Year:2001 | Volume:35 | Issue:1 (71)|Papers Count:9

In this paper, the periodic solution for certain nonlinear third order differential equation is studied and using implicit function theorem the existence of one periodic solution is proved. Then in the particular cases certain equations are solved with graphical methods' and approximation. It's interesting to note that periodic solution of the. above equation has a vast application in engineering and physics. We only used the mathematical model for brakes of heavy vehicle.

A semi-infinite transversely isotropic linear elastic medium due to vertical moving point load is analysed. Using modified Lekhnitskii potential functions introduced by Eskandari Ghadi and Noorzad, the equation of motion are uncoupled and solved using the Fourier integral transform. This way, the displacements and stresses are obtained in Fourier space. These functions are transformed into the real space using the inverse integral transform. Finally, displacements and stresses due to point load are obtained by applying the Fourier series. These results are numerically evaluated and graphically shown. The excellent agreement between the existing results in literature and the obtained ones in this paper for isotropic material validates the accuracy of the numerical evaluation.

Every year many bridges around the world fail most of them due to scouring at their piers and abutments. Collapse of bridges cause heavy damage, and therefore, study on the control of scouring at the bridge site plays an important rule in bridge design.In this study application of half collar on rectangular piers is proposed as a simple method to control scouring. Experiments show that installation of a small half collar with a width equal to half of the pier width, at 10% of flow depth under the streambed level could reduce depth of scour hole by 40%. Experiments also show that a larger collar with a width equal to the pier width when installed at streambed level reduces the scour hole by 80%. Double collar was also tested. It was found that a small collar at 10% of depth above another small collar at the bed level increases its efficiency by more than 16%.

Based on principles of virtual work, a general method of deriving stiffness matrix of non-prismatic curved Eluer- Bemoulli beam element is presented. Exact .satisfaction of equilibrium equations in any interior point of the element is the main characteristic of this method. Presented relations could be transformed based on the super-parametric formulation via piecewise mapping of element axis. This coordinate transformation helps to generate elements of complicated geometry and common to use. Various numerical examples proves that the results obtained by this method are compatible/comparable in both efficiency and economy with those obtained by other proposed formulations, if any.

The hydrogenated oils differ chemically from natural oils to a large extent. These hydrogenated products contain glycerides that may consist partially of positional and geometrical isomers. Trans fatty acids (t-FA) are geometrical isomers of unsaturated fatty acids. Epidemiological studies have shown a significant correlation between trans fatty acid intake and coronary heart disease. The aim of this study is to adjust the hydrogenation parameters to reduce the trans isomers formation.

Heat transfer in laminar flow in the thermal entry region of a semicircular duct with internally longitudinal fins has been studied. The fluid is the oil with Pr>5; therefore, it is assumed that the velocity profile is fully developed and the temperature profile is developing. As the physical properties of oil vary considerably with temperature, therefore, variations of physical properties with temperature have been considered. The momentum and energy equations have been solved numerically for different geometries, obtained by varying the number and heights of the fins. The results such obtained are compared with other research works and the agreement is bound to be very good.

In this paper, the exact stiffness matrix of curved beams with non-uniform cross section is derived using direct method. The considered element has two nodes and twelve degrees of freedom with three forces and three moments applied on each node. The effect where the shear center .and center of area do not coincide is considered in this element. The cross sections across the beam are deformed by bending, torsion, axial and shear loads. The curve representing center of area can have any curvature in the space and the cross section properties may change arbitrarily along it. The stiffness of three kinds of beams have been determined by this method. In one type the results have been compared with previous works and theoretical analyses. Finally it has been .shown that the determined stiffness matrix is exact and all kinds of beams can be analyzed by this method.

Damage detection in flexible structures is a research field and an industrial favorite. If damages in structures, air crafts and ships are not detected and repaired, they will possibly collapse. Damage detection in flexible structures using vibration signals and in particular modal test data is the most suitable method. This method is in fact an NOT technique. In this we will present an analytical method for damage detection in .undamped flexible structures using modal data (natural frequencies. and mode shapes). Reviewing past theories, eigenvalue and igenmode, sensitivity equations are used to derive a system of equations .relating the shifts in natural frequencies/mode-shapes to elemental physical parameters. Damage detection is then carried out by solving the extracted system of equations. Also, modal expansion and Nelson method are examined and the better method of solving for eigenmode perturbation is chosen. It is recommended that in solving for repeated eigenmode perturbation with generalized inverse techniques, orthogonally condition between theoretical mode shapes must be satisfied. The presented mathematical relations are applicable for trusses, beams and frames but the principles of the theory is general. Finally an experimental investigation is carried out and the position of a crack in a frame with this theory detected.

The objective of this study is to develop an integrated simulation model in a large complex casting system to assess existing system status and to introduce a set of optimizing alternatives. To achieve the above objective, visual SLAM and AWESIM, one of the most advanced simulation language in the world and a design of experiment methodology were utilized. The detailed conceptual models in formats of schematic diagrams, process flow charts and logical charts and collected data related to processes, operations, maintenance, repairs and quality control allowed creation of the infrastructure and development of the integrated simulation model. The integrated simulation model was verified and validated by structured analysis and t-test. Furthermore, the structures and findings of the simulation model was verified and accredited by both industrial engineering department and production engineers and managers of the casting system. An important feature of this study is integration of design of experiments with the simulation model. Moreover, a unique design of experiment is introduced to identify the impacts of various alternatives on production level Consequently, integration of the simulation model and design of experiments developed a set of optimizing alternatives for various situations. The unique features of this study are four folds. First, the integrated approach allows modeling of all processes, operations, repairs, maintenance and quality control activities. Second, managers and decision-makers can easily use the rule base of the simulation to assess various alternatives. Third, optimum conditions for various production setting and the required upgrading methods and alter mechanisms are introduced though integration of simulation and design of experiments. Finally, the simulation model is verified, validated and accredited and is composed of all local and global processes of the casting system. Therefore, it may by used for strategic planning and system's capacity development and consequently may result in billions of Dollars of profitability, presently, the integrated simulation model is being implemented at the casting system.