Junyoung Park

Finite element analysis to optimize forming conditions for lower control arm

Finite element simulations for the press forming of a lower arm are performed using the explicit dynamic finite element method (FEM) code PAM-STAMP. To optimize the press-forming conditions and secure a safe product without any failure, such as fractures and wrinkling, the FEM simulations are coupled with Taguchi’s orthogonal array experiment. Three design variables—the friction coefficient, plastic anisotropy parameter, and blank shape—are selected to be optimized. The numeric simulations reveal that the blank shape is the most important variable, and its modification is most effective in optimizing the press-forming conditions for a lower arm. In addition, the modified blank shape produces a high yield ratio for the in-come coil. The simulation results are confirmed with experimental ones.

AEffects of Impeller Blade Thickness on Performance of a Turbo Blower

This study is concerned with effects of impeller blade thickness on performance of a turbo blower. This turbo blower is developed as an air supply system in 250 kW MCFC system. The turbo blower consists of an impeller, two vaneless diffusers, a vaned diffuser and a volute. The three dimensional, steady state numerical analysis is simultaneously conducted for the impeller, diffuser and volute to investigate the performance of total system. To consider the non-uniform condition in volute inlet due to volute tongue, full diffuser passages are included in the calculation. The results of numerical analysis are validated with experimental results of thin blade thickness. Total pressure ratio, efficiency, slip factor and blade loading are compared in two cases. The slip factor is different in two cases and the comparison of two cases shows a good performance in thin blade thickness in all aspects.

Main factor causing “faster-is-slower” phenomenon during evacuation: rodent experiment and simulation

Understanding crowd flow at bottlenecks is important for preventing accidents in emergencies. In this research, a crowd evacuation passing through a narrow exit connected with guide-walls is analysed using the discrete element method based on physical and psychological modelling in parallel with empirical rodent research. Results of rodent experiment and simulation demonstrate the faster-is-slower (FIS) effect, which is a well-known phenomenon in pedestrian dynamics. As the angle of the guide-walls increases, agents rapidly evacuate the room even though they have low velocity. The increase in this angle causes agents to form lanes. It is validated that ordered agents evacuate expeditiously with relatively low velocity despite expectations to the contrary. The extracted experimental and simulation data strongly suggest that the agents’ standard deviation of velocity can be a key factor causing the FIS effect. It is found that the FIS effect can be eliminated by controlling the standard deviation.

An economical method to measure granular flow in a hopper using a commercial digital camcorder and particle image velocimetry

Abstract Numerous methods including X-ray imaging, magnetic resonance imaging, and particle image velocimetry (PIV) have been suggested to measure the flow of particles. However, most methods usually require costly equipment. In this study, we measure the velocities of particles in a hopper using a PIV system with open source software and an inexpensive commercial digital camcorder. The proposed system shows high accuracy. The measurement error is less than .5%, and the error of recording speed (frames per second) is about 2.5%. This error rate is negligible because it is lower than the experimental error. Consequently, our findings demonstrate that a PIV system with sufficient accuracy to measure particle flow in a hopper can be developed with a small budget.

Enhancement of an Optimization-Based Damage Detection Technique

Various structural health monitoring (SHM) techniques utilizing vibration signals have been developed for identification of damages in a structure. Many of these studies are based on sensitivity analysis, finite element model (FEM) updating, and optimization techniques. FEM updating technique is one of the major techniques that iteratively minimizes the difference between the modal parameters measured from the real structure and the corresponding analytical predictions. This method would be more beneficial for typical continuous systems such as beams, plates, and shells which cannot be reasonably discretized. One of the drawbacks of these techniques is the large number of unknowns to be estimated. These techniques in the literature that use FEM updating to estimate perturbed parameters for all elements in the model can be time-consuming and ill-conditioned, even for relatively simple structures. The technique also requires a full and accurate finite element model for each monitored structure.A new method to identify damages in a structure using embedded sensitivity functions and optimization algorithms is described and its performance is demonstrated in this paper. The perturbed frequency response function (FRF) is calculated using Taylor series expansion in terms of the baseline system and the embedded sensitivity functions. The optimization process minimizes the difference between the measured FRFs of the damaged structure and the perturbed FRFs calculated from the baseline structure. Structural damages are often characterized by changes in mechanical parameters such as stiffness, mass, and damping. Embedded sensitivity functions offer a means of determining the path that is followed from the baseline to the perturbed FRF of the structure.The robustness and efficiency of suggested structural health monitoring method are discussed in this paper. The accuracy of damage estimation is investigated with respect to various types and values of damages, objective functions, frequency ranges, scale factors, procedures, and noise levels. Precise measurement and monitoring of vibration signals are critical for accurate detection of the location, type, and level of damage. However, in most practical mechanical systems, vibration tests may result in noise on the input or output measurements. Noise on the measurement affects the accuracy of the FRFs and identification of damages in a structure. Based on the results of the study, several parameters and factors in the optimization process and structural dynamics are suggested to enhance the efficiency and robustness of damage identification process.It is shown that the iteration number of the optimization process is significantly reduced. Accurate estimate of damages can be obtained within the range of 2∼5% error with various enhancements applied to the technique.Copyright

200kW Turbine Development for Organic Rankine Cycle System

This paper presents the process of turbine development for Organic Rankine Cycle(ORC) system. Development of turbine for ORC system is hot issue in the electric generation market due to the characteristic of organic refrigerant which the evaporate temperature is lower than general refrigerant. Recently, the industry have an interest about ORC turbine development in Korea, and they presented numerous research results. In developing the turbine, several processes can be considered. However, there was few document about ORC turbine development because of the trade secret. This paper can be used as a reference in developing ORC turbine.