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THE paper reviews the problem of the influence of the walls of a closed tunnel in increasing the velocity in the neighbourhood of a model under test. It is shown that, for a perfect fluid, considerations of continuity suffice to establish an exact value of the mean interference velocity for any cross‐section of the tunnel. This mean interference velocity is expressed in terms of the perturbation velocity which would be caused by the same model in the absence of the walls. The linearized theory of subsonic compressible flow is applied and it is shown that the interference velocity for a small two or three dimensional model is increased in proportion to l/β3, where β=√(l—M2) and M is the Mach number. Interference caused by a body with a long parallel middle body, the influence of the wake from a model and of the boundary layer on the tunnel walls are briefly considered.

A laminar swirling jet impinging on to an adiabatic solid wall is investigated. The flow field is computed and entropy analysis is carried out for different flow configurations. The numerical scheme employing a control volume approach is introduced when solving the governing equations of flow and energy. In order to examine the effect of the nozzle exit velocity profile and the swirling velocity on the flow field and entropy generation rate, six nozzle exit velocity profiles and four swirl velocities are considered. It is found that the influence of swirl velocity on the flow field is more pronounced as the velocity profile number reduces. In this case, two circulation cells are generated in the flow field. The total entropy generation increases with increasing swirl velocity for low velocity profile numbers. The Merit number improves for low swirling velocity and high velocity profile numbers.

The purpose of this paper is to know airflow field and its distribution of pneumatic compact spinning systems. Complete compact spinning (CCS) and four-line rollers compact spinning (FRCS) are both two kinds of pneumatic compact spinning systems, which utilizes airflow in condensing equipment to condense fiber bundle and improve yarn properties.

The paper opted for an exploratory study using finite element method, the airflow field in the condensing area of CCS and FRCS were simulated. First, a periodic movement of the fibers in bundle in condensing area was detected, and the yarn tracks were described veritably under the high-speed-video-camera and AutoCAD Software. Then the physical models of the condensing zone were constructed according to the physical parameters of the practical system. The simulation of airflow velocities were extracted along the yarn tracks using ANSYS Software. Finally, the numerical results were verified by spinning experiments.

The results show that the negative velocity component along the Y-axis helps keeping beneficial hairiness. CCS has higher negative velocity value and more abundant beneficial hairiness than FRCS. The velocity component in the X-axis direction has a direct effect on yarn evenness. For the same liner density of CCS and FRCS, the larger the value of the velocity component on X-axis is, the better the yarn evenness is. For 9.7tex, CCS has larger velocity component in the X-axis direction and better yarn evenness than FRCS, showing that CCS is more suitable for spinning fine count yarn. The velocity component in the Z-axis direction has a direct effect on breaking strength. CCS has little velocity component in the Z-axis direction and little breaking strength than FRCS.

To know airflow field and its distribution by finite element method is helpful to investigate the condensing principles of the fiber bundle and improve yarn properties.

The purpose of this paper is to find the influence of the initial braking velocity and braking frequency on the tribological performance of the non‐asbestos brake shoe used in mine hoisters during some continuous emergency brakings.

The tribological performance experiments of the WSM‐3 non‐asbestos brake shoe braking on the 16 Mn steel are investigated on the X‐DM friction tester, by simulating continuous emergency brakings of a mine hoister ten times. Three kinds of tribological indexes: friction coefficient, its stability coefficient, and wearing rate are considered to score the tribological performance of the brake shoe.

When the initial braking velocity increases, the mean friction coefficient of the brake shoe decreases at first, then rises, and falls again finally. But when the braking frequency exceeds seven times, the falling process of the friction coefficient at low‐velocity period does not appear again. Second, when the initial braking velocity is no higher than 10 m/s, the mean friction coefficient rises with the braking frequency increasing. But when the velocity exceeds 10 m/s, the mean friction coefficient rises with the braking frequency increasing at first, then falls. Third, when the initial braking velocity is no higher than 12.5 m/s, the friction coefficient of the brake shoe has quite a favorable stability with the coefficient is no bigger than 75 percent. But when the velocity exceeds 12.5 m/s, the stability of the friction coefficient is diminishing obviously. Fourth, the wearing rate of the brake shoe increases quickly, during the process that the velocity rising from 10 to 12.5 m/s, but increases much more slowly after that period.

The paper investigates the tribological performance of the WSM‐3 non‐asbestos brake shoe during some continuous emergency brakings and finds that, when the initial braking velocity is no higher than 12.5 m/s and the braking frequency is no more than seven times, the WSM‐3 non‐asbestos brake shoe has quite a high friction coefficient, a good friction stability, and a low‐wearing rate, which indicate that it is very appropriate for using in the disk brake of mine hoisters in China.

Presents the influence of seam length, normal stitching velocity of a sewing machine and a working method on stitching velocity of sewing. Results show that better stitching velocities of sewing are gained by longer length of seams and higher than normal stitching velocities of a sewing machine. Reveals the working method and type of feeding of material affect the achievement of higher stitching velocities.

A confined laminar swirling jet is an interesting research topic due to flow and temperature fields generated in and across the jet. In the present study, a confined laminar swirling jet is studied, and flow and temperature fields are simulated numerically using a control volume approach. In order to investigate the influence of the jet exiting (exiting the nozzle and inleting to the control volume) velocity profiles on the flow and heat transfer characteristics, eight different velocity profiles are considered. To identify each velocity profile, a velocity profile number is introduced. Entropy analysis is carried out to determine the total entropy generation due to heat transfer and fluid friction. Merit number is computed for various swirling velocities and velocity profiles. It is found that swirling motion expands the jet in the radial direction and reduces the jet length in the axial direction. This, in turn, reduces the entropy generation rate and improves the Merit number. Increasing velocity profile number enhances the entropy production rate, but improves the Merit number.

The purpose of this paper is to determine the influence of the loading velocity on textile bonds and sewn seam strength.

Commercially produced polyamide and polyester knitted fabric, and polyester woven fabrics as well as three commercially available monolayer urethane thermoplastic films were used in this research. Two layers of each fabric were laminated at 160°C temperature at 5.6 kPa for 20 seconds. Sewn specimens were joined applying (301) and (514) stiches for woven and knitted fabrics, respectively. The bond and sewn seam strength was investigated at different delamination loading velocities (50, 100, 150, 200, 300 mm/min). These values of velocities lies in the velocity interval which covers the different standard requirements for testing of the quality of textiles and their seams or were applied in the research works of previous scientists. As the influence of loading velocity was more significant for bond strength, the bond strength results were analyzed together with the analysis of bond rupture character.

The determined influence of the loading velocity on textile bonds strength has proved that the loading velocity in bond strength test is of high importance for the prediction of the behavior of clothing being in exploitation under different conditions. The opposite tendency was determined for the sewn seams, the strength of which was independent on loading velocity.

The influence of the loading velocity on textile bond and sewn seam strength was not analyzed in the previous research works published by other scientists. It was known that the standard velocity is 50 mm/min for seams and 100 mm/min for textiles strength testing. It was shown there that the real exploitation of a garment as a whole complicated heterogenic dynamic system could be simulated with changing loading velocities during their seam strength testing. It was also determined that the loading velocity makes different influence on bonded and sewn seams of textiles.

The purpose of this study is to solve the problems of poor stability and high energy consumption of the dynamic window algorithm (DWA) for the mobile robots, a novel enhanced dynamic window algorithm is proposed in this paper.

The novel algorithm takes the distance function as the weight of the target-oriented coefficient, and a new evaluation function is presented to optimize the azimuth angle.

The jitter of the mobile robot caused by the drastic change of angular velocity is reduced when the robot is closer to the target point. The simulation results show that the proposed algorithm effectively optimizes the stability of the mobile robot during operation with lower angular velocity dispersion and less energy consumption, but with a slightly higher running time than DWA.

A novel enhanced dynamic window algorithm is proposed and verified. According to the experimental result, the proposed algorithm can reduce the energy consumption of the robot and improves the efficiency of the robot.

The purpose of this paper is to present a computational study to investigate the effects of rectangular cavity design of a piezoelectrically driven micro‐synthetic‐jet actuator on generated flow.

Flow simulations were done using a compressible Navier‐Stokes solver, which is based on finite element method implementation of a characteristic‐based‐split (CBS) algorithm. The algorithm uses arbitrary Lagrangian‐Eulerian formulation, which allows to model oscillation of the synthetic jet's diaphragm in a realistic manner. Since all simulated flows are in the slip‐flow‐regime, a second order slip‐velocity boundary condition was applied along the cavity and orifice walls. Flow simulations were done for micro‐synthetic‐jet configurations with various diaphragm deflections amplitudes, cavity heights, and widths. All of the simulation results were compared with each other and evaluated in terms of the exit jet velocities, slip‐velocities on the orifice wall and instantaneous momentum fluxes at the jet exit.

It is shown that compressibility and rarefaction have important effects on the flow field generated by the micro‐synthetic‐jet actuator. The effect of the geometrical parameters of the cavity to important flow features such slip and phase lag are presented.

The paper reports results of a systematical study of the flow field inside a micro‐scale synthetic‐jet actuator, providing designers of such devices additional information for sizing the cavity within slip flow regime. Furthermore, it is demonstrated that the CBS, together with slip boundary conditions can be successfully used to compute such flows.

Material extrusion-based additive manufacturing is a prominent manufacturing technique to fabricate complex geometrical three-dimensional (3D) parts. Despite the indisputable advantages of material extrusion-based technique, the poor surface and subsurface integrity hinder the industrial application of this technology. The purpose of this study is introducing the hot air jet treatment (HAJ) technique for surface treatment of additive manufactured parts.

In the presented research, novel theoretical formulation and finite element models are developed to study and model the polishing mechanism of printed parts surface through the HAJ technique. The model correlates reflow material volume, layer width and layer height. The reflow material volume is a function of treatment temperature, treatment velocity and HAJ velocity. The values of reflow material volume are obtained through the finite element modeling model due to the complexity of the interactions between thermal and mechanical phenomena. The theoretical model presumptions are validated through experiments, and the results show that the treatment parameters have a significant impact on the surface characteristics, hardness and dimensional variations of the treated surface.

The results demonstrate that the average value of error between the calculated theoretical results and experimental results is 14.3%. Meanwhile, the 3D plots of Ra and Rq revealed that the maximum values of Ra and Rq reduction percentages at 255°C, 270°C, 285°C and 300°C treatment temperatures are (35.9%, 33.9%), (77.6%,76.4%), (94%, 93.8%) and (85.1%, 84%), respectively. The scanning electron microscope results illustrate three different treatment zones and the treatment-induced and manufacturing-induced entrapped air relief phenomenon. The measured results of hardness variation percentages and dimensional deviation percentages at different regimes are (8.33%, 0.19%), (10.55%, 0.31%) and (−0.27%, 0.34%), respectively.

While some studies have investigated the effect of the HAJ process on the structural integrity of manufactured items, there is a dearth of research on the underlying treatment mechanism, the integrity of the treated surface and the subsurface characteristics of the treated surface.