Cavity-Shape Identification with Convective Boundary Conditions Using Non-Boundary-Fitted Meshes

This article presents a system identification scheme to determine the geometric shape of a cavity with convective boundary condition in a heat-conducting medium using the measured temperatures on the surface of the object. The proposed algorithm is based on the nonlinear minimization of the squared errors between the measured temperatures and the calculated ones. In this article, a new approach based on non-boundary-fitted meshes and gradient smoothing technique is presented for the solution of the direct problem and shape sensitivity analysis. In this method, the domain boundary can be moved independently from the mesh, and the solution of the variable-domain problems can be found easily. The domain parameterization technique using cubic splines is adopted to manipulate the shape variation of the cavity. The conjugate gradient method is used as the optimization algorithm. Some numerical examples are solved to evaluate the applicability of the proposed method in the solution of inverse-geometry problems. In the examples, the effects of mesh size, measurement errors, cavity-shape, cavity size, and the initial guess are examined.     

Novel Heat Transfer Issues Associated with the Design and Safe Operation of the MEGAPIE Spallation Source Target

Critical heat transfer problems are discussed in the context of the operation of a spallation source target, which represents a first demonstration of the feasibility of an innovative concept for generating energy using a particle accelerator. Within the framework of the umbrella project MEGAPIE, an R&D support group was organized to take responsibility for target cooling. This involved the use of advanced numerical methods — Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) — validated against suitable experimental data, and by means of appropriate benchmarking exercises. The design studies using CFD resulted in an optimum flow configuration being defined for the coolant circulation. Flow visualization tests were undertaken using a glass/water test section, with the velocity field mapped using optical and ultrasonic measuring techniques. These were followed by heat transfer tests, using the actual target materials (lead-bismuth-eutectic coolant and steel confinement). Further CFD/FEM work to analyze operational transients and accident sequences was also carried out, and is described in the paper.     

Dynamic Coverage Optimal Control for Multiple Spacecraft Interferometric Imaging

In this paper, we study and generalize a class of optimal control problems known in the literature as τ-elastic variational optimal control problems. In the τ-elastic optimal control, we want to minimize a cost function over trajectories that evolve on a Riemannian manifold and satisfy a second-order differential equation together with some smoothness and motion constraints. The cost function is a weighted sum of the squared norm of the acceleration and the squared norm of the velocity. Here, we generalize the τ-elastic variational problem to the dynamic coverage optimal control problem, which is a class of optimal control problems motivated by multiple spacecraft formation flying for imaging applications. The main novelty of this paper is an interesting connection between multiple spacecraft formation flying and the τ-elastic and coverage optimal control problems. This research is supported by NSF grants DMS-0103895, DMS-0305837, and CMS-0408542.     

Transportation: meeting the dual challenges of achieving energy security and reducing greenhouse gas emissions

As the population and economy continue to grow globally, demand for energy will continue to grow. The transportation sector relies solely on petroleum for its energy supply. The United States and China are the top two oil-importing countries. A major issue both countries face and are addressing is energy insecurity as a result of the demand for liquid fuels. Improvements in the energy efficiency of vehicles and the substitution of petroleum fuels with alternative fuels can help contain growth in the demand for transportation oil. Although most alternative transportation fuels — when applied to advanced vehicle technologies — can substantially reduce greenhouse emissions, coal-based liquid fuels may increase greenhouse gas emissions by twice as much as gasoline. Such technologies as carbon capture and storage may need to be employed to manage the greenhouse gas emissions of coal-based fuels. At present, there is no ideal transportation fuel option to solve problems related to transportation energy and greenhouse gas emissions. To solve these problems, research and development efforts are needed for a variety of transportation fuel options and advanced vehicle technologies.     

Application of the variational iteration method to nonlinear non‐Fourier conduction heat transfer equation with variable coefficient

In this paper, a variational iteration method (VIM) has been applied to nonlinear non‐Fourier conduction heat transfer equation with variable specific heat coefficient. The concept of the variational iteration method is introduced briefly for applying this method for problem solving. The proposed iterative scheme finds the solution without any discretization, linearization, or restrictive assumptions. The results of VIM as an analytical solution are then compared with those derived from the established numerical solution obtained by the fourth order Runge–Kutta method in order to verify the accuracy of the proposed method. The results reveal that the VIM is very effective and convenient in predicting the solution of such problems, and it is predicted that VIM can find a wide application in new engineering problems. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20362     

The approximate solution of nonlinear heat equation

Nowadays there are many approximate methods for thermal conductivity calculation, that lead to satisfactory outcomes in engineering practice. With the new approach, the solution of the nonlinear thermal conductivity equation was investigated. In addition to this, we reviewed the approximate solution of the nonlinear equation of thermal conductivity with cubic nonlinearity. To solve the problems of mathematical analysis, differential and integral equations, and boundary value problems of mathematical physics, difference, and interpolation are applied. Thus, for thinking of the effectiveness and reasonableness of these approaches, it is crucial for their theoretical investigation. The solution to these questions was found for each class of equation and each of its methods in their way and was often represented as significant difficulty, and in many cases was an obstacle for the current time. A natural approach to solving this issue is the use of the ideas of functional analysis. The variational principle initially was considered as a variational approach for solving linear functional equations and finding eigenvalues of linear operators. As in any variational approach, the problem of solving an equation will be brought to finding the extremum of the certain function of a special type, given over the entire space. It was found that the approach is useful in a way of minimizing functions of the more general type.     

The effect of life-cycle cost disclosure on consumer behavior: evidence from a field experiment with cooling appliances

Theory suggests that providing consumers with an estimated life-cycle cost (LCC) may make them buy more energy-efficient household appliances in cases where energy efficiency is cost effective. This article evaluates the link between the provision of LCC and consumer behavior by using an online field experiment for cooling appliances. Internet users arriving at a commercially operating price comparison website were randomly assigned to two experimental groups, and the groups were exposed to different visual stimuli. The control group received regular product price information, whereas the treatment group was offered additional information about estimated operating cost and total LCC. Consumers’ click behavior was evaluated with multiple regression controlling for several product characteristics (n = 1,969 clicks). We find that LCC disclosure reduces the mean specific energy use of chosen cooling appliances by 2.5% (p < 0.01), making it a potentially interesting approach for environmental policy regarding the market transformation toward more energy-efficient household appliances. However, LCC disclosure also decreases the number of clicks from the price comparison website to final retailers by about 23% (p < 0.01), which makes it—in the format chosen here—undesirable from a business perspective. Therefore, future research should clarify under what (if any) conditions can monetary energy cost disclosure be associated with more positive effects for price comparison websites.     

Elastoplastic frictional contact problem study on interference fits of compressor

The FE parametric quadratic programming (PQP) method developed from the parametric variational principle (PVP) was used for the analysis of the stress distribution of the 3D elastoplastic frictional contact of an impeller-shaft sleeve-shaft. A locomotive-type turbocharger compressor with 24 blades under combined centrifugal and interference-fit loading was considered in the numerical analysis. The solution of elastoplastic frictional contact problems belongs to unspecified boundary problems where the interaction between two kinds of nonlinearities should occur. To save time in the numerical computation, a multi-substructure technique was adopted in the structural modeling. The effect of fit tolerance, wall thickness of the shaft sleeve, and rotational speed on the contact stress was discussed in detail in the numerical computation. To decrease the difficulty of the assembly process and ensure the safety of the working state, the amount of interference between the shaft sleeve and shaft by press-fitting should be controlled strictly to avoid the rapid increase of contact stress. The numerical results show that the algorithm has high accuracy and good convergence. The study can be referred to in deciding the proper fit tolerance and improving the design and manufacturing technology of compressor impellers. __________ Translated from Engineering Mechanics, 2007, 24(1): 186–192, 177 [译自: 工程力学]     

A SEMIANALYTIC APPROACH TO GENERAL TRANSIENT PROBLEMS AND ITS APPLICATIONS TO HEAT TRANSFER

Abstract

In this article a new method of solving the transient problems is developed that is based on convolution-type variational principles, where finite-element discretization in the space domain and series representation in the time domain are considered. This approach can overcome the shortcomings of existing methods and combine the advantages of those methods for solving transient problems. The examples show that the new method is a most effective method of obtaining solutions for transient problems.     

Exact Variational Principle For 3-D Unsteady Heat Conduction With Second Sound

The exact variational formulation of the extended unsteady heat conduction equation with finite propagationspeed(the 2nd sound speed)of hyperbolic type is derived herein via a systematic and natural way.Moreover,theboundary- and the physically acceptable initial-value conditions are accommodated in the variational principle bya novel method suggested just recently.In this way a perfect justification of the variational theory of transient heatconduction and a rigorous theoretical basis for the finite element analysis of heat conduction are provided.     

A meshless local Petrov–Galerkin approach for solving the convection-dominated problems based on the streamline upwind idea and the variational multiscale concept

A meshless local Petrov–Galerkin (MLPG) approach based on the streamline upwind (SU) idea and the variational multiscale (VMS) concept, called as VMS-SUMLPG method, is herein proposed to solve the convection-dominated problems. In the present VMS-SUMLPG method, the streamline upwind is constructed in the test function to solve the non-self-adjoint matrix. Meanwhile, the VMS concept as a stability term is adopted to alleviate the numerical instability such as spurious oscillations, overshoots, and undershoots. Its numerical accuracy and stability are validated by comparing with the streamline upwind Petrov–Galerkin (SUMLPG) method and the finite volume method with high-order difference schemes for two classical convection-dominated problems at the Peclet number ranging from 10⁶ to 10⁸. It is shown that the numerical solutions of the present VMS-SUMLPG method are accuracy, smoothness, and stability.     

Concentrations of the Linear Fresnel Reflector with the Facets Orientated to the Immovable Receiver

A numerical model of a linear Frensel reflector (LFR) with oriented facets is suggested. The concentrating performances of linear Frensel reflectors are determined by considering the errors of manufacturing and facet positioning relative to the Sun. Rational optical—geometrical parameters of linear Frensel reflectors are revealed. It is shown that an LFR can operate efficiently for eight hours during the day.     

Variational setting for reversible and irreversible fluids with heat flow

This paper derives and discusses variational formulations for heat flows subject to physical constraints that involve the (generally) non-conserved balance of internal energy and the entropy representation kinetics in the form of the Cattaneo equation of heat. Another approach is also outlined which uses the (generally) non-conserved balance of the entropy and the energy-representation counterpart of the Cattaneo equation called Kaliski’s equation. Results of nonequilibrium statistical mechanics (Grad’s theory) lead to nonequilibrium corrections to entropy and energy of the fluid in terms of the nonequilibrium density distribution function, f. These results also yield coefficients of the wave model of heat such as: relaxation time, propagation speed and thermal inertia. With these data a quadratic Lagrangian and a variational principle of Hamilton’s type follows for a fluid with heat flux in the field representation of fluid motion. For an irreversible heat transfer we show that despite of generally non-canonical form of the matter tensor the coefficients in source terms of the variational conservation laws can be suitably adjusted, so that physical (source-less and canonical) conservation laws are obtained for the energy and momentum. We discuss canonical and generalized conservation laws and show the satisfaction of the second law under the constraint of canonical conservation laws.     

Anomalous temperature dependence of volt-ampere characteristics of pSi-n(Si2)1 ?x(ZnSe)x structures

The volt-ampere characteristics (VAC) of pSi-n(Si₂)_1−x (ZnSe) _x structures that are grown by liquidphase epitaxy from a limited volume of a tin solution (melt) have been studied. Their unusual property—decrease of the current with increase of the temperature from 100 to 140°C—is explained on the basis of a recombination model that takes into account the change of the concentration of the effectively functioning recombination impurity centers due to intensive creation of vacancies and defect-impurity complexes during photocell excitation.     

Variational multiscale methods for premixed combustion based on a progress-variable approach

In this study, novel computational techniques for the numerical simulation of premixed combustion based on a progress-variable formulation are proposed. Two new variational multiscale methods within a finite element framework are developed for the system of mass, momentum and progress-variable equations: a purely residual-based variational multiscale method and an algebraic variational multiscale-multigrid method. The proposed methods are tested for the numerical example case of a flame–vortex interaction using Arrhenius chemical kinetics. This actually laminar reactive flow problem may serve as a model problem for interactions of turbulent flows and (premixed) flames. The results obtained from this test case show that both methods are capable of accurately predicting the features expected during the progression of the flame–vortex interaction. The evolution of both a pocket of unburned gas and a secluded, drop-like structure, which detaches itself and moves upwards, are accurately predicted already for a relatively coarse discretization.     

Probability strength design of steam turbine blade and sensitivity analysis with respect to random parameters based on response surface method

Many stochastic parameters have an effect on the reliability of a steam turbine blade during practical operation. To improve the reliability of blade design, it is necessary to take these stochastic parameters into account. An equal cross-section blade is investigated and a finite element model is built parametrically. Geometrical parameters, material parameters and load parameters of the blade are considered as input random variables while the maximum deflection and maximum equivalent stress are output random variables. Analysis file of the blade is compiled by deterministic finite element method and applied to be loop file to create sample points. A quadratic polynomial with cross terms is chosen to regress these samples by step-forward regression method and employed as a surrogate of numerical solver to drastically reduce the number of solvers call. Then, Monte Carlo method is used to obtain the statistical characteristics and cumulative distribution function of the maximum deflection and maximum equivalent stress of the blade. Probability sensitivity analysis, which combines the slope of the gradient and the width of the scatter range of the random input variables, is applied to evaluate how much the output parameters are influenced by the random input parameters. The scatter plots of structural responses with respect to the random input variables are illustrated to analyze how to change the input random variables to improve the reliability of the blade. The results show that combination of the finite element method, the response surface method and Monte Carlo method is an ideal way for the reliability analysis and probability strength design of the blade. __________ Translated from Proceedings of the CSEE, 2007, 27(20): 12–17 [译自: 中国电机工程学报]     

What role for microgeneration in a shift to a low carbon domestic energy sector in the UK?

Domestic energy use accounts for more than a quarter of CO₂ emissions in the UK. Traditional approaches to energy reduction look at direct emissions savings, and recommend insulation and efficiency as more cost-effective than microgeneration. However, microgeneration has indirect, ‘soft’ benefits and could play a significant role in emissions reduction. Current uptake of microgeneration in the UK is low, with various barriers—economic, technical, cultural, behavioural and institutional—both to uptake and to maximising energy and emissions savings once installed. Subsidies and spreading information alone do not guarantee maximising uptake, and even if successful, this is not enough to maximise savings. The industry focuses on maximising sales, with no incentives to ensure best installations and use; householders do not have access to the best information, and user behaviour does not maximise energy and emission savings. This is related to a broader state of socio-technical ‘lock-in’ in domestic energy use; there’s a lack of connection between personal behaviour and energy consumption, let alone global climate change. This suggests that a major cultural–behavioural shift is needed to reduce energy/emissions in the home. Transition theory and strategic niche management provide insights into possible systemic change and a suitable framework for future policies, such as supporting a variety of radically innovative niches, both technological and social. Microgeneration, properly employed, has the potential to play a part in such a transition by increasing awareness and energy literacy and empowering people to seriously engage in energy debates as producers, as well as consumers, of energy. This deeper understanding and heightened responsibility are crucial in a shift toward bottom-up emission-reducing behaviour change and better acceptance of top-down energy-saving policy measures, as part of a new domestic energy paradigm. The implications for policy are that, as well as supporting the technologies, it needs to support existing niches and to develop new niche experiments. Policy needs to consider how to promote empowerment and responsibility and support or even develop new energy sector models; this will involve a range of stakeholders and multiple governance levels, not just national incentive schemes.     

Dynamical Systems for Solving Variational Inequalities

In this paper, we propose dynamical systems for solving variational inequalities whose mapping is paramonotone, strongly pseudomonotone or pseudomonotone and Lipschitz continuous, respectively. Solutions of these dynamical system are shown to converge to a desired solution of the variational inequalities. When the mapping is strongly pseudomonotone but is not necessarily Lipschitz continuous, the convergence rate of the new algorithm is established. This approach is novel and the new algorithms can be considered continuous versions of the existing ones for variational inequalities.

     

Thermoelastic diffusion with memory-dependent derivative

The constitutive equations are derived for the thermoelastic diffusion in anisotropic and isotropic solids, in the context of a new generalized thermoelasticity theory with two time delays and kernel functions. The coupled thermoelastic diffusion and the Lord–Shulman theories result from the given theory as particular cases. For anisotropic solid, the reciprocity theorem is proved; the convolutional variational principle is given and the uniqueness theorem based on the variational principle is proved.     

Nonhomogeneos Boundary-Value Problem for Semilinear Hyperbolic Equation. Stability

We discuss the solvability of the nonhomogeneous boundary-value problem for the semilinear equation of the vibrating string x _tt (t, y) − Δx(t, y) + f(t, y, x(t, y)) = 0 in a bounded domain and a certain type of superlinear nonlinearity. To this end, we deduce new dual variational method. Next, we discuss the stability of solutions with respect to the boundary control and initial conditions.