Thin-Shell Wormholes Admitting Conformal Motions in Spacetimes of Embedding Class One

This paper discusses the feasibility of thin-shell wormholes in spacetimes of embedding class one admitting a one-parameter group of conformal motions. It is shown that the surface energy density σis positive, while the surface pressure is negative, resulting in , thereby signaling a violation of the null energy condition, a necessary condition for holding a wormhole open. For a Morris-Thorne wormhole, matter that violates the null energy condition is referred to as “exotic”. For the thin-shell wormholes in this paper, however, the violation has a physical explanation since it is a direct consequence of the embedding theory in conjunction with the assumption of conformal symmetry. These properties avoid the need to hypothesize the existence of the highly problematical exotic matter.

Numerical Simulation and Experiment on Thin-Shell Object Separation from Aircraft

The unsteady aerodynamic loads generated by the thin-shell object separating from aircraft affects flying safety.To investigate the loads,a method combining numerical simulation and experiment is proposed.Firstly,the motional tendency of the thin-shell object separating from aircraft is calculated,and then the high-speed air blowing test on ground is designed.Thereafter,the external store is employed to avoid colliding with the thin-shell object in air.Finally,the hanging and flight test is conducted by a high-speed unmanned aerial vehicle(UAV),and the feasibility of the thin-shell object separating from aircraft at high speed is proved.Consequently,the separating problem of a thin-shell object with an unconventional aerodynamic configuration is solved,and the collisions with aircraft is prevented.

Additional observational features of the thin-shell wormhole by considering quantum corrections

By considering an asymmetric thin-shell wormhole(ATSW)surrounded by an optically and geometrically thin disk,we investigate the luminosity distribution of this ATSW with the spacetime on two sides encoded with the renormalization group improved(RGI)parameters(Ω,γ).Although some light rays are absorbed into the throat in the vicinity of the wormhole,they return through the throat with certain conditions,unlike in the case of black holes.The spacetime on one side of the wormhole can capture the additional photons emitted from the thin disk,resulting in several interesting observable features of the wormhole.The results in this paper show that there are two additional orbit numbers n in the ATSW and six transfer functions,rather than three as in the black hole case.In this case,the ATSW indeed has a more complex observable structure,where some additional light rings arise naturally.For instance,there are two additional photon rings for the emitted Model 1.Moreover,we also find a new wide hump between the first and second additional photon rings in Model 2.The effects of Ω and γ on the observed images are clearly addressed throughout this study,and the influence of Ω is found to be larger.Finally,we conclude that the observations of the RGI-ATSW can help further distinguish it from other ATSWs and black holes when a thin accretion disk exists around it.

Observational appearance and extra photon rings of an asymmetric thin-shell wormhole with a Bardeen profile

In this work,the optical appearance of an asymmetric thin-shell wormhole with a Bardeen profile is studied.To initiate the process,we need to construct an asymmetric thin-shell wormhole utilizing the cut-and-paste technique proposed by Visser and subsequently ascertain its pertinent physical quantities such as the radius of the photon sphere and critical impact parameters for different values of magnetic charge g.Then,the effective potential and motion behavior of photons are also investigated within the framework of asymmetric thin-shell wormholes with a Bardeen profile.It can be found that the effective potential,ray trajectory,and azimuthal angle of the thin-shell wormhole exhibit a strong correlation with the mass ratio of black holes.By considering the accretion disk as the sole background light source,we observe additional photon rings and lensing bands in the optical appearance of the asymmetric thin-shell wormhole with a Bardeen profile compared to those exhibited by the Bardeen black hole.One can find that there is an increase in the size of the specific additional light bands with increasing magnetic charge g,which is different from the black hole case.These exceptionally luminous rings can serve as a robust criterion for the identification and characterization of the thin-shell wormhole spacetime.

Non-exotic static spherically symmetric thin-shell wormhole solution in f(Q,T)gravity

In this study,we conduct an analysis of traversable wormhole solutions within the framework of linear f(Q,T)=αQ+βT gravity,ensuring that all energy conditions hold for the entire spacetime.The solutions presented in this paper are derived through a comprehensive analytical examination of the parameter space associated with the wormhole model.This involves considering the exponents governing the redshift and shape functions,as well as the radius of the wormhole throat(r_(0)),the redshift function value at the throat(∅_(0)),and the model parameters(αandβ).Moreover,we establish bounds on these free parameters,which guarantee the satisfaction of the energy conditions throughout spacetime and also provide two solutions.Furthermore,we use the Israel junction condition to observe the stability of a thin-shell around the wormhole.Finally,we calculate the null energy condition criteria as well as the potential for the thin-shell and how it varies with the chosen shape function.

Effects of torsion charge on optical appearance and additional photon rings of an asymmetric thin-shell wormhole

In this paper,we study the optical properties of asymmetric thin-shell wormholes(ATWs)under torsion charge.Utilizing the cut-and-paste method developed by Visser,we construct these wormholes and determine their key physical properties,such as the radius of the photon sphere and critical impact parameters,under different torsion charges.Furthermore,we investigate the effective potential and behavior of photon motion within the wormhole spacetime,identifying a relationship between photon trajectories and impact parameters.The study focuses on scenarios where thin accretion disks act as the primary light source.It reveals that the optical features of ATWs under torsion charge significantly differ from those of black holes(BHs).Notably,an increase in torsion charge leads to a reduction in the sizes of both extra photon rings and lensing bands,which serve as important markers for distinguishing and characterizing ATW spacetimes from those of BHs.

椭球形与圆柱形耐压薄壳承载特性对比研究

将水下无人潜航器耐压结构作为应用背景,为对比椭球形薄壳与圆柱形薄壳承载差异,以应力和弹性稳定性作为典型力学性能指标进行对比。基于第四强度理论,以Mises应力作为典型应力开展数值计算,同等重量下椭球薄壳应力峰值较圆柱薄壳应力峰值小4%左右。以等容积、等重量为前提,基于ISIGHT平台调用Ansys,采用NSGAⅡ优化算法开展椭球薄壳弹性稳定性优化,同等重量、同等有效容积下,椭球薄壳稳定性较圆柱壳提升1.78%~6%;仅要求同等容积时,椭球薄壳稳定性较圆柱壳最大提升约200%。研究成果可为超大潜深潜器耐压结构选型提供借鉴。

Full-Scale Isogeometric Topology Optimization of Cellular Structures Based on Kirchhoff-Love Shells

Cellular thin-shell structures are widely applied in ultralightweight designs due to their high bearing capacity and strength-to-weight ratio.In this paper,a full-scale isogeometric topology optimization(ITO)method based on Kirchhoff-Love shells for designing cellular tshin-shell structures with excellent damage tolerance ability is proposed.This method utilizes high-order continuous nonuniform rational B-splines(NURBS)as basis functions for Kirchhoff-Love shell elements.The geometric and analysis models of thin shells are unified by isogeometric analysis(IGA)to avoid geometric approximation error and improve computational accuracy.The topological configurations of thin-shell structures are described by constructing the effective density field on the controlmesh.Local volume constraints are imposed in the proximity of each control point to obtain bone-like cellular structures.To facilitate numerical implementation,the p-norm function is used to aggregate local volume constraints into an equivalent global constraint.Several numerical examples are provided to demonstrate the effectiveness of the proposed method.After simulation and comparative analysis,the results indicate that the cellular thin-shell structures optimized by the proposed method exhibit great load-carrying behavior and high damage robustness.

矩形大开孔外压薄壁圆柱壳结构稳定性研究

以含矩形大开孔的薄壁圆柱壳结构为研究对象,利用ANSYS Workbench软件对其进行了屈曲分析,研究了不同的几何影响因素和材料参数与其临界失稳载荷和屈曲行为的关系。结果表明:结构的临界失稳载荷主要影响因素为壳体的径厚比;在弹性模量不变的情况下,临界失稳载荷与材料的屈服强度近似为线性关系;径厚比和材料参数的改变并不会改变结构的屈曲行为和趋势。

The Key Path of the Shape Optimization Design of Isotropic Material Pressure Vessels

An optimization design was conducted for the shape of the pressure vessel with a thin-shell shell. During this process, the optimization calculation was performed with the aid of the genetic algorithm toolbox included in Matlab. Firstly, through the parametric modeling function of APDL, models such as arc-shaped, parabolic, elliptical, and those generated by the fitting curve command were successfully constructed. Meanwhile, the relevant settings of material properties were accomplished, and the static analysis was conducted. Secondly, the optimization calculation process was initiated using the genetic algorithm toolbox in Matlab. Eventually, through analysis and judgment, the model generated by the fitting curve command was relatively superior within the category of the best shape.

汽车后大灯镜壳大型薄壁精密注塑模设计

根据汽车后大灯镜壳的结构特点,设计了一副大型薄壁精密注塑模具。模具采用定模成型内表面、动模成型外表面及动模侧向抽芯机构,有效地解决了成型塑件脱模困难问题;模具采用三级定位机构,显著提高了模具刚度和寿命;模具采用随形水路温度控制系统,成型周期降低了10%,成型塑件最大变形量下降了20%,成型塑件的尺寸精度达到了设计要求的MT3;模具采用推杆先复位机构,有效地消除了滑块和推杆汽相撞的风险,保证了侧向抽芯机构安全可靠。模具投产后运行平稳,成型塑件尺寸稳定。

一种加工薄壁壳体零件的复合浮动式工装设计

为解决某大型薄壁壳体零件在加工中存在的变形、震颤等问题,通过对零件结构和工艺进行分析,从零件加工工艺安排和装夹方案等方面采取了措施,并根据加工过程中存在问题对工装夹具进行优化,设计了一款电动轻型复合浮动式工装。工装采用分体式空心结构、轻型材料和自动化控制方式,解决了零件的加工变形和震颤问题,保证了零件的加工质量。设计的工装对产品的不同加工状态、不同壁厚具有较强的自适应性,也对相同结构不同材料的产品具有较强的自适应性,进一步扩大了工装的应用范围,降低了产品的生产成本,提高了零件的生产效率,为类似产品的加工提供了思路与方法,具有一定的推广应用价值。

薄壁壳体零件的数字化制造研究

针对薄壁壳体的数控加工,通过计算机辅助设计与制造解决壳体零件表面复杂、各项精度要求高的问题,并通过调整切削加工时的工艺参数、加工策略等解决薄壁易形变的问题,以期为后续相同类型零件的数控加工提供借鉴。

易变形薄壁壳零件的数控加工技术

文章对影响薄壁壳零件数控加工质量的各种因素进行了深入分析,包括切削力、热变形、机床精度、装夹方式等。从工艺参数、夹具设计和机床性能3个方面入手,提出一系列优化策略,以有效降低薄壁壳体零件的加工变形,从而大幅提升薄壁壳体零件的加工精度,为数控加工提供新思路、新方法,促进我国产业技术进步与品质提升。

压电圆环径向弯曲振动与激励研究

针对压电圆环换能器的径向弯曲振动问题,从薄壳理论出发进行相关数理推导,讨论了压电效应的影响及电学短路与开路下的弯曲振动方程.进行相关解析求解,给出了两种条件下的多阶谐振频率预测公式,并利用有限元法分析了两式的适用范围.使用模态理论,定义模态权值函数,研究了电学激励条件对多阶弯曲振动模态的具体影响,得到了单模态激励、局部等幅激励和单端激励等作用于多个目标模态的有效方法.经有限元仿真(FEM)、实验与理论对比验证,三者吻合较好,相关结论可以为压电圆环弯曲振动模态识别、模态激励的精细化调控提供理论基础.

基于精细传递矩阵法的气囊隔振器横向刚度特性分析

构建并求解了预载条件下气囊隔振器的囊体力学模型,提出了一种气囊隔振器横向刚度特性的参数化计算方法。在考虑囊体预应力的条件下构建了囊体力学模型,引入位移中间向量并采用精细积分法推导了囊体状态向量间的传递矩阵,利用迭代法解析了囊体状态向量、内部压力以及结构参数之间的耦合变化关系,基于边界条件完成了囊体刚度的参数化求解,结合理想气体刚度模型完成了气囊隔振器横向刚度特性的计算分析。对比试验结果,验证了横向刚度特性计算方法的正确性,探究了主要设计参数对刚度特性的影响规律。

基于改进的Canopy-k-means的大跨屋盖表面风荷载分区方法

针对k-means聚类算法在大跨屋盖结构表面风荷载分区计算中,聚类数k值随机选取容易导致结果不稳定和计算效率低等问题,提出改进的Canopy-k-means聚类算法。首先,引入Canopy算法并对其初始阈值和聚类中心的选取方式进行改进,减少初始值选取的盲目性,以提高风荷载分区结果的可靠性;其次,通过改进Canopy算法对风荷载数据集进行预处理,快速准确地确定聚类数k值;第三,将改进Canopy算法与k-means结合使用,实现最优分类数k值的精准识别,使得改进的Canopy-k-means聚类算法进行大跨屋盖结构表面风荷载分区时能够快速准确地得到分区结果;最后,以一大跨柱面屋盖干煤棚结构为例,基于风洞试验所得结构表面风荷载数据测试结果,采用所提改进的Canopy-k-means聚类算法对其表面风荷载进行分区计算。结果表明,采用改进的Canopy-k-means聚类算法,将0°、50°和90°风向角时大跨屋盖表面风荷载划分为了3个不同的分区,其对应的SD值分别为2.36、3.51和2.52,较传统k-means聚类算法所得对应值明显降低,类内紧凑性和类间分散性明显提升。所提改进Canopy-k-means聚类算法能够快速准确地得到最优分区结果,对大跨屋盖表面风荷载分区具有工程参考价值。

双层薄壳钢-混组合桥梁钢塔建造线型控制技术

以安阳至罗山高速公路黄河大桥钢塔为例,双层薄壳桥梁钢-混组合塔建造线形控制是较为复杂的过程,需从横断面的分块设计,双层薄壳单元加工的精度控制,塔节段整体组装(预拼装)精度控制,桥位安装线形采用特征点控制,混凝土时间和浇筑量分别予以控制,针对各工序的控制要点,制定行之有效的实施方案,通过该项目的实践,塔壳的线型满足设计要求,为类似结构桥梁钢塔建造线型控制提供借鉴。

薄壁壳体构件力振耦合试验装置设计及应用

为满足某装备薄壁壳体构件在不断重复高/低载荷条件下可靠性试验需求,采用螺杆挤压随形工件的内平衡加载方式设计力加载装置,在振动环境下进行可行性验证,表明该装置满足薄壁壳体构件在(1~350)Hz频率范围内的力振耦合加载需求。

薄壁壳体构件复合加载试验及参数监测平台设计及应用

围绕复杂服役环境下某装备薄壁壳体构件失效模式不清和寿命评估困难等问题,研发复合加载试验及参数监测平台。通过静力加载装置和振动夹具组合设计的内平衡加载方式对薄壁壳体施加静力载荷,有效解决温湿振环境下力加载的解耦难题;通过多综合应力环境参数控制和监测系统集成设计,实现多应力监测和控制一体化功能。该平台能够赋予薄壁壳体构件相应的温度、湿度、力和振动环境,也能实时对温度、湿度、力、振动和应变等信号进行监测和记录,有效模拟装备更为真实的工作状态,为装备研制和考核提供有力支撑。