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1 – 10 of over 7000Suzan Alaswad and Sinan Salman
While steady-state analysis is useful, it does not consider the inherent transient characteristics of repairable systems' behavior, especially in systems that have relatively…
Abstract
Purpose
While steady-state analysis is useful, it does not consider the inherent transient characteristics of repairable systems' behavior, especially in systems that have relatively short life spans, or when their transient behavior is of special concern such as the motivating example used in this paper, military systems. Therefore, a maintenance policy that considers both transient and steady-state availability and aims to achieve the best trade-off between high steady-state availability and rapid stabilization is essential.
Design/methodology/approach
This paper studies the transient behavior of system availability under the Kijima Type II virtual age model. While such systems achieve steady-state availability, and it has been proved that deploying preventive maintenance (PM) can significantly improve its steady-state availability, this improvement often comes at the price of longer and increased fluctuating transient behavior, which affects overall system performance. The authors present a methodology that identifies the optimal PM policy that achieves the best trade-off between high steady-state availability and rapid stabilization based on cost-availability analysis.
Findings
When the proposed simulation-based optimization and cost analysis methodology is applied to the motivating example, it produces an optimal PM policy that achieves an availability–variability balance between transient and steady-state system behaviors. The optimal PM policy produces a notably lower availability coefficient of variation (by 11.5%), while at the same time suffering a negligible limiting availability loss of only 0.3%. The new optimal PM policy also provides cost savings of about 5% in total maintenance cost. The performed sensitivity analysis shows that the system's optimal maintenance cost is sensitive to the repair time, the shape parameter of the Weibull distribution and the downtime cost, but is robust with respect to changes in the remaining parameters.
Originality/value
Most of the current maintenance models emphasize the steady-state behavior of availability and neglect its transient behavior. For some systems, using steady-state availability as the sole metric for performance is not adequate, especially in systems that have relatively short life spans or when their transient behavior affects the overall performance. However, little work has been done on the transient analysis of such systems. In this paper, the authors aim to fill this gap by emphasizing such systems and applications where transient behavior is of critical importance to efficiently optimize system performance. The authors use military systems as a motivating example.
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Jianfei Li, Mengxia Sun, Li Ren and Bei Li
The advent of the new retail era witnessed the consumers’ demand shift from on the traditional product quality to on the full supply chain service quality, and product service and…
Abstract
Purpose
The advent of the new retail era witnessed the consumers’ demand shift from on the traditional product quality to on the full supply chain service quality, and product service and service manufacturing is gradually taking shape. The purpose of this paper is to propose whether there is a “quality bridge” in the dynamic evolution process of retail service supply chain (RSSC) and discuss the system role, steady-state characteristics and dynamic evolution mechanism of service quality in this dynamic evolution process.
Design/methodology/approach
This paper proposes the dissipation system structure of the RSSC under the steady-state quality constraint, constructs a Markov chain model (MCM) for the evolution of the service quality of RSSC, and tests the objective existence of the steady-state distribution of the service quality by taking Chinese HJ retail enterprises as samples.
Findings
The research value of this study is summarized as follows. The research finds that the evolution of service quality of RSSC is a dynamic and non-linear growth process, which has significant characteristics of complex adaptability and steady-state convergence. The study finds that the quality evolution process of the RSSC is a steady-state convergence process, and there is a steady-state distribution of quality in its co-evolution, in which different process input levels have a significant positive impact on the stable level of quality state. The study finds that the steady state of quality plays a crucial role in the collaborative evolution of the RSSC, that is, when the service quality reaches a certain steady state distribution, the operating efficiency and profit level of the whole chain will show an “explosive” growth trend.
Originality/value
Quality bridge, an original concept in this paper, represents the role of quality steady-state in the operation of RSSC. Based on Markov chain and system simulation tools, this paper verifies the existence of steady-state service quality and its positive effect on the co-evolution and sustainable development of RSSC. When the service quality reaches a certain steady distribution, the operating efficiency and income level of the whole chain will show n trend of explosive growth.
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EDMC represents extended dynamic matrix control, which can be applied to nonlinear process control. In this method, control inputs are determined based on a linear model that…
Abstract
EDMC represents extended dynamic matrix control, which can be applied to nonlinear process control. In this method, control inputs are determined based on a linear model that approximates the process and is updated during each sampling interval. Since nonlinear relation still exists between the prediction error and the control input, numerical (iterative) methods are used to solve the optimization problem defined in the method. For nonlinear processes with high variation and/or sign changes in their steady‐state gain, iterative methods do not converge properly to an acceptable solution for some desired outputs or external disturbances. To eliminate the problem, we augment the process with its steady‐state gain inverse (or pseudo inverse whenever required) such that the steady‐state gain for the new augmented system is constant or contains slow variations. In the case of unstable processes, the method may be applied after stabilizing the process using a proper state or output feedback. Effectiveness of the method has been examined using computer simulations of some benchmark processes. Some of the obtained results are presented in this paper.
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Guillaume Caron, Thomas Henneron, Francis Piriou and Jean-Claude Mipo
The purpose of this study is to determine the steady state of an electromagnetic structure using the finite element method (FEM) without calculation of the transient state. The…
Abstract
Purpose
The purpose of this study is to determine the steady state of an electromagnetic structure using the finite element method (FEM) without calculation of the transient state. The proposed method permits to reduce the computation time if the transient state is important.
Design/methodology/approach
In the case of coupling magnetic and electric circuit equations to obtain the steady state with periodic conditions, an approach can be to discretise the time with periodic conditions and to solve the equation system. Unfortunately, the computation time can be prohibitive. In this paper, the authors proposed to use the waveform relaxation method associated with the Newton method to accelerate the convergence.
Findings
The obtained results show that the proposed approach is efficient if the transient state is important. On the contrary, if the transient state is very low, it is preferable to use the classical approach, namely, the time-stepping FEM.
Research limitations/implications
The main limitation of the proposed approach is the necessity to evaluate or to know the time constant and consequently the duration of the transient state. Moreover the method requires some important memory resources.
Practical/implications
In the context of the use of the time-stepping FEM, one of the problems is the computation time which can be important to obtain the steady state. The proposed method permits avoidance of this difficulty and directly gives the steady state.
Social/implications
The proposed approach will permit to model and study the electromagnetic systems in the steady state, and particularly the transformers. Because of the gain in computing time, the use of optimisation techniques will be facilitated.
Originality/value
The novelty of this study is the proposal of the waveform relaxation–Newton method to directly obtain the steady state when applied to the three-phase transformer.
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The purpose of this paper is to present the Galerkin method for analysis of steady-state processes in periodically time-varying circuits.
Abstract
Purpose
The purpose of this paper is to present the Galerkin method for analysis of steady-state processes in periodically time-varying circuits.
Design/methodology/approach
A converter circuit working on a time-varying load is often controlled by different signals. In the case of incommensurable frequencies, one can find a steady-state process only via calculation of a transient process. As the obtained results will not be periodical, one must repeat this procedure to calculate the steady-state process on a different time interval. The proposed methodology is based on the expansion of ordinary differential equations with one time variable into a domain of two independent variables of time. In this case, the steady-state process will be periodical. This process is calculated by the use of the Galerkin method with bases and weight functions in the form of the double Fourier series.
Findings
Expansion of differential equations and use of the Galerkin method enable discovery of the steady-state processes in converter circuits. Steady-state processes in the circuits of buck and boost converters are calculated and results are compared with numerical and generalized state-space averaging methods.
Originality/value
The Galerkin method is used to find a steady-state process in a converter circuit with a time-varying load. Processes in such a load depend on two incommensurable signals. The state-space averaging method is generalized for extended differential equations. A balance of active power for extended equations is shown.
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Tadeusz Sobczyk, Michał Radzik and Jarosław Tulicki
This paper aims to omit the difficulties of directly finding the periodic steady-state solutions for electromagnetic devices described by circuit models.
Abstract
Purpose
This paper aims to omit the difficulties of directly finding the periodic steady-state solutions for electromagnetic devices described by circuit models.
Design/methodology/approach
Determine the discrete integral operator of periodic functions and develop an iterative algorithm determining steady-state solutions by a multiplication of matrices only.
Findings
An alternative method to creating finite-difference relations directly determining steady-state solutions in the time domain.
Research limitations/implications
Reduction of software and hardware requirements for determining steady-states of electromagnetic.
Practical implications
A unified approach for directly finding steady-state solutions for ordinary nonlinear differential equations presented in the normal form.
Originality/value
Eliminate the necessity of solving high-order finite-difference equations for steady-state analysis of electromagnetic devices described by circuit models.
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Suzan Alaswad, Richard Cassady, Edward Pohl and Xiaoping Li
The purpose of this paper is to explore the impact of the Kijima Type II imperfect repair model on the availability of repairable systems (RS). Since many individuals are…
Abstract
Purpose
The purpose of this paper is to explore the impact of the Kijima Type II imperfect repair model on the availability of repairable systems (RS). Since many individuals are interested in measuring the extent to which the system will be available after it has been run for a long time, the specific interest in this study is in the steady-state (limiting) availability behavior of such systems. Furthermore, the authors study the impact of age-based preventive maintenance (PM) on the RS performance.
Design/methodology/approach
Because of the complexity of the underlying assumptions of the Kijima Type II model, the authors use simulation modeling to estimate the system availability. Based on preliminary simulation results, the availability function achieves a steady-state value greater than zero. The system steady-state availability is then estimated from the simulation output by computing the average of the availability estimates beyond the initial transient period. Next, the authors develop a meta-model to convert the system reliability and maintainability parameters into the coefficients of the limiting availability estimate without the simulation effort. Using a circumscribed central composite experimental design, the authors confirm the accuracy of the meta-model.
Findings
The results show that the meta-model is robust, and provides good estimates of the system limiting availability. Also, the authors find that when using a Kijima Type II model for a system repair process, age-based PM can improve the steady-state availability value. Therefore, an optimal age-based PM policy that maximizes the system’s steady-state availability can be identified.
Originality/value
In practice, it is important to study the system steady-state availability because many individuals, i.e. engineers, are more interested in measuring the extent to which the system will be available after it has been run for a long time. Therefore, this study represents a significant addition to the body of knowledge related to virtual age modeling, in that it incorporates a Kijima type II model and considers system steady-state availability.
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Faïçal Jallali, Afef Bouchhima and Ahmed Masmoudi
The purpose of this paper is to investigate the steady‐state stability and features of the brushless cascaded doubly fed machine (BCDFM), which is made up of two wound‐rotor…
Abstract
Purpose
The purpose of this paper is to investigate the steady‐state stability and features of the brushless cascaded doubly fed machine (BCDFM), which is made up of two wound‐rotor induction machines: the power machine (PM) and the control one, with their rotors mechanically and electrically coupled.
Design/methodology/approach
The machine modelling is first treated considering a Park reference frame linked to the rotating field of the PM. Then, a state representation related to small perturbations is established following the linearisation of the BCDFM model around a steady‐state operating point. This allows the investigation of BCDFM steady‐state stability, power flow and the torque‐speed characteristics.
Findings
It has been found that the electrical variables of the control machine greatly affect the BCDFM steady‐state stability and characteristics.
Research limitations/implications
The work should be extended considering a validation of the established results through experimental tests.
Originality/value
The steady‐state small perturbation of the BCDFM model has been introduced for the first time, which is the key of the machine steady‐stability analysis and features investigation.
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S.L. Beh, K.‐K. Tio, G.A. Quadir and K.N. Seetharamu
The purpose of this paper is to apply asymptotic waveform evaluation (AWE) to the transient analysis of a two‐layered counter‐flow microchannel heat sink.
Abstract
Purpose
The purpose of this paper is to apply asymptotic waveform evaluation (AWE) to the transient analysis of a two‐layered counter‐flow microchannel heat sink.
Design/methodology/approach
A two‐layered counter‐flow microchannel heat sink in both steady state and transient conditions is analysed. Finite element analysis is used in the steady state analysis whereas AWE is used in the transient analysis.
Findings
A two‐layered microchannel produces different temperature distribution compared to that obtained for a single‐layered microchannel. The maximum temperature occurs at the middle of the bottom wall whereas the maximum temperature of a single‐layered microchannel is at the outlet of the bottom wall. The time taken to reach steady state is also investigated for different coolant flow rate and heat flux boundary conditions. It is observed that when fluid velocity increases, the time taken to reach steady state decreases, however, when the heat flux increases, the time taken to reach steady state does not change.
Research limitations/implications
The fluid is incompressible and does not undergo phase change. The use of AWE provides an alternative method in solving heat transfer problem.
Practical implications
New and additional data will be useful in the design of a microchannel heat sink for the purpose of cooling of electronic components.
Originality/value
AWE is widely used in analyses of signal delays in electronic circuits, and rarely applied to mechanical systems. The present study applies AWE to heat transfer problems, and reveals that it reduces the computational time considerably. The results obtained are compared with conventional methods available in the literature, and they show good agreement. Hence the computational time is reduced, and the accuracy of results is verified.
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The purpose of this paper is to study the behavior of a worker within an organization. There are two groups inside the firm that develop their work in different ways (sharing…
Abstract
Purpose
The purpose of this paper is to study the behavior of a worker within an organization. There are two groups inside the firm that develop their work in different ways (sharing different codes). The worker will choose to converge to one of those groups, through an investment in learning the correspondent languages and skills.
Design/methodology/approach
The convergence process is analyzed under an optimality setup. Also, the choice among investment alternatives is addressed.
Findings
The framework allows the determination of steady state points for both investment alternatives; it is not optimal to converge to a full identification with one group, given that the worker benefits from the proximity to both groups, and therefore, the steady state is found to be an intermediate point somewhere in between the groups’ locations. Under a discrete choice setup, where adaptation and entropy are considered, one observes that the least likely investment process might be chosen (there is a positive probability associated with such an option).
Originality/value
The paper considers a firm where two groups share different codes and cultures. It shows that the groups develop activities that are useful for the organization and that give rise to individual rewards.
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