Preliminary results of the spilling effects on the oscillation of a pipe with compressible fluid inside

It is known to all, the spilling of pipeline may cause serious problems, especially when the pipe conveying petroleum, natural gas or other toxic substance. There are countless accidents during past century. Once the spilling occurs, the vibration of the pipe would aggravate spill situation and even result in crack of the pipe. The consequence will be more severe when the fluid inside is compressible. To prevent the detriment of the spilling model is developed by assuming the leakages as orifices or nozzles and a 2-D vertical simply supported pipe is selected to analyze the phenomena of the oscillation. Combining these two models, the oscillation model for the pipe with leakage is set up and the spilling effect is analyzed by numerical method. The amplitude of the pipe oscillation and the normal stress enlarge as the internal velocity increased, while the shear stress changes very little.

Influence of Specimen Size on Compression Behavior of Cement Paste and Mortar under High Strain Rates

Static and dynamic compression tests were carried out on mortar and paste specimens of three sizes（Ф68 mm×32 mm,Ф59 mm×29.5 mm and Ф32 mm×16 mm）to study the influence of specimen size on the compression behavior of cement-based materials under high strain rates.The static tests were applied using a universalservo-hydraulic system,and the dynamic tests were applied by a spilt Hopkinson pressure bar（SHPB）system.The experimentalresults show that for mortar and paste specimens,the dynamic compressive strength is greater than the quasi-static one,and the dynamic compressive strength for specimens of large size is lower than those of smallsize.However,the dynamic increase factors（DIF）has an opposite trend.Obviously,both strain rate and size effect exist in mortar and paste.The test results were then analyzed using Weibull,Carpinteriand Ba？ant＇s size effect laws.A good agreement between these three laws and the test results was reached on the compressive strength.However,for the experimentalresults of paste and cement mortar,the size effect is not evident for the peak strain and elastic modulus of paste and cement mortar.

Preparation and Compressive Stress Effect of Polymer Matrix RE-Fe Giant Magnetostrictive Composite

Polymer matrix RE-Fe giant magnetostrictire composite （GMPC） was prepared using bonding and magnetic field forming technique, and magnetostriction of samples was measured for different compressive stress. The experimental results show thai there is certain compressive effect in GMPC. And the influence of compressive stress on magnetostriction of sample was investigated. It offers essential reference for application and device design of GMPC.

Effect of Deformation Condition on Axial Compressive Precision Forming Process of Tube with Curling Die

The effect of the deformation condition on the axial compressive precision forming process of tube with curling die was investigated by using a rigid-plastic FEM. The results show that the forming accuracy depends mainly on geometric condition rp/d0, little on tube material properties and friction condition; the relative gap △/2rp of double-walled tubes obtained decreases with Increasing rp/d0, and there is a parameter k for a given to/do or rp/t0, when rp/d0 >k, △/2rp< 1, otherwise △/2rp>1.

Acetic acid-assisted mild dealloying of fine CuPd nanoalloys achieving compressive strain toward high-efficiency oxygen reduction and ethanol oxidation electrocatalysis

Dealloying by which the transition metal is partially or completely leached from an alloy precursor is an effective way to optimize the fundamental effects for further enhancing the electrocatalysis of a catalyst.Herein,to address the deficiencies associated with the commonly used dealloying methods,for example,electrochemical and sulfuric acid/nitric acid treatment,we report an acetic acid-assisted mild strategy to dealloy Cu atoms from the outer surface layers of CuPd alloy nanoparticles to achieve high-efficiency electrocatalysis for oxygen reduction and ethanol oxidation in an alkaline electrolyte.The leaching of Cu atoms by acetic acid exerts an additional compressive strain effect on the surface layers and exposes more active Pd atoms,which is beneficial for boosting the catalytic performance of a dealloyed catalyst for the oxygen reduction reaction(ORR)and the ethanol oxidation reaction(EOR).In particular,for ORR,the CuPd nanoparticles with a Pd/Cu molar ratio of 2:1 after acetic dealloying show a half-wave potential of 0.912 V(vs.RHE)and a mass activity of 0.213 AmgPd^(-1) at 0.9 V,respectively,while for EOR,the same dealloyed sample has a mass activity and a specific activity of 8.4 Amg^(-1) and 8.23 mA cm^(-2),respectively,much better than their dealloyed counterparts at other temperatures and commercial Pd/C as well as a Pt/C catalyst.

Numerical Study on Low-Reynolds Compressible Flows around Mars Helicopter Rotor Blade Airfoil

High-speed rotor rotation under the low-density condition creates a special low-Reynolds compressible flow around the rotor blade airfoil where the compressibility effect on the laminar separated shear layer occurs. However, the compressibility effect and shock wave generation associated with the increase in the Mach number (M) and the trend change due to their interference have not been clarified. The purpose is to clear the compressibility effect and its impact of shock wave generation on the flow field and aerodynamics. Therefore, we perform a two-dimensional unsteady calculation by Computational fluid dynamics (CFD) analysis using the CLF5605 airfoil used in the Mars helicopter Ingenuity, which succeeded in its first flight on Mars. The calculation conditions are set to the Reynolds number (Re) at 75% rotor span in hovering (Re = 15,400), and the Mach number was varied from incompressible (M = 0.2) to transonic (M = 1.2). The compressible fluid dynamics solver FaSTAR developed by the Japan aerospace exploration agency (JAXA) is used, and calculations are performed under multiple conditions in which the Mach number and angle of attack (α) are swept. The results show that a flow field is similar to that in the Earth’s atmosphere above M = 1.0, such as bow shock at the leading edge, whereas multiple λ-type shock waves are observed over the separated shear layer above α = 3° at M = 0.80. However, no significant difference is found in the Cp distribution around the airfoil between M = 0.6 and M = 0.8. From the results, it is found that multiple λ-type shock waves have no significant effect on the airfoil surface pressure distribution, the separated shear layer effect is dominant in the surface pressure change and aerodynamic characteristics.

热处理对＜112＞轴向取向Tb－Dy－Fe合金磁致伸缩压力效应的影响

The magnetostrictive properties of <112> axial aligned Tb0.3Dy0.7(Fe1-xMx)1.95(M=Mn, Al, x=0～ 0.15) alloys prepared by directional solidification are reported. The influence of heat treatment on microstructure and the compressive stress effect of magnetostriction is discussed.

挤压型盆地构造热演化模拟研究综述

挤压过程对地质构造和沉积盆地的形成演化具有重要的作用.研究挤压型盆地的构造热演化模拟对认识岩石圈内部应力分布、力学属性和流变结构具有重要意义.本文介绍了挤压型盆地构造模拟的弹性模型、粘弹性模型和深度控制的弹塑性模型,对比了这几种模型的优缺点和适用范围.简单介绍了前人在研究地壳隆升时用到的几种热演化模拟方法.虽然挤压过程的构造模拟已经取得了很大进展,挤压型盆地的热演化模拟则具有很大的发展空间,这应是进一步研究的重点.

Recent progress in compressible turbulence

In this paper, we review some recent studies on compressible turbulence conducted by the authors＇ group, which include fundamental studies on compressible isotropic turbulence （CIT） and applied studies on developing a con- strained large eddy simulation （CLES） for wall-bounded turbulence. In the first part, we begin with a newly pro- posed hybrid compact-weighted essentially nonoscillatory （WENO） scheme for a CIT simulation that has been used to construct a systematic database of CIT. Using this database various fundamental properties of compressible turbulence have been examined, including the statistics and scaling of compressible modes, the shocklet-turbulence interac- tion, the effect of local compressibility on small scales, the kinetic energy cascade, and some preliminary results from a Lagrangian point of view. In the second part, the idea and for- mulas of the CLES are reviewed, followed by the validations of CLES and some applications in compressible engineering problems.

A basic model of unconventional gas microscale flow based on the lattice Boltzmann method

A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time was modified by considering the influence of the boundary Knudsen layer.On this basis,the second-order slip boundary condition of the wall was considered,and the key parameters in the corresponding combined bounce-back/specular-reflection boundary condition were deduced to build a new model of unconventional gas microscale flow simulation based on the lattice Boltzmann method suitable for high temperatures and high pressures.The simulation results of methane gas flow driven by body force in infinite micro-channels and flow driven by inlet-outlet pressure differential in long straight channels were compared with the numerical and analytical solutions in the literature to verify the accuracy of the model,and the dimensionless relaxation time modification was formally optimized.The results show that the new model can effectively characterize the slippage effect,compression effect,gas density and the effect of boundary Knudsen layer in the micro-scale flow of unconventional natural gas.The new model can achieve a more comprehensive characterization of the real gas flow conditions and can be used as a basic model for the simulation of unconventional gas flow on the micro-nano scale.

Direct Numerical Simulation on Mach Number and Wall Temperature Effects in the Turbulent Flows of Flat-Plate Boundary Layer

In this paper,direct numerical simulation(DNS)is presented for spatially evolving turbulent boundary layer over an isothermal flat-plate at Ma∞=2.25,5,6,8.When Ma∞=8,two cases with the ratio of wall-to-reference temperature T_(w)/T_(∞)=1.9 and 10.03 are considered respectively.The wall temperature approaches recovery temperatures for other cases.The characteristics of compressible turbulent boundary layer(CTBL)affected by freestream Mach number and wall temperature are investigated.It focuses on assessing compressibility effects and the validity of Morkovin’s hypothesis through computing and analyzing the mean velocity profile,turbulent intensity,the strong Reynolds analogy(SRA)and possibility density function of dilatation term.The results show that,when the wall temperature approaches recovery temperature,the effects of Mach number on compressibility is insignificant.As a result,the compressibility effect is very weak and the Morkovin’s hypothesis is still valid for Mach number even up to 8.However,when Mach number equal to 8,the wall temperature effect on the compressibility is sensitive.In this case,when T_(w)/T_(∞)=1.9,the Morkovin’s hypothesis is not fully valid.The validity of classical SRA depends on wall temperature directly.A new modified SRA is proposed to eliminate such negative factor in near wall region.Finally the effects of Mach number and wall temperature on streaks are also studied.

Simple and effective method to improve the signal-to-noise ratio of compressive imaging

This Letter presents a simple and effective method to improve the signal-to-noise ratio（SNR） of compressing imaging. The main principles of the proposed method are the correlation of the image signals and the randomness of the noise. Multiple low SNR images are reconstructed firstly by the compressed sensing reconstruction algorithm, and then two-dimensional time delay integration technology is adopted to improve the SNR. Results show that the proposed method can improve the SNR performance efficiently and it is easy to apply the a lgorithm to the real project.