检索结果-南通市图书馆

Extension of covariant derivative(Ⅲ): From classical gradient to shape gradient

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2015年第1期31卷 96-103页

作者： ya-jun yin Department of Engineering Mechanics School of Aerospace Tsinghua University

This paper further extends the generalized covari ant derivative from the first covariant derivative to the sec ond one on curved surfaces. Through the linear transforma tion between the first generalized covariant derivative and the second one, the second covariant differential transformation group is set up. Under this transformation group, the sec ond class of differential invariants and integral invariants on curved surfaces is made clear. Besides, the symmetric struc ture of the tensor analysis on curved surfaces are revealed.

关键词： Tensor analysis on curved surfaces The sec-ond generalized covariant derivative The second covariantdifferential transformation group The second class of dif-ferential and integral invariants

Extension of covariant derivative(Ⅱ): From flat space to curved space

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2015年第1期31卷 88-95页

作者： ya-jun yin Department of Engineering Mechanics School of Aerospace Tsinghua University

This paper extends the classical covariant deriva tive to the generalized covariant derivative on curved sur faces. The basement for the extension is similar to the pre vious paper, i.e., the axiom of the covariant form invariabil ity. Based on the generalized covariant derivative, a covari ant differential transformation group with orthogonal duality is set up. Through such orthogonal duality, tensor analy sis on curved surfaces is simplified intensively. Under the covariant differential transformation group, the differential invariabilities and integral invariabilities are constructed on curved surfaces.

关键词： Tensor analysis on curved surfaces Classicalcovariant derivative and generalized covariant derivative Axiom of the covariant form invariability Covariant differ-ential transformation group Differential invariabilities andintegral invariabilities

Fractal growth kinematics abstracted from snowflakes:topological evolution

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2015年第2期36卷 243-264页

作者： Fan yaNG ya jun yin Bin HE Qinshan FAN Department of Engineering Mechanics School of Aerospace Key Laboratory of Applied Mechanics Tsinghua University Division of Mechanics Nanjing University of Technology

Based on the kinematic viewpoint, the concept of proportional movement is abstracted to explain the strange behaviors of fractal snowflakes. A transformation group for proportional movement is defined. Under the proportional movement transformation groups, necessary and sufficient conditions for self-similarity of multilevel structures are presented. The characteristic topology of snowflake-like fractal patterns, identical to the topology of ternary-segment fractal line, is proved. Moreover, the topological evolution of N-segment line is explored. The concepts of limit growth and infinite growth are clarified,and the corresponding growth conditions are derived. The topological invariant properties of N-segment line are exposed. In addition, the proposition that the topological evolution of the N-segment line is mainly controlled by the topological invariant N is verified.

关键词： fractal snowflake proportional movement self-similarity N-segment line topological evolution and topological invariant

Temperature field simulations during selective laser melting process based on fully threaded tree

在线全文

学校读者我要写书评

暂无评论

China Foundry 2017年第5期14卷 405-411页

作者： Wei Duan ya-jun yin Jian-xin Zhou State Key Laboratory of Materials Processing and Die&Mould Technology Huazhong University of Science and TechnologyWuhan 430074China

Selective laser melting(SLM) is a promising technique for additive manufacturing. During SLM of metallic powder, the temperature field and thermal history are important to understand physical phenomena involved. The purpose of this study is to simulate the temperature field during the SLM process of a hollow cylinder shape part based on a fully threaded tree(FTT) technique, and to analyze the temperature variation with time in different regions of the part. A revised model for temperature field simulation in the SLM process was employed, which includes the transition of powder-to-dense sub-model and a moving volumetric Gaussian distribution heat source sub-model. The FTT technique is then adopted as an adaptive mesh strategy in the simulation. The simulation result shows that during the SLM process of cylinder part, the temperature of inner powder bed is obviously higher than external one. The temperature at the internal of the molten pool is also higher than external, which may lead to differences in microstructures and other properties between the two regions.

关键词： fully threaded tree selective laser melting temperature distribution numerical simulation

Finite element simulation of real cavity closure in cast Ti6Al4V alloy during hot isostatic pressing

在线全文

学校读者我要写书评

暂无评论

China Foundry 2022年第1期19卷 55-62页

作者： Qian Xu Wen Li ya-jun yin Jian-xin Zhou Hai Nan State Key Laboratory of Materials Processing and Die and Mould Technology Huazhong University of Science and TechnologyWuhan 430074China AECC Beijing Institute of Aeronautical Materials Beijing 100095China

The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing *** X-ray micro computed tomography was used to record the morphology changes before and after hot isostatic *** two-dimensional geometry obtained by the microCT scan was used in simulation to study the evolution of the real shrinkage cavity during hot isostatic *** cavities,shrinkage porosity and small gas pores can be effectively eliminated under proper HIP *** two-dimensional morphology in the simulation results agrees well with the experimental *** study reveals that plastic deformation,creep and diffusion are the main mechanisms of cavity closure during hot isostatic *** addition,the simplified elliptical pores with aspect ratios at different positions were used to replace the real pores to further study the factors affecting the position of dimples after HIP by *** is found that the position of the dimples mainly depends on the aspect ratio of the elliptical pore and the distance between the pore surface and the external surface of the geometric model.

关键词： cast Ti6Al4V alloy hot isostatic pressing shrinkage cavity simulation closure behavior

Phase field study on crystal orientation effects in eutectoid phase transformation

在线全文

学校读者我要写书评

暂无评论

China Foundry 2017年第5期14卷 435-442页

作者： Dong-qiao Zhang ya-jun yin Jian-xin Zhou Zhi-xin Tu State Key Laboratory of Materials Processing and Die&Mould Technology Huazhong University of Science and TechnologyWuhan 430074China

In this present work, a multi-phase field model was used to simulate the eutectoid transformation process, and on the basis of the nucleation model that was previously proposed by our research team, anisotropic and orientation relationship models were introduced to study the growth mechanism of the pearlite lamellae with anisotropy. It was found that the growth direction of the pearlite lamellae is related to its orientation and spacing. In the process of lamellar growth, deflection growth of pearlite will appear along with the adjustment of lamellar spacing, and the deflection angle is equal to the orientation difference between the austenite and the pearlite. Comparison between experimental and numerical results indicates a good consistency in pearlite morphology.

关键词： simulation phase field lamellar growth pearlite morphology growth direction

Optimal design of feeding system in steel casting by constrained optimization algorithms based on InteCAST

在线全文

学校读者我要写书评

暂无评论

China Foundry 2016年第6期13卷 375-382页

作者： Chang-chun Dong Xu Shen Jian-xin Zhou Tong Wang ya-jun yin State Key Laboratory of Materials Processing and Die & Mould Technology Huazhong University of Science and Technology

The traditional foundry industry has developed rapidly in recently years due to advancements in computer technology. Modifying and designing the feeding system has become more convenient with the help of the casting software, Inte CAST. A common method of designing a feeding system is to first design the initial systems, run simulations with casting software, analyze the feedback, and then redesign. In this work, genetic, fruit fly, and interior point optimizer(IPOPT) algorithms were introduced to guide the optimal riser design for the feeding system. The results calculated by the three optimal algorithms indicate that the riser volume has a weak relationship with the modulus constraint; while it has a close relationship with the volume constraint. Based on the convergence rate, the fruit fly algorithm was obviously faster than the genetic algorithm. The optimized riser was also applied during casting, and was simulated using Inte CAST. The numerical simulation results reveal that with the same riser volume, the riser optimized by the genetic and fruit fly algorithms has a similar improvement on casting shrinkage. The IPOPT algorithm has the advantage of causing the smallest shrinkage porosities, compared to those of the genetic and fruit fly algorithms, which were almost the same.

关键词： casting process design optimal solution Inte CAST

Optimization of steel casting feeding system based on BP neural network and genetic algorithm

在线全文

学校读者我要写书评

暂无评论

China Foundry 2016年第3期13卷 182-190页

作者： Xue-dan Gong Dun-ming Liao Tao Chen Jian-xin Zhou ya-jun yin State Key Laboratory of Materials Processing and Die & Mould Technology Huazhong University of Science and Technology School of Mechanical Engineering Hubei University of Technology

The trial-and-error method is widely used for the current optimization of the steel casting feeding system, which is highly random, subjective and thus ineff icient. In the present work, both the theoretical and the experimental research on the modeling and optimization methods of the process are studied. An approximate alternative model is established based on the Back Propagation(BP) neural network and experimental design. The process parameters of the feeding system are taken as the input, the volumes of shrinkage cavities and porosities calculated by simulation are simultaneously taken as the output. Thus, a mathematical model is established by the BP neural network to combine the input variables with the output response. Then, this model is optimized by the nonlinear optimization function of the genetic algorithm. Finally, a feeding system optimization of a steel traveling wheel is conducted. No shrinkage cavities and porosities are induced through the optimization. Compared to the initial design scheme, the process yield is increased by 4.1% and the volume of the riser is decreased by 5.48×10~6 mm3.

关键词： steel casting numerical simulation process parameters optimization BP neural network

Global heat transfer model and dynamic ray tracing algorithm for complex multiple turbine blades of Nibased superalloys in directional solidification process

在线全文

学校读者我要写书评

暂无评论

China Foundry 2019年第5期16卷 326-335页

作者： Wen Wang Jian-xin Zhou Zhao Guo ya-jun yin Xu Shen Xiao-yuan Ji State Key Laboratory of Materials Processing and Die &Mould Technology Huazhong University of Science and Technology

High-quality solidification microstructure during directional solidification relies on precise temperature gradient control, so accurate calculation of the temperature field is critical. In this study, a 3D transient global heat transfer model of directional solidification by the Bridgman method based on the finite difference method is developed. The radiation heat in this model is calculated by the discrete transfer method, and a modified method of external surface area for irregular geometric models is proposed to reduce the zigzag shape caused by finite difference grids. Considering the radiative heat transfer between any surface elements of all materials in the directional solidification furnace, a dynamic ray tracing algorithm is developed to simulate the entire process of directional solidification. Then, the simulated results are compared with the theoretical results and experimental results, respectively. Finally, based on the present model and method, the simulation program developed is applied to the directional solidification of actual castings. The simulated results are in good agreement with the experimental results, which indicate that the model and method developed in this study is effective and practical.

关键词： radiative heat transfer ray tracing turbine blade directional solidification numerical simulation