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Karlovac, Croatia

Jokic M.,University of Zagreb | Stegic M.,University of Zagreb | Butkovic M.,Polytechnic of Karlovac
Journal of Sound and Vibration | Year: 2011

This paper presents a novel technique for multiple tuned mass damper optimization based on the dissipativity inequalities for a class of descriptor systems. Under the assumptions of regularity, asymptotic stability and index one property of the descriptor system representing the structure with tuned mass dampers, optimization criterion is defined in terms of H∞ norm of the system. In doing so, special structure of the system matrices is utilized to eliminate some of the optimization variables. To overcome its high computational cost and make it applicable for optimization of large-scale structures, a novel reduced-order optimization algorithm is proposed. Unlike the existing approaches, the presented optimization framework does not impose restrictions regarding regularity and constantness of the mass matrix, and consequently allows simultaneous optimization of mass, damping and stiffness matrices. Numerical examples which clearly illustrate the applicability and effectiveness of the proposed optimization procedure, as well as the comparison with other methods, are presented. © 2011 Elsevier Ltd. Source

Pomenic L.,University of Rijeka | Jurac Z.,Polytechnic of Karlovac
Archives of Materials Science and Engineering | Year: 2013

Purpose: The aim of this article is to present problems in the production of energy from the renewable resources as is a biodiesel production. The use of human foods that are pure edible oils for biodiesel production is big ethical problem. This problem can be reduced with use of waste cooking oils for the biodiesel production. Besides this use of the waste cooking oils will reduce the raw material cost and also reduce the environment pollution that is a global problem. Design/methodology/approach: This article includes analysis and estimation of the methyl esters impact to the kinematic viscosity of biodiesels produced from various percentages of waste cooking oils and crude rapeseed oil blends. One of the most important physical properties of biodiesel that affect its use value is kinematic viscosity properties which are directly dependent on the composition of raw materials. After the transesterification process mono-alkyl esters (biodiesel), glycerol (main co-product), alcohol, catalyst, free fatty acids, residual glycerides compose the final mixture of biodiesel production process. Some important issues on the biodiesel quality control involve the monitoring of transesterification process with the quantification of mono-alkyl esters. Findings: With an increase of methyl esters content the kinematic viscosity of produced biodiesels decreases for both waste cooking oils WCO1 and WCO2, used for biodiesel production in various blends with crude rapeseed oil. Practical implications: The results presented in the paper can be applied in the industry for estimation and selection of the optimal percentages of waste cooking oils and crude rapeseed oil blends for the biodiesel production. Originality/value: This paper presents research of the influence of methyl esters on kinematic viscosity of biodiesels produced from the various blends of waste cooking oils and crude rapeseed oil. The further testing and improvements in waste oils purification and in transesterification process can lead to the better yield in biodiesel production. © International OCSCO World Press. All rights reserved. 2013. Source

In the production of biodiesel the need for using more inexpensive and alternative raw materials arises. This is due to the limited amount of traditional raw materials in the market and their high prices. Very convenient alternative raw material which is also cost effective is used frying oil (UFO). The quality of the final product greatly depends on the quality of raw materials. By using only used frying oil (UFO) as raw material it is not always possible to obtain a good quality product. Therefore, it is necessary to make a mixture of raw materials to obtain a high quality product and at the same time to minimize the costs. The purpose of this paper is to investigate the impact of various raw material mixtures of rapeseed and used frying oil on the most important physico-chemical characteristics of biodiesel, viscosity and cold flow properties. It is shown that portion of UFO in raw material mixtures does not have significant impact on viscosity of final product, but only cold flow properties. We discovered linear correlations between cold flow properties of product formed from mixtures of raw materials, and cold flow properties of the product formed from pure raw materials. Cold flow properties of raw materials and cold flow properties of products are also in linear correlation. CFPP of the final product from the raw material mixture is equal to the sum of the product of portion of particular raw materials in the mixture and CFPP products from the same raw material. These findings can be implemented in determining optimal raw material mixture. We made a short overview of one such model, which is also included in this work. © 2012 Elsevier B.V. Source

Kovacevic S.,University of Zagreb | Vucinic J.,Polytechnic of Karlovac | Kirin S.,Polytechnic of Karlovac | Pejnovic N.,Croatian Institute for Health Protection and Safety at Work
Periodicum Biologorum | Year: 2010

Basic properties of vehicle interior are described. Car seat design, upholstery fabrics and passenger safety have been particularly emphasized. Textile fabrics as products providing comfort, safety and esthetics of the vehicle interior were dealt with. Safety belts, airbags and car seat covers were specially pointed out. Specific problems related to the safety of passengers, whose anthropometric measurements deviate from the average ones, were addressed. Source

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