Approximating the Temperature–Entropy Saturation Curve of ORC Working Fluids From the Ideal Gas Isobaric Heat Capacity

Recently, we proposed an approximate expression for the liquid–vapor saturation curves of pure fluids in a temperature–entropy diagram that requires the use of parameters related to the molar heat capacity along the vapor branch of the saturation curve. In the present work, we establish a connection between these parameters and the ideal-gas isobaric molar heat capacity. The resulting new approximation yields good results for most working fluids in Organic Rankine Cycles, improving the previous approximation for very dry fluids. The ideal-gas isobaric molar heat capacity can be obtained from most Thermophysical Properties databases for a very large number of substances for which the present approximation scheme can be applied.

APPROXIMATE FUNCTION FOR UNSTEADY AERODYNAMIC KERNEL FUNCTION OF AEROELASTIC LIFTING SURFACES

ABSTRACT: Prediction of unsteady aerodynamic loads is still the most challenging task in flutter aeroelastic analysis. Generally the numerical estimation of steady and unsteady aerodynamic of thin lifting surface is conducted based on an integral equation relating aerodynamic pressure and normal wash velocity. The present work attempts to increase the accuracy of the prediction by using an approximate approach to evaluate kernel function occurring in the integral equation in the form of cylindrical function. Following previous approximation approach by other researchers to solve the cylindrical function for planar lifting surfaces, in the present work such approach is extended to non planar lifting surfaces. To increase the accuracy of the method, the integration region of the kernel function is divided into two parts namely near and far regions, where a nonlinear regression curve fitting technique is adapted to approximate the denominator part of the cylindrical function of each region.ABSTRAK: Penelahan daya aerodinamik tidak stabil merupakan satu tugas yang mencabar dalam menganalisis getaran aeroanjalan. Umumnya, anggaran berangka untuk daya aerodinamik stabil dan tidak stabil pada permukaan mengangkat yang nipis, adalah berdasarkan kepada persamaan kamiran di antara tekanan aerodinamik dan halaju aliran udara pada garis normal yang terhasil di bawah sayap pesawat. Kajian ini adalah bertujuan untuk menghasilkan penelahan daya aerodinamik yang lebih tepat dengan menggunakan pendekatan kira hampir untuk menilai fungsi Kernel yang terdapat dalam persamaan kamiran dalam bentuk fungsi silinder. Dengan menggunakan pendekatan kira hampir yang digunakan oleh penyelidik sebelumnya untuk menyelesaikan fungsi silinder pada permukaan mengangkat satah, kajian ini mengembangkan pendekatan tersebut kepada permukaan mengangkat tak sesatah. Untuk meningkatkan lagi ketepatan penelahan, kawasan pengamiran fungsi Kernel dibahagikan kepada dua bahagian, kawasan hampir dan kawasan jauh, di mana penyuaian lengkung regresi tak linear digunakan untuk kiraan hampir penyebut pada fungsi silinder pada setiap kawasan.

Strategies for Analyzing Random Vibration of Jointed Structures

Development of mathematical models for built-up structures, particularly those with many interfaces, is still primitive. This limitation is particularly evident when complex loads and load histories are considered, an example of which is random vibration. Two steps in simplifying this problem are explored here. First, the system response is approximated as that of the superposition of numerous decoupled modes, the coordinates of which evolve according to a constitutive model designed to capture the nonlinearity of the structure. Second, because among the categories of load for which dynamic analysis on nonlinear structures is particularly difficult is that of random loads and the resulting random vibration, and given the previous approximation, it is natural to apply the method of stochastic equivalent linearization to the governing equation of each mode. Both of these approximations are explored for the case where the nonlinear behavior of the interfaces is represented by a Masing-Prandtl-Ishlinskii-Iwan model employing a Palmov kernel.

CUTTING OUT POLYGONS WITH A CIRCULAR SAW

Given a simple (cuttable) polygon Q drawn on a piece of planar material R, we cut Q out of R by a (small) circular saw with a total number of cuts no more than twice the optimal. This improves the previous approximation ratio of 2.5 obtained by Demaine et al in 2001.

WEAK MEAN-FIELD APPROXIMATION FOR DISCRETE EPIDEMIC MODELS IN SCALE-FREE NETWORKS

Epidemic dynamics in networks have attracted a great deal of attention from many fields. Based on the previous work, we propose a weak discrete mean-field approximation, and the difference with the previous approximation approach is that it can result in more simple difference equations. We mainly consider the minimal SIS epidemic model in complex networks, and make comparisons amongst two kinds of approximation formulations on the prediction of epidemic prevalence and find that they are effective to model epidemic spreading. Moreover, we investigate its application to the risk feedback case and simulations indicate its effectiveness.

APPROXIMATING THE DISCRETE RESOURCE SHARING SCHEDULING PROBLEM

The goal of this work is to study the portfolio problem which consists in finding a good combination of multiple heuristics given a set of a problem instances to solve. We are interested in a parallel context where the resources are assumed to be discrete and homogeneous, and where it is not possible to allocate a given resource (processor) to more than one heuristic. The objective is to minimize the average completion time over the whole set of instances. We extend in this paper some existing analysis on the problem. More precisely, we provide a new complexity result for the restricted version of the problem, then, we generalize previous approximation schemes. In particular, they are improved using a guess approximation technique. Experimental results are also provided using a benchmark of instances on SAT solvers.

Antialiasing methods in Kirchhoff migration

This paper addresses some practical aspects of antialiasing in Kirchhoff migration. We show that the effective trace spacing related to the aliasing‐frequency limits for directions between the in‐line and cross‐line directions is smaller than values previously used and that the frequency limits for antialiasing may be increased. We present a corrected expression for the migration operator spatial derivative for 3-D time migration that avoids the overfiltering at nonzero offsets produced by a previous approximation. Simple operator truncation is shown to reduce aliasing noise; it is inexpensive but may lead to errors in interpretation. Triangle filtering and Gray’s method both produce similar results, but the relative costs of these two methods will vary with the size of the migration and the computational environment. Gray’s method takes more setup time for each input trace than does triangle filtering, but Gray’s method might be more cost effective when each input trace contributes to a large number of output traces.