Applied Mechanics and Materials Vols. 110-116

Abstract: 2D fluid flow around a circular cylinder is numerically studied where the input flow is oscillating at different values of forcing frequency. The input section of domain has constant horizontal velocity except a region in the middle of this section which has an oscillating transverse velocity. The uniform fluid flow around an oscillating circular cylinder is also studied. The results are obtained for these two cases and compared with other experimental and numerical results. A comparison of the numerical results with the experimental data indicates that the 2D simulation has excellent agreement with literature. The effect of oscillation on the flow field, wake pattern and drag coefficient has been studied. The results show that the lift coefficient diagram is pure sinusoidal for forcing frequency f=0.85 and is lied in the lock-in zone. The mean drag coefficient has a maximum value in this forcing frequency.

Abstract: In this work comparison of hybrid rapid moulds (prepared with three dimensional printing shells supported with dry, green and molasses sand) have been made for techno-economic analysis, for zinc (Zn) alloy shell casting. The comparison has been made on the basis of mechanical properties and dimensional accuracy. Time-temperature curves have been drawn to understand solidification of molten Zn alloy in hybrid moulds of different thicknesses. The results of study suggest that it is feasible to reduce shell wall thickness of hybrid mould cavity from recommended 12mm to 1mm. All castings prepared are consistent with the permissible range of IT grades and are acceptable as per ISO standard UNI EN 20286-1 (1995). Further green sand based hybrid prototypes at 3mm shell wall thickness, shows better dimensional accuracy and mechanical properties.

Abstract: The paper introduces two ad-hoc experimental models that emulate the real semi-automated and fully automated workstations of the die-casting production company. The simulation study aims to analyze behavior over time of both models. The intention of the paper is to show that the simulation can be used as a tool to support a decision-making process. It also presents effective approach how to forecast the real system performance.

Abstract: The present study investigated the effect of copper and nickel together on ductile iron. Ductile iron was produced by the sandwich method using induction furnace installed at local commercial foundry. Heats without copper & nickel and with copper 0.5 wt% and 1.0 wt% nickel in combination were made. Tensile samples were machined from Y Block castings. Tensile test was performed to find out the effect of copper and nickel together on tensile strength of ductile iron. Effect of austempering heat treatment was also studied to find out the effect of copper and nickel in combination on tensile strength. The samples were austenitized at 900 oC for one hour and austempered at 270 oC and 370 oC. It was found that with the addition of copper and nickel the tensile strength of ductile iron increased. The tensile strength was more than double when the samples were subjected to austempering heat treatment at 270°C.

Abstract: The main aim of suspension system is to isolate a vehicle body from road irregularities in order to maximize passenger ride comfort and retain continuous road wheel contact in order to provide road holding. The aim of the work described in the paper was to illustrate the application of fuzzy logic technique to the control of a continuously damping automotive suspension system. The ride comfort is improved by means of the reduction of the body acceleration caused by the car body when road disturbances from smooth road and real road roughness. The paper describes also the model and controller used in the study and discusses the vehicle response results obtained from a range of road input simulations. In the conclusion, a comparison of active suspension fuzzy control and Proportional Integration derivative (PID) control is shown using MATLAB simulations.

Abstract: In present work, an exergy based thermoeconomic optimization is applied to an actual cascade refrigeration system. The advantage of using exergy method of thermoeconomic optimization is that various elements of the system i.e. condenser, evaporator, compressor and cascade condenser can be optimized separately. A simplified cost minimization methodology based on thermoeconomic concept is applied to calculate the economic costs of all internal flows and products of the system by formulating thermoeconomic cost balance. Once these costs are determined, the system is thermoeconomically evaluated to identify the effects of the design variables on cost of the flows and products. This enables to suggest changes of the design variables that would make the overall system cost effective. Finally, an approximate optimum design configuration is obtained. The result shows that the increase in Coefficient of Performance and exergetic efficiency of the system by 13.76% and 16.20% respectively. The cost of the product and total investment cost are decreased by 19.71% and 19.18% respectively. This shows significant improvement in system performance as well as reduction in the cost of product and total investment cost. The reduction in cost and improvement in performance suggest the commercial acceptability of the cascade refrigeration system in a best efficient way.

Abstract: According to the structure features of gear system in co-rotating twin screw extruder, the model of the gear system is built, and multi-objective optimization genetic approach based on the Pareto-rank is proposed to optimize the parameters of the gear system. The advanced optimal design method for the gear unit in co-rotating twin screw extruder is studied. A typical gear system in co-rotating twin screw extruder is designed, and the results show that the gear system meets the requirements in all aspects. This design method of the gear system is synthetic optimization for the gear system in co-rotating twin screw extruder.

Abstract: Modern solid-propellant rocket motors (SRM) are laden with aluminum powder to increase the specific impulse. In SRM chamber, on the one hand, aluminum droplets evaporate and burn to form alumina smoke, on the other hand, the alumina smoke agglomerates to droplets as droplets collide with each other. The agglomeration model is employed to simulate the burning droplets. And breakup model also used. To avoid complex reaction theory, the article solves the mass, momentum and heat equations of disperse and continuity phases to simulate the chemic reaction. Results showed that burning efficiency and agglomeration of droplet varied by different initial diameters, and the temperature as well as smoke concentration also changed, especially in nozzle inlet.

Abstract: The entrance region flow of a Casson fluid in a tube has been investigated numerically without making prior assumptions on the form of velocity profile within the boundary layer region, which is determined by a cross sectional integration of the momentum differential equation for a given distance from the channel entrance. Using the macroscopic mass and momentum balance equations, the thickness of the core, the entrance length, and the pressure drop have been obtained at each cross section of the entrance region of the tube for specific values of Casson number.

Abstract: Reaction control subsystem (RCS) is an onboard satellite propulsion system used to provide required thrusting for orbit raising, orbit maintenance, and attitude control etc.. High pressure flow with high temperature could be generated in a chamber by chemical reactions or other power resources then expelled through a convergent-divergent nozzle to obtain thrust. In order to optimize the thrusting performance, numerical simulation is an efficient method to study the physics and parameters in design phase. In the current study, a hybrid method coupled continuum and particle methods is proposed to simulate flows involving continuum and rarefied regions. The Navier-Stokes (NS) solver named UNIC is developed by Chen and his coworkers. It employs the cell-centered finite-volume method with a hybrid 2D/3D unstructured-grid topology. The proposed particle code named Parallel DSMC Code (PDSC) is a parallelized solver based on the well-known Direct Simulation of Monte Carlo (DSMC) method, which was proposed by Bird in 1976. The physical domain is decomposed into several regimes and each sub-domain executes the serial DSMC code at different processor for speeding up the computing. A practical cold gas thruster with different chamber pressures is simulated by using this hybrid code to study the potential malfunction of the pressure regulator. Then the curve-fitting thrusting equation can be referred to satellite control operations.