Nonlinear Dynamic Responses of Shear-Deformable Composite Panels under Combined Supersonic Aerodynamic, Thermal, and Random Acoustic Loads

이홍범,김영남,최인준,박재상,김인걸 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.3

The skin panel structures of vehicles in supersonic flights are subjected to combined thermal, acoustic, and aerodynamic loads. These combined loads may cause a nonlinear dynamic response of the high-speed flight vehicle’s panel structures. Among these nonlinear dynamic responses, the snapthrough and limit cycle oscillation response seriously affect the fatigue failure of the panel structures. This work investigates the nonlinear dynamic responses using the numerical method, when combined supersonic aerodynamic, thermal, and random acoustic loads are applied to the panel structures simultaneously. To consider the thin and thick composite panels, the first-order shear deformation plate theory (FSDT) and the von Karman nonlinear displacement–strain relationship are applied. The aerodynamic load in the supersonic flow is modeled using the first-order piston theory. The thermal load distribution is assumed constant in the thickness direction of the composite panel. The random acoustic load is represented as stationary white-Gaussian random pressure with zero mean and uniform magnitude over the panels. The nonlinear equations of motion of the composite panel under combined loads are derived using the principle of virtual work and the finite element method. The static displacement, which is the solution of the nonlinear static equation, is calculated using the Newton–Raphson method, and the nonlinear dynamic equation is solved using the Newmark-β time integration method. Using these numerical methods, the nonlinear dynamic analyses are conducted under various loading conditions such as thermal–random acoustic loads, thermal–supersonic aerodynamic loads, and supersonic aerodynamic–thermal–random acoustic loads. Numerical results show the nonlinear dynamic response of the composite thin and thick panels such as snapthrough and limit cycle oscillation responses. Particularly, the snapthrough response is caused when the random acoustic load is applied appropriately to the thermally buckled composite plate when the aerodynamic load is not applied or applied with the relatively small magnitude of the dynamic pressure.

PRT 차량의 열/유동 해석 및 성능 평가

강석원(Seok-Won Kang),권순박(Soon-Bak Kwon),정락교(Rag-Gyo Jeong),김백현(Baek-Hyun Kim) 한국철도학회 2013 한국철도학회 학술발표대회논문집 Vol.2013 No.5

수요응답형 순환교통시스템(PRT: Personal Rapid Transit)은 친환경적이고 지속 가능한 개인(혹은 소규모 그룹) 맞춤형 신 교통시스템으로 최근 주목 받고 있다. 한국형 PRT차량은 유도급전에 의해 충전되고 전기모터에 의해 구동된다. 전기 구동 차량의 하부에 있는 주요 기기들의 작동 허용 온도를 유지하고 냉/난방 기기의 효율적인 운영을 통한 실내 열적쾌적성 향상은 차량의 신뢰성 및 성능과 연관된다. 이에 본 연구에서는 차량 하부의 주요 전장품의 열 관리와 실내 쾌적성 평가를 목표로 전산유체역학(CFD) 해석을 수행하였다. 그 결과, 정차 중 급전장치 및 콘덴서로부터 발생하는 열이 축적되어 온도가 급격히 상승하는 문제가 있었고, 이는 전면부의 공기유입구 및 전륜부에 기류유도판을 추가로 설치하여 저감할 수 있었다. 또한, 혹서기/혹한기 조건에서 차량의 초기설계 형상에 대해 냉난방 성능을 평가하였다. The Personal Rapid Transit(PRT) system has recently attracted much attention in future transportation developments due to its possibilities as green and sustainable transport solutions for demandresponsive mobility services. Korean PRT system is an electric vehicle powered by inductive power transfer. Most importantly, the thermal management strategies to maintain an operating temperature as well as to provide optimized thermal comfort to passengers are very challenging, and these issues are related to reliability and system performance. In this study, computational fluid dynamics(CFD) simulations were carried out to assess the thermal performance of the vehicle. As a result, the high thermal loads from pick-up coil and condenser were observed during charging mode, but it was demonstrated that heat accumulation was attenuated by utilizing the flow separator and additional air intake hole. In addition, the predictions of thermal comfort under hot summer and cold winter conditions were performed by evaluation based on the predicted mean vote(PMV) and predicted percentage of dissatisfied(PPD) indices.

동적 주파수 조절 기법을 적용한 3D 구조 멀티코어 프로세서의 온도 분석

증민(Min Zeng),박영진(Young-Jin Park),이병석(Byeong-Seok Lee),이정아(Jeong-A Lee),김철홍(Cheol-Hong Kim) 한국컴퓨터정보학회 2010 韓國컴퓨터情報學會論文誌 Vol.15 No.11

집적회로 공정기술이 급속도로 발달하면서 멀티코어 프로세서를 설계하는데 있어서 내부 연결망 (interconnection)은 성능 향상을 방해하는 주요 원인이 되고 있다. 멀티코어 프로세서의 내부 연결망에서 발생하는 병목 (bottleneck) 현상을 해결하기 위한 방안으로 최근에는 2D 평면 구조에서 3D 적층 구조로 설계 방식을 변경하는 기법이 주목을 받고 있다. 3D 구조는 칩 내부의 와이어 길이를 크게 감소시킴으로써 성능 향상과 전력 소모 감소의 큰 이점을 가져오지만, 전력 밀도 증가로 인한 온도 상승의 문제를 발생시킨다. 따라서 효율적인 3D 구조 멀티코어 프로세서를 설계하기 위해서는 내부의 온도 문제를 해결할 수 있는 설계 기법이 우선적으로 고려되어야 한다. 본 논문에서는 실험을 통해 다양한 측면에서 3D 구조 멀티코어 프로세서 내부의 온도 분포를 분석하고자 한다. 3D 구조 멀티코어 프로세서에서 수행되는 프로그램의 특성, 냉각 효과, 동적 주파수 조절 기법 적용에 따른 각 코어의 온도 분포를 상세하게 분석함으로써 저온도 3D 구조 멀티코어 프로세서 설계를 위한 가이드라인을 제시하고자 한다. 실험 결과, 3D 구조 멀티코어 프로세서의 온도를 효과적으로 관리하기 위해서는 더 높은 냉각 효과를 갖는 코어를 상대적으로 더 높은 동작 주파수로 작동 시켜야 하고 온도에 영향을 많이 주는 작업 또한 더 높은 냉각 효과를 갖는 코어에 할당해야 함을 알 수 있다. As the process technology scales down, an interconnection has became a major performance constraint for multi-core processors. Recently, in order to mitigate the performance bottleneck of the interconnection for multi-core processors, a 3D integration technique has drawn quite attention. The 3D integrated multi-core processor has advantage for reducing global wire length, resulting in a performance improvement. However, it causes serious thermal problems due to increased power density. For this reason, to design efficient 3D multi-core processors, thermal-aware design techniques should be considered. In this paper, we analyze the temperature on the 3D multi-core processors in function unit level through various experiments. We also present temperature characteristics by varying application features, cooling characteristics, and frequency levels on 3D multi-core processors. According to our experimental results, following two rules should be obeyed for thermal-aware 3D processor design. First, to optimize the thermal profile of cores, the core with higher cooling efficiency should be clocked at a higher frequency. Second, to lower the temperature of cores, a workload with higher thermal impact should be assigned to the core with higher cooling efficiency.

New DTR Estimation Method Without Measured Solar and Wind Data

Zhan-Feng Ying,Yuan-Sheng Chen,Kai Feng 대한전기학회 2017 Journal of Electrical Engineering & Technology Vol.12 No.2

Dynamic thermal rating (DTR) of overhead transmission lines can provide a significant increase in transmission capacity compared to the static thermal rating. However, the DTR are usually estimated by the traditional thermal model of overhead conductor that is highly dependent on the solar, wind speed and wind direction data. Consequently, the estimated DTR would be unreliable and the safety of transmission lines would be reduced when the solar and wind sensors are out of function. To address this issue, this study proposed a novel thermal model of overhead conductor based on the thermal-electric analogy theory and Markov chain. Using this thermal model, the random variation of conductor temperature can be simulated with any specific current level and ambient temperature, even if the solar and wind sensors are out of function or uninstalled. On this basis, an estimation method was proposed to determine the DTR in the form of probability. The laboratory experiments prove that the proposed method can estimate the DTR reliably without measured solar and wind data.

Thermal transport in thorium dioxide

박정규,Eduardo B. Farfan,Christian Enriquez 한국원자력학회 2018 Nuclear Engineering and Technology Vol.50 No.5

In this research paper, the thermal transport in thorium dioxide is investigated by using nonequilibriummolecular dynamics. The thermal conductivity of bulk thorium dioxide was measured to be 20.8 W/m-K,confirming reported values, and the phonon mean free path was estimated to be between 7 and 8.5 nmat 300 K. It was observed that the thermal conductivity of thorium dioxide shows a strong dependencyon temperature; the highest thermal conductivity was estimated to be 77.3 W/m-K at 100 K, and thelowest thermal conductivity was estimated to be 4.3 W/m-K at 1200 K. In addition, by simulatingthorium dioxide structures with different lengths at different temperatures, it was identified that shortwavelength phonons dominate thermal transport in thorium dioxide at high temperatures, resulting indecreased intrinsic phonon mean free paths and minimal effect of boundary scattering while

New DTR Estimation Method Without Measured Solar and Wind Data

Ying, Zhan-Feng,Chen, Yuan-Sheng,Feng, Kai The Korean Institute of Electrical Engineers 2017 Journal of Electrical Engineering & Technology Vol.12 No.2

Dynamic thermal rating (DTR) of overhead transmission lines can provide a significant increase in transmission capacity compared to the static thermal rating. However, the DTR are usually estimated by the traditional thermal model of overhead conductor that is highly dependent on the solar, wind speed and wind direction data. Consequently, the estimated DTR would be unreliable and the safety of transmission lines would be reduced when the solar and wind sensors are out of function. To address this issue, this study proposed a novel thermal model of overhead conductor based on the thermal-electric analogy theory and Markov chain. Using this thermal model, the random variation of conductor temperature can be simulated with any specific current level and ambient temperature, even if the solar and wind sensors are out of function or uninstalled. On this basis, an estimation method was proposed to determine the DTR in the form of probability. The laboratory experiments prove that the proposed method can estimate the DTR reliably without measured solar and wind data.

Modeling of a Building System and its Parameter Identification

Herie Park,Nadia Martaj,Marie Ruellan,Rachid Bennacer,Eric Monmasson 대한전기학회 2013 Journal of Electrical Engineering & Technology Vol.8 No.5

This study proposes a low order dynamic model of a building system in order to predict thermal behavior within a building and its energy consumption. The building system includes a thermally well-insulated room and an electric heater. It is modeled by a second order lumped RC thermal network based on the thermal-electrical analogy. In order to identify unknown parameters of the model, an experimental procedure is firstly detailed. Then, the different linear parametric models (ARMA, ARX, ARMAX, BJ, and OE models) are recalled. The parameters of the parametric models are obtained by the least square approach. The obtained parameters are interpreted to the parameters of the physically based model in accordance with their relationship. Afterwards, the obtained models are implemented in Matlab/Simulink® and are evaluated by the mean of the sum of absolute error (MAE) and the mean of the sum of square error (MSE) with the variable of indoor temperature of the room. Quantities of electrical energy and converted thermal energy are also compared. This study will permit a further study on Model Predictive Control adapting to the proposed model in order to reduce energy consumption of the building.

Molecular Dynamics Simulations of Kapitza Length for Argon-Silicon and Water-Silicon Interfaces

An Truong Pham,김보흥,Murat Barisik 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

A comprehensive understanding of heat conduction between two parallel solid walls separated by liquid remains incomplete in nanometer scale. In addition, the solid/liquid interfacial thermal resistance has been an important technical issue in thermal/fluid engineering such as micro electro-mechanical systems and nano electro-mechanical systems with liquid inside. Therefore, further advancements in nanoscale physics require an advanced understanding of momentum and energy transport at solid/liquid interfaces. This study employs three-dimensional molecular dynamics (MD) simulations to investigate the thermal resistance at solid/liquid interfaces. Heat conduction between two parallel silicon walls separated by a thin film of liquid water is considered. The density distribution of liquid water is discussed with the simulation results to further understanding of the dynamic properties of water near solid surfaces. Meanwhile, temperature profiles appear discontinuous between liquid and solid temperatures due to the dissimilarity of thermal transport properties of the two materials, which validates thermal resistance (or Kapitza length) at solid/liquid interfaces. MD results also investigate the temperature dependence of the Kapitza length, demonstrating that the Kaptiza lengths fluctuate around an average value and are independent of the wall temperature at solid/liquid interfaces. Our study provides useful information for the design of thermal management or heat dissipation devices across silicon/water and silicon/argon interfaces in nanoscale.

Effect of Non-isothermal Phase Change on Multiple Bubble Pulsations

김성학,최경준,김종암 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.4

Main reasons for the damage to submerged structures include shock waves and high-velocity jetting hits at the collapse of the cavitation bubbles, which repeatedly occur in subsequent bubble periods. Although other methods, e.g., experiments and theoretical approaches, have been conducted to gain knowledge of bubble dynamics, these approaches have difficulty in capturing microscopic phase changes and are not suitable for largely deforming motion, respectively. Therefore, numerical simulations using Navier–Stokes equations or Euler equations have been used to describe the bubble’s dynamic behaviors and detailed physical phenomena inside the bubble. Nevertheless, previous numerical simulations had limitations in expressing realistic and accurate bubble dynamics. For example, their results focused only on the first bubble period, not on multiple periods; thus, they could not obtain the information about the continuous shock loading near the structures. More noticeably, the thermal effect in multiple pulsations has never been addressed; since the pressure and temperature inside the bubble are formed near the critical point, the thermal effect has to be considered for accurate computations. Herein, the isothermal and non-isothermal phase change models are applied to observe the phase change effect and thermal effect on the bubble dynamics, respectively. Contrary to the isothermal model, which captures bubble dynamics up to the second bubble period, the non-isothermal model accurately expresses bubble dynamics up to the third bubble period, which is closely related to the thermal effect at the collapse region.

Calculation of Temperature Rise in Gas Insulated Busbar by Coupled Magneto-Thermal-Fluid Analysis

Hong-Kyu Kim,Yeon-Ho Oh,Se-Hee Lee 대한전기학회 2009 Journal of Electrical Engineering & Technology Vol.4 No.4

This paper presents the coupled analysis method to calculate the temperature rise in a gas insulated busbar (GIB). Harmonic eddy current analysis is carried out and the power losses are calculated in the conductor and enclosure tank. Two methods are presented to analyze the temperature distribution in the conductor and tank. One is to solve the thermal conduction problem with the equivalent natural convection coefficient and is applied to a single phase GIB. The other is to employ the computational fluid dynamics (CFD) tool which directly solves the thermal-fluid equations and is applied to a three-phase GIB. The accuracy of both methods is verified by the comparison of the measured and calculated temperature in a single phase and three-phase GIB.