Unsteady magnetohydrodynamic couette flow

The effect of a uniform transverse magnetic field on the Couette flow of an electrically conducting fluid between two parallel plates for impulsive and uniformly accelerated motion of one of the plates is discussed. The magnetic lines of force are assumed to be fixed relative to the moving plate. The Laplace transform technique has been used to obtain the expressions for the velocity field and skin friction. The effect of the magnetic field is to increase the velocity field in both cases.     

Unsteady flow between rectangular plates and between circular plates

An analysis is presented of the unsteady flow of a viscous incompressible fluid between two parallel infinitely long rectangular plates and between two parallel circular plates. The lower plate is fixed and the upper plate moves towards the lower plate. Full Navier-Stokes equations are used to obtain the pressure distribution as a function of the film thickness h(t) and the velocity $\text{h}\text{?}\text{(t)}$ of the upper plate. The inertia is taken into account and, for a given load on the upper plate, the sinkage relation between h and t is determined for various values of the Reynolds number. The departure from the classical inertialess solution is exhibited for various values of the two dimensionless parameters involved, one characterizing the load and the other gravity.     

Unsteady flow simulations in a three-lobe positive displacement blower

To improve the performance of the positive displacement blower, it is imperative to understand the detailed internal flow characteristics or enable a visualization of flow status. However, the existing two-dimensional unsteady, three-dimensional steady or quasi-unsteady numerical simulation and theoretical analysis cannot provide the detailed flow information, which is unfavorable to improve the performance of positive displacement blower. Therefore, the unsteady flow characteristics in a three-lobe positive displacement blower are numerically investigated by solving the three-dimensional, unsteady, compressible Navier-Stokes equations coupled with RNG k-e turbulent model. In the numerical simulation, the dynamic mesh technique and overset mesh updating method are adopted. Due to the air being compressed in the process of the rotors rotating, the variation of the temperature field in the positive displacement blower is considered. By comparing the experimental measurements and the numerical results on the variation of flow rate with the outlet pressure, the maximum relative error of the flow rate is less than 2.15% even at the maximum outlet pressure condition, which means that the calculation model and numerical computational method used are effective. The numerical results show that in the intake region, the fluctuations of the inlet flow are greatly affected by the direction of the velocity vectors. In the exhaust region, the temperature changes significantly, which leads to the increase of the airflow pulsation. Through analysis on the velocity, pressure and temperature fields obtained from the numerical simulations, three-dimensional unsteady flow characteristics in the positive displacement blower are revealed. The studied results will provide useful reference for improving the performance and empirical correction in the design of the positive displacement blower.     

膜片稳压溢流阀的设计计算

在对低压大流量的溢流阀建立平衡方程及确定设计基本原则的基础上，进行了阀的设计计算及性能分析。     

Unsteady flow generator for gases using an isothermal chamber

We propose a chamber called an ‘isothermal chamber’ that can produce almost isothermal conditions due to its large heat transfer area obtained by filling it with steel wool. Using this chamber, a simple method to measure flow rates of ideal gases has been developed. In this paper, we propose an unsteady flow generator for gases using the isothermal chamber that can be useful for measuring the dynamic characteristics of gaseous flow meters. The mass flow rate is generated by controlling the pressure change during air discharge in the isothermal chamber using a servo valve. Steady and unsteady oscillatory flow is generated with the generator, and the effectiveness of the generator is demonstrated.     

Unsteady characteristics of flow over a realistic heavy vehicle

Journal of Mechanical Science and Technology - Large-eddy simulation of turbulent flow around a 1:8 scale 15-ton heavy vehicle model is performed at Reynolds number of 9.1×105 to study...     

Tribology of total artificial joints.

The tribology of total artificial replacement joints is reviewed. The majority of prosthesis currently implanted comprise a hard metallic component which articulates on ultra high molecular weight polyethylene surface. These relatively hard bearing surfaces operate with a mixed or boundary lubrication regime, which results in wear and wear debris from the ultra high molecular weight polyethylene surface. This debris can contribute to loosening and ultimate failure of the prostheses. The tribological performance of these joints has been considered and a number of factors which may contribute to increased wear rates have been identified. Cushion bearing surfaces consisting of low elastic modulus materials which can articulate with full fluid film lubrication are also described. These bearing surfaces have shown the potential for greatly reducing wear debris.     

The effects of the tilt angle of a bileaflet mechanical heart valve on blood flow and leaflet motion

Diseased heart valves can be replaced with bileaflet mechanical heart valves (BMHVs), which may be affected by complications such as hemolysis, platelet activation and device failure. These complications are closely related to the characteristics of blood flow through mechanical valves and leaflet dynamics, and can become worse with tilted implantation of BMHVs. This study simulated the interactions of blood flow and leaflet motion for BMHVs implanted at different tilt angles. A fluid-structure interaction (FSI) method was employed to solve the problems of blood flow and leaflet motion interactively. A validation of the present numerical methods was performed against data produced in a previous work, indicating that the method presented in this study is reliable. Our results reveal detailed blood flow and leaflet motion in an aorta caused by the systole and diastole of the ventricle. As the tilt angle increased, the degree of asymmetry of blood flow and the time delay in the motions of the two different leaflets also increased, which may cause worsening of complications.     

Computation of wear in artificial heart valves.

In order to assist with the prognosis of wear processes in low profile disc heart valves, an approximate haemodynamic theory has been used for the determination of opening and closing dynamics of these valves, together with the most developed theory to date of frictional fatigue. The heart valve element wear was defined by solving the contact problem, which takes account of changes to the contact surface form as a consequence of wear. Calculated values are compared with in vivo wear data for artificial heart valves. The proposed model for estimating wear in artificial heart valves allows an optimization to be made of the wear resistance in available designs and to predict the wear resistance of artificial heart valves at the design stage.     

非定常复杂流动诱发的调节阀不稳定性研究综述

综述了国内外对非定常复杂流动诱发的调节阀不稳定性研究的情况 ,介绍了笔者今后进行此项研究的计划和内容     

Unsteady viscous flow model on moving the domain through a stenotic artery

An unsteady Navier-Stokes (N-S) solver based on the method of operator splitting and artificial compressibility has been studied for the moving boundary problem to simulate blood flow through a compliant vessel. Galerkin finite element analysis is used to discretize the governing equations. The model has been applied to a time-varying computational domain (two-dimensional tube) as a test case for validation. Consideration has been given to retaining the space conservation property. The same code is then applied to a hypothetical critical high-pressure gradient over a short length of blood vessel based on the spring and dashpot model. The governing equation for the blood vessel is based on two-dimensional dynamic thin-shell theory that takes into account the curvature of the stenotic portion of the vessel. Progressing the solution towards steady state is considered, as the main objective is to show the viability of the current technique for fluid/structure interactions. Preliminary results of the wall velocity and displacement based on steady state prediction agree well with data in the literature. Results, such as the streamlines, wall pressures and wall shear stress depict the possible progression of arterial disease.     

单对立色流运动下的抠图跟踪

当目标与周围背景相似性较高,且目标运动形式复杂时,很难精确跟踪目标。针对传统目标跟踪方法因目标外观的不精确建模致使模型退化而产生漂移的问题,提出了一种单对立色流特征下的抠图跟踪方法。首先,根据彩色视频帧包含的丰富颜色信息,将单对立色颜色编码方式与Lo G兴趣点检测器结合,获取颜色兴趣点作为目标表示集合;其次,在目标运动预测阶段,通过估计相邻帧兴趣点的流匹配关系,获得预测帧的前景目标兴趣点估计;最后,利用获得的前景兴趣点估计进行抠图,重新划分当前帧的前背景标记,并对模型进行更新。该算法在Segtrack视频跟踪数据集上进行验证,定性定量分析了跟踪目标快速运动,目标形变和光照干扰下的跟踪效果。实验结果表明该算法可有效提高形变目标跟踪的准确性,优于当前目标跟踪的先进算法。     

A numerical analysis on the curved bileaflet mechanical heart valve (mhv): leaflet motion and blood flow in an elastic blood vessel

In blood flow passing through the mechanical heart valve (MHV) and elastic blood vessel, hemolysis and platelet activation causing thrombus formation can be seen owing to the shear stress in the blood. Also, fracture and deformation of leaflets can be observed depending on the shape and material properties of the leaflets which is opened and closed in a cycle. Hence, comprehensive study is needed on the hemodynamics which is associated with the motion of leaflet and elastic blood vessel in terms of fluid-structure interaction. In this paper, a numerical analysis has been performed for a three-dimensional pulsatile blood flow associated with the elastic blood vessel and curved bileaflet for multiple cycles in light of fluid-structure interaction. From this analysis fluttering phenomenon and rebound of the leaflet have been observed and recirculation and regurgitation have been found in the flow fields of the blood. Also, the pressure distribution and the radial displacement of the elastic blood vessel have been obtained. The motion of the leaflet and flow fields of the blood have shown similar tendency compared with the previous experiments carried out in other studies. The present study can contribute to the design methodology for the curved bileaflet mechanical heart valve. Furthermore, the proposed fluid-structure interaction method will be effectively used in various fields where the interaction between fluid flow and structure are involved.     

Unsteady viscous flow over elliptic cylinders at various thickness with different reynolds numbers

Two-dimensional incompressible Navier-Stokes equations are solved using SIMPLER method in the intrinsic curvilinear coordinates system to study the unsteady viscous flow physics over two-dimensional ellipses Unsteady viscous flows over various thickness-to-chord ratios of 06, 08, 10, and 1 2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000 This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces The present numerical solutions are compared with available experimental and numerical results and show a good agicement Through this study, it is observed that the Reynolds number and the cylinder thickness affect significantly the frequencies of the force oscillations as well as the mean values and the amplitudes of the drag and lift forces     

Unsteady air flow measurement method based on adaptive tracking differentiator for pneumatic system

When using a flowmeter to measure unsteady air flow in the pneumatic control system, problems such as high cost and pressure loss are often encountered. It is an available method to measure the unsteady flow rate using isothermal chamber through direct differentiation of pressure signal with a traditional fixed parameter differentiator, but the adaptability of this method is insufficient due to its narrow dynamic range. To this end, an improved adaptive tracking differentiator which can adaptively adjust the control parameters according to the changes of pressure signal and pressure tracking error was proposed for unsteady air flow measurement. The algorithm structure of the adaptive tracking differentiator was designed. Moreover, theoretical simulation and flow measurement experiments under multiple working conditions were carried out. The simulation and experiment results showed that the flow measurement method based on improved adaptive tracking differentiator effectively measured the unsteady flow in a wide dynamic range, and had the advantages of more simplified process and lower cost than traditional method.     

Three-phase flow meters based on X-rays and artificial neural network to measure the flow compositions

The methodology presented in this study is based on a 149.5 keV X-ray beam and two planar germanium detectors for X-ray transmission and scattering measurements for prediction of volume fractions in a three-phase system. Fluid volume fractions have been modeled using the MCNP6 code for an annular flow regime. A mathematical algorithm based on an artificial neural network was used to correlate the energy spectra from both detectors with the fluids volume fractions. The pulse height distributions obtained by the detectors are used as input data of the network that outputs the volume fractions of gas and water. The mean relative error, using the procedure presented here, for all data, was below 2.5% for both phases investigated. These results show that the methodology based on an X-ray beam has the potential to be used with flow meters.     

Establishing a range of motion boundary for total hip arthroplasty

Range of motion of the hip joint is a major contributor to dislocation post total hip replacement. Impingement is often treated as a surrogate for dislocation and occurs--prosthetically--when the neck of the femoral component contacts with the rim of the pelvic acetabular cup. This impingement is caused by movement of the leg during activities of daily living. This article analyses hip joint range of motion and its implication for impingement. A systematic literature review was undertaken with the purpose of establishing a range of motion benchmark for total hip replacement. This paper proposes a method by which a three-dimensional range of motion boundary established from the literature can be presented. The nominal boundary is also validated experimentally using a number of configurations of a neutral hip joint coordinate frame.     

Unsteady computation of flow field and convective heat transfer over tandem cylinders at subcritical Reynolds numbers

Unsteady flow and convective heat transfer over single and two tandem cylinders at constant-heat-flux condition in subcritical range of Reynolds number was numerically investigated. Two-dimensional computations were performed by adopting 3-equation k-kl-ω turbulence model using a commercial software FLUENT®. The aim was to investigate the capabilities of k-kl-ω turbulence model for collective flow and heat transport conditions past cylindrical bodies and then to identify a critical spacing ratio for the maximum heat transport. The center-to-center spacing ratio (L/D) was varied in the range from 1.2 to 4.0. Instantaneous path lines and vorticity contours were generated to interpret the interaction of shear layer and vortices from upstream cylinder with the downstream cylinder. Comparison of pressure coefficients, fluctuating and average lift as well as drag coefficients, Strouhal number and the local and average Nusselt numbers with the available literatures indicated a reasonably good agreement. The combined outcome of flow field and heat transfer study revealed a critical spacing ratio of L/D = 2.2. Based on the present investigation, a correlation has been suggested to calculate overall average Nusselt number of the two cylinders placed in tandem.