The temperature distribution due to frictional heat generated between a stationary cylinder and a rotating cylinder

An analytical model has been developed to find the distribution of heat between two cylinders placed at right angles to one another. One cylinder is stationary and the other rotates at high speed. The model assumes that the contact width is very small compared with the overall dimensions of the cylinders. The heat conduction problem has been solved for both the rotating and the stationary cylinder, the average temperature over the contact area has been determined and the heat distribution between them obtained by matching the average temperatures. Allowance has been made for surface heat transfer from both bodies.     

Static friction between a cup leather seal and a cylinder wall

If a hydraulic jack used in the vertical position has a cup leather seal and the pressure is released after being held for a length of time, there will be a significant static friction force required to move the ram in the cylinder. The cause of the friction force has been studied experimentally as well as some of the variables which control its value. The subject is of considerable importance in the use of free fall jacks as hydraulic pit props.     

Simulation of transient friction of a cylinder between two planes

The need for good friction models for transient motions has increased as a consequence of the increased use of mechatronics and control engineering principles in precision mechanics. The machine elements in such equipment often involve rolling and sliding contacts. Most studies of friction in rolling and sliding contacts running under dry or boundary lubricated conditions have examined steady-state conditions.This paper describes simulations of the motion of a cylinder between two planes, first with a step change in velocity and then with an oscillating motion of the upper plane. The motion of the cylinder is determined by the friction in the contacts and the inertia. The friction in the rolling and sliding contacts is simulated with a brush model. The surfaces are assumed to be ideally smooth.For the step change in velocity, there is initially a period of complete sliding in the upper contact. During the sliding period, the friction force is the maximum possible, but it decreases as the complete sliding ends. The simulations show heavily damped oscillations, with frequencies corresponding to the natural translatory and torsional frequencies of the system. For the oscillating motions the sliding increases with the frequency of the motion, as expected.     

The effect of a friction modifier on piston ring and cylinder bore friction and wear

The addition of friction modifiers to crankcase lubricants has been shown to significantly reduce the mechanical losses of critical components in internal combustion (ic) engine; thereby improving fuel economy.In this study the friction and wear of a piston ring/cylinder bore material combination was studied using a pin-on-plate laboratory tribo-test machine developed to reproduce the wear mechanisms encountered in an ic engine. Two lubricants were evaluated: (i) a standard SAE 30 grade diesel formulation, and (ii) the same formulation with the addition of a 5% soluble MoS₂ friction modifier.Analysis of the wear results identified three periods of wear: (1) running-in, (2) transient wear and (3) terminal wear. Throughout this study particular emphasis has been placed on the simulation of the wear mechanisms occurring within engines. Surface analysis confirmed that both abrasive wear and delamination wear was produced.Friction benefits attributable to the addition of MoS₂ friction modifier were obtained. However, under specific conditions the wear rate increased due to increased abrasion of the plate.     

The free vibrations of a thin circular finite rotating cylinder

The natural frequencies of a finite circular thin cylinder are obtained by employing an exponential matrix expansion of the so-called “fundamental matrix”. It is shown that the method is general enough and able to handle any system of linear differential equations of constant coefficients together with arbitrary boundary conditions. Results are given for rotating cylinders with clamped and free edges. The vibration frequencies of a stationary finite cylinder, previously obtained by other methods of solution, are used as a check on the present method with the special case of zero spinning velocity.     

On the influence of a pin type on the friction losses in pin bearings

The aim of this paper is to analyze lubricated revolute joints from the viewpoint of friction losses. The paper deals with the lubricated revolute joints composed of a pin and two more elements connected by means of the pin. It is considered here how different pin types affect friction losses in pin bearings. Three existing pin types are investigated: a pin press-fitted either in the first or in the second element or the one free to rotate in both elements. As a measure of friction losses, a dissipation function is determined in all three cases. Using the results obtained, the advantages of using the full-floating pin with respect to two other types are demonstrated by means of a numerical example.     

圆柱、圆筒式称重传感器非线性和旋转误差分析

圆柱、圆筒式称重传感器以其结构简单紧凑、刚度大、固有频率高、动态响应快等特点,广泛应用于静、动态大型电子衡器中,但其固有线性差、容易产生旋转误差等缺点也是非常致命的。为作好圆柱、圆筒式弹性元件结构设计、非线性补偿和控制旋转误差,本文分析了面积效应、泊松比效应、焊接密封膜片对非线性误差的影响,电阻应变计定位偏差等引起的非测量应变量对旋转误差的影响。     

Numerical simulation of a binary gas flow inside a rotating cylinder

A new approach to calculate the axially symmetric binary gas flow is proposed. Dalton’s law for partial pressures contributed by each species of a binary gas mixture (argon and helium) is incorporated into numerical simulation of rarefied axially symmetric flow inside a rotating cylinder by using the time relaxed Monte-Carlo (TRMC) scheme and the direct simulation Monte-Carlo (DSMC) method. The results of flow simulations are compared with the analytical solution and results obtained by Bird [1]. The results of the flow simulations show better agreement than the results obtained by Bird [1] in comparison with the analytical solutions. However, the results of the flow simulations using the TRMC scheme show better agreement than those obtained using the DSMC method in comparison with the analytical solutions.     

A model of friction for a pin-on-disc configuration with imposed pin rotation

A friction model is developed by considering the Coulomb friction model, a probabilistic approach of wear prediction, the kinematics of the pin-on-disc configuration and the elastic theory of bending. The model estimates the magnitude and direction of the frictional force, the pin torque, the probability of asperity contact and the real area of contact distinguishing between the part due to elastic and plastic asperity contacts respectively. Therefore, the proposed model is suitable for the prediction of adhesive wear. It can be applied to metal contacts for conductance characterisation through the plastically deformed asperities which is of great interest for electrical contact resistance studies.     

薄壁圆筒干摩擦减振设计

振动对薄壁圆筒结构的危害性很大,附加开口阻尼环可以有效的减小薄壁圆筒结构的振动。首先运用相关力学理论,通过改变开口阻尼环的轴向尺寸,得到不同尺寸下组合结构间的接触压力;其次施加接触压力模拟阻尼环过盈安装;再次通过有限元仿真求解结构的预应力瞬态响应;最后使用快速傅里叶变换得到频域结果,给出阻尼环轴向尺寸改变对振动的影响规律。     

Stability of stationary and rotating discs under edge load

The dominant dynamic instability mechanism in circular cutters, grinding wheels and the like is a moving load resonance excited by a constant transverse load at the “critical rotation speed.” The critical speed theory is extended here to include the effects of concentrated in-plane edge loads similar to loading occurring in engineering processes. The theoretical analysis shows the critical speed is only sensitive to edge load when the resonance mode and the mode of static edge load buckling are identical. This always occurs with large edge load, but it is not the case with the smaller edge loads typical of engineering processes. These analyses are confirmed through prediction and measurement of static buckling loads for centrally clamped discs with in-plane, concentrated loads inclined between 0° and 80° to the edge normal.     

Comparison of DNS and Reynolds stress modelling of flow around a rotating cylinder

The low Reynolds number stress-omega model is applied to flow associated with a rotating cylinder operating in a larger, stationary cylinder. The working fluid fills the gap between the cylinders. Direct numerical simulation data are used to test the predictions by this turbulence model. Previous work has shown that simpler models are unable to predict with reasonable accuracy the wall shear stress experienced by the rotating cylinder. The present study with a more complex turbulence model shows that the wall shear stress on the rotating cylinder is underestimated significantly. Examination of turbulence velocity fluctuation intensity distributions points to underprediction of the streamwise turbulence level and excessive values of the wall normal turbulence level. Results are given for no shear and a wall shear at the outer cylinder surface but no effect on the inner cylinder statistics was found. An examination of the Reynolds stress anisotropy tensor components highlights a significant deficiency in this parameter which is an essential component of the pressure-strain modelling of Reynolds stress models. The most significant aspect is a rapid decrease of the streamwise component of the Reynolds stress anisotropy tensor relative to the direct numerical simulation results and values which are too low for the other two components.     

Load bearing capacity of tool pin during friction stir welding

Although friction stir welding (FSW) is now widely used for the welding of aluminum and other soft alloys, premature tool failure limits its application to hard alloys such as steels and titanium alloys. The tool pin, the weakest component of the tool, experiences severe stresses at high temperatures due to both bending moment and torsion. It is shown that the optimum tool pin geometry can be determined from its load bearing capacity for a given set of welding variables and tool and work-piece materials. The traverse force and torque during friction stir welding are computed using a three-dimensional heat transfer and viscoplastic material flow model considering temperature and strain rate-dependent flow stress of the work-piece material. These computed values are used to determine the maximum shear stress experienced by the tool pin due to bending moment and torsion for various welding variables and tool pin dimensions. It is shown that a tool pin with smaller length and larger diameter will be able to sustain more stress than a longer pin with smaller diameter. The proposed methodology is used to explain the failure and deformation of the tool pin in independent experiments for the welding of both L80 steel and AA7075 alloy. The results demonstrate that the short tool life in a typical FSW of steels is contributed by low values of factor of safety in an environment of high temperature and severe stress.     

Leakage from labyrinth seals under stationary and rotating conditions

Although the leakage flow through labyrinth seals under stationary conditions has been examined by many investigators a reliable prediction of the effect of various labyrinth parameters on leakage rate has not been reported so far. The theoretical models for the seals proposed in most of the previous literature provided results with considerable differences and contradictions in some cases. The structure of the laminar incompressible flow and the performance of a number of seals of various shapes for both stationary and rotating conditions are investigated in this paper. The theoretical treatment is based on the formulation of three-dimensional axisymmetric momentum and continuity equations for labyrinth shapes having small height to radius ratio as is always the case in turbomachinery, rotodynamic pumps and many hydraulic devices. It is found in this paper that shaft rotation is only beneficial for the up-the-step seal, has no effect on grooved shaft and grooved casing seals and has an adverse effect on the down-the-step seal. It is also found that the use of a smaller clearance size at the entrance makes some improvement in the performance of the grooved shaft and down-the-step seals depending on the value of the height to width ratio of the seal.     

Characteristics of pressure and force considering friction in a closed cylinder with a holed piston

A mathematical model for a closed cylinder with a holed piston was established to investigate the operational characteristics of a gas spring. An ideal gas working fluid and an adiabatic process were assumed in the model. Simulation and experimental results for a typical design and operational condition showed good agreement. The model was then used to investigate the effects of the orifice diameter, the filling pressure, and the velocity of the piston on the applied force and operating pressures of two chambers in the gas spring. The results showed that the orifice diameter and the piston velocity had significant effects on the pressure difference between the two chambers. A 0.05-mm reduction in the orifice diameter led to an approximately two-fold increase in the pressure difference. A 10% increase in the piston velocity resulted in an approximately 25% increase in the pressure difference. The orifice diameter and the piston velocity had a greater effect on the chamber with lower pressure than on the chamber with higher pressure. The force applied to the piston also varied with the piston velocity, the orifice diameter, and the filling pressure due to irreversibilities including the throttling process through the orifice and friction between the wall and the piston. The present model and results are expected to supply useful information about a new gas spring design.     

Stability analysis of a rotating multi-layer annular plate with a stationary frictional follower load

This paper is concerned with examining the critical rotational speeds of a annular laminated disk and instability due to the existence of a stationary frictional follower load. A refined higher order layerwise zigzag theory (RHOT) is used to derive the governing equations of motion of a laminated disk. A four-node sector finite element incorporating RHOT is developed and applied for the stability analysis of a rotating multi-layer disk. The critical rotational speeds of a laminated disk made of isotropic layers and a laminated disk made of polar—orthotropic layers are calculated using the state—space method with respect to a moving frame and an inertial frame. The effect of a frictional follower load on the system stability is investigated using the frequency—speed diagram and the state—space method. It is found that the frictional follower load makes all forward modes with nodal diameters unstable over the entire rotational speed range. Total Lagrangian kinematics with the modified Newton method is used in the solution finding procedure.     

Experimental investigation of hexagonal boron nitride filled friction composites using a pin on disc tribometer

Journal of Mechanical Science and Technology - In earlier friction composites, higher thermal conductive copper and copper-based alloys were the main functional fillers to regulate stable friction...     

Solid-liquid mixture flow through a slim hole annulus with rotating inner cylinder

An experimental study was conducted to study solid-liquid mixture upward hydraulic transport of solid particles in vertical and inclined annuli with rotating inner cylinder. Lift forces acting on a fluidized particle play a central role in many important applications, such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs and sediment transport, etc. Annular fluid velocities varied from 0.4 m/s to 1.2 m/s. Effect of annulus inclination and drill pipe rotation on the carrying capacity of drilling fluid, particle rising velocity, and pressure drop in the slim hole annulus have been measured for fully developed flows of water and of aqueous solutions of sodium carboxymethyl cellulose (CMC) and bentonite, respectively. For higher particle feed concentration, the hydraulic pressure drop of mixture flow increases due to the friction between the wall and solids or among solids. This paper was recommended for publication in revised form by Associate Editor Gihun Son Sang-Mok Han received a B.S. degree in Mechanical Engineering from Sung-kyunkwan University in 2001. He then went on to receive his M.S. degrees from Sungkyunkwan University in 2003. He is a candidate for Ph.D. from 2006 to the present at the School of Mechanical Engineering at Sungkyunkwan University in Suwon, Korea. His research interests are in the area of Multi-phase flow and drilling. Nam-Sub Woo received a B.S. degree in Mechanical Engineering from Sungkyunkwan University in 1997. He then went on to receive his M.S. and Ph.D. degrees from Sunkyunkwan University in 1999 and 2007, respectively. Dr. Woo is currently a Senior Researcher at the Fire & Engineering Services Research Center at Korea Institute of Construction and Technology in Goyang, Korea. Dr. Woo’s research interests are in the area of fluid dynamics and plant engineering. Young-Kyu Hwang received a B.S. degree in Mechanical Engineering from Sungkyunkwan University in 1977. He then went on to receive his M.S. from University of Wis-consin at Madison in 1980 and Ph.D. degrees from State Uni-versity of New York at Buffalo in 1984, respectively. Dr. Hwang has served as a Professor, from 1984 to the present at the School of Mechanical Engineering at Sungkyunkwan University in Suwon, Korea. His research interests are in the area of drilling hydraulics, molecular gas flow and hydrodynamic instability.