The dual reciprocity method applied to free vibrations of 2D structures using compact supported radial basis functions

This paper presents a new boundary element application for free vibration analysis of 2D elastic structures. The dual reciprocity method is applied using four compact supported radial basis functions for approximating the domain inertia terms. The eigen-problem of displacement is then solved considering the traction contribution by means of static condensation. The formulation is also extended to consider additional internal nodes to improve accuracy. Three numerical problems are studied to demonstrate the validity and accuracy of the developed formulation. The results are compared to those obtained from analytical and other numerical solutions. A parametric study is set up to demonstrate the effect of the compact support radius on the final results and on the sparsity of system matrices.     

Simulation and cost estimate for biodiesel production using castor oil

Brazilian government has established a regulation that imposes the commercialization of diesel blended with 3% of biodiesel by volume. Castor oil has being considered an option to guarantee the supply of biodiesel needed. For this reason, in this work, a continuous biodiesel plant was designed and simulated in HYSYS simulator using castor oil as feedstock. The developed process was capable of producing biodiesel at high purity using an alkali catalyst. Material and energy flows, as well as sized unit operations were used to conduct an economic assessment of the process. Total capital investment, total manufacturing cost and after annual equivalent cost were also calculated. A study of production costs was performed considering the fluctuations of the raw material prices and the glycerin purification step.     

On the Courant–Friedrichs–Lewy criterion of rotating grids in 2D vertical-axis wind turbine analysis

The Courant–Friedrichs–Lewy (CFL) criterion for the stability of numerical schemes is herein investigated at the conservative interface that divides rotating grids embedded within fixed grids. This issue is of specific interest to correctly assess the power coefficient and the energy production of vertical-axis wind turbines (VAWTs).The CFL number is here manipulated in a convenient form to tackle rotating grids; this manipulation discloses the dependence of the CFL number from the angular location of rotating grid elements and also from the tip speed ratio of the rotating grid. An upper bound of the CFL number that does not depend on the angular location of the rotating grid element is derived. The angular marching step has dramatic effects on the accuracy of results and strongly affects the calculation of the most important integral property (the power coefficient); however, local quantities are affected to a lesser extent and this fact is misleading. Large errors are generated if the angular marching step is too coarse or, in other words, if the CFL criterion is violated. Angular marching steps as small as only 1° do not warrant accurate results, particularly for very small tip speed ratios and fine spatial discretizations. It is found in this study that rotating grids call for a more restrictive (lower) bound (e.g., CFL number less than 0.15) as compared with the literature criterion. This restriction prompts severe limitations to obtain trustable results from numerical simulations of VAWTs.     

Investigating the surface quality of the burnished brass C3605—fuzzy rule-based approach

In this work, prediction of burnished surface roughness (R _a) is achieved by using a fuzzy rule-based system. The process state variables used were burnishing speed, feed, and depth. The fuzzy rule-based system has achieved an accuracy of 95.4 % to predict the burnished surface roughness and proved to be convenient in terms of least computational complexity and dealing with nonlinear data such as that obtained in this work.     

Analysis and revamping of heat exchanger networks for crude oil refineries using temperature driving force graphical technique

Clean Technologies and Environmental Policy - The refining industry is an energy-intensive industry; most of the energy is consumed in heating and cooling requirements. Revamping or retrofitting of...     

A computer program for non-linear curve fitting

Recently several techniques for non-linear curve fitting have been developed. The implementation of a non-linear curve fitting procedure is treated for mathematical models in which the linear and the nonlinear parameters are separable. The technique of Golub and Pereyra is used so that a minimization algorithm only for the non-linear parameters is needed. The minimization algorithm of Marquardt has been completed with an eigenvalue analysis. In order to reduce the computation steps the inverses of matrices of the form A + λI are calculated with the eigenvalues and eigenvectors of the matrix A. Of particular interest is the obtained convergence speed and the ease with which the method can be applied.     

Improved material balance equation (MBE) for gas-condensate reservoirs considering significant water vaporization

The phenomenon of retrograde condensation occurs when the reservoir pressure declines below the dew-point pressure causing gas condensation and developing two-phase flow. Material balance equation (MBE) of gas condensate reservoirs is a real challenge because of the change in fluid composition and complexity of phase behavior.Neglecting the effect of water vaporization may lead to inaccurate predictions of the material balance equation. Therefore, the main objective of this study is to develop an improved MBE model capable to describe gas condensate reservoirs under significant vaporization of connate water and water influx driving mechanism.A new parameter is developed to consider water vaporization. This parameter is used to derive equations for gas condensate reservoirs considering vaporization effect with and without consideration of water influx. Numerical examples have been developed and used to compare the accuracy of the newly-developed model with conventional ones using actual reservoir depletion and production data.The results indicated that water vaporization has an important effect and should be considered for accurate MBE predictions. Error analysis showed that the newly-developed equations are more accurate than previously-developed models. The accuracy of the new MBE is attributed to the additional parameter introduced considering high pressure and high temperature conditions.The application of the new material balance equation will have important impact on predictions of initial gas in place, reserve calculation and future simulation studies.     

Designing a hierarchical structure of nickel-cobalt-sulfide decorated on electrospun N-doped carbon nanofiber as an efficient electrode material for hybrid supercapacitors

The intent of designing and exploring novel active electrode materials is to enhance the electrochemical performance of supercapacitors. Herein, a hierarchical structure of nickel-cobalt-sulfide nanostructures (NiCo₂S₄) decorated on the electrospun N-doped carbon nanofiber (CNF), NiCo₂S₄@CNF, is manipulated using a one-step and simple hydrothermal approach. The fabricated hierarchical structure of the NiCo₂S₄@CNF is featured by a large surface area and a high porosity that serve as ion diffusion channels. Therefore, it manifests high specific capacitance and specific capacity values of 377.2 C g^?1 and 754.4 F g^?1 at a current density of 1 A g^?1, respectively. Furthermore, a NiCo₂S₄@CNF//CNF hybrid supercapacitor in which a positive electrode of NiCo₂S₄@CNF is assembled with a negative electrode of CNF to estimate the electrochemical performance of the NiCo₂S₄@CNF. As a result, the device has a superior energy density of 65.6 and 52.5 Wh kg^?1 at a power density of 665 and 1313.8 W kg^?1, respectively. Moreover, the device reveals good stability with capacitance retention of 72% after 3000 charge/discharge cycles. These outstanding results enable the designed hierarchical structure of the NiCo₂S₄@CNF to be a promising electrode material for supercapacitors (SCs) applications.     

Electronic conductivity of catalyst layers of polymer electrolyte membrane fuel cells: Through-plane vs. in-plane

In this work, novel procedures are developed to measure in-plane and through-plane electronic conductivities of catalyst layers (CLs) for polymer electrolyte membrane fuel cells. The developed procedures are used in a parametric study on different CL designs to investigate effects of different composition and fabrication parameters, including ionomer to carbon weight ratio (I/C ratio), dry milling time of the catalyst powder, and drying temperature of the catalyst ink. Results show that CLs have anisotropic electronic conductivity with through-plane values being three orders of magnitude lower than the in-plane values. The reason for this anisotropy is speculated to be alignment of fibrillar nanostructures of ionomer by large shear forces during coating, which could result in better carbon-carbon contact in the in-plane direction. A simple order of magnitude analysis shows the significance of poor through-plane conduction for fuel cell performance.     

Microwave-assisted synthesis of Co-doped SnO2/rGO for indoor humidity monitoring

The evaluation of indoor humidity is challenging compared to other environmental parameters such as light intensity, temperature, sound and so forth. The proper selection of sensing materials and structural tuning will lead to high-performance humidity sensors. Herein, the SnO₂/rGO and SnO₂/rGO doped with Co nanocomposite were produced by microwave route. The obtained nanocomposite was characterized by XRD, SEM, EDAX, DTA, TGA, FTIR, Raman, and HRTEM. The successful incorporation of Co onto the rGO/SnO₂ is affirmed by the XRD and supported with matching SEM and TEM outcomes where nanoscale particles exist. FTIR reveals the existence of the CC stretching band at ～1570 cm^?1 indicating graphene network sustaining upon reduction. Micro-pores presence is claimed by the adsorption-desorption isotherm curve. The humidity sensing behavior of both structures was evaluated in a wide range of humidity (11–97% RH). The obtained results confirmed that best working frequency for highest humidity change is 50 Hz. Furthermore, upon doping the SnO₂/rGO composite with Co, sensitivity, the response time and recovery time has improved reaching 52 s and 100 s respectively.