Search Results - (Author, Cooperation:S. H. Lo)

2014-04-18

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1435-5663

Discretised surfaces ; Intersections ; Mesh generation ; Solid objects ; Topology

Springer Online Journal Archives 1860-2000

Computer Science

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Technology

Abstract Triangulation of complex three-dimensional objects is a time-consuming process, and the boundary surfaces of the object have to be checked very carefully to ensure no crror is made. With the increased use of computer graphics in the generation of complicated object shapes, such as aircraft, space vessels, machine parts, physical models, etc., visual inspection alone is not good enough to affirm the validity of the object, and a thorough verification of the output from a CAD system is necessary to ensure that the object is well defined and complies with the input requirements of the mesh generator. This paper describes such a data verification procedure for general curved surfaces and objects defined by the boundary surface modelling technique. The quality of individual elements, the overall topological structures, and geometrical correctness in terms of intersections, close touches and sharp angles will all be studied and verified. Several engineering objects are analysed to illustrate the practical applications of the procedure.

Electronic Resource

1432-0924

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract A simple and efficient refinement procedure for the three-dimensional tetrahedral element mesh based on successive bisection of edges is proposed. The quality of the elements generated can be guaranteed if the subdivision is performed in the sequence according to the length of the line segments to be divided. Such an order of priority can be determined by a simple sorting process on all the line segments for which refinement is needed. This list of ordered line segments has to be updated from time to time to take into account of the new line segments generated during the subdivision process. From the examples studied, the CPU time for mesh refinement bears a linear relationship with the number of elements generated, with a refinement rate of more than 50 000 elements per second on a IBM Power Station 3BT. Shape optimization procedures can be applied to the refined mesh to further improve the quality of the elements. The refinement scheme is useful as part of a general three-dimensional mesh generation package, or as the mesh refinement module in an adaptive finite element analysis.

Electronic Resource

1432-2064

Springer Online Journal Archives 1860-2000

Mathematics

Summary We study the estimation of a density and a hazard rate function based on censored data by the kernel smoothing method. Our technique is facilitated by a recent result of Lo and Singh (1986) which establishes a strong uniform approximation of the Kaplan-Meier estimator by an average of independent random variables. (Note that the approximation is carried out on the original probability space, which should be distinguished from the Hungarian embedding approach.) Pointwise strong consistency and a law of iterated logarithm are derived, as well as the mean squared error expression and asymptotic normality, which is obtain using a more traditional method, as compared with the Hajek projection employed by Tanner and Wong (1983).

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Copper-nickel alloys used in marine applications, are known for their anti-fouling properties. However, they are generally of low strength and are moderately susceptible to corrosion when used in a marine environment. Attempts at adding iron to Copper-nickel alloys by conventional ingot metallurgy, to improve their mechanical and corrosion resistant properties, have met with limited success. In this work, rapid solidification technology was employed to produce rapidly solidified (RS) Cu-10Ni and Cu-10Ni-8Fe. It was found that both the RS Cu-10Ni and Cu-10Ni-8Fe exhibited superior mechanical and corrosion resistant properties, compared with their sand-cast counterparts. Furthermore, the addition of iron to Cu-10Ni alloy, produced by RS, increased the corrosion resistance of the alloy, whereas the addition of iron to Cu-10Ni alloy produced by conventional means, had an adverse effect.

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Recently, commercial Zn-Al foundry alloys such as ZA-27 have found increasing use for many applications and have competed effectively against copper, aluminium and iron-based foundry alloys. However, the elevated temperature (〉 100°C) properties of zinc-aluminium alloys are unsatisfactory and restrict their use in some applications. One viable approach to improving the elevated temperature properties is to reinforce the zinc-aluminium alloys with alumina fibres. In this investigation, the mechanical properties of a Zn-Al alloy reinforced with alumina fibres were evaluated. Tensile, compression and impact properties were determined at 25, 100 and 150°C. Lubricated wear tests were also performed on the unreinforced alloy and composites. It was found that although fibre reinforcement did result in some improvement of tensile and compression properties at elevated temperatures, the composites had poor toughness and ductility. The presence of a brittle SiO2 layer at the fibre/matrix interfaces resulted in fibre/matrix decohesion under tensile loading, impairing the performance of the reinforced materials. Some improvement in wear resistance was noted for the composite materials but fibre reinforcement did not yield significant improvement in fatigue resistance.

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Exposure of graphite fibre/aluminium composites to elevated temperatures, such as those used for processing, can lead to degradation of the mechanical properties. Analytical electron microscopy has been used to examine the phases formed during the heat treatment of the following materials: (a) wire tows of AA6061 aluminium, reinforced with TiB x -coated fibres, and (b) bulk composites produced by hot pressing the tows within a cladding of AA6061. In the tow material, relatively little interaction between the fibres and matrix was observed. Precipitation at the fibre/matrix interface was considerably more advanced in the as-processed bulk composite. Heat-treating both materials at temperatures in the range 580–700 °C resulted in increasingly severe interfacial reactions. Generally, the microstructures at the fibre/matrix interfaces were considerably more complex than reported in previous work. The following phases have been identified following processing or heat-treatment: Al4C3, α′FeSiAl, magnesium spinel, elemental silicon, TiAl3, MgO, βFeSiAl and a “quarternary phase”, MgSiAl(NiCu), together with amorphous oxides and porosity.

Electronic Resource

1573-4811

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1573-4811

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1573-4811

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1573-4811

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

0029-5981

Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

This paper describes a new algorithm to generate interior nodes within any arbitrary multi-connected regions. The boundary nodes and the interior nodes are then linked up to form the best possible triangular elements by a completely revised technique in an efficient and stable manner. Owing to the generality of the central generation program, the global domain is allowed to be divided into as many irregular subdomains as desired, in order to model closely the actual physical situation. Moreover, the boundaries of the sub-domains are updated from time to time when necessary to include the possibilities of progressive refinement around a sharp corner, generating radiating mesh from a prescribed node, generating mesh between two circular arcs, etc. Despite its flexibility and capabilities, data for triangulation have been kept to a minimum by a logical input module; no connectivity information between subregions is needed, and common boundaries are defined once only. All these features have contributed to a powerful method to generate 3-node or 6-node triangular element meshes of great variety within the most irregular heterogeneous regions.

28 Ill.

Electronic Resource

0029-5981

Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

The stress integration algorithm for hypoelastic constitutive equations proposed by Pinsky et al.3 is extended for the treatment of finite deformation elastoplastic constitutive relations. Another approach based on the polar decomposition of the deformation gradient tensor F = R · U is also introduced. Numerical examples and a discussion on these two approaches are given.

5 Ill.

Electronic Resource

1588-2780

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Abstract The production rates (numbers of atoms per gram of the respective elements per second) of 40 radioactive nuclides of 34 elements by neutron capture reactions in a reactor were determined from about 130 photopeaks of the γ-ray spectra. The ratios of these production rates were called R-matrix elements. These production rates and the respective thermal neutron capture cross sections were used to calculate the respective apparent neutron fluxes at the position of irradiation and the κ-matrix elements which were the ratios of these apparent neutron fluxes. These matrix elements express clearly the correlations among various elements and thus may be used in the mono-standard or small-number-standards method in neutron activation analysis.

Electronic Resource

0029-5981

Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

This paper investigates the possibility of integrating the two currently most popular mesh generation techniques, namely the method of advancing front and the Delaunay triangulation algorithm. The merits of the resulting scheme are its simplicity, efficiency and versatility. With the introduction of ‘non-Delaunay’ line segments, the concept of using Delaunay triangulation as a means of mesh generation is clarified.An efficient algorithm is proposed for the construction of Delaunay triangulations over non-convex planar domains. Interior nodes are first generated within the planar domain. These interior nodes and the boundary nodes are then linked up together to produce a valid triangulation. In the mesh generation process, the Delaunay property of each triangle is ensured by selecting a node having the smallest associated circumcircle. In contrast to convex domains, intersection between the proposed triangle and the domain boundary has to be checked; this can be simply done by considering only the ‘non-Delaunay’ segments on the generation front.Through the study of numerous examples of various characteristics, it is found that high-quality triangular element meshes are obtained by the proposed algorithm, and the mesh generation time bears a linear relationship with the number of elements/nodes of the triangulation.

11 Ill.

Electronic Resource

0029-5981

Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

An algorithm is presented for removing hidden lines for isometric and perspective projections of three-dimensional objects. An object can be regarded as being made up of a number of planes, and the whole picture can therefore be visualized as only a collection of planes. Considering planes as the basic element of a picture, non-convex polyhedra can be displayed directly without prior subdivisions into convex ones. Lines connecting nodal points are first retrieved from the model to be plotted by a simple but efficient technique. On the picture planes, each unique line is examined in turn to see if it is totally or partially hidden. The intersections between a unique line and a projected plane (with or without openings) are determined by a new method which, even in the presence of numerical errors, will always give correct intersection information. Unlike many classical algorithms, intersections are determined by a single formula without tedious case subdivisions. With little additional calculations, object penetrations can also be tackled.

16 Ill.

Electronic Resource

0029-5981

surface intersection ; finite element generation ; triangular facets ; Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

A fully automatic general scheme is proposed to determine and analyse the intersections between two groups of surfaces composed of triangular facets. By carefully maintaining the spatial position of the lines of intersection in regenerating mesh locally around surface intersections, pieces of surfaces can be arbitrarily combined and merged. A great variety of objects can be easily created by selectively putting together different surface parts derived from surface intersections. The new algorithm is best applied in conjunction with an existing surface mesh generator to enhance its general capability in dealing with objects built from intersecting surfaces. In fact, it is a powerful surface mesh manipulator, and through the repeated use of the process, complex structures can be rapidly and accurately constructed.

9 Ill.

Electronic Resource

0029-5981

Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

An automatic adaptive refinement procedure for finite element analysis is presented. The procedure is applied to two-dimensional elastostatic problems to obtain solutions of prescribed accuracy. Through the combined use of new mesh generator using contour developed by Lo1 and the concept of strain energy concentration, high-quality graded finite element meshes are generated. The whole process is fully automatic and no user intervention is required during the successive cycles of the mesh refinements. The Zienkiewicz and Zhu2 error estimator is found to be effective and has been adopted for the present implementation. In the numerical examples tested, the error estimator gives an accurate error norm estimation and the effectivity index of the estimator converges to a value close to unity.

12 Ill.

Electronic Resource

0029-5981

Delaunay triangulation ; Voronoï tesselation ; convex hull ; Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

An efficient algorithm for Delaunay triangulation of a given set of points in d dimensions is presented. Various steps of the point insertion algorithm are reviewed and many acceleration procedures are implemented to speed up the triangulation process. New features include the search for a neighbouring point by a layering scheme, locating the containing simplex by a random walk, formulas of important geometrical quantities of a new simplex based on those of an old one, a novel approach in establishing the adjacency relationship using connection matrices. The resulting scheme seems to be one of the fastest triangulation algorithms known, which enables us to generate tetrahedra in ∝3 with a linear generation rate of 15 000 tetrahedra per second for randomly generated points on an HP 735 workstation.

35 Ill.

Electronic Resource

0029-5981

Engineering ; Engineering General

Wiley InterScience Backfile Collection 1832-2000

Mathematics

Technology

A general and efficient remeshing algorithm is presented for the discretization of arbitrary planar domains into triangular elements in consistency with the given node spacing function.The contour lines of the node spacing function at suitable calculated levels provide the natural lines of division of the problem domain into subregions, where finite element meshes of different element sizes are generated using the available general-purpose mesh generators.1, 2Examples of remeshing for various node spacing functions are given to illustrate that high-quality gradation meshes can be generated automatically without any user's intervention by this simple contour line method.

20 Ill.

Electronic Resource