穿孔式双浮体装置水动力及波能转换特性研究

为进一步解决波能转换装置向深水环境推进过程中存在能量转换效率问题,在现有双浮体点吸式波能装置基础上考虑穿孔阻尼板,提出新的穿孔双浮体带支撑立柱的结构形式。基于线性微幅波假设,通过特征函数展开和边界匹配的势流半解析方法,并结合多自由度振动理论,探索穿孔阻尼板对获能系统水动力、运动响应及俘获宽度比的影响。计算结果表明,阻尼板开孔会降低浮子及阻尼板自身受到的波浪激励力,浮子、阻尼板以及它们之间的耦合辐射作用力会随着阻尼板开孔半径增大而减小;阻尼板的开孔半径增大能有助于浮子与阻尼板的相对响应振幅;阻尼板会使系统出现两个耦合共振频率,在较小共振频率处的最优俘获宽度比均随着阻尼板开孔半径的增加先增大后减小。研究结果可为深水波浪能利用的工程应用提供理论基础,为后续振荡浮子波浪能发电装置优化提供依据。     

Mathematical modeling of sway, roll and yaw motions: order-wise analysis to determine coupled characteristics and numerical simulation for restoring moment’s sensitivity analysis

This paper investigates sway, roll and yaw motions of a floating body with the aim to determine coupled motion characteristics based on the order-wise analysis of hydrodynamic coefficients. To compute the hydrodynamic coefficients and wave force exerted on the floating body, we employ speed-dependent strip theory. The governing equations are solved analytically for linear restoring moment. For nonlinear restoring moment which is expressed as an odd-order polynomial of fifth degree in roll angle, we apply the Runge–Kutta–Gill method to solve the coupled equations. To investigate the effect of initial disturbances on sway, roll, yaw and speed of the body, numerical experiments have been carried out for a Panamax Container ship under the action of a sinusoidal wave of periodicity 11.2 s with varying wave height and speed. For the linear restoring moment, we first derive associated motion equations for various cases based on the relative magnitude of the hydrodynamic coefficients. The order-wise analysis leads to the classification of coupled characteristics exhibiting the nature of coupling. For the nonlinear restoring moment, we notice that the initial disturbance plays an important role in the ship’s stability. The effects of forward speed and variation in wave heights are illustrated through typical numerical experiments.     

地震作用下桥墩动水压力及Morison方程适用性试验研究EI北大核心CSCD

深水桥梁的抗震分析需要考虑地震作用下动水压力的影响。目前,广泛采用的Morison方程由波浪力的计算公式演化而来,用于计算地震动水压力尚缺乏验证;同时,对于地震作用下桥墩动水压力的变化规律缺乏试验研究。该文设计一套水下振动台试验系统,以不同尺寸的桥墩试件为研究对象,采用正弦波为输入激励,通过不同工况的振动台试验,研究桥墩加速度和地震动水压力的分布规律及其随激励幅值、激励频率、截面直径和水深的变化规律;将动水压力的试验结果与Morison方程的计算结果进行对比,以验证地震作用下Morison方程的适用性。结果表明:地震作用下桥墩加速度和动水压力应考虑激励幅值、激励频率、截面直径和水深的影响,Morison方程不适用于计算地震作用下桥墩动水压力,应通过大量的水下振动台试验加以修正。     

Hydrodynamic coefficients for water-wave diffraction by spherical structures

Evaluation of hydrodynamic coefficients and loads on submerged or floating bodies is of great significance in designing these structures. Some special regular-shaped geometries such as those of cylindrical (circular, elliptic) and spherical (hemisphere, sphere, spheroid) structures are usually considered to obtain analytical solutions to wave diffraction and radiation problems. The work presented here is the result of water-wave interaction with submerged spheres. Analytical expressions for various hydrodynamic coefficients and loads due to the diffraction of water waves by a submerged sphere are obtained. The exciting force components due to surge and heave motions are derived by solving the diffraction problem. Theory of multipole expansions is used to express the velocity potentials in terms of an infinite series of associated Legendre polynomials with unknown coefficients and the orthogonality of the polynomials is utilized to simplify the expressions. Since the infinite series appearing in various expressions have excellent truncation properties, they are evaluated by considering only a finite number of terms. Gaussian quadrature is used to evaluate the integrals. Numerical estimates for the analytical expressions for the hydrodynamic coefficients and loads are presented for various depth to radius ratios. Consideration of more values for depth makes it easy to compare the results with those available. The results obtained match closely with those obtained earlier by Wang and Wu and their coworkers     

深水铰接塔平台的非线性动力特性分析

研究了铰接塔平台在波浪和海流作用下的非线性动力特性。将平台顶部工作单元简化为集中质量,塔柱和浮力仓简化为均匀直杆,建立了铰接塔平台动力分析模型。考虑海流和波浪对平台的作用,应用Morison公式计算铰接塔平台瞬时位置所受水动力,依据拉格朗日原理建立了铰接塔平台的强非线性运动方程。分别考虑波浪作用和波流联合作用,采用数值计算的方法研究了铰接塔平台超谐共振和混沌运动。研究表明,波流联合作用下平台的超谐共振运动响应增加,在大幅和较高频率波浪激励下,平台系统出现混沌运动。     

流体动压滑动轴承动态特性参数现场识别方法

本文讨论了在不施加人工激振的前提下,处于工作状态的转子系统流体动压滑动轴承油膜刚度及阻尼参数的现场识别方法.由于是在油膜的正常工作状态下识别其参数,所得结果更加接近于真实情况.此外,该方法还可以作为一种现场动平衡方法.     

Dramatic Effect of Vibrations on Dynamics of Rotating Hydrodynamic Systems

The results of theoretical and experimental investigation of the average dynamics of inhomogeneous systems in rotating cavity in the presence of oscillating force field are highlighted and analyzed. Average behavior of nonisothermal liquid as well as different multiphase systems (two liquids, liquid and gas, solid in liquid, granular matter in liquid) in quickly rotating horizontal cylinder subjected to vibrations of different direction is described. The specificity of dynamics of all the systems is determined by the Coriolis force which defines not only the average flows but the fluid oscillations also. The resonant excitation of inertial oscillations of liquid results in generation of intensive mean flows. The structure of vibrational streams is essentially determined by the type of inertial waves. So, excitation of an azimuthal wave generates azimuthal streams (outrunning or lagging, depending on frequency of the wave), three-dimensional standing waves (in the systems with deformable interface) generate regular spatial flows of high intensity. Under the resonant conditions the influence of vibrations appears to be very strong, the speed of mean streaming can achieve the values comparable with the speed of rotation of the container.     

Note on sway, roll and yaw motions of a ship with forward speed: analytical study

Summary The paper deals with the prediction of coupled sway-roll-yaw motions of a ship with constant forward speed, subject to regular wave force. The governing equations derived in time domain after balancing the hydrodynamic and exciting forces are solved analytically while considering the motion variables, wave frequency and external force are complex quantities. Numerical experiments were carried out for a Panamax container ship under the action of a sinusoidal wave of periodicity 11.2 sec with the variations of speed and wave height. The effect of various parameters on motion responses and system stability is investigated.     

Analysis of coupling between two slab waveguides in the presence of ring resonators

The coupling phenomena between two slab waveguides in the presence of ring resonators are investigated through a rigorous integral equation analysis. A Green's-function-theory approach is utilized to develop the integral equation formulation. The solution is obtained by applying an entire-domain Galerkin technique, using the orthogonality properties of involved wave functions in the ring resonators. The field's transmission and reflection coefficients are accurately computed and a practical directional-coupler approach is discussed. The presented results reveal strong resonant coupling phenomena between the two waveguides and the resonators.     

考虑水底柔性反射边界的深水桥墩地震动水压力分析

在深水桥墩地震动水压力分析中一般假定水底为完全反射边界,而忽略水底柔性介质对动水压力波的吸收作用。该文考虑水底柔性反射边界,基于辐射波浪理论,建立了深水桥墩地震动水压力的计算公式,深入分析了水底柔性反射边界对动水压力的影响。研究表明:水底柔性反射边界会在特定的荷载激励频率范围内对深水桥墩动水压力产生影响,且动水压力随水底反射系数的减小而减小,深水桥墩地震动水压力分析可以忽略水底柔性边界的影响。从而为长大桥梁地震灾变过程精细化模拟提供了理论依据。     

钢悬链线输流立管顶部浮体激励非线性响应研究

钢悬链线立管在上部附体激励作用下的动力响应在立管的性能化设计中是非常重要的。本文作者考虑钢悬链线立管轴向大应变的特性以及弯曲刚度和内流的影响,利用Hamilton原理和拉格朗日应变理论建立了立管的二维动力学模型。将外部流体的非线性作用力用Morison方程表示,通过Hermite插值函数对动力学方程进行离散,采用平均加速度法求解立管的动力响应。探讨了弯曲刚度的存在、内流流动和外部流体的非线性作用力对立管受浮体激励顺流向动力响应的影响。     

Dynamics of Vesicle Suspensions in Shear Flow Between Walls

The behaviour of a vesicle suspension in a simple shear flow between plates (Couette flow) was investigated experimentally in parabolic flight and sounding rocket experiments by Digital Holographic Microscopy. The lift force which pushes deformable vesicles away from walls was quantitatively investigated and is found to be rather well described by a theoretical model by Olla (J Phys II (France) 7:1533, 1997). At longer shearing times, vesicles reach a steady distribution about the center plane of the shear flow chamber, through a balance between the lift force and shear induced diffusion due to hydrodynamic interactions between vesicles. This steady distribution was investigated in the BIOMICS experiment in the MASER 11 sounding rocket. The results allow an estimation of self-diffusion coefficients in vesicle suspensions and reveal possible segregation phenomena in polydisperse suspensions.     

沿水平向运动的水中截断圆柱体辐射波浪问题的解析解答

根据线性势波理论,分析了水中截断圆柱体作水平简谐运动时结构周围的辐射波浪。利用分离变量法,分别得到了含有未知常数的三个流体子域速度势的简谐表达形式,并采用一个较为简单的匹配方法使其在流体子域的共同边界上满足压力和法向速度的连续条件。于是求解得到了速度势,进而可得到由等效附加质量和附加阻尼表示的柱体侧面上的动水力。不仅能考虑自由表面波对动水压力的影响,也适用于位于任意水深处的截断圆柱体。实例分析表明,该方法具有较高的计算精度;同时对于截断圆柱体,采用Morison方程中的动水附加惯性力项会高估柱体侧面上的动水力。     

规则波作用下开孔圆盘阵列绕射效应研究

在势流理论和线性波理论的假设下,运用特征函数展开法和贝塞尔函数加法理论,研究了规则波作用下开孔圆盘阵列的绕射效应。阵列中每个圆盘都是刚性、开孔的,固定在静水面以下,其厚度相对于入射波波长可以忽略,且通过其表面的流体运动满足达西定律。根据推导出的速度势,进一步得到圆盘的垂荡力和流场的自由表面高程解析表达式。利用该解析解与已发表的孤立圆盘计算结果进行验证;分析了四盘阵列在各种波浪和结构参数下的绕射现象。研究表明：当圆盘开孔率、吃水深度及入射波波长在一定范围内时,圆盘阵列内部将发生显著的相互作用现象,主要表现为迎浪侧圆盘对背浪侧圆盘的遮蔽效应。在特定的入射波波数下,选择适当的四盘阵列圆盘间距,最大可将背浪侧圆盘垂荡力降低至迎浪侧圆盘的76%。同时还发现,四盘阵列中,迎浪侧圆盘上可能发生波能聚焦现象,引起自由表面高程的急剧增大,但这种波能聚焦现象会随着圆盘开孔率的增大而逐渐减弱。     

行波效应对深水连续刚构桥地震响应的影响

跨海或库区的大跨度桥梁在地震作用下不仅需要考虑水体与桥墩的动力相互作用,同时由于各桥墩间跨度较大应考虑地震输入的行波效应。该文采用辐射波浪理论求解桥墩地震动水压力,建立了考虑地震动输入空间效应的深水桥梁地震响应分析方法,并考虑行波效应对深水连续刚构桥进行地震响应分析。研究表明：动水压力增大了桥梁结构的地震响应,其影响程度随着输入地震波和墩梁约束条件的不同而有所差异;考虑行波效应时地震动水压力对桥梁结构动力响应的影响较一致激励而言有所差别,同时地震动水压力对桥梁地震响应的影响随着视波速的不同而变化。由此得出结论,为合理评价地震动水压力对深水长大桥梁动力响应的影响应考虑地震动输入的行波效应。     

自锚式悬索桥的平稳/非平稳随机地震响应

通过引入均匀调制演变函数,考虑了地震激励幅值的非平稳性。同时考虑了地震动空间效应,包括行波效应、部分相干效应和局部场地效应的影响,对一自锚式混凝土悬索桥结构进行了地震反应分析。计算了平稳/非平稳地面激励下主塔弯矩以及剪力反应。计算结果表明,考虑非平稳因素可使地震反应峰值减小,行波效应和相干效应使结构地震反应增大。     

三质体声共振混合机的动力学特性及其性能分析

为研究三质体声共振混合机的动力学特性,建立了三质体声共振混合机的动力学模型,进而分析了系统物理参数对动力学特性的影响,阐明了物料质量和阻尼变化对声共振混合机动力学响应的影响规律,提出了系统在共振频率附近工作的振幅控制策略。进一步分析了典型声共振混合机在额定载荷下的对地动载荷和所需激振力,并与额定载荷所需的最大推力进行了比较。结果表明,通过选择合理的系统物理参数,三质体声共振混合机在三阶共振频率附近工作,其振幅变化较平缓、负载质体和激振质体的运动相位相反,系统能够兼具能量转换率高、对地动载荷小且激振力小等优点。所得结论有助于进一步提高声共振混合机的工作性能和设计水平。     

A new boundary element formulation for wave load analysis

A new boundary element (BEM) formulation is proposed for wave load analysis of submerged or floating bodies. The presented formulation, through establishing an impedance relation, permits the evaluation of the hydrodynamic coefficients (added mass and damping coefficients) and the coefficients of wave exciting forces systematically in terms of system matrices of BEM without solving any special problem, such as, unit velocity or unit excitation problem. It also eliminates the need for scattering analysis in the evaluation of wave exciting forces. The imaginary and real parts of impedance matrix give, respectively, added mass and damping matrices whose elements describe the fluid resistance against the motion of the body. The formulation is explained through the use of a simple fluid-solid system under wave excitations, which involves a uniform fluid layer containing a solid cylindrical body. In the formulation, the solid body is taken first as deformable, then, it is specialized when it is rigid. The validity of the proposed method is verified by comparing its result with those available in literature for rigid submerged or floating bodies.     

Nonlinear random vibration of the slender deep-water pier under seismic excitation

The present study investigates the nonlinear random vibration of the deep-water pier exposed to horizontal seismic excitation. First of all, the stochastic dynamic model of the pier is formulated. During the process, the pier is simplified as a cantilever beam fixed on the rock foundation, the seismic excitation is treated as Gaussian white noise, the hydrodynamic pressure is described with the radiation wave theory, and the equation for the nonlinear kinematic of the pier is deduced by the means of Kane’s method. Then, with the application of the stochastic averaging (SA) technique, the Fokker–Plank–Kolmogorov (FPK) equation governing the transient probability density function (PDF) of the amplitude envelope and the backward Kolmogorov (BK) equation for the conditional reliability function (CRF) are derived, respectively. The closed-form stationary PDF can be yielded directly from the reduced FPK equation, while the CRF and the conditional PDF of first-passage time are given after solving the BK equation numerically. Numerical discussions are performed to illustrate the trend of excitation intensity, mass ratio, immersion ratio, and inner and outer hydrodynamic effect on the stationary response and first-passage failure are examined, respectively. It has been shown that increases in the excitation intensity, mass ratio, and immersion ratio can amplify the response and reduce the reliability of the deep-water pier system. The hydrodynamic effect also leads to an amplification of the system response and a reduction in the reliability of the system. Similarly, the presence of inner water can also exacerbate these effects, and this phenomenon becomes more pronounced with increasing immersed ratios. Additionally, the analytical solution is validated by the result obtained by pertained Monte Carlo simulations (MCS). It is noted that this work will be helpful for the optimal seismic design of deep-water piers.     

Interaction of antiplane cracks with elastic waves in transversely isotropic materials

Summary The interaction of plane time-harmonic SH-waves with micro-cracks in transversely isotropic materials is investigated. Elastic wave scattering by a single micro-crack is first analyzed. The scattered displacement is expressed as a Fourier integral containing the crack opening displacement. By using this representation formula and by invoking the traction-free boundary condition on the faces of the crack, a boundary integral equation for the unknown crack opening displacement is obtained. Expanding the crack opening displacement into a series of Chebyshev polynomials and adopting a Galerkin method, the boundary integral equation is converted into an infinite system of inear algebraic equations for the expansion coefficients which is solved numerically. Numerical results are presented for the elastodynamic stress intensity factors, the scattered far-field and the scattering cross section of a single crack. Then, propagation of plane time-harmonic SH-waves in a transversely isotropicmaterial permeated by a random and dilute distribution of micro-cracks is investigated. The effects of the micro-crack density on the attenuation coefficient and the phase velocity are analyzed by appealing to a simple energy consideration and by using Kramers-Kronig relations.