이산요소법의 소개 및 응용 분야

손권중,박준영 대한기계학회 2020 기계저널 Vol.60 No.9

비포장 노면의 디지털 트윈 구현을 위한 토양 정보 획득 및 입자 이산요소 모델링

손권중 한국정보기술학회 2023 한국정보기술학회논문지 Vol.21 No.1

우주 탐사, 농업, 건설, 군사 분야 등에서 비포장도로 위를 운행하는 각종 수송기계의 설계 및 운용 단계에서 컴퓨터 시뮬레이션에 기반한 디지털 트윈 기술의 활용도가 점점 높아지고 있다. 비포장도로에 대한 보다 사실적인 디지털 트윈 환경을 구현하기 위해서는 지형 정보뿐만 아니라 토양의 마찰과 응집력과 같은 지면의 분체학적 특성 정보를 획득하여 반영해야 한다. 이 논문은 비포장 주행 시험장에서 채취한 두 종류의 토양을 대상으로 입도, 수분함유량, 안식각 등 토질 정보를 수집하고 이를 바탕으로 입자의 크기와 입자 간 접촉 인자를 보정한 이산요 모델을 제시한다. 보정된 입자 모델은 안식각 예측 시뮬레이션 검증 결과에서 실험 결과를 정확히 예측하는 것으로 확인되어 향후 융합 정보 분야 연구에 활용성이 높을 것으로 기대한다.

OPTIMAL POWER DISTRIBUTION OF HIGH-VOLTAGE COOLANT HEATER FOR ELECTRIC VEHICLES THROUGH ELECTRO-THERMOFLUIDIC SIMULATIONS

손권중 한국자동차공학회 2023 International journal of automotive technology Vol.24 No.4

There is a lot of focus on improving the heating performance and efficiency of high-voltage coolant heaters for electric vehicles. It has been noticed that the geometry design of the coolant flow path in a heat-exchanging unit plays a primary role in enhancing the efficiency of the high-voltage heater. However, no previous study has been carried out on power distribution to heating elements, which are usually layered thin-film structures. This paper presents multiphysics-based computational work to explore the heat-exchanging characteristic of high-voltage heater systems with varying power distribution schemes via split electrodes. For a 7 kW heater with symmetric serpentine flow channels and two-split heating layers with a dual-input terminal, two power distribution cases of 3.75 kW : 3.25 kW and 4.00 kW : 3.00 kW showed better performance than the conventional single-input port configuration equivalent to the 3.50 kW : 3.50 kW case in terms of temperature uniformity in the working fluid and solid structures.

합성곱 신경망 기반 물체 인식과 탑승 감지 센서를 이용한 개인형 이동수단 주행 안전 보조 시스템 개발

손권중,배성훈,이현준,Son, Kwon Joong,Bae, Sung Hoon,Lee, Hyun June 한국융합학회 2021 한국융합학회논문지 Vol.12 No.10

최근에 전동킥보드와 같은 개인형 이동수단의 보급이 급격히 확대되면서 교통사고 발생 건수도 크게 늘고있다. 개인형 모빌리티가 자세 안정성이 낮고 탑승자가 외부로 노출되어 전도 사고나 낙상 사고의 위험이 크기 때문이다. 전동킥보드 사고 방지를 위해 본 논문은 주행 보조 장치로써 자동긴급제동시스템과 안전시동시스템을 제안하였다. 인공지능 기반 물체 인식 기술을 이용하여 주변 위험 요소를 탐지하고 자동으로 제동을 걸 수 있는 시스템을 개발하였다. 또한 운전자의 탑승이 확인되기 전까지 장치의 시동을 보류하는 안전시동시스템도 개발하였다. 상용차와 주행 조건이 매우 다른 개인형 이동 수단에 특화된 첨단 운전자 보조 시스템 융합 기술을 제안한다는 점에서 본 연구의 의의가 있다. A recent spread of personal mobility devices such as electric kickboards has brought about a rapid increase in accident cases. Such vehicles are susceptible to falling accidents due to their low dynamic stability and lack of outer protection chassis. This paper presents the development of an automatic emergency braking system and a safe starting system as driving assistance devices for electric kickboards. The braking system employed artificial intelligence to detect nearby threaening objects. The starting system was developed to disable powder to the motor until when the driver's boarding is confirmed. This study is meaningful in that it proposes the convergence technology of advanced driver assistance systems specialized for personal mobility devices.

이산요소법을 이용한 금속 분말 분무 과립화 공정의 생산성 시뮬레이션 연구

손권중 한국융합학회 2021 한국융합학회논문지 Vol.12 No.1

과립 분말 야금법은 기존 분말 야금법보다 치밀도가 높은 소결 부품을 얻을 수 있는 제조 기술이다. 하지만 추가 과립화 공정에 따른 생산 비용 증가가 상당하다는 단점이 있다. 과립 분말 야금법의 생산성 향상을 위해서는 과립 분말 제조 시 높은 회수율이 보장되어야 한다. 본 논문에서는 분체 동역학 전산 해석법인 이산요소법을 이용하여 과립 분말의 수율에 영향을 미치는 과립화 공정의 특성에 대해 살펴보았다. 분무 과립 공정 중 과립화 분말의 비산, 충돌 및 소착 현상을 시뮬레이션함으로써 분무 건조기의 운전 조건에 따른 과립화 분말의 파손 및 회수 가능 여부를 예측하였다. 본 논문의 가상 공정 시뮬레이션 융합 연구 결과는 실제 금속 분말의 분무 과립화 공정의 생산성 향상에 이바지할 것으로 기대한다. A powder metallurgy process with granules is the manufacturing technology that can achieve higher-density sintered parts than conventional powder metallurgy processes. However, there is a disadvantage in that the production cost increases significantly due to the additional granulation step. High granule productivity must be guaranteed for affordable material costs in this manufacturing technology. This paper performed a series of scattering, collision, and adhesion simulations of agglomerated powders to investigate the characteristics of granulation process affecting the manufacturing yield rate. The results of this simulation-based convergence study can contribute to improving productivity in the metal powder spray granulation process.

A discrete element model for the influence of surfactants on sedimentation characteristics of magnetorheological fluids

손권중 한국유변학회 2018 Korea-Australia rheology journal Vol.30 No.1

Hindering particle agglomeration and re-dispersion processes, gravitational sedimentation of suspended particles in magnetorheological (MR) fluids causes inferior performance and controllability of MR fluids in response to a user-specified magnetic field. Thus, suspension stability is one of the principal factors to be considered in synthesizing MR fluids. However, only a few computational studies have been reported so far on the sedimentation characteristics of suspended particles under gravity. In this paper, the settling dynamics of paramagnetic particles suspended in MR fluids was investigated via discrete element method (DEM) simulations. This work focuses particularly on developing accurate fluid-particle and particle-particle interaction models which can account for the influence of stabilizing surfactants on the MR fluid sedimentation. Effect of the stabilizing surfactants on interparticle interactions was incorporated into the derivation of a reliable contact-impact model for DEM computation. Also, the influence of the stabilizing additives on fluid-particle interactions was considered by incorporating Stokes drag with shape and wall correction factors into DEM formulation. The results of simulations performed for model validation purposes showed a good agreement with the published sedimentation measurement data in terms of an initial sedimentation velocity and a final sedimentation ratio.

전기차용 7kW급 고전압 히터 유로 형상 설계를 위한 열유동 시뮬레이션

손권중 한국융합학회 2022 한국융합학회논문지 Vol.13 No.3

Unlike an international combustion engine car, a battery-powered electric vehicle requires an additional heat source for its heating system. A high-voltage coolant heater has the advantages of high efficiency and a wide operating temperature range. In its development, the geometry design of the coolant flow path is essential. This paper presents the thermal flow simulations of a 7kW high-voltage heater with symmetric serpentine flow channels arranged parallelly. The heater performance was evaluated from the simulation results in terms of the pressure and temperature differences and the flow uniformity. The proposed design showed a greater flow resistance and similar heat exchanging capability than the existing parallel serpentine design. It has the advantage of a relatively wide low-temperature surface area, where the control circuit board susceptible to high temperatures can be located. 내연기관 자동차 히터는 연소과정 중에 발생하는 엔진 열을 이용하므로 열원이 추가로 필요치 않지만, 배터리로부터 동력원을 얻는 전기자동차용 히터는 별도의 전열 장치가 요구된다. 지금까지 개발된 전기차용 히터 중에서 냉매를 이용하는 고전압 히터는 효율이 높고 작동 온도 범위가 넓은 장점이 있다. 고전압 히터 내부의 냉각수 유로의 형상은 열교환 성능을 크게 좌우하므로 히터 개발 시 유로 설계는 기술적으로 매우 중요하다. 본 논문에서는 대칭형 서펜타인 유로를 갖는 7kW급 고전압 히터의 유로 형상 설계를 위해 고전압 열유동 시뮬레이션을 수행하였다. 해석 결과로부터 입출구간 차압과 차온 및 유로에서의 유동 균일도를 계산하여 히터의 성능을 평가하였다. 도출된 대칭형 서펜타인 유로 설계안은 기존 평행 서펜타인 비해 차압은 높지만, 열교환 성능은 비등하며 저온부가 비교적 넓게 존재하여 제어 회로의 설치 공간으로 활용할 수 있다는 장점이 있다.

국가 산,학,연 협력 연구개발을 위한 과제목표관리 정보시스템의 설계 및 효과 분석

손권중,유왕진,이철규 기술경영경제학회 2008 Journal of Technology Innovation Vol.16 No.1

We studied how to achieve successful implementation of massive research and development projects requiring collaboration among industries, universities and government-supported research institute. We have set up an engineering process innovation model to be deemed most adequately for all practical purposes, relying on the theoretical studies on the merits and analysis of the effect of the information system based on Milestone Management, Work Breakdown Structures and Web, which is known to be effective for research project (schedule) management and the objective management, and implemented a real-world web-based project objective management system. After a review of various R & D Project Schedule Management methods, we found that this information system was very compatible with project objective management. This project objective management information system carries out research and development projects effectively and efficiently, getting together in cyber-space and sharing information, and has been equipped with an Early Warning Subsystem to allow for pre-analysis and timely response to potential problems arising from the course of the project. The system also contains an Executive Information System that in real time, automatically provides the management information required by managers with the rate of project progress (achievement, fulfillment and delay). Lastly, actual progress can be cross-checked through both on-line objective management on the web-based information system and design review meeting held on site, to improve the efficiency and validity of the information system. Moreover, overall effect was analyzed through questionnaires on how well the system and generated information meet requirements and on the ultimate impact of the system upon objective management and communication. The questionnaire on the system effect revealed that the information system was useful to objective management and communication, and that the quality of the system was more than acceptable as well.

A numerical study of the influence of rheology of cohesive particles on blade free planetary mixing

손권중 한국유변학회 2018 Korea-Australia rheology journal Vol.30 No.3

High-speed planetary mixers with no impellers have been used to blend various types of industrial powders and viscous fluids rapidly and uniformly by means of centrifugal agitation resulting from the combined rotating and revolving motion of a mixing vessel. However, there is still a lack of in-depth understanding of their mixing dynamics at both meso and macro scales. This paper presents a discrete element simulation of the effect of cohesive powder rheology on mixing performance in a blade-free planetary mixer at particle scale. The interparticle cohesive forces were computed using the Johnson-Kendall-Roberts (JKR) model where the surface energy of each particle is a control parameter for the rheological behavior of the bulk powder. A series of mixing simulations were conducted for cohesive and non-cohesive particles in a planetary mixer. The degree of mixing in each simulation was evaluated with the performance parameters such as the mixing index, mixing time, and relative particle fraction. The simulation results showed that cohesion retards the particle mixing rate, but an increasing cohesion does not deteriorate mixing performance in a high-speed planetary mixer. The simulation method adopted in this study can be used in optimizing the design and operation conditions of a planetary mixer.

A nonlinear rheological model for the ultrasonically induced squeeze film effect in variable friction haptic displays

손권중 한국유변학회 2017 Korea-Australia rheology journal Vol.29 No.3

A squeeze film induced by ultrasonic vibration between two solid surfaces in contact can dramatically reduce the friction between them. This phenomenon, so-called the squeeze film effect, has been utilized in variable friction tactile displays for texture rendering purposes. Such tactile displays can provoke a haptic sensation to a finger pad in a controllable way. A real-time adjustment of the coefficient of lateral friction between the human finger pad and the tactile display can be accomplished by modulating the vibration amplitude of the tactile panel. Therefore, driving a reliable friction model is a key step towards designing and controlling tactile displays utilizing the squeeze film effect. This paper derives a modified HerschelBulkley rheological model to express the lateral friction exerted on a human fingertip via an air squeeze film as a function of the operating parameters such as the driving voltage amplitude, the finger sliding speed, and the contact pressure. In contrast to the conventional Coulomb friction model, such a rheology model can account for the sliding velocity dependence. This modeling work may contribute to the optimal control of the ultrasonic variable friction tactile displays.