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  • Author or Editor: Károly Jármai x
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Efficient algorithms are needed for optimization of objects and systems, because the user would like to be sure that the optimum is global. The paper shows a very well scalable discrete firefly algorithm, developed for solving a supplier selection problem. The built in general reduced gradient and evolutionary algorithms of the Excel solver are also compared solving this problem. The results show that the firefly algorithm solves the problem in the fragment of the running time of the evolutionary algorithm. In the second part of the article, a mathematical model was formulated to solve the fixed destination multidepot multiple tour multiple traveling salesmen problem (mdmMTSP).

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Abstract

Stability is one of the most critical problems in the design of welded metal structures, since in many cases instability causes failure or collapse of the structures. The present study aims to show the minimum mass design procedure for welded steel box columns loaded by a compression force. The normal stresses and overall stability are calculated for pinned columns. The dimensions of the box columns are optimized by using constraints on global stability, local buckling of webs and flanges. Different design rules and standards are compared: Eurocode 3, Japan Railroad Association, American Petroleum Institute, and American Institute of Steel Construction. The calculations are made for different loadings, column length and steel grades. The yield stress varies between 235 and 690 MPa. Optimization is carried out using the generalized reduced gradient method in Excel solver. Cost calculations and comparisons show the most economical structure.

Open access

Abstract

A welded steel protective cover used for the heat treatment of steel sheet coils is investigated. The protective cover is made of austenitic stainless steel and consists of three main segments, welded together, which have 1400 mm height each. The plate thicknesses at the lower, middle and upper segments are different. The investigation aimed to improve the lifetime and the number of heat cycles of the protective cover by changing the geometry, the effect of the thicknesses and the material. Damaged covers have been evaluated, made calculations of stress and deformations, and carried out a series of finite element simulations. Both horizontal and vertical corrugated sheets were simulated and compared. The non-corrugated plates were also investigated, but their performance was behind the corrugated ones. The original geometry and that of the horizontal corrugated plate are identical from the stress level point of view. The vertical position of the corrugated plate provided a better result than the horizontal one. The calculated and simulated results for the original geometry are close to the measured damage.

Open access

Abstract

The aim of the paper is to fulfill the parametric analysis on the heating performance of a compact automotive radiator using computational fluid dynamics. The analysis has been carried out at different air velocities with different fins modeling as real fins and as porous media. SC-Tetra computational fluid dynamics software was used for this study. The fluids are incompressible; the flow was three-dimensional and turbulent. The geometry of the fins has a high impact to the heat transfer coefficient and the heat performance, so the shape, the size and the thickness of the fins are compared to each other. The results show that the ratio of the fin pitch, the wall thickness of the fins, the number of the fins, the flow depth and the geometry of the tube are the main factors of the heat transfer. The main goal is to find a dependable Nu-number correlation for this type of heat exchanger. Furthermore with the usage of this function the goal is to find the optimal shape of the radiator, which can decrease the temperature of the cooling liquid to the necessary value and has the smallest weight.

Open access

Abstract

In this paper a detailed description of a method is presented to estimate the minimum structural dimensions of the robot arms. A comparative study is conducted between the harmony search and artificial bee colony algorithms in this scientific application. The comparison process was done through the kinematic equations of the serial robot manipulator to find the optimum lengths of links of the robot. A novel design for a seven-degrees-of-freedom robot arm was presented to conduct the comparative study on the presented optimization algorithms. This novel robot mimics the functionality of the SANDVIK robot arm for tunnelling works, but the presented type synthesis was designed to overcome the restrictions on the original SANDVIK arm.

Open access