Search

This article showcases the development of a dynamic Arbitrary Lagrangian Eulerian (ALE) formulation to account for inelastic material models within a finite element framework. Such a formulation is commonly utilized in research domains like fluid mechanics, fluid‐structure interaction, quasi static remeshing techniques, and quasi static load movement. The work at hand describes the application of the ALE formulation to efficiently analyse structures subjected to moving loads in the field of transient inelastic solid mechanics. In particular, structures such as pavements, gantry crane girders etc., which are subjected to moving loads, can be numerically simulated, and their transient response in the relevant region around the load can be obtained without relying on moving loads. The focus of this article is to facilitate the treatment of history variables stemming from inelastic material models. Of particular interest is the advection procedure required to transport the history variables through the mesh, as the material appears to flow through it. The mathematical framework necessary to treat this advection process is described in detail, considering a nonlinear viscoelastic material model on a neo‐Hookean base at finite deformations. Then, four methods for numerically achieving the advection are implemented within a transient finite element ALE formulation. These methods are compared against each other, and additionally with the conventional Lagrangian method for validation. The results demonstrate satisfactory agreement with conventional simulation methods, while offering a significant improvement in terms of computation speed. With the work at hand, the dynamic response of inelastic materials subjected to moving loads can be numerically simulated in a computationally efficient manner. [ABSTRACT FROM AUTHOR]

AbstractRecent interest in molten salt reactors (MSRs) has initiated research projects on their safety and performance compared to light water reactors. Maintaining the fuel salt in a molten state during reactor operation at all power levels is a significant safety concern for these reactors. Various strategies can be used to maintain the fuel salt temperature above its melting point during low-power reactor operation. This study analyzed the impact of using electric heaters on the stability and performance of an operating MSR. For this purpose, a simulation tool was developed for reactor dynamics and stability analysis studies. The simulation tool was validated against the Molten Salt Reactor Experiment reactivity insertion tests. The dynamics of an MSR with and without operating electric heaters at steady state and following initiated transients were investigated and compared. Simulation results showed that the usage of these heaters is more pronounced during transients rather than in the steady-state operation. The stability of the system degraded following transients due to the operation of heaters. However, using heaters remains an alternative strategy to maintain fuel salt molten at low power levels. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic-phasor-based, average-value modeling method for power systems with extensive converter-tied subsystems. In the proposed approach, the overall system model is constructed using modular functions, interfacing both conventional and converter-tied resources. Model validation is performed against detailed Electro-Magnetic Transient (EMT) simulations. The analytical capabilities offered by the proposed modeling method are demonstrated on a modified IEEE 9-bus system. A Graphics Processing Unit (GPU)-based parallel computing approach for the solution of the resulting model is presented and exemplified on a modified IEEE 118-bus system, showing significant improvements in computing efficiency over EMT solvers. A co-simulation approach using a Central Processing Unit (CPU) and a GPU is also presented and exemplified using a modified version of the IEEE 118-bus system, demonstrating the model's parallelization. [ABSTRACT FROM AUTHOR]

• Development of a thermal power dispatch (TPD) system to transfer thermal energy from boiling water reactors to hydrogen plants. • TPD system heat exchangers designed with Aspen Exchanger Design and Rating software. • System thermal hydraulics analysis of TPD using Simulink Simscape. • TPD system performance assessed for both transient and steady state operations. Nuclear power plants are crucial to meeting net zero emission goals and achieving energy sustainability. Integrating these plants with clean energy technologies such as high-temperature steam electrolysis (HTSE) may improve the efficiency and economic competitiveness of these plants. The current study investigates the design and operation of a thermal power dispatch (TPD) system for coupling boiling water reactors (BWRs) to HTSE plants. The TPD system extracts a portion of the steam from the reactor's main steam line and transfers its thermal energy to an HTSE plant through a power transport loop. A TPD system for 5 % steam extraction has been designed and the system performance during steady and transient operations has been analyzed. The TPD system dispatched a total of 197 MW thermal energy to the HTSE plant under nominal design conditions. Saturated steam at 7.17 MPa from the BWR plant was condensed and subcooled to a temperature of 168 °C, while a mass flow rate of 91.1 kg/s of superheated steam was dispatched to the HTSE plant. Furthermore, the system performance during transient operation showed a continuous transition from the initial hot standby mode to the nominal power dispatch level. The transient simulation results emphasized the importance of investigating component level performance for the TPD system design. The current results will guide future works on the development of integrated energy systems for hydrogen production or process heat applications. [ABSTRACT FROM AUTHOR]

As a new generation of reactor type, lead-cooled fast reactors, have better safety behaviors, higher reliability, and better economic performance, aiming at island power supply through nuclear energy, seawater desalination, optimization of nuclear submarines, etc. Its evolution of nuclear waste and the advantages of nuclear non-proliferation provide a good prospect for development. This paper studied the safety performances of an offshore stationary lead-cooled reactor (OSLR) proposed in the National Key Research and Development Program of China. The transient analysis code SAS4A/SASSYS-1 was used to perform simulations of unprotected over-power accidents (UTOP) and unprotected loss of heat sink (ULOHS) accidents. The results indicated that offshore stationary lead-cooled reactors can withstand a maximum positive reactivity insertion of 0.5$ within 1 s during UTOP accidents without exceeding the working limits of the core. In ULOHS accidents, the inherent safety characteristics of OSLR allowed it to withstand 75 % heat removal capability of IHX. The simulation results were used to analyze the response of this stationary offshore reactor to transient accident conditions and the limits of its ability to withstand accidents in order to provide reference data for subsequent design and ideas for possible development of natural cycle lead-cooled reactors in the future. [ABSTRACT FROM AUTHOR]

• The CO 2 /propane mixtures are used for PCHE applied in supercritical Brayton cycle. • Various transient scenarios of the mixture-mixture PCHE are numerically investigated. • The mixtures exhibit lower pressure loss and higher heat transfer coefficient in the PCHE. • The mixtures are helpful for parameter stabilization and equilibrium time reduction. CO 2 /propane mixtures benefit the safe operation of the supercritical Brayton cycle while improving economic efficiency and mitigating environmental impact. Due to the intermittency of energy resources, understanding the dynamic characteristics of the supercritical mixture Brayton cycle is essential. The transition time of the cycle depends on the total time of the unsteady-state heat transfer. As a typical heat exchanger, the transient analysis of the printed circuit heat exchanger (PCHE) is necessary and significant. In this paper, the dynamic response of the straight PCHE in the supercritical CO 2 /propane mixture Brayton cycle is thoroughly studied. First, the dynamic behavior of the mixture-mixture PCHE is analyzed when the inlet temperature or mass flow rate abruptly changes. Furthermore, the equilibrium times of the mixture-mixture PCHE under different disturbances are compared. CO 2 /propane mixtures are more favorable for the stability of the parameters (outlet temperature and pressure drop). The mixture-mixture PCHE exhibits better flow and heat transfer properties than the CO 2 CO 2 PCHE. Compared to CO 2 , CO 2 /propane mixtures could reduce the equilibrium time by more than 32 % when the molar fraction of propane is equal to 0.5. However, the outlet temperature of the mixtures in the hot channel is higher than that of CO 2 , because the energy is not fully utilized. [ABSTRACT FROM AUTHOR]

The low-frequency evolution of Indian rainfall mean-state and associated interannual-to-decadal variability is discussed for the last 6000 years from a multi-configuration ensemble of fully coupled global transient simulations. This period is marked by a shift of Indian Summer Monsoon Rainfall (ISMR) distribution towards drier conditions, including extremes, and a contraction of the rainy season. The drying is larger in simulations with higher horizontal resolution of the atmosphere and revised land surface hydrology. Vegetation–climate interactions and the way runoff is routed to ocean modulate the timing of the monsoon onset but have negligible effects on the evolution of seasonal rainfall amounts in our modeling framework in which carbon cycling is always active. This drying trend is accompanied by changes in ISMR interannual-to-decadal variability decreasing over north and south India but increasing over central India (20°–25° N). The ISMR interannual-to-decadal variability is decomposed into six physically consistent regimes using a clustering technique to further characterize its changes and associated teleconnections. From 6 to 3.8 kyr bp, the century-to-century modulations in the frequency of occurrence associated to the regimes are asynchronous between the simulations. Orbitally-driven trends can only be detected for two regimes over the whole 6–0 kyr bp period. These two regimes reflect increased influence of ENSO on both ISMR and Indian Ocean Dipole as the inter-hemispheric energy gradient weakens. Severe long-term droughts are also shown to be a combination of long-term drying and internally generated low-frequency modulations of the interannual-to-decadal variability. [ABSTRACT FROM AUTHOR]

A numerical investigation of dynamic raceway formation in an industrial-scale blast furnace is performed using Computational Fluid Dynamics (CFD) coupled with a Discrete Element Method (DEM). The industrial-scale simulations are made feasible by incorporating the Flamelet Generated Manifold (FGM) method and a coarse-graining method to reduce the computational cost while ensuring effective modeling of gas phase combustion and a large number of solid particles, respectively. The model considers the interactions between pulverized coal (PC) and coke, as well as their interaction with gas. The simulations reveal a different size and shape of the physical and chemical raceway, indicating that not all crucial reactions occur within the physical raceway. According to the model, the physical raceway formation is primarily determined by the blast air momentum, and the PC combustion has a negligible effect on its dimensions. The chemical raceway formation heavily depends on the oxidation rate of coke. The utilization of PC is quantified in terms of burnout. Smaller PC particles are found to undergo a higher degree of burnout due to faster convective heating and oxidation rates. Modifying the angle of the PC injection lance in current configuration is found to be inconsequential to PC burnout. The presented results highlight the significance of enhancing PC-blast mixing to improve PC utilization and provide new insights into optimizing blast furnace operations. • A novel and comprehensive transient model describing the dynamics of raceway formation in an industrial-scale blast furnace. • Physical raceway and chemical raceway differ in size and shape, as well as the formation mechanism. • Accumulation of unburnt char within the coke channels, closely corresponding to the bird's nest formation. • Enhancing the mixing of pulverized coal and hot blast is crucial for improving PC utilization. [ABSTRACT FROM AUTHOR]

Given the substantial energy use for space cooling in buildings, integrating energy-efficient and sustainable cooling systems into buildings has become increasingly more important. Even though the cooling potential of a near-surface earth-to-air heat exchanger (EAHE) with grass cover was demonstrated in previous studies, the energy savings and environmental benefits resulting from using the EAHE have not yet been quantified. Therefore, in this study, we quantify the energy savings resulting from using a near-surface earth-to-air heat exchanger (EAHE) with grass-covered ground as a precooling unit in hot desert climates. The outlet air conditions of the EAHE during 9 months of the year (March to November), where space cooling is required, are predicted using a 3D transient CFD model, which is validated against field measurements. The EAHE is fabricated from a 1 mm thick aluminum tube with a diameter of 0.15 m and a length of 21.5 m, buried 0.4 m deep. The results showed that the EAHE can cool ambient air by up to 8.5 °C at an air flow rate of 607 m3/h, corresponding to a cooling capacity of 1700 W and a COP of 17. The daily average cooling capacity of the EAHE is about 560 W for an average operation period of 15.1 h per day. When used as a precooling unit for conventional cooling systems, the highest estimated monthly energy savings is 115 kWh, and the estimated annual savings is 741 kWh.

Back-to-back modular multilevel converter–high-voltage direct current (MMC–HVDC) can realise the asynchronous interconnection of two regional power grids. It can effectively solve the power grid stability problems caused by AC–DC power transfer and avoid the risk of large-scale blackouts. Existing MMC–HVDC modelling methods are usually based on Power Systems Computer Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC), immensely simplifying the AC system. The simplified model is incapable to reflect the interaction characteristics accurately. To solve this problem, a hybrid simulation model of an actual back-to-back MMC–HVDC system is built using Advanced Digital Power System Simulator (ADPSS). ADPSS is a software developed by China Electric Power Research Institute that can realise multi-time scale hybrid simulation to simulate the mutual coupling characteristics accurately. The model includes the electromagnetic transient simulation model of the DC system, and the control system is designed. Steady-state and transient simulations are carried out to verify its function. In summary, the study provides a better reference for the analysis and designing of the practical system.

Corona can be a major factor influencing the attenuation and deformation of switching surge transients. Experimental measurements of corona characteristics are needed for realistic simulations. This paper presents an experimental study of the corona characteristics of solid and stranded conductors under switching impulse voltages. The results include the corona inception voltage, the apparent change in the capacitance of the line conductor, a comparison of charge-voltage (Q-V) curves for positive and negative corona, and the effect of surface roughness. A theoretical corona model represented by an enlarged conductor diameter above inception voltage is proposed and compared with the experimental measurements. [ABSTRACT FROM AUTHOR]

Experimental and numerical investigations of the hygrothermal behaviour of cross laminated timber using the example of an exterior wall – Within the scope of the project "massive_living" in Graz (AT), sensors were installed within an external wall section in a solid wood construction with cross laminated timber and observed over a period of more than two years. Due to the hygroscopic behaviour of wood, the moisture content of the wood adapts to the surrounding climate (equilibrium moisture content). The wood moisture content has a significant influence on all mechanical, physical and chemical properties of wood. Therefore, the knowledge of wood moisture content is of great importance for the realisation of wooden structures. According to ÖNORM EN 1995‐1‐1‐1:2019 [1], load‐bearing timber components are divided into service classes with regard to the surrounding air, which have a significant influence on the verification in the limit states of load‐bearing capacity and serviceability. The question now arises as to which values the wood equilibrium moisture content of a building component can assume in the course of several years. The aim of this research project was to gain an understanding of the hygrothermal behaviour of a cross laminated timber wall (CLT wall) and then to compare the measurement data obtained with those from the simulations. The simulation results show a strong influence of the indoor conditions on the wood equilibrium moisture, whereby a good‐natured behaviour with regard to moisture buffering can also be observed at high moisture loads. In addition, further measurements showed a dependence of the relative air humidity on the room height, which should be taken into account in hygrothermal calculations (as for example in the area near the ceiling). [ABSTRACT FROM AUTHOR]

• Two-tier model reduction solves transient responses for linear viscoelastic models. • Tier-one model reduced with real modes linearized about various frequencies. • Tier-two model reduced with complex modes from nonlinear eigenvalue problem. • Demonstrated on a cantilevered sandwich plate structure at various temperatures. • Reduction scheme accurately and efficiently predicts transient response. Transient simulations of linear viscoelastically damped structures require excessive computational resources to directly integrate the full-order finite element model with time-stepping algorithms. Traditional modal reduction techniques are not directly applicable to these systems since viscoelastic materials depend on time and frequency. A more appropriate reduction basis is obtained from the nonlinear, complex eigenvalue problem, whose eigenvectors capture the appropriate kinematics and enable frequency-based mode selection; unfortunately, the computational cost is prohibitive for computing these modes from large-scale engineering models. To address this shortcoming, this work proposes a novel two-tier reduction procedure to reduce the upfront cost of solving the complex, nonlinear eigenvalue problem. The first reduction step reduces the full-order model with real mode shapes linearized about various centering frequencies to capture the kinematics over a full range of viscoelastic material behavior (glassy, rubbery, and glass-transition zones). This tier-one reduction preserves time-temperature superposition and allows the equations to depend parametrically on operating temperature. The second-level reduction then solves the complex, nonlinear eigenmode solutions in the tier-one reduced space about a fixed temperature to further reduce the equations-of-motion. The method is demonstrated on a cantilevered sandwich plate to showcase its accuracy and efficiency in comparison to full-order model predictions. [ABSTRACT FROM AUTHOR]

The results of a computational fluid dynamics (CFD) study of a three-bladed horizontal axis tidal turbine (HATT) using both quasi-steady and transient numerical approaches are presented. The wake from the turbine is studied numerically and compared to experimental results carried out by a French research group at IFREMER. All results provided incorporate the Reynolds Averaged Navier Stokes (RANS) Shear Stress Transport (SST) turbulence model. Simulations cover a range of tip speed ratios (TSR = 0.5–8) with a constant inflow velocity of 0.8 m/s. The resulting power and thrust coefficients, C p and C t , are compared to experimental results for validation purposes. The results show a good level of agreement with further discussions of differences addressed herein. In order to garner meaningful information on which numerical methods should be used for wake studies, two families of simulations are performed at TSR = 3.67, using either the frozen-rotor quasi-steady approach, or the fully transient one. For both approaches, near and far field wake propagation is investigated and discussed. Results from both series of simulations are compared to experimental ones. • Wake of a three-bladed HATT was simulated numerically using two approaches. • For quasi steady-state simulations, the frozen rotor approach was used. • Transient simulations were also performed using a complete transient-rotor approach. • The results from the transient approach are more physically accurate and compare well with experimental wake data. [ABSTRACT FROM AUTHOR]

Back-to-back modular multilevel converter–high-voltage direct current (MMC–HVDC) can realise the asynchronous interconnection of two regional power grids. It can effectively solve the power grid stability problems caused by AC–DC power transfer and avoid the risk of large-scale blackouts. Existing MMC–HVDC modelling methods are usually based on Power Systems Computer Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC), immensely simplifying the AC system. The simplified model is incapable to reflect the interaction characteristics accurately. To solve this problem, a hybrid simulation model of an actual back-to-back MMC–HVDC system is built using Advanced Digital Power System Simulator (ADPSS). ADPSS is a software developed by China Electric Power Research Institute that can realise multi-time scale hybrid simulation to simulate the mutual coupling characteristics accurately. The model includes the electromagnetic transient simulation model of the DC system, and the control system is designed. Steady-state and transient simulations are carried out to verify its function. In summary, the study provides a better reference for the analysis and designing of the practical system. [ABSTRACT FROM AUTHOR]

The presented paper aims to study the influence of mineral diesel fuel and synthetic Gas-To-Liquid fuel (GTL) on the injection process, fuel flow conditions, and cavitation formation in a modern common-rail injector. First, the influence on injection characteristics was studied experimentally using an injection system test bench, and numerically using the one-dimensional computational program. Afterward, the influence of fuel properties on internal fuel flow was studied numerically using a computational program. The flow inside the injector was considered as multiphase flow and was calculated through unsteady Computational Fluid Dynamics simulations using a Eulerian–Eulerian two-fluid approach. Finally, the influence of in-cylinder back pressure on the internal nozzle flow was studied at three distinctive back pressures. The obtained numerical results for injection characteristics show good agreement with the experimental ones. The results of 3D simulations indicate that differences in fuel properties influence internal fuel flow and cavitation inception. The location of cavitation formation is the same for both fuels. The cavitation formation is triggered regardless of fuel properties. The size of the cavitation area is influenced by fuel properties and also from in-cylinder back pressure. Higher values of back pressure induce smaller areas of cavitation and vice versa. Comparing the conditions at injection hole exit, diesel fuel proved slightly higher average mass flow rate and velocities, which can be attributed to differences in fluid densities and viscosities. Overall, the obtained results indicate that when considering the injection process and internal nozzle flow, GTL fuel can be used in common-rail injection systems with solenoid injectors.

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents simulations of stationary and transient (fault condition) regimes for a three-phase concentric HTS cable with and without a standalone superconducting fault current limiter (SFCL). The stationary study carried out previously to the transient analysis verifies the viability of the proposed cable design. The response of the HTS cable to fault currents by varying the thickness of copper stabilization layers is analyzed. As an option, an SFCL is supposed to be connected in series to the same HTS cable to investigate if and how an SFCL device could protect the HTS cable as well as the power network. Results show that fault currents can be limited by adapting the copper layer thickness of the HTS tapes in the cable, but this may result in too high temperatures in the coolant. Only a carefully designed SFCL device can prevent longer cable outages or even damages in the HTS cable caused by too high temperatures. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, the transient nitrogen oxide reduction performance of a urea selective catalytic reduction system installed on a non-road diesel engine was tested on an engine dynamometer bench over a scheduled non-road transient cycle mode. Based on the measurement results, the characteristics of the transient selective catalytic reduction behaviours of nitrogen oxide reduction were evaluated. Also, in this study, the effects of several thermal management strategies for improving the selective catalytic reduction efficiency was investigated by transient selective catalytic reduction simulations. The kinetic parameters of the current simulation code for selective catalytic reduction were calibrated and validated by comparison with the measurement data. As a result of this study, it was found that a thermal management strategy utilizing a partial temperature rise in the transient time domain can be an efficient approach for improving the transient selective catalytic reduction efficiency, in comparison with the temperature rise over the entire cycle period. Furthermore, this study can provide some guideline data for the magnitude and the duration of the temperature rise required to obtain the target selective catalytic reduction efficiency over the non-road transient cycle mode. In the last part of this study, the impact of the variation in the space velocity on the transient selective catalytic reduction efficiency was assessed using transient selective catalytic reduction simulations. [ABSTRACT FROM AUTHOR]

This work presents the assessment of the mean flow field and low frequency disturbances in the stay vane channel of a model pump turbine using transient numerical simulations and LDV-based measurements. The focus is laid on transient CFD simulations of characteristic flow states in the stay vane channel when operating at off-design conditions in pump mode. Experimental and numerical investigations obtained a shifting velocity distribution between the shroud and hub of the distributor when continuously increasing the discharge in the part-load range. Simulations captured the occurrence of this changing flow state in the stay vane channel reasonably well. A further increase of the discharge showed a uniformly redistributed mean flow of both hub and shroud side. Monitoring points and integral quantities from measurements and transient simulations were used to interpret the development of transient flow patterns in the stay vane channel at the operating point of strongest asymmetrical flow. During simulation and measurement, a dominant rotating stall inception was observed near the design flow of the pump turbine. At this point where the stall becomes severe, a high level of correlation between the signals of the upper and lower stalled flow in the stay vane channel was calculated. Further simulations for different guide vane positions predicted a strong influence of the guide vane position on the structure of rotating stall. [ABSTRACT FROM AUTHOR]

A wide range of alternative jet fuels is studied in this work for use in a small two-spool turbofan engine. These embrace the five production pathways currently approved by the American Society for Testing and Materials. Both neat products and blends (within certified limits) have been considered. The present analysis is based on a 0-D thermodynamic modeling of the aero-engine for off-design and transient simulations. In addition, the selected approach incorporates fuel effects on combustion and the impact of fuel properties on the flame temperature, as well as on the droplet evaporation rate. Predicted performance and pollutant emission outputs for the alternative fuels are presented at different operating conditions, namely: take-off, top of climb, cruise, low power and ground idle. The results are discussed and comprehensively compared with data available in the literature. It was concluded that the combustion of alternative fuels generally leads to enhancements in engine performance with respect to the use of conventional kerosene. Reductions in pollutant emissions occur mostly in soot, but also in nitrogen oxides and carbon monoxide, depending on the fuel and operating conditions. In contrast, increased emissions of unburned hydrocarbons are generally observed. Concerns about the aero-engine dynamic response are raised only in very few cases, involving the use of neat products. [ABSTRACT FROM AUTHOR]

An advanced hybrid lumped parameter code for the simulation of Pulsating Heat Pipes is developed. Being able to simulate transient operative conditions and removing common physical simplified assumptions, it represents a step forward with respect to the present models of passive two-phase systems. Mass, momentum and energy balances account for the thermal and fluid-dynamics phenomena. Heterogeneous and homogeneous phase changes are directly integrated. In addition, a fitting correlation for the wall/vapour heat transfer coefficient is implemented and tuned against experimental data in order to evaluate the influence of the liquid film on conjugate heat transfer. The resulting numerical tool have been validated against experimental data achieved testing a copper pulsating heat pipe during the 58th ESA Parabolic Flight Campaign in several operative conditions and transient gravity levels. The predicted results show very good matching with the actual thermo-physical behaviour of the system. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

State‐of‐the‐art time‐domain models of power cables account for the frequency dependency of physical parameters to enable accurate transient simulations of high‐voltage transmission schemes. Owing to their formulation, these models cannot be directly converted into a state‐space form as required for small‐signal eigenvalue analysis. Thus, dc cables are commonly represented in high‐voltage direct current (HVDC) power system stability studies by cascaded pi‐section equivalents that neglect the frequency‐dependent effects. This study demonstrates how the conventional cascaded pi‐section model is unable to accurately represent the damping characteristic of the cable and how this can lead to incorrect stability assessments. Furthermore, an alternative model consisting of cascaded pi‐sections with multiple parallel branches is explored, which allows for a state‐space representation while accounting for the frequency dependency of the cable parameters. The performance of the proposed model is benchmarked against state‐of‐the‐art cable models both in the frequency domain and in the time domain. Finally, the study provides a comparative example of the impact of the cable modelling on the small‐signal dynamics of a point‐to‐point voltage‐source converter (VSC) HVDC transmission scheme. [ABSTRACT FROM AUTHOR]

Deciphering the variations of past glaciations over southeastern Tibet which holds the largest mass of contemporary temperate glaciers over Asia helps to advance our understanding of the ice-climate interactions and how glaciers may respond to future climate change. Using an ice sheet model forced by the reconstructed climatic change during the past 88 ka, we investigate the timing and extent of glaciations over southeastern Tibet and explore the potential influences of model parameters and horizontal resolution. Our results illustrate a long-term decreasing trend in the glacierized area during the past 88 ka, suggesting progressively restricted glaciations over southeastern Tibet. Apart from the long-term trend, there are multiple glacier advance events on millennial timescales. The maximum extent of glaciation occurs at late MIS 4 (∼58 ka) and early MIS 3 (∼51 ka), with the minimum glacier extent predicted in the late Holocene (∼4 ka). The evolution of glaciations during the past 88 ka is dominated by the change in air temperature in our simulations in which temperature and precipitation serve as the climatic forcing. Regarding modeling uncertainty, we show that the pattern of glacier evolution is independent of the values of model parameters and horizontal resolution used, but the amplitude of glacier extent is significantly affected, especially for model parameters. Compared with glacial geological evidence, the timing of the modeled widespread glaciations broadly matches with the ages of known moraines, but the mapped glacier bounds across specific mountain ranges are generally underestimated. The adoption of a spatially uniform climatic forcing and the related uncertainty may contribute to the model-data discrepancy. Our results aid in the establishment of a testable link between climate change and glacier response during the last glacial stage and have important implications for glacier behavior in the future. • A general long-term decreasing trend in glacier extent during the past 88 ka. • The maximum extent of glaciation occurs at late MIS 4 and early MIS 3. • The minimum glacier extent occurs in the late Holocene (∼4 ka). • Temperature change dominates the variations of glaciations. • The pattern of glacier evolution is independent of model parameters and resolution. [ABSTRACT FROM AUTHOR]

A numerical model for transdermal drug delivery (TDD) has been developed by treating skin as a composite, dynamic, porous medium. Governing unsteady mass transport equations in porous medium was solved for different cases for up to a period of drug-patch application of 10 hrs. The effects of cell migration and anisotropic diffusive properties of stratum corneum (SC) on TDD are analyzed. Each of the above factors and their combination are found to significantly affect TDD. The cell migration in SC decreases the predicted amount of drug considerably. Their combined effect in TDD helped in identifying four distinct regimes of pharmacological as well as engineering importance within the domain. [ABSTRACT FROM AUTHOR]

The study presents a theoretical investigation of the impact of individual electron and hole dynamics on the photovoltaic characteristics of InAs/GaAs quantum dot solar cells. The analysis is carried out by exploiting a model which includes a detailed description of quantum dots (QD) kinetics within a drift‐diffusion formalism. Steady‐state and transient simulations show that hole thermal spreading across the closely spaced QD valence band states allows to extract the maximum achievable photocurrent from the QDs; on the other hand, slow hole dynamics turns QDs into efficient traps, impairing the short circuit current despite the extended light harvesting provided by the QDs. [ABSTRACT FROM AUTHOR]

Simulation of groundwater withdrawal has been conducted with a groundwater modeling system (GMS) version 3.1 software at a regional scale. The simulation was conducted from ten year groundwater withdrawal data in Merapi Aquifer, DIY, Indonesia, for two assumed scenarios, with an emphasis in Sleman area. The result for the ten year groundwater simulation was conducted spatially distributed in the Merapi Aquifer after the steady state simulation was reached. With two different types of transient simulations, the total withdrawal of 28,968 m3/day for the whole Merapi Aquifer is still acceptable with caution, as long as the . recharge is not decreasing. However, less withdrawal as the existing withdrawal condition is recommended until local site investigation is sufficient to avoid the danger of overdraft.

Most of Egypt’s population is concentrated in the Nile Valley (5% of Egypt’s area), while the western desert occupies an area of 50% of the total area of Egypt with a small number of inhabitants. The New Valley is the largest governorates in Egypt which occupies 45.8% of the total area of the Country and 65% of the Western Desert and it is the least densely populated governorate in Egypt. However, New Valley has started to receive the migrated people from the Nile valley and Delta region and the demand for the energy is continuously increasing. However, the rural area in New Valley still suffers from lack of access to energy services. The very high transmission losses and costs are the main challenges for electrification in this area. Then, it is worth to investigate the opportunities for distributed energy generation. This area of Egypt receives some of the highest solar radiation in the world (up to 3000 kW h per square meters per year), making it a prime location for use of this resource. In this study, performance and economic assessment of a small scale stand-alone solar thermal co-generation plant using diathermic oil is presented. This configuration is considered as a promising and sustainable solution to provide electricity and heat to an isolated area satisfying the local loads. Parabolic trough plant has been modeled in TRNSYS simulation environment integrated with the Solar Thermal Electric Components (STEC) model library. Both solar and power cycle performances have been modeled based on the solar energy data of the plant site. The mirrors area and the solar collectors have been designed to optimize the incident solar energy. As a result, the parabolic trough solar power plant can produce 6 MW of electric power and 21.5 MW of heat power with an overall efficiency of about 85%. The analysis demonstrated that the solar operation time of the CSP plant in the selected site can be expanded to run during the all day without recurring to fossil fuel backup. The levelized cost of electricity (LCOE) of the proposed power plant is estimated to be equal to 1.25 USD/kW h. The avoided GHG emissions are equal to about 7300 toe/year. [ABSTRACT FROM AUTHOR]

This paper reports on the design optimization done for Double Sided silicon microStrip Detectors (DSSDs) to reduce the Equivalent Noise Charge (ENC) and to maximize the breakdown voltage and Charge Collection Efficiency. Various isolation techniques have been explored and a detailed comparison has been studied to optimize the detector performance. To evaluate the performance of the silicon detectors, a radiation damage model has been included. The neutron fluence is expected to be 2\times 10^13\ neq{\cm}^{-2} per year for five years of expected CBM run with intermediate periods of warm maintenance, cold maintenance and shutdown. Transient simulations have been performed to estimate the charge collection performance of the irradiated detectors and simulations have been verified with experimental data. [ABSTRACT FROM PUBLISHER]

Abstract: Transient simulations of a resonant tunneling diode oscillator are presented. The semiconductor model for the diode consists of a set of time-dependent Schrödinger equations coupled to the Poisson equation for the electric potential. The one-dimensional Schrödinger equations are discretized by the finite-difference Crank–Nicolson scheme using memory-type transparent boundary conditions which model the injection of electrons from the reservoirs. This scheme is unconditionally stable and reflection-free at the boundary. An efficient recursive algorithm due to Arnold, Ehrhardt, and Sofronov is used to implement the transparent boundary conditions, enabling simulations which involve a very large number of time steps. Special care has been taken to provide a discretization of the boundary data which is completely compatible with the underlying finite-difference scheme. The transient regime between two stationary states and the self-oscillatory behavior of an oscillator circuit, containing a resonant tunneling diode, is simulated for the first time. [Copyright &y& Elsevier]

Abstract: Operability of Very High Temperature Reactor (VHTR) hydrogen cogeneration systems in response to abnormal transients initiated by the hydrogen production plant is one of the important concerns from economical and safety points of views. The abnormal events in the hydrogen production plant could initiate load changes and induce temperature variations in a primary cooling system. Excessive temperature increase in the primary cooling system would cause reactor scrams since the temperature increase in the primary cooling system is restricted in order to prevent undue thermal stresses from reactor structures. Also, temperature decrease has a potential propagation path for reactor scrams by reactivity insertions as a consequence of the reactivity feedbacks. Since suspensions of reactor operation and electricity generation should be avoided even in case of abnormal events in the hydrogen production plant from an economical point of view, an establishment of a control scheme against abnormal transients of hydrogen production plant is required for plant system design. In the present study, basic controls and their integration for the GTHTR300C, a VHTR cogeneration system designed by JAEA with a direct Brayton cycle power conversion unit and thermochemical Iodine–Sulfur process hydrogen production plant (IS hydrogen production plant), against abnormal transients of IS hydrogen production plant are presented. Transient simulations for selected load change events in the IS hydrogen production plants are performed by an original system analysis code which enables to evaluate major phenomena assumed in process heat exchangers of the IS hydrogen production plant. It is shown that abnormal load change events are successfully simulated by the system analysis code developed. The results demonstrated the technical feasibility of proposed controls for continuous operation of the reactor and power conversion unit against load change events in the IS hydrogen production plant. [Copyright &y& Elsevier]

Abstract: Transient simulation of retinal laser irradiation is performed for a square array comprising 3 × 3 uniformly distributed spots under sequential and simultaneous mode. A finite volume formulation of the Pennes bio-heat transfer model is employed as the governing equation to generate the temperature distribution within the eye domain. Temperature distribution developed due to laser power of 0.2 W/spot and time duration of 100 ms/spot is used to compare the merits of sequential and simultaneous irradiation of spots. Simultaneous mode is preferred when the time of surgery is limited, with possible excess heating in the inter-spot retinal regions. The inter-spot spacing D is also varied between one diameter and one and half diameter of the spot size (diameter) to evaluate the safe placement of consecutive spots. D ≥ 0.75 mm can be considered as the optimum spot distance for non-interference due to excess heating. Effect of pulsation of incident laser power is observed to favorably reduce the average temperature of the irradiated regions of the retina toward photocoagulation temperature. [Copyright &y& Elsevier]

Abstract: The purpose of this work consists in thermodynamic modeling of hybrid photovoltaic–thermal (PV/T) solar systems, pursuing a modular strategy approach provided by Simulink/Matlab. PV/T solar systems are a recently emerging solar technology that allows for the simultaneous conversion of solar energy into both electricity and heat. This type of technology present some interesting advantages over the conventional “side-by-side” thermal and PV solar systems, such as higher combined electrical/thermal energy outputs per unit area, and a more uniform and aesthetical pleasant roof area. Despite the fact that early research on PV/T systems can be traced back to the seventies, only recently it has gained a renewed impetus. In this work, parametric studies and annual transient simulations of PV/T systems are undertaken in Simulink/Matlab. The obtained results show an average annual solar fraction of 67%, and a global overall efficiency of 24% (i.e. 15% thermal and 9% electrical), for a typical four-person single-familiar residency in Lisbon, with p-Si cells, and a collector area of 6m2. A sensitivity analysis performed on the PV/T collector suggests that the most important variable that should be addressed to improve thermal performance is the photovoltaic (PV) module emittance. Based on those results, some additional improvements are proposed, such as the use of vacuum, or a noble gas at low-pressure, to allow for the removal of PV cells encapsulation without air oxidation and degradation, and thus reducing the PV module emittance. Preliminary results show that this option allows for an 8% increase on optical thermal efficiency, and a substantial reduction of thermal losses, suggesting the possibility of working at higher fluid temperatures. The higher working temperatures negative effect in electrical efficiency was negligible, due to compensation by improved optical properties. The simulation results are compared with experimental data obtained from other authors and perform reasonably well. The Simulink modeling platform has been mainly used worldwide on simulation of control systems, digital signal processing and electric circuits, but there are very few examples of application to solar energy systems modeling. This work uses the modular environment of Simulink/Matlab to model individual PV/T system components, and to assemble the entire installation layout. The results show that the modular approach strategy provided by Matlab/Simulink environment is applicable to solar systems modeling, providing good code scalability, faster developing time, and simpler integration with external computational tools, when compared with traditional imperative-oriented programming languages. [Copyright &y& Elsevier]

Abstract: A validated two-dimensional computational model of the human eye solving the discretized form of the bio-heat transfer equation using finite volume formulation has been developed. Using the model, the transient temperature evolution and associated thermal effects in various regions of the human eye subjected to laser radiation during retinopathy are investigated. It is shown that the transient evolution of the retinal temperature during laser heating could reach values higher than that required for irreversible cell damage. This is because the time scale for spatial diffusion of heat towards the choroid, containing blood vessels for cooling, is much larger than that of the actual laser surgical process (100ms). This excess temperature could cause cell damage to the adjoining retinal region due to heat diffusion. Based on the simulation results, a method is proposed to maintain the retinal pigmented epithelium (RPE) temperature close to the required 60°C by pulsating the laser source between suitable maximum and minimum heat flux values. [Copyright &y& Elsevier]

Abstract: The paper describes the experimental investigations of the performance of a multi-stage water desalination still connected to a heat pipe evacuated tube solar collector with aperture area of 1.7m2. The multi-stage solar still water desalination system was designed to recover latent heat from evaporation and condensation processes in four stages. The variation in the solar radiation during a typical mid-summer day in the Middle East region was simulated on the test rig using an array of 110 halogen floodlights covering the area of the collector. The results of tests demonstrate that the system produces about 9kg of fresh water per day and has a solar collector efficiency of about 68%. However, the overall efficiency of the laboratory test rig at this stage of the investigations was found to be at the level of 33% due to excessive heat losses in the system. The analysis of the distilled water showed that its quality was within the World Health Organization guidelines. The still''s operation was numerically simulated by employing a mathematical model based on a system of ordinary energy and mass conservation differential equations written for each stage of the still. A computer program was developed for transient simulations of the evaporation and condensation processes inside the multi-stage still. Experimental results obtained and theoretical predictions were found to be in good agreement. The results on the determination of rational design dimensions and number of stages of the still for a given aperture of the solar collector are also presented in this work. [Copyright &y& Elsevier]

Energy consumption of heating and/or cooling auxiliary devices in solar sorption cooling systems is one of the major factors of reduction in primary energy savings. This work simulates and analyzes the dynamic operation of a solar thermal double effect absorption cooling system for three strategies of employing hot and/or cold auxiliary devices and the influence of instituting the entire solar collector field in series versus parallel arrangement. An auxiliary heater is installed in the hot storage to absorption chiller loop in configuration-1 (C-1) to maintain the desired generator temperature. An auxiliary cooler is employed in configuration-2 (C-2) to furnish the cooling load in conjunction with an absorption chiller energized only by the evacuated tube solar collector (ETC). In configuration-3 (C-3) both auxiliary heater in the storage to chiller loop and auxiliary cooler in the chiller to load loop are modeled for three percentage contributions of the required cooling load by the double effect absorption and water-cooled vapor compression chiller i.e., 50-50 (C-3a), 70–30 (C-3b), and 30–70 (C-3c), respectively. Simulation results demonstrated that at lower collector areas C-2 resulted in considerably higher primary energy savings (∼58%) and solar fraction (∼14.4%) in comparison to C-1 and C-3. The serial connection of the entire solar field resulted in better primary energy savings in C-2 while for C-1 and C-3 parallel arrangement gave rise to higher primary energy savings than the serial arrangement. • Analysis of solar cooling system with different options of auxiliary heater/cooler. • Configuration with only auxiliary cooler resulted in the highest energy savings. • Serial connection of solar field resulted in better primary energy savings in C-2. • Parallel arrangement of solar field showed higher energy savings for C-1 and C-3. [ABSTRACT FROM AUTHOR]

The heat insulating potential of straw, an agricultural residue, used as part of the envelope of unconditioned buildings is the focus of the current work. Using a CFD software with experimentally validated boundary conditions, transient thermal analysis is performed on a 3-D model room of dimensions 3 m × 3 m × 2.5 m with vents and heat source representing a naturally ventilated indoor space. The thermal performances of a reference uninsulated concrete envelope and a straw insulation-based envelope are compared in terms of quantitative parameters such as indoor air temperature, decrement factor, and time lag as well as a qualitative discussion on the need for occupant adaptation, namely closing or opening of inlet vent and requirement of additional heating. The assessment and subsequent recommendation of straw insulation utilization is done for representative summer and winter days of the five different climatic zones of India. A maximum reduction of up to 3.5 °C in the peak indoor air temperature is achievable with inlet temporarily closed when straw insulation is included in the envelope in summer conditions. In winter conditions of cold climatic zone, with inlet always closed, use of straw insulation leads to the lessening of additional active heat source requirement by as much as 600 W for the considered model room. Further, the effects of increased straw insulation thickness, removal of heat source, varying inlet air velocity, and changing the position of the straw insulation to the outside are also analyzed for the extreme warm and cold conditions. • Transient thermal analysis of ventilated 3-D room without and with straw insulation. • Recommendations for insulation usage, vent operation for Indian climatic zones. • In hot summer, inlet temporarily closed with insulation improves thermal comfort. • In cold winter, with inlet always closed, insulation reduces active heating needed. • Effects of insulation thickness, position, inlet velocity, and heat source are studied. [ABSTRACT FROM AUTHOR]

This paper outlines the results of a physical simulation (at a 1:700 - 1:1000 geometric scale) of a thunderstorm downburst. Three different methods are examined in order to generate the time dependent nature of a downburst: directly controlling the fans and via two different types of opening apertures. Similarities are shown to exist between each method, although the results obtained from one approach are favoured since they appear to be independent of the downdraft velocity. Significant run-to-run variations between each experiment are discovered and in general it is found beneficial to interpret the results in terms of 10 run ensemble averages. An attempt to simulate a translating downburst is also undertaken and the results are shown to compare favourably with full-scale data. [ABSTRACT FROM AUTHOR]

We describe the evolutionary response of northern and southern hemisphere summer monsoons to orbital forcing over the past 280,000 years using a fully coupled general circulation ocean-atmosphere model in which the orbital forcing is accelerated by a factor of 100. We find a strong and positive response of northern (southern) summer monsoon precipitation to northern (southern) summer insolation forcing. On average, July (January) precipitation maxima and JJA (DJF) precipitation maxima have high coherence and are approximately in phase with June (December) insolation maxima, implying an average lag between forcing and response of about 30° of phase at the precession period. The average lag increases to over 40° for 4-month precipitation averages, JJAS (DJFM). The phase varies from region to region. The average JJA (DJF) land temperature maxima also lag the June orbital forcing maxima by about 30° of phase, whereas ocean temperature maxima exhibit a lag of about 60° of phase at the precession period. Using generalized measures of the thermal and hydrologic processes that produce monsoons, we find that the summer monsoon precipitation indices for the six regions all fall within the phase limits of the process indices for the respective hemispheres. Selected observational studies from four of the six monsoon regions report approximate in-phase relations of summer monsoon proxies to summer insolation. However other observational studies report substantial phase lags of monsoon proxies and a strong component of forcing associated with glacial-age boundary conditions or other factors. An important next step will be to include glacial-age boundary condition forcing in long, transient paleoclimate simulations, along with orbital forcing. [ABSTRACT FROM AUTHOR]

The topological structure and basic approaches for parameter estimation for a new hybrid transformer model are presented in Part I of this two-paper set. Part II deals with the model benchmarking and also discusses additional methods for parameter estimation based on laboratory measurements. The simulation results confirm the validity of the model for the low- and medium-frequency range. [ABSTRACT FROM AUTHOR]