In contrast to the traditional black box machine learning model, the white box model can achieve higher prediction accuracy and accurately evaluate and explain the prediction results. Cavity water depth and cavity length of aeration facilities are predicted in this research based on Extreme Gradient Boosting (XGBoost) and a Bayesian optimization technique. The Shapley Additive Explanation (SHAP) method is then utilized to explain the prediction results. This study demonstrates how SHAP may order all features and feature interaction terms in accordance with the significance of the input features. The XGBoost–SHAP white box model can reasonably explain the prediction results of XGBoost both globally and locally and can achieve prediction accuracy comparable to the black box model. The cavity water depth and cavity length white box model developed in this study have a promising future application in the shape optimization of aeration facilities and the improvement of model experiments.
To investigate the confining effect and axial compressive behavior of rubberized concrete (RuC) confined by steel tube, axial compression tests were carried out on 12 circular RuC cylinders confined by steel tube. The cylinders considered parameters such as steel tube thicknesses (2 mm, 3 mm, 4 mm) and rubber volume replacement ratios of the fine aggregates (0%, 10%, 20%, and 30%). It was observed that the compressive strength of RuC decreases as the rubber volume replacement ratio increases. However, an increase in steel tube thickness enhances the confining effect of the core RuC, leading to an increase in its compressive strength and the corresponding strain, similar to that of conventional concrete. Moreover, post-peak curves are more likely to exhibit a strengthening part in confined concrete with more rubber content. Furthermore, a model was developed to determine the compressive strength of RuC confined by steel tube. Finally, an axial stress-strain model of steel tube confined RuC was proposed, which was validated against test results.
In order to study the effect of high-performance fiber cement composites (HPFRCC) on the mechanical properties of the joint of the frame structure, pseudo-static tests were conducted on seven beam-column subassemblies. Compared with the RC subassembly, the shear capacity of the HPFRCC beam-column connection was increased by 11.4%, and the shear deformation was reduced by 10.3%. The contribution ratio of the shear deformation to the drift was reduced by 22.7%. The value of the coefficient ηc and the flange width of the slab had a significant impact on the shear deformation of the HPFRCC joint. The shear deformation corresponding to the peak load of the joint can be controlled at about 0.01 when the coefficient ηc is 1.6, or the flange width is eight times the width of the slab thickness. The shear strength-shear deformation calculation model of the joint was established through the Bayesian parameter estimation, and the model analysis results were in good agreement with the test results.
The galloping of iced conductors is a serious threat to the safe operation of power systems. Establishing an accurate galloping model of iced conductors has always been a difficult point in galloping research. Therefore, the sparse identification of nonlinear dynamics (SINDy) algorithm is used to identify the galloping model from noise measurement data. A theoretical model of galloping of iced quad bundle conductors is established. Meanwhile, the algorithm is used to identify the simulated data of the theoretical model. The parameter identification ability of the algorithm under noisy velocity measurement is analyzed. An excellent denoising method was selected for data preprocessing, and then the model identification effect of the algorithm after data preprocessing is studied. Besides, the accuracy of the prediction model based on this algorithm and the support vector regression (SVR) prediction model under different training data lengths are compared. The results show that the model identified by the SINDy algorithm in the noise measurement data after data preprocessing has high accuracy and robustness. Moreover, the amount of data used is small. The model identified by this algorithm plays an important role in the rapid investigation, prediction and early warning of galloping phenomena.
Skin tissue is a kind of complex biological material abundant with fibers. A new constitutive model, relating macroscopic responses with microstructural fiber configuration alteration, is developed to investigate the stress softening behaviors of skin tissue observed during cyclic loading–unloading tests. Two influential factors are introduced to describe the impact of fiber configuration change and stretch-induced damage. The present model achieves good agreement between predicted stress distribution of human skin and corresponding ex vivo experimental data obtained from the literature, affirming its capability to effectively capture the characteristic softening behaviors of human skin under cyclic loading conditions.
目前先进航空发动机的风扇叶片均采用复合材料结构,为了研究其在工作过程中可能受到的冲击损伤,即碳纤维增强树脂基复合材料受到高速冲击后的损伤与破坏过程,对其准静态下的正交各向异性本构模型和失效准则进行修正,建立了应变率相关的三维动态本构及损伤模型.该模型考虑了材料模量、强度和断裂韧性与应变率的相关性,并采用基于断裂韧性的渐进损伤模式对刚度进行折减来控制破坏过程.开展了不同应变率下的动态试验,得到基体方向拉伸与剪切的动态响应数据,拟合得到相应的动态修正因子.将该模型结合修正因子植入数值软件进行仿真计算,分析结果表明,所建立的率相关本构及损伤模型能够更准确地模拟层合板受冲击过程的损伤和破坏,与试验吻合较好.
拓扑互锁结构是一种通过具有特殊形状的元素(块)彼此啮合拼接组成的整体结构,具有很好的增韧和抗冲击特性.目前对拓扑互锁结构的静荷载分析研究逐渐成熟,而对冲击条件下结构的强度、稳定性等性能分析以及对结构吸能性能的定量分析尚有发展空间;另外,对影响拓扑互锁结构力学性能的因素、结构设计优化等研究也有待完善.本文选择四面体元素拓扑互锁结构,通过ABAQUS有限元仿真软件对其进行冲击试验仿真,得出拓扑互锁结构在冲击作用下的变形机制,探索了元素互锁角度、元素间摩擦对冲击性能的影响;指出结构被冲穿的决定因素为冲击能量而非冲击速度;最后研究了局部榫卯对结构力学性能的影响.结果验证了拓扑互锁结构较好的缓冲吸能特性,同时表明拓扑互锁结构的力学性能是各个因素综合作用的结果,实际应用中可以根据使用场景和功能需求等对拓扑互锁元素进行调整优化.
以大展弦比机翼为研究对象,利用流固耦合方法对复合材料机翼铺层参考方向进行了数值模拟研究,分析了铺层参考方向轴偏角的改变对大展弦比机翼静气动弹性的影响.研究表明:铺层参考方向轴偏角的改变会对机翼气动弹性产生显著的影响.机翼的总体变形与扭转变形随着参考方向轴偏角的改变呈现周期分布;沿着机翼各个方向的挠度也会因为参考方向轴偏角的改变而产生不同的响应.
本文研究了分数阶粘弹性Pasternak地基上四边固支薄板的自由振动问题．通过引入分数阶导数，将传统整数阶粘弹性模型修正为分数阶导数粘弹性模型，增强了模型的灵活性．基于所提出的分数阶粘弹性Pasternak地基模型，导出相应的应力-应变本构关系的复弹性模量．在此基础上进一步研究Pasternak地基上四边固支矩形板的固有频率对粘弹性地基的依赖特性．在数值算例中，计算了分数阶粘弹性地基上四边固支板的前四阶复固有频率，以及双轴对称、双轴反对称、一轴对称另外一轴反对称等不同振动模态下的振型图．基于数值结果讨论了粘弹性地基分数阶参数及粘性参数对复数固有频率及振动衰减的影响规律．
针对几种经典和新发展的蠕变-疲劳寿命模型开展综述介绍,并建立预测航空涡轮盘在循环热-机蠕变-疲劳载荷谱下蠕变-疲劳行为的数值流程,对某型航空涡轮盘的蠕变-疲劳损伤和寿命进行预测和对比.结果表明:等效应变法与临界平面法得出的疲劳损伤差距较小,等效应变法由于数值计算简单,工程适用性更强.寿命-时间分数(TF)法由于无法考虑应力松弛效应,给出了最为保守的蠕变损伤预测,其对盘体应力三轴度引起的损伤不敏感;延性耗竭法(DE)法仅以蠕变应变率作为损伤因素,虽考虑多轴蠕变因子的影响,但是给出的蠕变损伤过小;修正应变能密度耗竭(MSEDE)法综合考虑蠕变应变与应力松弛,并且考虑多轴蠕变因子与弹性跟随效应的影响,结合疲劳损伤模型可以给出合理的蠕变、疲劳损伤比例,其预测结果更加合理.
针对大展弦比机翼的结构轻量化优化设计,提出了一种高效的布局和尺寸混合优化方法.在CFD/CSD气动弹性计算的基础上,对不同的结构变量进行统一编码,使用一维卷积神经网络建立代理模型,并使用松鼠优化算法建立了混合优化模型进行搜索寻优.以某型太阳能无人机的机翼结构优化为例,优化结果表明翼肋的布局变量和翼梁的尺寸变量之间存在着耦合关系,使用松鼠优化算法相比于遗传算法节省了 35％～45％的计算成本,且混合优化后的结构比原始结构减重4.1％,验证了该方法的有效性.
本文研究了弹性地基上梁主共振响应的时滞效应.基于Hamilton原理,建立了时滞影响下弹性地基上梁的非线性运动微分方程,采用多尺度法,求得了时滞效应下主共振响应调制方程以及稳定性条件.通过数值算例,分析了时滞和调谐参数影响下主共振响应的峰值及幅频响应特性.结果表明,地基反力中的时滞效应对主共振响应影响较大,会导致共振域偏移,在一定区间内,响应幅值随时滞变化先减小再增大,呈现出周期性,并导致幅频曲线弯曲程度增大.
研究Nielsen方程的广义梯度表示以及方程零解稳定性.首先给出4类广义梯度系统及其性质.其次,给出完整系统和非完整系统的Nielsen方程转化成广义梯度系统的条件;将两类Nielsen方程分别化为广义梯度系统并研究方程的零解稳定性.最后,举例验证结果的应用并通过数值模拟验证结论的准确性.
利用复变函数方法和保角变换技术研究了压电效应下一维六方准晶双材料中圆孔边单裂纹的反平面问题．考虑电不可渗透型边界条件，运用保角变换和Stroh公式得到了弹性体受远场剪切力和面内电载荷作用下裂纹尖端应力强度因子和能量释放率的解析解.数值算例分析了几何参数、远场受力、电位移载荷对能量释放率的影响．结果表明：裂纹长度、耦合系数和远场剪切力的减小可以抑制裂纹的扩展．不考虑电场时，声子场应力对能量释放率的影响较小．本文的研究结果可作为研究一维六方压电准晶双材料孔边裂纹问题的理论基础，同时为压电准晶及其复合材料的设计、制备、优化和性能评估提供理论依据．
文章以流体科学进入二十一世纪后,在大规模超算、云存储、数据通信和人工智能为支撑的大数据时代背景下,结合目前在复旦大学航空航天系所构建的热流体湍流直接数值仿真数据库,以及复旦大学团队近期与美国德州大学刘超群教授、上海理工大学蔡小舒教授以及国内水动力学杂志编辑部所合作开展的第三代涡识别技术研究,初步概念性地展示旋涡和湍流,特别是针对有工程实际背景和直接应用价值的壁湍流,在这两个流体力学关键基础议题上的最新认知,和基于大数据深度学习的相关湍流工程模拟实践成果.这些成果包括:(1)基于第三代涡识别技术的尾迹湍流中的涡运动学和动力学探索;(2)流-热统一完整的类-1、类-2湍流边界层壁面律构建;(3)基于第三代涡识别量对Kolmogorov幂次律的再认知;(4)基于DNS统计数据和神经网络深度学习构建新型湍流封闭模型及RANS计算实践.通过这些成果展示,论证解决这两个基础流体科学议题的技术路径,进而促进流体及相关学科研究在现代大数据背景下取得实质性进展和突破,并惠及现代流体、气动、水利、动力和化工等工程领域.
本文采用一种新的半解析法,即独特利用Heaviside函数建立与加筋板等效的变刚度模型来开展复合材料双向正交加筋板在横向载荷下的弯曲挠度分析.此模型可以准确地描述筋条在板面上的分布,以及由于筋条的存在而导致的板面刚度不均匀分布.使用Galerkin加权残值法求解该模型的控制方程,得到不同边界条件和载荷情况下的级数解.对于双向正交加筋板,将此半解析法的结果与传统均匀化方法和使用商业有限元软件ABAQUS建立的有限元模型所得到的弯曲挠度结果比较,验证了此方法的准确性和优越性.不同于传统均匀化方法,本双向正交加筋板的弯曲挠度半解析法可精确、有效地获取加筋间的局部弯曲挠度,可以促进复合材料结构的设计分析与优化的研究进展.
本文基于上海线高速磁浮列车现场噪声测试,结合数值仿真分析了磁浮列车行驶时的噪声特性以及气动噪声分布规律.数值仿真采用延时分离涡结合声比拟的方法,并对比现场测试噪声数据,给出了高速列车气动噪声特性以及噪声源分布规律.研究结果表明:列车行驶时噪声时程呈现很强脉冲性,频率小于100 Hz噪声主要来源于与高架桥梁结构振动相关的二次辐射噪声,特别是次声频段内,桥梁自振会产生显著的噪声.磁浮列车表面气动噪声分布规律与噪声频率相关,低频噪声与列车的车尾涡脱相关,高频噪声由车头边界层分离以及再附着、车身边界层流动等引起,而中频噪声主要产生于列车底部、抱轨与轨道梁表面相对运动作用.因此,高速磁浮列车除了要重点考虑车头、车尾的气动外形对气动噪声的影响外,还应考虑轨道间隙处气动噪声及其分布规律.
针对深埋隧道断面形状优化问题,考虑复杂受力下洞周可能存在拉应力情况,提出基于摩尔-库伦屈服准则的新的优化准则,基于解析解用模拟退火法获得洞周最小破坏范围的最优断面形状.优化模型中,以断面映射函数系数为优化的设计变量,利用混合罚函数使优化孔形满足一定的约束条件,设立孔边最大有效应力(与屈服准则相关)最小的优化准则.针对存在内压的深埋隧道断面形状优化问题,对不同内压、不同侧压系数、不同宽高比限制等情况进行优化计算,并对比两种优化准则在该情况下优化结果的异同.结果表明,对压应力主导优化的情况,新准则与原准则没有差别;对可能出现拉应力的复杂应力情况,新准则有更好的适应性,可以获得更优断面形状.
高强混凝土(High-Strength Concrete,HSC)的力学性能受温度影响较大,尤其在高温环境下性能衰退剧烈,因此在结构分析中宜采用随温度变化的材料性能参数.断裂相场方法基于Griffith变分断裂准则,无需复杂的裂纹拓展追踪技术便可处理多裂纹的问题,可方便地模拟裂纹的萌生、扩展、分岔及汇合过程.本文采用适宜进行结构断裂分析的断裂相场方法,基于能量泛函变分原理,将温度对混凝土材料弹性模量及断裂能的影响引入断裂相场分析方法中,用于高强混凝土高温环境下的强度和破坏分析.以高温作用下高强混凝土梁三点弯曲试验为算例,进行方法验证,通过与实测结果对比,证实了算法的有效性.
辅助索被认为是一种具有潜力的减振手段,但仅在拉索间发生异步振动时才能取得良好的效果.然而,目前对拉索同/异步振动机理尚缺乏系统研究,为此对双水平索进行了模型试验研究.试验主要关注两根不同垂跨比水平拉索跨中面内响应的相位关系.首先对模型进行不同激励频率和保持激励幅值不变下的振动测试,发现垂跨比相同时,两根索相位差基本保持一致;垂跨比不同时,两根索由同步振动转为异步振动.同时采用有限元软件模拟测试实验,其结果与实验吻合良好.为更进一步探究其机理,对试验模型进行了相同激励幅值下的扫频试验.通过对双索幅频特性和相频特性的分析,发现拉索相近参数导致共振区错位是双索存在异步振动现象的根本原因.
