Efficient Correlation Method for Satellite Thermal Analysis Model Using Multiple Linear Regression and Optimization Algorithms

Jaewon Kang,김건웅,Somin Shin,김정호 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.5

As the thermal analysis model of satellites is used as an important indicator for thermal design, it must accurately simulate the thermal behaviour of actual satellites for precise thermal design. To increase the accuracy of the thermal analysis model, it must be correlated using the thermal balance test data for actual satellite models. To achieve this, we herein propose an efficient correlation method for satellite thermal analysis models using multiple linear regression techniques with quadratic terms and optimization algorithms. The proposed method reduces the amount of computation by choosing dominant parameters through sensitivity analysis and creating a multiple linear regression model that can replace the thermal analysis model in the subsequent optimization process. Subsequently, optimization algorithms are applied to the multiple linear regression model to perform the correlation of the thermal analysis model. In this study, the numerical validation of the proposed method was performed using numerical data from a reference thermal analysis model to verify the reliability and accuracy of the proposed method before it was applied to the correlation of the thermal analysis model using experimental data. The thermal analysis result of the reference thermal analysis model was set as the target value to correlate, and quantitative performance evaluation was performed for various combinations of optimization algorithms and design of experiments methods by comparing the estimated analysis parameters. The results of this study demonstrate that the proposed method can efficiently produce an accurate correlation model for thermal analysis.

DEVELOPMENT OF A FLOW NETWORK SIMULATION PROGRAM PART II – THERMAL ANALYSIS

J. LIM,K. Y. YANG 한국자동차공학회 2013 International journal of automotive technology Vol.14 No.3

An in-house simulation program is developed that can conveniently be utilized to predict flow and thermal characteristics such as velocity, pressure and temperature in any flow network systems comprising multiple flow components such as pipe, pump, heat exchanger, valves, etc. The program consists of two parts, the flow analysis for computing velocity and pressure and thermal analysis for temperature. The flow analysis portion of the program was dealt with in the Part I of the paper. Here, the thermal analysis part of the program is discussed. For the thermal analysis, first the flow analysis should be carried out to find out velocity and pressure in the network system, since this flow information is used as the input data for the thermal analysis. The mathematical and numerical formulations in the thermal analysis are very similar to those in the flow analysis. A thermal energy balance equation is applied to each thermal element with the unknown temperatures at nodes, while in the flow analysis both energy and mass conservation equation are applied to each flow element with two unknowns,velocity and pressure, at each node, so as to establish a set of non-linear algebraic equations that is to be iteratively solved by the Newton-Raphson scheme. In the program, five different flow and thermal elements respectively are treated, and believed to represent a variety of the network flow system in many practical engineering applications. However, the program can easily be extended to incorporate additional elements if necessary. In order to demonstrate the validity and applicability of the program, a comprehensive example of the engineering problems encountered in the vehicle development is introduced, and the solution process as well as accuracy of obtained results are discussed. Throughout the study, it is found that the program can most efficiently be used to find an optimal design concept among many potential design options in an early conceptual design phase of the vehicle development.

Electromagnetic, Vibration and Thermal Analysis of 1.1 kw Switched Reluctance Motor for Electric Vehicle Application

Karunakaran Vijayalakshmi,Kandadai Nagaratnam Srinivas 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.3

This paper presents the electromagnetic analysis, vibration analysis and thermal analysis of a 6/4 pole, 1.1 kW switched reluctance motor (SRM), focusing on its application to EV, in the sense that the vibration and thermal analyses are carried out at speeds of range more than 1000 rpm, which usually experienced by EV SRM. At first, electromagnetic analysis is performed for six different silicon steel materials viz., 35JN210, 35JN300, 50JN470, 50JNA350, 50JNA600 and 50JNE350, and from the results, it has been noted that the material 35JN210 has less torque ripple and a good efficiency compared to all other materials. So this material is selected for SRM structure to perform thermal and vibration analysis. SRM proves to be a suitable candidate in electric vehicle application with the limitation with respect to its vibration and noise. The noise generation during motor operation is a major concern for SRM. The main source of vibration, the radial force, is calculated using two- dimensional (2D) transient finite-element analysis (FEA).The electromagnetic analysis is performed to find out the force exerted on the stator and deformations due to that. Using these nodal forces as input, transient analysis is performed to examine the motor's vibration characteristics. By this analysis, the motor modal frequencies are examined so that the motor operation could be skipped from operating in this vibrating region when it is used in electric vehicle applications. For thermal analysis, FEA is used to calculate the heat generation and temperature distribution on different parts of the machine to estimate the thermal behaviour of the motor.

Thermal Model Correlation and Validation of a 6U Nanosatellite with Multiple Payloads

김지석,김해동 한국항공우주학회 2022 International Journal of Aeronautical and Space Sc Vol.23 No.1

Due to the miniaturization of satellite components and advantages of low costs and short periods of development, nanosatellites are rapidly being developed to operate a wide variety of missions beyond only education purposes, such as Earth observation, relay communication, scientific objective, and even space exploration. As the role of nanosatellite grew, the reliability of nanosat’s thermal subsystem is also becoming very important to successfully carry it out. However, there is rare to find a research on thermal design reliability validation of 6U nanosatellite with increasingly large, diverse, and complex missions. Since reliability of satellite thermal design can be evaluated by on-orbit thermal analysis with the thermal mathematical model, more accurate analysis results can be obtained through more accurate thermal model. In addition, the thermal model can be improved by process of model correlation. The process begins with conducting thermal vacuum test (TVT) and is a flow that reduces thermal uncertainties by comparing the test results with analytical results. Nanosatellite systems are thermally closely connected within a limited space, so that thermal design cannot proceed conclusively for each subsystem and module. Therefore, it should always be done from a system perspective when thermal model of nanosatellite with multiple payloads is correlated especially. In this paper, we introduced a 6U nanosatellite of SNIPE (Small scale magNetospheric and Ionospheric Plasma Experiment) Mission that developing from KARI (Korea Aerospace Research Institute) and KASI (Korea Astronomy and Space Science Institute) for the near-Earth space environment scientific missions. For the successful mission operation, we conducted TVT for simulating space thermal vacuum environment to verify thermal design of thermal control system in the worst case. In addition, thermal model correlation of SNIPE nanosatellite was conducted through the TVT results with not only system level but each component and module. Based on the updated thermal model via the model correlation, we performed on-orbit thermal analysis to demonstrate the validity of thermal model and thermal design of the system level. As a result, we have confirmed that all components of the SNIPE nanosat satisfy the allowable temperature limit, which has correlated the thermal model and validated the thermal design successfully. The performed process can be applied to 6U or bigger nanosatellite for the objectives of practical missions or technology demonstrations that need the validity of thermal design and improvement of thermal model through the test and analysis. Therefore, this study is expected to contribute to the successful performance of the more complex and sophisticated nanosatellite missions to be developed.

Prediction of ground thermal diffusivity from thermal response tests

Yoon, Seok,Kim, Min-Jun Elsevier 2019 Energy and buildings Vol.185 No.-

<P><B>Abstract</B></P> <P>Ground-coupled heat pump (GCHP) systems are being increasingly utilized in recent years. There are several important parameters in the design of GCHP systems. As ground thermal conductivity is one of the most crucial parameters, it should be measured by conducting in-situ thermal response tests (TRTs). This paper presents the experimental results and analysis of thermal response tests to estimate the ground thermal conductivity and ground thermal diffusivity for three types of ground heat exchangers (GHEs), including U, 2U, and W-type ground heat exchangers (GHEs). Three different types of GHEs were installed in a dredged soil deposit, and continuous TRTs were conducted for 48 h. This study suggests a method to predict ground thermal diffusivity using the infinite line source model from the TRTs. Furthermore, soil samples were collected from different ground layers, and ground thermal properties were measured using laboratory tests. The equivalent ground thermal conductivity and ground thermal diffusivity measured through laboratory tests were compared with the in-situ TRT results that were newly derived in this paper. In addition, ground thermal diffusivity and ground thermal conductivity values that were obtained through research were used as input parameters in numerical analysis. The in-situ TRT results were numerically modeled using the finite element method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> In-situ TRTs were conducted for 48 h with U, 2 U, and W type GHEs. </LI> <LI> The ground thermal diffusivity is derived by using an infinite line source model and regression analysis. </LI> <LI> The method to derive ground thermal diffusivity from in-situ TRTs was validated with laboratory test results. </LI> <LI> An in-situ TRT for W type GHE was numerically modeled by using ground thermal diffusivity and ground thermal conductivity as input parameters. </LI> </UL> </P>

지역난방 열배관망 운영데이터 기반의 파손확률 모델 개발

김형석 ( Hyoung Seok Kim ),김계범 ( Gye Beom Kim ),김래현 ( Lae Hyun Kim ) 한국화학공학회 2017 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.55 No.3

지역난방은 국내에 1985년 처음 도입되었다. 지하 열배관망의 사용연한이 30년 이상 증가함에 따라, 지하에 매설된 열수송 배관 특성상 유지관리가 중요한 문제로 대두되고 있다. 노후화가 진행된 열배관망 유지보수를 위한 정기적인 점검, 운영관리 시 다양한 복합 기술이 필요하다. 특히 현장에서 경제적 관점에서 최적 유지보수 및 교체시점을 도출하기 위하여 의사결정에 활용될 수 있는 모형개발이 요구되고 있다. 본 연구에서는 한국지역난방공사 수도권 5개 지사열 배관망 운영 시 보수이력과 사고성 데이터를 바탕으로 분석하였다. 정성적 분석과 이항 로지스틱 회귀분석의 통계적 기법을 도입하여 파손확률 모델을 개발하였다. 보수이력 및 사고성 자료의 정성적 분석 결과, 파이프라인 손상의 가장 중요한 원인으로 건설 시공불량, 배관의 부식과 자재 불량이 전체의 약 82%를 차지했다. 통계 모델 분석에서는 분류의 분리 점을 0.25로 설정함으로써 열배관 파손 및 비 파손 분류의 정확도가 73.5%로 향상 되었다. 파손확률 모델 수립을 위해 Hosmer와 Lemeshow 검정과 독립변수의 유의성 검정, 모델의 Chi-Square 검정을 통해 모델의 적합성을 검증 하였다. 열배관망 파손의 위험순위 분석결과에 따르면 파손확률을 가장 높이는 경우는 겨울철 서울지역 자동차 도로에 있는 10년 이상 된 250mm이하 배관 Reducer에서 F 건설회사가 시공했던 열배관망으로 분석되었다. 본 연구 결과는 열배관망 시스템의 유지관리 및 예방점검, 교체 사업 우선순위를 정할 때 활용 가능하다. 또한 이를 통하여 점검·유지보수 등 사전에 사고예방 계획을 수립하여 대처함으로써 열배관 파손의 빈도를 감소시키고 보다 적극적인 열배관망 관리에 이용할 수 있을 것으로 사료된다. District heating was first introduced in Korea in 1985. As the service life of the underground thermal piping network has increased for more than 30 years, the maintenance of the underground thermal pipe has become an important issue. A variety of complex technologies are required for periodic inspection and operation management for the maintenance of the aged thermal piping network. Especially, it is required to develop a model that can be used for decision making in order to derive optimal maintenance and replacement point from the economic viewpoint in the field. In this study, the analysis was carried out based on the repair history and accident data at the operation of the thermal pipe network of five districts in the Korea District Heating Corporation. A failure probability model was developed by introducing statistical techniques of qualitative analysis and binomial logistic regression analysis. As a result of qualitative analysis of maintenance history and accident data, the most important cause of pipeline damage was construction erosion, corrosion of pipe and bad material accounted for about 82%. In the statistical model analysis, by setting the separation point of the classification to 0.25, the accuracy of the thermal pipe breakage and non-breakage classification improved to 73.5%. In order to establish the failure probability model, the fitness of the model was verified through the Hosmer and Lemeshow test, the independent test of the independent variables, and the Chi-Square test of the model. According to the results of analysis of the risk of thermal pipe network damage, the highest probability of failure was analyzed as the thermal pipeline constructed by the F construction company in the reducer pipe of less than 250mm, which is more than 10 years on the Seoul area motorway in winter. The results of this study can be used to prioritize maintenance, preventive inspection, and replacement of thermal piping systems. In addition, it will be possible to reduce the frequency of thermal pipeline damage and to use it more aggressively to manage thermal piping network by establishing and coping with accident prevention plan in advance such as inspection and maintenance.

ASSESSMENT OF THERMAL FATIGUE IN MIXING TEE BY FSI ANALYSIS

Jhung, Myung Jo Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.1

Thermal fatigue is a significant long-term degradation mechanism in nuclear power plants. In particular, as operating plants become older and life time extension activities are initiated, operators and regulators need screening criteria to exclude risks of thermal fatigue and methods to determine significant fatigue relevance. In general, the common thermal fatigue issues are well understood and controlled by plant instrumentation at fatigue susceptible locations. However, incidents indicate that certain piping system Tee connections are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentations. Therefore, in this study thermal fatigue evaluation of piping system Tee-connections is performed using the fluid-structure interaction (FSI) analysis. From the thermal hydraulic analysis, the temperature distributions are determined and their results are applied to the structural model of the piping system to determine the thermal stress. Using the rain-flow method the fatigue analysis is performed to generate fatigue usage factors. The procedure for improved load thermal fatigue assessment using FSI analysis shown in this study will supply valuable information for establishing a methodology on thermal fatigue.

Investigation of the Thermal Mode-based Thermal Error Prediction for the Multi-heat Sources Model

Jun An Han(한준안),Gyu Ha Kim(김규하),Sun-Kyu Lee(이선규) Korean Society for Precision Engineering 2013 한국정밀공학회지 Vol.30 No.7

Thermal displacement is an important issue in machine tool systems. During the last several decades, thermal error compensation technology has significantly reduced thermal distortion error; this success has been attributed to the development of a precise, robust thermal error model. A major advantage of using the thermal error model is instant compensation for the control variables during the modeling process. However, successful application of thermal error modeling requires correct determination of the temperature sensor placement. In this paper, a procedure for predicting thermal-mode-based thermal error is introduced. Based on this thermal analysis, temperature sensors were positioned for multiple heat-source models. The performance of the sensors based on thermal-mode error analysis, was compared with conventional methods through simulation and experiments, for the case of a slide table in a transient state. Our results show that for predicting thermal error the proposed thermal model is more accurate than the conventional model.

Thermal and structural analysis of a cryogenic conduction cooling system for a HTS NMR magnet

In, Sehwan,Hong, Yong-Ju,Yeom, Hankil,Ko, Junseok,Kim, Hyobong,Park, Seong-Je The Korea Institute of Applied Superconductivity a 2016 한국초전도저온공학회논문지 Vol.18 No.1

The superconducting NMR magnets have used cryogen such as liquid helium for their cooling. The conduction cooling method using cryocoolers, however, makes the cryogenic cooling system for NMR magnets more compact and user-friendly than the cryogen cooling method. This paper describes the thermal and structural analysis of a cryogenic conduction cooling system for a 400 MHz HTS NMR magnet, focusing on the magnet assembly. The highly thermo-conductive cooling plates between HTS double pancake coils are used to transfer the heat generated in coils, namely Joule heating at lap splice joints, to thermal link blocks and finally the cryocooler. The conduction cooling structure of the HTS magnet assembly preliminarily designed is verified by thermal and structural analysis. The orthotropic thermal properties of the HTS coil, thermal contact resistance and radiation heat load are considered in the thermal analysis. The thermal analysis confirms the uniform temperature distribution for the present thermal design of the NMR magnet within 0.2 K. The mechanical stress and the displacement by the electromagnetic force and the thermal contraction are checked to verify structural stability. The structural analysis indicates that the mechanical stress on each component of the magnet is less than its material yield strength and the displacement is acceptable in comparison with the magnet dimension.

마찰면의 압력 분포를 고려한 제동디스크의 열응력 해석

이영민(Y. M. Lee),박재실(J. S. Park),석창성(C. S. Seok),이찬우(C. W. Lee),김재훈(J. H. Kim) 한국정밀공학회 2005 한국정밀공학회 학술발표대회 논문집 Vol.2005 No.10월

A brake disk and a pad are important parts that affect the braking stability of a railway vehicle. Especially, because a brake disk stops the vehicle using conversion of the kinetic energy to frictional energy, thermal fatigue cracks are generated by the cyclic thermal load, as frictional heat, on a frictional surface and these cracks cause the fracture of a brake disk. Therefore, many researches for the thermal stress must be performed to improve the efficiency of brake disk and ensure the braking stability. In this study, we performed the thermal stress analysis for a ventilated brake disk with 3-D analysis model. For that, we simplified the shape of a ventilated hole to minimize problems that could be occurred in analysis process . Thermal stress analysis was performed in case that pressure distributions on a frictional surface is constant and is not. To determine pressure distributions of irregular case, pressure distribution analysis for a frictional surface was carried out. Finally using the results that were obtained through pressure distribution analysis, we carried out thermal stress analysis of each case and investigated the results of thermal stress analysis.