A Free Surface Frequency Domain Green Function with Viscous Dissipation and Partial Reflections from Side Walls

The free-surface Green function method is widely used in solving the radiation or diffraction problems caused by a ship or ocean structure oscillating on the waves. In the context of inviscid potential flow, hydrodynamic problems such as multi-body interaction and tank side wall effect cannot be properly dealt with based on the traditional free-surface frequency domain Green function method, in which the water viscosity is omitted and the energy dissipation effect is absent. In this paper, an open-sea Green function with viscous dissipation was presented within the theory ofvisco-potential flow. Then the tank Green function with a partial reflection from the side walls in wave tanks was formulated as a formal sum of open-sea Green functions representing the infinite images between two parallel side walls of the source in the tank. The new far-field characteristics of the tank Green function is vitally important fur improving the validity of side-wall effects evaluation, which can be used in supervising the tank model tests.

Reflection and Transmission of Regular Waves from/Through Single and Double Perforated Thin Walls

In this paper, reflection and transmission coefficients of regular waves from/through perforated thin walls are investigated. Small scale laboratory tests have been performed in a wave flume firstly with single perforated thin Plexiglas plates of various porosities. The plate is placed perpendicular to the flume with the height from the flume bottom to the position above water surface. With this thin wall in the flume wave overtopping is prohibited and incident waves are able to transmit. The porosities of the walls are achieved by perforating the plates with circular holes. Model settings with double perforated walls parallel to each other forming so called chamber system, have been also examined. Several parameters have been used for correlating the laboratory tests’ results. Experimental data are also compared with results from the numerical model by applying the multi-domain boundary element method （MDBEM） with linear wave theory. Wave energy dissipation due to the perforations of the thin wall has been represented by a simple yet effective porosity parameter in the model. The numerical model with the MDBEM has been further validated against the previously published data.

Impedance Analytical Method of Wave Run-up and Reflection from A Slotted-Wall Caisson Breakwater

An impedance analytical method （IAM） is developed to study the interaction of plane water wave with a slotted-wall caisson breakwater. The non-linear boundary condition at the slotted-wall is expressed in terms of flow resistance. A set of algebraic expressions are obtained for free surface elevation inside and outside chamber, and reflection coefficient. The prediction of the reflection coefficients shows that the relative widths of the chamber inducing the minimum reflection coefficient for a slotted-wall caisson breakwater are in a range of 0.10～0.20, which are smaller than that （0.15～0.25） for a perforated-wall caisson breakwater. The reflection coefficients and free surface elevation obtained by the present model are compared with that of laboratory experiments carried out by previous researchers.

Meshless Method for Analysis of Permeable Breakwaters in the Proximity of A Vertical Wall

In the present work, the improved version of the meshless singular boundary method(ISBM) is developed for analyzing the performance of bottom standing submerged permeable breakwaters in regular normally incident waves and in the proximity of a vertical wall. Both single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with appropriate mixed type boundary conditions, and solved numerically using the ISBM. To model the permeability of the breakwaters fully absorbing boundary conditions are assumed. Numerical results are presented in terms of hydrodynamic quantities of the reflection coefficients. These are firstly validated against the results of a multi-domain boundary element method(BEM) developed independently for a previous study. The agreement between the results of the two methods is excellent. The coefficients of reflection are then computed and discussed for a variety of structural conditions including the breakwaters height, width, spacing, and absorbing permeability. Effects of the proximity of the vertical plane wall are also investigated. The breakwater's width is found to have only marginal effects compared with its height. Permeability tends to decrease the minimum reflections. These coefficients show periodic variations with the spacing relative to the wavelength. Trapezoidal breakwaters are found to be more cost-effective than the rectangular breakwaters. Dual breakwater systems are confirmed to perform much better than single structures.

The theoretical study on diagonal wave interaction with perforated-wall breakwater with rock fill

The interaction of diagonal waves with perforated-wall breakwater partially filled with rock fill is studied using the linear potential theory. By means of the matched eigenfunction expansion method, an analytical method is presented to calculate the reflection coefficient and the wave force coefficient of the breakwater. The calculated results of the reflection coefficient for limiting cases are the same to the existing results. The main effect factors of the reflection coefficient and the wave force coefficient are analyzed by numerical examples. With the increasing of thickness of rock fill, the wave force coefficient on the perforated wall generally decreases, while the reflection coefficient increases. With the increasing of the incident angle of the wave, the reflection coefficient of the breakwater first decreases, reaches its minimum, and then increases monotonously.

Oblique Wave Motion over Multiple Submerged Porous Bars near a Vertical Wall

This study examines oblique wave motion over multiple submerged porous bars in front of a vertical wall. Based on linear potential theory, an analytical solution for the present problem is developed using matched eigenfunction expansions. A complex dispersion relation is adopted to describe the wave elevation and energy dissipation over submerged porous bars. In the analytical solution, no limitations on the bar number, bar size, and spacing between adjacent bars are set. The convergence of the analytical solution is satisfactory, and the correctness of the analytical solution is confirmed by an independently developed multi-domain BEM （boundary element method） solution. Numerical examples are presented to examine the reflection and transmission coefficients of porous bars, CR and Cv, respectively, for engineering applications. The calculation results show that when the sum of widths for all the porous bars is fixed, increasing the bar number can significantly improve the sheltering function of the bars. Increasing the bar height can cause more wave energy dissipation and lower CR and Cr. The spacing between adjacent bars and the spacing between the last bar and the vertical wall are the key parameters affecting CR and Ct. The proposed analytical method may be used to analyze the hydrodynamic performance of submerged porous bars in preliminary engineering designs.

EXPONENTIAL CONVERGENCE FOR NONLINEAR SPDES WITH DOUBLE REFLECTING WALLS

The present article is devoted to nonlinear stochastic partial differential equations with double reflecting walls driven by possibly degenerate,multiplicative noise.We prove that the corresponding Markov semigroup possesses an exponentially attracting invariant measure through asymptotic coupling,in which Foias-Prodi estimation and the truncation technique are crucial for the realization of the Girsanov transform.

部分反射直墙前二维物体的绕射和辐射问题

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。

基于DIALux的运营公路隧道墙面反射系数对照明节能的影响研究

为了量化分析墙面反射系数对运营公路隧道照明节能的实际效果、节能率与经济性的影响,本文基于DIALux照明计算软件对公路隧道全段照明环境进行仿真,模拟了9种不同反射系数(0.1~0.9)下的隧道内照明情况,结合20条实例隧道共180种工况进行模拟,研究墙面反射系数对隧道内路面照明效果的影响,通过降低照明配置得出节能率,并运用静态投资回收期进行经济性分析。

有限壁厚圆管的声辐射

为研究有限壁厚圆管的声辐射特性,使用二维(2D)轴对称时域计算流体动力学(computational fluid dynamics,CFD)方法计算了管口反射系数和端部修正。无限薄圆形管道计算结果与理论值吻合良好,从而证明了计算方法的正确性。研究了壁厚对管口声辐射的影响,计算结果表明,随着壁厚的增加,反射系数的幅值逐渐减小,端部修正系数则明显增大。通过对计算结果的多项式拟合,给出了反射系数和端部修正的拟合公式。最后应用该拟合公式计算管口的辐射声阻抗,结合有限元方法计算了有限壁厚膨胀腔消声器的减噪量(noise reduction,NR),通过与使用自动匹配层计算得到的结果对比,验证了拟合公式的准确性和实用性。

水下爆炸冲击波反射压力计算方法的改进

重力坝是一类常见大型混凝土水工建筑。为探寻适用于其近区水下爆炸冲击波反射压力的计算方法,利用冲击波阵面上的质量、动量和能量3个守恒基本关系式,以及凝聚介质状态方程,严格推导出物理内涵明晰的刚性壁面水下爆炸冲击波反射压力计算方法。通过连续介质中冲击波速与粒子速度之间的关系,给出其中水的状态参数k的确定方法,揭示状态参数k随入射冲击波压力呈双指数衰减规律,发现入射压力在725 MPa以上时,k值的变化对冲击波反射压力计算结果有着重大影响。通过与Cole[12]、Henrych[14]和罗泽立等[15]提出的计算方法及数值仿真进行对比验证分析,结果表明:新提出的计算方法具有适用范围更广、计算精度更高的特点,且首次从理论上揭示水下爆炸冲击波反射压力系数范围为2.00~4.49。

解开西安城墙历史保护的成功密码

西安城墙是我国目前规模最大、保护最完整的古城垣,在20世纪下半叶经历了历次拆城浪潮后成功保留至今,不得不说是一个奇迹,是我国在遗产保护领域为数不多的具有成功经验的代表。在对西安城墙保护历程回顾的基础上,本文将详细剖析保护规划得以顺利实施背后的深层次原因,并思考其中的得失。希望通过对这段尘封历史的探寻与反思,能够起到以史为镜的作用,推动我国文化遗产保护事业进一步发展。

建筑玻璃幕墙光反射影响分析

玻璃幕墙作为现代公共建筑外围护结构的常用形式,为建筑实现不同立面效果提供了更多的创作选择,但大面积、高反射的玻璃幕墙在建筑中的应用也对周边环境造成了光污染。以厦门市某幕墙建筑为例,通过现场调研确定受影响对象后,采用Ecotect软件进行光反射影响模拟,根据GB/T 18091—2015《玻璃幕墙光热性能》的相关要求进行评价分析,并提出该方法在幕墙光反射影响分析中的作用及不足,为相关设计单位进行建筑玻璃幕墙光反射影响评价分析提供参考。

浅谈玻璃幕墙高层建筑照明一致性设计手法——以粤海城(南北地块)为例

现代玻璃幕墙建筑在城市中扮演着至关重要的角色,其设计与价值愈发凸显。随着现代建筑幕墙结构出现的多样性,同时考虑建筑景观的统一性,建筑立面与景观照明在表达上更加注重方式与细节,以适应市民不断升级的美感追求。因此,照明的一致性设计逐渐成为新的潮流。以粤海城(南北地块)的景观照明设计为例,结合人体感官舒适的需求,从设计理念、技术挑战等方面展开分析,旨在为建筑设计师、照明设计师、业主及施工单位提供参考和借鉴。

控制玻璃幕墙的有害光反射

本文探讨控制玻璃幕墙的有害光反射问题。通过现状调查论证了玻璃幕墙存在的“光污染”即由玻璃幕墙反射阳光(强光)而产生的有害光反射。本文就限制玻璃幕墙有害反射主要技术指标作了分析论证。

防爆墙迎爆面反射压力系数计算方法研究

研究防爆墙迎爆面荷载计算方法有助于防爆墙的科学设计和合理使用。爆炸产生的反射冲击波压力是作用在防爆墙上的主要荷载,由入射压力和与相应的反射压力系数的乘积得到。针对墙体变形情况下作用于防爆墙上的反射压力系数的计算方法进行了研究,发现作用于墙体的反射压力系数和墙体变形没有直接关系。基于这一现象,将墙体变形和冲击波墙面反射解耦考虑,提出了反射压力系数的计算方法。对比了地面爆炸及近地表空中爆炸对墙体反射压力系数分布规律的差异,建议了近地表空中爆炸时墙体反射压力系数的计算方法。

柱形爆炸容器内爆炸冲击波的传播规律研究

为了研究柱形爆炸容器内炸药爆炸冲击波的传播规律,利用空中爆炸传感器测量了不同药量和不同距离条件下冲击波压力时程曲线,发现实验测试值与传统的理论经验公式计算值存在较大误差。通过实验结果和理论分析,探讨了误差产生的原因,并对柱形爆炸容器内超压测试曲线出现多峰值超压的原因进行了分析。最后,基于实验测试结果及爆炸相似律原理拟合出适用于该环境下的冲击波超压计算公式,经过拟合修正后计算误差由70%~80%降至0.57%~15%。该研究可为爆炸容器的设计和应用提供理论参考。

浅层地震技术在大堤防(隔)渗墙质量检测中的应用

采用浅层地震反射波法和瑞雷面波法相结合 ,对大堤防渗墙 (或隔渗墙 )的质量进行检测。结果表明 ,两者的综合应用 ,不仅能有效地检测防渗墙 (或隔渗墙 )的连续性和顶底板埋深 ,而且能较为准确地获取墙的厚度。这种综合方法为无损检测墙的质量提供了一种行之有效的检测手段。

双层局部开孔板沉箱对波浪反射的理论研究

提出了一种用于研究由双层开孔板和一个不透水后板的开孔结构对斜向波反射率的理论分析方法。整个流域被分成三个子域,在每个子域内应用特征函数展开法以得到该域内包含未知展开系数的势函数的表达式,在速度势的展开中,考虑了非传播模态波浪的影响。通过匹配开孔板处的边界条件可以求解待定的展开系数,继而求解双层开孔板防波堤结构对斜向波的反射率。数值计算结果与试验结果进行了比较,符合较好。并进一步讨论了几个重要因素对反射系数的影响。

热反射外墙涂料的节能机理与效果分析

就热反射外墙涂料或隔热外墙涂料的热工性能进行了分析研究,在此基础上得到了热反射外墙涂料的宏观热工参数。引入了传热系数修正值即外墙采用热反射涂料后(ρ=ρr)的传热量与采用普通饰面的传热量比例,来表示热反射涂料对建筑热工性能的影响,并计算出了典型夏热冬冷与夏热冬暖地区热反射涂料的传热系数修正值。供同行在设计及研究工作中参考。