Numerical investigation of hydro-morphodynamic characteristics of a cascading failure of landslide dams

A cascading failure of landslide dams caused by strong earthquakes or torrential rains in mountainous river valleys can pose great threats to people’s lives,properties,and infrastructures.In this study,based on the three-dimensional Reynoldsaveraged Navier-Stokes equations(RANS),the renormalization group(RNG)k-εturbulence model,suspended and bed load transport equations,and the instability discriminant formula of dam breach side slope,and the explicit finite volume method(FVM),a detailed numerical simulation model for calculating the hydro-morphodynamic characteristics of cascading dam breach process has been developed.The developed numerical model can simulate the breach hydrograph and the dam breach morphology evolution during the cascading failure process of landslide dams.A model test of the breaches of two cascading landslide dams has been used as the validation case.The comparison of the calculated and measured results indicates that the breach hydrograph and the breach morphology evolution process of the upstream and downstream dams are generally consistent with each other,and the relative errors of the key breaching parameters,i.e.,the peak breach flow and the time to peak of each dam,are less than±5%.Further,the comparison of the breach hydrographs of the upstream and downstream dams shows that there is an amplification effect of the breach flood on the cascading landslide dam failures.Three key parameters,i.e.,the distance between the upstream and the downstream dams,the river channel slope,and the downstream dam height,have been used to study the flood amplification effect.The parameter sensitivity analyses show that the peak breach flow at the downstream dam decreases with increasing distance between the upstream and the downstream dams,and the downstream dam height.Further,the peak breach flow at the downstream dam first increases and then decreases with steepening of the river channel slope.When the flood caused by the upstream dam failure flows to the downstream dam,it can produce a surge wave that overtops and erodes the dam crest,resulting in a lowering of the dam crest elevation.This has an impact on the failure occurrence time and the peak breach flow of the downstream dam.The influence of the surge wave on the downstream dam failure process is related to the volume of water that overtops the dam crest and the erosion characteristics of dam material.Moreover,the cascading failure case of the Xiaogangjian and Lower Xiaogangjian landslide dams has also been used as the representative case for validating the model.In comparisons of the calculated and measured breach hydrographs and final breach morphologies,the relative errors of the key dam breaching parameters are all within±10%,which verify the rationality of the model is applicable to real-world cases.Overall,the numerical model developed in this study can provide important technical support for the risk assessment and emergency treatment of failures of cascading landslide dams.

Effect of geometrical parameters on forming quality of high-strength TA18 titanium alloy tube in numerical control bending

The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clarified by finite element simulation. The results show that the distribution of wall thickness change ratio Δt and cross section deformation ratio ΔD are very similar under different β; the Δt and ΔD decrease with the increase of R/D, and to obtain the qualified bent tube, the R/D must be greater than 2.0; the wall thinning ratio Δto slightly increases with larger D and t, while the wall thickening ratio Δti and ΔD increase with the larger D and smaller t; the Δto and ΔD firstly decrease and then increase, while the Δti increases, for the same D/t with the increase of D and t.

Mesoscopic-Scale Numerical Investigation Including the Influence of Process Parameters on LPBF Multi-Layer Multi-Path Formation

As a typical laser additive manufacturing technology,laser powder bed fusion(LPBF)has achieved demonstration applications in aerospace,biomedical and other fields.However,how to select process parameters quickly and reasonably is still themain concern of LPBF production.In order to quantitatively analyze the influence of different process parameters(laser power,scanning speed,hatch space and layer thickness)on the LPBF process,the multilayer and multi-path forming process of LPBF was predicted based on the open-source discrete element method framework Yade and the open-source finite volume method framework OpenFOAM.Based on the design of experiments method,a four-factor three-level orthogonal test scheme was designed,and the porosity and surface roughness data of each calculation scheme were extracted.By analyzing the orthogonal test data,it was found that as the laser power increased,the porosity decreased,and as the scanning speed,hatch space,and layer thickness increased,the porosity increased.In addition,the influence of laser power and scanning speed on surface roughness showed a trend of decreasing first and then increasing,while the influence of scanning distance and layer thickness on surface roughness showed amonotonous increasing trend.The order of the influence of each process parameter on porosity was:scanning speed>laying thickness>laser power>hatch space,and the order of the influence of each process parameter on surface roughness was:hatch space>layer thickness>laser power>scanning speed.So the porosity of the part is most sensitive to scanning speed,and the surface roughness is the most sensitive to hatch space.The above conclusions are expected to provide process control basis for actual LPBF production of the 316L stainless steel alloy.

Numerical calculation of JWL EOS parameters for explosives

JWL equation of state（EOS） parameter for most energetic materials is blank,that makes it impossible for the numerical simulation of the explosive dynamic response and damage effects.In this paper,the numerical calculation of JWL EOS parameters for the gaseous,liquid and condensed source of the explosion was performed,the numerical simulation for the bottleneck problem of the dynamic response and damage effects for the aluminized explosives and some other non-ideal explosion source was solved,the visualization software for the detonation parameters and numerical parameters of JWL equation was developed.The results were relatively consistent with the experimental data.

NUMERICAL SIMULATION FOR DYNAMIC INITIAL SHOCK PARAMETERS OF COUPLING CHARGE ON BOREHOLE WALL UNDER THE ACTION OF HIGH EXPLOSIVES

According to detonation theory and hydrodynamic principle, a physical model has been set up in this paper. Based on the model a methodology for calculating dynamic initial shock parameters such as shock pressure pm shock wave velosity Dm etc. of coupling charge on borehole wall has ben developed. The shock parameters have been calculated when high explosives works on granite, limestone and marble respectively. The magnitude of every parameter on borehole wall has been obtained from ignited dot to the end of borehole along axial direction. Some important conclusions are also gained.

Numerical Investigation of the Effect of Process and Sheet Parameters on Bending Angle in the Laser Bending Process

In this work, the effects of process parameters such as laser output power, beam diameter and scan speed and also sheet thickness on the bending angle have been numerically investigated in the laser bending process. For this purpose, Abaqus software is used for investigating the effect of various process and sheet parameters on the bending angle. The results show that with increasing the laser output power, bending angle is increased. Also, the bending angle is decreased with increasing the beam diameter, scan speed and sheet thickness.

Optimization of anchorage support parameters for soft rock tunnel based on displacement control theory

In the construction of a soft rock tunnel,it is critical to accurately estimate the pre-stressed anchor support parameters for surrounding rock reinforcement;otherwise,engineering disasters may occur.This paper presents a support parameter selection method that aims to allow deformation as a control objective,which was applied to the tunnel located in Muzailing Highway,Min County,Dingxi City,Gansu Province,China.Through theoretical analysis,we have identified five factors that influence pre-stressing anchorages.The selection of mechanical parameters for the rock mass was carried out using an inverse analysis method.Compared with the measured data,the maximum displacement error of the numerical simulation results was only 0.07 m.The length of anchor cable,circumferential spacing of anchor cable,longitudinal spacing,and pre-stress index are adopted as the input parameters for the support vector machine neural network model based on particle swarm optimization(PSO-LSSVM).Besides,the vault subsidence and the maximum deformation of surrounding rock are considered as output values(performance indices).The goodness of fit between the predicted values and the simulated values exceeds 0.9.Finally,all support parameters within the acceptable deformation range are calculated.The optimal support variables are derived by considering the construction cost and duration.The field application results show that it is feasible to construct the sample database utilizing the numerical simulation approach by taking the displacement as the control target and using the neural network to specify the appropriate support parameters.

Numerical Study on Hydraulic Characteristics and Discharge Capacity of Modified Piano Key Weir with Various Inlet/Outlet Width Ratio

A modified piano key weir with a rounded nose and a parapet wall (MPKW) can improve the discharge capacity significantly compared to a standard piano key weir. However, the optimum of the inlet/outlet width ratio (Wi/Wo) on the discharge efficiency of MPKW is still not investigated numerically. The present work utilized the numerical modeling to investigate and analyze the effects of the inlet/outlet key width ratios on the hydraulic characteristics and discharge capacity of the MPKW. To validate the numerical model with the experimental data, the results indicate that the average relative error is 2.96%, which confirms that the numerical model is fairly well to predictthe specifications of flow over on the MPKW. Numerical simulation results indicated that the discharge capacity of the MPKW can be improved up to 8.5% by optimizing the Wi/Wo ratio ranging from 1.53 to 1.67 even if the other parameters of the MPKW keep unchanged. A big Wi/Wo ratio generally leads to an increase in discharge capacity at low heads and a little effect on the discharge efficiency at high heads. The discharge efficiency of the inlet and outlet crests increases up to 9.6% for high heads, while discharge efficiency of the lateral crest decreases up to 23.5% compared with the reference model. The findings of the study revealed that the intrinsic influencing mechanism of the Wi/Wo ratio on the discharge performance of MPKWs.

考虑锚杆预应力作用下隧道围岩力学分析及参数设计

隧道工程中锚杆设计多依靠经验法和类比法,为研究预应力锚杆支护体系下围岩的力学效应,建立预应力锚杆与围岩力学耦合模型,考虑围岩开挖损伤效应,通过弹塑性力学理论推导出隧道开挖后围岩应力分布及径向位移解析表达式,采用有限差分软件FLAC3D进行算例验证并分析预应力锚杆参数对围岩状态的影响。研究结果表明:理论解析和数值模拟中最大切向应力和围岩塑性区半径分别为4.77 MPa、15 m和4.49 MPa、15.86 m,理论解析与数值模拟所计算隧道围岩应力分布、位移基本一致,在Ⅳ、Ⅴ级围岩地层中验证了理论解析解的合理性;随着预紧力增大,处于塑性区的围岩径向位移及塑性区半径逐渐减小,弹性区基本不受影响;当锚杆自由段长度位于塑性区时,随着锚杆长度增加,围岩塑性区径向位移及塑性区半径逐渐减小。在实际工程中应尽量增大锚杆预紧力,锚杆长度增加对围岩位移以及塑性区的发展控制效果有限,应控制锚杆自由段长度在塑性区内。

Simulation Research on the Effect of Spreading Process Parameters on the Quality of Lunar Regolith Powder Bed in Additive Manufacturing

Lunar surface additive manufacturing with lunar regolith is a key step in in-situ resource utilization.The powder spreading process is the key process,which has a major impact on the quality of the powder bed and the precision of molded parts.In this study,the discrete element method(DEM)was adopted to simulate the powder spreading process with a roller.The three powder bed quality indicators,including the molding layer offset,voidage fraction,and surface roughness,were established.Besides,the influence of the three process parameters,which are roller’s translational speed,rotational speed,and powder spreading layer thickness on the powder bed quality indicators was also analyzed.The results show that with the reduction of the powder spreading layer thickness and the increase of the rotational speed,the offset increased significantly;when the translational speed increased,the offset first increased and then decreased,which resulted in an extreme value;with the increase of the layer thickness and the decrease of the translational speed,the values for voidage fraction and surface roughness significantly reduced.The powder bed quality indicators were adopted as the optimization objective,and the multi-objective parameter optimization was carried out.The predicted optimal powder spreading parameters and powder bed quality indicators were then obtained.Moreover,the optimal values were then verified.This study can provide informative guidance for in-situ manufacturing at the moon in future deep space exploration missions.

四川盆地涪陵南地区奥陶系五峰组—志留系龙马溪组页岩古构造应力场及裂缝特征

通过岩石力学实验、声发射实验和地震资料综合解释,利用有限元数值模拟方法,对涪陵南地区奥陶系五峰组—志留系龙马溪组海相页岩古构造应力场进行了数值模拟,并结合岩心实测结果,预测了构造裂缝的发育特征。研究结果表明:①涪陵南地区裂缝主要形成期(燕山晚期)构造应力和裂缝的分布受断层、岩石力学性质和构造应力的影响,断层广泛发育的区域容易出现应力集中,并引起较大的应力梯度。②利用库伦-莫尔破裂准则预测了研究区构造裂缝的发育,同时引入剪切破裂指数R定量表征裂缝发育的强度,其值越大反映裂缝发育程度越高。窄陡断背斜和断层附近裂缝发育,以高角度剪切裂缝为主,而在宽缓向斜部位裂缝发育程度最弱,研究区五峰组—龙马溪组底部硅质页岩应力集中,裂缝最发育。③涪陵南地区海相页岩气保存有利区主要为3个区带:远离大断层的凤来向斜内部,主要构造变形期未遭受大的破坏作用,其位于应力低值区,具有良好的保存条件,为Ⅰ类有利区;白马向斜内部小断层发育,应力值位于中等水平,保存条件中等,为Ⅱ类较有利区;石门—金坪断背斜遭受到强烈改造作用,容易产生大规模剪切裂缝,破坏了保存条件,为Ⅲ类不利区。

不同建筑环境下平均风速剖面的数值模拟

基于计算流体力学(CFD)方法对具有不同建筑环境参数的城市上空的风场进行系统性的数值模拟,并对平均风速剖面指数的变化规律进行讨论。研究结果表明,建筑平均高度对平均风速剖面指数的影响较大,建筑密度对平均风速剖面指数的影响较小。文中还给出了以建筑平均高度和建筑密度为自变量的平均风速剖面指数经验公式。

珠江口盆地潜山储层地质力学及压裂参数优化研究

珠江口盆地珠一坳陷惠州27-1井区作为潜山油气储层,压裂层段厚度大、层数多、非均质性强、压裂改造难度大,对于人工裂缝的在潜山储层中的拓展延伸规律认识困难。针对此问题,首先建立动态参数测井解释模型,并与静态岩石力学数据协同校正,建立一维岩石力学剖面;结合深部成岩理论,建立三维地质力学模型,真实模拟研究区块成岩环境;最后基于三维地质力学模型,研究排量、液量、砂比、前置液占比、射孔层位厚度等参数对裂缝纵向和平面延伸规律的影响,优化压裂设计。结果表明:惠州27-1区块,杨氏模量平均值为45.47 GPa,最大水平主应力平均值为100.91 MPa,最小水平主应力平均值为80.98 MPa,泊松比平均值为0.30。排量6~7 m^(3)/min、液量600~700 m^(3)、砂比10%~15%、前置液比例50%~60%、射孔厚度8~11 m为最优施工参数,为现场施工提供指导意见。

高铁泥岩隧道围岩蠕变对仰拱底鼓的影响

研究目的:针对泥岩地区高铁隧道修建过程中出现的仰拱底鼓病害,本文采用参数反演与数值模拟相结合的方法,全面分析围岩蠕变对仰拱底鼓的影响,并采用锚杆支护与仰拱加强的工程措施对仰拱底鼓进行治理。研究结论:(1)Burgers模型能较好地符合泥岩表现出的明显的衰减蠕变和稳定蠕变特征;(2)随着时间的增加,围岩不断向洞内发生变形,且隧道拱顶沉降、水平收敛和拱底隆起一直在增大,并经历了三个阶段:瞬时变形阶段、衰减蠕变阶段与稳定蠕变阶段;(3)仰拱结构内力随着蠕变时间增加同样在增大,并在蠕变一定年限后,仰拱填充中心的拉应力将超过混凝土的抗拉强度,导致仰拱填充沿中心位置开裂;(4)锚杆支护的最优长度为5 m,最佳间距为0.9~1.2 m,在此基础上通过加强仰拱来进一步抑制仰拱底鼓变形,并且建议仰拱支护强度选用C30~C40;(5)本研究结果可为类似工程的建设与施工提供建议与参考。

C70600白铜空心锭立式连铸工艺参数对凝固过程的影响

为了获得Ф260×Ф80 C70600白铜空心锭立式连铸合理的工艺参数,通过数值模拟定量分析了各种工艺参数对温度场和应力场的影响。结果表明:浇铸温度每提高20℃,液穴深度增加10 mm;拉坯速度每提高10 mm/min,液穴深度增加20 mm;液穴深度随着石墨芯管冷却强度的增大而减小。基于正交试验和方差分析发现,F_(A)>F_(0.01)(3,3),F_(B)>F_(D)>F_(0.1)(3,3),F_(C)<F_(0.1)(3,3),因此,拉坯速度对液穴深度的影响最显著,一冷强度对其影响不显著。根据模拟结果提出了合理工艺参数为:一冷强度24 m^(3)/h、拉坯速度80 mm/min、浇铸温度1280℃、芯管采用空冷。在此基础上成功试制出了合格的C70600白铜空心锭成品。

附壁旋流风幕集尘系统数值模拟与试验研究

大型设备工作时产生的粉尘浓度过高、粉尘扩散等问题,会影响工作人员的身体健康,甚至可能造成“粉尘爆炸”等安全问题。基于此现状提出了一种新型风幕集尘系统并介绍了其构造及应用。为了使系统的集尘效果更好,采用计算流体力学FLUENT软件进行数值模拟分析并对风幕集尘系统的工作参数进行了试验研究,得到最佳的设备工作参数及风幕的集尘效率。结果表明:(1)附壁旋流集尘风幕系统可形成稳定的螺旋风流场,大部分粉尘可以控制在风幕内侧,达到良好的集尘效果;(2)附壁旋流风幕集尘系统的射流腔条缝口的喷射角度对风幕形成效果影响最明显,风幕闭合性会随着射流腔工作角度变化而变化;(3)当射流腔条缝口角度为45°、风幕入口速度为15~25 m/s时,风幕的闭合性最好;(4)风幕的入口速度过大或过小都会使风幕的集尘效果下降;(5)吸尘盘的负压区域与风幕交界处会产生微弱湍流,但对风幕整体闭合性影响较小;(6)模拟与试验结果吻合,验证了新型附壁旋流集尘风幕技术的有效性。

三锚式浮标综合观测平台不同系泊参数的响应分析

文中基于建立的三锚式浮标数值计算模型进行频域分析,通过改变投锚距离、三锚式浮标特有的两类锚链长度,计算主浮标在不同风浪流作用下的运动响应以及锚链张力.结果表明:投锚距离对锚链张力有显著影响,但对纵荡、横荡以及垂荡影响不大;增加链接锚链和固定锚链长度,会显著增加横荡、纵荡和垂荡的响应幅值,并显著减小系泊系统的张力;随着入射方向从0°增加到60°,链接锚链张力略微增大,固定锚链张力略微减小;最后根据不同的工程需求给出了三锚式浮标的布放建议,确保其安全和服役寿命.

立式双曲面网板水动力性能优化研究

为研究结构型式及尺寸对立式双曲面网板水动力性能的影响机理,基于计算流体力学方法,建立立式双曲面网板三维数值模型,计算分析其水动力性能,并通过设计制作缩比模型开展动水槽试验,验证数值结果的有效性。开展曲面板弯曲度、弯曲度位置、支撑板间距等不同结构参数对立式双曲面网板水动力性能的影响规律研究,以探究最优化的结构设计方案。研究结果表明:曲面板弯曲度的同步改变和单一改变均会对立式双曲面网板的水动力性能产生不同程度的影响。如果只考虑扩张效果,曲面板A、B的弯曲度均设置为20%左右,或曲面板A弯曲度设置为15%、曲面板B弯曲度设置为25%左右,均可在一定范围内将立式双曲面网板的最大升力系数提高到最大值;但从网板综合性能考虑,后一方案可获得更高的最大升阻比。当曲面板弯曲度位置同步设置为50%时,网板升力系数可达到最大值,此时扩张效果最佳,而当曲面板弯曲度位置同步设置为20%时,最大升阻比达到峰值,网板综合性能相对更好。支撑板间距对立式双曲面网板水动力性能的影响不明显,将支撑板间距设置为420 mm左右,可在小冲角范围内提升其最大升阻比。

基于数值的鲫鱼游泳能力影响参数分析

鱼类游泳行为机理及游泳能力的影响因素是目前鱼类仿生学研究的热点问题。本文选取鲹科游动模式(carangiform)的典型—鲫鱼(crucian carp)作为研究对象,采用数值模拟的方法,利用动网格技术结合用户自定义函数(UDF),围绕运动参数、鱼体体型及游泳环境(壁面边界),以仿生鲫鱼到达动态稳定的巡游速度这一过程衡量鲫鱼游泳能力,对鲫鱼游泳能力的影响开展研究。结果表明:当摆动频率在0.07~5.50 Hz之间,摆幅系数在0.03~0.06之间,随着鱼体摆动频率和摆动幅度的增大,仿生鲫鱼获得动态稳定巡游速度的时间逐渐缩短,且巡航游速相应增加。将不同厚长比、体长的鲫鱼经过量化处理后进行数值计算,研究结果表明:以相同的摆幅和摆频向前游动,厚长比与游泳速度呈负相关,当厚长比小于0.166,仿生鲫鱼可获得更快的游泳速度;体长方面,将仿生鱼的体长设置为L,仿生稚鱼可更快速地到达巡游阶段,但到达动态稳定的巡航游速较低,约为0.6L s^(–1),仿生幼鱼在加速阶段速度较快,巡游阶段与仿生成鱼的动态稳定巡航游速基本一致,约为1L s^(–1);鱼体在壁面附近游动所产生的壁面效应会导致游泳速度降低,且双侧壁面对仿生鲫鱼游泳速度的影响较单侧壁面更为显著,当鱼体距单侧壁面0.5L,距双侧壁面0.8L时将不受壁面的影响。本文的研究结果可为鱼类仿生学研究提供有益参考。

矿井瓦斯抽采参数调控实验教学系统研制

为了满足工程流体专业相关课程的教学需求,自主研发了煤矿井下瓦斯抽采参数调控实验教学系统,可实现不同管道阻力、漏气程度、抽采负压等条件下瓦斯-空气流动规律的实验模拟。该系统由井下煤层抽采环境和瓦斯压力状态子系统,井下瓦斯抽采管网、阀门、动力结构子系统,气体体积流量、瓦斯体积分数、气体压力等气体参数采集子系统以及参数上传和数据分析处理子系统四部分组成;利用单片机控制各个阀门的开度、泵的转速,实时监测各个区域流经的气体体积流量、瓦斯体积分数、气体压力等数据。该系统可以开展工程流体专业相关课程的教学实验,培养学生对专业的认识,提升学生的动手能力。