Search results

This paper aims to develop a numerical model to investigate coupled conduction radiation heat transfer in a multilayer semi-transparent polymeric foam.

The model uses a multi-phase approach in which the radiative transfer is determined by solving the radiative transfer equation explicitly in the whole medium incorporating an interface condition valid in the geometric optics rgime. This is executed by using a combination of ray splitting and a discrete curved ray tracing technique. Both partial photon reflection and total internal reflection at the interface are considered in the present investigation.

The directional distribution of intensity within the whole medium can be determined, which is used to obtain the detailed temperature profile inside the domain. The performance of the proposed methodology has been tested by simulating the modelled foam at ambient conditions. The results obtained from the simulations are in good agreement with the published results and shows that there is a global non-linearity in the temperature profile in problems where conduction to radiation parameter is small.

Specular nature of radiative transfer at the interface is accounted for in the present analysis. Instead of working with direction integrated quantities (as in the case of P1 approximation), each bundle of rays is treated separately within the whole medium. This model serves as a starting point for a detailed spatially three dimensional study of heat transfer in foams and the mathematical nature of the formulation is such that it may result in an implementation to three-dimensions.

The solution of radiative heat transfer problems in participating media is often obtained using the standard discrete ordinates method (SDOM). This method produces anomalies caused by ray effects if radiative boundary conditions have discontinuities or abrupt changes. Ray effects may be mitigated using the modified discrete ordinates method (MDOM), which is based on superposition of the solutions obtained by considering separately radiation from the walls and radiation from the medium. The purpose of this paper is to study the role of ray effects in combined conduction‐radiation problems and investigate the superiority of the MDOM over SDOM.

The MDOM has been used to calculate radiative heat transfer in irregular geometries using body‐fitted coordinates. Here, the blocked‐off region concept, originally developed in computational fluid dynamics, is used along with the finite volume method and SDOM or MDOM to solve combined conduction‐radiation heat transport problems in irregular geometries. Enclosures with an absorbing, emitting and isotropically or anisotropically scattering medium are analyzed.

The results confirm the capability of the MDOM to minimize the anomalies due to ray effects in combined heat transfer problems, and demonstrate that MDOM is more computationally efficient than SDOM.

The paper demonstrates the application of MDOM to combined conduction‐radiation heat transfer problems in irregular geometries using blocked‐off method.

T-spline is the latest powerful modeling tool in the field of computer-aided design. It has all the merits of non-uniform rational B-spline (NURBS) whilst resolving some flaws in it. This work applies T-spline surfaces to additive manufacturing (AM). Most current AM products are based on Stereolithograph models. It is a kind of discrete polyhedron model with huge amounts of data and some inherent defects. T-spline offers a better choice for the design and manufacture of complex models.

In this paper, a direct slicing algorithm of T-spline surfaces for AM is proposed. Initially, a T-spline surface is designed in commercial software and saved as a T-spline mesh file. Then, a numerical method is used to directly calculate all the slicing points on the surface. To achieve higher manufacturing efficiency, an adaptive slicing algorithm is applied according to the geometrical properties of the T-spline surface.

Experimental results indicate that this algorithm is effective and reliable. The quality of AM can be enhanced at both the designing and slicing stages.

The T-spline and direct slicing algorithm discussed here will be a powerful supplement to current technologies in AM.

This paper aims to deal with characterisation of the thermal performance of a hybrid tubular and cavity solar thermal receiver.

The coupled optical-flow-thermal analysis is carried out on the proposed receiver design. Modelling is performed in two and three dimensions for estimating heat loss by natural convection for an upward-facing cavity. Heat loss obtained in two dimensions by solving coupled continuity, momentum and energy equation inside the cavity domain is compared with the loss obtained using an established Nusselt number correlation for realistic receiver performance prediction.

It is found that radiation emission from a heated cavity wall to the ambient is the dominant mode of heat loss from the receiver. The findings recommend that fluid flow path must be designed adjacent to the surface exposed to irradiation of concentrated flux to limit conduction heat loss.

On-sun experimental tests need to be performed to validate the numerical study.

Numerical analysis of receivers provides guidelines for effective and efficient solar thermal receiver design.

Pressurised air receivers designed from this method can be integrated with Brayton cycles using air or supercritical carbon-dioxide to run a turbine generating electricity using a solar heat source.

The present paper proposes a novel method for coupling the flux map from ray-tracing analysis and using it as a heat flux boundary condition for performing coupled flow and heat transfer analysis. This is achieved using affine transformation implemented using extrusion coupling tool from COMSOL Multiphysics software package. Cavity surface natural convection heat transfer coefficient is obtained locally based on the surface temperature distribution.

This paper aims to propose an automatic and direct method to manipulate global parameters of the object for prototyping and simulation, given an STL mesh model of a thin-walled object. Proposed method is useful in rapid prototyping, where changing the global parameters such as thickness, scaling local features or draft of walls of an STL mesh is often required. Presently, user needs to iterate over the cycle of modification of the computer-aided design (CAD) model and tessellating it to change the global parameters. The proposed algorithm eliminates the need for CAD model while manipulating those global properties, as it works directly with the mesh model.

Proposed algorithm automatically identifies walls and its thickness, and then, it extracts mid-surface from each wall. Global parameters are then modified by using these mid-surfaces.

Mesh directly modified and the mesh obtained by tessellating modified CAD model has same global properties; proposed method can also allow multiple parameters to be modified at the same time.

Input STL model is assumed to be error-free, where models containing errors like self-intersection will lead to incorrect mid-surfaces. Present algorithm assumes that the mid-surface represent of the input STL model is a manifold surface.

A novel algorithm of directly manipulating global parameters of a thin-walled object in its STL mesh model is proposed. The paper also presents a novel method of extracting mid-surface representation from a thin-wall STL mesh.

This paper aims to provide a series of new methods for projecting a three-dimensional (3D) object onto a free-form surface. The projection algorithms presented can be divided into three types, namely, orthogonal, perspective and parallel projection.

For parametric surfaces, the computing strategy of the algorithm is to obtain an approximate solution by using a geometric algorithm, then improve the accuracy of the approximate solution using the Newton–Raphson iteration. For perspective projection and parallel projection on an implicit surface, the strategy replaces Newton–Raphson iteration by multi-segment tracing. The implementation takes two mesh objects as an example of calculating an image projected onto parametric and implicit surfaces. Moreover, a comparison is made for orthogonal projections with Hu’s and Liu’s methods.

The results show that the new method can solve the 3D objects projection problem in an effective manner. For orthogonal projection, the time taken by the new method is substantially less than that required for Hu’s method. The new method is also more accurate and faster than Liu’s approach, particularly when the 3D object has a large number of points.

The algorithms presented in this paper can be applied in many industrial applications such as computer aided design, computer graphics and computer vision.

Present study aims to extend the lattice Boltzmann method (LBM) to simulate radiation in geometries with curved boundaries, as the first step to simulate radiation in complex porous media. In recent years, researchers have increasingly explored the use of porous media to improve the heat transfer processes. The lattice Boltzmann method (LBM) is one of the most effective techniques for simulating heat transfer in such media. However, the application of the LBM to study radiation in complex geometries that contain curved boundaries, as found in many porous media, has been limited.

The numerical evaluation of the effect of the radiation-conduction parameter and extinction coefficient on temperature and incident radiation distributions demonstrates that the proposed LBM algorithm provides highly accurate results across all cases, compared to those found in the literature or those obtained using the finite volume method (FVM) with the discrete ordinates method (DOM) for radiative information.

For the case with a conduction-radiation parameter equal to 0.01, the maximum relative error is 1.9% in predicting temperature along vertical central line. The accuracy improves with an increase in the conduction-radiation parameter. Furthermore, the comparison between computational performances of two approaches reveals that the LBM-LBM approach performs significantly faster than the FVM-DOM solver.

The difficulty of radiative modeling in combined problems involving irregular boundaries has led to alternative approaches that generally increase the computational expense to obtain necessary radiative details. To address the limitations of existing methods, this study presents a new approach involving a coupled lattice Boltzmann and first-order blocked-off technique to efficiently model conductive-radiative heat transfer in complex geometries with participating media. This algorithm has been developed using the parallel lattice Boltzmann solver.

The purpose of this paper is to put forward a path planning method in complex environments containing dynamic obstacles, which improves the performance of the traditional A* algorithm, this method can plan the optimal path in a short running time.

To plan an optimal path in a complex environment with dynamic and static obstacles, a novel improved A* algorithm is proposed. First, obstacles are identified by GoogLeNet and classified into static obstacles and dynamic obstacles. Second, the ray tracing algorithm is used for static obstacle avoidance, and a dynamic obstacle avoidance waiting rule based on dilate principle is proposed. Third, the proposed improved A* algorithm includes adaptive step size adjustment, evaluation function improvement and path planning with quadratic B-spline smoothing. Finally, the proposed improved A* algorithm is simulated and validated in real-world environments, and it was compared with traditional A* and improved A* algorithms.

The experimental results show that the proposed improved A* algorithm is optimal and takes less execution time compared with traditional A* and improved A* algorithms in a complex dynamic environment.

This paper presents a waiting rule for dynamic obstacle avoidance based on dilate principle. In addition, the proposed improved A* algorithm includes adaptive step adjustment, evaluation function improvement and path smoothing operation with quadratic B-spline. The experimental results show that the proposed improved A* algorithm can get a shorter path length and less running time.

Mask projection micro‐stereolithography (MPμSLA) is an additive manufacturing process capable for fabricating true three‐dimensional microparts and hence, holds promise as a potential 3D MEMS fabrication process. With only a few MPμSLA systems developed and studied so far, the research in this field is inchoate and experimental in nature. In order to employ the MPμSLA technology for microfabrication, it is necessary to model its part building process and formulate a process planning method to cure dimensionally accurate microparts. The purpose of this paper is to formulate a process planning method for curing dimensionally accurate layers.

A MPμSLA system is designed and assembled. The process of curing a single layer in resin using this system is modeled as the layer cure model. The layer cure model is validated by curing test layers. This model is used to formulate a process planning method to cure dimensionally accurate layers. The process planning method is tested by conducting a case study.

The layer cure model is found to be valid within 3 percent for most of the features and within 10 percent for very small features (<250μm). The paper shows that ray tracing can be effectively used to model the process of irradiation of the resin surface in a MPμSLA system.

The process planning method is applicable only to those imaging systems, which are aberration limited as opposed to diffraction limited. The dimensional errors in the lateral dimensions of single layers cured by MPμSLA have been modeled, but not the vertical errors in 3D parts.

In this paper, a process planning method for MPμSLA has been presented for the first time.

The purpose of this paper is to present the results obtained from numerical models of radiant energy exchange in instruments typically used to measure various characteristics of the Earth's ocean‐atmosphere system.

Numerical experiments were designed and performed in a statistical environment, based on the Monte Carlo ray‐trace (MCRT) method, developed to model thermal and optical systems. Results from the derived theoretical equations were then compared to the results from the numerical experiments.

A rigorous statistical protocol is defined and demonstrated for establishing the uncertainty and related confidence interval in results obtained from MCRT models of radiant exchange.

The methodology developed in this paper should be adapted to predict the uncertainty of more comprehensive parameters such as the total radiative heat transfer.

Results can be used to estimate the number of energy bundles necessary to be traced per surface element in a MCRT model to obtain a desired relative error.

This paper offers a new methodology to predict the uncertainty of parameters in high‐level modeling and analysis of instruments that accumulate the long‐term database required to correlate observed trends with human activity and natural phenomena. The value of this paper lies in the interest in understanding the climatological role of the Earth's radiative energy budget.