【摘要】：近年來,節(jié)能減排日益成為人們關(guān)注的焦點,而汽車輕量化作為節(jié)能減排的有效途徑之一,也受到人們的重視。為降低發(fā)動機質(zhì)量,達到節(jié)能減排的目的,發(fā)動機中越來越多的金屬零件被工程塑料制件所取代,而機油冷卻器蓋也是其中的一個。但塑料機油冷卻器蓋距離振動激勵源較近且屬于薄壁件,容易產(chǎn)生較大的輻射噪聲;同時采用工程塑料材質(zhì),剛度小強度低,容易產(chǎn)生裂紋等強度問題。所以本文以塑料機油冷卻器蓋為研究對象,對其進行振動噪聲和結(jié)構(gòu)強度仿真計算并以低噪聲和高強度為目標對其進行結(jié)構(gòu)優(yōu)化。主要研究內(nèi)容如下:建立塑料機油冷卻器蓋結(jié)構(gòu)有限元模型并通過模態(tài)試驗對該模型的正確性進行了驗證;建立機油冷卻器蓋內(nèi)腔流體模型并與機油冷卻器蓋一起構(gòu)成流固耦合模型,對其進行耦合模態(tài)分析與對比,結(jié)果表明機油冷卻器蓋內(nèi)腔冷卻液的存在對其頻率和振型都有著較大的影響,在后續(xù)的仿真計算及優(yōu)化過程中應(yīng)當考慮流體與固體的耦合作用。選定典某型工況,測取螺栓點處的加速度信號,采用模態(tài)疊加法對塑料機油冷卻器蓋進行頻響分析,得到罩蓋速度響應(yīng)并對其振動特性進行分析;基于上述計算結(jié)果進行虛擬聲功率級預(yù)測,提取其中的關(guān)鍵頻率作為優(yōu)化目標;同時,計算了機油冷卻器蓋內(nèi)腔流體壓力,將其映射到機油冷卻器蓋上進行應(yīng)力應(yīng)變計算分析;最后計算了等壓下的應(yīng)變能并將其作為優(yōu)化目標。在塑料機油冷卻器蓋底面增加一層設(shè)計空間,采用加權(quán)指數(shù)法將各優(yōu)化目標歸一化為一個總目標,同時施加約束條件,對塑料機油冷卻器蓋進行多目標拓撲優(yōu)化。在塑料機油冷卻器底面布置加強筋并定義加強筋參數(shù)變量,根據(jù)最優(yōu)拉丁超立方進行樣本點設(shè)計,得到加強筋試驗設(shè)計矩陣;根據(jù)試驗設(shè)計矩陣建立流固耦合模型并計算得到各優(yōu)化目標的取值;將加強筋各參數(shù)變量作為輸入,各優(yōu)化目標計算結(jié)果作為輸出,采用響應(yīng)面模型(RSM)建立輸入與輸出的近似模型并對該近似模型的正確性進行驗證;以低噪聲、高強度和加強筋體積小為優(yōu)化目標,采用第二代非劣排序遺傳算法(NSGA-II)對加強筋參數(shù)進行優(yōu)化。優(yōu)化后塑料機油冷卻器蓋振動噪聲都有所下降且整體結(jié)構(gòu)強度增加,為塑料機油冷卻器蓋的設(shè)計提供指導(dǎo)。
[Abstract]:In recent years, energy saving and emission reduction have increasingly become the focus of attention, and as one of the effective ways of energy saving and emission reduction, automobile lightweight has also been paid attention to. In order to reduce the engine quality and achieve the purpose of energy saving and emission reduction, more and more metal parts are replaced by engineering plastic parts in the engine, and the oil cooler cover is one of them. But the plastic oil cooler cover is close to the vibration excitation source and belongs to the thin-walled parts, which is easy to produce large radiation noise. At the same time, using engineering plastic material, the stiffness is low and the strength is low, and cracks are easy to occur. So this paper takes the plastic oil cooler cover as the research object, carries on the vibration noise and the structural strength simulation calculation to it, and takes the low noise and the high strength as the target to carry on the structure optimization. The main research contents are as follows: the finite element model of plastic oil cooler cover structure is established and the correctness of the model is verified by modal test. The fluid model of the inner cavity of the oil cooler cap is established and the fluid-solid coupling model is constructed together with the oil cooler cover. The coupling modal analysis and comparison are carried out. The results show that the existence of coolant in the inner cavity of the oil cooler has a great influence on its frequency and mode shape. The coupling effect between fluid and solid should be considered in the subsequent simulation and optimization. The acceleration signal at the bolt point is measured under a typical working condition, and the frequency response of the plastic oil cooler cover is analyzed by modal superposition method, and the velocity response of the cover is obtained and its vibration characteristics are analyzed. Based on the above calculation results, the virtual acoustic power level is predicted and the key frequency is extracted as the optimization objective. At the same time, the pressure of fluid in the inner cavity of the oil cooler cap is calculated and mapped to the oil cooler cover for the stress and strain calculation and analysis. Finally, the strain energy under isobaric pressure is calculated and used as the optimization objective. A layer of design space is added to the bottom surface of the plastic oil cooler cover. Each optimization objective is normalized to a general objective by using the weighted exponent method. At the same time, the multi-objective topology optimization of the plastic oil cooler cover is carried out by applying the constraint condition. The reinforcement bars are arranged on the bottom surface of the plastic oil cooler and the parameter variables of the reinforcement bars are defined. According to the optimal Latin hypercube sample point design matrix is obtained. Based on the experimental design matrix, the fluid-solid coupling model is established and the values of each optimization target are calculated. The parameter variables of reinforcement bar are taken as input and the calculation results of each optimization objective are taken as output. The approximate model of input and output is established by using response surface model (RSM) and the correctness of the approximate model is verified. The second generation noninferior sorting genetic algorithm (NSGA-II) is used to optimize the reinforcement parameters with the aim of low noise, high strength and small reinforcement volume. After optimization, the vibration and noise of the plastic oil cooler cover are decreased and the overall structural strength is increased, which provides guidance for the design of the plastic oil cooler cover.
【學位授予單位】：天津大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：U464.13

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