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1 – 10 of over 10000Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community…
Abstract
Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community. Observes that computer package implementation theory contributes to clarification. Discusses the areas covered by some of the papers ‐ such as artificial intelligence using fuzzy logic. Includes applications such as permanent magnets and looks at eddy current problems. States the finite element method is currently the most popular method used for field computation. Closes by pointing out the amalgam of topics.
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Abstract
Purpose
An improved simulation model of switched reluctance motor (SRM) for steady-state operation that considers the core losses in the stator and rotor is established to obtain the steady performance of the high-speed SRM during the design, analysis and control of SRM driving system more accurately.
Design/methodology/approach
The transient core loss model for the material and SRM is presented. Then a new method for calculating the flux density of the motor in real time is introduced, and a steady-state simulation model of the SRM including real-time transient core losses calculation model is established according to the transient flux density. Because the transient core losses calculated by above method are the total core losses of the motor, a core losses distribution method is proposed and the steady-state simulation model of the SRM including the distributed core losses’ effect on the phase winding is established.
Findings
The comparison results show that the proposed model has higher accuracy than the traditional model, excluding core losses, especially at the moments when phase voltage is turn-on and turn-off. The proportion of the core losses to the motor losses increases with the increase in speed. So, the core losses’ effect on the steady-state performance of the high-speed SRM cannot be ignored.
Originality/value
The method to obtain flux density in the real time is presented and the improved steady-state simulation model of SRM that considering transient core losses is proposed.
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Sergey E. Zirka, Yuriy I. Moroz and Ebrahim Rahimpour
The purpose of this study is to develop a topological model of a three-phase, three-limb transformer for low-frequency transients. The processes in the core limbs and yokes are…
Abstract
Purpose
The purpose of this study is to develop a topological model of a three-phase, three-limb transformer for low-frequency transients. The processes in the core limbs and yokes are reproduced individually by means of a dynamic hysteresis model (DHM). A method of accounting for the transformer tank with vertical magnetic shunts at the tank walls is proposed and tested on a 120 MVA power transformer.
Design/methodology/approach
The model proposed has been implemented independently in a dedicated Fortran program and in the graphical pre-processor ATPDraw to the ATP version of the electromagnetic transient program.
Findings
It was found that the loss prediction in a wide range of terminal voltages can only be achieved using a DHM with variable excess field component. The zero sequence properties of the transformer can be accurately reproduced by a duality-derived model with Cauer circuits representing tank wall sections (belts).
Research limitations/implications
In its present form, the model proposed is suitable for low-frequency studies. Its usage in the case when transformer capacitances are involved should be studied additionally.
Practical/implications
The presented model can be used either as an independent tool or serve as a reference for subsequent simplifications.
Social/implications
The model proposed is aimed at meeting the needs of electrical engineering and ecology-minded customers.
Originality/value
Till date, there were no experimental data on zero-sequence behavior of three-phase, three-limb transformer with vertical magnetic shunts, so no verified transient model existed. The model proposed is probably the first that matched this behavior and reproduced measured no-load losses for a wide voltage range.
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Xian Zhang, Gedong Jiang, Hao Zhang, Xialun Yun and Xuesong Mei
The purpose of this paper is to analyze the time-dependent reliability of harmonic drive.
Abstract
Purpose
The purpose of this paper is to analyze the time-dependent reliability of harmonic drive.
Design/methodology/approach
The transient finite element analysis (FEA) of harmonic drive is established to calculate the stress under different loads. Combined with the residual strength model and random variables, the time-dependent reliability model of harmonic drive is deduced by the stochastic perturbation method and Edgeworth series. Based on accelerated life tests, the degradation parameters are estimated by maximizing likelihood function. Under variable load, the key stress from transient FEA is transformed into probability density function by kernel density estimation, and the residual strength model is modified by adding adjustment factors to deal with strength degradation under different loads.
Findings
The critical position of stress concentration from transient FEA is consistent with the fatigue fracture position at the accelerated life test sample. Compared with the time-dependent reliability method with equivalent circular-shell static stress or empirical degradation parameters, the proposed method has the smallest prediction error of failure life. Under variable load, the state function should be expanded to second-order series for avoiding error items relevant to variance. The failure life expectation under random variable load is smaller than that under constant load.
Originality/value
The time-dependent reliability method of harmonic drive is firstly proposed under constant and variable load. The transient FEA of harmonic drive is established to calculate the stress for strength analysis. The accelerated life test of harmonic drive is conducted for degradation parameters estimation. The adjustment factor is added to the residual strength model for strength degradation under different loads.
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Yogesh Fulpagare, Yogendra Joshi and Atul Bhargav
The paper aims to capture the rack-level thermal dynamics in data center. It proposes the rack-level response experiments as well as transient Computational Fluid Dynamics (CFD…
Abstract
Purpose
The paper aims to capture the rack-level thermal dynamics in data center. It proposes the rack-level response experiments as well as transient Computational Fluid Dynamics (CFD) analysis to characterize the local thermal environment of the system.
Design/methodology/approach
A single sever simulator rack and its two neighboring racks with its cold and hot aisle containment have been modeled with known cold air supply temperature and flow rate for transient CFD analysis. The heat load was kept constant initially and varied case-to-case basis, which includes capturing the rack-level response with respect to changes in input. However, the response experiments on simulator rack were performed for 14 h by variation of server heat loads as step and ramp input.
Findings
The paper provides the detailed transient CFD analysis of data center racks. The local cold air flow rates and temperature at the vicinity of the racks showed significant effect due to changes in input. It was concluded that the rack-level dynamics impacts the thermal environment of data center and hence cannot be ignored.
Research limitations/implications
The high computing devices and faster internet demands have led to major thermal management concerns for data center operators. To tackle this issue, capturing the system thermal dynamics is imperative. However, the system-level CFD analysis is computationally expensive. Therefore, this paper deals with the rack-level transient CFD study using commercial tool STAR CCM+.
Practical implications
This paper includes the modeling of the servers as a porous media as well as the multigrid method to enhance the computational speed. The successful implementation of this approach validated through experiments. This would help to establish a base for research in any type of data center.
Originality/value
This paper provides the porous media approach to model servers and multigrid method to enhance the computational speed. At the same time, the thought of characterizing the local dynamics at the vicinity of data center racks is unique.
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Thomas Gernay and Mohamed Salah Dimia
The paper aims to give an insight into the behaviour of reinforced concrete columns during and after the cooling phase of a fire. The study is based on numerical simulations as…
Abstract
Purpose
The paper aims to give an insight into the behaviour of reinforced concrete columns during and after the cooling phase of a fire. The study is based on numerical simulations as these tools are frequently used in structural engineering. As the reliability of numerical analysis largely depends on the validity of the constitutive models, the development of a concrete model suitable for natural fire analysis is addressed in the study.
Design/methodology/approach
The paper proposes theoretical considerations supported by numerical examples to discuss the capabilities and limitations of different classes of concrete models and eventually to develop a new concrete model that meets the requirements in case of natural fire analysis. Then, the study performs numerical simulations of concrete columns subjected to natural fire using the new concrete model. A parametric analysis allows for determining the main factors that affect the structural behaviour in cooling.
Findings
Failure of concrete columns during and after the cooling phase of a fire is a possible event. The most critical situations with respect to delayed failure arise for short fires and for columns with low slenderness or massive sections. The concrete model used in the simulations is of prime importance and the use of the Eurocode model would lead to unsafe results.
Practical implications
The paper includes implications for the assessment of the fire resistance of concrete elements in a performance‐based environment.
Originality/value
The paper provides original information about the risk of structural collapse during cooling.
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Casimiro Álvarez‐Mariño, Xose M. Lopez‐Fernandez, Antonio J.M. Jacomo Ramos, Ricardo A.F. Castro Lopes and José Miguel Duarte Couto
This paper aims to present and define a factor to assess the severity supported along transformer windings when the transformer is subjected to a transient voltage waveform due a…
Abstract
Purpose
This paper aims to present and define a factor to assess the severity supported along transformer windings when the transformer is subjected to a transient voltage waveform due a switching operation of a vacuum circuit breaker (VCB). This factor is identified as time domain severity factor (TDSF).
Design/methodology/approach
Since each of switching waveforms depend on the electrical interaction between transformer and the VCB, it implies that each of those combinations is characterized by a TDSF. To obtain the TDSF implies to manage two different models of the transformer under consideration. Firstly, a terminal model (black box model) of the transformer is built to compute the switching waveform at transformer terminals during VCB operation. Then, a detailed model (white box model) of the transformer is used to compute the internal transient voltage distribution along transformer windings.
Findings
A practical application of a power system consisting of a real transformer connected to a VCB is performed to show the sensibility of the TDSF coefficient.
Originality/value
Previous works found in the literature already consider the evaluation of the overvoltages in transformer associated to switching transient by coefficients, such as the frequency domain severity factor (FDSF). But this factor, as a global coefficient, could not assess the severity along windings to localize dielectrically weak points. Therefore, this paper overcomes this limitation proposing an alternative coefficient identified as time domain severity factor (TDSF).
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Discusses the 27 papers in ISEF 1999 Proceedings on the subject of electromagnetisms. States the groups of papers cover such subjects within the discipline as: induction machines;…
Abstract
Discusses the 27 papers in ISEF 1999 Proceedings on the subject of electromagnetisms. States the groups of papers cover such subjects within the discipline as: induction machines; reluctance motors; PM motors; transformers and reactors; and special problems and applications. Debates all of these in great detail and itemizes each with greater in‐depth discussion of the various technical applications and areas. Concludes that the recommendations made should be adhered to.
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Yogendra Joshi, Banafsheh Barabadi, Rajat Ghosh, Zhimin Wan, He Xiao, Sudhakar Yalamanchili and Satish Kumar
Information technology (IT) systems are already ubiquitous, and their future growth is expected to drive the global economy for the next several decades. However, energy…
Abstract
Purpose
Information technology (IT) systems are already ubiquitous, and their future growth is expected to drive the global economy for the next several decades. However, energy consumption by these systems is growing rapidly, and their sustained growth requires curbing the energy consumption, and the associated heat removal requirements. Currently, 20-50 percent of the incoming electrical power is used to meet the cooling demands of IT facilities. Careful co-optimization of electrical power and thermal management is essential for reducing energy consumption requirements of IT equipment. Such modeling based co-optimization is complicated by the presence of several decades of spatial and temporal scales. The purpose of this paper is to review recent approaches for handling these challenges.
Design/methodology/approach
In this paper, the authors illustrate the challenges and possible modeling approaches by considering three examples. The multi-scale modeling of chip level transient heating using a combination of Progressive Zoom-in, and proper orthogonal decomposition (POD) is an effective approach for chip level electrical/thermal co-design for mitigation of reliability concerns, such as Joule heating driven electromigration. In the second example, the authors will illustrate the optimal microfluidic thermal management of hot spots, and large background heat fluxes associated with future high-performance microprocessors. In the third example, data center facility level energy usage reduction through a transient measurements based POD modeling framework will be illustrated.
Findings
Through modeling based electrical/thermal co-design, dramatic savings in energy usage for cooling are possible.
Originality/value
The multi-scale nature of the thermal modeling of IT systems is an important challenge. This paper reviews some of the approaches employed to meet this challenge.
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Hongbin Mu, Wei Wei, Alexandrina Untaroiu and Qingdong Yan
Traditional three-dimensional numerical methods require a long time for transient computational fluid dynamics simulation on oil-filling process of hydrodynamic braking. The…
Abstract
Purpose
Traditional three-dimensional numerical methods require a long time for transient computational fluid dynamics simulation on oil-filling process of hydrodynamic braking. The purpose of this paper is to investigate reconstruction and prediction methods for the pressure field on blade surfaces to explore an accurate and rapid numerical method to solve transient internal flow in a hydrodynamic retarder.
Design/methodology/approach
Dynamic braking performance for the oil-filling process was simulated and validated using experimental results. With the proper orthogonal decomposition (POD) method, the dominant modes of transient pressure distribution on blades were extracted using their spatio-temporal structural features from the knowledge of computed flow data. Pressure field on blades was reconstructed. Based on the approximate model (AM), transient pressure field on blades was predicted in combination with POD. The causes of reconstruction and prediction error were, respectively, analyzed.
Findings
Results show that reconstruction with only a few dominant POD modes could represent all flow samples with high accuracy. POD method demonstrates an efficient simplification for accurate prediction of the instantaneous variation of pressure field in a hydrodynamic retarder, especially at the stage of high oil-filling rate.
Originality/value
The paper presents a novel numerical method, which combines POD and AM approaches for rapid and accurate prediction of braking characteristics during the oil-filling period, based on the knowledge of computed flow data.
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