Search results

1 – 10 of over 11000
Article
Publication date: 19 January 2015

Miguel Castilho, Barbara Gouveia, Inês Pires, Jorge Rodrigues and Manuel Pereira

This paper aims to study the influence of the binder saturation level on the accuracy and on the mechanical properties of three-dimensional (3D)-printed scaffolds for bone…

Abstract

Purpose

This paper aims to study the influence of the binder saturation level on the accuracy and on the mechanical properties of three-dimensional (3D)-printed scaffolds for bone tissue engineering.

Design/methodology/approach

To study the influence of the liquid binder volume on the models accuracy, two quality test plates with different macropore sizes were designed and produced. For the mechanical and physical characterisation, cylindrical specimens were used. The models were printed using a calcium phosphate powder, which was characterised in terms of composition, particle size and morphology, by X-ray diffraction (XRD), laser diffraction and Scanning electron microscopy (SEM) analysis. The sample’s physical characterisation was made using the Archimedes method (porosity), SEM, micro-computer tomography (CT) and digital scan techniques, while the mechanical characterisation was performed by means of uniaxial compressive tests. Strength distribution was analysed using a statistical Weibull approach, and the dependence of the compressive strength on the porosity was discussed.

Findings

The saturation level is determinant for the structural characteristics, accuracy and strength the models produced by three-dimensional printing (3DP). Samples printed with the highest saturation showed higher compressive strengths (24 MPa), which are over the human trabecular bone. The models printed with lower saturations presented the highest accuracy and pore interconnectivity.

Originality/value

This study allowed to acquire important knowledge concerning the effects of shell/core saturation on the overall performance of the 3DP. With this information it is possible to devise scaffolds with the required properties for bone scaffold engineering.

Details

Rapid Prototyping Journal, vol. 21 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 4 January 2016

Mohamed Arbi Khlifi and Habib Rehaoulia

When magnetic saturation in ac machines is evolved, the theory of main flux saturation in d-q axes remains the best. Because of its simplicity, it is the most used in…

Abstract

Purpose

When magnetic saturation in ac machines is evolved, the theory of main flux saturation in d-q axes remains the best. Because of its simplicity, it is the most used in either motoring or generating mode for synchronous or asynchronous machines. Although, it is considered as a global way of introducing the iron saturation, compared to other methods, today, its fidelity has no contest in predicting complex ac machine operations. For this purpose, the aims of this paper consists of modeling these machines whatever the state-space variables values are taking into account the magnetic saturation. Two unified procedures are proposed. The first one deals with a common approach to establishing a complete and detailed model synthesis in d-q axes. The second also presents a unified approach to introducing magnetic saturation of the iron core in the characteristic equations. The analysis takes the salient pole synchronous machine as a general case of study. Then the approaches are extended to undamped and smooth air gap synchronous machines as well as induction machines. The paper aims to discuss these issues.

Design/methodology/approach

The present paper, which is a first part of a work under study dealing with a unified method to derive multiple models of saturated ac machines, is intended to the description of an alternative method and its application for induction and synchronous machines. It mainly consists of the following parts: first, after writing the stator and rotor space vector d-q equations, the number of possible models is immediately discussed. By considering the currents and fluxes as state-space variables, 14 models are obtained for AC induction machine (IM and SM). They are classified into three families, current (three), flux (three) and mixed models (eight). Second, in order to easily introduce the magnetic saturation in the 14 developed models, a method is presented. It consists of just elaborating the model with the winding currents as state variables, then deriving all the other models from it. Third, to emphasize the influence of the presence of magnetic saturation, in each model, each inductance along the d and q axes is written with a fundamental expression which exists with or without saturation and an additional one due purely to saturation. Hence the additional terms can be studied and quantified in an easy way or simply removed when linear case is assumed. Fourth, adopting such strategy to write the different coefficients of the models had led to the definition of common saturation factors. In turn, the definition of common saturation factors had allowed the definition of different groups of models within each family. Fifth, an alternative to evaluate the static and dynamic saturation coefficients is also proposed. It is shown that by proper fitting of the experimental magnetizing curve, all saturation coefficients can be written only in terms of which is simply the magnitudes ratio of the magnetizing flux and current. Sixth, although the theory of the main flux saturation is now admitted, an investigation was carried out on a self-excited induction generator and the build-up of voltage and current phases of a standalone alternator, to prove the equivalence between the all developed models.

Findings

The number of models based on the state-space variables choice, of a saturated ac machine, is reviewed. A simple method consisting of elaborating just the winding currents model, with magnetic saturation and deriving all the other models from it, is presented. In this study special interest was particularly focussed on either novel models or existing models cited in the literature but cannot be obtained by other approaches. In all cases, if the differential equations of the machine are formulated in terms of a set of variables other than the winding currents, a noticeable reduction in the size of equations may be obtained and consequently less time computing. The approach seems to be able to derive any possible model whatever the state-space variables and the type of the ac machine and hence can be classified as a general approach.

Practical implications

The experiments of synchronous and induction machine transients prove the validity of the method.

Originality/value

By suitable choice of state-space characteristic vectors among the fluxes and the currents, a synthesis of AC machine models in d-q axes is established. To introduce magnetic saturation in each model, an approach-based uniquely on the elaboration of the winding currents model is exposed and applied. In addition, the analysis gives a detailed classification of all found models taking into account the state variables nature as well as the cross-coupling coefficient considered as a saturation factor. The study is completed with a simple alternative to evaluate all saturation factors by just calculating the static magnetizing inductance.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 35 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 20 August 2020

Md. Kausar Alam

The study aims to explore the case study method with the formation of questions, data collection procedures and analysis, followed by how and on which position the…

4745

Abstract

Purpose

The study aims to explore the case study method with the formation of questions, data collection procedures and analysis, followed by how and on which position the saturation is achieved in developing a centralized Shariah governance framework for Islamic banks in Bangladesh.

Design/methodology/approach

Using purposive and snowball sampling procedures, data have been collected from 17 respondents who are working in the central bank and Islamic banks of Bangladesh through face-to-face and semi-structured interviews.

Findings

The study claims that researchers can form the research questions by using “what” question mark in qualitative research. Besides, the qualitative research and case study could explore the answers of “what” questions along with the “why” and “how” more broadly, descriptively and extensively about a phenomenon. Similarly, saturation can be considered attaining the ultimate point of data collection by the researchers without adding anything in the databank. Overall, this study proposes three stages of saturation: First, information redundancy. Second, referring the respondents (already considered in the study) without knowing anything about the data collection and their responses. Third, through the NVivo open coding process due to the decrease of reference or quotes in a certain position or in the saturation position as a result of fewer outcomes or insufficient information. The saturation is thus achieved in the diversified positions, i.e. three respondents for regulatory, nine for Shariah scholars and officers and five for the experts concerning the responses and respondents.

Research limitations/implications

The study has potential implications on the qualitative research method, including the case study, saturation process and points, NVivo analysis and qualitative questions formation.

Originality/value

This research defines a case study with the inclusion of “what” and illustrates the saturation process in diverse positions. The qualitative research questions can also be formed with “what” in addition “why” and “how”.

Details

Qualitative Research in Organizations and Management: An International Journal, vol. 16 no. 1
Type: Research Article
ISSN: 1746-5648

Keywords

Article
Publication date: 1 December 2005

Zdzisław Włodarski, Jadwiga Włodarska and Andrzej Brykalski

The increase of the accuracy of a mathematical model of hysteresis by the choice of the optimum saturation curve for a given material.

1025

Abstract

Purpose

The increase of the accuracy of a mathematical model of hysteresis by the choice of the optimum saturation curve for a given material.

Design/methodology/approach

Hysteresis loops of typical soft magnetic materials are approximated with the help of the Taka´cs magnetization model using different saturation curves. The quality of approximations is determined by the deviation of computed magnetic induction amplitudes, iron losses, apparent remanences and coercivities from the measured values.

Findings

By the proper choice of saturation curve, the relative inaccuracy of approximations can be reduced with reference to the original model based on tangent hyperbolic function.

Research limitations/implications

The accuracy of approximations worsens close to saturation because of the excessive rise of magnetization due to the linear term of the model. This effect should be minimized by the application of complex saturation curves using greater number of parameters.

Practical implications

Owing to the convenient analytical form and increased accuracy, the model equations can be used in simpler practical evaluations of hysteresis effects and for teaching purposes.

Originality/value

Presented form of model equations enables approximation of hysteresis loops and the evaluation of main characteristics of magnetic materials on the basis of any saturation curve.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 24 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 1 June 2003

Ahmed Masmoudi

The doubly fed machine (DFM) is presently given an increasing attention in high power variable speed drives and in wind power generation systems, where it exhibits high…

Abstract

The doubly fed machine (DFM) is presently given an increasing attention in high power variable speed drives and in wind power generation systems, where it exhibits high performances. This has been gained thanks to the stator flux oriented control. Nevertheless, beyond the effect of heating, the robustness of such control strategy is affected by saturation especially the main magnetic one. Accounting for the effect of the magnetizing branch saturation in steady‐state stability analysis, considering the case of a voltage‐controlled DFM and the case of a current‐controlled one, represents the aim of the study. To this end, a numerical procedure based on a combination of the eigenvalue and the fixed point methods has been developed. It has been found that, in both cases, accounting for saturation yields a stabilization effect which is more or less significant depending on the rotor supply parameters.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 22 no. 2
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 4 January 2016

Peyman Naderi

The purpose of this paper is to obtain an integrated method for inter-turn short circuit fault detection for the cage-rotor induction machine (CRIM) considering saturation

Abstract

Purpose

The purpose of this paper is to obtain an integrated method for inter-turn short circuit fault detection for the cage-rotor induction machine (CRIM) considering saturation effect.

Design/methodology/approach

The magnetic equivalent circuit (MEC) is proposed for machine modeling and nonlinear B-H curve is considered for saturation effect. The machine has some differential equations which are converted to algebraic type by trapezoidal method. On the other hand, some nonlinear equations are present due to saturation effect. A set of nonlinear algebraic equation should be solved by numerical method. Therefore, the Newton-Raphson technique is used for equation solving during of the considered time step.

Findings

Generally, the operating point of electrical machines is close to the saturation zone due to designing considerations. Moreover, some current and torque harmonics will be produced due to time and space harmonics combination, which cannot be studied when saturation modeling is neglected. Considering both space and time harmonics, a method is proposed for inter-turn short circuit fault detection based on the stator current signatures and the machine performance is analyzed in healthy and faulty cases. In order to obtain the integrated method, two sample machines (two and also four-pole machines) are modeled and finally the accuracy of the proposed method is verified through the experimental results.

Research limitations/implications

The calculations have been done in this work is limited to CRIM considering. However, the presented modeling method can be used for another types of electrical machines by some minor modifications.

Originality/value

Obtaining of an integrated formula for the inter-turn short circuit fault detection which has been presented for first time is the more advantages of present work. Moreover, in order to saturation effect considering, a new method is presented for solving of nonlinear equations which is another novelty of paper.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 35 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 11 May 2010

Tarik Abdulahovic, Sercan Teleke, Torbjorn Thiringer and Jan Svensson

The purpose of this paper is to investigate the influence of time steps, integration methods, and saturation modeling on the accuracy of the synchronous machine model…

1200

Abstract

Purpose

The purpose of this paper is to investigate the influence of time steps, integration methods, and saturation modeling on the accuracy of the synchronous machine model. This model is compared with the PSCAD built‐in synchronous machine model in order to compare the accuracy of one of the most used synchronous machine models in a commercially available software versus a well‐documented and widely accepted state‐space synchronous machine model.

Design/methodology/approach

In the paper, a synchronous condenser with the saturation phenomenon is modeled using state‐space equations in the rotating dq‐reference frame and is implemented both in Matlab/Simulink and PSCAD. Integration methods of up to the fifth order are implemented for increased accuracy. The saturation modeling includes modeling of the saturation in both d‐ and q‐axis. A steady‐state and dynamic performance comparison towards the built‐in PSCAD synchronous machine model is performed. The saturation modeling does not include the saturation of the leakage fluxes.

Findings

When the forward Euler method is used, in order to obtain less than 5 percent error, the time step should not exceed 5 μs. The third‐order Runge‐Kutta method is the preferred choice and it provides desired accuracy when the time step is equal or smaller than 1,000 μs. The built‐in PSCAD model satisfies the error criteria for time steps smaller than 300 μs. A small discrepancy of 2 percent is found during the steady‐state test.

Originality/value

The paper presents the performance of the higher order integration methods in an EMTP‐type software environment where the trapezoidal integration method is most often used. It provides a good guide for building an owner‐defined model. A comparison of a dynamic performance between the publicly documented state‐space and a synchronous machine models commonly used for power system transient studies is presented.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 29 no. 3
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 4 January 2016

Jion Sean Pau, William Pao and Suet Peng Yong

The purpose of this paper is to introduce the solution to two-phase flow in CO2/brine system with salt precipitation by applying mixed hybrid finite element (MHFE) method…

Abstract

Purpose

The purpose of this paper is to introduce the solution to two-phase flow in CO2/brine system with salt precipitation by applying mixed hybrid finite element (MHFE) method to pressure equation and finite volume (FV) method to saturation equation. Mixed finite element method solves pressure and velocity in two subspaces while hybrid method is an extension of mixed method, where the Lagrange multiplier is added to the former in order to ensure the continuity from one element to the adjacent elements. The authors propose the modeling of salt precipitation using core flood experimental result and adapt to be applicable for numerical modeling.

Design/methodology/approach

The governing equations are discretized using Mixed Hybrid Finite Element-Finite Volume (MHFE-FV) method. This method has the feature of localized conservation which is attractive for application on heterogeneous porous media. In addition to this, the salt precipitation effect is modeled using the data from core flood experiment (Ott et al., 2011). The random data are linearized to obtain the relationship between salt precipitate and CO2 saturation and implemented to the algorithm for two-phase flow in CO2 and brine system.

Findings

The solution of MHFE-FV scheme has good agreement with the solution using implicit pressure and explicit saturation (IMPES) reported by Negara et al. (2011), with average error of 4.20 percent. Localized conservation is demonstrated in the case of randomized heterogeneous porous media where fingering effects are explicitly observed. Salt precipitation prediction using the proposed method is able to predict the decrement of porosity by 16.71 percent and permeability by 22.19 percent. This results in the decreased amount of CO2 injected by 64.70 percent.

Research limitations/implications

This paper presents the solution of two-phase flow in CO2 brine system during CO2 injection in saline aquifer using MHFE-FV method with the additional salt precipitation model obtained based on core flood experiment result.

Practical implications

A methodology to predict the salt precipitation based on CO2 saturation.

Social implications

Contribution to green house gas reduction.

Originality/value

The authors use MHFE-FV to solve hyperbolic PDE to obtain accurate results of CO2 saturation, and subsequently use this to compute the salt precipitation.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 4 September 2018

Neha Agarwal and Haranath Kar

The purpose of this paper is to establish a criterion for the global asymptotic stability of fixed-point state–space digital filters using saturation overflow arithmetic.

Abstract

Purpose

The purpose of this paper is to establish a criterion for the global asymptotic stability of fixed-point state–space digital filters using saturation overflow arithmetic.

Design/methodology/approach

The method of stability analysis used in this paper is the second method of Lyapunov. The approach in this paper makes use of a precise upper bound of the state vector of the system and a novel passivity property associated with the saturation nonlinearities.

Findings

The presented criterion leads to an enhanced stability region in the parameter-space as compared to several existing criteria.

Practical implications

When dealing with the design of fixed-point state–space digital filters, it is desirable to have a criterion for selecting the filter coefficients so that the designed filter becomes free of overflow oscillations. The criterion presented in this paper provides enhanced saturation overflow stability region and therefore facilitates the designer greater flexibility in selecting filter parameters for overflow oscillation-free realization of digital filters.

Originality/value

The approach uses the structural properties of the saturation nonlinearities in a greater detail. The exploitation of upper bound of the system state vector together with a new passivity property of saturation nonlinearities is a unique feature of the present approach. The presented approach may lead to results not covered by several existing approaches.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 6
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 2 October 2017

Mohamed El-Amin, Jisheng Kou and Shuyu Sun

This paper aims to introduce modeling, numerical simulation and convergence analysis of the problem of nanoparticles’ transport carried by a two-phase flow in a porous…

Abstract

Purpose

This paper aims to introduce modeling, numerical simulation and convergence analysis of the problem of nanoparticles’ transport carried by a two-phase flow in a porous medium. The model consists of equations of pressure, saturation, nanoparticles’ concentration, deposited nanoparticles’ concentration on the pore-walls and entrapped nanoparticles concentration in pore-throats.

Design/methodology/approach

A nonlinear iterative IMPES-IMC (IMplicit Pressure Explicit Saturation–IMplicit Concentration) scheme is used to solve the problem under consideration. The governing equations are discretized using the cell-centered finite difference (CCFD) method. The pressure and saturation equations are coupled to calculate the pressure, and then the saturation is updated explicitly. Therefore, the equations of nanoparticles concentration, the deposited nanoparticles concentration on the pore walls and the entrapped nanoparticles concentration in pore throats are computed implicitly. Then, the porosity and the permeability variations are updated.

Findings

Three lemmas and one theorem for the convergence of the iterative method under the natural conditions and some continuity and boundedness assumptions were stated and proved. The theorem is proved by induction states that after a number of iterations, the sequences of the dependent variables such as saturation and concentrations approach solutions on the next time step. Moreover, two numerical examples are introduced with convergence test in terms of Courant–Friedrichs–Lewy (CFL) condition and a relaxation factor. Dependent variables such as pressure, saturation, concentration, deposited concentrations, porosity and permeability are plotted as contours in graphs, whereas the error estimations are presented in a table for different values of the number of time steps, number of iterations and mesh size.

Research limitations/implications

The domain of the computations is relatively small; however, it is straightforward to extend this method to the oil reservoir (large) domain by keeping similar definitions of CFL number and other physical parameters.

Originality/value

The model of the problem under consideration has not been studied before. Also, both solution technique and convergence analysis have not been used before with this model.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 10
Type: Research Article
ISSN: 0961-5539

Keywords

1 – 10 of over 11000