bluuebunny/crossref_metadata_2025_split huggingface dataset:
Committee neural network for estimating preconsolidation pressure from piezocone test result
Authors: Kim Y.S. , Park H.I. 
Published: March 2013

PurposeThe purpose of this paper is to examine the feasibility of committee neural network (CNN) theory for the improvement of accuracy and consistency of the neural network model on the estimation of preconsolidation pressure from the field piezocone measurements.Design/methodology/approachIn this study, CNN theory is introduced to improve the initial weight dependency of the neural network model on the prediction of preconsolidation pressure of soft clay from a piezocone test result. It was found that the proposed CNN model can improve the initial weight dependency of the NN model and provide a more consistent and precise inference result than existing NN models, as well as empirical and theoretical models.FindingsIt was found that the CNN overcomes the initial weight dependency of the single neural network model. Various committees of the single multilayer perceptrons (MLPs) were tested. It was found that if eight single MLPs, which have the same structure but have been trained with a different initial weight and bias, are accumulated in the committee with the same weighting factor, any variation on the prediction of the preconsolidation pressure from the piezocone test result can be simply and successfully eliminated.Originality/valueIn recent years, ANN has been found to be a powerful theory for analyzing complex relationships involving a multitude of variables, on many geotechnical applications. However, single MLP, when repeatedly trained on the same patterns, tends to reach different minima of the objective function each time and hence give a different set of neuron weights, because the solution is not unique for noisy data, as in most geotechnical problems. The authors observed that a committee neural network system is able to provide improved performance compared with a single optimal neural network.
Least squares and stochastic gradient parameter estimation for multivariable nonlinear Box‐Jenkins models based on the auxiliary model and the multi‐innovation identification theory
Authors: Chen Jing , Ding Feng 
Published: March 2013

PurposeThe purpose of this paper is to study the identification methods for multivariable nonlinear Box‐Jenkins systems with autoregressive moving average (ARMA) noises, based on the auxiliary model and the multi‐innovation identification theory.Design/methodology/approachA multi‐innovation generalized extended least squares (MI‐GELS) and a multi‐innovation generalized ex‐tended stochastic gradient (MI‐GESG) algorithms are developed for multivariable nonlinear Box‐Jenkins systems based on the auxiliary model. The basic idea is to construct an auxiliary model from the measured data and to replace the unknown terms in the information vector with their estimates (i.e. the outputs of the auxiliary model).FindingsIt is found that the proposed algorithms can give high accurate parameter estimation compared with existing stochastic gradient algorithm and recursive extended least squares algorithm.Originality/valueIn this paper, the AM‐MI‐GESG and AM‐MI‐GELS algorithms for MIMO Box‐Jenkins systems with nonlinear input are presented using the multi‐innovation identification theory and the proposed algorithms can improve the parameter estimation accuracy. The paper provides a simulation example.
Unsteady internal flow field simulations in a double suction centrifugal fan
Authors: Yang Jing , Meng Long , Zhou Lingjiu , Luo Yongyao , Wang Zhengwei 
Published: March 2013

PurposeThermal power plants have many problems regarding noise and vibration. Previous studies have shown that such problems are often related to the fans. However, the internal flows are difficult to analyze to find the cause of vibration and noise in fans in actual tests. Therefore, the unsteady internal flow field in a centrifugal fan was simulated numerical to identify the source. This paper aims to present these issues.Design/methodology/approachThe unsteady Reynolds‐averaged Navier‐Stokes equations with the SST k‐ω turbulence model were solved to simulate the flow within the entire flow path of the fan. The conservation of mass and moment and energy equations were used to solve the flow field distribution. The time‐dependent pressure pulsations on the impeller were analyzed for the dynamics problem. The finite volume method with the SIMPLEC algorithm was used to discretize the time‐dependent equations. The second‐order upwind scheme was used for the convection terms and the central difference scheme was chosen for the diffusion terms in the momentum and transport equations.FindingsThe numerical simulations illustrated the flow characteristics inside the double suction centrifugal fan. The predicted efficiency is almost the same as the experimental value. The estimated pressure and temperature fields are quite reasonable. The results showed that the interaction between the non‐uniform impeller flow and the fixed volute aroused the significant pressure fluctuations, which is an important source of vibration and noise in centrifugal machinery.Research limitations/implicationsIt is assumed that there is no change in the density in the whole flow passage, and the predicted outlet temperature is about 1.15 per cent lower than the experimental result.Originality/valueThe simulation study indicates that the prediction of noise is possible by using pressure pulsation. It is recommended to control the pressure pulsation in the fans, to decrease the vibration and noise of thermal power plants.
Investigation of heat and mass transfer of rotating MHD viscous flow between a stretching sheet and a porous surface
Authors: Sheikholeslami M. , Ashorynejad H.R. , Barari A. , Soleimani Soheil 
Published: March 2013

PurposeThe purpose of this paper is to analyze hydromagnetic flow between two horizontal plates in a rotating system. The bottom plate is a stretching sheet and the top one is a solid porous plate. Heat transfer in an electrically conducting fluid bounded by two parallel plates is also studied in the presence of viscous dissipation.Design/methodology/approachDifferential Transformation Method (DTM) is used to obtain a complete analytic solution for the velocity and temperature fields and the effects of different governing parameters on these fields are discussed through the graphs.FindingsThe obtained results showed that by adding a magnetic field to this system, transverse velocity component reduces between the two plates. Also as the Prandtl number increases, in presence of viscous dissipation, the temperature between the two plates enhances while an opposite behavior is observed when the viscous dissipation is negligible.Originality/valueThe equations of conservation of mass, momentum and energy are reduced to a non‐linear ordinary differential equations system. Differential Transformation Method is utilized to approximate the solution for velocity and temperature profiles.
An initial solution estimation method based on As‐Rigid‐As‐Possible mesh parameterization for one‐step simulation
Authors: Liu Qiaosheng , Xi Juntong , Wu Zhuoqi 
Published: March 2013

PurposeThe purpose of this paper is to propose a universal, robust and efficient method to obtain a reliable initial guess solution for the one‐step finite element simulation.Design/methodology/approachIn one‐step simulation, getting initial guess solutions effectively is essential to ensure the success of the non‐linear resolution in the implicit static solver and to speed up the convergence of the Newton‐Raphson iterations. A newly emerging mesh parameterization approach named As‐Rigid‐As‐Possible method, which is widely used in computer graphics, is proposed as an effective initial guess estimation method in this paper. It is almost an isometric parameterization and showing excellent area‐preserving capability than other state‐of‐the‐art approaches. Several numerical examples are provided to verify the validity and efficiency of the presented method.FindingsCompared with the geometry mapping methods, the presented ARAP method shows its universality in handling types of workpieces whether they have quasi‐vertical walls or they are long and complicated. Complex 3D workpieces with many local convex and concave features can also be well handled without large element shape distortions. In contrast to the energy based mapping algorithm, the method presented in this paper does not need to predefine the boundary nodes which will introduce less distortion to the elements near the boundary.Originality/valueThis paper is the first to utilize the As‐Rigid‐As‐Possible mesh parameterization algorithm to obtain an initial guess for the one‐step simulation. The numerical experiments show that the approach is universal, robust and efficient and can be further utilized in the optimum blank design or blank shape optimization.
Coupling of the evolution strategy algorithm and genetic algorithm with finite element mesh adaptation
Authors: Komęza Krzysztof , Napieralska Juszczak Ewa , Napieralski Piotr , Di Barba Paolo 
Published: March 2013

PurposeThe purpose of this paper is to find a more performing and automated procedure for linking an identification algorithm implemented in a general‐purpose environment with a commercial finite‐element code for magnetic field analysis. In particular, the use of a multiprocessor computer makes it possible to perform parallel computations keeping the calculation time reasonably low.Design/methodology/approachThe method is applied to identify the B‐H curve of anisotropic magnetic laminations in the direction normal to the sheet surface. In total, three different optimization methods have been applied. First an evolution strategy algorithm for solving the identification problem was used; then genetic algorithm (GA) was applied. The results obtained using different methods were compared and discussed. The computation time is reduced by adjusting the refinement of the FEM mesh.FindingsThe key point has been the use of a derivative‐free and global‐search oriented algorithm. Even if a starting point far from the solution is chosen, a suitably large initial value of the search radius makes the convergence possible. The effect of the historical parameter of the minimization algorithm on convergence has also been investigated.Originality/valueThe main new idea presented in this paper is equipping a GA‐based identification procedure with an additional objective function describing the sensitivity of the flux density against a small perturbation in parameters. This approach gives a multiple objective problem which introduces possibility of choosing a compromise solution among many optimal solutions instead of only one, as in classical GA optimization algorithm. The paper is mainly addressed to readers interested in the efficient use of GA‐based identification.
Topology optimization of electromagnetic devices using oriented iron microstructures
Authors: Labbé Thibaut , Matagne Ernest , Dehez Bruno 
Published: March 2013

PurposeThe purpose of this paper is to propose a mechanism avoiding the topology optimization methods, and particularly those using gradient‐based algorithms, to be trapped in local minimizers when applied to the design of electromagnetic devices made of iron and permanent magnet.Design/methodology/approachTopology optimization methods aim at finding the optimal distribution of some materials in cells subdividing a design space, regarding a specific objective function. This paper suggests to consider that each cell contains an oriented microstructure of iron whose direction and shape are optimized by the method.FindingsCoupled with convexity and sensitivity mappings quite common in the field of topology optimization, the use of the microstructure allows the optimization algorithm to converge systematically toward the same design. This achievement is illustrated on a practical case, i.e. the optimization of the rotor of a permanent magnet synchronous motor regarding its mean torque and under mass constraint. Also, this paper shows that intermediate iron materials can either be penalized or interpreted, thanks to the realistic physical relations derived from the iron microstructures.Originality/valueThis paper proposes a mechanism based on an iron microstructure for avoiding the topology optimization methods and the trap of local minimizers when applied to the design of electromagnetic devices made of iron and permanent magnet.
Optimization of the magnetic circuits of the column voltage transformers using the field‐circuit method
Authors: Lesniewska Elzbieta , Tulodziecki Bogdan 
Published: March 2013

PurposeThe purpose of this paper is to consider a constructional solution of the combined instrument transformer: constructed so that the voltage part is a column transformer, which means that the magnetic circuit of it is open and situated into a composite insulator. The aim of this research was to achieve optimal configuration of open magnetic circuit of the column voltage transformer.Design/methodology/approachThe authors made analyses of electromagnetic field distribution and computed the voltage error and phase displacement for many different cases of magnetic circuits of the column voltage transformers. The analyses of the electromagnetic field distribution and computations were carried out using the 3D field‐circuit method based on the finite‐element numerical method. The results were compared with tests of a real‐life model.FindingsThe result of research is the selection of the best constructional version of the column voltage transformer; the research also gives some guidelines for design and manufacture of this construction of combined transformers.Originality/valueThe paper is meant for constructors of instrument transformers and presents results of research into new constructional solutions of combined transformer.
Interlaminar short circuit detection: modeling and measurement
Authors: Luísa Müller Juliana , Romary Raphaël , Benabou Abdelkader , Henneron Thomas , Piriou Francis , Pedro Assumpção Bastos João , Roger Jean‐Yves 
Published: March 2013

PurposeInterlaminar short circuits in turbo generator stators can lead to local damage of the iron core. The purpose of this paper is to model an interlaminar short circuit diagnosis test on an existing structure.Design/methodology/approachThis work presents the modeling of short‐circuited laminations in a stator yoke of a turbo‐generator. A 3D finite element model, associated to a homogenization technique, is used to calculate the short‐circuit current. The diagnosis test known as El Cid has been modelled as well.FindingsCalculation results are compared with the experiment. The same tendency has been observed both in experimental and numerical results.Research limitations/implicationsAdditional calculations may be performed (parametric studies) in order to investigate El Cid measuring under different conditions (different material properties, fault position, size), which may lead to a better interpretation of the results.Practical implicationsModelling of short circuit diagnosis tests under different conditions may help with the interpretation of measuring results, predicting the fault size/seriousness and location. So, only the concerned parts of the stator have to be disassembled and repaired/rebuilt.Originality/valueIt is not easy to model numerically a structure with a short circuit inside, since different dimensions are involved: the fault and the varnish between laminations are much smaller than the stator itself. Thus, homogenization techniques have been used to model the lamination stack region. The combination of this technique with the modelling of the El Cid test constitutes a tool to study this kind of fault and calculate its severity and location in a stator.
Synthesis and analysis of a high‐performance low‐cost permanent magnet brushless DC motor
Authors: Petkovska Lidija , Lefley Paul , Cvetkovski Goga 
Published: March 2013

PurposeThe paper presents design development of a novel high‐performance low‐cost 6/4 pole permanent magnet brushless DC (PMBLDC) motor. The objective is to show how the cogging torque of this new design is minimised by determining the optimum stator pole arc length and the best shoe thickness.Design/methodology/approachAt the beginning a step‐by‐step design synthesis of a reference 6/4 pole PMBLDC motor with concentrated 3‐phase windings and asymmetric stator pole arcs is presented. It is followed by a full performance analysis of the reference motor. The FEM for electromagnetic field computation is employed. The characteristics of the motor are calculated and analysed. By simple variation of the stator pole geometry, two‐stage design optimisation for cogging torque minimisation is performed, and an optimised motor model is proposed. The comparative analyses of the reference and optimised motor models show the advantages of the proposed novel design.FindingsThe focus is to show the sensitivity of the cogging torque due to changes in the stator pole shoe design parameters, such as arc length and thickness, which are discretely changed inside the prescribed constraints, and the solution matrix is derived. It was found the optimised stator pole design, providing minimum cogging torque, has the original arc length 85° and pole shoe thickness 4 mm. Thus, the peak‐cogging torque from 0.294 Nm is reduced to respectable value 0.142 Nm.Originality/valueThe paper presents an original approach to synthesis of 6/4 PMBLDC new structured motor. A two‐step design procedure is introduced and optimised stator geometry is defined, minimising the cogging torque and, at the same time, improving the profile of back electromotive force (EMF) of the motor.
Analysis of high speed permanent magnet motor with powder core material
Authors: Wojciechowski Rafal M. , Jedryczka Cezary , Lukaszewicz Piotr , Kapelski Dariusz 
Published: March 2013

PurposeThe purpose of this paper is to investigate application possibilities of soft magnetic composites (SMC) in the design of high speed permanent motors for home appliances.Design/methodology/approachThe design of high speed permanent magnet motor (HSPM) with core made of SMC has been proposed. The governing information about SMC has been presented. The possible advantages and disadvantages of applying magnetic powder materials in the design of electrical machines have been studied. To solve the partial differential equations describing magnetic vector distribution in considered HSPM, the edge element method (EEM) has been applied. The formulas of permanent magnet and winding descriptions, and electromagnetic torque calculations have been presented and studied. To verify accuracy of methodology and functionality of the elaborated software, a prototype of the considered motor has been built and the experimental setup for testing torque and electromotive force has been elaborated. The comparison between measured and simulated motor characteristics have been presented and discussed.FindingsComparison between measured and simulated motor characteristics proves the model accuracy. The obtained results show that the designed HSPM motor has sinusoidal electromotive force waveforms, low cogging torque value and the sinusoidal torque versus rotor angle characteristics. Moreover, it has been indicated that the application of SMC materials can reduce power losses in the high speed motors.Originality/valueThe paper describes the development of the numerical method and software for analysis of HSPM with core made of powder materials.
Calculating boundaries for the natural voltage balancing time‐constant of the constant duty cycle single leg flying capacitor converter
Authors: van der Merwe J.W. , du T. Mouton H. , Thielemans S. 
Published: March 2013

PurposeThe flying capacitor converter (FFC) balances the clamping capacitor voltages naturally when phase shifted carrier modulation is used. Several models that describe this mechanism, and to estimate the time constants following a perturbation, are discussed in the literature. However, due to the model complexity, numerical methods must be used to evaluate these models. This paper aims to present a closed form expression, using a reference table, that describes a maximum bound for the voltage balancing time constant.Design/methodology/approachThe FCC is analysed in the frequency domain. A decomposition of the characteristic matrix that describes the voltage balancing mechanism is used. The resulting real symmetric matrix is factorised by using approximations of the load characteristics at the frequencies of interest.FindingsThe minimum eigenvalue of the factorised matrix is used to determine a maximum bound for the time constant of the voltage balancing. Since the factorised matrix is independent of variations in switching frequency and load, the eigenvalue of interest can be calculated once and tabulated.Originality/valueThe closed form expression can be used for quick calculations of the maximum time constant under different operating conditions. Furthermore, the expression provides considerable insight into the influences circuit design choices have on the balancing mechanism.
Lyapunov stability of the single‐leg flying capacitor converter natural voltage balancing mechanism
Authors: van der Merwe J.W. , du T. Mouton H. 
Published: March 2013

PurposeThe flying capacitor converter (FFC) balances the clamping capacitor voltages naturally when phase shifted carrier modulation is used. Several models that describe this mechanism are discussed in the literature. However, due to the model complexity, the stability of the mechanism is inferred from the circuit operation. This paper aims to show that the expressions describing the balancing mechanism can be simplified and used to prove Lyapunov stability.Design/methodology/approachThe FCC is analysed in the frequency domain. An equivalent circuit that describes the converter operation in terms of total and difference parameters is used. A concerted effort is made to simplify the resulting convolution expressions to their most basic forms by using the characteristics of the phase shifted switching functions' Fourier series coefficients.FindingsIt is shown that the system matrix decomposes naturally into the sum of a symmetric and a skew‐symmetric matrix. Through use of Lyapunov's theorem it is shown that the system is stable if the symmetric part of the decomposition is positive definite. A proof is provided that this matrix is positive semidefinite and the system is therefore Lyapunov stable.Research limitations/implicationsThe simplified expressions describing the convolution and the decomposition of the system matrix can be used in future studies to provide maximum bounds on the rebalancing time constant.Originality/valueThis study provides a proof that the natural voltage balancing mechanism is stable. This stability had to be inferred from circuit operation in previous studies. Secondly, the decomposition of the system matrix provides an avenue for future research.