Robot manipulators are highly nonlinear system with multi-inputs multi-outputs, and various control methods for the robot manipulators have been developed to acquire good trajectory tracking performance and improve the system stability lately. The computed torque controller has nonlinear feedforward control elements and so it is very effective to control robot manipulators. If the control gains of the computed torque controller is adjusted according the payload, then more precise control performance is attained. This paper extends the conventional computed torque controller in the joint space to the Cartesian space, and optimize the control gains for some specified payloads in both joint and Cartesian spaces using genetic algorithms. Also a neural network is employed to have proper control gains for arbitrary payloads using generalization properties of the neural network. Computer simulation results show that the proposed control system for robot manipulators has excellent performance in various conditions.
This paper presents the theoretical analysis for the flow driven by surface tension and gravity force in an inclined circular tube. The previously developing equation for Power-Law model is a simple ordinary differential type. A governing equation is developed for describing the displacement of a non-Newtonian fluid(Casson model) that continuously flows into a circular tube by surface tension, which represents a second-order, nonlinear, non-homogeneous, and ordinary differential form. It was found that the theoretical predictions of the governing equation were in good agreement with the results for considering the Newtonian model.
In this study, velocity distribution characteristics by location and uniformity according to exit straight length in a 180° mixed pipes were numerically analyzed using RSM (Reynolds Stress Model) turbulent model by changing various flow parameters such as working fluids, inlet air velocity etc. As a result of it, the working fluids characteristics was highly indicated by the viscous force difference, the maximum velocity points according to main pipe’s inlet velocity were indicated when 90° sectional location was distributed at X/D=0.5~0.6 region and 180° sectional location was distributed at Y/D=0.5 region. And the flow characteristics according to branch pipe’s inlet velocity when 90° sectional location was distributed at X/D=0.4~0.6 region and 180° sectional location was distributed at Y/D=0.5 region. Based on the results that the most stable exit straight length in flow uniformity was indicated at L/D=25~30 region, 40D is suggested as the effective measurement distance in the straight pipe downstream curved pipe of mixed pipe.
Recently magnesium alloy sheet has been used as a lightweight material in transportation area. Warm forming is a forming method that improves formability and reduces springback. The magnesium alloy sheet has a characteristic that large difference of flow stress increases depending on strain rate at high temperature. These characteristics cause low dimensional accuracy of formed products. In this study, experiments were performed on the 2D-draw bending with respect to the temperature and forming speed in order to investigate the effects of strain rate and temperature. It was found that as the temperature increases, spinrgback of 2D-draw bending decreased and formability of AZ31B increased. Additionally, the effect of the punch speed was investigated. At 250°C, as the punch speed increased, the springback of 2D-draw bending decreased.
The wastegate valve regulates the maximum boost pressure inside the turbocharger to prevent damage to the engine and turbocharger which can occur from overload. However, even though the opening and closing behaviors of the valve should be controlled accurately, thermal deformations of the turbocharger system can lead to excessive distortion of the actuator rod, which can have a significant effect on the turbocharger performance. In this study, thermal deformation analysis of the turbocharger assembly has been analyzed through finite element analysis under operation condition. The result shows that the deformation in the turbine housing is relatively large and actuator rod is bent by thermal load. It causes rotational deformation at the wastegate valve face connected to the rod. And it is efficient to increase the stiffness of the EWGA rod to minimize the rotational deformation of the valve face. It means that the actuator rod should be placed in a position close to the center of the turbocharger to minimize the length of the rod that has the greatest effect on stiffness enhancement.
SUS hexagonal bar have been widely used to manufacture the hexagonal bolt/nut, adapter and fittings. Raw SUS circular bar is used to make SUS hexagonal bar using drawing system. The purpose of this study is to investigate the characteristics, for instance, such as stress, strain and reduction ratio of area for bar. As the results, it was confirmed that the maximum stresses were occurred at edge of hexagonal bar, thus it could be worked as residual stress of hexagonal bar. The phenomenon of spring back was almost no found in all parts of hexagonal bar. Furthermore it showed that the reduction ratios of area were about mean 26% when SUS circular bar was changed to SUS hexagonal bar in this study.
In this paper, the boom of a 30m class refracted insulation with outrigger on aerial elevating work platform is modeled as 3D CAD program of CATIA. The static and dynamic analyses are performed by using ANSYS and ADAMS programs, respectively. The refracted insulation boom uses acetal and the composite boom for insulation. And the composite insulation boom is modeled by using ACP (Ansys Composite Prepost) of ANSYS program. In order to analyze the durability of refracted insulation boom, the static analysis is performed and each analyzed part is stored as =MNF-type flexible body model. The dynamic analysis is performed with ADAMS by using the flexible model. As the result, these analyzes clarify the structural stability and dynamic durability (hot spot) of the refracted insulation boom.
The flow characteristics around the vertical wall with the flap were visualized in the water channel using PIV. And the effect of flap angle change was investigated to see how quickly the spreading can be prevented and confined if oil spill occurs at sea. As a result, the fluid in the front of the vertical wall flows constantly, Nearing a boundary layer on the vertical wall, and a flow separation phenomenon occurs. Thereafter, flow loss or depth loss to the bottom of the vertical wall was confirmed. Also, it was observed that irregular reverse circulation flow occurred due to flap angle change and pressure gradient at the back of vertical wall. In this study, it was analyzed that it is most effective at 20 degrees angle. In the future, it is necessary to confine the flow characteristics of PIV and CFD by assuming that there is a double vertical wall in which oil having a lower specific gravity than water is trapped in the oil fence.
In this study, to reduce the weight of cross member assembly for small truck. In order to optimize the design of the cross member structure by changing the equation into the rivet coupling method, The size and the hole spacing of the large sheet plate, the rivet hole size of the large sheet plate, In the structural analysis, we looked at what was going to happen, and the tensile, shear The load test was carried out to investigate the damage caused by the maximum load acting on the rivet. Riveting work, but to improve productivity, we developed automated riveting device using robot To reduce the number of workers, reduce jig transfer and installation time, and reduce load factor. To produce the maximum output of the product.
To understand the effect of high pressure on nitrogen oxides (NOx) formation in water added methane flames, opposed nonpremixed Water-methane/air (H2O-CH4/air) flames are numerically studied with high initial pressure. With GRI 3.0 detailed kinetic mechanism, NOx emissions are predicted for various strain rates. Due to high pressure, the chemical species are distributed in a narrow region, which means the thickness of the flame is thin. This can be clearly seen with high strain rate. Elevated pressure increases maximum temperature of flames which results in increased NOx emission. Even with elevated initial pressure, NOx emissions for H2O added methane flames are significantly decreased compare to pure methane flame. In addition, increased strain rate is also significant factor for decreasing NOx emission. With detailed rate of production analysis, in case of high pressure, it is confirmed that NO2 pathway is the most dominant reaction pathway than any other pathways.
The structural performance of a vehicle can be evaluated by the static and dynamic structural analyses which predict the amount of deformation, stiffness. And the static analysis should be done first. Another important aspect to be considered in the design process is crashworthiness, because a structurally sturdy vehicle body may be overdesigned with excessive strength and durability standards. The ideal condition of a body structure is to absorb impact load at a certain level of local deformation, to distribute the load to each structure adequately, and to prevent excessive stress concentration and deformation. This paper is the result of the consideration of automotive body, bending and torsional stiffness for structure stiffness estimation of automotive body through finite element modeling.
Indirect evaporative coolers (IECs) are widely used for cooling of outdoor air in building air-conditioning and for cooling of indoor air in data center air-conditioning. However, for each case, the inlet air temperature and humidity condition to IEC are different, which may yield different cooling efficiency. In this study, tests were conducted at the two air conditions using two IEC samples having different channel pitch (3 mm × 5 mm, 5 mm × 5 mm). Results showed that the efficiencies of the 3 mm × 5 mm sample were 12~32% larger than those of the 5 mm × 5 mm sample due to 25% larger heat transfer area and the usage of smaller diameter channel. The efficiency was 10% larger at the data center condition than at the building condition. The reason may be attributed to a larger absolute humidity difference between the liquid film and the air at the data center condition. At the same air velocity, the pressure drops at the wet channel were 64~128% larger than those at the dry channel due to the presence of liquid film at the wet channel. Comparison of the data with predictions by the analytical model revealed that both the efficiency and the pressure drop were over-predicted. Possible reason may be the simplification of the channel geometry and the assumption of fully developed flow, which may be improved in the future.
Most structures require high reliability to ensure safety and soundness. The materials used for these structures are not only defective in the manufacturing process and construction process, but also cause generation and progress of defects due to operation of various complex use environments. In order to improve the reliability of the structure, it is very important to detect and estimate the defect size. The method of evaluating these defects without damaging the structure is a non-destructive method. In this paper, an aluminum probe of AC potential drop(ACPD) method is applied to the evaluation of two-dimensional artificial defects in ferromagnetic materials. Since the potential drop of the defect end is larger than that of the sound area, the defect can be detected and its position can be clearly confirmed, and the potential drops are changed according to the depth of the defect. The potential drop ratio (Vjmax/Vs) of the defective area has a large value for the defect. The relationship between the potential drop ratio (Vjmax/Vs) of 10 kHz and the defect depth can reduce the error in predicting the depth.
The effect of inclination angle and attack angle on heat transfer enhancement of trapezoidal vortex generator was numerically investigated. The commercial package STAR-CCM+ was utilized to analyze the heat transfer and flow characteristics with various inclination and attack angle of vortex generator. The result shows that the optimum inclination angles are α =30°~40° in terms of the heat transfer and pressure drop. At more than 40° of inclination angle, the transverse vortex is dominant, so that the pressure drop is severe and the heat transfer is reduced. As the attack angle is increased, the transverse vortex is reduced, so that the pressure drop is improved. The optimum attack angle is β =30° because the heat transfer performance is maintained. However, more than 30° of attack angle, the heat transfer is decreasing.
In this study, the cooling capacity and the pressure drop of a condenser for 10kW refrigerator unit were experimentally investigated. The performance characteristics of the condenser was studied by changing the fin shape(4 types), fin pitch(5 types), tube row(4 types) and air flow rate(6 types), using the calorimeter. The optimum heat exchanger specifications were selected by comparing the capacity and the pressure drop of the condenser. In order to select the heat exchanger suitable for the condenser for 10kW refrigerator unit, both the cooling capacity and the pressure drop should be considered. From the condenser performance test by pin type, the wavy pin was selected. The optimal performance of the condenser for 10kW refrigerator unit was observed at the fin pitch of 3 mm, the tube row of 4 row, and the air flow rate of 90㎥/min.
The purposes of improving air pollution and suggesting energy resources have intensified research on various alternative energy for diesel combustion engines to solve severe environmental influences caused by air pollution. In this study, the applicable possibility of biodiesel and oxygenates (EGBE) was investigated as a cuspy method on decreasing the smoke emission. The smoke emission of blending fuel (biodiesel and EGBE) was reduced in comparison with commercial diesel fuel and it was reduced almost 63% at 2000 rpm, full load. But torque and brake specific energy fuel consumption rate didn't have any large changes. Also, the effectiveness of exhaust gas recirculation (EGR) for the reduction of NOx emission has been investigated. It was shown that simultaneous reduction of NOx and smoke emission was achieved with biodiesel(90%), oxygenates (10%) and cooled EGR rates (10%) in an IDI diesel engine.
Biodiesel is a remarkable alternative fuel for the diesel engine among various countries. Various studies are carried out on the environmental and economic effects as well as the nature of diesel engine fuel biodiesel in the combustion process and emission characteristics. In this study, CRDI diesel engines used diesel fuel and 20 % biodiesel blend fuel (BD 20 %) as fuel, with City-mode exceeding 300 hours. Engine performance and emissions were sampled at one-hour intervals for analysis. The engine was inspected after testing to check the engine parts (valves and injectors). It was concluded that 300 hours of operation using BD 20 % does not cause abnormal deterioration of the engine or abnormal changes in engine power and exhaust gas.
The design and analysis of the rigidity and deformation of the vehicle body are basically performed in two forms. First, the relative response of components separated from a parent system or connected as a model of a subsystem is examined. Second, the entire model is used to consider the absolute response of the components to the externally transmitted vehicle service load, which is defined as that of the entire vehicle body system. In this paper, we propose the finite element modeling for the structural design of the car body. First, we will explain the simple finite element modeling of the car body, explain the method of formulating the stiffness of the joint, and finally the shell element. The proposed finite element modeling is proposed. By applying the proposal, it is possible to propose finite element modeling of all medium and large passenger cars less than 3 tons.
In this study, the cooling and heating amount, temperature, flow rate of turbine type heat meter for water source heat-pump system were experimentally investigated at the standard operating conditions. The obtained cooling and heating capacity from the heat meter were deviated within 5.0%, 3.8% comparing with the precise values calculated from an accredited test facility. Even though the accumulated cooling and heating amount values of the heat meter had a small difference comparing with the precise values, the temperatures of heat meter showed greatly different values comparing with the precise temperature. Therefore, it is highly recommended to develop the heat meter which is appropriate for the water source heat pump systems.
The study conducted finite element analysis in advance to understand the natural frequency, con-ducted static structural analysis and analyzed stress behavior occurring on the boundary of wheel and rail when passing the straight line and curve line. According to the FEA, the wheel had natural frequency of 1st mode 238.4Hz to 10th mode 1,320Hz, and the rail had natural frequency of 457.4Hz to 619.7Hz. When looking at the correlated frequency range, the natural frequency of 4th~6th mode of wheel and 3rd~9th mode of rail track were correlated. As for the result of stress behavior translation occurring on the boundary of wheel and track, it was 53.4MPa when passing the curve line, which was 16MPa higher than when passing the straight line.