Sensitivity analysis of torsional vibration characteristics of helicopter rotor blades. Part 1: Structural dynamics analysis

A theoretical investigation of structural vibration characteristics of rotor blades was carried out. Coupled equations of motion for flapwise bending and torsion were formulated for rotor blades with noncollinear elastic and mass axes. The finite element method was applied for a detailed representation of blade structural properties. Coupled structural mass and stiffness coefficients were evaluated. The range of validity of a set of coupled equations of motion linearized with respect to eccentricity between elastic and mass axes was investigated. The sensitivity of blade vibration characteristics to torsion were evaluated by varying blade geometric properties, boundary conditions, and eccentricities between mass and elastic axes

Sensitivity analysis of torsional vibration characteristics of helicopter rotor blades. Part 2: Aerodynamics and sensitivity analysis

A theoretical investigation of dynamic response characteristics of rotor blades was carried out with special emphasis on torsional degrees-of-freedom. Coupled equations of motion for flapwise bending and torsion were formulated at varying azimuth positions for rotor blades with noncollinear aerodynamic, elastic and mass axes. Both structural and aerodynamic mass, damping and stiffness coefficients were included. The variations of a sample blade at different flight conditions were investigated from these equations. The obtained numerical results were illustrated. The sensitivity of overall blade vibration characteristics to torsional oscillations was also investigated from the equations of motion for the sample blade. The illustrated results show the importance of torsional degrees-of-freedom in rotor blade analysis. Various possibilities of improving the overall response by tuning blade geometric, structural and aerodynamic characteristics are discussed

Multimarket Contact in Vertically Related Markets

We analyze collusion in two comparable market structures. In the first market structure only one firm is vertically integrated; there is one more independent firm in the upstream industry and another independent firm in the downstream industry. In the second market structure, there are only two vertically integrated firms that can trade among themselves in the intermediate good market. The second market structure mimics markets like the California gasoline market where firms vertically integrated through refinery, and retail markets. We rank these two market structures in terms of ease of collusion and show that while under some circumstances collusion is not possible in the market with one vertically integrated firm, collusion is possible in the market structure with two vertically integrated firms. We conclude that vertical (multimarket) contact facilitates collusion and vertical mergers suspected to lead to subsequent vertical mergers in an industry should receive higher antitrust scrutiny relative to single isolated vertical mergers.Multimarket; collusion; vertical integration; gasoline markets

Finite element analysis of transonic flows in cascades: Importance of computational grids in improving accuracy and convergence

The finite element method is applied for the solution of transonic potential flows through a cascade of airfoils. Convergence characteristics of the solution scheme are discussed. Accuracy of the numerical solutions is investigated for various flow regions in the transonic flow configuration. The design of an efficient finite element computational grid is discussed for improving accuracy and convergence

Numerical calculations of velocity and pressure distribution around oscillating airfoils

An analytical procedure based on the Navier-Stokes equations was developed for analyzing and representing properties of unsteady viscous flow around oscillating obstacles. A variational formulation of the vorticity transport equation was discretized in finite element form and integrated numerically. At each time step of the numerical integration, the velocity field around the obstacle was determined for the instantaneous vorticity distribution from the finite element solution of Poisson's equation. The time-dependent boundary conditions around the oscillating obstacle were introduced as external constraints, using the Lagrangian Multiplier Technique, at each time step of the numerical integration. The procedure was then applied for determining pressures around obstacles oscillating in unsteady flow. The obtained results for a cylinder and an airfoil were illustrated in the form of streamlines and vorticity and pressure distributions

A NEW APPROACH TOWARDS EVAULATION AND SELECT‹ON OF SALESPERSON CANDIDATES: FUZZYTOPSIS

The aim of the study is to introduce Fuzzy TOPSIS method and to show how to benefit it for evaluation of salesperson candidates. Foundation of Fuzzy TOPSIS method which is one of Multiple Criteria Decision Making (MCDM) methods and to allow group decision-making in fuzzy environment is calculation of the closeness coefficients by means of Fuzzy Positive Ideal Solution (FPIS) and Fuzzy Negative Ideal Solution (FNIS). According to the calculated closeness coefficients, alternatives are ranked. In the study, salesperson candidates were assessed in accordance with seven decision criteria by three decision makers (DM’s). Decision makers have done their assessments with linguistic variables then these variables transformed to positive trapezoidal fuzzy numbers. The study shows that Fuzzy TOPSIS method is very well suited method, as a decision tool, towards using for salesperson candidates evaluation and selection decisions.Fuzzy TOPSIS, Trapezoidal Fuzzy Numbers, Salesperson.

PRIORITIZING THE WEIGHTS OF THE EVALUATION CRITERIA UNDER FUZZINESS: THE FUZZY FULL CONSISTENCY METHOD – FUCOM-F

Values, opinions, perceptions, and experiences are the forces that drive almost each and every kind of decision-making. Evaluation criteria are considered as sources of information used to compare alternatives and, as a result, make selection easier. Seeing their direct effect on the solution, weighting methods that most accurately determine criteria weights are needed. Unfortunately, the crisp values are insufficient to model real life problems due to the lack of complete information and the vagueness arising from linguistic assessments of decision-makers. Therefore, this paper proposes a novel subjective weighting method called the Fuzzy Full Consistency Method (FUCOM-F) for determining weights as accurately as possible under fuzziness. The most prominent feature of the proposed method is obtaining the most accurate weight values with very few pairwise comparisons. Consequently, thanks to this model, consistency and reliability of the results increase while the processing time and effort decrease. Moreover, an illustrative example related to the green supplier evaluation problem is performed. Finally, the robustness and effectiveness of the proposed fuzzy model is demonstrated by comparing it with fuzzy best-worst method (F-BWM) and fuzzy AHP (F-AHP) models

Değişken En Kesitli Çubukların Karışık Sonlu Elemanlar Yöntemi İle Boyuna Titreşim Analizi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2015Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2015Titreşim problemlerini, titreşim hareketinin yönüne göre boyuna titreşim, enine titreşim ve burulma şeklinde birkaç başlık altında incelemek mümkündür. Bu çalışmada Gâteaux türevi ve fonksiyonel analiz ile farklı sınır koşullarına ve kesitlere sahip elastik çubuklara ait boyuna titreşim hareketi incelenmiştir. İlk olarak analiz sırasında kullanılacak olan temel denklemler elde edilmiş ve bu denklemler operatör formda yazılarak potansiyellik koşulunu sağladığı gösterilmiştir. Daha sonra Gâteaux türevi yöntemi ile çubukların boyuna titreşim hareketine ait ilgili fonksiyoneller elde edilmiştir. Bu fonksiyonellerde normal kuvvet ve boyuna yer değiştirme olmak üzere iki değişken bulunmaktadır. Probleme uygun doğrusal şekil fonksiyonları belirlenmiş ve bu şekil fonksiyonları mevcut fonksiyonellere uygulanarak her iki fonksiyonel için de eleman matrisleri ayrı ayrı elde edilmiştir. Elde edilen eleman matrisleri ile farklı sınır koşullarına sahip çubuklar üzerinde boyuna titreşim frekansları elde edilmiştir. Titreşim frekanslarının, hesaplanması için Fortran programlama dili kullanılarak bir kod yazılmıştır. Hazırlanan program ile elde edilen sonuçların karşılaştırılması için literatürde yer alan örnekler kullanılmıştır.The vibrations can be categorized as longitudinal, transverse and torsional according to their directions. In this work, using the Gâteaux derivative and functional analysis, the longitudinal vibrations of elastic bars which has various boundary conditions and cross sections were researched. Firstly, the essential equations which will be used in the analysis were obtained. Then they were written in operator forms and so it was shown that they fit the potency conditions. Subsequently the related functionals of longitudinal vibrations of bars were obtained using the Gâteaux derivative method. In these functionals there exist two variables as normal force and longitudinal displacement. The longitudinal shape functions suitable for the problem were determined. Through the application of these shape functions to the existing functionals the element matrices were separately obtained for both functionals. With these element matrices the longitudinal vibration frequencies on the bars, which have various boundary conditions, were obtained. The results were compared and verified with the results in the related literature

Applying grey relational analysis to Italian football clubs: A measurement of the financial performance of serie a teams

Extant literature on the financial analysis of football clubs has applied a vast array of techniques in determining the fiscal stability of such entities. Although many studies have provided useful comparisons and analyses of the states of various clubs, direct research comparing the financial performance among various clubs is still scant. Hence, we present an application of financial ratio analysis to the greater Italian football market within the Serie A. The main purpose of this study is to assess the financial performance of the top three Italian football clubs currently listed on the Borsa Italiana (Italian Stock Exchange), those being: Juventus F.C., A.S. Roma, and S.S. Lazio. In accomplishing this, we offer a comparative analysis of these clubs through the usage of grey relational analysis (GRA), an optimal performance technique derived from engineering. Overall, our results suggest that S.S. Lazio appears to be the most financially stable club among the sampled, publicly traded Serie A teams. In light of these findings, this study furthers the application of economic evaluation into larger segments of international football