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Realistic Case (realistic + case)
Selected AbstractsA ,-coordinate three-dimensional numerical model for surface wave propagationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2002Pengzhi Lin Abstract A three-dimensional numerical model based on the full Navier,Stokes equations (NSE) in , -coordinate is developed in this study. The , -coordinate transformation is first introduced to map the irregular physical domain with the wavy free surface and uneven bottom to the regular computational domain with the shape of a rectangular prism. Using the chain rule of partial differentiation, a new set of governing equations is derived in the , -coordinate from the original NSE defined in the Cartesian coordinate. The operator splitting method (Li and Yu, Int. J. Num. Meth. Fluids 1996; 23: 485,501), which splits the solution procedure into the advection, diffusion, and propagation steps, is used to solve the modified NSE. The model is first tested for mass and energy conservation as well as mesh convergence by using an example of water sloshing in a confined tank. Excellent agreements between numerical results and analytical solutions are obtained. The model is then used to simulate two- and three-dimensional solitary waves propagating in constant depth. Very good agreements between numerical results and analytical solutions are obtained for both free surface displacements and velocities. Finally, a more realistic case of periodic wave train passing through a submerged breakwater is simulated. Comparisons between numerical results and experimental data are promising. The model is proven to be an accurate tool for consequent studies of wave-structure interaction. Copyright © 2002 John Wiley & Sons, Ltd. [source] Two-stage computing budget allocation approach for the response surface methodINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 6 2007J. Peng Abstract Response surface methodology (RSM) is one of the main statistical approaches to search for an input combination that optimizes the simulation output. In the early stages of RSM, an iterative steepest ascent search procedure is frequently used. In this paper, we attempt to improve this procedure by considering a more realistic case where there are computing budget constraints, and formulate a new computing budget allocation problem to look into the important issue of allocating computing budget to the design points in the local region of experimentation. We propose a two-stage computing budget allocation approach, which uses a limited budget to estimate the response surface in the first stage and then uses the rest of the budget to improve the lower bound of the estimated response at the center of the next design region in the second stage. Several numerical experiments are carried out to compare the two-stage approach with the regular factorial design, which allocates budget equally to each design point. The results show that our two-stage allocation outperforms the equal allocation, especially when the system noise is large. [source] Non-linear bending waves in Keplerian accretion discsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006G. I. Ogilvie ABSTRACT The non-linear dynamics of a warped accretion disc is investigated in the important case of a thin Keplerian disc with negligible viscosity and self-gravity. A one-dimensional evolutionary equation is formally derived that describes the primary non-linear and dispersive effects on propagating bending waves other than parametric instabilities. It has the form of a derivative non-linear Schrödinger (DNLS) equation with coefficients that are obtained explicitly for a particular model of a disc. The properties of this equation are analysed in some detail and illustrative numerical solutions are presented. The non-linear and dispersive effects both depend on the compressibility of the gas through its adiabatic index ,. In the physically realistic case , < 3, non-linearity does not lead to the steepening of bending waves but instead enhances their linear dispersion. In the opposite case , > 3, non-linearity leads to wave steepening and solitary waves are supported. The effects of a small effective viscosity, which may suppress parametric instabilities, are also considered. This analysis may provide a useful point of comparison between theory and numerical simulations of warped accretion discs. [source] Ein einheitliches Rentensystem für Ost- und Westdeutschland: Simulationsrechnungen zum Reformvorschlag des SachverständigenratesPERSPEKTIVEN DER WIRTSCHAFTSPOLITIK, Issue 1 2010Axel Börsch-Supan In this paper, we quantify the effects of this proposal. We show that the direction and size of the effects largely depend on the development of future wages. In the most realistic case we assume that the average wages in East Germany remain a constant fraction of the average wage in the West over time. In this case, the Council's proposal only weakly affects the size of pensions in East and West Germany. Thus, the effect on the contribution rate to the pension system is also weak. On the contrary, if average wages in East and West fully converge in the future, this reform would lead to redistribution from pensioners in the East to pensioners in the West. In the most unrealistic case, where average wages in East and West Germany continue to diverge in the future, pensioners in both East and West Germany would be worse off with the reform. However, contribution rates to the pension system would be relatively lower, leading to redistribution from the old to the young. [source] Performance analysis of optically preamplified DC-coupled burst mode receiversEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2009T. J. Zuo Bit error rate and threshold acquisition penalty evaluation is performed for an optically preamplified DC-coupled burst mode receiver using a moment generating function (MGF) description of the signal plus noise. The threshold itself is a random variable and is also described using an appropriate MGF. Chernoff bound (CB), modified Chernoff bound (MCB) and the saddle-point approximation (SPA) techniques make use of the MGF to provide the performance analyses. This represents the first time that these widely used approaches to receiver performance evaluation have been applied to an optically preamplified burst mode receiver and it is shown that they give threshold acquisition penalty results in good agreement with a prior existing approach, whilst having the facility to incorporate arbitrary receiver filtering, receiver thermal noise and non-ideal extinction ratio. A traditional Gaussian approximation (GA) is also calculated and comparison shows that it is clearly less accurate (it exceeds the upper bounds provided by CB and MCB) in the realistic cases examined. It is deduced, in common with the equivalent continuous mode analysis, that the MCB is the most sensible approach. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modelling of source-coupled logic gatesINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 4 2002M. Alioto Abstract In this paper, the modelling of CMOS SCL gates is addressed. The topology both with and without output buffer is treated, and the noise margin as well as propagation delay performance are analytically derived, using standard BSIM3v3 model parameters. The propagation delay model of a single SCL gate is based on proper linearization of the circuit and the assumption of a single-pole behaviour. To generalize the results obtained to cascaded gates, the effect of the input rise time and the loading effect of an SCL gate are discussed. The expressions obtained are simple enough to be used for pencil-and-paper evaluations and are helpful from the early design phases, as they relate SCL gates performance to design and process parameters, allowing the designer to gain an intuitive understanding of performance dependence on design parameters and technology. The model has been validated by comparison with extensive simulations using a 0.35-µm CMOS process. The model agrees well with the simulated results, since in realistic cases the difference is less than 20% both for noise margin and delay. Therefore, the model proposed can be profitably used for pencil-and-paper evaluations and for computer-based timing analysis of complex SCL circuits. Copyright © 2002 John Wiley & Sons, Ltd. [source] A two-stage procedure for comparing hazard rate functionsJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 1 2008Peihua Qiu Summary., Comparison of two hazard rates is important in applications that are related to times to occurrence of a specific event. Conventional comparison procedures, such as the log-rank, Gehan,Wilcoxon and Peto,Peto tests, are powerful only when the two hazard rates do not cross each other. Because crossing hazard rates are common in practice, several procedures have been proposed in the literature for comparing such rates. However, most of these procedures consider only the alternative hypothesis with crossing hazard rates; many other realistic cases, including those when the two hazard rates run parallel to each other, are excluded from consideration. We propose a two-stage procedure that considers all possible alternatives, including ones with crossing or running parallel hazard rates. To define its significance level and p -value properly, a new procedure for handling the crossing hazard rates problem is suggested, which has the property that its test statistic is asymptotically independent of the test statistic of the log-rank test. We show that the two-stage procedure, with the log-rank test and the suggested procedure for handling the crossing hazard rates problem used in its two stages, performs well in applications in comparing two hazard rates. [source] ENTRY AND EXIT OF LABOR AND CAPITAL IN A FISHERYNATURAL RESOURCE MODELING, Issue 2 2005ASGEIR DANIELSSON ABSTRACT. Exit and entry of fishermen, as well as vessels, is modeled explicitly. If the speed of exit and entry of fishermen is less than instantaneous the wage rate varies with the fortunes of the fishing firms and affects the endogenous labor supply creating a second transmission mechanism from profits to effort. There are realistic cases where this mechanism has important effects on the stability of the dynamic system and on the effects of taxes (subsisdies) on the size of the fish stock. If labor supply depends negatively on the wage rate, the immediate effect of an increase in the tax rate is to increase effort and harvest. This condition makes it also more probable that the dynamic system is unstable. In those cases where the dynamic system is unstable the increase in the tax rate increases overexploitation not only in the short-term but also in the long-term. [source] | |||||||||||||