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Article
Publication date: 4 September 2017

Marcin Figat

This paper aims to present the results of aerodynamic calculation of impact the main rotor on the fuselage and the tail of a light gyroplane. This kind of vehicle is a…

Abstract

Purpose

This paper aims to present the results of aerodynamic calculation of impact the main rotor on the fuselage and the tail of a light gyroplane. This kind of vehicle is a type of rotorcraft which uses a non-powered rotor in autorotation to develop lift and engine-powered propeller to provide the thrust. Both of them disturb the flow around the gyroplane body (gyroplane fuselage and tail) and influence on its static stability. The main goal of the presented research was to find the magnitude of this influence. To measure this effect, the main stability derivatives changes of gyroplane body were investigated.

Design/methodology/approach

The CFD analysis of the complete gyroplane was made. Computation was performed for the model of gyroplane which was equipped with the two sub-models of the main rotor and the engine-powered propeller. Both of them were modelled as the actuator discs. This method allows to compute the aerodynamic impact of rotating components on the gyroplane body. All aerodynamic analysis was made by the MGAERO software. The numerical code of the software bases on the Euler flow model. Next, the resulting aerodynamic coefficients were used to calculate the most important stability derivatives of the gyroplane body.

Findings

The result obtained by computation presents the change in the most important aerodynamic coefficients and stability derivatives of the gyroplane body caused by the impact of its main rotor. Moreover, the result includes the change of the aerodynamic coefficients and stability derivatives caused by change of the main rotor configuration (change of rotation rate and angle of incidence) and change of the flight condition (gyroplane angle of attack sideslip angle and flight speed).

Practical implications

Analysis of the main rotor impact will be very useful for evaluation of dynamic stability of the light gyroplane. Moreover, the results will be helpful to design the horizontal and vertical tail for the light gyroplane.

Originality/value

This paper presents the method of the numerical analysis of the static stability of the light gyroplane’s body. The results of analysis present the impact of disturbance generated by the rotating main rotor on the static stability of the gyroplane body. Moreover, the impact of the main rotor configuration change and the flight condition change on the static stability were investigated too. The evaluation of the gyroplane’s body static stability was made by the stability derivatives. The methodology and obtained result will be very useful for analysis of the dynamic stability of the light gyroplanes. Moreover, the results will be helpful during design the main components of the gyroplane like vertical and horizontal tail.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 5
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 1 March 2015

Jacob L. Petter, Jonathan D. Ritschel and Edward D. White

Delineating where stability occurs in a contract provides the window of opportunity for procurement officials to positively affect cost and schedule outcomes. While the…

Abstract

Delineating where stability occurs in a contract provides the window of opportunity for procurement officials to positively affect cost and schedule outcomes. While the concept of a Cost Performance Index (CPI) "stability rule" has been routinely cited by Earned Value Management (EVM) authors since the early 1990's, more recent research questions the veracity of this stability rule. This paper resolves the controversy by demonstrating that the definition of stability matters. We find a morphing of the stability definition over time, with three separate definitions permeating the literature. Next, an analysis of Department of Defense contracts for both cost and schedule stability properties finds that the veracity of the stability rule is intricately tied to the definition used.

Details

Journal of Public Procurement, vol. 15 no. 3
Type: Research Article
ISSN: 1535-0118

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Article
Publication date: 12 October 2010

Alireza Ahangar‐Asr, Asaad Faramarzi and Akbar A. Javadi

Analysis of stability of slopes has been the subject of many research works in the past decades. Prediction of stability of slopes is of great importance in many civil…

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1451

Abstract

Purpose

Analysis of stability of slopes has been the subject of many research works in the past decades. Prediction of stability of slopes is of great importance in many civil engineering structures including earth dams, retaining walls and trenches. There are several parameters that contribute to the stability of slopes. This paper aims to present a new approach, based on evolutionary polynomial regression (EPR), for analysis of stability of soil and rock slopes.

Design/methodology/approach

EPR is a data‐driven method based on evolutionary computing, aimed to search for polynomial structures representing a system. In this technique, a combination of the genetic algorithm and the least square method is used to find feasible structures and the appropriate constants for those structures.

Findings

EPR models are developed and validated using results from sets of field data on the stability status of soil and rock slopes. The developed models are used to predict the factor of safety of slopes against failure for conditions not used in the model building process. The results show that the proposed approach is very effective and robust in modelling the behaviour of slopes and provides a unified approach to analysis of slope stability problems. It is also shown that the models can predict various aspects of behaviour of slopes correctly.

Originality/value

In this paper a new evolutionary data mining approach is presented for the analysis of stability of soil and rock slopes. The new approach overcomes the shortcomings of the traditional and artificial neural network‐based methods presented in the literature for the analysis of slopes. EPR provides a viable tool to find a structured representation of the system, which allows the user to gain additional information on how the system performs.

Details

Engineering Computations, vol. 27 no. 7
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 1 June 1997

Jaroslav Mackerle

Gives a bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the…

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5240

Abstract

Gives a bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the theoretical as well as practical points of view. The range of applications of FEMs in this area is wide and cannot be presented in a single paper; therefore aims to give the reader an encyclopaedic view on the subject. The bibliography at the end of the paper contains 2,025 references to papers, conference proceedings and theses/dissertations dealing with the analysis of beams, columns, rods, bars, cables, discs, blades, shafts, membranes, plates and shells that were published in 1992‐1995.

Details

Engineering Computations, vol. 14 no. 4
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 1 February 1990

Krzysztof Wiśniewski and Robert L. Taylor

Numerical aspects of initial stability analysis of a cylindrical shell of non‐constant parameters along the generator and under non‐symmetrical loads are considered. A…

Abstract

Numerical aspects of initial stability analysis of a cylindrical shell of non‐constant parameters along the generator and under non‐symmetrical loads are considered. A variational approach based on Sanders' and Donnell's non‐linear equations of thin, elastic shells is applied. The problem is decomposed to determine: the stability vectors in the axial direction in the first step, and the critical load and the stability vector in the circumferential direction in the second step. The discretization is based on finite Fourier representations and the finite difference method. To find the approximate stability vector in the axial direction an auxiliary problem for axisymmetric loads is solved. The error of the method is defined and the effectiveness of the method is estimated. The decomposition leads to small and fast algorithms suitable for personal computers. Shells with constant and stepped thicknesses under wind loads are calculated as examples. Tested algorithms show considerable effectiveness and good accuracy of results.

Details

Engineering Computations, vol. 7 no. 2
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 10 January 2020

Hawraa Alateya and Alireza Ahangar Asr

This study is an attempt to estimate the influence of the presence of cavities on the stability of slopes in earth dams under rapid drawdown conditions. The purpose of…

Abstract

Purpose

This study is an attempt to estimate the influence of the presence of cavities on the stability of slopes in earth dams under rapid drawdown conditions. The purpose of this paper is to study the influence of different factors, such as the diameter and location of cavities, in addition to their existence effects.

Design/methodology/approach

A series of finite element simulation models were developed using PLAXIS 2D finite element software to analyse the stability of slopes in earth dams while considering various effects from cavities in the subsoil under rapid drawdown conditions.

Findings

The results indicated that the presence of cavities and an increase in the diameter of cavities decreased the stability of the upstream face dramatically for all examined locations in a horizontal direction; however, this effect was less on the downstream side. The results also showed that variations in the location of cavities in the horizontal direction have a greater effect on the stability than those in the vertical direction. The results revealed that increasing shear strength parameters of embankment does not reduce the influence of cavities on stability when those cavities are in critical locations.

Originality/value

A numerical model has been developed to simulate the effects of cavities on the stability of slopes in water-retaining structures/earth dams. The stability of earth dam slopes on upstream and downstream sides under rapid drawdown conditions considering various cavity effects, including their existence, diameter and location, were numerically analysed.

Details

Engineering Computations, vol. 37 no. 4
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 31 August 2021

Zbigniew Rarata

The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial…

Abstract

Purpose

The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability analyses.

Design/methodology/approach

Flow field calculations over smooth and wavy-surface NACA 0012 airfoils at 2° angle of attack and at Reynolds number of 200,000 are performed using the large eddy simulation (LES) approach. Three geometrical configurations are considered: a smooth NACA 0012 airfoil, wavy surface on the suction side (SS) and wavy surface on the pressure side (PS). The spatial stability analyses using the LES-generated flow fields are conducted and validated against the Orr-Sommerfeld stability analysis for the smooth airfoil configuration.

Findings

The spatial stability analyses show that inclusion of the wavy-type modification on the SS of the airfoil does not lead to altering of the acoustic feedback loop mechanism, with respect to the mechanism observed for the smooth airfoil configuration. In contrast, applying the surface modifications to the airfoil PS leads to a significant reduction of the amplification range of disturbances in the vicinity of the trailing edge for the frequency of the acoustic feedback loop mechanism.

Practical implications

The spatial analyses using, for example, LES-generated flow fields can be widely used to determine acoustic sources and associated distributions of amplifications for a wide range of applications in the aeroacoustics.

Originality/value

The spatial stability analysis approach based on flow fields computed a priori using the LES method has been introduced, validated and used to determine behaviour of the acoustic feedback loop when accurate reconstruction of geometry effects is required.

Details

Aircraft Engineering and Aerospace Technology, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 2 March 2015

Zhanhong Wan, Saihua Huang, Zhilin Sun and Zhenjiang You

The present work is devoted to the numerical study of the stability of shallow jet. The effects of important parameters on the stability behavior for large scale shallow…

Abstract

Purpose

The present work is devoted to the numerical study of the stability of shallow jet. The effects of important parameters on the stability behavior for large scale shallow jets are considered and investigated. Connections between the stability theory and observed features reported in the literature are emphasized. The paper aims to discuss these issues.

Design/methodology/approach

A linear stability analysis of shallow jet incorporating the effects of bottom topography, bed friction and viscosity has been carried out by using the shallow water stability equation derived from the depth averaged shallow water equations in conjunction with both Chézy and Manning resistance formulae. Effects of the following main factors on the stability of shallow water jets are examined: Rossby number, bottom friction number, Reynolds number, topographic parameters, base velocity profile and resistance model. Special attention has been paid to the Coriolis effects on the jet stability by limiting the rotation number in the range of Ro∈[0, 1.0].

Findings

It is found that the Rossby number may either amplify or attenuate the growth of the flow instability depending on the values of the topographic parameters. There is a regime where the near cancellation of Coriolis effects due to other relevant parameters influences is responsible for enhancement of stability. The instability can be suppressed by the bottom friction when the bottom friction number is large enough. The amplification rate may become sensitive to the relatively small Reynolds number. The stability region using the Manning formula is larger than that using the Chézy formula. The combination of these effects may stabilize or destabilize the shallow jet flow. These results of the stability analysis are compared with those from the literature.

Originality/value

Results of linear stability analysis on shallow jets along roughness bottom bed are presented. Different from the previous studies, this paper includes the effects of bottom topography, Rossby number, Reynolds number, resistance formula and bed friction. It is found that the influence of Reynolds number on the stability of the jet is notable for relative small value. Therefore, it is important to experimental investigators that the viscosity should be considered with comparison to the results from inviscid assumption. In contrast with the classical analysis, the use of multi-parameters of the base velocity and topographic profile gives an extension to the jet stability analysis. To characterize the large scale motion, besides the bottom friction as proposed in the related literature, the Reynolds number Re, Rossby number Ro, the topographic parameters and parameters controlling base velocity profile may also be important to the stability analysis of shallow jet flows.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 29 October 2019

Homa Hajibaba, Bettina Grün and Sara Dolnicar

Data-driven market segmentation is heavily used by academic tourism and hospitality researchers to create knowledge and by data analysts in tourism industry to generate…

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1043

Abstract

Purpose

Data-driven market segmentation is heavily used by academic tourism and hospitality researchers to create knowledge and by data analysts in tourism industry to generate market insights. The stability of market segmentation solutions across repeated calculations is a key quality indicator of a segmentation solution. Yet, stability is typically ignored, risking that the segmentation solution arrived at is random. This study aims to offer an overview of market segmentation analysis and propose a new procedure to increase the stability of market segmentation solutions derived from binary data.

Design/methodology/approach

The authors propose a new method – based on two independently proposed algorithms – to increase the stability of market segmentation solutions. They demonstrate the superior performance of the new method using empirical data.

Findings

The proposed approach uses k-means as base algorithm and combines the variable selection method proposed by Brusco (2004) with the global stability analysis introduced by Dolnicar and Leisch (2010). This new approach increases the stability of segmentation solutions by simultaneously selecting variables and numbers of segments.

Practical implications

The new approach can be adopted immediately by academic researchers and industry data analysts alike to improve the quality of market segmentation solutions derived from empirical tourist data. Higher quality market segmentation solutions translate into competitive advantage and increased business or destination performance.

Originality/value

The proposed approach is newly developed in this study. It helps industry data analysts and academic researchers to reduce the risk of deriving random segmentation solutions by analyzing the data in a systematic way, then selecting the most stable solution using the segmentation variables contributing to this most stable solution only.

Details

International Journal of Contemporary Hospitality Management, vol. 32 no. 4
Type: Research Article
ISSN: 0959-6119

Keywords

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Article
Publication date: 1 February 1988

Carlos A. Felippa and Thomas L. Geers

Partitioned analysis is a method by which sets of time‐dependent ordinary differential equations for coupled systems may be numerically integrated in tandem, thereby…

Abstract

Partitioned analysis is a method by which sets of time‐dependent ordinary differential equations for coupled systems may be numerically integrated in tandem, thereby avoiding brute‐force simultaneous solution. The coupled systems addressed pertain to fluid—structure, fluid—soil, soil—structure, or even structure—structure interaction. The paper describes the partitioning process for certain discrete‐element equations of motion, as well as the associated computer implementation. It then delineates the procedure for designing a partitioned analysis method in a given application. Finally, examples are presented to illustrate the concepts. It is seen that a key element in the implementation of partitioned analysis is the use of integrated, as opposed to monolithic software.

Details

Engineering Computations, vol. 5 no. 2
Type: Research Article
ISSN: 0264-4401

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