Emerald | Engineering Computations | Table of Contents

Micropolar Fluid Improve Dynamic Response of Gear Pair System Supported by Journal Bearings

literatinetwork@emeraldinsight.com (Cai-Wan Chang-Jian) — Fri, 12 Jul 2013 00:00:00 +0100

Abstract

Purpose - The results presented in this study provide some useful insights into the design and development of a gear-bearing system for rotating machinery that operates in highly rotational speed and highly nonlinear regimes.Design/methodology/approach - The non-dimensional equation of the gear-bearing system is then solved using the Runge-Kutta method. The non-periodic behavior of this system is characterized using phase diagrams, power spectra, Poincaré maps, bifurcation diagrams, Lyapunov exponents and the fractal dimension of the system.Findings - The onset of chaotic motion is identified from the phase diagrams, power spectra, Poincaré maps, Lyapunov exponents and fractal dimension of the gear-bearing system. The numerical results reveal that the system exhibits a diverse range of periodic, sub-harmonic, quasi-periodic and chaotic behaviors. The micropolar fluid would be a useful lubricating fluid to suppress nonlinear dynamic responses and improve the dynamic regularity of the systems.Originality/value - The current study performs a nonlinear analysis of the dynamic behavior of a gear pair system equipped with journal bearings lubricated with micropolar fluid under nonlinear suspension. The results presented in this study provide some useful insights into the design and development of a gear-bearing system for rotating machinery that operates in highly rotational speed and highly nonlinear regimes.

Fracture simulation for zirconia toughened alumina microstructure

Fri, 12 Jul 2013 00:00:00 +0100

Abstract

Purpose - This paper describes finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures.Design/methodology/approach - A two-dimensional finite element model is developed with an actual Al2O3-10 vol% ZrO2 microstructure. A bilinear, time-independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro-void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models.Findings - Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro-void brings about the increase of crack density rate.Originality/value - This proposed finite element method allows describing fracture and fatigue behaviours of alumina-zirconia microstructures for hip prosthesis provided that a microstructure image is available.

Vague Reliability Assessment of Combustion System using Petri Nets and Vague Lambda-Tau Methodology

literatinetwork@emeraldinsight.com (Manjit Verma, Amit Kumar, Yaduvir Singh) — Fri, 12 Jul 2013 00:00:00 +0100

Abstract

Purpose - A new methodology named as vague lambda-tau, is proposed for reliability analysis of the repairable systemsDesign/methodology/approach - This paper involves the qualitative and quantitative analysis of combustion system. In qualitative analysis, the Petri net model is obtained from its equivalent fault tree and in quantitative analysis, the reliability parameters are evaluated using vague lambda-tau methodology. Further, a decision support system based on vague sets is developed to overcome the limitations of traditional risk analysis.Findings - The reliability parameters (such as expected number of failures, mean time between failures, availability, and reliability) of the compressor system are evaluated. The proposed, vague sets based reliability analysis and risk analysis not only overcome the limitations associated with traditional approaches but also integrates the confidence level of domain experts and expert’s experience, in more flexible and realistic manner. Originality/value - Instead of fuzzy sets, this paper used vague sets for reliability analysis because in real life problems, there may be hesitation regarding the belongingness of an object to a set or not. In fuzzy set theory, there is no means to incorporate such type of hesitation.

Anisotropic Hierarchic Finite Elements for the Simulation of Piezoelectric Smart Structures

literatinetwork@emeraldinsight.com (Sascha Duczek, Ulrich Gabbert) — Fri, 12 Jul 2013 00:00:00 +0100

Abstract

Purpose - Piezoelectric actuators and sensors are an invaluable part of lightweight designs for several reasons. They can either be used in noise cancellation devices as thin-walled structures are prone to acoustic emissions, or in shape control approaches to suppress unwanted vibrations. Also in Lamb wave based health monitoring systems piezoelectric patches are applied to excite and to receive ultrasonic waves.Design/methodology/approach - In the paper the development of a new fully three-dimensional piezoelectric hexahedral finite element based on the p-version of the finite element method (FEM) is presented. Hierarchic Legendre polynomials in combination with an anisotropic ansatz space are utilized to derive an electro-mechanically coupled element. This results in a reduced numerical effort. The suitability of the proposed element is demonstrated using various static and dynamic test examples.Findings - In the current contribution it is shown that higher order coupled-field finite elements hold several advantages for smart structure applications. All numerical examples have been found to agree well with previously published results. Furthermore, it is demonstrated that accurate results can be obtained with far fewer degrees of freedom compared to conventional low order finite element approaches. Thus, the proposed finite element can lead to a significant reduction in the overall numerical costs.Originality/value - At least to the author’s knowledge no piezoelectric finite element based on the Hierarchical-Finite-Element-Method has been published in literature, yet. Thus, the proposed finite element is a step towards a holistic numerical treatment of structural health monitoring (SHM) related problems using p-version finite elements.

Mathematical model for dispersion and diffusion of chemically reactive pollutants from various sources into a boundary Layer with dry deposition

literatinetwork@emeraldinsight.com (Yasir Khan) — Fri, 12 Jul 2013 00:00:00 +0100

Abstract

Purpose - Aims to propose mathematical model for dispersion and diffusion of chemically reactive primary pollutants emitted from an elevated line sources into a stable atmospheric boundary layer with generalized wind velocity of quadratic function of vertical height z.Design/methodology/approach - The governing partial differential equations are converted into the two-dimensional time dependent partial differential equation by suitable choice of meteorological parameters and non-dimensional variables, which is solved by the multiple inverse Laplace transform through Green’s Function technique.Findings - The three different types’ sources viz. continuous, an instantaneous and step-function type sources are studied. The pollutants considered to be of chemically reactive primary pollutants emitted from the above said sources. In many of the previous works solution obtained through numerical technique (Arora et al., 1991) or numerical inversion of the Laplace transform by (Robson, 1987). But whereas here an analytical method is carried out in ?nding the exact solution through multiple inversion of Laplace transform which yield the effective and accurate solution.Originality/value - The paper describes how the authors obtained exact solutions for the elevated line sources into a stable atmospheric boundary layer arising in the chemically reactive primary pollutants model by inverse Laplace transform through Green’s Function technique. The graphical results show that this method is very accurate. The gaseous pollutants converted into particulate matter is settled on surface terrain are also considered in this theoretical model.

Thermo-hygro-mechanical meso-scale analysis of concrete as a viscoelastic-damaged material

Fri, 12 Jul 2013 00:00:00 +0100

Abstract

Purpose - Knowledge of the behavior of concrete at mesoscale level requires, as a fundamental aspect, to characterize aggregates and specifically, their thermal properties if fire hazards (e.g. spalling) are accounted for. The assessment of aggregates performance (and, correspondingly, concrete materials made of aggregates, cement paste and ITZ –interfacial transition zone-) is crucial for defining a realistic structural response as well as damage scenarios.Design/methodology/approach - It is here assumed that concrete creep is associated to cement paste only and that creep obeys to the B3 model proposed by Bažant and Baweja since it shows good compatibility with experimental results and it is properly justified theoretically.Findings - First, the three-dimensionality of the geometric description of concrete at the meso-level can be appreciated; then, creep of cement paste and ITZ allows to incorporate in the model the complex reality of creep, which is not only a matter of fluid flow and pressure dissipation but also the result of chemical-physical reactions; again, the description of concrete as a composite material, in connection with porous media analysis, allows for understanding the hygro-thermal and mechanical response of concrete, e.g. hygral barriers due to the presence of aggregates can be seen only at this modelling level. Finally, from the mechanical viewpoint, the remarkable damage peak effect arising from the inclusion of ITZ, if compared with the less pronounced peak when ITZ is disregarded from the analysis, is reported.Originality/value - The fully coupled 3D F.E. code NEWCON3D has been adopted to perform fully coupled thermo-hygro-mechanical meso-scale analyses of concrete characterized by aggregates of various types and various thermal properties. The 3D approach allows for differentiating each constituent (cement paste, aggregate and ITZ), even from the point of view of their rheologic behaviour. Additionally, model B3 has been upgraded by the calculation of the effective humidity state when evaluating drying creep, instead than using approximate expressions. Damage maps allows for defining an appropriate concrete mixture to withstand spalling and to characterize the coupled behaviour of ITZ as well.

Exciting electrode optimization of a piezoceramic plate type ultrasonic motor by combining artificial immune algorithm and finite element analysis

literatinetwork@emeraldinsight.com (cun-cen li) — Fri, 12 Jul 2013 00:00:00 +0100

Abstract

Purpose - An optimization method by combining artificial immune algorithm and finite element analysis is proposed to find the optimal exciting electrode of a piezoceramic plate type ultrasonic motor vibrator. Design/methodology/approach - The artificial immune algorithm is selected as optimizer for its merit of fast convergence to global optimal solution. The finite element analysis is used to calculate the motion trajectory of contact point. The objective function is the work that the vibrator does to rotor. The design variables are the boundaries of exciting electrode on piezoceramic plate vibrator surface. Findings - The calculated results and experimental results show that using this method, both the position and size of optimal exciting electrode of this ultrasonic motor can be quickly and accurately determined.Originality/value - In order to successfully design an ultrasonic motor, both the position and the size of the exciting electrode must be investigated, so as to change more electric energy into mechanical energy. In this paper, an optimization method by combining artificial immune algorithm and finite element analysis is proposed for the exciting location optimization of a piezoceramic plate type ultrasonic motor to obtain large power output.