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1 – 10 of 189Ahmed S Dalaq and Shivakumar I. Ranganathan
– The purpose of this paper is to study the statistics of thermal conductivity and resistivity tensors in two-phase random checkerboard microstructures at finite mesoscales.
Abstract
Purpose
The purpose of this paper is to study the statistics of thermal conductivity and resistivity tensors in two-phase random checkerboard microstructures at finite mesoscales.
Design/methodology/approach
Microstructures at finite scales are generated by randomly sampling an infinite checkerboard at 50 percent nominal fraction. Boundary conditions that stem from the Hill-Mandel homogenization condition are then applied as thermal loadings on these microstructures.
Findings
It is observed that the thermal response of the sampled microstructures is in general anisotropic at finite mesoscales. Based on 1,728 boundary value problems, the statistics of the tensor invariants (trace and determinant) are obtained as a function of material contrast, mesoscale and applied boundary conditions. The histograms as well as the moments (mean, variance, skewness and kurtosis) of the invariants are computed and discussed. A simple analytical form for the variance of the trace of mesoscale conductivity tensor is proposed as a function of individual phase conductivities and the mesoscale.
Originality/value
A rigorous methodology to determine the evolution of the invariants of thermal conductivity (and resistivity) tensors across a variety of length scales (microscale to macroscale) is presented. The objective is to enable setting up of constitutive equations applicable to heat conduction that are valid across all length scales.
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Haixia Wang, Xiao Lu, Zhanyi Hu and Yuxia Li
The purpose of this paper is to present a fully automatic calibration method for hand-eye serial robot system is presented in this paper. The so-called “fully automatic” is meant…
Abstract
Purpose
The purpose of this paper is to present a fully automatic calibration method for hand-eye serial robot system is presented in this paper. The so-called “fully automatic” is meant to calibrate the robot body, the hand-eye relation, and the used measuring binocular system at the same time.
Design/methodology/approach
The calibration is done by controlling the joints to rotate several times one by one in the reverse order (i.e. from the last one to the first one), and simultaneously take pictures of the checkerboard patterns by the stereo camera system attached on the end-effector, then the whole robot system can be calibrated automatically from these captured images. In addition, a nonlinear optimization step is used to further refine the calibration results.
Findings
The proposed method is essentially based on an improved screw axis identification method, and it needs only a mirror and some paper checkerboard patterns without resorting to any additional costly measuring instrument.
Originality/value
Simulations and real experiments on MOTOMAN-UP6 robot system demonstrate the feasibility and effectiveness of the proposed method.
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Mohamed Abdelhamid and Aleksander Czekanski
This is an attempt to better bridge the gap between the mathematical and the engineering/physical aspects of the topic. The authors trace the different sources of…
Abstract
Purpose
This is an attempt to better bridge the gap between the mathematical and the engineering/physical aspects of the topic. The authors trace the different sources of non-convexification in the context of topology optimization problems starting from domain discretization, passing through penalization for discreteness and effects of filtering methods, and end with a note on continuation methods.
Design/methodology/approach
Starting from the global optimum of the compliance minimization problem, the authors employ analytical tools to investigate how intermediate density penalization affects the convexity of the problem, the potential penalization-like effects of various filtering techniques, how continuation methods can be used to approach the global optimum and how the initial guess has some weight in determining the final optimum.
Findings
The non-convexification effects of the penalization of intermediate density elements simply overshadows any other type of non-convexification introduced into the problem, mainly due to its severity and locality. Continuation methods are strongly recommended to overcome the problem of local minima, albeit its step and convergence criteria are left to the user depending on the type of application.
Originality/value
In this article, the authors present a comprehensive treatment of the sources of non-convexity in density-based topology optimization problems, with a focus on linear elastic compliance minimization. The authors put special emphasis on the potential penalization-like effects of various filtering techniques through a detailed mathematical treatment.
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K.J. Meessen, J.J.H. Paulides and E.A. Lomonova
The purpose of this paper is to present a semi‐analytical modeling technique to describe magnetic fields due to PMs in 3D cylindrical structures. The model is based on 2D Fourier…
Abstract
Purpose
The purpose of this paper is to present a semi‐analytical modeling technique to describe magnetic fields due to PMs in 3D cylindrical structures. The model is based on 2D Fourier series and is applied to model the magnetic field of checkerboard magnetization patterns for rotary‐linear actuators.
Design/methodology/approach
The modeling technique based on Fourier series provides a direct solution of the Poisson and Laplace equation by means of separation of variables and is widely used to describe magnetic fields in electromagnetic devices in 2D coordinate systems. In this paper the magnetic scalar potential is used in the Poisson and Laplace equations.
Findings
The magnetic field calculated by the semi‐analytical model is compared with that obtained by Finite Element Modeling and shows excellent agreement. The calculation time of the semi‐analytical model is approximately 60 times shorter than that of finite element analysis.
Research limitations/implications
The method as presented in the paper assumes linear material properties, e.g. the non‐linear B‐H characteristics of iron cannot be taken into account. Furthermore, the structure is assumed to be slotless, that is, stator slots or end‐effects cannot be taken into account.
Practical implications
The semi‐analytical modeling technique is applied to checkerboard magnetization patterns for 2‐DoF actuators in this paper. However, it can be applied to a wide range of slotless cylindrical electromagnetic devices.
Originality/value
As an addition to the common 2D modeling by means of Fourier series, this paper extends the applicability to 3D cylindrical structures. Furthermore, a new checkerboard magnetization is presented which can be used in 2‐DoF rotary linear actuators.
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Keywords
Ge Wu, Duan Li, Yueqi Zhong and PengPeng Hu
The calibration is a key but cumbersome process for 3D body scanning using multiple depth cameras. The purpose of this paper is to simplify the calibration process by introducing…
Abstract
Purpose
The calibration is a key but cumbersome process for 3D body scanning using multiple depth cameras. The purpose of this paper is to simplify the calibration process by introducing a new method to calibrate the extrinsic parameters of multiple depth cameras simultaneously.
Design/methodology/approach
An improved method is introduced to enhance the accuracy based on the virtual checkerboards. Laplace coordinates are employed for a point-to-point adjustment to increase the accuracy of scanned data. A system with eight depth cameras is developed for full-body scanning, and the performance of this system is verified by actual results.
Findings
The agreement of measurements between scanned human bodies and the real subjects demonstrates the accuracy of the proposed method. The entire calibration process is automatic.
Originality/value
A complete algorithm for a full human body scanning system is introduced in this paper. This is the first publically study on the refinement and the point-by-point adjustment based on the virtual checkerboards toward the scanning accuracy enhancement.
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In Schelling’s “checkerboard” model of segregation, individuals’ moderately held preferences about the proportion of their neighbors who are similar versus dissimilar to them can…
Abstract
Purpose
In Schelling’s “checkerboard” model of segregation, individuals’ moderately held preferences about the proportion of their neighbors who are similar versus dissimilar to them can, through an automatic and mathematical process, yield dramatic population-level segregative behaviors. The notion of such an automatic segregative process would seem to have implications for spatial dynamics when a group home for persons with disabilities is introduced into a community. This study sought to examine those implications alongside data in the research literature regarding community acceptance of group homes.
Design/methodology/approach
Using an agent-based modeling approach, computer simulations were constructed to apply Schelling’s model, as well as an alternative model, to community reaction to the introduction of group homes for persons with disabilities. Simulation conditions were set to roughly correspond to the proportion of group homes or other congregate living situations, as well as vacant dwellings, in a typical community in the United States.
Design/methodology/approach
The simulations predict that group homes will, to varying degrees, become spatially isolated within their communities. These predictions conflict with previous research findings that suggest minimal relocation of neighbors and rapid adjustment of communities to the presence of group homes.
Social implications
Simulations of an automatic segregative process might offer a baseline or a “null hypothesis” of sorts, allowing us to more fully understand the extent of the social and socioeconomic forces that serve to moderate or override such an automatic process, allowing communities to adjust to group homes’ presence.
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Keywords
Qing Li, Grant P. Steven, Osvaldo M. Querin and Y.M. Xie
This paper shows how the evolutionary structural optimization (ESO) algorithm can be used to achieve a multiple criterion design for a structure in a thermal environment. The…
Abstract
This paper shows how the evolutionary structural optimization (ESO) algorithm can be used to achieve a multiple criterion design for a structure in a thermal environment. The proposed thermal ESO procedure couples an evolutionary iterative process of a finite element heat conduction solution and a finite element thermoelastic solution. The overall efficiency of material usage is measured in terms of the combination of thermal stress levels and heat flux densities by using a combination strategy with weighting factors. The ESO method then works by eliminating from the structural domain under‐utilized material. In this paper, a practical design example of a printed circuit board substrate is presented to illustrate the capabilities of the ESO algorithm for thermal design optimization in multiple load environments.
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Meng Xia and Jan Sykulski
The purpose of this paper is to propose a novel methodology based on budget constrained Min-Cut theorem to solve constrained topology optimization (TO).
Abstract
Purpose
The purpose of this paper is to propose a novel methodology based on budget constrained Min-Cut theorem to solve constrained topology optimization (TO).
Design/methodology/approach
This paper establishes a weighted network with budget, which is derived from the sensitivity with respect to the constraint function. The total budget carried by the topology evaluates the extent to which the constraint is satisfied. By finding the Min-Cut under budget constraint in each step, the proposed method is able to solve constrained TO problem.
Findings
The results obtained from a magnetic actuator including a yoke, a coil and an armature have demonstrated that the proposed method is effective to solve constrained TO problem.
Originality/value
A novel methodology based on budget constrained Min-Cut is proposed to solve constrained TO problem.
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Francisco Barros, Susana Aguiar, Pedro J. Sousa, António Cachaço, Nuno V. Ramos, Paulo Tavares, P.M.G. Moreira, Luís Oliveira Santos, Min Xu and Elsa Franco
Part of the runway at Madeira Airport is a platform above the sea at a 60 m height, supported by a series of frames. When aircraft land on this section, a load is exerted on the…
Abstract
Purpose
Part of the runway at Madeira Airport is a platform above the sea at a 60 m height, supported by a series of frames. When aircraft land on this section, a load is exerted on the structure, resulting in bending of the beams which constitute the frames. A vision-based monitoring system was devised and implemented to measure the deflection of the runway's beams when a landing occurs.
Design/methodology/approach
An area on the midspan of two beams, located on the area where aircraft are most likely to land, was prepared with a speckle pattern, and a camera was assembled above a column on each of the adjacent frames, enabling the computation of displacements using digital image correlation (DIC). The camera continuously acquires images of the monitored area and compares them to a reference using DIC. If a displacement is detected, a number of frames before and after this event are saved for further DIC processing.
Findings
The installed systems successfully detected several events corresponding to landings and, for each of those events, measured the deflection of the beams over time and computed displacement fields for critical images, with strain values obtained up to this point being too small to measure using the current system.
Originality/value
This work provides novel insights into the behaviour of a unique structure and constitutes the first use of a vision system in its structural monitoring operations. It is also a valuable development in the implementation of automated DIC monitoring systems in locations of difficult access.
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Keywords
D. McBride, N. Croft and M. Cross
To improve flow solutions on meshes with cells/elements which are distorted/ non‐orthogonal.
Abstract
Purpose
To improve flow solutions on meshes with cells/elements which are distorted/ non‐orthogonal.
Design/methodology/approach
The cell‐centred finite volume (FV) discretisation method is well established in computational fluid dynamics analysis for modelling physical processes and is typically employed in most commercial tools. This method is computationally efficient, but its accuracy and convergence behaviour may be compromised on meshes which feature cells with non‐orthogonal shapes, as can occur when modelling very complex geometries. A co‐located vertex‐based (VB) discretisation and partially staggered, VB/cell‐centred (CC), discretisation of the hydrodynamic variables are investigated and compared with purely CC solutions on a number of increasingly distorted meshes.
Findings
The co‐located CC method fails to produce solutions on all the distorted meshes investigated. Although more expensive computationally, the co‐located VB simulation results always converge whilst its accuracy appears to grace‐fully degrade on all meshes, no matter how extreme the element distortion. Although the hybrid, partially staggered, formulations also allow solutions on all the meshes, the results have larger errors than the co‐located vertex based method and are as expensive computationally; thus, offering no obvious advantage.
Research limitations/implications
Employing the ability of the VB technique to resolve the flow field on a distorted mesh may well enable solutions to be obtained on complex meshes where established CC approaches fail
Originality/value
This paper investigates a range of cell centred, vertex based and hybrid approaches to FV discretisation of the NS hydrodynamic variables, in an effort characterize their capability at generating solutions on meshes with distorted or non‐orthogonal cells/elements.
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