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排序方式: 共有283条查询结果,搜索用时 15 毫秒
1.
对喷射成形高温合金的组织形成及其从雾化过程的树枝晶向等轴晶组织的演变过程进行了分析,结果表明,半液态层中发生的枝晶破碎,重熔所造成的核心增殖作用为等轴晶组织的形成提供了大量结晶核心,在此基础上枝晶臂的合并,粗化以及未严重固相枝晶的粗化和均匀化产生了喷射成形材料所持有的非枝非等轴晶组织。 相似文献
2.
A general topology-based framework for adaptive insertion of cohesive elements in finite element meshes 总被引:1,自引:1,他引:0
Glaucio?H.?PaulinoEmail author Waldemar?Celes Rodrigo?Espinha Zhengyu??Zhang 《Engineering with Computers》2008,24(1):59-78
Large-scale simulation of separation phenomena in solids such as fracture, branching, and fragmentation requires a scalable
data structure representation of the evolving model. Modeling of such phenomena can be successfully accomplished by means
of cohesive models of fracture, which are versatile and effective tools for computational analysis. A common approach to insert
cohesive elements in finite element meshes consists of adding discrete special interfaces (cohesive elements) between bulk
elements. The insertion of cohesive elements along bulk element interfaces for fragmentation simulation imposes changes in
the topology of the mesh. This paper presents a unified topology-based framework for supporting adaptive fragmentation simulations,
being able to handle two- and three-dimensional models, with finite elements of any order. We represent the finite element
model using a compact and “complete” topological data structure, which is capable of retrieving all adjacency relationships
needed for the simulation. Moreover, we introduce a new topology-based algorithm that systematically classifies fractured
facets (i.e., facets along which fracture has occurred). The algorithm follows a set of procedures that consistently perform
all the topological changes needed to update the model. The proposed topology-based framework is general and ensures that
the model representation remains always valid during fragmentation, even when very complex crack patterns are involved. The
framework correctness and efficiency are illustrated by arbitrary insertion of cohesive elements in various finite element
meshes of self-similar geometries, including both two- and three-dimensional models. These computational tests clearly show
linear scaling in time, which is a key feature of the present data-structure representation. The effectiveness of the proposed
approach is also demonstrated by dynamic fracture analysis through finite element simulations of actual engineering problems.
相似文献
Glaucio H. PaulinoEmail: |
3.
Fragmentation of a coating possessing orthogonal preferential crack propagation directions is modeled for equibiaxial tensile loading. Two plausible cracking scenarios are compared, caused by flaws randomly distributed over the area of the coating or along the coating fragment edges. The two fragmentation scenarios considered are shown to yield qualitatively different fragment patterns. 相似文献
4.
One of the important features of database fragmentation and allocation techniques is the fact that they depend not only on the entries of a database relation, but also on their empirical frequencies of use. Distributed processing is an effective way to improve performance of database systems. However, for a Distributed Database System (DDBS) to function efficiently, fragments of the database need to be allocated carefully at various sites across the relevant communications network. Therefore, fragmentation and proper allocation of fragments across network sites is considered as a key research area in distributed database environment. However, fragments allocation to the most appropriate sites is not an easy task to perform. This paper proposes a synchronized horizontal fragmentation, replication and allocation model that adopts a new approach to horizontally fragment a database relation based on attribute retrieval and update frequency to find an optimal solution for the allocation problem. A heuristic technique to satisfy horizontal fragmentation and allocation using a cost model to minimize the total cost of distribution is developed. Experimental results are consistent with the hypothesis and confirm that the proposed model can efficiently solve dynamic fragmentation and allocation problem in a distributed relational database environment. 相似文献
5.
Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst proneness.As such,it is of high practical value to correctly evaluate rock brittleness.However,the definition and measurement method of rock brittleness have been very diverse and not yet been standardized.In this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly discussed.The development and role of rock brittleness in different fields of rock engineering are also studied.Eighty brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are discussed.The results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock brittleness.On the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness.It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness.This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term. 相似文献
6.
针对福州地铁强承压性裂隙水碎裂状岩层,研究有效的盾构防喷涌技术,提高掘进效率,保证施工安全。首先,通过涌水量预测计算,找到了渗透系数过大、水量充足、极易发生喷涌的区段;然后,通过实践探索提出了采取地面降水井工程措施降低水压、对盾构螺旋输送机进行改造控制出渣和排水的防喷涌技术。通过该项技术的应用,盾构在通过易发生喷涌地段时,减少了喷涌的发生次数和喷涌量,保证了工期,降低了施工成本,地表沉降也满足了沉降控制标准的要求。 相似文献
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9.
Alan Jay Smith 《Performance Evaluation》1981,1(2):104-117
The file system, and the components of the computer system associated with it (disks, drums, channels, mass storage, tapes and tape drives, controllers, I/O drivers, etc.) comprise a very substantial fraction of most computer systems; substantial in several aspects including amount of operating system code, expense for components, physical size and effect on performance. In this paper we survey the state of the art file and I/O system design and optimization as it applies to large data processing installations. In a companion paper, some research results applicable to both current and future system designs are summarized.Among the topics we discuss is the optimization of current file systems, where some material is provided regarding block size choice, data set placement, disk arm scheduling, rotational scheduling, compaction, fragmentation, I/O multipathing and file data structures. A set of references to the literature, especially to analytic I/O system models, is presented. The general tuning of file and I/O systems is also considered. Current and forthcoming disk architectures are the second topic. The count key data architecture of current disks (e.g. IBM 3350, 3380) and the fixed block architecture of new products (IBM 3310, 3370) are compared. The use of semiconductor drum replacements is considered and some commercially available systems are briefly described. 相似文献
10.
The cohesive and adhesive properties, and related critical radius of curvature of thin multilayer insulator coatings on a 152 μm thick flexible steel substrate were investigated using tensile experiments carried out in-situ in an optical microscope. This method was found to be well adapted for the two types of coatings studied: SiO2 single layers with different thickness and SiO2/SiNx/polyimide stacks. Special attention was paid to the influence of surface roughness and yielding of the steel substrate. Coating delamination and spallation was observed at low strain in case of SiO2 coatings on unpolished steel, resulting from roughness-induced stress concentrations and slippage of grain boundaries. Polishing the steel substrate, or using a polyimide interlayer, was found to be useful to avoid premature delamination of the layers. In all investigated cases, a critical radius of curvature for layer damage of approximately 5 mm was found. 相似文献