结构冲击动力学进展(2010-2020)

本文综述结构冲击动力学的国内外研究进展,在时间区间上聚焦于2010—2020这十来年发表的文献,同时提及在此之前的奠基性工作。在内容上,首先着眼于结构冲击动力学的基本科学问题,如概念、模型和工具,它们源于和用于结构在爆炸与冲击下的塑性动力响应、失效和重复受载等;也介绍典型薄壁结构件的动力行为,以及运动的物体和结构物对固壁的撞击和反弹。注意到近十多年来由于轻质材料(如多胞材料、3D打印的超材料等)和以它们为芯层的轻质结构的大量涌现,以及对生物材料和仿生结构的极大兴趣,对这些材料和结构的冲击动力学行为的研究构成了本文的后半部分。最后指出,在多尺度框架下以更全面的视角研究材料-结构-性能的内在规律,已成为推动冲击动力学继续发展的一个强大的新趋势。

Analytical Solution for Plastic Responses of Metal Beams under Repeated Impacts Based on Membrane Factor Method

Marine structures are frequently subjected to repeated impact loadings,resulting in failure of the structures,even causing serious accidents.The analytical expressions of dimensionless permanent deflection and impact force of a metal beam based on maximal normal yield surface are derived by membrane factor method(MFM),then the results are compared with repeated impact tests.It can be found that the solutions based on MFM are between the upper and lower bounds,and very close to the results of the repeated impact tests,indicating the theoretical model proposed can predict the plastic responses of the metal beam accurately.What’s more,the influences of impact location and boundary condition on the dynamic responses of the beam subjected to repeated impacts are determined.Results show that,as the distance of impact location from the middle span of the beam increases,the permanent deflection decreases,while the impact force increases.Meanwhile,the influences of impact location enhance as the impact number increases.When the permanent deflection is smaller than the thickness,the effect of boundary condition on the plastic responses is significant.However,when the deflection is larger than the thickness,the beam will be like a string and only axial force works,resulting in little influence of boundary condition on the plastic responses of the beam.

Forming and Springback Prediction of Strips Under Multi-square Punch Concave Forming Process Considering Partial-unloading Effects

To further investigate the forming mechanism and springback characteristics of strips under multi-square punch forming (MSPF) considering partial-unloading effects, a series of concave form ing tests of strips are conducted on the MSPF machine. This paper aims to reveal the physical mecha nism of the elastic-plastic deformation in the MSPF process considering the effect of the forming ap proaches, and derive appropriate mathematical interpretations. The theoretical model is firstly estab lished to analyse the concave forming mechanism and springback characteristics of the strip, and its accuracy is then validated by experimental data. The forming history and load evolutions are depicted to explore the required forming capacity through the proposed analytical method. Besides, the paramet ric studies are carried out to discuss their effects on the springback of the strip. The results suggest that the deformation paths of the strip are influenced by the forming approach, and the springback of the strip in convex forming is larger than that in concave forming.

Design of Ocean Floating Structures:Prediction of Hydrodynamic Coefficients

[Introduction] Accurate calculation of the hydrodynamic coefficients for floating structures and the investigation of the flow field distribution around floating bodies on the marine free surface are essential for improving the engineering design and application of marine structures.[Method] This study utilized the computational fluid dynamics(CFD) approach and the Reynolds Averaged NavierStokes(RANS) method and considered the effects of viscosity and free surface interactions on the hydrodynamic behavior of floating structures.By employing the dynamic mesh technique,this study simulated the periodic movements of simplified three-dimensional(3D)shapes:spheres,cylinders,and cubes,which were representative of complex marine structures.The volume of fluid(VOF) method was leveraged to accurately track the nonlinear behavior of the free surface.In this analysis,the added mass and damping coefficients for the fundamental modes of motion(surge,heave,and roll) were calculated across a spectrum of frequencies,facilitating the fast determination of hydrodynamic forces and moments exerted on floating structures.[Result] The results of this study are not only consistent with the results of the 3D potential flow theory but also further reflect the role of viscosity.This method can be used for precise calculation of the hydrodynamic coefficients of floating structures and for describing the flow field of such structures in motion on a free surface.[Conclusion] The methodology presented goes beyond the traditional potential flow approach.

生成式人工智能在数字出版中的应用与挑战——以ChatGPT为例

本文旨在探讨以ChatGPT为代表的生成式人工智能对数字出版行业带来的赋能与挑战。通过回顾并总结ChatGPT的优越性,本文分别从内容创作角度、编辑校对角度、整体行业角度分析了AI应用的正向价值,认可ChatGPT在内容创作提效、编校产能升级、版税分配、作者培养等方面提供的有力支持,并针对其引发的出版物泛娱乐化、版权难以界定等挑战提出思考。

基于API极限工况下钻机结构安全性分析

以现场使用的某型号ZJ80钻机为研究对象,API设计验证为背景,结合现有对钻机井架力学特性的研究方法,提出一种结合稳定性研究的力学分析方法,旨在为井架设计安全性验证提供一种更为准确的分析方法。结合稳定性分析中的非线性屈曲分析研究方法,模拟井架及底座结构在受扰动及含缺陷状态下的失稳极限点,在此状态下分析结构强度及安全性。研究结果表明:在考虑井架及底座受到扰动及含缺陷时,各工况下井架及底座结构等效应力值均小于许用应力值,各工况计算UC值均小于1;其中当作业中存在钩载时,结构危险位置出现在天车梁处,无钩载状态下结构危险位置出现在底座转盘梁处;钻机井架在临近失稳状态时,结构综合强度依然满足设计需求。该计算方法及结果更符合现场作业情况,满足API规范要求。研究结果可为钻机井架结构改进提供理论支撑。

基于深度学习的旋转机械大数据智能故障诊断方法

深度学习作为一种智能高效的模式识别技术,已得到基于大数据驱动的机械装备故障诊断领域学者的广泛关注。为了更加有效地从多传感器原始故障数据中提取出故障特征,解决单一诊断算法提取时序数据特征时的信息丢失问题,提出一种基于改进的长短期记忆循环神经网络-全局均值池化卷积神经网络(LSTM-GCNN)的深度循环卷积神经网络新算法,用于机械装备大数据的故障智能诊断。该算法首先运用长短时记忆循环神经网络(LSTM)从多通道原始数据中提取时间关联性记忆特征,然后再将特征数据输入到一维卷积神经网络(1D-CNN)中进行微小差异特征辨识,并且为了减少模型参数量和提高算法检测速度,设计了一个一维全局均值池化层用于代替传统1D-CNN算法中的全连接层结构。通过将提出的算法用于滚动轴承在1马力、2马力和3马力多种负载工况下采集的3通道振动信号数据进行诊断验证,分别得到100%、99.85%和99.78%的诊断准确率,实验结果相比传统的DNN、LSTM和CNN算法具有更加优越的诊断性能;对齿轮箱在空载和承载两种运行工况下的8通道原始数据进行故障诊断的准确率分别高达99.93%和99.8%,具有良好的迁移通用性能。