Applied Mechanics and Materials Vols. 110-116

Abstract: Foldable structures are very important for the purpose of rapid construction and bridging system. Such structural element can be utilized in disaster relief operations. In the early days, portable structure such as military bridges were made from steel, causing the weight of the structure to be huge, subsequently it will be costly to operate. To overcome these problems, aluminium and metal alloy were introduced to reduce the weight of such structure. Use of composite material such as Carbon Fiber Reinforced Polymer (CFRP) emerges as a lighter alternative being considered to be the primary material for the portable structure. The use of the CFRP as a primary material is due to its high strength to weight ratio, thus make it lighter than steel and other alloy. In this research, a long-span portable structure is analysed and designed using finite element method. Several dynamic simulations are made to test various possible lay-up including use of core in order to increase strength and stiffness of the member. From the trials it can be concluded that with proper design and fabrication, CFRP is capable of carrying the designed dynamic load. Furthermore, use of core layers for top flange can improve the performance of the structure significantly, while use of core to the webs stiffen the webs against buckling and further improve the overall performance of the structure.

Abstract: Accuracy of the net-shape manufacturing such as forging becomes critical as the process depends on many factors. Defect will harm the assembly tend to affect the performance of the part. Therefore, it must be detected and minimized it as soon as the manufacturing begins. Small size and complexity of the part limits the defective part to be assessed. The paper presents an investigation on the defect of the cold embossing pin. In this work, the effect of design and process parameters to the formation of defect was studied using 2-D FE analysis. The defect can be measured based on the incomplete filling of the region from the FE result. The results show that, the FE observations are in good agreement with the experimental result.

Abstract: This paper constructs the bioprosthetic valve leaflets’ parametric model via computer aided design, a series of accurate parameters of the bioproshtetic heart valve, such as such as radius of the sutural ring, height of the supporting stent and inclination of the supporting stent, are determined. Numerical simulation is used to determine the effect of different shape designs and attachment edge fixed ways on the mechanical performance of the bioprosthetic valve leaflet. The dynamic behavior of the valve during diastolic phase is analyzed. The finite element analysis results show that the stress distribution of the ellipsoidal leaflet valve is comparatively reasonable. The ellipsoidal leaflet valve has the following advantages over the cylindrical leaflet valve, lower peak von Mises-stress, smaller stress concentration area, and relatively uniform stress distribution. The different ways of the attachment edge fixed also have a significant effect on the dynamic behavior of the valve. Attachment edge with some degrees of rotation when seamed to the stent can act to reduce the pressure and make the stress distribution reasonable. Reasonable attachment edge fixation may contribute to the long term durability of the valve. This indicates the need to account for the attachment edge seamed way, when manufacturing the bioproshetic heart valve with long term durability. This work is very helpful to manufacture valvular leaflets with reasonable shapes and to prolong the lifetime of the bioprosthetic heart valve.

Abstract: Effects on structure designs on free vibrations of integrated bladed rotor (IBR) have been conducted in this research through finite element simulations. Migration of natural frequencies is characterized through parameter studies considering changes of blade angle and blade thickness on an underlying uniform axis-symmetric rotor. Recurring coupled repeated doublet modes, defined as replica modes, has been observed in this study by characterizing blade’s vibrations in-phase or out-of-phase to disk’s vibrations. Veering and cluster of replica modes’ natural frequencies are observed with respect to the blade design parameters. Fourier content for low frequency replica component is found to be sensitive and tunable to blade angle design, which has implications on forced response of spinning IBR in engineering applications.

Abstract: To speed the domestic research on double pulse motor,and specify the research direction,analyzed the pulse separation device (PSD) of external double pulse motors,classified them according to certain characteristics,expounded research status of domestic double pulse motor,pointed out problems in the study.With the future needs of the missile force,proposed suggestions of future development for domestic research on double pulse motor,and specified the research direction of it.

Abstract: Nowadays, many researchers works in fluid dynamics has been concentrated on determine the suitable turbulent model for better describing the flow structure and heat transfer characteristics in a specific problem, there are a lot of cases which are necessary about designation of an optimized turbulent model. In the present work, a ribbed roughened square duct has been investigated numerically. A two-dimensionally study has been done to evaluate the flow structure, heat transfer and computational efforts of seven turbulent RANS models, contemporaneously. In the Part 1 of this study turbulence models, which are used in these type of problems has been investigated. In the next, advantages of introduced turbulence models has been present and explained. The results of numerical simulations will be presented in the Part 2.

Abstract: In the part 1 of this research, some useful turbulence models presented. In that part advantages of those turbulence models has been gathered. In the next, numerical details and procedure of solution are presented in details. By use of different turbulence models, it has been found that Spallart-Allmaras predicted the lowest value of heat transfer coefficient; in contrast, RSM¹ has projected the more considerable results compared with other models; besides, it has been proven that the two-equation models prominently taken lesser time than RSM model. Eventually, the RNG² model has been introduced as the optimized model of this research; moreover.

Abstract: The purpose of this paper is developing a method for simulation of a cryogenic staged combustion-closed cycle engine. Since, aerospace systems are usually complicated and important; the simulation task becomes extremely important. If the propulsion system of space vehicle is not successfully simulated, then designers must rely on huge tests which are time and money consuming and also dangerous. The mathematical model of the engine includes a set of equations which describe all the system's elements operation. These equations correspond to mass, momentum and energy conservation principles and are simplified to make easy the process of calculations. A Fortran 90 code is developed for this simulation. Comparison of the simulation code with the actual values, demonstrates that the model can accurately predict the behavior of the real engine

Abstract: Journal bearings are widely applied in different rotating machineries. These bearings allow for transmission of large loads at mean speed of rotation. These bearings are susceptible to large amplitude lateral vibration due to self-exited instability which is known as oil whirl or synchronous whirl. This oil whirl depends on many parameters such as oil film thickness, viscosity of lubricant, load on bearing, inertia of fluid etc. out of which oil film thickness plays an important role in operation of Journal bearings. As oil film thickness decreases metal to metal contact occurs this further can damage the journal bearing. So during the operation minimum oil film thickness should be maintained which can avoid the metal to metal contact and further increases the life of bearing. This paper presents a theoretical calculation of oil film thickness and experimental verification of same on journal bearing test rig. Different journal speeds and loads are considered for the analysis.

Abstract: The objective of this paper was to perform a comparative study among multiobjective optimization methods on practical problem by using modeFRONTIER optimization software, to determine the efficiency of each method. In order to measure the effectiveness and competence of each method, the lifting arm problem was chosen from the literature [1]. Two numerical performance metrics and one visual criterion were chosen for qualitative and quantitative comparisons:(1) the variance of solution distribution in the Pareto optimal regions, (2) the ratio between the number of resulting Pareto front members to total numbers fitness function calculations which is denoted by hit rate [2], and lastly (3) graphical representation of the Pareto fronts for discussion. These metrics were chosen to represent the quality, as well as speed of the algorithms by ensuring well extends solutions. The definition of the variance as the sum of the square difference between the distance of each Pareto solutions and the average distance between Pareto solutions, over the total number of Pareto solutions. Comparisons among the results obtained using different algorithms have been performed to verify their performance. The experiments carried out indicate that FMOGA-II obtains remarkable results regarding all metrics used.