Effect of wall friction on oscillation of velocity at the head of the gravity current

Velocity oscillations at the head of the gravity current were investigated in experiments and numerical simulations of a locked-exchange flow.A comparison of the experimental and numerical simulations showed that the depth and volume of the released fluid affected the oscillations in the velocity of the gravity current.At the initial stage,the head moved forward at a constant velocity,and velocity oscillations occurred.The head maximum thickness increased at the same time as the head,which did not have a round,and accumulated buoyant fluid due to the buoyancy effect intrusion force.The period of accumulation and release of the buoyant fluid was almost the same as that observed for the head movement velocity;the head movement velocity was faster when the buoyant fluid accumulated and slower when it was released.At the viscous stage,the forward velocity decreased proportionally to the power of 1/2 of time,since the head was not disturbed from behind.As the mass concentration at the head decreased,the gravity current was slowed by the viscous stage in its effect.At the viscous stage,the mass concentration at the head was no longer present,and the velocity oscillations also decreased.

Numerical analysis of effect of friction between diaphragm wall and soil on braced excavation

A plane strain finite element model was established to investigate the effect of friction between diaphragm wall and soil on braced excavation. The behavior of interface between diaphragm wall and soil was simulated with the interface model of ABAQUS. Parametric studies were conducted with different diaphragm wall external friction angles δ. The results show that deflection of diaphragm wall and ground surface settlement decrease with the decrease of δ. However, the reduction effect on diaphragm wall deflection is the most significant at the depth where the maximum wall deflection occurs and can be neglected at the wall base. The ratio between wall deep inward component and wall cantilever component reaches its peak value 2.7 when δ=5°. The ratio of the maximum ground surface settlement to the maximum wall lateral deflection decreases at a reduced rate with the increase of δ. For excavation with braced diaphragm wall, the effect of friction between diaphragm and soil on the deflection of diaphragm wall and ground settlement, especially the distribution of ground surface settlement behind diaphragm, should be taken into account.

An Experimental and Analytical Study on Cross-Laminated Bamboo Rocking Walls with Friction Dampers

Cross-laminated bamboo(CLB)have a high strength to weight ratio and stable bidirectional mechanical properties.Inspired by the investigation on cross-laminated timber(CLT)rocking walls,CLB rocking walls with conventional friction dampers(CFDs)are studied in this paper.To investigate the mechanical properties of the CLB rocking wall,seven tests are conducted under a cyclic loading scheme,and different test parameters,including the existence of the CFDs,the moment ratio,and the loading times,are discussed.The test results show a bilinear behavior of the CLB rocking wall.The small residual displacements of the CLB rocking wall demonstrate an idealized self-centering capacity.The cumulative energy dissipation curves indicate that the energy dissipation capacity of the CLB rocking wall can be greatly improved with CFDs.The limit states of the CLB rocking wall under a lateral force are proposed based on the strains,stress,and damage level of the CLB material and posttensioned rebar.In addition,an analytical model of the CLB rocking wall is developed based on the proposed limit states of the CLB rocking wall to evaluate the hysteretic response of the CLB rocking wall,and the model is validated by the experimental data.The comparison results show the potential value of the analytical model for engineering design.

Study on the cutting plane friction law of sandstone

The friction characteristics of rock damage plane have important impact on the stability of block structure formed after the stratum is broken. The mechanics properties of rock damage plane are described by parameters such as roughness coefficient, wall compress strength and basic friction angle. These three coefficients for fine grain sandstone and medium granular sandstone and grit sandstone are test. The friction stress is researched at the condition of different normal compressive stress acting on the tension damage plane. The friction law of tension damage plane of sandstone abided by is summed up. This law will provide scientific basis for block structure stability judging in basic roof stratum and roof pressure intensity calculating.

Effect of frictions on cross section quality of thin-walled tube NC bending

The effect of frictions between dies and tube on the cross section quality of thin-walled tube numerical controlled(NC) bending was studied by numerical simulation method, combined with theoretical analysis and experiment. The results show that the frictions between mandrel, wiper, pressure die, bending die and tube have a significant and complicate effect on the section quality of thin-walled tube NC bending. To improve the section quality, frictions between mandrel, wiper and tube should be decreased, but the frictions between the pressure die, bending die and tube increase. The effect on the section distortion is more significant from mandrel, wiper, pressure die to bending die and the effect on the wall thinning more significant from mandrel, pressure die, wiper, to bending die. The effects of frictions between all dies and tube on wall thinning are smaller than their effects on section distortion. Mandrel and wiper should be lubricated well and drawing oil is used to lubricate them in actual production. The frictions between pressure die, bending die and tube should be increased and the dry friction is used between pressure die, bending die and tube in actual production.

Management of the late effects of disconnected pancreatic duct syndrome: A case report

BACKGROUND There have been few reports about the late effects of disconnected pancreatic duct syndrome(DPDS). Although few reports have described the recurrence interval of pancreatitis, it might be rare for recurrence to occur more than 5 years later.Herein, we describe a case of recurrence in an 81-year-old man after the treatment of walled-off necrosis(WON) with pancreatic transection 7 years ago.CASE SUMMARY An 81-year-old man visited our hospital with chief complaints of fever and abdominal pain 7 years after the onset of WON due to severe necrotic pancreatitis. His medical history included an abdominal aortic aneurysm(AAA),hypertension, dyslipidemia, and chronic kidney disease. Computed tomography(CT) scan showed that the pancreatic fluid collection(PFC) had spread to the aorta with inflammation surrounding it, and CT findings suggested that bleeding occurred from the vasodilation due to splenic vein occlusion. First, we attempted to perform transpapillary drainage because of venous dilation around the residual stomach and the PFC. However, pancreatic duct drainage failed because of complete main pancreatic duct disruption. Second, we performed endoscopic ultrasound-guided drainage. After transmural drainage, the inflammation improved and stenting for the AAA was performed successfully. The inflammation was resolved, and he has been free from infection for more than 2 years after the procedure.CONCLUSION This case highlights the importance of continued follow-up of patients for recurrence after the treatment of WON with pancreatic transection.

Influence of wall friction on granular column

Granular packings under gravity in frictional and frictionless silos were simulated and the influence of the wall friction on the normal force distribution was investigated. Although there is an obvious Janssen effect in frictional silos, only a slight influence on the geometry of packing was found. The law of normal force distribution is different for frictional and frictionless walls, which is related to the pressure profile. A modified formula with consideration of the pressure profile was well fitted to the simulation results.

Influence of Wall Effect on Comprehensive Controllability for Ducted Fan Aircraft

A novel coaxial ducted fan structure aircraft is proposed to enable the aircraft near vertical walls at high altitudes.The state space equation of the system can be obtained by correlation deduction and identification of the whole prototype model.Based on the duct test bench experiment and computational fluid dynamics(CFD)simulation analysis,the expressions between the different distances dWE from the rotor center of the prototype to the wall and the thrust,reaction torque,and tilting moment of the system under hovering conditions are obtained.The influence of the wall effect of the prototype is incorporated into the system model to analyze the relationship between distance dWE and the comprehensive controllability of the system.The results show that the system comprehensive controllability vector of other channels changes little with the decrease of the distance dWE,and only the controllability vector of the rolling channel increases significantly.At the same time,the tilting moment also increases significantly,which strengthens the tendency of the prototype to tilt towards the wall.

Effect of cylinder wall parameters on the final packing density of mono-disperse spheres subject to three-dimensional vibrations Author links open overlay panel

Achieving densely packed particles is desirable within the industries of ceramics,pharmaceuticals,defence and additive manufacturing.In this work,we use the discrete element method(DEM)to determine the effect of wall parameters on the final packing density of mono-disperse spheres subject to 4 varying three-dimensional vibration and fill conditions.We focus specifically on the impact of the container wall parameters on the particles'final packing density.Following on from the validation of the DEM simulation the particle-wall coefficient of restitution,the particle-wall coefficient of rolling friction and the particle-wall coefficient of sliding friction were varied individually and the effect on the final packing density analysed.For relatively low particle-particle friction glass beads,the effect of these wall properties had no discernible effect on the final packing density achieved.Following on from these findings the particle-wall properties were varied at the extreme values of particle-particle coefficient of rolling friction and particle-particle coefficient of sliding friction.For a particle-particle coefficient of sliding friction=1,increases in particle-wall coefficient of restitution resulted in a minor increase in the final packing density of particles though this was not statistically significant.For a particle-particle coefficient of sliding friction=1,increases in particle-wall coefficient of rolling friction resulted in a minor decrease in the final packing density of the particles though again not to a degree where the trend can,with complete certainty,be distinguished from the random error across the repeats.Finally,when the particle-particle coefficient of sliding friction=1,increases in particle-wall coefficient of sliding friction resulted in a significant decrease in the final packing density of particles.This decrease was attributed to the propagation of force chains throughout the packing.The significant decrease in final packing density with particle-wall coefficient of sliding friction highlights the need to choose appropriate vessel materials to optimise packing of particles with a high particle-particle coefficient sliding friction.Conversely,for particles with minimal particle-particle friction,the particle-wall friction coefficient has no effect on the final packing density of particles-a potentially valuable finding for certain industrial applications.All simulations were run using the open-source DEM package LIGGGHTS on the University of Birmingham's high-performance computer:BlueBEAR.All the code files used within this paper can be found on Github:https://github.com/Jack-Grogan/DEM-Vibropacking-Wall-Effects.

Scaling study of the combustion performance of gas gas rocket injectors

To obtain the key subelements that may influence the scaling of gas-as injector combustor performance, the combustion performance subelements in a liquid propellant rocket engine combustor are initially analysed based on the results of a previous study on the scaling of a gas gas combustion fiowfield. Analysis indicates that inner wall friction loss and heat-flux loss are two key issues in gaining the scaling criterion of the combustion performance. The similarity conditions of the inner wall friction loss and heat-flux loss in a gas-gas combustion chamber are obtained by theoretical analyses. Then the theoretical scaling criterion was obtained for the combustion performance, but it proved to be impractical. The criterion conditions, the wall friction and the heat flux are further analysed in detail to obtain the specific engineering scaling criterion of the combustion performance. The results indicate that when the inner fiowfields in the combustors are similar, the combustor wall shear stress will have similar distributions qualitatively and will be directly proportional to pc0.8dt-0.2 quantitatively. In addition, the combustion peformance will remain unchanged. Furthermore, multi-element injector chambers with different geometric sizes and at different pressures are numerically simulated and the wall shear stress and combustion efficiencies are solved and compared with each other. A multi- element injector chamber is designed and hot-fire tested at several chamber pressures and the combustion performances are measured in a total of nine hot-fire tests. The numerical and experimental results verified the similarities among combustor wall shear stress and combustion performances at different chamber pressures and geometries, with the criterion applied.

Enhanced heat transfer in a heat exchanger square-duct with discrete V-finned tape inserts

The article presents an experimental and numerical study on thermal performance enhancement in a constant heatfluxed square-duct inserted diagonally with 45° discrete V-finned tapes(DFT).The experiments were carried out by varying the airflow rate through the tested square duct with DFT inserts for Reynolds number from 4000 to 25000.The effect of the DFT with V-tip pointing upstream at various relative fin heights and pitches on heat transfer and pressure drop characteristics was experimentally investigated.Both the heat transfer and pressure drop were presented in terms of Nusselt number and friction factor respectively.Several V-finned tape characteristics were introduced such as fin- to duct-height ratio or blockage ratio(R_B=e/H = 0.075,0.1,0.15 and 0.2),fin pitch to duct height ratio(R_P= P/H=0.5,1.0,1.5 and 2.0) and fin attack angle,α = 45°.The experimental results reveal that the heat transfer and friction factor values with DFT inserts increase with the increment of R_B but the decrease of R_P.The inserted square-duct at R_B = 0.2 and R_P = 0.5 provides the highest heat transfer and friction factor while the one with R_B= 0.1 and R_P= 1.5 yields the highest thermal performance.Also,a numerical simulation was conducted to investigate the flow structure and heat transfer mechanism inside the tested duct with DFT inserts.

STUDY ON MECHANISM OF FIBRE DEPOSITION IN OE FRICTION SPINNING

This paper deals with the mechanism of fibre deposition in OE friction spinning.A fibremodel has been established to analize and evaluate fibre.straightness after deposition.Exper-iments have been done on the measurement of air flow speed at the entrance and exit of thefeed duct which is mounted in an experimental friction spinning unit.Conclusion has beendrawn:the weakness of friction spun yarn is mainly due to its poor fibre straigthness after dep-osition.

Management of“Wall to Wall Heart”in a Transient Neonatal Tricuspid Regurgitation

We present a case of a one-day-old newborn,without prenatal diagnosis,referred to our cardiologic intensive care unit in critical condition presenting sub-cyanosis and peripheral oxygen saturation of 80%.Echocardiography diagnosis was tricuspid valve dysplasia with severe regurgitation,functional pulmonary valve atresia with intact ventricular septum and reversal flow in the large patent ductus arteriosus(PDA).Chest X-ray showed severe cardiomegaly and wall to wall heart.Prostaglandin E1 infusion was started once after birth.After few days,clinical conditions progressively worsened because of right heart failure;a first pharmacological approach to close PDA failed and surgery ligation of PDA was necessary to restore anterograde pulmonary flow and heart size.

Numerical Simulation of Single Bubble Deformation in Straight Duct and 90°Bend Using Lattice Boltzmann Method

The paper aims to give a comprehensive investigation of the two dimensional deformation of a single bubble in a straight duct and a 90° bend under the zero gravity condition. For this, the two phase flow lattice Boltzmann equation (LBE) model is used. An averaging scheme of boundary condition implementation has been applied and validated. A generalized deformation benchmark has been introduced. By presenting and analyzing the shape of the bubbles moving through the channels, the effects of the all important nondimensional numbers on the bubble deformation are examined thoroughly. It is seen that by increasing the Weber number the rate of the deformation enhances. Besides, because of the velocity dissimilarity between the particles constructing the bubble, the initial coordinates and the diameter of the bubble play a great role in the future behavior of the bubble. The density ratio has a little effect on the shape of the bubble within the assumed range of the density ratio. Moreover, as the Reynolds number or the viscosity ratio is decreased, higher rate of deformation is exhibited. Finally it is found that there is an inverse proportionality between the amplitude and frequency of the bubble deformation.

IDRIZI Infill Wall System for Seismic Protection of Residential Buildings

It is widely acknowledged that masonry walls in RC （reinforced concrete） frame structures, although often omitted in the design process, contribute significantly on the seismic resistance of buildings. Their contribution toward seismic response improvement is proportional to their participation level on buildings. The more abundant they are on buildings, their lateral strength contribution gets more significant, especially for ＂frame systems＂ of both RC and steel structures. This paper presents an ＂innovative＂ solution which aims to provide a seismic protection to masonry walls and to improve the seismic performance of the entire building structure. These goals are achieved through use of so called ＂IDRIZI＂ seismic devices. These ＂box-like＂ devices are placed at characteristic locations between the masonry infill walls and the structural frame system of the building. They act as special link elements between the top of wall panels and the bottom of beams and/or slabs. The assemblage of a wall panel, IDRIZI seismic devices and other boundary structural elements forms an integral structural system that is shortly called ＂IDRIZI＂ wall system. In addition, as part of this paper is shown selected experimental investigations, which demonstrate that under ＂optimal design＂ of buildings integrated with IDRIZI wall system, up to 80% of earthquake energy input in the structure can be dissipated by the friction mechanism of the IDRIZI devices. This feature provides remarkable improvements on the seismic performance of residential buildings or any other type of building where masonry walls are abundantly present.

低温高雷诺数下摩擦阻力测量及多孔介质减阻研究

为研究低温高雷诺数条件下多孔介质湍流减阻规律及雷诺数效应,在0.3 m低温连续式风洞开展了壁面摩擦阻力测量及多孔介质减阻试验。分别在光滑平板和多孔介质区域下游布置低温脉动压力传感器和油流,对脉动压力功率谱及下游全局摩擦阻力进行测量。结果表明:摩擦阻力系数随雷诺数的增大而减小;多孔介质减阻率随雷诺数的增大(增大马赫数或降低来流总温),呈无固定规律下降趋势,且多孔介质的引入,使下游脉动压力的低频信号强度增加,高频信号强度减弱;在马赫数Ma=0.300、雷诺数Re=7.51×10^(6)、来流总温T_(0)=140 K这一典型工况下,多孔介质仍具有11.4%的减阻率,初步验证了在低温高雷诺数条件下使用多孔介质减阻控制策略的可行性。

基于离散元模拟的不同挡土墙位移模式下非极限主动土压力

针对刚性挡土墙主动位移过程中砂土非极限主动土压力问题,利用PFC 2D分别对挡土墙绕墙顶转动(RB)模式、绕墙顶转动(RT)模式和平动(T)模式下砂土主动破坏过程进行模拟分析。分析结果表明,不同位移模式下土体内摩擦角及墙土摩擦角调动规律存在差异。挡土墙主动位移过程中,RB模式下土体破坏从墙顶开始,向墙脚发展,土楔体内部只有靠近墙背侧区域出现主应力偏转现象,并且土楔体中内摩擦角调动值均能达到极限值。RT模式下,土体破坏沿着墙背和滑裂面从墙脚开始,向土体表面发展,墙后土楔体中上部区域主应力偏转角度较大,形成了大主应力拱,与此对应的是该区域内摩擦角调动值相对初始内摩擦角减小。T模式下,土体破坏分别沿着墙背从墙顶向墙脚发展以及沿着滑裂面从墙脚向土体表面发展,墙后土楔体内部会出现小主应力拱,且内摩擦角调动值从初始内摩擦角增加,但达不到极限值。

单室与四室井筒式地下连续墙竖向承载特性研究

以井筒式地下连续墙为研究对象,采用数值模拟的研究方法,应用弹性本构模型,考虑墙土界面的参数影响,对单室和四室井筒式地下连续墙基础的沉降特性、内外侧摩阻力、端阻力、土芯顶部反力及其荷载分担比进行分析和研究。研究表明:外摩阻力主要由墙身深度范围内的外侧下部土体提供,内摩阻力主要由土芯下部土体提供;外摩阻力自上而下发挥作用,而内摩阻力自下而上发挥作用。随着荷载的增加,单室井筒式地下连续墙的外侧摩阻力的荷载分担比逐渐减小,而端承反力、内侧摩阻力和土芯顶反力的荷载分担比都在增加,而四室井筒式地下连续墙的外侧摩阻力、墙端反力、土芯顶反力都在减小,仅有内摩阻力的荷载分担比在增加。

扇形涡轮过渡段流动特性及改型特征

为了探讨某扇形涡轮过渡段的气动性能,本文进行了互补互证的数值与试验研究,分析扇形过渡段内损失的区域以及原因。通过采用试验和数值模拟方法,结合经验公式对过渡段型线进行改型设计并进行周期性数值模拟,对原型扇形涡轮过渡段进行了研究,分析了扇形过渡段中损失的主要来源。结果表明:0.07Ma、0.14Ma时扇形涡轮过渡段损失主要在机匣两侧,其余马赫数时在端壁摩擦和流动逆向压差共同作用下使损失区域向支板与左右端壁的中心靠近,周期性模拟时出口面损失区域位于支板后中心区域。本文发现不同型线模型拥有不同的流动过程,等压梯度型线先快速扩压后缓慢扩压的扩压流动方式能有效降低过渡段损失,损失相较于原型减小。

剪力墙类型对钢木混合结构抗震性能的影响

钢框架-木剪力墙结构是一种适用于多高层的绿色低碳结构体系.木剪力墙可分为轻木剪力墙和重木剪力墙两种类型,掌握不同剪力墙类型对结构地震响应的影响规律可为结构设计提供依据.本文使用专为木结构开发的新型单轴滞回模型DowelType,模拟轻木、重木剪力墙混合结构,建立4层有、无墙顶摩擦型阻尼器的混合结构模型,进行频遇地震和罕遇地震下的非线性时程分析,得到层间位移角、结构内力水平、阻尼器耗能等响应的分布,总结了剪力墙类型对上述响应的影响规律.