. 相似文献
2.
箱式超大型浮体结构在规则波中的水弹性响应研究 总被引：3，自引：5，他引：3
利用三维线性水弹性理论研究了箱式超大型浮体结构在正弦规则波中的动力响应，用Bernoulli-Euler梁解析解计算结构在真空中的动力特性，用弹性体三维势流理论计算结构的水动力系数，浮体结构在单位波幅规则波中的刚体运动幅值与DNV／WADAM程序的计算结果进行了比较，并给出了垂向弯曲模态的位移，弯矩随波浪频率的变化规律，由于箱式浮体结构的低阶固有频率很低，相应的弹性振型的响应与刚体运动耦合，结构在波浪中没有发现明显的低阶弹性模态谐振。 相似文献
3.
A simplified method to determine the minimum length of reinforcement required for the external stability of waterfront reinforced soil structures under seismic conditions is presented. In the present analysis, strain-dependent dynamic properties (shear modulus and damping ratio) are used. The results obtained from the present method are well compared with the results of pseudo-static method of analysis. For the set of input parameters, the estimated minimum length of reinforcement required against sliding failure is nearly 27–29% higher for an input normalized frequency of 1.06 and is nearly 22–25% lower for another input normalized frequency of 1.94 when compared with the results of pseudo-static approach. This can be attributed to the mode change behaviour of the waterfront structure. In addition, the effect of foundation type on the external stability of waterfront reinforced soil structures has also been presented and it is found that the foundation type has a significant effect on the same. For the given set of input parameters, the length of minimum reinforcement required for a slope and vertical wall having a flexible foundation are about 26–28% and 32–38% larger than that of a slope and vertical wall with rigid foundation, respectively. 相似文献
4.
For consideration of both the eccentric rotatable rigid body and the translational rigid body, the dynamic model of the underwater glider is derived. Dynamical behaviors are also studied based on the model and can be used as the guidance to underwater gliders design. Gibbs function of the underwater glider system is derived first, and then the nonlinear dynamic model is obtained by use of Appell equations. The relationships between dynamic behaviors and design parameters are studied by solving the dynamic m... 相似文献
5.
This paper,with a finite element method,studies the interaction of a coupled incompressible fluid-rigid structure system with a free surface subjected to external wave excitations.With this fully coupled model,the rigid structure is taken as "fictitious" fluid with zero strain rate.Both fluid and structure are described by velocity and pressure.The whole domain,including fluid region and structure region,is modeled by the incompressible Navier-Stokes equations which are discretized with fixed Eulerian mesh.However,to keep the structure's rigid body shape and behavior,a rigid body constraint is enforced on the "fictitious" fluid domain by use of the Distributed Lagrange Multiplier/Fictitious Domain(DLM/FD) method which is originally introduced to solve particulate flow problems by Glowinski et al.For the verification of the model presented herein,a 2D numerical wave tank is established to simulate small amplitude wave propagations,and then numerical results are compared with analytical solutions.Finally,a 2D example of fluid-structure interaction under wave dynamic forces provides convincing evidences for the method excellent solution quality and fidelity. 相似文献
6.
浮基多体系统自激运动响应的时域分析方法 总被引：2，自引：2，他引：2
浮基多体系统上部机构作业时不仅存在多体系统内部各物体间的耦合作用 ,还存在浮基与流场间的耦合作用。本文将浮基在流场中引起的辐射势表示为浮基加速度与时域规范化速度势乘积的卷积形式 ,导出流体动压力及静水系泊恢复力与浮基运动的关系。使用多刚体力学的凯恩方法得到系统的动力学方程。最后给出了在时域中数值求解系统运动响应的具体步骤 相似文献
7.
This paper deals with the prediction of the dynamic response of steel offshore platforms to high energy impacts from typical supply vessels. The contribution of the high modes of a cantilever beam type structure with a concentrated top mass subjected to transverse impact from rigid and deformable strikers is analysed. A procedure to develop simplified equivalent systems for efficient structural response analysis is presented and its reliability tested by comparing the results from the explicit non-linear FE simulations. Effects such as the overall rotation of the installation, plastic deformations in the contact area, different impact locations and different hinge mechanisms are taken into account. It is shown that the use of the proposed equivalent systems with a reduced number of DOF's can provide accurate results at significantly less computational efforts as compared to the FE simulations. The derivation of some parameters of the equivalent dynamic elastic–plastic SDOF/2SDOF systems, however, needs to consider the complexity of the analysed steel frames and perform preliminary non-linear static analyses. Therefore, further studies of different impact scenarios on platforms with different configurations are recommended to augment the results presented here. 相似文献
8.
Dynamic and static analysis of a marine riser 总被引：1，自引：0，他引：1
A frequency domain normal mode solution is presented for the dynamic response of an unbuoyed marine riser subjected to periodic excitation from a surface vessel in the direction of wave propagation. The variable tension beam-column equation is solved in terms of normal modes of free vibration of the riser and the rigid body displacement. Drag forces on the riser are represented by Morison's formula taking account of the velocity of the riser and wave-induced fluid velocity. A periodic solution for the flexural motion of the riser and the bending stress is then obtained by means of an iterative solution of the frequency response function. The drag force induced stresses arising from a linearly varying current are also determined. The results presented compare favourably with those obtained by other methods. 相似文献
9.
For Cconsideration ofing both the eccentric rotatable rigid body and the translational rigid body, the dynamic model of the underwater glider is derived. Dynamical behaviors are also studied based on the model and can be used as the guidance to underwater gliders design. Gibbs function of the underwater glider system is derived first, and then the nonlinear dynamic model is obtained by use of Apell Equations. The relationships between dynamical behaviors and design parameters are studied by solving the dynamic model. The spiral motion, swerving motion in three dimensions and the saw-tooth motion of the underwater glider in vertical plane are studied. Lake trials are carried out to validate the dynamic model. 相似文献
10.
对称式布置锚链系统的线性化处理 总被引：6，自引：2，他引：6
用悬链线方程求解了不同锚链状态的锚链力 ,并用多项式回归了锚链力与锚固点位移的关系 ,由此求得锚链恢复力刚度系数。分析了对称式布置锚链系统的非线性程度 ,阐述对称式布置锚链系统所提供的恢复力作线性化处理的可行性及方法 ,并给出了对称布置锚链系统的线性刚度矩阵。为各类受对称式布置锚链系统约束的浮动结构物的动力分析提供了理论依据 相似文献
11.
《Applied Ocean Research》2004,26(1-2):23-33
The dynamic behaviour of vertical slender structures for marine applications under parametric excitation is considered. The governing equations are treated using two different numerical schemes. The effect of parametric excitation is examined in cases where the excitation frequency lies in the vicinity of nonlinear resonances. First, the un-damped case is considered and the features of the dynamic response are properly identified and discussed. For explaining the particulars of the un-damped behaviour, the governing equations are treated analytically by applying the method of normal forms. The effect of damping is examined through comparative numerical computations of the system's behaviour. It is shown that the inclusion of hydrodynamic drag in the describing model eliminates the impacts of internal resonances excited due to the parametrically imposed motions. Finally, the paper demonstrates the significance of the terms that describe the coupling between the longitudinal and transverse vibrations. 相似文献
12.
Kuang Zhiping Cao Guoao Dr. Lecturer Tongji University Shanghai Dr. Professor Tongji University Shanghai 《中国海洋工程》1993,(2)
- An approximate method is presented to investigate the earthquake response of the fluid-single leg (shortened for S. L.) gravity platform-soil interaction system. By assuming a suitable form of the velocity potential of the radiation waves and by using the motion equation and the boundary conditions, the unknown coefficients can be obtained. Thereafter the function of frequency for the interaction system may also be obtained. In this paper, the difference of the system dynamic response between rigid foundation is analyzed and the influences of the various foundation geometric dimension and the various water-depth on the hydrodynamic loading and dynamic response of the system is illustrated. 相似文献
13.
The objective of this paper is to present the effect of sediment characteristics on the dynamic response of sea walls and breakwaters during earthquakes. A finite-difference method is used to calculate the earthquake-induced hydrodynamic pressures of seawater and the pore water in seabed sediment. The water-filled soil mixture is used to model sediment and back-fill soil. The dynamic response of a rigid coastal structure induced by constant ground acceleration is studied, using variable sediment depths and porosity. The dynamic characteristics of the water–embankment–sediment system are investigated, applying four earthquake-records as exciting forces. The result of a quay-walled caisson demonstrates the significance of the seismic-induced dynamic force and the seismic effects should be considered for the design of coastal structures in seismic zone. The damaged wharves of Taichung Port during Chi-Chi earthquake, 21 September 1999 is also reported in the paper. 相似文献
14.
Radiation of sound from a spherical piston, set in the side of a rigid sphere, undergoing harmonic radial surface vibrations in an acoustic halfspace is analyzed in an exact fashion using the classical method of separation of variables. The method of images in combination with the translational addition theorems for spherical wave functions is employed to take the presence of the flat boundary into account. The analytical results are illustrated with numerical examples in which the piston is pulsating near the rigid/compliant boundary of a water-filled halfspace. Subsequently, the basic acoustic field quantities such as the acoustic radiation impedance load and the radiation intensity distribution are evaluated for representative values of the parameters characterizing the system. Numerical results reveal the important effects of excitation frequency, source position, and cap angle on the acoustic radiation impedance load and the radiation intensity distribution. The presented work can lead to a better understanding of dynamic response of near-surface underwater transducers. 相似文献
15.
A three-dimensional Lump-Mass formulation of a catenary riser, capable of handling irregular seabed interaction, with bending and torsional stiffness is presented in this paper. This formulation uses only three degrees of translational freedom and one independent torque variable for each computational node. The generality of the present formulation permits static and dynamic analyses of a wide range of offshore-related slender structure systems such as mooring cables, rigid and flexible risers as well as submarine pipelines. Four sets of results are presented for (i) a hanging catenary, (ii) as (i) but subjected to end torsion, (iii) a wire, chain and spring buoy mooring and (iv) a steel catenary riser on an irregular seabed. 相似文献
16.
A finite differences formulation for the linear and nonlinear dynamics of 2D catenary risers 总被引：1，自引：0，他引：1
A finite differences (FD) solution method is proposed for the numerical treatment of the dynamic equilibrium problem of 2D catenary risers. The method is based on the so-called Box approximation, which in the scope of the present contribution is applied to the complete nonlinear model as well as to the reduced linearized formulation. The application of the Box method transforms the original governing systems into convenient sets of algebraic equations, which in turn are solved efficiently by the relaxation method. Extensive numerical calculations are presented that describe the dynamic behaviour of the structure and evaluate the amplification in loading due to the dynamic components. The effect of the geometric nonlinearities is assessed through comparative calculations that concern both mathematical formulations examined in the present, i.e. the complete nonlinear, and the reduced linearized model. Special attention is paid to the heave excitations as they amplify significantly the magnitudes of the loading components. 相似文献
17.
In this paper, the buoyancy, kinetic properties and stability of air floated structures have been studied by theoretical and experimental methods. The ecpjations for calculation of the buoyancy of the air floated buoy are derived according to the Boyler law and the equilibrium equations of the air floated structure are established. Through simplification of the air floated structure as a single freedom rigid body and spring system, the natura! period of heaving and some kinetic properties are discussed. In the stability analysis, the formulas for calculation of the meta centric height are presented. The theoretical results are in good agreement with the data observed from the model test and prototype test. The air buoyancy de-crease coefficient presented in this paper has a large influence on the floating state, stability and dynamic properties of the air floated structure. The stability of the air floated structure can also be judged by the parameter of meta centric height, and calculations show that t 相似文献
18.
Interaction of solitary waves with emergent, rigid vegetation 总被引：3，自引：0，他引：3
In this study, solitary wave interaction with emergent, rigid vegetation was studied numerically and experimentally. Laboratory experiments were carried out in a wave flume with vegetation models of different lengths and porosities; the Boussinesq equations with the effects of the vegetation being modeled by a quadratic drag law are used to simulate the wave scattering by and the wave propagation through vegetation. Effects of incident wave height, vegetation density, and vegetation length are discussed. An empirical expression for the mean drag coefficient of emergent, rigid vegetation is presented and compared with other available data. The results are useful for studying tsunami hazard mitigation by coastal forests. 相似文献
19.
The deployment of suitable configurations of mutually interacting floating bodies for efficiently controlling their hydrodynamic interactions towards the reduction of the wave drift forces and, thus, of the mooring lines’ loads, has, nowadays, gained a great scientific interest. In this paper, the hydrodynamic behaviour of a floating cylinder and a concentric annular flexible plate is analysed in the frequency domain aiming at the minimization of the drift forces acting on the cylinder by optimizing the flexural rigidity of the plate. The diffraction/radiation problem is solved using a higher-order boundary element method. The analysis is implemented assuming that both floating bodies oscillate freely in heave, while for the plate, flexible modes are, additionally, considered for describing its structural deformations. The required modes shapes are determined in vacuum (“dry” mode superposition approach) through analytical expressions. The flexural rigidity of the plate, D, is optimized at a specific wave number using a real-coded genetic algorithm. Initially, results are compared with numerical results of other investigators for the case of two rigid concentric floating cylinders. Next, extended results are presented, focusing on the effect of D, including its optimum value, on various physical quantities describing the behaviour of both the cylinder and the plate. Contrary to the isolated cylinder, the presence of the plate introduces sharp peaks in the variation pattern of the drift force of the cylinder, bounded at specific wave numbers, where resonance of the seiche mode of water motion in the annular cavity or of specific flexible modes of the plate occurs. However, by reducing D to its optimum value, the cylinder’s drift force obtains practically zero values at the target wave number, due to an efficient improvement of the wave field in the annular cavity around the cylinder. Moreover, a great reduction of the drift force compared to the isolated cylinder is achieved in the subsequent high frequency range. 相似文献
20.
The determination of hull-girder loads in a seaway is of particular importance for the design of marine vehicles. This paper shows how the loads can be determined, considering also the impact loads due to slamming. Results have been presented for a fast patrol boat, although the method can be used for other kinds of surface vessels. The theoretical approach presented in the paper is an extension of the linear strip method used extensively in predicting both ship motions and dynamic loads. The equations have been solved by simulating the ship behaviour in an irregular seaway. 相似文献