Qualitative Description of Swashing Motion States on Mild Beach Slope

The swashing motion on mild beach slope is dominated by the motion of low frequency waves (LFWs). Companying such a motion, there are two types of swashing motion states, occurrence or no occurrence of LFW’s collision. The present study distinguishes the two states qualitatively by relating it to the number of generated LFWs for the case of two incident wave groups. A simplified swashing index is established theoretically for this purpose. A series of related experiments were performed to observe the generated out-going LFWs on different mild slope from 1:20 to 1:160 and to determine the critical value of the swashing index. Numerical simulations based on higher order Boussinesq equations are also performed to help the recognition of the LFWs generated in the experiment.

典型地形条件下的滨海工程波浪及波生流计算研究

波浪是滨海工程中需要考虑的主要水动力要素之一,直接影响滨海电厂防洪设计及码头等涉水工程的设计、运行。为研究波浪在典型近岸地形下的传播变化特点及波生流特性,选取具有代表性的近岸时域波浪模型,即基于非静压浅水方程的近岸波浪模拟(simulating waves till shore,SWASH)模型,对波浪在几种复杂近岸地形下的传播变形进行数值模拟计算,研究波浪在不同地形下的变化特点,可为分析研究滨海工程在类似地形条件下的波浪变化规律提供参考;同时探讨不同地形条件下波生流的基本特性,发现不同地形条件下产生不同形态的波生环流,可为进一步研究滨海工程区域的近岸地貌变迁、泥沙输运等提供依据。

珊瑚礁地形上波浪传播变形的非静压数值模拟

珊瑚礁广泛分布于我国南海等海域,具有重要的生态、旅游、港口和军事价值。波浪是珊瑚礁环境最重要的动力因素之一。基于非静压浅水方程波浪模型SWASH,模拟了典型岸礁地形上的波浪传播过程,并采用Demirbilek等的水槽实验数据分别对有效波高、波浪增水与爬高进行了验证,模拟结果与实测数据符合良好,展示了非静压模型在珊瑚礁地形上良好的适用性。通过波浪频率谱和波面小波谱,分析了波浪谱在该珊瑚礁地形上的演化规律,并揭示了礁坪上波浪能量从高频向低频转移的现象。本研究结果可为珊瑚礁环境动力研究以及相关的工程建设提供有益的参考依据。

基于时域模型的一种新的波浪能计算方法

针对波浪能站点的输入能量计算,提出了一种基于时域模型的方法.采用SWASH模型得到波浪能站点的时序列波浪条件,通过计算时序列波列中每一个波的能量,叠加得到该波列的总波浪能.选取成山头海上试验场2个近岸点和1个深水点作为计算站点,分别采用频域方法和时域方法对各点的输入波浪能量进行计算.结果表明,在深水和近岸站点,频域方法都得到了偏大的输入波能值,而时域方法计算得到的短期输入能量被认为更接近真实值,同时该方法也提供了一种检测波浪能发电装置实时发电效率的思路.

非静压波浪模型无反射造波

非静压波浪模型是一种近年来得到迅速发展且有望在工程计算中获得广泛应用的波浪模型。为了在非静压波浪模型中实现无反射造波,在连续性方程中添加了质量源项进行域内源造波,并采用阻尼消波方法进行数值消波。数值算例结果表明,所建立的无反射造波方法可以较好地避免非静压波浪数学模型中的二次反射,实现长时间稳定波浪模拟。

决口海堤洪水波传播模拟和分析研究Ⅰ:方法和验证

选用水槽和港池物理模型方法以及已有的一些物理模型试验成果,结合SWASH模型,对孤立波在海堤斜坡上的爬高和越浪进行验证,确定合适的计算参数;计算和分析几种不同内坡形式的海堤堤顶决口,确定合适的海堤内坡边界条件。研究分析表明,验证后的SWASH模型可以用来进行海侧来波和陆域越堤波浪的联合计算,为决口海堤洪水波传播模拟和分析奠定了基础。

浅滩地形上波浪破碎对低频波能放大的影响

低频长波对港湾共振、泥沙输运、波浪爬高与越浪等过程有重要影响。采用非静压模型SWASH模拟了不规则波在浅滩上的传播及破碎过程,重点探讨了滩顶短波破碎程度对低频波能演变的影响。模拟结果显示,当滩顶短波处于临界破碎状态时,低频波能流沿浅滩持续增长,浅滩对低频长波的放大效应(滩后与滩前低频波能流之比)显著;当滩顶短波轻微破碎、破波仅发生在外破波区时,低频波能流的沿滩增长率进一步变大;当滩顶短波剧烈破碎、破波延续到内破波区时,低频波能流沿滩先增长而后转为衰减,滩后放大率较临界破碎时明显减小。研究结果表明,浅滩顶部水深改变了短波破碎程度,进而影响低频长波的演化过程,浅滩上长波总体增长率随滩顶水深的减小呈现先增大后减小的规律,在短波轻微破碎时最大。

时域模型FUNWAVE与SWASH的对比研究

本文采用Berkhoff为验证缓坡方程的不同计算方法可信度所使用的地形,对基于Boussinesq方程的FUNWAVE和基于NS方程的SWASH两种时域模型进行了比较分析,通过与实测数据对比,结果显示两种模型都能达到较好的精度,整体上FUNWAVE略好于SWASH,但基于相同的模型设置,SWASH运行速度远远快于FUNWAVE。综合考虑两种模型的精度与运行速度,SWASH模型被认为更具实用性。

Analysis of the Beach Face with High-Frequency Oscillations and Dynamic Functions in the Swash Zone in the Houjiang Beach of Guangdong Province

Using the data of beach face high oscillations and waves and flows of the surf zones influenced by the swells, the characteristics including beach face variation trends, trend shapes, oscillation periods, oscillation intensions of different profile shapes, and the characteristic relations between different stake points on the same profile were analyzed comparatively. The relations between the beach face with high oscillations erosion and sediment and the surf zone infragravity waves were also analyzed based on the cress spectrum analysis. The results showed that the swash diffluences caused by the beach cusp rhythm topography hasten the sediment transport from the beach ridge to beach paddy, and the beach face of the swash zones has the infragravity periodic oscillations, and the oscillation intensions descend from the bottom to the top of the beach face, and the infragravity waves of the surf zones have significant effect on the high-frequency variations of erosion and sediment of the beach face.

岛礁三维SWASH模型的时空敏感性分析

为了探究SWASH模型中计算网格尺寸及计算时间步长对于解决深海至浅水三维复杂地形下波浪和水流运动的影响程度,在对其控制方程、边界条件、数值求解等介绍的基础上,采用多组不同的计算网格尺寸和不同的计算时间步长对三维地形试验下珊瑚岛礁概化模型进行波流场的模拟,并将模拟结果与物理模型试验的实测结果进行对比。结果表明:SWASH模型的数值模拟结果对计算网格尺寸表现得比较敏感,对计算时间步长表现得并不敏感,并且在合适的参数选取下,SWASH模型可以较好地模拟波浪在近岸区域所发生的浅水变形,以及在岛礁地形区域的波浪破碎和绕射等物理现象,其流速和波高沿波浪入射方向的模拟值与物理模型的试验值结果吻合程度较好,说明SWASH模型能够较好地适用于近岸复杂地形下波浪传播的数值模拟。

基于SWASH模型的近岸波浪传播变形数值模拟

SWASH模型是一种新型的非静压时域波浪模拟。为了探讨SWASH模型对于解决近岸波浪传播变形问题的适用性,在对其控制方程、边界条件、数值解法等进行介绍的基础上,采用该模型分别模拟了正向规则波、斜向规则波和斜向不规则波入射条件下L形防波堤附近水域的波浪场和波生流场,并与物理试验结果进行对比。结果表明,SWASH模型较好地复演了波浪在近岸区域所发生的浅水变形、折射、破碎,以及堤前反射、堤内绕射等物理现象,波高沿断面的定量分布与试验结果吻合良好,同时较好地模拟了不同波况下防波堤附近水域的波生流场,说明该模型适用于复杂岸线和地形条件下波浪传播变形的数值模拟。

基于SWASH模型的珊瑚岛礁波生环流模拟研究

珊瑚礁地形是热带和亚热带近岸浅海地区的显著特征之一。不同于以往常见的近岸缓变地形的水动力环境,岛礁附近水深剧烈变化且存在潟湖和裂口等,导致礁坪上产生显著的波浪增水、波生流现象。采用非静压模型SWASH模拟研究了不同外海波高、周期和礁坪淹没水深对礁坪波高和波浪增水的影响。结果表明波浪通常在礁缘处发生破碎,波高在礁坪上沿程减小,礁坪上的波浪增水随入射波高、周期增大而增大,随礁坪的淹没水深增大而减小。在增水正压力和辐射应力的驱动下在礁坪上形成向岸流、在裂口中形成离岸出流,产生外海-礁坪-潟湖-裂口的水平环流系统。岛礁环流随外海入射波高的增大而增大,礁坪上流速随周期增大而增大,其他区域随礁坪淹没水深和周期变化不明显。

长江口围垦工程越浪数值模拟研究

运用基于非线性浅水方程的SWASH模型对长江口围垦工程的越浪进行模拟研究。采用垂向结构提高了模型的色散性,使模型适用于深水区,考虑垂向加速度的作用,使浅水区域的模拟更加精确。根据实际具体工程对模型进行验证并与海堤规范计算结果进行比较。研究表明:该模型和海堤规范都能很好地对越浪量进行计算,模型计算结果更为精确,工程中栅栏板对波浪的耗散等还需在数模中进一步概化和优化。

Lubrication characteristics of external return spherical hinge pair of axial piston pump or motor under combined action of inclination and offset distance

External return mechanism is a mechanical structure applied to axial piston pumps.To study its lubrication characteristics,the Reynolds equation applied to an external return spherical hinge pair was deduced based on the vector equation of relative-motion velocity of the external return spherical hinge pair under the influence of external swash plate inclination and offset distance.The results show that the total friction,axial leakage flow,and maximum value of the maximum oil-film pressure increase with increasing pump-shaft speed and decrease with increasing offset distance in one working cycle when the external-swash-plate inclination is constant.However,the varying offset distance has little effect on the axial leakage flow.The maximum value of the maximum oil-film pressure decreases with increasing external-swash-plate inclination and the total leakage flow increases with increasing external-swash-plate inclination in one working cycle when the offset distance is constant.It can be seen that the abovementioned parameters are important factors that affect the lubrication characteristics of external return spherical hinge pairs.Therefore,the complex effects of different coupling parameters should be comprehensively considered in the design of the external return mechanism.

Infra-Gravity Wave Generation by the Shoaling Wave Groups over Beaches

A physical parameter, fib, which was used to meet the forcing of primary short waves to be off-resonant before wave breaking, has been considered as an applicable parameter in the infra-gravity wave generation. Since a series of modulating wave groups for different wave conditions are perfonned to proceed with the resonant mechanism of infra- gravity waves prior to wave breaking, the amplitude growth of incident bound long wave is assumed to be simply controlled by the normalized bed slope, fib. The results appear a large dependence of the growth rate, a, of incident bound long wave, separated by the three-array method, on the normalized bed slope, fib. High spatial resolution of wave records enables identification of the cross-correlation between squared short-wave envelopes and infra-gravity waves. The cross- shore structure of infra-gravity waves over beaches presents the mechanics of incident bound- and outgoing free long waves with the formation of free standing long waves in the nearshore region. The wave run-up and amplification of infra-gravity waves in the swash zone appear that the additional long waves generated by the breaking process would modify the cross-shore structure of free standing long waves. Finally, this paper would further discuss the contribution of long wave breaking and bottom friction to the energy dissipation of infra-gravity waves based on different slope conditions.

潜堤地形对随机波浪非线性特征量影响的数值模拟研究

利用基于非静压和浅水方程的SWASH模型,模拟随机波在潜堤地形上的传播变形,通过与物理模型实验和理论靶谱的对比,证明了该模型的有效性。应用该模型研究潜堤地形对随机波非线性参数的影响,及潜堤上畸形波的产生和演化。发现不规则波在向浅水传播的过程中,波浪偏度和峰度先增后减,最大值出现在堤顶左端,而波浪不对称度则先减后增,其最小值、最大值分别出现在堤顶左端和右端。如果堤顶宽度足够长,不对称度、偏度和峰度会在距堤顶左端2~3倍特征波长范围内达到稳定状态。此外,发现堤顶左端附近出现畸形波的概率最大,应用傅里叶变换和小波变换分析几个典型位置波面过程线,对比畸形波演化过程中能量分布、频率组成变化,分析畸形波的生成原因。

近岸波浪模型MIKE21BW与SWASH的比较

波浪是滨海电厂等电力工程中需要考虑的主要水动力要素之一,为了实现近岸波要素的准确计算,目前多采用数值模拟的方式,在近岸,特别是工程区附近的波浪模拟中,多采用时域解析的波浪模型(以下简称时域波浪模型)来进行计算。本文选取了两个具有代表性的近岸时域波浪模型,分别是基于Boussinesq方程的MIKE21BW模型和基于非静压浅水方程的SWASH模型,对两个模型的理论基础、计算流程、计算效率、后处理等方面进行了简单的介绍和对比,以期为工程中模型的应用和选择提供参考。

岛礁防浪建筑物水动力场数值模拟研究

【目的】针对岛礁防浪建筑物的水动力场变化问题,利用数值模拟方法进行探究。【方法】采用非静压波浪数值模型SWASH模拟了筑堤岛礁的波生环流和涡量场。【结果】筑堤对模型区域内流速有较为显著的影响,当防波堤堤长越长、防波堤堤距越小时,模型区域内整体流速越小,其断面内沿岸流速的变化也越小。礁坪上方最大向岸流速和沿岸流速随防波堤堤距的增大而增大。当防波堤越靠近礁坪后方、防波堤长度越短时,裂口内的向岸流速越趋近于无堤时的流速。模型内最大涡量值随堤长和堤距的变化并不明显,但总出现在堤尾处。【结论】SWASH模型能够较好地模拟筑堤岛礁工程周围水域的流场情况,为复杂流环境下的岛礁筑堤建设提供科学依据。

Theoretical study of flow ripple for an aviation axial-piston pump with damping holes in the valve plate

Based on the structure of a certain type of aviation axial-piston pump＇s valve plate which adopts a pre-pressurization fluid path （consisting a damping hole, a buffer chamber, and an orifice） to reduce flow ripple, a single-piston model of the aviation axial-piston pump is presented. This sin- gle-piston model comprehensively considers fluid compressibility, orifice restriction effect, fluid resistance in the capillary tube, and the leakage flow. Besides, the instantaneous discharge areas used in the single-piston model have been calculated in detail. Based on the single-piston model, a multi-piston pump model has been established according to the simple hydraulic circuit. The sin- gle- and multi-piston pump models have been realized by the S-function in Matlab/Simulink. The developed multi-piston pump model has been validated by being compared with the numerical result by computational fluid dynamic （CFD）. The effects of the pre-pressurization fluid path on the flow ripple and the instantaneous pressure in the piston chamber have been studied and opti- mized design recommendations for the aviation axial-piston pump have been given out.

Numerical investigation of swash zone hydrodynamics

This paper presents a novel numerical model using a fully three-dimensional(3D),incompressible,two-phase flow NavierStokes(NS)solver,which are discretized by the finite volume method.A high-resolution STACS-VOF method is used to capture the interface between the air and water phases.The validity of the simulation following this model is examined through3D shear flow and collapsing cylinder of water.Then,this proposed model is adopted to simulate the dynamics of flow involved with surge bore propagating over a slope in the swash zone.The computed uprush shoreline motion and the tip of runup water surface agreed well with experimental data,which indicates that this model can describe the aerated flow accurately.Numerical analyses are also applied to the spatial and temporal distributions of free-surface,instantaneous flow field,and maximal bed shear stress in the bore collapse,uprush and backwash processes.The results from the analyses reveal that the flow dynamics is complicated after the bore breaks,and the proposed model can well capture the structure characteristics of sheet flow,which are better than the previous results.All these findings are of help to understand the pattern of sediment transport and coastal evolution in the swash zone.