Journal of Engineering Research

AVOIDABLE AND UNAVOIDABLE EXERGY DESTRUCTIONS AND THE ASSOCIATED INVESTMENT COST FOR EVALUATING THE PERFORMANCE OF A GAS TURBINE CYCLE

2024-08-25T10:25:29+00:00

ABSTRACT

The objective of the current work is to provide a deeper awareness about the thermodynamic performance and cost effectiveness of thermal systems. To seek the potential for improvement, the avoidable part of the exergy destruction and the avoidable investment cost must be identified. The exergy destruction and the associated investment cost are split into avoidable and unavoidable parts. Modified exergatic efficiency (effectiveness) and a modified exergoeconomic factor are introduced and compared with the corresponding conventional effectiveness and exergoeconomic factor.

A simple gas turbine cycle is taken as an example to explore the advantages of such approach to give a rational judgment of the performance of thermal systems. The results show that, for the whole plant the conventional exergoeconomic factor is calculated as 16.15% and the conventional effectiveness as 24.67%, while the modified exergoeconomic factor is calculated as 36.85%, and the modified effectiveness as 40.14%.

EXACT FINITE ELEMENT FORMULATION FOR COUPLED FLEXURAL-LATERAL-TORSIONAL-WARPING STATIC ANALYSIS OF THIN-WALLED ASYMMETRIC SHEAR DEFORMABLE MEMBERS

2024-08-25T10:53:42+00:00

Abstract

A super-convergent finite beam element is developed for the coupled flexural-lateral-torsional-warping static analysis of thin-walled beams with asymmetric open sections subjected to general loading. The present formulation is based on a generalized Timoshenko-Vlasov beam theory and fully captures the effects of shear deformation, the St. Venant and warping torsion as well as the coupling between bending and torsion due to the nonsymmetry of the cross-section. A family of exact shape functions is derived based on the closed form solution of the coupled equilibrium static equations. The exact shape functions developed are then employed to formulate the stiffness matrix and the energy equivalent load vector. The beam element developed has two-nodes and six degrees of freedom per node and is able to fully capture the flexural-torsional coupling. In order to demonstrate the exactness and efficiency of the element, comparisons are provided against other established finite element solutions under Abaqus. The element is shown to be free from discretization errors encountered under other interpolation schemes and yields results in excellent agreement with those based on other finite element solutions at a fraction of the computational and modeling cost.https://jer.ly/PDF/Vol-32-2021/JER-02-32-Abstract.php?f=a

MODELLING OF STRAIN HARDENING OF DUAL PHASE STEELS

2024-08-25T11:08:28+00:00

ABSTRACT

The strain hardening behaviors of dual phase steel with different volume fraction were studied using empirical models. The applicability of Log-method in describing the true stress-true plastic strain of dual phase steels was investigated. The tensile test data were analyzed by Hollomon equation and the results showed that the equation was not applicable for total plastic deformation stage.

The root-mean-square of residual percentage (RMSRP) was calculated for the curves obtained by regression formulae. The values of the Log-method parameters obtained by regression formulae were in good agreement with the experimental data.

It was found that increasing the volume fraction of martensite has a noticeable effect on the value of true strain at necking instability , when Log-method model is used. On the other hand, by using Hollomon model, the value of true strain at necking instability was moderately increased by increasing the volume fraction of martensite. https://jer.ly/PDF/Vol-32-2021/JER-03-32-Abstract.php?f=a

CFD-MODELLING AND THERMAL CHARACTERIZATION OF FRICTION STIR WELDING USING TOOL WITH POLYGONAL PINS

2024-08-25T11:25:46+00:00

ABSTRACT

In the last two decades, Friction Stir Welding (FSW) has shown a capability to produce high strength joints particularly for the materials that cannot be welded by the conventional welding processes. Hence, optimizing the FSW process parameters to improve the quality of welded joint is still a subject of active research. In view of that, the efficient control of the welding thermal cycle through the geometrical and operational parameters may lead to produce sound weldments where defects can be avoided. Various studies have been carried out considering different tool pin profiles to improve the mechanical strength of welded joint, but the influences of the polygonal pin profiles on the thermal characterizations have been rarely reported in details. Besides, the experimental work has often showed that it is cost and time consuming particularly when the effect of geometrical variables is investigated. The present work focuses on the integral employment of analytical approaches and Computational Fluid Dynamics (CFD) tool to simulate the heat generation and the thermal field associated to the FSW when using tool with polygonal pins. A three-dimensional CFD model considering both dynamic mesh and sliding mesh techniques has been used to investigate the effect of a wide range of geometrical and operational parameters on the temperature distribution and peak temperature within thick FS welded workpieces. A set of novel analytical formulas have been developed to calculate the amount of heat generation corresponding to the pin shape. The improved numerical model has captured the temporal and spatial temperature distribution throughout the weldments and succeeded to monitor the liquid fraction when the material temperature exceeding the solidus temperature. Moreover, the acquired numerical results have then been used to develop a novel semi-empirical prediction model for the peak temperature. https://jer.ly/PDF/Vol-32-2021/JER-04-32-Abstract.php?f=a

Study the Effect of the Use of Treated and Untreated Recycled Aggregates on Concrete Properties

2024-08-25T11:32:56+00:00

ABSTRACT

The recycling of concrete rubble can contribute in reducing the total environmental impact of the building sector. In this research, recycled coarse aggregate (RCA) obtained from destroyed buildings in Libya were used to produce a new concrete by replacing Natural aggregate (NA) by (RCA) in the concrete. The percentage of the replacement was (30%, 50%, 70%, 100%).

This study was conducted in two phases, the first phase was conducted without making any treatment for recycled coarse aggregate for producing a concrete. The second phase was treated by soaking recycled coarse aggregate in hydrochloric acid after dilution as an attempt to clean and remove the mortar attached to the aggregate surface (RCAT). The results obtained indicate that the workability, compressive strength and tensile strength of concrete decreases as the percentage of (RCA) in the mixture increases. A gradual improvement in results has been observed when using (RCAT). However, the results encourage using up to 50% of the recycled aggregate (RCA) and up to 70% of the aggregate soaked in hydrochloric acid for producing environmentally friendly concrete (Green concrete) in order to fulfill good concrete specifications.