¹ Department of Mechanical Engineering,
Vilnius Gediminas Technical University,
Basanavičiaus str. 28, 03224, Vilnius, Lithuania,
audrius.cereska@vgtu.lt
² Department of Mathematical Statistics,
Vilnius Gediminas Technical University,
Saulėtekio al. 11, 10223, Vilnius, Lithuania,
valentinas.podvezko@vgtu.lt

Abstract: The paper presents multi-criteria analysis of operating characteristics of rotor systems with tilting pad bearings. Special stand with measuring equipment was used for experimental researches. Three types of bearings were tested while changing the speed of rotor rotation and the clearance between the rotor and the bearing pad. Results of 27 measurements have been processed using multi-criteria analysis. Three methods have been used for estimating criteria weights: entropy and new methods CILOS (Criterion Impact LOS) and Objective criteria of weight determination IDOCRIW integrated (Integrated Determination of Objective Criteria Weights). For the selection of priority several well-known and widely used MCDM methods such as COPRAS, SAW and TOPSIS have been used.

Keywords: rotor system, bearing, characteristics, MCDM, objective weight, entropy method, CILOS method, IDOCRIW method.

>>Full text<<
CITE THIS PAPER AS: Audrius ČEREŠKA, Valentinas PODVEZKO, Edmundas Kazimieras ZAVADSKAS, Operating Characteristics Analysis of Rotor Systems Using MCDM Methods, Studies in Informatics and Control, ISSN 1220-1766, vol. 25(1), pp. 59-68, 2016. https://doi.org/10.24846/v25i1y201607

1. Introduction

Hydrodynamic bearings are one of the most important components in rotary systems. They are used in various technological machines, turbo generators, turbo compressors, steam turbines, pumps, grinding machine spindles, generators, gas turbines, fans, propulsion machinery, and a number of other mechanisms, but it is designed to significantly less work for systems with hydrodynamic bearings diagnosis methods and analysis than for systems with rolling bearings [1, 2, 3].

When the temperature of the bearing in the operating zone has reached critical values [4], the oil viscosity and the clearance between the rotor and the bearing segment are decreased. Then bearing is operating in a semi-fluid lubrication mode. As a result, operating time of rotor systems is shortened and it can cause failures. Such phenomena could disturb the work process and cause large losses.

Dynamic parameters of the system “rotor – oil – bearing” and parameters of the oil taken together define the stability of the rotor system, expressed by the speed of rotor rotation.

When this rate of rotation of the rotor system is reached and exceeded, occur automatic transverse rotor vibrations, caused by turbulence in the oil bearing clearances [5, 6, 7]. Stability may be achieved through the design of a hydrodynamic bearing using dampening elements [8, 9].

In order to increase stiffness of the hydrodynamic bearing and stability of rotor rotation in a wider rotation frequencies range, together with the sliding sleeve bearings were designed bearings with various structural features: sleeve, sleeve with the ring, elliptical, tilting pad, etc., etc. [10, 11]. Hydrodynamic bearings with tilting pad demonstrated good performance on adaptation options, but in order to improve rotational stability of the rotor a variety of bearing structures with additional segments spanning elastic elements have been used. These elements are regulating distribution of the loads between pad. This ensures a uniform thickness of oil hydrodynamic film as well as increased stability of the rotor rotation. It also increases the stiffness of the rotor system.

Having information about the performance characteristics of the rotor system one can determine the current status of the system and to choose the most optimal variant during design process. For latter a MCDM (Multiple Criteria Decision Making) techniques can be applied, which are successfully utilized for the optimization of technical solutions in laser technologies [12] and other technical solutions [13, 14, 15].

MCDM methods are based on decisions matrix R = ‖r_ij‖, criterion statistics (experimental criterion values) and criteria weights (weights) vector Ω = (ω_i), where i = 1, 2, …, n; j = 1, 2, …, m – the number of criteria; n – compared the number of options [16].

For the comparison of 27 variants customized MCDM (Multiple Criteria Decision Making) methods were utilized: COPRAS (Complex Proportional Assessment) [17, 18], SAW (Simple Additive Weighting) [18-21], TOPSIS (The Technique for Order of Preference by Similarity to Ideal Solution) [19 – 21].

Subjective criteria weighting methods have been used the most in practice [19, 22-27].

Data structure can be evaluated and degree of dominance (or objective weights of criteria) of each criteria can be estimated. Objective weights compared with subjective are applied in practice much less frequently [19, 28]. Combination weighting is based on the integration of subjective weighting and weighting objective [29-32].

Doing analysis of operating performance of rotor systems it is not possible to value the importance of the criteria for significance quantitatively, that is to estimate subjective weights of criteria. Therefore there are used effective setting methods of criteria weights in this work: entropy, criterion impact loss CILOS (Criterion Impact LOS) and aggregate objective weights IDOCRIW (Integrated Determination of Objective Criteria Weights).

REFERENCES

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