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모장오,이영호 한국자동차공학회 2020 International journal of automotive technology Vol.21 No.6
The electronic stability control (ESC) system is a computerized technology that improves vehicle stability by detecting and reducing the loss of traction. The hydraulic control unit for an anti-lock braking system (ABS) or an ESC system in a car includes a hydraulic pump located between the wheel and master cylinder. The function of the hydraulic pump is to allow the brake fluid to return from the wheel to the master cylinder when the ABS or ESC is actuating. This study performs numerical investigations with the aim of predicting the performance of the hydraulic pump by better understanding the dynamic behavior characteristics of the inlet ball under instantaneous fluid forces during the suction cycle and the corresponding flow characteristics under various motor speeds. A fluid-structure interaction (FSI) simulation of the hydraulic pump is conducted under various motor speeds with an unsteady three-dimensional approach considering laminar flow and the user-defined function (UDF). Experimental verification of the simulation results at the standard pump pumping test system of the Mando Corporation in Korea indicates considerable reliability. The findings of this research can provide valuable insights into designing high-efficiency pumps.
모장오,최재혁 한국자동차공학회 2021 International journal of automotive technology Vol.22 No.2
An anti-lock braking system (ABS) is an anti-skid braking system commonly used as a safety feature in vehicles. The hydraulic control unit for the ABS of a vehicle includes a plunger pump between the wheel and master cylinder. This paper presents numerical investigations of the effect of valve shapes on the performance improvement provided by a plunger pump, focusing on two different valve shapes, ball-type and hat-type. Transient laminar flow analyses of plunger pumps with ball and hat-type inlet valves are performed under motor speeds from 1000 to 5000 rpm using the fluid-structure interaction (FSI) and user-defined function (UDF) techniques. An experimental verification of the simulation results for the plunger pump with a ball-type valve was conducted using the standard pump test of the Mando Corporation, South Korea. A comparison of the simulation and experimental results suggests that these are in good agreement. The simulation results indicate that the hat-type valve outperforms the ball-type valve due to a shorter delay in the closing time at the end of the suction cycle. These findings suggest that valve shape has a considerable impact on the performance improvement provided by a plunger pump, providing crucial insights into the future design of high-efficiency pumps.
모장오,이영호 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.1
The objective of this investigation is to clearly understand the aerodynamic characteristics of a small-sized wind turbine of NREL Phase VI, operating with a stall-regulated method using CFD code. Based on this, it is possible to provide turbine designers with the aerodynamic design data to increase efficiency and improve performance in the design phase of future small-sized wind turbine blades. Moreover, a comparison was made between experimental datasets, in order to verify the reliability and validity of the analysis results. The first height in the normal direction from the surface of a rotor blade is about 0.2 mm, and the average value of y+ is about 7 at 7 m/s. The domain is chosen to consist of only two hexahedral mesh regions, namely the interior region, including the wind turbine blade, and the external region excluding the rectangle. The total cell number of the numerical grid is about Ng = 3.0 × 106. Five different inflow velocities, in the range Vin = 7.0-25.1 m/s, are used for the rotor blade calculations. The calculated power coefficient is about 0.35 at a TSR of 5.41, corresponding to 7 m/s, and showed considerably good agreement with the experimental measurements, to within 0.08%. It was observed that the 3-D stall begins to generate near the blade root at a wind speed of 7 m/s. Therefore, root design approaches considering the appropriate selection of the angle of attack and the thickness are very important in order to generate the stall on the blade root. Through a clear understanding of aerodynamic characteristics of a small-sized NREL Phase VI wind turbine, it is expected that this useful aerodynamic data will be made available to designers as guidance in designing stall-regulated wind turbine blades in the development phase of small-sized wind turbine systems in the future.
모장오 한국자동차공학회 2021 International journal of automotive technology Vol.22 No.2
This study investigates the compressible-brake-fluid flow characteristics within an electric parking brake (EPB) caliper during the bleeding cycles, subsequently determines the fundamental cause for reduction in brake-bleeding performance, and suggests a new design for its improvements. Three-dimensional simulation validation of the brake-fluid consumption curve is conducted through the parameter study of the air mass flow and bulk modulus. A numerical approach utilizing a three-phase (air, brake-fluid, and brake-fluid vapor) mixture model and a standard k-ω turbulence model is adopted to investigate the flow field details. Based on the unsteady simulation results and experimental verifications for the current and new models of the nut-spindle of a driving part in the EPB caliper, the primary cause for the reduction in the bleeding performance in the EPB caliper is determined to be the trapped air in the thread gap and in the space between the spindle and nut-spindle. Consequently, the head chamfer effect for the nut spindle is beneficial for removing trapped air and leads to performance improvement of 30.3 %.
Numerical simulation for prediction of aerodynamic noise characteristics on a HAWT of NREL phase VI
모장오,이영호 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.5
The purpose of this study is to numerically predict the characteristics of aerodynamic noise generated from rotating wind turbine blades according to wind speeds using commercial CFD code, FLUENT. The near-field flow around a HAWT of NREL Phase VI is simulated directly by LES, whereas the far-field aerodynamic noise for frequencies below 500 Hz is modeled using FW-H analogy. As there was no experimental noise data, we first compared aerodynamic noise analysis with experimental data. This result showed a difference of power outputs by 0.8% compared with the experimental one with 6.02 kW. Then the characteristics of aerodynamic noise were predicted at a specific location P1 according to IEC 61400-11 international standard. When the wind turbine blades rotate with time, tipvortices occur at the tip of two blades and are generated periodically in a circle. These vortices in the vicinity of the blade tip cause intense aerodynamic noise due to the tip vortex-trailing edge interaction by local cross flows along the trailing edge. In a wind speed of 7m/s the sound intensity ratio of quadrupole to dipole at P1 location is about 21.1%, but as wind speed increases the sound intensity ratio increases up to 54.3% in the case of no-weighted correction. This means that there is a considerably close relation between the quadrupole noise by small and large scales and the increase of wind speeds. With the purpose of a rough prediction of sound power level, CFD results were compared with a simple model of previous researchers and showed a good agreement with one by Hagg of three other models.
NREL Phase VI 풍력발전기 저주파 소음방사 특성
모장오(Mo, Jang-Oh),김병윤(Kim, Byoung-Yun),류병남(Ryu, Byeng-Nam),이영호(Lee, Young-Ho) 한국신재생에너지학회 2009 한국신재생에너지학회 학술대회논문집 Vol.2009 No.06
The purpose of this work is to predict the low frequency aero-acoustic noise generated from the horizontal axis wind turbine, NREL Phase VI using large eddy simulation and Ffowcs-Williams and Hawkings model provided in the commercial code, FLUENT. Calculated aerodynamic performances such as shaft torque and power are compared with experimentally measured value. Performance results show a good agreement with experimental data within about 0.8%. If the distance by two times is changed from 32D to 64D toward the downstream region, sound pressure level is reduced by about 6.4dB.