Applied Mechanics and Materials Vol. 786

Abstract: In the torque converter, a damper with a piecewise-linear spring is used to reduce the forced vibration, and the subharmonic vibration occurs when the spring restoring torque characteristics approach the switching point. This research analyzed the effect of stiffness ratio between the neighboring piecewise-linear springs on the occurrence of the subharmonic nonlinear vibration in automatic transmission powertrain. The powertrain is modeled with multi degree-of-freedom nonlinear system as an actual vehicle. The result shows higher value of the stiffness ratio between the neighboring springs creates larger value of the subharmonic vibration.

Abstract: To this date, there were numerous studies that investigate the prevalence of work related musculoskeletal problems related to vibration. This review paper discuss recent studies related to subjective and objective assessment among workers around the world. The two main objectives of this review are: to examine published subjective and objective assessment related to vibration among workers and to extract and comprehend the detailed process of each assessment. Thirteen relevant studies were identified and chosen from electronic databases. “Vibration”, “musculoskeletal problem”, “worker”, and “subjective and objective measures” were the keywords search terms for this review paper. Past studies demonstrated various purposes for implementing subjective and objective assessments of vibration effects among industrial and non-industrial workers. It provides better understanding for future researchers and industrial practitioners to deal with vibration issues among workers. Many mixed methodology research that combines subjective and objective assessments among the workers have been applied in the past studies. However, extensive assessment were not covered by many researchers in dealing with vibration issues. Therefore, investigation and evaluation of the vibration exposure at the workplace is necessary because these groups of workers are frequently exposed to vibration in their daily work and thus faced higher risks of vibration related health effects.

Abstract: The prevalence of work related musculoskeletal problems with respect to vibration is prominent. This review paper gather recent studies related to objective assessment among work force from all over the world. The three main objectives of this review are: to analyse published objective assessment related to vibration among the work force; to extract and understand in detail the process of each assessment; and to identify whether or not there is a relationship between each variables. Twenty relevant studies were identified and chosen from electronic databases, dating as far back as 2001. “Vibration”, “musculoskeletal problem”, “worker”, and “objective measures” were the keyword search terms for this paper. Past studies demonstrated various purposes and implementation of objective assessment among the work force in evaluating vibration effects. It provides better understanding for the future researchers and industry to deal with vibration issues among work force. Many objective assessment methods among the work force have been applied in the past studies. However, they are still many concerns found in past studies that need to be investigated in the future studies. Therefore, there is a need to perform and apply different objective assessment for evaluating human vibration issues.

Abstract: It is well known fact that vibrations contribute to excessive wear, fatigue failure and other premature failure of machine components. Thus, various methods have been applied to control these vibrations. One of the commonly used is vibration absorber. The aim of this paper is to explore the potential of epoxy reinforced natural fibers as an alternative material for vibration absorber. Both mechanical properties and dynamic characteristic of the composites are investigated through tensile test and transmissibility test, respectively. Two types of natural fibers were selected for the study; coconut coir and pineapple leaf. The results show that the tensile modulus of composites increases with the increase of fiber content, although the strength was found decreases. This reduction indicates an ineffective stress transfer between the fiber and matrix. From the tensile test result, 20 vol% of pineapple leaf fiber was found to be the optimum fraction, in which afterward was employed for fabrication vibration absorber. Meanwhile, from the transmissibility test, it was noticed that when base excitation increases, the resonance peak and attenuation frequency were changed to the lower value. The fixed-fixed end beam with attached composite vibration absorbers showed that the resonance amplitude of the beam decreased significantly. More absorbers attached on the beam produce better result in attenuating the global structural vibration.

Abstract: CFD modelling of drag reduction agents (also called Flow Improvers) polymer additives dissolved in a newtonian solvent (UTP tap Water) was carried out in a curved conduit, A 7 equation Reynolds stress set of equations was used to simulate this flow. The purpose of this simulation is validate experimental results that show unusual pressure drop behaviour. CFD experiments show that there is pressure build-up near the end of the curved conduit due to severe centrifugal forces produced by the fluid, confirming the validity of the experimental results.

Abstract: Mixing is one of the important processes to the many industries. Fluid mixing process typically involves three phases of fluid in the form of liquids, gases and solids. To obtain a desired type of mixing, one of the devices that can be use is a static mixer. In this study, a perforated plate static mixer with circle grid fractal design with two grades of porosity which are 50% and 75% will introduce. The purpose of implementing the two grades porosity of perforated plate in this study is to determine a performance of the two static mixers. In order to achieve the objective, the simulations of mixing fluid were carried out by using ANSYS CFX software. The simulation was carrying out primarily in cylindrical pipe with insertions of circle grid perforated plate. Three levels of laminar flow had been used which is Reynolds numbers (Re) equal to 100, 200 and 400. The performance of circle grid perforated plate static mixer will be evaluated by determining the Coefficient of Variation (COV). The simulation results also were compared in term of homogeneity level of mixing fluids to the Kenics static mixer. Based on the simulation results, the value of COV at selected plane in pipeline simulated for Kenics static mixer and the two grades porosity of perforated plate at Re = 400 are 0.000703, 0.0247and 0.00427 respectively. Since the values of COV between 0.01 and 0.05 are a reasonable target for many industry applications, the results for new approach of static mixer represent completely homogeneous mixing fluid for this application. Definitely this new approach of circle grid perforated plate with fractal design gave better results because of lower number of inserts and simple design of static mixer.

Abstract: The focus of present study is to investigate the influence of discrete heating by an isothermal heater placed at the inner radius of a vertical annular cylinder containing porous medium between its inner and the outer radius. Finite element method is used to solve the governing partial differential equations by employing 3 noded triangular elements. Darcy model is used to represent the flow behavior inside the porous medium. It is assumed that the thermal non-equilibrium condition exists between the fluid and solid phases of the porous medium. The study is conducted for different lengths of heater corresponding to 20%, 35% and 50% of the total height of the cylinder. It is found that the Nusselt number for fluid, solid phases as well as total Nusselt number initially decreases and the increases along the length of heater.

Abstract: The present study is undertaken to investigate the effect of geometrical and physical parameters on discrete heating of an annular vertical porous cylinder heated isothermally at center portion of inner radius. Finite element method is employed to convert the governing partial differential equations into matrix form of equations by employing 3 noded triangular elements. Darcy model is assumed to represent the flow behavior inside the porous medium. Two temperature model is used to describe energy flow in the medium. The study is conducted for different lengths of heater corresponding to 20%, 35% and 50% of the total height of the cylinder. It is found that the flow pattern for aspect ratio 1 is smoother than that of the 0.5.

Abstract: Wind energy has seen a rapid growth worldwide. Wind turbines are typical devices that convert the kinetic energy of wind into electricity. Researches in the past have proved that Vertical Axis Wind Turbines (VAWTs) are more suitable for urban areas than Horizontal Axis Wind Turbines (HAWTs). In the present design of the VAWT, the power prodused depends on the drag force generated by the individual blades and interactions between them in a rotating configuration. Numerical simulation for the aerodynamics of VAWT with tow different rotors (Three and Foure blades ) having movable vanes are curred out. The For numerical simulation, commercially available computational fluid dynamic (CFD) softwares GAMBIT and FLUENT are used. In this work the Shear Stress Transport (SST) k-ω turbulence model was used which is better than the other turbulence models available as suggested by some researchers. The predicted results show agreement with those reported in the literature for VAWT having different blades designs.

Abstract: Computational Fluid Dynamic (CFD) was used to simulate the injection molding process of a tray. The study focuses on pressure distribution and velocity drop during the injection process. CFD simulation software ANSYS FLUENT 14 was utilized in this study. The melt front pressure in the mold cavity shows that it was affected by the shape of mold cavity and filling stage. The melt front pressure will decrease as the flow move further than the sprue but it will increase rapidly when the mold was about to be fully filled. The slight pressure drop was detected when the molten flow meets the rib of the tray. The velocity of higher injection pressure was greater than the lower injection pressure but the velocity rapidly dropped when the melt front fully filled the cavity. The current predicted flow profile was validated by the experimental results, which demonstrates the excellent capability of the simulation tool in solving injection-molding problems.