Performance evaluation of a twin-shaft gas turbine engine in mechanical drive service

Mohammadreza Tahan,Masdi Muhammad,Z. A. Abdul Karim 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.2

This study aimed at quantifying the effect of mechanical load on the performance of an 18.7 MW offshore gas turbine engine. The targeted engine is of two-shaft free power turbine configuration that operates as a mechanical driver for a process compressor in the gas compression service. The study is a part of a comprehensive performance health monitoring program to address the diagnostic and prognostic requirements in oil and gas offshore platforms and is motivated by the need to provide in-depth knowledge of the gas turbine engine performance. In this work, only the context of some design point key performance parameters and a limited set of collected operational data from the gas turbine in the real plant are available. Therefore, three major tasks, namely design point calculation, characteristic map tuning and off-design performance adaption, were needed to be performed. In order to check the validity of the proposed model, the obtained simulation results were compared with the operational data. The results indicate the maximum inaccuracy of the proposed model is 3.04 %. Finally, by employing the developed model, the engine capability for power generation when exposed to various load speeds is investigated. The obtained result demonstrates at the maximum gas generator speed, every 3 % decrease in mechanical speed leads to 1 % decline in the gas turbine power output. Moreover, when the gas turbine operates under design power load and mechanical speed is lower than 80 % of design speed, every 1 % decrease in load speed results in 0.2 % loss in thermal efficiency. The established relationship will assist proper assessment of mechanical drive gas turbines for performance health monitoring.

On Corsini hypergroups and their productional hypergroups

M. Al Tahan,B. Davvaz 강원경기수학회 2019 한국수학논문집 Vol.27 No.1

In this paper, we consider a special hypergroup defined by Corsini and we name it Corsini hypergroup. First, we investigate some of its properties and find a necessary and sufficient condition for the productional hypergroup of Corsini hypergroups to be a Corsini hypergroup. Next, we study its regular relations, fundamental group and complete parts. Finally, we characterize all Corsini hypergroups of orders two and three up to isomorphism.

On Isomorphism Theorems and Chinese Remainder Theorem in Hypernear Rings

M. Al Tahan,B. Davvaz 한국수학교육학회 2023 純粹 및 應用數學 Vol.30 No.4

The purpose of this paper is to consider the abstract theory of hypernear rings. In this regard, we derive the isomorphism theorems for hypernear rings as well as Chinese Remainder theorem. Our results can be considered as a generalization for the cases of Krasner hyperrings, near rings, and rings.

Uncertainty in Operational Modal Analysis of Hydraulic Turbine Components

Gagnon, Martin,Tahan, S.-Antoine,Coutu, Andre Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.4

Operational modal analysis (OMA) allows modal parameters, such as natural frequencies and damping, to be estimated solely from data collected during operation. However, a main shortcoming of these methods resides in the evaluation of the accuracy of the results. This paper will explore the uncertainty and possible variations in the estimates of modal parameters for different operating conditions. Two algorithms based on the Least Square Complex Exponential (LSCE) method will be used to estimate the modal parameters. The uncertainties will be calculated using a Monte-Carlo approach with the hypothesis of constant modal parameters at a given operating condition. In collaboration with Andritz-Hydro Ltd, data collected on two different stay vanes from an Andritz-Hydro Ltd Francis turbine will be used. This paper will present an overview of the procedure and the results obtained.

Spectral SFEM analysis of structures with stochastic parameters under stochastic excitation

Galal, O.H.,El-Tahan, W.,El-Tawil, M.A.,Mahmoud, A.A. Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.28 No.3

In this paper, linear elastic isotropic structures under the effects of both stochastic operators and stochastic excitations are studied. The analysis utilizes the spectral stochastic finite elements (SSFEM) with its two main expansions namely; Neumann and Homogeneous Chaos expansions. The random excitation and the random operator fields are assumed to be second order stochastic processes. The formulations are obtained for the system solution of the two dimensional problems of plane strain and plate bending structures under stochastic loading and relevant rigidity using the previously mentioned expansions. Two finite element programs were developed to incorporate such formulations. Two illustrative examples are introduced: the first is a reinforced concrete culvert with stochastic rigidity subjected to a stochastic load where the culvert is modeled as plane strain problem. The second example is a simply supported square reinforced concrete slab subjected to out of plane loading in which the slab flexural rigidity and the applied load are considered stochastic. In each of the two examples, the first two statistical moments of displacement are evaluated using both expansions. The probability density function of the structure response of each problem is obtained using Homogeneous Chaos expansion.

Solution of randomly excited stochastic differential equations with stochastic operator using spectral stochastic finite element method (SSFEM)

Hussein A.,El-Tawil M.,El-Tahan W.,Mahmoud, A. A. 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.28 No.2

This paper considers the solution of the stochastic differential equations (SDEs) with random operator and/or random excitation using the spectral SFEM. The random system parameters (involved in the operator) and the random excitations are modeled as second order stochastic processes defined only by their means and covariance functions. All random fields dealt with in this paper are continuous and do not have known explicit forms dependent on the spatial dimension. This fact makes the usage of the finite element (FE) analysis be difficult. Relying on the spectral properties of the covariance function, the Karhunen-Loeve expansion is used to represent these processes to overcome this difficulty. Then, a spectral approximation for the stochastic response (solution) of the SDE is obtained based on the implementation of the concept of generalized inverse defined by the Neumann expansion. This leads to an explicit expression for the solution process as a multivariate polynomial functional of a set of uncorrelated random variables that enables us to compute the statistical moments of the solution vector. To check the validity of this method, two applications are introduced which are, randomly loaded simply supported reinforced concrete beam and reinforced concrete cantilever beam with random bending rigidity. Finally, a more general application, randomly loaded simply supported reinforced concrete beam with random bending rigidity, is presented to illustrate the method.

Spectral SFEM analysis of structures with stochastic parameters under stochastic excitation

O.H. Galal,W. El-Tahan,M.A. El-Tawil,A.A. Mahmoud 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.28 No.3

In this paper, linear elastic isotropic structures under the effects of both stochastic operators and stochastic excitations are studied. The analysis utilizes the spectral stochastic finite elements (SSFEM) with its two main expansions namely; Neumann and Homogeneous Chaos expansions. The random excitation and the random operator fields are assumed to be second order stochastic processes. The formulations are obtained for the system solution of the two dimensional problems of plane strain and plate bending structures under stochastic loading and relevant rigidity using the previously mentioned expansions. Two finite element programs were developed to incorporate such formulations. Two illustrative examples are introduced: the first is a reinforced concrete culvert with stochastic rigidity subjected to a stochastic load where the culvert is modeled as plane strain problem. The second example is a simply supported square reinforced concrete slab subjected to out of plane loading in which the slab flexural rigidity and the applied load are considered stochastic. In each of the two examples, the first two statistical moments of displacement are evaluated using both expansions. The probability density function of the structure response of each problem is obtained using Homogeneous Chaos expansion.

On Picture Fuzzy Ideals of Near-Rings

Mani Parimala,Intan Muchtadi-Alamsyah,Madeleine Al-Tahan 한국지능시스템학회 2021 INTERNATIONAL JOURNAL of FUZZY LOGIC and INTELLIGE Vol.21 No.3

In managing vagueness and complexity, the theory of picture fuzzy sets has important advantages. In addition, picture fuzzy data are useful for modeling the uncertain existence of subjective decisions and for more flexibly assessing the fuzziness and imprecision. The goal of this study is to establish and discuss their desirable properties by defining the picture fuzzy ideals of a near-ring. Based on new definitions, this paper presents some examples and properties of picture fuzzy subsets of such rings.

Creep damage and life assessment of thick cylindrical pressure vessels with variable thickness made of 304L austenitic stainless steel

Mosayeb Davoudi Kashkoli,Khosro Naderan Tahan,Mohammad Zamani Nejad 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.6

Using firstfirst-order shear deformation theory (FSDT), a semi semi-analytical solution is employed to analyze creep damage and remaining life assessment of 304L austenitic stainless steel thick (304L ASS) cylindrical pressure vessels with variable thickness subjected to the temperature gradient and internal non non-uniform pressure. Damages are obtained in thick cylinder using RobinsonRobinson’s linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson Larson-Miller Parameter (LMP). The thermo-elastic creep response of the material is described by Norton Norton’s law. The novelty of the present work is that it seeks to investigate creep damage and life assessment of the vessels with variable thickness made of 304L ASS using LMP based on first first-order shear deformation theory. A numerical solution using finite element method (FEM) is also presented and good agreement is found. It is shown that temperature gradient and non non-uniform pressure have significant influences on the creep damages and remaining li fe of the vessel vessel.

Evaluation of Machined Part Surface Roughness using Image Texture Gradient Factor

Rene Kamguem,Victor Songmene,Souheil Antoine Tahan 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.

In mechanical manufacturing, the state of a machined part surface is very crucial, particularly in aeronautics, and as a result, great care must be exercised in its measurement. Over the past few years, many research studies have been carried out to mitigate the disadvantages (contact, off-line inspection, speed of limited measurement) inherent in the classic measurement of the roughness by contact with a stylus. The contribution of this paper is to demonstrate the feasibility of the contactless inspection of part surface roughness using an optical microscope. Unlike most works in the domain that use image average of grey level and the average cycle of the texture, a new image characteristic named the gradient factor of the image is defined and used to estimate the part roughness parameters. The effect of the vision system parameters on image quality is investigated then the statistical characteristics of the images best describing the machined surface are determined and used to estimate the roughness parameters. The study shows that several roughness parameters (Ra, Rq, Rv, Rt and Rz) can be estimated using only image-extracted features and models, without the need to know the machining parameters used to generate the surface. The results obtained with the vision system are comparable to those obtained with a stylus contact surface roughness measurement system, and could help in the online monitoring of the surface roughness.