Abdullah M. Al-Shabibi

Transient solution of a thermoelastic instability problem using a reduced order model.

Above a certain critical speed, slidingsystems with frictional heatingsuch as brakes and clutches can exhibit thermoelastic instability in which non-uniform perturbations develop in the pressure and temperature .elds. A method is described in which the transient thermomechanical behaviour of such systems is approximated by a reduced order model, describing one or more dominant perturbations or eigenfunctions. The goal is to construct a mathematical model of the system with a modest number of degrees of freedom. If a single dominant perturbation is used, an integral expression can be written for the evolution of the perturbation with time. A more accurate description involvingseveral terms requires that the transient behaviour be generated by a sequence of operations in which the sliding speed is piecewise constant. Both models are evaluated by comparison with a direct numerical simulation and prove to give good accuracy with a dramatic reduction in computingtime. ? 2002 Elsevier Science Ltd. All rights reserved.

Transient solution of the unperturbed thermoelastic contact problem

Automotive brake and clutch systems experience temperature and contact pressure variation due to frictional heat generation. Due to geometrical complexity and the coupled thermo-mechanical nature of this class of problems, direct finite element simulation is found to be computer-intensive. This paper explores a more time-efficient method that can be used to obtain the transient solution for the unperturbed clutch and brake system based on an eigenfunction expansion and a particular solution. An approximate solution can also be sought based on the same method in which only a subset of the eigenfunctions are used.

Transient Behavior of Initial Perturbation in Multidisk Clutch System

Above a certain critical speed, a perturbation in the contact pressure or the temperature field of a clutch system can grow, leading to areas of high heat generation or hot spots. The aim of the present study is to investigate the transient evolution of a sinusoidal perturbation in a multidisk clutch system. Eigenfunction expansion is used to solve the coupled thermomechanical heat conduction problem. A reduced-order model is also investigated in which a few dominant eigenfunctions are used in the expansion series.

Finite element implementation of the eigenfunction series solution for transient heat conduction problems with low Biot number

Analytical solutions to transient heat conduction problems are often obtained by superposition of a particular solution (often the steady-state solution) and an eigenfunction series, representing the terms that decay exponentially with time. Here, a finite element realization of this method is presented in which conventional finite element discretization is used for the spatial distribution of temperature and analytical methods for the time dependence. This leads to a linear eigenvalue problem whose solution then enables a general numerical model of the transient system to be created. The method is an attractive alternative to conventional time-marching schemes, particularly in cases where it is desired to explore the effect of a wide range of operating parameters. The method can be applied to any transient heat conduction problem, but particular attention is paid to the case where the Biot number is small compared with unity and where the evolution of the system is very close to that with zero heat loss from the exposed surfaces. This situation arises commonly in machines such as brakes and clutches which experience occasional short periods of intense heating. Numerical examples show that with typical parameter values, the simpler zero heat loss solution provides very good accuracy. One also shows that good approximations can be achieved using a relatively small subset of the eigenvectors of the problem.

Solution of heat conduction problem in automotive clutch and brake systems

This paper is investigating the transient solution for a heat conduction problem in solids with insulated boundary. This class of problem is often encountered in automotive brake and clutch systems where the frictional heat generated at contact surface is much larger than that the system is capable of dissipating. The heat conduction equation can be solved through the superposition of the homogenous solution and the particular solution. The use of the steady state solution as a particular solution can however result in a lack of numerical accuracy because of its order of magnitude driven by the nearly insulated boundary. A special solution form is proposed for the particular solution to account for such boundary condition. The proposed solution was tested in the context of a typical clutch disk sliding between two non-conductive rigid bodies. The solution has proven to be time efficient and free of numerical accuracy associated with the order of magnitude of the particular solution.Copyright

Manufacturing of low alloy steel sucker rods by continuous process — heat treatment and characterization

ABSTRACT Sucker rods are typically made of steel, and are important components of equipment such as reciprocating and progressive pumps used in various downhole applications in oil and gas wells. Chemical and mechanical characterizations were carried out on heat treated continuous sucker rods. These sucker rods were manufactured out of three types of steels by joining a series of coils together and subjecting them to continuous heat treatment during manufacturing. Tensile properties and hardness values were in the accepted ranges required by the operator. The fracture surfaces however demonstrated a shear type brittle fracture despite relatively high elongation-to-fracture. The fracture surface revealed unusual features in which very flat surfaces with sharp edges are present. Conventional sucker rods of grades H and D that were subjected to conventional heat treatments show completely different fracture mode. Comparison of microstructure and fracture surfaces of conventional and continuous sucker rods indicates that continuous rods were perhaps under-tempered, with insufficient tempering time.

EXPERIMENTAL STUDY ON THE EFFECT OF DRILL QUALITY ON BONE TEMPERATURE IN DRILLING

Bone drilling is widely performed in orthopedics for fixation and reconstruction of bone. In bone drilling, a hard metallic drill penetrates into the bone tissue which may cause trauma. Shear deformation of the bone material and friction between the drill and bone may induce elevated temperature in bone tissue. Temperature above a certain level may seriously harm the tissue, leading to several postoperative complications. The purpose of the current study is to measure and compare temperature in bone drilling using sharp and worn drill. Drilling tests were performed on cortical bone obtained from femoral shaft of a cow. A parametric study was conducted to quantify bone temperature using a range of drilling speeds and feed rates using drills having sharp and worn cutting edges with and without cooling environment. The temperature was measured using thermocouples, and wear of the cutting edges of the drill was measured using a scanning profilometer. Experimental results demonstrated lower temperature in bone...

Single Slope Solar Water Still with Enhanced Solar Heating System

This paper experimentally investigates the thermal performance of a conventional solar water still with an enhanced solar heating system in Oman. A number of variables have been considered, including the water depth inside the still and the saline water temperature inlet to the solar still from the preheater solar collector system. A single slope, single effect conventional solar still with a solar preheating unit was constructed and experimentally tested under different Omani weather conditions. The still had been modified to include a preheating solar energy system so that saline water would be preheated before entering the solar still and this preheating would enhance hourly or daily yield of pure water. Different quantities of water in the solar still basin were tested to find the effect of water quantity on the hourly yield and also to assess the thermal efficiency of the still.

Finite Element Modelling of Elastic-Plastic Contact of Rough Surfaces

An improved mathematical elastic-plastic model for the contact of rough surfaces that is based on an accurate finite elements solution of a deformable single asperity and a rigid flat surface is developed to provide dimensionless expressions for the contact area and contact load. This model differs from the existing models, in that it accounts for the level of interference beyond expected failure. The finite element solution is used to define the limits at which failure occurs. The derivation of the contact model is facilitated through the definition of the ultimate-stress asperities that are assumed to be embedded at a critical depth within the actual surface asperities. This model considers a realistic picture of elastic– plastic deformation where elastic, plastic and failure behaviors can occur simultaneously for an asperity. Subsequent comparison of the results for estimating contact area and load using the present model and the earlier methods shows identical results for pure elastic contacts with plasticity index values at about 0.5 but substantial difference for the net elastic-plastic contacts having plasticity index values above 0.8. When plasticity index reaches 6 and beyond the three models predicts similar total contact area and load values and that the contact is purely plastic.

Solution of a Non-Linear Heat Conduction Problem in Automotive Clutch and Brake Systems

This paper investigates the transient solution for a non-linear heat conduction problem in automotive clutch system. The frictional heat generated during clutch disks engagement is known to cause thermoelastic distortion which in turn modifies the contact pressure distribution. The contact boundary condition that defines the area over which the heat is to be generated is also known to change and shift if the engagement process is run long enough. The thermal boundary in this case is time dependent and the problem becomes nonlinear. To account for such boundary condition, a solution methodology is proposed in this paper and tested in the context of a clutch disk sliding between two rigid bodies.Copyright