近岸波浪传播的非静压数值模型

基于均匀网格,建立了沿水深积分的非静压波浪传播数值模型,模型的求解分静压步和动压步两部分。静压步的控制方程为全非线性浅水方程,采用有限体积格式求解,通过采用线性重构技术和全隐式离散底摩阻项,保证了格式的和谐性、守恒性和水深非负性,有效处理了海岸动边界问题。动压步通过应用有限差分方法求解泊松方程考虑动压力,使得模型具备模拟色散性波浪传播的能力。引入波浪破碎指标,波浪破碎后模型退化为静压模型,破碎波自动捕捉为间断。通过算例对所建立模型进行了验证。     

水库滑坡涌浪传播有限元数值模拟

库岸滑坡涌浪危害巨大,正确预测库区可能的滑坡涌浪非常重要,是工程可行性论证的重要内容之一。将浅水控制方程应用于滑坡涌浪数值模拟,控制方程采用简便且具有较高精度的两步Taylor-Galerkin方法进行求解。通过算例对数值模型的应用进行验证,结果表明,涌浪产生后将以入水点为源点迅速向四周推进并不断衰减,且随传播距离的增加浪高降幅逐渐减小。计算的涌浪高度及水位变化规律与实测资料吻合得很好,并将滑坡涌浪的沿程传播过程可视化。研究结果表明,文中方法模拟滑坡涌浪传播是有效可行的,可用于滑坡涌浪灾害的预测和防治。     

基于NAD算法的声波方程时间四阶差分解法

波动方程数值模拟是研究地震波传播机理的重要工具,有限差分求解波动方程是当前地震波数值模拟的主要方法之一。当地下介质中的地震波速度较低或地震波高频成分丰富时,常规有限差分技术常常产生严重的数值频散误差,这种误差会降低数值模拟的精度,影响对地震波传播机理的分析。为压制地震波数值模拟时产生的数值频散误差,提高波场模拟精度,提出了基于NAD算子的时间四阶精度波动方程差分格式。根据对应的差分格式,分析了该差分格式的数值频散关系。与常规四阶精度差分算法的频散曲线相比,基于NAD时间四阶精度差分方法不但能够实现时间频散的有效压制,同时其基于更多网格点的位移分量和位移梯度分量空间微分求解方法还能够实现空间频散的有效压制。另外在相同模型条件下,基于NAD算法的声波方程时间四阶差分解法可采用大网格对模拟空间进行差分离散,减少网格数,提高计算效率。     

土质滑坡失稳、运动及冲击压力物质点法模拟研究

大型滑坡灾害往往带来巨大的人员伤亡和财产损失,开展滑坡灾害全过程数值模拟研究对滑坡风险定量评估具有重要意义。本文采用更新拉格朗日控制方程的物质点法,基于Drucker-Prager屈服准则下的理想弹塑性模型,考虑孔隙水压力效应推导等效内摩擦角,建立深圳“12 ·20”滑坡二维物质点法数值模型,再现了该滑坡失稳、运动和冲击过程。采用K均值聚类算法结合物质点的相对位移识别滑裂面,对滑坡运动过程中特征物质点速度变化进行分析,并参考泥石流冲击压力计算方法对滑坡运动物质的冲击压力和冲击荷载进行了初步计算。结果表明,物质点法模拟分析获得的深圳滑坡滑裂面形态、失稳和运动特征、冲击强度和堆积形态等与实际观察结果吻合较好,是再现滑坡稳定—失稳—运动—冲击—停积全生命周期的可靠数值模拟方法。     

波流共存场中多向随机波浪传播变形数学模型

基于波作用量守恒方程建立了波流共存场中多向随机波浪传播变形数学模型,模型中考虑了波浪绕射的影响和水流引起的波浪弥散多普勒效应,应用包含水流和地形影响的激破波模式计算波浪破碎的能量耗散,采用一阶上迎风有限差分格式离散控制方程。分别计算了有无近岸流情况下单向和多向随机波浪的波高分布,考虑水流影响的数值计算结果与物理模型实验数据吻合良好,比较分析表明,所建立的数学模型能够复演由于离岸流引起的波高增大,可用于波流共存场多向随机波浪传播变形的模拟和预报。     

非线性波浪荷载作用下海上风机管桩基础周围海床液化研究

为研究近浅海领域内海上风机大直径单桩基础周围的砂质海床在非线性荷载作用下的瞬时液化的稳定性,在OpenFOAM平台上建立波浪-单桩-海床三维数值模型(WSSI模型),采用olaFoam求解器求解RANS方程模拟波浪的非线性运动,将Biot方程作为海床模型的控制方程研究单桩周围海床的液化规律。对以往的数值解析结果和实验结果进行对比分析,验证本文建立三维波浪模型和海床模型的准确性和有效性。将建立的波浪-管桩-海床相互作用三维数值模型应用到实际工况中,对数值模型在实际工程中的海床响应进行分析评估。研究结果表明,单桩周围海床的孔隙水压力场和有效应力场在水深方向发生较大变化,在水平方向变化较小。在该工况下海床的最大液化深度可达到10 m,且在垂直于波浪运动方向的海床更容易发生液化,为实际工程预测海床液化提供一定的技术支持。     

基于FLUENT的二维滑坡涌浪数值模拟

本文从N-S方程出发,建立了二维滑坡涌浪控制方程,使用二维非定常分离隐式PISO算法求解方程。通过UDF(User-Defined Function)编程,采用动网格技术控制滑体的运动,结合RNGk-ε湍流模型并采用VOF方法跟踪非线性自由表面流场,基于流体计算软件FLUENT模拟滑体下滑所引起的水的速度、自由表面高度变化以及流动过程,并将数值计算结果与Monaghan和Kos的试验数据进行比较。算例表明:本模型能很好地模拟出滑体下滑过程中孤立波的产生和传播以及涡流的形成。在此基础上,本文还研究了滑体速度对水体自由表面变形的影响。     

应用二阶完全非线性Boussinesq方程模拟破碎波浪

建立了基于高阶Boussinesq水波方程的一维波浪破碎数值模型。基于一组具有二阶完全非线性特征的Boussinesq水波方程,建立了交错网格下的高精度差分格式,推导了适用于该组方程的永形波解析解,其和松弛造波技术相结合实现了数值波浪水槽中(强)非线性波浪的无反射入射。通过模拟封闭容器内水体晃动问题对数值格式进行了验证,通过模拟孤立波在斜坡海岸上的浅化过程说明了将方程从弱非线性发展到完全非线性的必要性。采用涡粘方法处理波浪破碎,利用物理模型实验数据,分析了模型中各波浪破碎参数对数值结果的影响并对参数进行了率定。应用该模型对规则波在斜坡海岸上的传播、变浅以及破碎过程进行了数值模拟研究,数值结果同实验数据吻合良好,验证了模型的有效性。     

径向点插值法在波浪传播数值模拟中的应用

针对波浪数值模拟中基于矩形网格的数值方法在深水到浅水的网格间距选择与复杂边界处理上的缺陷,以及基于正交曲线网格和无结构网格的数值方法前处理工作复杂的问题,引入最近在计算力学中发展起来的无网格法——径向点插值法,对经典的双曲型缓坡方程进行空间离散,并在时间上采用四阶Adams-Bashforth-Moulton格式求解建立近岸波浪传播数学模型,通过椭圆形浅滩地形和环形河道的波浪传播计算验证,表明该无网格方法可较为有效地模拟近岸波浪的传播变形,且在处理复杂边界时具有较高的精度.     

土质滑坡运动全过程物质点法模拟及其应用

物质点法（MPM）属于一种无网格数值计算方法,它可导入各种土体本构模型,考虑土体流固耦合行为,能够有效模拟土质滑坡大变形及超大变形。本文介绍了物质点法基本原理、控制方程与求解格式;基于5种物质点法的多孔介质表征模型,简要回顾了土质滑坡运动全过程物质点法模拟的最新研究进展。采用单套单相物质点模型,对深圳“12·20”人工堆填土滑坡全过程进行了物质点法模拟,使用了线性加载方式确定初始应力场,并使用了Drucker-Prager屈服准则弹塑性本构模型、GIMP算法与MUSL求解格式。模拟结果表明,该边坡发生失稳后,最大滑距达510m,滑坡范围纵向间距为1050m,最小滑坡角5.95°,均与观测结果相吻合。土体内部等效塑性应变区的演化趋势显示,滑坡机制为渐进式破坏,具体表现为:坡趾土体首先沿基岩界面发生剪切破坏,随后坡顶出现拉张裂隙,坡趾与坡顶塑性区分别沿基岩界面向坡体内部发育,形成贯通滑动面后滑动加速,超大变形出现。物质点法模拟滑坡运动全过程有助于理解滑坡致灾行为,可为滑坡防治提供参考。     

A non-hydrostatic model for the numerical study of landslide-generated waves

This paper proposes and demonstrates a two-layer depth-averaged model with non-hydrostatic pressure correction to simulate landslide-generated waves. Landslide (lower layer) and water (upper layer) motions are governed by the general shallow water equations derived from mass and momentum conservation laws. The landslide motion and wave generation/propagation are separately formulated, but they form a coupled system. Our model combines some features of the landslide analysis model DAN3D and the tsunami analysis model COMCOT and adds a non-hydrostatic pressure correction. We use the new model to simulate a 2007 rock avalanche-generated wave event at Chehalis Lake, British Columbia, Canada. The model results match both the observed distribution of the rock avalanche deposit in the lake and the wave run-up trimline along the shoreline. Sensitivity analyses demonstrate the importance of accounting for the non-hydrostatic dynamic pressure at the landslide-water interface, as well as the influence of the internal strength of the landslide on the size of the generated waves. Finally, we compare the numerical results of landslide-generated waves simulated with frictional and Voellmy rheologies. Similar maximum wave run-ups can be obtained using the two different rheologies, but the frictional model better reproduces the known limit of the rock avalanche deposit and is thus considered to yield the best overall results in this particular case.     

A rigorous finite volume model to simulate subaerial and submarine landslide-generated waves

This paper presents a new landslide-generated wave (LGW) model based on incompressible Euler equations with Savage-Hutter assumptions. A two-layer model is developed including a layer of granular-type flow beneath a layer of an inviscid fluid. Landslide is modeled as a two-phase Coulomb mixture. A well-balanced second-order finite volume formulation is applied to solve the model equations. Wet/dry transitions are treated properly using a modified non-linear method. The numerical model is validated using two sets of experimental data on subaerial and submarine LGWs. Impulsive wave characteristics and landslide deformations are estimated with a computational error less than 5 %. Then, the model is applied to investigate the effects of landslide deformations on water surface fluctuations in comparison with a simpler model considering a rigid landslide. The model results confirm the importance of both rheological behavior and two-phase nature of landslide in proper estimation of generated wave properties and formation patterns. Rigid slide modeling often overestimates the characteristics of induced waves. With a proper rheological model for landslide, the numerical prediction of LGWs gets more than 30 % closer to experimental measurements. Single-phase landslide results in relative errors up to about 30 % for maximum positive and about 70 % for maximum negative wave amplitudes. Two-phase constitutive structure of landslide has also strong effects on landslide deformations, velocities, elongations, and traveling distances. The complex behaviors of landslide and LGW of the experimental data are analyzed and described with the aid of the robust and accurate finite volume model. This can provide benchmark data for testing other numerical methods and models.     

Finite element simulation of impulse wave generated by landslides using a three-phase model and the conservative level set method

A numerical model has been developed using the finite element method for the simulation of impulse waves generated by landslides. The fluid-like landslide is modeled as a generalized non-Newtonian visco-plastic fluid. A three-phase flow model based on the incompressible viscous Navier–Stokes equations is solved using the finite element method to describe the motion of the three types of fluid in landslide. The conservative level set method is expanded to n-phase flow cases and employed to capture the interface of the three phases: air, water, and the landslide. The overall performance of the approach is checked by a number of validation cases: a Rayleigh–Taylor instability problem to illustrate the capability of the proposed method to deal with interface capturing, a benchmark test of a subaerial landslide generated by an impulse wave is carried out and compared with the published experimental data and numerical results, and finally, the 1958 Lituya Bay landslide generated impulse wave, and its results are compared against a scaled-down experiment and other published numerical results. It can be noted that the current model has an excellent ability to capture the complex phenomena that occurs during the whole process of the landslide-generated impulse wave, and considering the simplified treatment of the landslide and the numerical model, fairly good agreement between computed and experimental results has been observed for all simulation cases.     

Numerical simulation of wave generated by landslide incidents in dam reservoirs

In this work, a two-dimensional fourth-order Boussinesq-type numerical model is applied to estimate the impact of landslide-generated waves in dam reservoirs. This numerical model has recently been extended for simulating subaerial landslides. The extended model is validated using available three-dimensional experimental data, and a good agreement is obtained. The numerical model is then employed to investigate the impact of landslide-generated waves in two real cases, the Maku and Shafa-Roud dam reservoirs in the northwestern and the north of Iran, respectively. Generated wave heights, wave run-up, maximum wave height above dam crest, and dam overtopping volume have been estimated for each case. The amplitude of generated waves about 18 and 31 m and the volume of dam overtopping up to 80,000 m³ emphasize the importance of the estimation of the landslide-generated waves in dam sites.     

Risk management study on impulse waves generated by Hongyanzi landslide in Three Gorges Reservoir of China on June 24, 2015

On June 24, 2015, Hongyanzi slope located in Wushan County of the Three Gorges Reservoir collapsed, generating 5–6-m-high impulse waves, which overturned 13 boats, killed 2 persons, and injured 4 persons. It is the second incident of landslide-generated impulse waves since the 175-m experimental impoundment in 2008. The emergency investigation shows that Hongyanzi landslide is a bedding soil landslide with a volume of 23?×?10⁴ m³ induced by a series of triggering factors such as rainfall, flooding upstream, and reservoir drawdown. The nonlinear Boussinesq water wave model is used to reproduce the impulse waves generated by the landslide of June 24th. The numerical simulation results suggest that the wave propagation process was influenced by the T-shaped geomorphic conditions of river valley, and the coastal areas in the county seat were the major wave-affected areas, which is opposite to the landslide. The numerical wave process accord well with the observed incident, and the investigation values were in good agreement with the calculated values. Moreover, the worst-case scenario of the 7?×?10⁴ m³ deformation mass beside Hongyanzi landslide is potential to generate impulse waves, which was predicted with the same numerical model. This adjacent deformation mass will probably generate impulse waves with maximum height and run-up of 2.2 and 2.0 m, respectively, and only a very few areas in the water course had waves rising to a height of 1 m or above. The research results provide a technical basis for emergency disposal to Hongyanzi landslide and navigation restriction in Wushan waterway. More importantly, it pushes the risk management of the navigation based on the impulse wave generated by landslide. It is advised that the Three Gorges Reservoir and other reservoirs around the world should put more efforts in performing special surveys and studies on the potential hazards associated with landslide-generated impulse waves.     

Godunov格式下高精度二维水流-输运耦合模型

针对复杂流体运动中物质输运方程的数值求解面临地形复杂、数值阻尼过大以及数值振荡等难题,建立了Godunov格式下求解二维水流-输运方程的高精度耦合数学模型,提出了集成输运对流项的HLLC (Harten-Lax-van Leer-Contact)型近似黎曼算子,可同时计算水流通量及输运通量,不仅有效模拟了复杂地形上水流运动,而且解决了输运方程中对流项产生的数值阻尼过大和不稳定振荡等难题。采用水深-水位加权重构技术和Minmod限制器,提高了模型处理复杂混合流态的能力,同时结合Hancock预测-校正方法,使模型具有时空二阶精度。算例结果表明,模型精度高、稳定性好,能有效抑制数值阻尼,适合模拟实际复杂流体运动中物质的输运过程,具有较好的推广应用价值。     

波生沿岸流数值模拟

为了更好地研究近岸海域波生沿岸流,建立了基于高阶Boussinesq水波方程的波生沿岸流时域数值模型。控制方程在中等水深范围内具有较好的色散性和变浅作用性能,同时具有二阶完全非线性特征,适合描述近岸区域波浪强非线性运动。通过采用松弛造波方法实现了非线性波浪的无反射入射,采用周期性侧边界条件模拟开敞边界。通过数值试验,讨论了模型中主要参数对数值结果的影响。利用率定后的参数模拟了均匀坡度海岸上产生的沿岸流,通过和实验数据的对比验证了模型的准确性和适用性。利用模型数值模拟了不同波浪入射条件(包括周期、波高和波浪入射角度)对波生沿岸流的影响。