A physical perspective of the element‐based finite volume method and FEM‐Galerkin methods within the framework of the space of finite elements

The literature shows an increasing number of works focused on investigating the behaviour of methods that uses concepts of control volumes in the solution of structural problems. In recent years, new approaches using unstructured meshes have been proposed, most of which addressing new applications and, to a lesser extent, the underling physical perspective. This paper presents a unified approach to the element‐based finite volume method and FEM‐Galerkin within the framework of the finite element space. Numerical examples highlight some accuracy issues associated with the element‐based finite volume method developed in this work. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparing of pellets by extrusion/spheronization using different types of equipment and process conditions

Introduction: The focus of this work was to produce matrix pellets made by extrusion/ spheronization using two types of equipment. The aim was to accomplish the laboratory-scale I process that has been already optimized and accepted with another type of equipment (laboratory-scale II).

Methods: A matrix pellet formulation consisting of MCC, Eudragit NE 30D and diclofenac sodium was used in the two types of equipment. Physico-chemical parameters and the dissolution profiles of the pellets in phosphate buffer pH 6.8 were compared.

Results: Pellets from both processes were similar in shape and tensile strength. They differed in particle size and dissolution profile. This may be contributed to different spheronization conditions.     

The Vortex Path Model Analysis of the Field Angle Dependence of the Critical Current Density in Nanocomposite YBa2Cu3 O 7−x – BaZrO3 Films Obtained by Low Fluorine Chemical Solution Deposition

In the present paper, we analyze the role of in situ grown BaZrO₃ (BZO) inclusions in YBa₂Cu₃O_7?x (YBCO) thin films prepared by chemical solution deposition using a low fluorine coating solution, on the field angle dependence of the critical current density, J _c (??), data using the vortex path model. In order to form a coherent picture on the BZO doping influence on the pinning properties of the YBCO matrix, detailed structural analyses performed by X-ray diffraction techniques and microstructural evaluation by transmission electron microscopy are also presented. The evaluation of different contributions to the overall, J _c , permitted us to prove the effectiveness of the BZO inclusions acting as isotropic pinning centers, reflected in a uniform component of high relative value with respect to other components. For the studied 10 mol % BZO doping concentration, a threefold increase in the critical current density, J _c , of the YBCO host is measured, in self-field at 77 K, corresponding to a value of J _c =2.9MA/cm², whereas a factor 10 is measured at 1 T (J _c =0.35 MA/cm²).     

Probabilistic cumulative damage model to estimate fatigue life

This paper introduces a numerical model to estimate fatigue life under step‐stress conditions, using the Weibull and lognormal distributions. The maximum likelihood method was used to estimate the free parameters of the distributions. The model was fitted to an experimental data on fatigue life in the specimens of steel SAE 8620, by using evolutionary computation to optimize the likelihood function. Results are reported on the values of the parameters and their confidence interval. Also, a validation of the model is discussed using analysis of residuals.     

Demonstration of the environmental and demand-side management benefits of grid-connected photovoltaic power systems

This study investigated the pollutant emission reduction and demand-side management potential of 16 photovoltaic (PV) systems installed across the US during 1993 and 1994. The US Environmental Protection Agency (EPA) and 11 electric power companies sponsored the project. This article presents results of analyses of each PV system's ability to offset power plant emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_x), carbon dioxide (CO₂) and particulates and to provide power during peak demand hours for the individual host buildings and peak load hours for the utility. The analyses indicate a very broad range in the systems' abilities to offset pollutant emissions, due to variation in the solar resource available and the emission rates of the participating utilities' load following generation plants. Each system's ability to reduce building peak demand was dependent on the correlation of that load to the available solar resource. Most systems operated in excess of 50% of their capacity during building peak load hours in the summer months, but well below that level during winter peak hours. Similarly, many systems operated above 50% of their capacity during utility peak load hours in the summer months, but at a very low level during winter peak hours.     

An approximate model for sizing and costing a solar thermal collector-central receiver system

An approximate generalized theoretical model is presented for the geometry and energy transfer of a solar thermal collector-central receiver system. Equations permit sizing the receiver, tower, and heliostat field. Cost functions correlate data from Department of Energy studies. Based on a set of assumed conditions, simplified, optimized sizing equations yield the minimum capital cost. The costs of the tower and central receiver will change with plant and equipment cost indices, while heliostat costs are expected to diminish as annual production increases. The heliostat cost is the major cost component even at lowest projected unit cost; therefore optimization tends toward minimum heliostat area. The model permits order-of-magnitude cost estimates to be made very quickly, compared to detailed simulation.     

Hierarchical composites: Analysis of damage evolution based on fiber bundle model

A computational model of multiscale composites is developed on the basis of the fiber bundle model with the hierarchical load sharing rule, and employed to study the effect of the microstructures of hierarchical composites on their damage resistance. Two types of hierarchical materials were considered: “hierarchical tree” (bundles-of-bundles of fibers) and self-similar particle and fiber reinforced composite (in which reinforcements at each scale level represents composites in turn consisting of lower level reinforcements and matrix). For the case of the hierarchical tree (“bundle-of-bundles” material), it was observed that the increase in the amount of hierarchy levels leads to the lower strength of material. In the self-similar fiber reinforced matrix materials, as differed from the hierarchical trees, the damage resistance of the hierarchical materials increases with increasing the amount of hierarchy levels. The effect of mixed fiber and particle reinforcement on the damage resistance of the hierarchical composites is investigated as well.     

Power loss in photovoltaic arrays due to mismatch in cell characteristics

Variations in the current-voltage characteristics of photovoltaic cells can lead to significant power loss “due to mismatch” when the cells are connected together in a network. This study explores how this mismatch loss depends on variations in max-power current and max-power voltage from cell to cell. An analysis of a series string is first performed. Losses in a parallel string are also determined. Estimates of mismatch losses in more complex arrays are then obtained. In addition to generally excellent comparison with several numerical studies, results show that, for a series string, there exists a critical magnitude of deviation in cell max-power current beyond which the power loss due to mismatch is sensitive to both the number of cells placed in series and the shape of the probability density function defining variations in max-power current. This critical level also depends on the cell fill-factor.     

Preliminary isotopic studies of fluids from the Cerro Prieto geothermal field

Preliminary isotopic studies of Cerro Prieto geothermal fluids and earlier studies of Mexicali Valley ground waters suggest local recharge of the geothermal system from the area immediately to the west. Oxygen isotope exchange of water with reservoir rock minerals at temperatures increasing with depth has produced fluids with oxygen-18 contents increasing with depth, and pressure drawdown in the southeastern part of the field has allowed lower oxygen-18 fluids to invade the production aquifer from above. The contents of tritium and carbon-14 in the fluid suggest only that the age of the fluid is between 50 and 10,000 years. The isotopic compositions of carbon and sulfur are consistent with a magmatic origin of these elements but a mixed sedimentary-organic origin appears more likely for carbon and is also possible for sulfur. Investigations of the isotopic compositions of geothermal and cold ground waters continue and are being expanded as fluids become available and as separation and analysis methods are improved.     

采用Kalman滤波器的实时混合试验方法

等效力控制方法采用力反馈控制代替隐式积分方法中的迭代过程,从而使等效力控制方法在避免隐式积分方法的迭代过程的同时仍具有隐式积分方法的无条件稳定性。利用该力反馈控制,等效力控制方法还具有对实时子结构试验中的时滞进行补偿的作用。但是,在实际的实时子结构试验中,能够影响等效力控制方法时滞补偿效果的因素有很多,噪声就是其中之一。本文研究了噪声对等效力控制方法稳定性的影响。提高等效力PID控制器的比例增益可对系统时滞起到补偿作用,但是当比例增益较大时,等效力反馈中的噪声会降低等效力控制方法的稳定性。为了对等效力反馈中的噪声进行滤波,本文采用了基于作动器模型设计的Kalman滤波器,并通过实时子结构实验方法对其滤波效果进行研究。研究结果表明此滤波器能够有效地过滤噪声,消除噪声对等效力控制方法稳定性的影响。