A methodological approach for finite element modeling of pretensioned concrete members at the release of pretensioning

This paper presents a methodological approach for finite element simulation of pretensioned concrete members. The three-dimensional analysis presented in this paper involves a rectangular [150 mm (6 in.) tall × 150 mm (6 in.) wide × 2440 mm (96 in.) long] concrete member hosting one 15-mm (0.6 in.) diameter 7-wire low-relaxation Grade 1860 MPa (270 ksi) prestressing strand. The finite element models are divided into two general classifications: (i) concentrically pretensioned, and (ii) eccentrically pretensioned. The finite element models are analyzed based on elastoplastic material behaviors as well as mesh sensitivity. Two approaches are examined for finite element modeling of the pretensioned concrete specimens: (i) the extrusion technique utilizing friction-based contact simulations, and (ii) the embedment technique simulating equivalent responses while being a computationally less expensive solution. A comparative analysis is presented to measure the validity as well as accuracy of the findings by the finite element techniques against the commonly used closed-form solutions based on elastic beam theory. The validity of the finite element approach is further verified by comparative analysis of the analytical data against the experimental findings. The paper concludes that the embedment technique provides an accurate and numerically efficient alternative in comparison with the extrusion method for the simulation of the pretensioned concrete members. While the extrusion technique provides more detailed information corresponding to the regions located immediately around the prestressing strands, including the interface overstresses and bond slippage, the embedment technique appears to have the ability to simulate the overall response of the concrete members with comparable accuracy.     

Minimum Depth of Soil Cover above Soil–Steel Bridges

Soil–steel bridges are built of flexible corrugated steel panels buried in well-compacted granular soil. Their design is based on the composite interaction between the soil pressures and the displacements of the conduit wall. The structure failure could be initiated by shear or tension failure in the soil cover above the steel conduit. The provisions for design given in different codes, such as the Canadian Highway Bridge Design Code, managed to avoid some of the problems associated with the failure of soil above soil–steel bridges by requiring a minimum depth of soil cover over the crown of the conduit taking into consideration the geometric shape of the conduit. However, the present code requirements for a minimum depth of cover were developed for a maximum span of 7.62 m and using nonstiffened panels of 51 mm depth of corrugation. The effect of having larger spans or using more rigid corrugated panels has not been examined before and is the subject of this paper. The present study uses the finite-element analysis to re-examine the possible soil failures due to centric live loads (i.e., loads acting symmetrically about the mid span of conduit) or eccentric live loads. The study deals with spans up to 15.24 m of circular conduits and 21.3 m of arches with deep corrugations. It has been found that, in addition to the conduit geometry, the actual dimension of the span should be considered to determine the required depth of soil cover.     

Parallel Poisson and Biharmonic solvers

In this paper we develop direct and iterative algorithms for the solution of finite difference approximations of the Poisson and Biharmonic equations on a square, using a number of arithmetic units in parallel. Assuming ann×n grid of mesh points, we show that direct algorithms for the Poisson and Biharmonic equations require 0(logn) and 0(n) time steps, respectively. The corresponding speedup over the sequential algorithms are 0(n ²) and 0(n ²logn). We also compare the efficiency of these direct algorithms with parallel SOR and ADI algorithms for the Poisson equation, and a parallel semi-direct method for the Biharmonic equation treated as a coupled pair of Poisson equations.     

A broad-range power-law form scalar-based seismic intensity measure

This paper aims at studying the efficiency and robustness of a proposed enhanced broad-range, spectrum shape-dependent, power-law form, scalar-based seismic Intensity Measure (IM). It is intended for estimation of structural performance for probability-based seismic assessment of structures. When traditional IMs are used, such as the peak ground acceleration or the first-mode spectral acceleration, the corresponding Engineering Demand Parameters (EDP) can display large record-to-record variability, forcing the use of many records to achieve reliable results. The ordinates of the elastic spectrum and the spectral shape of each individual record are found to significantly influence the seismic performance and they are shown to provide promising candidates for highly efficient IMs. The efficiency of the proposed broad-range IM in reducing the scatter in estimated peak lateral inelastic displacement and ductility demands is investigated herein through an extensive analytical program. The program considers a large database of 80 records and a broad spectrum of first mode-dominant structures encompassing a wide range of design-inherent inelastic displacement demands. Two different constitutive material models representing steel and concrete structures covering scenarios of non-degrading and degrading response are also studied. Statistical results show the versatility and efficiency of the proposed IM in satisfactorily–by minimizing the scatter of the resulting EDPs–dealing with structures designed to undergo various levels of inelastic displacement demands.     

Technoeconomic study for the optimization of turbine size and wind farm layouts

A technoeconomic analysis and optimization of wind turbine size and layout are performed using WAsP software. A case study of a 100‐MW wind farm located in Egypt is considered. Wind atlas for Egypt was used as the input data of the WAsP software. Two turbine models of powers 52 and 80 MW are considered for this project. The wind turbine size and distributions are selected based on the technoeconomic optimization, namely minimum wake effect, maximum annual energy production (AEP) rate, optimum cash flow, and payback period. The future worth method is adopted in economic comparison between the two alternatives, and the cash flow diagram provided the payback period and future worth after the lifetime of the plant. The results showed that (1) the AEP dramatically decreases for a wind farm area less than 15 km²; (2) the turbine spacing, spacing‐to‐diameter ratio, and the setback distances decrease and the wind turbine density and wake losses increase with decreasing the wind turbines size; (3) the total net AEP using G52 is lower than that of using G80 by about 16%; (4) the technoeconomic analysis recommended using G80 as it has higher profit than those of G52 by about $20 million.     

Magnetic micropolar nanofluids flow in double lid-driven enclosures using two-energy equation model

Impacts of an inclined electromagnetic force on a mixed convective process in two-sided lid-driven geometries using the two-energy equation model are examined in this study. The flow domain is filled by a porous medium and the local thermal nonequilibrium model is applied. Magnetic micropolar nanofluids are assumed as working fluids consisting of water as a base fluid and CuO as nanoparticles. The forced convection situation is due to the moving of the upper and lower walls in the right direction with a constant velocity. The used methodology depends on the finite volume method, together with the SIMPLE algorithm. The obtained outcomes are visualized using contours of the streamlines, isotherms for the nanofluid phase, isotherms for the solid phase, and angular velocity. The main findings revealed that the increase in lengths of the heated parts and the Nield number reduces the Nusselt number for the nanofluid phase. Also, the average heat transfer rate for the nanofluid and solid phases are boosted with the increase in the vortex viscosity.     

Parameters extraction of PEMFC's model using manta rays foraging optimizer

In this article, a recently developed bio-inspired based manta rays foraging optimizer (MRFO) is attempted for reliable and accurate extraction of the model uncertain parameters of proton exchange membrane fuel cells (PEMFCs). The parameter estimation is formulated as a non-linear optimization problem subject to set of restrictions. The great development and tremendous revolution of computation heuristic-based algorithms are the impetus of the authors to apply the MRFO to solve this constrained optimization problem resulting in a precise PEMFC model. Three case studies of typical field PEMFC stacks namely Ballard type Mark V, NedStack type PS6, and Horizon type H-12. Various I to V datasets are demonstrated to appraise the performance of MRFO among other recent optimizers available in the literature. To be objective and for sake of quantifications, the best scores of minimum fitness values are 0.8533, 2.1360, and 0.0966 for the later said PEMFC stacks, correspondingly. At a later stage, production of various characteristics under varying operating conditions such as changeable cell temperature and regulating pressures are established using the generated best values of PEMFCs model. Further calculations of statistical indices are performed to validate the robustness of obtained results by the MRFO. Through comprehensive performance assessments, it can be confirmed that MRFO is very promising tool for the effective extraction of PEMFCs' model and suggested to be applied for solving other engineering problems.     

VAE/MPM/GA Technique for DoA Estimation Using Optimized Antenna Arrays

Many algorithms have been proposed to estimate the direction of arrival for the targets, but through using a large number of snapshots. In real time applications such as automotive radar, this is unacceptable as it causes delay and heavy processing. Instead, if only a small number of snapshots or, optimally, a single snapshot is available for DoA estimation, it will be fast and efficient. Single snapshot algorithms have a drawback as they require a large number of antenna elements, which considered a limiting factor. In this paper, a single snapshot DoA estimation technique is introduced by using optimized antenna arrays. The proposed algorithm is based on utilization of virtual array extension, matrix pencil method, and the genetic algorithm. The use of virtual array extension greatly improves the MPM performance. Furthermore, it exhibits a high DoA estimation accuracy by using a reduced number of antenna elements. The genetic algorithm is employed to determine the minimum number of antenna elements, which are required to estimate the DoAs with minimal root mean square error.

     

Influence of electrical discharge machining parameters on cutting parameters of carbon fiber-reinforced plastic

Today the use of high-strength carbon fiber-reinforced plastics (CFRP) composite as a material for many engineering applications is showing an increasing demand in the industry. These composites are replacing the traditional use of steel because they offer many advantages such as very light weight, high strength, and high stiffness associated with good corrosion-resistant properties. Unfortunately, there is little technological knowledge on the electrical discharge machining (EDM) process of high-strength composite materials, especially about the CFRP. In this work, a study has made into the possibility of using EDM process as a means of machining CFRP composite. Various cutting conditions such as peak current, pulse-on time, pulse-off time and open-circuit voltage were selected to perform electrical discharge machining. The effect of electrode rotation was also studied. Optimum cutting conditions and machine settings for EDM were chosen for machining CFRP composites.