基于LBM的波浪作用下动量射流数值模拟

为了进一步研究射流在有限水深波浪环境下的流动规律,拓宽LBM在水利工程学科中的应用范围,将LB方法的原理应用于自由表面处理、边界条件设定、紊流模型的耦合求解、造波及消波等关键问题上,建立了二维多松弛LB数值波浪水槽模型。运用该模型模拟不同波浪环境下动量射流的紊动特征及变化规律,得到射流在不同工况下的轴线速度衰减、扩展半宽变化和横断面速度分布等规律。研究表明,该模型具有很好的适用性,可以较好地模拟射流问题。     

管袋堤坝波浪作用下波浪压力的数值模拟研究

波浪作用是影响管袋筑坝的最主要外部荷载,关系到管袋结构的安全与稳定。为了解管袋堤坝在波浪作用下的波浪压力,基于流体力学计算软件FLUENT建立数值水槽模型,通过设定不同的边界条件,采用源造波法模拟不同波高、周期、水深、坡率下波浪与管袋坝面的相互作用,计算管袋受力和波陡、坡率之间的关系,并拟合相应关系曲线得到管袋坝的受力和波陡、坡率之间的函数关系式。结果表明,该方法的结果与物理试验过程中获得的规律相符,具有一定的实用性。     

波浪中非流线型浮体运动的动网格分析研究

使用Fluent软件,利用推板造波法和阻尼消波法建立数值波浪水池,用VOF方法追踪自由表面,采用RNG k-ε两方程湍流模型,基于动网格技术和用户自定义函数,提出一种模拟波浪中非流线型浮体运动的数值方法。应用该方法模拟波浪中二维非流线型浮体的大幅运动,将得到的运动响应曲线与实验值比较,分析误差产生原因,证明该方法的准确性,为浮力超常建造过程中的精度控制提供依据。     

装卸式防汛墙在波浪作用下的变形分析

为计算分析新型装卸式防汛墙在波浪作用下的变形挠度、校核其安全性能,基于推板造波机理论,利用CFD商业软件FLUENT二次开发建立二维数值波浪水槽模型模拟数值波浪,并通过有限元分析软件ANSYS现有接口程序导入FLUENT波浪荷载,获得了波浪荷载沿防汛墙断面分布、防汛墙在波浪作用下的位移分布及变形挠度曲线。结果表明,波浪形态较好,荷载分布合理,为装卸式防汛墙的设计和运行提供了参考依据。     

三维数值波浪水槽内孤立波特性分析

内孤立波对密度层化水体的水动力及分层特性具有显著影响。为揭示内孤立波特性,建立了规则地形下可有效模拟弱非线性内孤立波的分层流三维数值波浪水槽,研究了内孤立波在规则地形条件下的传播,成功捕捉到了水体表面存在的辐聚流和辐散流,探讨了内孤立波传播过程中流速、紊动能和紊动能耗散率的分布与演化特性,为进一步利用数值波浪水槽研究内孤立波能量特性分布、改善层化水体的水生态环境提供了可靠的方法与手段。     

主动吸收式造波机的设计及初步实现

主动吸收式造波机能够实时消除水池干扰波对模型试验产生的影响,保证试验结果的准确性。基于微幅波理论,提出主动吸收式造波方法,推导摇板式造波机的控制方程,设计了基于该造波方法的主动吸收造波控制系统,通过多条反馈路线实现了造波机的精确控制,达到对造波板前干扰波的实时吸收,保证了水槽中波浪为目标波形。最后,在相同造波条件下,对比采用主动吸收造波方法和非主动吸收造波方法的试验结果,充分验证了主动吸收式造波方法具有可行性,时效性。主动吸收式造波机的实现,有助于提高波浪试验的准确性,节省试验成本,提供良好的试验环境。     

滑动挡板式越浪发电装置结构受力研究

研究在正向规则波入射下不同斜坡高度及不同水深情况时越浪式波浪发电装置的受力规律。在波浪水槽中进行模型试验;使用FLOW-3D软件进行数值模拟,通过对不同波高、不同波浪周期、极端工况进行数值模拟,得出不同波浪要素下斜坡的受力规律。通过对试验结果和模拟结果的对比分析得出:越浪斜坡在波浪入射过程中受力有先后顺序;斜坡在波浪作用下的周期受力数值在一定范围内波动;斜坡在波浪作用下波浪要素条件不变时,斜坡受力与斜坡高度、试验水深有关,呈线性关系。试验结果对滑动挡板式越浪发电装置结构的设计提供依据。     

海浪谱的二维仿真及验证

海浪仿真是海洋工程的热点话题。本文总结了一种可以适应于各种随机波浪谱来仿真海浪环境的方法,利用C语言将该方法转换为过程简单、编写方便的计算机程序得到大量仿真波浪数据,并作为造波机输入数据,通过实测数据检验仿真结果。试验证明,采用文中提出的数值方法,采集模拟波高数据利用相关函数法进行频谱估计,得到的模拟谱和靶谱误差较小。该数值仿真方法在海浪仿真上具有实际应用价值。     

具有波浪能转换功能的浮式防波堤性能研究

文章对具有波浪能转换功能的浮式防波堤性能进行评估。根据有限元空间离散法和VOF技术建立二维数值波浪水槽,模拟波浪和浮体之间的相互作用以及浮体的运动,同时记录浮体前后的波高,讨论浮子尺寸和阻尼系数对波浪透射系数和波浪能提取效率的影响。结果表明:波浪透射系数随着阻尼系数的增加而减小;在文章研究的浮子尺寸范围内,最大能量提取效率和最佳阻尼系数都随着浮子尺寸的增加而增加。     

风波联合作用下的风力机塔架疲劳特性分析

研究了海上风力机圆筒型塔架在随机风载荷和波浪载荷作用下的动力响应数值分析方法;建立了基于Palmgren Miner线性累积损伤法则的混泥土塔架安全寿命估计方法.应用线性波理论仿真非规则的海浪,分析作用在圆筒型塔架上的波浪载荷.通过坐标变换,将二维线性波理论扩展为三维线性波理论,建立了波浪力的分析计算模型;用有限元数值分析方法,求解了塔架在风波联合作用下的位移、速度、加速度以及应力响应等;用雨流计数法统计循环参量,将工作循环应力水平等寿命转换成对称循环下疲劳载荷谱,分析了变幅载荷谱下塔架的疲劳损伤及疲劳寿命.算例表明:该文的工作为海上风力机系统气动弹性分析、风力机塔架振动分析和疲劳寿命分析等提供了实用的分析方法.     

Reflection of plane wave in a micropolar thermoelastic solid half-space with diffusion

In this article, the governing equations of micropolar thermoelasticity with diffusion are formulated in the context of Lord–Shulman theory of generalized thermoelasticity. The plane wave solutions of these equations indicate the existence of six plane waves, namely, coupled longitudinal displacement (CLD) wave, coupled thermal wave, coupled mass diffusion wave, coupled transverse microrotational wave, coupled transverse displacement wave, and longidudinal microrotational wave. Reflection of CLD wave from a stress-free thermally insulated/isothermal surface is considered. The appropriate potentials of incident and reflected waves satisfy the required boundary conditions at a stress-free thermally insulated/isothermal surface to obtain the reflection coe?cients of various reflected waves for an incident CLD wave and to obtain an extension of Snell’s law. The expressions for energy ratios of various reflected waves are also obtained. A particular material aluminum–epoxy composite is chosen to compute the values of reflection coe?cients and energy ratios of reflected waves. The effects of diffusion and thermal parameters are observed on the reflection coe?cients and energy ratios.     

GL Model on Reflection of P and SV Waves from the Free Surface of Thermoelastic Diffusion Solid Under Influence of the Electromagnetic Field and Initial Stress

This article is devoted to estimating the influence of magnetic field, electric field and initial stress in an elastic solid half-space under thermoelastic diffusion. The governing equations in the xz-plane are solved taking into consideration the Green–Lindsay (GL) model. The Reflection of dilatational (P) wave and Shear Vertical (SV) wave split into four waves: namely, P wave, thermal wave, mass diffusion wave and SV wave. The reflection phenomena of P and SV waves from the free surface of an elastic solid with thermoelastic diffusion under influence of magnetic field, electric field and initial stress is considered. The expressions for the reflection coefficients for the four reflected waves are obtained. These reflection coefficients are found to depend upon the angle of incidence θ of P and SV waves, thermoelastic diffusion, magnetic field, electric field and initial stress and other material parameters. The numerical values for the reflection coefficients are calculated analytically and presented graphically for varying values of these parameters.     

Reflection of plane waves in a thermoelastic diffusive medium under the effect of microtemperatures

Abstract

The present analysis is aimed to model and study the characteristics of various reflected waves in a homogeneous and isotropic thermoelastic diffusive half-space with microtemperatures. It is shown that there exist four kinds of coupled longitudinal waves in addition to transverse and microtemperature waves in such type of medium. The reflection coefficients and energy ratios of these reflected waves have been computed numerically with the help of MATLAB programing when (i) a set of coupled longitudinal waves is made incident and (ii) a transverse wave is made incident. The numerical values of modulus of reflection coefficients are presented graphically to depict the effect of thermodiffusive parameter. It has been verified that there is no dissipation of energy at the free plane boundary during reflection phenomena.     

Numerical investigation on the effects of re-organized shock waves on the flow separation for a highly-loaded transonic compressor cascade

This paper presents a detailed numerical investigation of the influence of re-organized shock waves on the flow separation for a highly-loaded transonic compressor cascade. The boundary layer suction (BLS) was used to control the location and strength of shock waves, with the aspirated slot locating at 49% chord, where is just downstream of the impingement point of shock wave at the leading edge. The numerical simulation is based on NUMECA, a commercial software, where the cell-centered control volume approach with third-order spatial accuracy is used to solve the 3-D Reynolds-averaged Navier-Stokes equations under the Cartesian coordinate system. Several conclusions can be made through the observation of the numerical results. (1) Multiple shock waves in cascade passage leaded the velocity deficits of boundary layer on suction surface downstream of shock wave, resulting in seriously separated flow on the suction side of blade, especially when the front shock wave is much stronger than the rest of the shocks. (2) BLS with small mass flow rate can not effectively improve the boundary layer. When the impingement point of oblique shock wave coming from cascade leading edge is bled to downstream of the passage shock wave by BLS, the boundary layer flow is greatly improved. However, if the BLS mass flow rate exceeds a critical value (1.2%), the boundary layer downstream of shock wave would separate from suction surface. (3) At the blade mid-span, the aerodynamic performance of compressor blade is improved as BLS mass flow rate increases. The optimum BLS is about 1.2%. Compared with the baseline case, the BLS with flow rate of 1.2% increases the total pressure recovery coefficient by 12%, and decreases diffusion factor by 18% and deviation angle to 7 ° while keeping the pressure rise constant. (4) The three dimensional flow structure of the compressor cascade ranged from 25% span to 75% span was improved greatly with the 1.2% BLS flow rate. However it could not control the development of the corner boundary layer effectively.     

LATTICE BOLTZMANN SCHEME FOR HYPERBOLIC HEAT CONDUCTION EQUATION

An extended lattice Boltzmann (LB) equation, the lattice Boltzmann equation with a source term, is developed for the system of equations governing the hyperbolic heat conduction equation. Mathematical consistence between the proposed extended LB equation and the governing equations are accomplished by the Chapman-Enskog expansion. Four illustrative examples, with both finite and semi-infinite computational domains and subjected to linear and nonlinear boundary conditions, are simulated. All numerical predications agree very well with the existing solutions in the literature. It is also demonstrated that the present scheme is stable and free of numerical oscillations especially around the wave front, where sharp change in temperature occurs.     

Thermoelastic Analysis of an Annulus Using the Green-Naghdi Model

ABSTRACT

The linear theory of thermoelasticity of Green-Naghdi (GN) types II and III for homogeneous and isotropic materials are employed to study the thermal and mechanical waves in an annulus domain. The disturbances are generated by sudden application of temperature to the boundary. The nondimensional form of the governing equations are solved utilizing the Laplace transform method. Locally transversal linearization (LTL) technique, and a numerical inverse Laplace transform method are used to obtain the temperature, displacement, and stress fields in the physical time domain. The thermomechanical wave propagation and reflection from the boundary are investigated and the influence of the damping parameter on temperature, displacement, and stress fields in the Green-Naghdi type III is discussed.     

Application of CESE method to simulate non-Fourier heat conduction in finite medium with pulse surface heating

This study employs the space–time conservation element and solution element (CESE) method to simulate the temperature and heat flux distributions in a finite medium subject to various non-Fourier heat conduction models. The simulations consider three specific cases, namely a single phase lag (SPL) thermal wave model with a pulsed temperature condition, a SPL model with a surface heat flux input, and a dual phase lag (DPL) thermal wave model with an initial deposition of thermal energy. In every case, the thermal waves are simulated with respect to time as the thermal wave propagates through the medium with a constant velocity. In general, the simulation results are found to be in good agreement with the exact analytical solutions. Furthermore, it is shown that the CESE method yields low numerical dissipation and dispersion errors and accurately models the propagation of the wave form even in its discontinuous portions. Significantly, compared to traditional numerical schemes, the CESE method provides the ability to model the behavior of the SPL thermal wave following its reflection from the boundary surface. Further, a numerical analysis is performed to establish the CESE time step and mesh size parameters required to ensure stable solutions of the SPL and DPL thermal wave models, respectively.     

THERMOELASTICITY SOLUTION OF A LAYER USING THE GREEN–NAGHDI MODEL

The Green–Naghdi (GN) linear theory of thermoelasticity of types II (without energy dissipation) and III (with energy dissipation) for homogeneous and isotropic materials is employed to study thermal and mechanical waves in a layer. The disturbances are generated by sudden application of temperature to the boundary. The dimensionless forms of the governing equations are solved utilizing the Laplace transform method. Closed-form solutions are obtained for a layer in the Laplace domain, and a numerical inversion of the Laplace transform method is used to obtain the temperature, displacement, and stress fields in the physical time domain. Thermomechanical wave propagation and reflection from the boundary layer are investigated and the influence of the damping parameter on the temperature, displacement, and stress fields in the GN type III theory is discussed.     

Numerical investigation of the effect of inlet mass flow rates on H2/air non-premixed rotating detonation wave

In this paper, a three dimensional numerical investigation was carried out to study the formation and propagation characteristics of non-premixed rotating detonation wave using H₂/air as reactive mixtures. At a constant global equivalence ratio, the effects of inlet mass flow rates of H₂ and air on various performance parameters of rotating detonation wave and based on it combustor were analyzed in detail. On this basis, the mode switching process of rotating detonation wave caused by transiently changing the inlet mass flow rates was also discussed. The numerical results showed that inlet mass flow rates of H₂ and air played a very critical role in the formation, propagation and mode switching of rotating detonation wave. With the increase of inlet mass flow rates, rotating detonation wave could be switched from single wave to double waves. The propagation direction of double waves depended on the changing process of inlet mass flow rates. Meanwhile, compared to the single wave, double waves or its based combustor had the obvious advantages in formation time, stability and thrust, but had disadvantage in pressure ratio. In addition, both fill characteristics and mixing quality of fresh reactive mixtures are the underlying important mechanisms to explain the effects of inlet mass flow rates on rotating detonation waves.