Ary Conditions Research Articles

N-Times Absorbing Boundary Conditions for Compact Finite-Difference Modeling of Acoustic and Elastic Wave Propagation in the 2D TI Medium

This article presents decoupling n-times absorbing boundary conditions designed to model acoustic and elastic wave propagation in a 2D transversely iso- tropic (TI) medium. More general n-times boundary conditions with absorbing pa- rameters are also obtained by cascading first-order differential operators with param- eters. These boundary conditions are approximated with simple finite-difference schemes for numerical simulations. The numerical results show that the absorbing for the reflection waves strengthens with increasing the absorbing times n and the discretization boundary formulas are stable. Specially, the n-times absorbing bound- ary condition with absorbing parameters is better than that without the absorbing parameters under the case of same absorbing order. Elastic wave fields and three- component synthetic seismograms, generated by using the compact finite-difference and the decoupling n-times absorbing boundary, also illustrate that the n-times ab- sorbing boundary condition can eliminate effectively the spurious numerical reflec- tions in the acoustic and elastic wave modeling for the TI medium case.

Left-right symmetry in 5D and neutrino mass in TeV-scale gravity models

We construct a left-right symmetric model based on the gauge group SU(2)L × SU(2)R × U(1)B−L in five dimensions where both the gauge bosons and fermions reside in all five dimensions. The orbifold bound- ary conditions are used not only to break the gauge symmetry down to SU(2)L × U(1)Y × U(1)Ybut also to project the right handed neutrino out of the zero mode part of the spectrum, providing a new way to under- stand the small neutrino masses without adding (singlet) bulk neutrinos. This formulation of the left-right model has also two new features: (i) it avoids most existing phenomenological bounds on the scale of the right handed WR boson allowing for the possibility that the right handed gauge bosons could have masses under a TeV, and (ii) it predicts a stable lepton with mass of order of the inverse radius of the fifth dimension.

Use of liquid desiccant cooling to improve the performance of vapor compression air conditioning

A hybrid air conditioning system, which consists of sections of desiccant dehumidification, evaporative cooling and vapor compression air conditioning, has been established in this paper. Experimental investigation demonstrates that cooling production and COP of the new hybrid system can be increased significantly, if they are compared with those of vapor compression system (VCS) alone. Assuming that the outlet temperature and humidity of the system are constant, psychrometric analysis at ARI conditions has been conducted under three different cases. The benefits are represented by lower electricity consumption of the compressor, higher COP of the system, less flow rate of condensation air, and reduced size of VCS, etc. The reason that the hybrid system is superior in performance to conventional systems lies in that desiccant dehumidification and evaporative cooling changes the inlet states of the air entering into VCS. Furthermore, the effects of dehumidification and evaporative cooling are analyzed in the paper.

Parabolic approximation of nonlocal boundary conditions for elastic seabeds

A parabolic approximation of the nonlocal boundary condition is constructed to model the elastic seabed of an ocean acoustic waveguide. The construction departs from the Neumann to Dirichlet (NtD) map that transfers the seabed dynamics at the interface of the coupled acousto-elastic system. The main tool is an appropriate asymptotic decomposition of the kernel of the NtD map, which reveals the outgoing and incoming compo nents of the trace of the wavefleld on the interface far from the sources. This decomposition, in combination with the narrow-angle parabolic approximation of the field in the interior of the waveguide, leads to a Volterra-type nonlocal boundary condition for the parabolic equation (impedance bound ary condition). This boundary condition is radically different from the con dition derived by assuming from the beginning the narrow-angle parabolic approximation of the wave field in the elastic seabed.

A Method Based on the Radon Transform for Three-Dimensional Elastodynamic Problems of Moving Loads

An integral transform procedure is developed to obtain fundamental elastodynamic three- dimensional (3D) solutions for loads moving steadily over the surface of a half-space. These solutions are exact, and results are presented over the entire speed range (i.e., for subsonic, transonic and supersonic source speeds). Especially, the results obtained here for the tangential loads (one of these loads is along the direction of motion and the other is orthogonal to the direction of motion) are quite new in the literature. The solution technique is based on the use of the Radon transform and elements of distribution theory. It also fully exploits as auxiliary solutions the ones for the corresponding plane- strain and anti-plane shear problems (the latter problems are 2D and uncoupled from each other). In particular, it should be noticed that the plane-strain problem here is completely analogous to the original 3D problem, not only with respect to the field equations but also with respect to the bound- ary conditions. This makes the present technique more advantageous than other techniques, which require first the determination of a fictitious auxiliary plane-strain problem through the solution of an integral equation. Our approach becomes particularly simple when there is no angular dependence in the boundary conditions (i.e., when axially symmetric problems regarding their boundary conditions are considered). On the contrary, no such constraint needs to be fulfilled as regards the material response (and, therefore, the governing equations of the problem) and/or also possible loss of ax- isymmetry due to the generation of shock (Mach-type) waves in the medium. Therefore, the solution technique can easily deal with general 3D problems having a largely arbitrary radial dependence in the boundary conditions and involving: (i) material anisotropy in static and dynamic situations, and (ii) asymmetry caused by changes in the nature of governing PDEs due to the existence of different velocity regimes (super-Rayleigh, transonic, supersonic) in dynamic situations.

On the Landau-Ginzburg description of boundary CFTs and special lagrangian submanifolds

We consider Landau-Ginzburg (LG) models with boundary conditions pre- serving A-type N = 2 supersymmetry. We show the equivalence of a linear class of boundary conditions in the LG model to a particular class of boundary states in the cor- responding CFT by an explicit computation of the open-string Witten index in the LG model. We extend the linear class of boundary conditions to general non-linear bound- ary conditions and determine their consistency with A-type N = 2 supersymmetry. This enables us to provide a microscopic description of special Lagrangian submani- folds in C n due to Harvey and Lawson. We generalise this construction to the case of hypersurfaces in P n . We nd that the boundary conditions must necessarily have vanishing Poisson bracket with the combination (W () W ()), where W ( )i s the appropriate superpotential for the hypersurface. An interesting application considered is the T 3 supersymmetric cycle of the quintic in the large complex structure limit.

Performance comparative study of new alternatives to R-502 inside air/refrigerant enhanced surface tubing

In this paper the test results of a performance evaluation of new alternatives; R-407B, R-507, R-408A and R-404A as substitutes to CFC-502 are presented. The test results were obtained using an air-source heat pump with enhanced surface tubing under standard ARI conditions. The data demonstrated that, as an interim replacement, R-408A blend has a superior performance among the proposed blends including R-502, in the range investigated. Furthermore, the alternatives to R-502 are characterised by high discharge pressure compared to R-502. In particular, R-407B and R-408A have higher discharge temperatures compared to R-502. Copyright © 2000 John Wiley & Sons, Ltd.

Existence and convergence of solutions to the H sampled-data estimation problem

The problem of H filtering for time-invariant linear systems with sampled measurements is considered. Sufficient and neces ary conditions are derived that ensure the existence of a finite-horizon filter and the convergence of this filter to the infinite-horizon one. The convergence conditions are given in terms of allowable regions for the initial state error weighting matrix.

Optimal design of infinite repetitive structures

An approach for designing optimal repetitive struc- tures under arbitrary static loading is presented. It is shown that the analysis of such infinite structures can be reduced to the analy- sis of the repeating module under transformed loading and bound- ary conditions. Consequently, both the design parameters and the analysis variables constitute a relatively small set which facilitates the optimization process. The approach hinges on the representa- tive ceil method. It is based on formulating the analysis equations and the continuity conditions for a sequence of typical modules. Then, by means of the discrete Fourier transform this problem translates into a boundary value problem of a representative cell in transformed variables, which can be solved by any appropriate analytical or numerical method. The real structural response any- where in the structure is then obtained by the inverse transform. The sensitivities can also be calculated on the basis of the sensi- tivities of the representative cell. The method is illustrated by the design for minimum compliance with a volume constraint of an infinite plane truss. It is shown that by employing this analysis method within an optimal design scheme one can incorporate a reduced analysis problem in an intrinsically small design space.

Photophysics of metal atoms in rare-gas complexes, clusters and matrices

Experimental studies of electronic spectra and dynamics of metal atoms M of groups I, II and III of the periodic system interacting with rare-gas atoms G in 1:1 MG complexes, MGn clusters and M/G centres in matrices are reviewed. It is shown that the necess n ary condition for a good understanding of the properties of M/G solids is a detailed knowledge of the M-G interactions in diatomic MG molecules. In spite of their apparent simplicity, the electronic spectra of MG and M/G systems are complex because of a drastic difference between the M-G potentials in ground and excited states of M atoms.

Resonant generation of a difference harmonic at a quantized metallic film

The difference-harmonic susceptibility due to in- tersubband transitions of electrons in quantized metallic films is calculated. The double-resonant contributions to suscepti- bility are analyzed based on the quasi-classical quantization of electron states. The roles of anisotropic and non-parabolic energy spectra are discussed. Numerical results are presented for the parabolic model of the dispersion laws and the bound- ary conditions of the third kind at interfaces.

Forced convection adsorption cycles

The convective thermal wave is part of a patented cycle which uses heat transfer intensification to achieve both high efficiency and small size from a solid adsorption cycle. Such cycles normally suffer from low power density because of poor heat transfer through the adsorbent bed. Rather than attempting to heat the bed directly, it is possible to heat the refrigerant gas outside the bed and to circulate it through the bed in order to heat the sorbent. The high surface area of the grains leads to very effective heat transfer with only low levels of parasitic power needed for pumping. The cycle presented here also utilizes a packed bed of inert material to store heat between the adsorption and desorption phases of the cycle. The highest degree of regeneration possible leads to good COP. Thermodynamic modelling, based on measured heat transfer and porosity data, predicts a cycle COP (for a specific carbon) of 0.95 when evaporating at 0°C and condensing at 42°C. These temperatures are compatible with ARI conditions. Further improvement is possible. Experimental heat transfer measurements and cycle simulations are presented which show the potential of the concept to provide the basis of a gas-fired air conditioner in the range 10–100 kW cooling. A research project to build a 10 kW water chiller is underway. The laboratory system, which is being commissioned at the time of writing, is described.

Angular Differential Cross-Section for Electron Transfer in ION-ION Collision

Angular differential cross-sections for the formation of He 0 in collision between fast He+ ions are calculated using distorted wave Coulomb—Born approximation. The interaction potentials satisfy necessary Coulomb bound- ary conditions. In absence of any other theoretical results the present results are compared with the existing experimental data.

Energy storage in open cycle liquid desiccant cooling systems

Energy for air dehumidification and cooling can be stored efficiently and non-dissipatively in liquid desiccants. For optimal storage capacity, new dehumidifiers have been developed and tested, dehumidifying air by a cooled microflow of a hygroscopic aqueous salt solution, e.g. LiClH 2O in an almost isothermal absorption process. A small, theoretically sufficient solution flow of about 0.21 l/(hm 2) could be distributed uniformly over a cooled exchanger surface. An air dehumidification of 5.5 g/kg and a storage solution has been measured under steady state ARI ∗ ∗ ARI conditions indoor: 26.7°C, 11 g/kg, 50% r.h., outdoor: 35°C, 14.5 g/kg, 40% r.h., wet bulb temperature of ARI ambient conditions: 23.9°C conditions with an experimental dehumidifier for an air flow of 1000 m 3/h.

Predictability of Eutectic Microstructures

AbstractThe interphase spacings σ in the microstructures of most binary and pseudobinary “normal” metallic eutectics can roughly be quan‐ tified with regard to their respective solidification rates v according to a general relationship constant the constant being commonly between 10−10 and 10−11 cm3 −1 The designation “normal” relates to similar degrees of undercooling of either phase on a plain‐front solidification process at variance with anomaleous eutectics which solidify at different degrees of under‐ cooling in an uncoupled or weakly‐coupled manner. The “constant”, however, is an individual value for each eutectic system. It is lowest for “simple” eutectics forming no intermetallic com‐ pounds and having low terminal solid solutions. The constant is raised for systems by 3 orders of magnitude or more if extensive terminal solid solutions are present. A closer fit for deliberate normal eutectics is presented in this pragmatic approach if the concentration differences between the terminal phases in eutectics ΔCE [at%] are attributed to them as a square term according to λ2 + · v · ΔCE2 = constant. The data based on this relation still show some scatter but they are grouping to distinct material families e. g. to Pb‐, Ag‐ or Al‐based eutectics. The remanent differences are estimated to disappear as soon as the relation is extended by the interdiffusion coefficient D according to as is confirmed in cases where reliable D values are available. These findings are in contrast to the current published theories on eutectic solidification. Suggestions are given where the bound‐ ary conditions have to be altered in order to attain full accord be‐ tween experiment and theory.

Nonstationary Initial Boundary Value Contact Problems of Generalized Elastothermodiffusion

The initial boundary value problems with mixed bound- ary conditions are considered for a system of partial dierential equa- tions of generalized electrothermodiusion. Approximate solutions are constructed and a mathematical substantiation of the method is given. It is well known that a wide range of problems of mathematical physics includes boundary value and initial boundary value problems for dieren- tial equations. Such problems are rather dicult to solve because of an enormous variety of geometrical forms of the investigated objects and the complexity of boundary conditions. Hence an important and timely task has arisen to develop suciently eective methods and tools for solving the above-mentioned problems and obtaining their numerical solutions. Until recently no methods were known for solving problems of elasticity by means of conjugate Þelds. However, in the past few years there have appeared and keep on appearing numerous published works dedicated to this topic. The results of our studies in this direction are presented mainly in (1, 2, 3). In this paper, using the generalized Green-Lindsay theory of elastother- modiusion as an example, the approaches to the solution of nonstationary initial boundary value contact problems with mixed boundary conditions are described for a system of partial dierential equations of this theory in a nonhomogeneous medium. These approaches are based on the method of discrete singularities known as the Riesz-Fischer-Kupradze method. The particular case is treated in (4).

Effect of Operating Conditions on Optimal Performance of Rotary Dehumidifiers

The design-point dehumidification performance (i.e., at ARI conditions) of a rotary dehumidifier wheel depends on its rotational speed, the sorption properties of the desiccant, the heat and mass transfer characteristics of the matrix, and the size of the dehumidifier. However, the real operating conditions of a rotary dehumidifier can vary significantly from the design point, given the large variations in operating conditions (i.e., the outdoor, indoor, and regeneration temperatures and humidities) for various locations during different times of the year. This paper investigates the variability of the dehumidification performance of a rotary dehumidifier and its dependence on operating conditions. Also, the effect of the operating conditions on the optimum rotational speed of a rotary dehumidifier, where the performance of a rotary dehumidifier is optimized, is described.

Forced Convective-Diffusive Heat Flow in Insulations: A New Analytical Technique Applied to Air Leakage through a Slit

Forced convective-diffusive heat flow in porous insulation materials is governed by an equation for the air pressure distribution with an ensuing air flow and a heat equation with convection and diffusion. The pressure equation for a ho mogeneous material may be solved analytically with simple geometries and bound ary conditions. The new technique uses a transformed form of the convective-diffusive equation for which the awkward first-order derivatives of the temperature (the convective part) are removed. New explicit solutions for certain two-dimensional, steady-state cases may be derived. The considered example concerns air leakage through an insulation which is open on one side and airtight on the other except for an open slit. Air infiltrates through the slit and leaves through the open side. The solution gives the complete pressure and temperature fields. The extra heat loss due to air leakage is given by an explicit expression which contains only a single, dimensionless parameter.

Absorbing boundary conditions for the linearized Euler equations in $2$-D

In this paper we shall derive some approximate absorbing bound- ary conditions for the initial value problem for the unsteady linearized Euler equations in 2-D. Since we assume that the coefficients of the system are con- stant, we can describe the transformation of the system to a decoupled system of ODE's and the related absorbing boundary conditions explicitly. We shall verify the usefulness of these boundary conditions in some numerical tests for the nonlinear Euler equations in 2-D.

Transfinite element methodology for non‐liner/linear transient thermal modelling/analysis: Progress and recent advances

AbstractRecent progress and advances in the development and applicability of a novel ‘transfinite element’ computational methodology is presented for general non‐linear/linear transient thermal problems. The proposed methodology and concepts are new and unique, and demonstrate the applicability to general transient non‐linear/linear thermal analysis situations by combining classical Galerkin schemes and transform approaches with contemporary finite element methods to preserve the modelling versatility and numerical features–thereby, a hybrid computational methodology is proposed. Characteristic features and pertinent details of the approach are described for non‐linear/linear transient thermal problems, wherein non‐linearities due temperature dependence of thermophysical properties and/or general non‐linear bound ary conditions to include radiation, effects due to phase change, etc., are considered. In addition, the use of high‐continuity formulations in conjuction with the proposed methodology to furnish accurate temperature distributions and temperature gradients making use of a relatively smaller number of degrees of freedom is also demonstrated. Numerical test cases are presented for a variety of problems to demonstrate the fundamental features and applicability of the proposed formulations. The proposed hybrid transfinite element methodology and concepts offer significant potential for extension to several areas of mathematical physics and engineering and to interdisciplinary research areas.