Papers by Author: Young Jin Choi

Abstract: On the human-rifle system, the human body is affected by the firing impact. The firing impact will reduce the firing accuracy and change the initial shooting posture. Therefore the study of biomechanical characteristics using human-rifle modeling and numerical investigation is needed. The muscle-skeleton model was developed by the finite element method using beam and spar elements. In this study, a structural analysis has been performed in order to investigate the human body impact by firing a 5.56mm small caliber machine gun. The firing experiments with a standing shooting posture were performed to verify analytical results. The result of this study shows analytical displacements of the human-rifle system and experimental displacements of real firing. In the results, the analytical displacement on the human body is presented.

Abstract: During fuel irradiation tests of material and fuel rods, all parts of cylindrical shells with multiple holes act as heat sources due to fission heat and γ-flux. The thermal stress is induced by a temperature difference among the heat sources. In this study, the thermal stress of the cylindrical structure is minimized by using an optimization method about the geometric variables. The circular shapes of the multi-specimens are investigated. For the thermal analysis of the structure, the finite element method code, ANSYS 8.1 is used. A sub-problem approximation method is used for the structural design optimization.

Abstract: The foot plays an important role in supporting the body and keeping body balance. An abnormal walking habit breaks the balance of the human body as well as the function of the foot. The foot orthotics which is designed to consider biomechanics effectively distributes the load of the human body on the sole of the foot. In this paper, gait analysis is performed for subjects wearing the orthotics. In this study, three male subjects were selected. The experimental apparatus consists of a plantar pressure analysis system and digital EMG system. The gait characteristics are simulated by ADAMS/LifeMOD. The COP (Center of Pressure), EMG and ground reaction force were investigated. As a result of gait analysis, the path of COP was improved and muscle activities were decreased with orthotics on the abnormal walking subjects.

Abstract: A fuel channel, which is the major structure of a nuclear reactor, is excited by the flow of cooling water during the operation of the nuclear reactor. This flow of cooling water can cause excessive vibration of the structure by the resonance. So, in the design process of a nuclear structure, the exact evaluation of the effect of water to modal characteristics and stiffness characteristics is very important to generate an exact analysis model. In this study, the effect of water height for modal characterisics of the fuel channel is investigated and the stiffness evaluation of that is conducted using the modal test results.

Abstract: The combat car used the heavy duty diesel engine must have a large output for maintaining excellent mobility. The compacted graphite iron (CGI) is a material currently under study for the heavy duty diesel engine demanded for high torque, durability, stiffness, fatigue. In this study, three dimensional finite element model of a heavy-duty diesel engine was developed to conduct the stress analysis by using property of CGI. The use of CGI property on the FE model was expected to result in improved distribution of distortions and stresses. The loading conditions of engine are assembly load and operational gas load.

Abstract: The hit rate is affected by the shooting impact of the human-rifle system. The impact response of the human-rifle system is determined mainly by the geometrical parameters and contact boundary conditions. In this study, the height and weight of the considered human model are 170 cm and 60 kg, as these parameters mirror 50 per cent of Korean males in their twenties. The rifle model is applied on the K-2. The impact path analysis of three typical shooting postures: the standing, kneeling and prone shooting postures is performed with experimental impulse-time history during a shooting test. The biomechanical response such as impact transfer path, force history and displacement history are investigated.

Abstract: AFO is a device, which is usually recommended for hemiplegics to help their pathologic gait. To date, no good engineering guidance is available. We analyze mechanical characteristics of AFO and evaluate structural stability effect of thickness of ankle foot orthosis (AFO). The study is to provide a guidance to make a functional AFO. Basic material characteristics such as Young’s modulus and Possion’s ratio were measured through material tests. Finite element models were made and analyzed based on various shapes and gait analysis. Young’s modulus of polypropylene is 1.15 GPa and Possion’s ratio is 0.35. Rigidity of AFO is more affected by the ankle width than the thickness of ankle area. The strain calculated by finite element analysis (FEA) in the neck area is twice as much as experimental results but the both of their trend show similar pattern. AFO was studied through its structural and functional analysis. Experimental structural analysis and FEA were made and compared.

Abstract: This study is conducted in order to estimate the structural characteristics for inlet port of air breathing engine under flight condition at 12 ~ 15 km height and Mach Number 2 ~ 4. Inlet port of air breathing engine is heated up from 307 oC to 427 oC, so that is reached plastic zone partially. The material properties at high temperature such as young’s modulus, thermal expansion coefficients and thermal conductivity are applied to the analysis. The transient temperature and stress analysis are performed by the finite element method using nonlinear commercial code ABAQUS. The analysis is performed for the two materials, Titanium alloy and AISI4130 Steel and two FEM element type, shell and solid, to select preliminary design model for flight condition. Thermal boundary conditions are applied at inlet port until 5 s, and these conditions are maintained until 150 s. The results of the analysis recommend tendency of thermal stress and temperature contour. This study is expected useful to select the structural material and to determine shape of air inlet port of air breathing engine which satisfied the structural design safety.

Abstract: The laminated composite structures applied to the wing and the speed brake of an aircraft or the turbine blade of a compressor. These structures may be impacted by birds and hails during operation. They may also be impacted by drop of a tool during manufacture or repair. Unlike high velocity impact damage, which can be easily found by the naked eye, the damage due to low velocity impact may be difficult to detect. Damage which is not detected may cause failure of a structure and result in damage propagation. Growth of damage means reduction of stiffness on the structure. So, exact prediction of damage caused by a low velocity impact is very important in order to guard against sudden failure of the structure. In this study, modified delamination failure criterion has suggested in order to predict the failure behavior of a composite plate subjected to low-velocity impact. The criterion includes the assumption which is matrix cracking mode causes delamination failure. Predicted damage using supposed delamination criterion is similar to experiment results.

Abstract: The hot gas casing of the gas turbine has operated in high temperatures and thermal gradients. The structure safety of hot gas casing will be highly depend on the thermal stress. In this paper, flow and thermal stress analysis of the hot gas casing is carried out using ANSYS program. The obtained temperature data by flow analysis of hot gas casing is applied to the load condition of the thermal analysis. The thermal stress analysis is carried out the elastic-plasticity analysis. The pressure, temperature and velocity of the flow and thermal stress of the hot gas casing are presented