Transient State Analyses Research Articles

Estimation of the Frequency-Dependent Parameters of Transmission Lines by Using Synchronized Measurements

Transmission line parameters are usually calculated based on technical and environmental approximations, e.g. line height, cable conductivity, etc. These characteristics vary depending on the environment and technical issues, meaning that the transmission line should be considered as a dynamic system with time-varying parameters. Estimation methods are a useful way to determine line parameters taken into account such characteristics. Most methods estimate these parameters at 50 ~ 60 Hz, useful for steady state analysis. However, for transient state or harmonic distortion analyses, a frequency range should be estimated, which varies according to the phenomenon to be investigated. In this matter, considering the gap existent of studies to estimate frequency-dependent parameters, we propose an efficacious and simplified method based on the two-port line representation and the well-known least squares method to estimate these parameters of a transmission line with 400 km length, considering a minimum number of synchronized measurements from 1 Hz up to 250 Hz.

Investigation of using pumpkin seed oil methyl ester as a fuel in a boron coated diesel engine

In this study, pumpkin seed oil was converted into biodiesel using alkali-catalyzed transesterification. Physicochemical properties were examined based on ASTM standards and compared with commercial diesel fuel (D-2). To improve the performance of engine, combustion chamber components like piston head, cylinder liner, intake and exhaust valves were thermally coated. Boronizing method was applied for the first time in the coating of conventional cast iron cylinder liner surface to reduce heat transfer. 150 μm thick Fe2B layer was deposited on the surfaces. So, the conventional engine was converted into low heat rejection engine. In order to determine the insulation affect of Fe2B layer, 3-D finite element transient-state analyses were done to the both coated and standard cylinders. D-2 and PSME fuel blends were used as test fuels. Emission and performance of the coated engine (CE) have been investigated for both fuels. CE showed lower emission and higher performance. For D-2 and B-20 fuels; results showed that, CO decreased by 13–15%, HC decreased by 53–36%, smoke density decreased by 15–36%, respectively. But NOx emission increased by 11–37% for D-2/B-20 fuels, respectively. Besides, BTE for D-2/B-20 fuel increased by 10-10% while BSEC decreased by 3–9%, respectively.

Steady and Transient State Analyses on Conjugate Laminar Forced Convection Heat Transfer

The term ‘conjugate heat transfer’ refers to a heat transfer process involving an interaction of heat conduction within a solid body with either of the free, forced, and mixed convection from its surface to a fluid flowing over it. It finds application in numerous fields starting from thermal interaction between surrounding air and fins to thermal interaction between flowing fluid and turbine blades. In this article, a systematic literature review of studies pertinent to laminar conjugate conduction-forced convection heat transfer analysis subjected to internal and external flow conditions is performed. The review reports both steady and unsteady state analyses related to experimental, analytical and numerical investigations, in both rectangular and cylindrical geometries with an exemption to micro and mini channel related studies. The studies are categorically put forth initially and an overview of these studies is presented in tabular and graphical form for a swift glance later under each section. This paper is concluded highlighting the salient features of the review, with respect to physical and mathematical models, methodology and applications. The challenges and scope for future study reported at the end of this paper gives the reader an insight into the gaps in the area of conjugate heat transfer analysis of steady and transient state under laminar forced convection flow regimes.

Comparative performance and emission characteristics of peanut seed oil methyl ester (PSME) on a thermal isolated diesel engine

In this research, cylinder liners of a diesel engine were coated with a 150 μm thick Fe2B layer using boronizing method. The upper surface of the piston was coated with a 300 μm thick CoNiCrAlYttra + NiCrBSi layer by using plasma spraying method. D-2, biodiesel (PSME-100) and blend (PSME-50) were used as test fuels. PSME fuel was produced through alkali catalyzed transesterification method. As-prepared fuels were used separately in coated (CE) and standard engines (SE) to compare performance and exhaust emission of both engines. In order to see the isolation effect of Fe2B layer, 3-D finite element transient-state analyses were carried out. According to the results, brake thermal efficiency (BTE) and exhaust gas temperature (EGT) of coated engine were considerably enhanced while brake specific fuel consumption (BSFC), CO, HC and smoke emission were decreased compared to those of standard engine. However, NOx emission of CE was higher than that of uncoated one, which was attributed to high combustion temperature and long combustion process in CE. These results were further confirmed with finite element simulation. The decreasing BSFC and increasing BTE for coated engine has been attributed to the elevated temperature of the combustion chamber by the effect of thermal insulation.

Bridge-arm current reduction in DC-AC inverter

ABSTRACTWhen building single-phase inverter with power Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), switching action may cause poor reverse recovery characteristic due to body parasitic diode of MOSFET, which can produce peak current in the circuit loop and the high transient voltage and current (dv/dt, di/dt) during the turning-on period. In this article, a novel method to reduce the bridge arm current spike in DC-AC inverter is proposed. The presented method uses the improved and simplified coupled inductor which is connected between the upper and lower power devices. The parasitic capacitors of MOSFET are charged and discharged by the coupled inductor and the energy is released in the new loop; therefore, the bridge peak current is diminished. The time-domain model of transient-state analyses is given in detail. The current spike of the main switch is clamped efficiently. By increasing switching frequency, the volume of the magnetic core can be further reduced which is resulted from reduction in the reverse recovery current in parasitic diode. Because of the suppression of the spike current via the device, the switch-on loss of the power loss is reduced, and low on-state resistor of the power device can be adopted to suppress the conduction loss. The proposed approaches are validated with experimental results.

Steady- and Transient-State Analyses of Fully Ceramic Microencapsulated Fuel with Randomly Dispersed Tristructural Isotropic Particles via Two-Temperature Homogenized Model—II: Applications by Coupling with COREDAX

In Part I of this paper, the two-temperature homogenized model for the fully ceramic microencapsulated fuel, in which tristructural isotropic particles are randomly dispersed in a fine lattice stochastic structure, was discussed. In this model, the fuel-kernel and silicon carbide matrix temperatures are distinguished. Moreover, the obtained temperature profiles are more realistic than those obtained using other models. Using the temperature-dependent thermal conductivities of uranium nitride and the silicon carbide matrix, temperature-dependent homogenized parameters were obtained. In Part II of the paper, coupled with the COREDAX code, a reactor core loaded by fully ceramic microencapsulated fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure is analyzed via a two-temperature homogenized model at steady and transient states. The results are compared with those from harmonic- and volumetric-average thermal conductivity models; i.e., we compare keff eigenvalues, power distributions, and temperature profiles in the hottest single channel at a steady state. At transient states, we compare total power, average energy deposition, and maximum temperatures in the hottest single channel obtained by the different thermal analysis models. The different thermal analysis models and the availability of fuel-kernel temperatures in the two-temperature homogenized model for Doppler temperature feedback lead to significant differences.

Wavelet Transform - A New Tool for Analysis of Harmonics in Power Systems

This paper presents a review of application of discrete wavelet transform in power system transient analyses. Based on the discrete time domain approximation, the system components such as resistor and inductor are modeled respectively in discrete wavelet domain for the purpose of transient and steady state analyses. Numerical results for transient inductor model can be implemented by any kind of power system including normal and emergency operating modes.

Numerical Modelling of Prestresssing Steel Tendons under Fire and Post-Fire Conditions

The behaviour of prestressing steel tendons under fire and post-fire conditions is investigated numerically employing the ABAQUS package and its user-defined material subroutine UMAT which allows comprehensive constitutive relationships to be implemented. Based on an existing thermal creep model, a new set of parameters are proposed and calibrated against available test results in the literature. The proposed numerical model is versatile in predicting thermal creep, isothermal response and transient thermal relaxation of prestressing steel tendons. Moreover, parametric studies are conducted to investigate the effects of heating rate, heated length ratio, initial stress and various boundary conditions on the thermal relaxation of prestressing steel tendons. Besides, transient state analyses are carried out with constant heating rate and initial stress to investigate the rupture properties of prestressing steel tendons.

Forced convection through open cell foams based on homogenization approach: Transient analysis

Thermal transportation in case of open cell foams is a complex process that comprises of all the modes of heat transfer. In macroscopic numerical models the key parameters that govern these modes of heat transfer are stagnant effective thermal conductivity, ke, dispersion conductivity, kd, effective radiative conductivity, kr and volumetric heat transfer coefficient, hv. The purpose of this study is to determine these key parameters for the forced convection of air through open cell alumina foams. It is achieved by performing two different types of experiments on alumina foams having different PPI number (10, 20 and 30) and porosity (0.79–0.87). The first sets of experiments are based on the transient heat transfer and the aim of performing these experiments is to determine the volumetric heat transfer coefficient, hv. The second sets of experiments are based on the steady state heat transfer and they are the outcome of our previous study. The aim of implementing steady state experiments is to determine dispersion conductivity, kd by supplying the values of hv as an input parameter from the transient analysis. Further, to supply effective thermal conductivity data to both transient and steady state analyses, the Kelvin cell model is implemented. The findings of this study exhibit that the convection heat transfer in case of transient analysis and the thermal dispersion in case of steady state analysis are the dominant modes of heat transfer. Further, this study reveals that by employing the proposed combined analysis, it is possible to predict the values of key parameters rather accurately. But still, the accuracy of the results predicted through the macroscopic models largely depends on the accuracy of the experiments.

Spray combustion of Jet-A and diesel fuels in a constant volume combustion chamber

This work investigates the spray combustion of Jet-A fuel in an optical constant-volume combustion chamber under different ambient initial conditions. Ambient temperature was varied at 800K, 1000K, and 1200K and five different ambient O2 concentrations were used, spanning 10–21%. These ambient conditions can be used to mimic practical diesel engine working conditions under different fuel injection timings and exhaust gas recirculation (EGR) levels. Both transient and quasi-steady state analyses were conducted. The transient analysis focused on the flame development from the beginning to the end of the combustion process, illustrating how the flame structure evolves with time. The quasi-steady state analysis concentrated on the stable flame structure and compared the flame emissions in terms of spatially integrated intensity, flame effective area, and intensity per pixel. The transient analysis was based on measurements using high-speed imaging of both OH∗ chemiluminescence and broadband natural luminosity (NL). For the quasi-steady state analysis, three flame narrow-band emissions (OH∗ at 310nm, Band A at 430nm and Band B at 470nm) were captured using an ICCD camera. Based on the current Jet-A data and diesel data obtained from previous experiments, a comparison between Jet-A and diesel was made in terms of flame development during the transient state and spatially integrated intensity, flame effective area, and intensity per pixel during the quasi-steady state. For the transient results, Jet-A shares a similar flame development trend to diesel, but featuring a narrower region of NL and a wider region of OH∗ with the increase of ambient temperature and O2 concentration. The soot cloud is oxidized more quickly for Jet-A than diesel at the end of combustion, evident by comparing the area of NL, especially under high O2 concentration. The quasi-steady state results suggest that soot is oxidized effectively under high O2 concentration conditions by the wider region of OH∗ in the downstream locations where only OH∗ emission is observed. The intensity of OH∗ is higher for Jet-A than diesel under low O2 concentration but lower under high O2 concentration. The intensity of NL is higher for Jet-A for all the conditions investigated. However, the intensities of Band A and Band B are lower for Jet-A for all these conditions. Based on the imaging of multiple-band flame emissions, the spray flame structures were further analyzed for the two fuels under both low temperature and conventional combustion modes. Conceptual flame structures were proposed to complement the previous conceptual models for spray combustion under different combustion modes.

Steady- and transient-state analyses of fully ceramic microencapsulated fuel loaded reactor core via two-temperature homogenized thermal-conductivity model

Fully ceramic microencapsulated (FCM) fuel, a type of accident-tolerant fuel (ATF), consists of TRISO particles randomly dispersed in a SiC matrix. In this study, for a thermal analysis of the FCM fuel with such a high heterogeneity, a two-temperature homogenized thermal-conductivity model was applied by the authors. This model provides separate temperatures for the fuel-kernels and the SiC matrix. It also provides more realistic temperature profiles than those of harmonic- and volumetric-average thermal conductivity models, which are used for thermal analysis of a fuel element in VHTRs having a composition similar to the FCM fuel, because such models are unable to provide the fuel-kernel and graphite matrix temperatures separately.In this study, coupled with a neutron diffusion model, a FCM fuel-loaded reactor core is analyzed via a two-temperature homogenized thermal-conductivity model at steady- and transient-states. The results are compared to those from harmonic- and volumetric-average thermal conductivity models, i.e., we compare keff eigenvalues, power distributions, and temperature profiles in the hottest single-channel at steady-state. At transient-state, we compare total powers, reactivity, and maximum temperatures in the hottest single-channel obtained by the different thermal analysis models. The different thermal analysis models and the availability of fuel-kernel temperatures in the two-temperature homogenized thermal-conductivity model for Doppler temperature feedback cause significant differences as revealed by comparisons.

Numerical modelling of load bearing light gauge steel frame wall systems exposed to realistic design fires

Fire safety has become an important part in structural design due to the ever increasing loss of properties and lives during fires. Conventionally the fire rating of load bearing wall systems made of Light gauge Steel Frames (LSF) is determined using fire tests based on the standard time–temperature curve in ISO834 (ISO 834-1, 1999 [1]). However, modern commercial and residential buildings make use of thermoplastic materials, which mean considerably high fuel loads. Hence a detailed fire research study into the fire performance of LSF walls was undertaken using realistic design fire curves developed based on Eurocode parametric (ENV 1991-1-2, 2002 [2]) and Barnett's BFD (Barnett, 2002 [3]) curves using both full scale fire tests and numerical studies. It included LSF walls without cavity insulation, and the recently developed externally insulated composite panel system. This paper presents the details of finite element models developed to simulate the full scale fire tests of LSF wall panels under realistic design fires. Finite element models of LSF walls exposed to realistic design fires were developed, and analysed under both transient and steady state fire conditions using the measured stud time–temperature curves. Transient state analyses were performed to simulate fire test conditions while steady state analyses were performed to obtain the load ratio versus time and failure temperature curves of LSF walls. Details of the developed finite element models and the results including the axial deformation and lateral deflection versus time curves, and the stud failure modes and times are presented in this paper. Comparison with fire test results demonstrate the ability of developed finite element models to predict the performance and fire resistance ratings of LSF walls under realistic design fires.

Study of the Properties of Impulse-Like Pulses in Finite-Difference Time-Domain Simulation of Grounded-Dielectric-Slab-Like Microstrips

The study of nine different voltage pulses (exponential, rectangular, unit step, trapezoidal, logarithmic, triangular, quadratic, gaussian, and tangential), which approximate the unit impulse or dirac delta in finite difference time-domain (fdtd) simulation of grounded dielectric slab-like microstrips, was carried out in order to know how each one behaves when transient and steady state analyses are considered. All these pulses lead to almost identical responses (except the unit step) in the frequency regime but to very different performances in the time regime. The convenience of use one pulse instead of other is dicussed on the context of specific applications.

Calculation method of convective heat transfer coefficients for thermal simulation of a spindle system based on RBF neural network

Results from the temperature field and thermal deformation simulation of a spindle system are greatly affected by the accuracy of convective heat transfer coefficients (CHTCs). This paper presents a new method based on radial basis function (RBF) neural network to calculate CHTCs. First, the temperature field and thermal deformations of a spindle system were obtained by experimental and finite-element (FE) methods. However, the simulation results are significantly different from the experimental results because boundary conditions used for the FE model were derived empirically. Second, the relationship between the simulated temperature values and CHTCs were established by a RBF neural network. Using the experimental temperature values as an input vector of the RBF neural network, CHTCs of the spindle system can be predicted through an iterative calculation taking 14 cycles. Finally, the effectiveness of the proposed method was proved using steady-state and transient-state analyses of the spindle system. Results from the steady-state simulation show that temperature errors were less than 4 % at the seven thermal-critical points and deformation errors in the three directions were less than 6 %. Results from the transient-state simulation of the spindle system show that the variations for each of the thermal characteristics are in good agreement with the experimental results. The method provides guidance for modifying boundary conditions of a FE model.

Stability Augmentation of Wind Farm using Variable Speed Permanent Magnet Synchronous Generator

This paper presents a new control strategy of variable speed permanent magnet wind generator for stability augmentation of wind farm including fixed speed wind turbine with Induction Generator (IG). A new control scheme is developed for two levels back-to-back converters of Permanent Magnet Synchronous Generator (PMSG), by which both active and reactive powers delivered to the grid can be controlled easily. To avoid the converter damage, the DC link protection controller is also proposed in order to protect the dc link circuit during fault condition. To evaluate the control capability of the proposed controllers, simulations are performed on two model systems composed of wind farms connected to an infinite bus. From transient and steady state analyses by using PSCAD/EMTDC, it is concluded that the proposed control scheme is very effective to improve the stability of wind farm for severe network disturbance and randomly fluctuating wind speed.

Simulation of fuel behaviour during aircraft in‐flight refueling

PurposeIn‐flight refueling is one of the most important technologies developed in military aviation. The purpose of this paper is to analyze the dynamic behaviour of fuel during a refuel process by means of an internal flow analysis software program.Design/methodology/approachThe dynamic behaviour of fuel during a refuel process is analyzed by means of an internal flow analysis software program called Flowmaster. The refueling system is analyzed by representing physical components as flow resistances and control volumes and calculating the flow rates and pressures along the system. Both steady and transient state analyses are performed to identify the locations where high‐pressure surges are likely. The peak pressures are compared to allowable proof pressures of system components to ensure that they are not exceeded.FindingsIt was found that a transient analysis of the fuel behaviour in the refuel pod system for a complete refueling process can be completed successfully with Flowmaster software.Originality/valueThe paper models a complete refueling process with the sequence of trail, fuel transfer and rewind phase in order to analyse the fuel‐transient behaviour, in particular near to the times where the valves are activated.

Laboratory longitudinal diffusion tests: 1. Dimensionless formulations and validity of simplified solutions

To obtain reliable diffusion parameters for diffusion testing, multiple experiments should not only be cross-checked but the internal consistency of each experiment should also be verified. In the through- and in-diffusion tests with solution reservoirs, test interpretation of different phases often makes use of simplified analytical solutions. This study explores the feasibility of steady, quasi-steady, equilibrium and transient-state analyses using simplified analytical solutions with respect to (i) valid conditions for each analytical solution, (ii) potential error, and (iii) experimental time. For increased generality, a series of numerical analyses are performed using unified dimensionless parameters and the results are all related to dimensionless reservoir volume (DRV) which includes only the sorptive parameter as an unknown. This means the above factors can be investigated on the basis of the sorption properties of the testing material and/or tracer. The main findings are that steady, quasi-steady and equilibrium-state analyses are applicable when the tracer is not highly sorptive. However, quasi-steady and equilibrium-state analyses become inefficient or impractical compared to steady state analysis when the tracer is non-sorbing and material porosity is significantly low. Systematic and comprehensive reformulation of analytical models enables the comparison of experimental times between different test methods. The applicability and potential error of each test interpretation can also be studied. These can be applied in designing, performing, and interpreting diffusion experiments by deducing DRV from the available information for the target material and tracer, combined with the results of this study.

Water diffusion coefficients during copper electropolishing

Cu electropolishing was studied using a rotating disc electrode in a variety of phosphoric acid-based electrolytes, including several with ethanol and other species added as diluents. Diluents allow a wider range of water concentrations and electrolyte viscosities to be accessed and also reduce the removal rate during Cu electropolishing, simplifying possible application to damascene processing. Transient and steady state currents in the mass transfer limited regime are shown to depend on both the number of water acceptor molecules associated with each dissolving Cu ion and on the effective diffusion coefficient of water. Transient analysis samples the bulk transport properties, whereas steady state analysis integrates them through the diffusion layer. Assuming that the effective diffusion coefficients appropriate to transient and steady state behavior are the same, about one water molecule is associated with each dissolving Cu ion. This analysis yields effective diffusion coefficients for water on the order of 10−9cm2s−1. However, the data is also consistent with an assumption that six water molecules are associated with each dissolving Cu ion, but the effective diffusion coefficient appropriate for a Levich analysis is somewhat lower than that in the bulk electrolyte. This analysis yields effective diffusion coefficients for water on the order of 10−8–10−7cm2s−1. The latter interpretation, that six water molecules are associated with each dissolving Cu ion, appears more likely since it provides almost exact agreement with the effective diffusion coefficient reported previously by Vidal and West. In combination with previously published impedance results ruling out a salt film mechanism, the good agreement between the transient and steady state analyses confirm that water is the acceptor species that complexes dissolving Cu ions in phosphoric acid-based electropolishing baths.

Steady-state and transient-state analyses of aerobic fermentation in

Steady-state and transient-state analyses of aerobic fermentation in

Matching objective and subjective information in groundwater inverse analysis by Akaike's Bayesian information criterion

In order to overcome the illposedness of groundwater inverse analysis it is inevitable to introduce prior information of some form and thus Bayesian statistics. One of the essential problems in Bayesian inverse formulation is the optimum matching between the objective information (i.e., the observation) and the subjective information (i.e., the prior information). In this study, Akaike's Bayesian Information Criterion (ABIC) is introduced to overcome this problem. ABIC is also effective in the model identification problem, and this aspect is also emphasized. The effectiveness of the method is illustrated by analyses on an actual aquifer system. Both steady and transient state analyses are carried out. The paper also provides the background of ABIC in some detail.