The synchronous virtual machine uses inverter power to imitate the performance of the conventional synchronous machine.It also has the same inertia,damping,frequency,voltage regulation,and other external performance a...The synchronous virtual machine uses inverter power to imitate the performance of the conventional synchronous machine.It also has the same inertia,damping,frequency,voltage regulation,and other external performance as the generator.It is the key technology to realize new energy grid connections’stable and reliable operation.This project studies a dynamic simulation model of an extensive new energy power system based on the virtual synchronous motor.A new energy storage method is proposed.The mathematical energy storage model is established by combining the fixed rotor model of a synchronous virtual machine with the charge-discharge power,state of charge,operation efficiency,dead zone,and inverter constraint.The rapid conversion of energy storage devices absorbs the excess instantaneous kinetic energy caused by interference.The branch transient of the critical cut set in the system can be confined to a limited area.Thus,the virtual synchronizer’s kinetic and potential energy can be efficiently converted into an instantaneous state.The simulation of power system analysis software package(PSASP)verifies the correctness of the theory and algorithm in this paper.This paper provides a theoretical basis for improving the transient stability of new energy-connected power grids.展开更多
The purpose of this research is to develop a SolidWorks? model for transient temperature field of laser welding of PMMA/SS 304 materials for application in fabrication of the ultrasonic back-plate, with a view of opti...The purpose of this research is to develop a SolidWorks? model for transient temperature field of laser welding of PMMA/SS 304 materials for application in fabrication of the ultrasonic back-plate, with a view of optimizing the experimental conditions. The study is carried out on these materials because of the increasing application of both metals and non-metals. The work focuses specifically on these materials because they have been experimentally studied previously and as such, this study can be accepted as an assessment into feasibility of using SolidWorks? model to study the temperature field of the laser welding processes of metals and non-metals. The results of the SolidWorks? transient thermal model show that there is a concentration of high temperatures at the point of contact. It also shows that temperature decreases as we move in (between laser and the top face) to the thickness of the part. Additionally the maximum temperature occurs at the last point of the welding;this may be due to the accumulation of the temperature before arriving at the end. These findings are comparable to the previous simulated and experimental results on temperature field during laser welding of PMMA/SS 304 materials. However, SolidWorks? is shown to present a challenge in modeling a moving source of laser power.展开更多
The utilization of hydraulic fracturing for the extraction of natural gas hydrates in maritime environments has been relatively underexplored in the existing literature.This study introduces a novel approach by employ...The utilization of hydraulic fracturing for the extraction of natural gas hydrates in maritime environments has been relatively underexplored in the existing literature.This study introduces a novel approach by employing a fully implicit integration method to construct a two-dimensional temperature distribution model of the wellbore.The model considers critical parameters such as fracturing fluid time,initial temperature,and fracturing fluid displacement to forecast the temperature data of the wellbore and its surrounding environments throughout the entire fracturing process.The investigation reveals that the initial temperature of the fracturing liquid and the duration of the fracturing process exert a substantial influence on the wellbore temperature,whereas the impact of fracturing fluid displacement is found to be minimal.Furthermore,a comparative analysis between the results derived from the proposed model and those obtained from traditional steady-state formulas substantiates the accuracy and efficacy of the developed model.This study significantly advances our comprehension of temperature dynamics within wellbores during hydraulic fracturing operations in maritime environments,thereby offering valuable insights for future endeavors in natural gas hydrate extraction.展开更多
A modified one-dimensional transient hygrothermal model for multilayer wall was proposed using air humidity ratio and temperature as the driving potentials.The solution for the governing equations was obtained numeric...A modified one-dimensional transient hygrothermal model for multilayer wall was proposed using air humidity ratio and temperature as the driving potentials.The solution for the governing equations was obtained numerically by implementing the finite-difference scheme.To evaluate the accuracy of the model,a test system was built up to measure relative humidity and temperature within a porous wall and compare with the prediction of the model.The prediction results have good agreement with the experimental results.For the interface close to indoor side,the maximum deviation of temperature between calculated and test data is 1.87 K,and the average deviation is 0.95 K;the maximum deviation of relative humidity is 11.4%,and the average deviation is 5.7%.For the interface close to outdoor side,the maximum deviation of temperature between prediction and measurement is 1.78 K,and the average deviation is 1.1 K;the maximum deviation of relative humidity is 9.9%,and the average deviation is 4.2%.展开更多
A new analytical model of a 3-degree-of-freedom （3-DOF） gyro-accelerometer system consisting of a 1-DOF drive and 2-DOF sense modes is presented. The model constructs lumped differential equations associated with ea...A new analytical model of a 3-degree-of-freedom （3-DOF） gyro-accelerometer system consisting of a 1-DOF drive and 2-DOF sense modes is presented. The model constructs lumped differential equations associated with each DOFof the system by vector analysis. The coupled differential equations thus established are solved analytically for their responses in both the time and frequency domains. Considering these frequency response equations, novel device design concepts are derived by forcing the sense phase to zero, which leads to a certain relationship between the structural frequencies, thereby causing minimization of the damping effect on the performance of the system. Furthermore, the feasibility of the present gyro-accelerometer structure is studied using a unique discriminatory scheme for the detection of both gyro action and linear acceleration at their events. This scheme combines the formulated settled transient solution of the gyro-accelerometer with the processes of synchronous demodulation and filtration, which leads to the in-phase and quadrature components of the system＇s output signal. These two components can be utilized in the detection of angular motion and linear acceleration. The obtained analytical results are validated by simulation in a MATLAB/Simulink environment, and it is found that the results are in excellent agreement with each other.展开更多
Transient electronics are an emerging class of electronics with the unique characteristic to completely dissolve within a programmed period of time. Since no harmful byproducts are released, these electronics can be u...Transient electronics are an emerging class of electronics with the unique characteristic to completely dissolve within a programmed period of time. Since no harmful byproducts are released, these electronics can be used in the human body as a diagnostic tool, for instance, or they can be used as environmentally friendly alternatives to existing electronics which disintegrate when exposed to water. Thus, the most crucial aspect of transient electronics is their ability to disintegrate in a practical manner and a review of the literature on this topic is essential for understanding the current capabilities of transient electronics and areas of future research. In the past, only partial dissolution of transient electronics was possible, however, total dissolution has been achieved with a recent discovery that silicon nanomembrane undergoes hydrolysis. The use of single- and multi-layered structures has also been explored as a way to extend the lifetime of the electronics. Analytical models have been developed to study the dissolution of various functional materials as well as the devices constructed from this set of functional materials and these models prove to be useful in the design of the transient electronics.展开更多
Experimental stroke research commonly employs focal cerebral ischemic rat models （Bederson et al., 1986a; Longa et al., 1989）. In human patients, ischemic stroke typically results from thrombotic or embolic occlusio...Experimental stroke research commonly employs focal cerebral ischemic rat models （Bederson et al., 1986a; Longa et al., 1989）. In human patients, ischemic stroke typically results from thrombotic or embolic occlusion of a major cerebral artery, usually the mid- dle cerebral artery （MCA）. Experimental focal cerebral ischemia models have been employed to mimic human stroke （Durukan and Tatlisumak, 2007）. Rodent models of focal cerebral ischemia that do not require craniotomy have been developed using intraluminal suture occlusion of the MCA （MCA occlusion, MCAO） （Rosamond et al., 2008）. Furthermore, mouse MCAO models have been wide- ly used and extended to genetic studies of cell death or recovery mechanisms （Liu and McCullough, 2011）. Genetically engineered mouse stroke models are particularly useful for evaluation of isch- emic pathophysiology and the design of new prophylactic, neuro- protective, and therapeutic agents and interventions （Armstead et al., 2010）. During the past two decades, MCAO surgical techniques have been developed that do not reveal surgical techniques for mouse MCAO model engineering. Therefore, we compared MCAO surgical methods in rats and mice.展开更多
This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials （FGMs）. First, a Laplace transform approach is used to handle the time variable. Then, a f...This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials （FGMs）. First, a Laplace transform approach is used to handle the time variable. Then, a fundamental solution in Laplace space for FGMs is constructed. Next, a hybrid graded element is formulated based on the obtained fundamental solution and a frame field. As a result, the graded properties of FGMs are naturally reflected by using the fundamental solution to interpolate the intra-element field. Further, Stefest＇s algorithm is employed to convert the results in Laplace space back into the time-space domain. Finally, the performance of the proposed method is assessed by several benchmark examples. The results demonstrate well the efficiency and accuracy of the proposed method.展开更多
In the course of completion of an ultra-deep well newly drilled in the Yuanba Gasfield,Sichuan Basin,long-section and large-scale deformation occurred in the heavy casing section and nickel base alloy casing section o...In the course of completion of an ultra-deep well newly drilled in the Yuanba Gasfield,Sichuan Basin,long-section and large-scale deformation occurred in the heavy casing section and nickel base alloy casing section of the sealing Triassic limestone interval,so a new hole had to be sidetracked,which impels us to rediscover the applicability of conventional drilling and completion technology in ultra-deep wells.In this paper,based on the borehole condition and field operation data of this well,the borehole pressure field variation initiated by lost circulation in the low-pressure formation was analyzed from the perspective of dynamics,then,the variation pattern of differential pressure inside and outside the well bore at different time intervals was depicted,and the primary cause of such complication was theoretically revealed,i.e.,the pressure wave generated by instant lost circulation in low-pressure formation would result in redistribution of pressure inside the downhole confined space,and then the crush of casing in the vicinity of local low-pressure areas.Pertinent proposals for avoiding these kinds of engineering complexities were put forward:①when downhole sealing casing operation is conducted in open hole completion,liner completion or perforated hole,the potential damage of lost circulation to casing should be considered;②the downhole sealing point and sealing mode should be selected cautiously:the sealing point had better be selected in the section with good cementing quality or as close to the casing shoe as possible,and the sealing mode can be either cement plug or mechanical bridge plug.This paper finally points out that good cementing quality plays an important role in preventing this type of casing deformation.展开更多
The dynamic behaviors of hydrodynamic journal bearings can be influenced by several coupling factors,including cavitation,elastic deformation,surface asperity,and even electromagnetic fields in systems.In this study,w...The dynamic behaviors of hydrodynamic journal bearings can be influenced by several coupling factors,including cavitation,elastic deformation,surface asperity,and even electromagnetic fields in systems.In this study,we establish a transient lubrication model to investigate the dynamic lubrication process of journal bearings,fully considering these physical phenomena in the application of micropumps.Rotor trajectory measurements are conducted to validate the proposed model,which results in an error margin of less than 9.6%.Furthermore,the tribodynamic responses of hydrodynamic journal bearings are analyzed theoretically under various operational conditions,such as start-up,shock loading,and speed variation.The variation in the flow field from the mixed-lubrication regime to the hydrodynamic lubrication regime is investigated and qualified during the start-up stage.The analytical model enables the prediction of the transient lubrication performance under various load conditions,such as sharp shock,helping verify the design effectiveness of the journal bearing.Additionally,the dynamic relationships between the motion parameters and forces are demonstrated and compared.Our findings indicate that the gyroscopic torque can suppress the deflection of the rotor and that the hydrodynamic force can inhibit the rotor's radial displacement,thus maintaining the rotor's dynamic stability.The methods proposed in this work are instructive for the theoretical modeling and optimization of inclined journal bearings.展开更多
Unmanned Aerial Vehicle（UAV） is developing towards the direction of High Altitude Long Endurance（HALE）. This will have an important influence on the stability of its airborne electronic equipment using passive the...Unmanned Aerial Vehicle（UAV） is developing towards the direction of High Altitude Long Endurance（HALE）. This will have an important influence on the stability of its airborne electronic equipment using passive thermal management. In this paper, a multi-node transient thermal model for airborne electronic equipment is set up based on the thermal network method to predict their dynamic temperature responses under high altitude and long flight time conditions. Some relevant factors are considered into this temperature prediction model including flight environment,radiation, convection, heat conduction, etc. An experimental chamber simulating a high altitude flight environment was set up to survey the dynamic thermal responses of airborne electronic equipment in a UAV. According to the experimental measurement results, the multi-node transient thermal model is verified without consideration of the effects of flight speed. Then, a modified way about outside flight speed is added into the model to improve the temperature prediction performance. Finally, the corresponding simulation code is developed based on the proposed model. It can realize the dynamic temperature prediction of airborne electronic equipment under HALE conditions.展开更多
As the classical transient flow model cannot simulate the water hammer effect of gas well, a transient flow mathematical model of multiphase flow gas well is established based on the mechanism of water hammer effect a...As the classical transient flow model cannot simulate the water hammer effect of gas well, a transient flow mathematical model of multiphase flow gas well is established based on the mechanism of water hammer effect and the theory of multiphase flow. With this model, the transient flow of gas well can be simulated by segmenting the curved part of tubing and calculating numerical solution with the method of characteristic curve. The results show that the higher the opening coefficient of the valve when closed, the larger the peak value of the wellhead pressure, the more gentle the pressure fluctuation, and the less obvious the pressure mutation area will be. On the premise of not exceeding the maximum shut-in pressure of the tubing, adopting large opening coefficient can reduce the impact of the pressure wave. The higher the cross-section liquid holdup, the greater the pressure wave speed, and the shorter the propagation period will be. The larger the liquid holdup, the larger the variation range of pressure, and the greater the pressure will be. In actual production, the production parameters can be adjusted to get the appropriate liquid holdup, control the magnitude and range of fluctuation pressure, and reduce the impact of water hammer effect. When the valve closing time increases, the maximum fluctuating pressure value of the wellhead decreases, the time of pressure peak delays, and the pressure mutation area gradually disappears. The shorter the valve closing time, the faster the pressure wave propagates. Case simulation proves that the transient flow model of gas well can optimize the reasonable valve opening coefficient and valve closing time, reduce the harm of water hammer impact on the wellhead device and tubing, and ensure the integrity of the wellbore.展开更多
A transient molecular network model is built to describe the non- linear viscoelasticity of polymers by considering the effect of entanglement loss and regeneration on the relaxation of molecular strands. It is an ext...A transient molecular network model is built to describe the non- linear viscoelasticity of polymers by considering the effect of entanglement loss and regeneration on the relaxation of molecular strands. It is an extension of previous network theories. The experimental data on three thermoplastic polymers (ABS, PVC and PA6) obtained under various loading conditions are used to test the model. Agreement between the theoretical and experimental curves shows that the suggested model can describe successfully the relaxation behavior of the thermoplastic polymers under different loading rates by using relatively few relaxation modes. Thus the mi- cromechanism responsible for strain-rate dependence of relaxation process and the origin of nonlinear viscoelasticity may be disclosed.展开更多
A practical approach is discussed for sub-sea pipeline monitoring and leak detection based on the real time transient model . The characteristic method of transient simulation is coupled with the Extended Kalman Filt...A practical approach is discussed for sub-sea pipeline monitoring and leak detection based on the real time transient model . The characteristic method of transient simulation is coupled with the Extended Kalman Filter to estimate the system state where the only observed data are inlet and outlet flow rate and pressure. Because EKF has a time variant track under the non-stationary stochastic process with additive Gaussian noise, the high sensitivity of RTTM to non-stationary operating condition is reduced. A leak location recursion estimation formula is presented based on the real time observed data. The results of 27 groups of test data indicate that the procedure presented is sensitive to a wide range of detectable leak sizes and has a low average relative error of leak location .展开更多
Porous electrodes with three-phase reaction in low temperature fuel cells have attracted much attention by their flooding phenomena. In order to have a better understanding of the flooding phenomena inside electrode, ...Porous electrodes with three-phase reaction in low temperature fuel cells have attracted much attention by their flooding phenomena. In order to have a better understanding of the flooding phenomena inside electrode, it is important to evaluate various discharge conditions of the flooded electrodes. A model of flooded porous electrode under the influence of potential sweep was developed to evaluate the flooding conditions in-situ. The hysteresis of current density vs. time was observed at high sweep rates （1 O0 mV.sl）. It was not observed at low sweep rate （0.1 mV-s~）. In this study, these characteristics of flooding and hysteresis conditions were found to be markedly dependent on the potential scan rate. These dynamic behaviors are interpreted in terms of water saturation response, velocity of water movement, and evaporation rate of water.展开更多
Aiming to efficiently simulate the transient process of transpiration cooling with phase change and reveal the convection mechanism between fluid and porous media particles in a continuum scale,a new two-phase mixture...Aiming to efficiently simulate the transient process of transpiration cooling with phase change and reveal the convection mechanism between fluid and porous media particles in a continuum scale,a new two-phase mixture model is developed by incor-porating the local thermal non-equilibrium effect.Considering the low-pressure and high overload working conditions of hypersonic flying,the heat and mass transfer induced by capillary and inertial body forces are analyzed for sub-cooled,saturated and super-heated states of water coolant under varying saturation pressures.After the validation of the model,transient simulations for different external factors,includ-ing spatially-varied heat flux,coolant mass flux,time-dependent external pressure and aircraft acceleration are conducted.The results show that the vapor blockage patterns at the outlet are highly dependent on the injection mass flux value and the external pressure,and the reduced saturation temperature at low external pressure leads to early boiling off and vapor blockage.The motion of flying has a large influence on the cooling effect,as the inertial force could change the flow pattern of the fluid inside significantly.The comparison of the results from 2-D and 3-D simulations sug-gests that 3-D simulation shall be conducted for practical application of transpiration cooling,as the thermal protection efficiency may be overestimated by the 2-D results due to the assumption of an infinite width length of the porous plate.展开更多
Grid-forming converters(GFMs)are faced with the threat of transient inrush current and synchronization instability issues when subjected to grid faults.Instead of disconnecting from the grid unintentionally,GFMs are r...Grid-forming converters(GFMs)are faced with the threat of transient inrush current and synchronization instability issues when subjected to grid faults.Instead of disconnecting from the grid unintentionally,GFMs are required to have fault ride through(FRT)capability to maintain safe and stable operation in grid-connected mode during grid fault periods.In recent studies,different FRT control strategies with distinguishing features and that are feasible for different operation conditions have been proposed for GFMs.To determine their application scope,an intuitive comparison of the transient performance of different FRT control strategies is presented in this paper.First,three typical FRT control strategies(virtual impedance,current limiters,and mode-switching control)are introduced and transient mathematical models are established.A detailed comparison analysis on transient inrush current and transient synchronization stability is then presented.The results will be useful for guiding the selection and design of FRT control strategies.Finally,simulation results based on PSCAD/EMTDC are considered to verify the correctness of the theoretical analysis.展开更多
C_(5)F_(10)O/CO_(2)gas mixture is one of the most promising alternatives to SF_(6)as an insulating gas in high-voltage switchgear.As a key performance index in product design,the temperature rise characteristics are r...C_(5)F_(10)O/CO_(2)gas mixture is one of the most promising alternatives to SF_(6)as an insulating gas in high-voltage switchgear.As a key performance index in product design,the temperature rise characteristics are rarely reported.In this paper,the thermodynamic parameters of C_(5)F_(10)O/CO_(2)gas mixture were calculated first.Then,the calculation model of transient temperature rise was constructed for a 252 kV/3150 A bus,and a temperature rise experimental platform was built to verify the reliability of the proposed calculation model.On this basis,the influence of different factors such as load current,charging pressure,mixing ratio,and structure size on the temperature rise of the bus was further analysed,and it is found that increasing the charging pressure and the mixing ratio of C5F10O could effectively reduce the bus temperature rise but it still could not reach the level of SF_(6).The main structure size that affects the temperature rise of the bus is the outer diameter of the conductor,which increases by 10.2%,and the temperature rise is the same as that of the original SF_(6)bus.Finally,a high-precision bus temperature rise surrogate model,which combined with the Latin hypercube model,the coefficient of prognosis,and the Kriging fitting method was established to facilitate the structural design.展开更多
Solar-air source heat pump(solar-ASHP)system has a potential application in the field of hot water and space heating in residential buildings.Such system features the complementary advantages to solve the discontinuou...Solar-air source heat pump(solar-ASHP)system has a potential application in the field of hot water and space heating in residential buildings.Such system features the complementary advantages to solve the discontinuous operation of the single solar system and the frosting issue of the single ASHP system.This paper built the solar-ASHP systems in Kunming and Shangri-La,and tested the system performance under different weather conditions in these two regions of plateau.Meanwhile,the transient heat balance models of the system were established under the sunlight time and non-sunlight time and were verified by the experimental results.Moreover,the verified model was applied to reveal the energy balance performance between the energy supply and building heat demand.The law of the system performance affected by the ambient temperature,effective heat collecting area,and cumulative heating capacity of collector was explored by the validated model.The results indicate that when the ambient temperature decreases by 1℃during non-sunlight time,the energy efficiency ratio decreases by about 0.07.A square meter decline in the effective heat collecting area pushes an increase in the heating capacity of 5.75 MJ.Meanwhile,the cumulative heating capacity of collector increases by 5 MJ,and the ASHP energy consumption decreases by 0.54 kWh.The dynamic changes of the ambient temperature and instantaneous solar radiation are the main reasons of the heat balance errors.Therefore,both the developed system and model are feasible and reliable in different climate regions.展开更多
Integration of renewable energy generators has greatly altered both static and dynamic characteristics of the system.Combined with the uncertainties it introduced,the risk of a system being transient instable is signi...Integration of renewable energy generators has greatly altered both static and dynamic characteristics of the system.Combined with the uncertainties it introduced,the risk of a system being transient instable is significantly alleviated.This paper proposes a multi-objective coordinated post-contingency control method.It aims to increase post-contingency system security with emergence control(EC)while minimizing the total control cost.Two ECs are adopted in this paper:energy storage systems(ESSs)and emergency load shedding(ELS).ESSs are immediately connected to the network after contingency occurrence to provide both active and reactive power support.ELS will be triggered when the support from ESSs is insufficient to stabilize the system to prevent further deterioration of system security.Performance of the proposed method was evaluated on a modified New England 39-bus benchmark system.The results indicate that the proposed method can find solutions to stabilize the system against credible contingencies and optimally balance between system stability and economy.展开更多
文摘The synchronous virtual machine uses inverter power to imitate the performance of the conventional synchronous machine.It also has the same inertia,damping,frequency,voltage regulation,and other external performance as the generator.It is the key technology to realize new energy grid connections’stable and reliable operation.This project studies a dynamic simulation model of an extensive new energy power system based on the virtual synchronous motor.A new energy storage method is proposed.The mathematical energy storage model is established by combining the fixed rotor model of a synchronous virtual machine with the charge-discharge power,state of charge,operation efficiency,dead zone,and inverter constraint.The rapid conversion of energy storage devices absorbs the excess instantaneous kinetic energy caused by interference.The branch transient of the critical cut set in the system can be confined to a limited area.Thus,the virtual synchronizer’s kinetic and potential energy can be efficiently converted into an instantaneous state.The simulation of power system analysis software package(PSASP)verifies the correctness of the theory and algorithm in this paper.This paper provides a theoretical basis for improving the transient stability of new energy-connected power grids.
文摘The purpose of this research is to develop a SolidWorks? model for transient temperature field of laser welding of PMMA/SS 304 materials for application in fabrication of the ultrasonic back-plate, with a view of optimizing the experimental conditions. The study is carried out on these materials because of the increasing application of both metals and non-metals. The work focuses specifically on these materials because they have been experimentally studied previously and as such, this study can be accepted as an assessment into feasibility of using SolidWorks? model to study the temperature field of the laser welding processes of metals and non-metals. The results of the SolidWorks? transient thermal model show that there is a concentration of high temperatures at the point of contact. It also shows that temperature decreases as we move in (between laser and the top face) to the thickness of the part. Additionally the maximum temperature occurs at the last point of the welding;this may be due to the accumulation of the temperature before arriving at the end. These findings are comparable to the previous simulated and experimental results on temperature field during laser welding of PMMA/SS 304 materials. However, SolidWorks? is shown to present a challenge in modeling a moving source of laser power.
基金supported by National Natural Science Foundation of China(52074248)Fundamental Research Funds for the Central Universities(2652022207).
文摘The utilization of hydraulic fracturing for the extraction of natural gas hydrates in maritime environments has been relatively underexplored in the existing literature.This study introduces a novel approach by employing a fully implicit integration method to construct a two-dimensional temperature distribution model of the wellbore.The model considers critical parameters such as fracturing fluid time,initial temperature,and fracturing fluid displacement to forecast the temperature data of the wellbore and its surrounding environments throughout the entire fracturing process.The investigation reveals that the initial temperature of the fracturing liquid and the duration of the fracturing process exert a substantial influence on the wellbore temperature,whereas the impact of fracturing fluid displacement is found to be minimal.Furthermore,a comparative analysis between the results derived from the proposed model and those obtained from traditional steady-state formulas substantiates the accuracy and efficacy of the developed model.This study significantly advances our comprehension of temperature dynamics within wellbores during hydraulic fracturing operations in maritime environments,thereby offering valuable insights for future endeavors in natural gas hydrate extraction.
基金Project(51078127) supported by the National Natural Science Foundation of ChinaProject(JJ201109091631) supported by the Foundation for Young Scientists of Jiangxi Education Department, China
文摘A modified one-dimensional transient hygrothermal model for multilayer wall was proposed using air humidity ratio and temperature as the driving potentials.The solution for the governing equations was obtained numerically by implementing the finite-difference scheme.To evaluate the accuracy of the model,a test system was built up to measure relative humidity and temperature within a porous wall and compare with the prediction of the model.The prediction results have good agreement with the experimental results.For the interface close to indoor side,the maximum deviation of temperature between calculated and test data is 1.87 K,and the average deviation is 0.95 K;the maximum deviation of relative humidity is 11.4%,and the average deviation is 5.7%.For the interface close to outdoor side,the maximum deviation of temperature between prediction and measurement is 1.78 K,and the average deviation is 1.1 K;the maximum deviation of relative humidity is 9.9%,and the average deviation is 4.2%.
文摘A new analytical model of a 3-degree-of-freedom （3-DOF） gyro-accelerometer system consisting of a 1-DOF drive and 2-DOF sense modes is presented. The model constructs lumped differential equations associated with each DOFof the system by vector analysis. The coupled differential equations thus established are solved analytically for their responses in both the time and frequency domains. Considering these frequency response equations, novel device design concepts are derived by forcing the sense phase to zero, which leads to a certain relationship between the structural frequencies, thereby causing minimization of the damping effect on the performance of the system. Furthermore, the feasibility of the present gyro-accelerometer structure is studied using a unique discriminatory scheme for the detection of both gyro action and linear acceleration at their events. This scheme combines the formulated settled transient solution of the gyro-accelerometer with the processes of synchronous demodulation and filtration, which leads to the in-phase and quadrature components of the system＇s output signal. These two components can be utilized in the detection of angular motion and linear acceleration. The obtained analytical results are validated by simulation in a MATLAB/Simulink environment, and it is found that the results are in excellent agreement with each other.
基金the start-up fund provided by the Engineering Science and Mechanics Department, College of Engineering, and Materials Research Institute at the Pennsylvania State University (215-37 1001 cc:H.Cheng)
文摘Transient electronics are an emerging class of electronics with the unique characteristic to completely dissolve within a programmed period of time. Since no harmful byproducts are released, these electronics can be used in the human body as a diagnostic tool, for instance, or they can be used as environmentally friendly alternatives to existing electronics which disintegrate when exposed to water. Thus, the most crucial aspect of transient electronics is their ability to disintegrate in a practical manner and a review of the literature on this topic is essential for understanding the current capabilities of transient electronics and areas of future research. In the past, only partial dissolution of transient electronics was possible, however, total dissolution has been achieved with a recent discovery that silicon nanomembrane undergoes hydrolysis. The use of single- and multi-layered structures has also been explored as a way to extend the lifetime of the electronics. Analytical models have been developed to study the dissolution of various functional materials as well as the devices constructed from this set of functional materials and these models prove to be useful in the design of the transient electronics.
基金supported by the 2013 Inje University Research Grant
文摘Experimental stroke research commonly employs focal cerebral ischemic rat models （Bederson et al., 1986a; Longa et al., 1989）. In human patients, ischemic stroke typically results from thrombotic or embolic occlusion of a major cerebral artery, usually the mid- dle cerebral artery （MCA）. Experimental focal cerebral ischemia models have been employed to mimic human stroke （Durukan and Tatlisumak, 2007）. Rodent models of focal cerebral ischemia that do not require craniotomy have been developed using intraluminal suture occlusion of the MCA （MCA occlusion, MCAO） （Rosamond et al., 2008）. Furthermore, mouse MCAO models have been wide- ly used and extended to genetic studies of cell death or recovery mechanisms （Liu and McCullough, 2011）. Genetically engineered mouse stroke models are particularly useful for evaluation of isch- emic pathophysiology and the design of new prophylactic, neuro- protective, and therapeutic agents and interventions （Armstead et al., 2010）. During the past two decades, MCAO surgical techniques have been developed that do not reveal surgical techniques for mouse MCAO model engineering. Therefore, we compared MCAO surgical methods in rats and mice.
文摘This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials （FGMs）. First, a Laplace transform approach is used to handle the time variable. Then, a fundamental solution in Laplace space for FGMs is constructed. Next, a hybrid graded element is formulated based on the obtained fundamental solution and a frame field. As a result, the graded properties of FGMs are naturally reflected by using the fundamental solution to interpolate the intra-element field. Further, Stefest＇s algorithm is employed to convert the results in Laplace space back into the time-space domain. Finally, the performance of the proposed method is assessed by several benchmark examples. The results demonstrate well the efficiency and accuracy of the proposed method.
文摘In the course of completion of an ultra-deep well newly drilled in the Yuanba Gasfield,Sichuan Basin,long-section and large-scale deformation occurred in the heavy casing section and nickel base alloy casing section of the sealing Triassic limestone interval,so a new hole had to be sidetracked,which impels us to rediscover the applicability of conventional drilling and completion technology in ultra-deep wells.In this paper,based on the borehole condition and field operation data of this well,the borehole pressure field variation initiated by lost circulation in the low-pressure formation was analyzed from the perspective of dynamics,then,the variation pattern of differential pressure inside and outside the well bore at different time intervals was depicted,and the primary cause of such complication was theoretically revealed,i.e.,the pressure wave generated by instant lost circulation in low-pressure formation would result in redistribution of pressure inside the downhole confined space,and then the crush of casing in the vicinity of local low-pressure areas.Pertinent proposals for avoiding these kinds of engineering complexities were put forward:①when downhole sealing casing operation is conducted in open hole completion,liner completion or perforated hole,the potential damage of lost circulation to casing should be considered;②the downhole sealing point and sealing mode should be selected cautiously:the sealing point had better be selected in the section with good cementing quality or as close to the casing shoe as possible,and the sealing mode can be either cement plug or mechanical bridge plug.This paper finally points out that good cementing quality plays an important role in preventing this type of casing deformation.
基金supported by the Open Fund of Science and Technology on Thermal Energy and Power Laboratory(Grant No.TPL2022B02)。
文摘The dynamic behaviors of hydrodynamic journal bearings can be influenced by several coupling factors,including cavitation,elastic deformation,surface asperity,and even electromagnetic fields in systems.In this study,we establish a transient lubrication model to investigate the dynamic lubrication process of journal bearings,fully considering these physical phenomena in the application of micropumps.Rotor trajectory measurements are conducted to validate the proposed model,which results in an error margin of less than 9.6%.Furthermore,the tribodynamic responses of hydrodynamic journal bearings are analyzed theoretically under various operational conditions,such as start-up,shock loading,and speed variation.The variation in the flow field from the mixed-lubrication regime to the hydrodynamic lubrication regime is investigated and qualified during the start-up stage.The analytical model enables the prediction of the transient lubrication performance under various load conditions,such as sharp shock,helping verify the design effectiveness of the journal bearing.Additionally,the dynamic relationships between the motion parameters and forces are demonstrated and compared.Our findings indicate that the gyroscopic torque can suppress the deflection of the rotor and that the hydrodynamic force can inhibit the rotor's radial displacement,thus maintaining the rotor's dynamic stability.The methods proposed in this work are instructive for the theoretical modeling and optimization of inclined journal bearings.
基金the financial support of National Key R&D Program of China (No.2017YFB1201100)
文摘Unmanned Aerial Vehicle（UAV） is developing towards the direction of High Altitude Long Endurance（HALE）. This will have an important influence on the stability of its airborne electronic equipment using passive thermal management. In this paper, a multi-node transient thermal model for airborne electronic equipment is set up based on the thermal network method to predict their dynamic temperature responses under high altitude and long flight time conditions. Some relevant factors are considered into this temperature prediction model including flight environment,radiation, convection, heat conduction, etc. An experimental chamber simulating a high altitude flight environment was set up to survey the dynamic thermal responses of airborne electronic equipment in a UAV. According to the experimental measurement results, the multi-node transient thermal model is verified without consideration of the effects of flight speed. Then, a modified way about outside flight speed is added into the model to improve the temperature prediction performance. Finally, the corresponding simulation code is developed based on the proposed model. It can realize the dynamic temperature prediction of airborne electronic equipment under HALE conditions.
基金Supported by National Science and Technology Major Project of the Ministry of Science and Technology of China(2016ZX05026-002,2016ZX05028-001,2016ZX05024-005)
文摘As the classical transient flow model cannot simulate the water hammer effect of gas well, a transient flow mathematical model of multiphase flow gas well is established based on the mechanism of water hammer effect and the theory of multiphase flow. With this model, the transient flow of gas well can be simulated by segmenting the curved part of tubing and calculating numerical solution with the method of characteristic curve. The results show that the higher the opening coefficient of the valve when closed, the larger the peak value of the wellhead pressure, the more gentle the pressure fluctuation, and the less obvious the pressure mutation area will be. On the premise of not exceeding the maximum shut-in pressure of the tubing, adopting large opening coefficient can reduce the impact of the pressure wave. The higher the cross-section liquid holdup, the greater the pressure wave speed, and the shorter the propagation period will be. The larger the liquid holdup, the larger the variation range of pressure, and the greater the pressure will be. In actual production, the production parameters can be adjusted to get the appropriate liquid holdup, control the magnitude and range of fluctuation pressure, and reduce the impact of water hammer effect. When the valve closing time increases, the maximum fluctuating pressure value of the wellhead decreases, the time of pressure peak delays, and the pressure mutation area gradually disappears. The shorter the valve closing time, the faster the pressure wave propagates. Case simulation proves that the transient flow model of gas well can optimize the reasonable valve opening coefficient and valve closing time, reduce the harm of water hammer impact on the wellhead device and tubing, and ensure the integrity of the wellbore.
基金The project supported by the National Natural Science Foundation of China and Doctorial Fund
文摘A transient molecular network model is built to describe the non- linear viscoelasticity of polymers by considering the effect of entanglement loss and regeneration on the relaxation of molecular strands. It is an extension of previous network theories. The experimental data on three thermoplastic polymers (ABS, PVC and PA6) obtained under various loading conditions are used to test the model. Agreement between the theoretical and experimental curves shows that the suggested model can describe successfully the relaxation behavior of the thermoplastic polymers under different loading rates by using relatively few relaxation modes. Thus the mi- cromechanism responsible for strain-rate dependence of relaxation process and the origin of nonlinear viscoelasticity may be disclosed.
文摘A practical approach is discussed for sub-sea pipeline monitoring and leak detection based on the real time transient model . The characteristic method of transient simulation is coupled with the Extended Kalman Filter to estimate the system state where the only observed data are inlet and outlet flow rate and pressure. Because EKF has a time variant track under the non-stationary stochastic process with additive Gaussian noise, the high sensitivity of RTTM to non-stationary operating condition is reduced. A leak location recursion estimation formula is presented based on the real time observed data. The results of 27 groups of test data indicate that the procedure presented is sensitive to a wide range of detectable leak sizes and has a low average relative error of leak location .
文摘Porous electrodes with three-phase reaction in low temperature fuel cells have attracted much attention by their flooding phenomena. In order to have a better understanding of the flooding phenomena inside electrode, it is important to evaluate various discharge conditions of the flooded electrodes. A model of flooded porous electrode under the influence of potential sweep was developed to evaluate the flooding conditions in-situ. The hysteresis of current density vs. time was observed at high sweep rates （1 O0 mV.sl）. It was not observed at low sweep rate （0.1 mV-s~）. In this study, these characteristics of flooding and hysteresis conditions were found to be markedly dependent on the potential scan rate. These dynamic behaviors are interpreted in terms of water saturation response, velocity of water movement, and evaporation rate of water.
基金This research is supported by the National Natural Science Foundation of China-Deutsche Forschungsgemeinschaft Mobility Programme(M-0368).
文摘Aiming to efficiently simulate the transient process of transpiration cooling with phase change and reveal the convection mechanism between fluid and porous media particles in a continuum scale,a new two-phase mixture model is developed by incor-porating the local thermal non-equilibrium effect.Considering the low-pressure and high overload working conditions of hypersonic flying,the heat and mass transfer induced by capillary and inertial body forces are analyzed for sub-cooled,saturated and super-heated states of water coolant under varying saturation pressures.After the validation of the model,transient simulations for different external factors,includ-ing spatially-varied heat flux,coolant mass flux,time-dependent external pressure and aircraft acceleration are conducted.The results show that the vapor blockage patterns at the outlet are highly dependent on the injection mass flux value and the external pressure,and the reduced saturation temperature at low external pressure leads to early boiling off and vapor blockage.The motion of flying has a large influence on the cooling effect,as the inertial force could change the flow pattern of the fluid inside significantly.The comparison of the results from 2-D and 3-D simulations sug-gests that 3-D simulation shall be conducted for practical application of transpiration cooling,as the thermal protection efficiency may be overestimated by the 2-D results due to the assumption of an infinite width length of the porous plate.
基金supported by the National Natural Science Foundation of China(Grant No.52207190)Jiangsu Excellent Postdoctoral Program,China(Grant No.2022ZB80).
文摘Grid-forming converters(GFMs)are faced with the threat of transient inrush current and synchronization instability issues when subjected to grid faults.Instead of disconnecting from the grid unintentionally,GFMs are required to have fault ride through(FRT)capability to maintain safe and stable operation in grid-connected mode during grid fault periods.In recent studies,different FRT control strategies with distinguishing features and that are feasible for different operation conditions have been proposed for GFMs.To determine their application scope,an intuitive comparison of the transient performance of different FRT control strategies is presented in this paper.First,three typical FRT control strategies(virtual impedance,current limiters,and mode-switching control)are introduced and transient mathematical models are established.A detailed comparison analysis on transient inrush current and transient synchronization stability is then presented.The results will be useful for guiding the selection and design of FRT control strategies.Finally,simulation results based on PSCAD/EMTDC are considered to verify the correctness of the theoretical analysis.
基金Sichuan Science and Technology Program,Grant/Award Number:2023NSFSC0297。
文摘C_(5)F_(10)O/CO_(2)gas mixture is one of the most promising alternatives to SF_(6)as an insulating gas in high-voltage switchgear.As a key performance index in product design,the temperature rise characteristics are rarely reported.In this paper,the thermodynamic parameters of C_(5)F_(10)O/CO_(2)gas mixture were calculated first.Then,the calculation model of transient temperature rise was constructed for a 252 kV/3150 A bus,and a temperature rise experimental platform was built to verify the reliability of the proposed calculation model.On this basis,the influence of different factors such as load current,charging pressure,mixing ratio,and structure size on the temperature rise of the bus was further analysed,and it is found that increasing the charging pressure and the mixing ratio of C5F10O could effectively reduce the bus temperature rise but it still could not reach the level of SF_(6).The main structure size that affects the temperature rise of the bus is the outer diameter of the conductor,which increases by 10.2%,and the temperature rise is the same as that of the original SF_(6)bus.Finally,a high-precision bus temperature rise surrogate model,which combined with the Latin hypercube model,the coefficient of prognosis,and the Kriging fitting method was established to facilitate the structural design.
基金This work was supported by the National Natural Science Foundation of China(No.51666018,No.51966019)Department of Education Foundation in Yunnan Province of China(No.2018JS147).
文摘Solar-air source heat pump(solar-ASHP)system has a potential application in the field of hot water and space heating in residential buildings.Such system features the complementary advantages to solve the discontinuous operation of the single solar system and the frosting issue of the single ASHP system.This paper built the solar-ASHP systems in Kunming and Shangri-La,and tested the system performance under different weather conditions in these two regions of plateau.Meanwhile,the transient heat balance models of the system were established under the sunlight time and non-sunlight time and were verified by the experimental results.Moreover,the verified model was applied to reveal the energy balance performance between the energy supply and building heat demand.The law of the system performance affected by the ambient temperature,effective heat collecting area,and cumulative heating capacity of collector was explored by the validated model.The results indicate that when the ambient temperature decreases by 1℃during non-sunlight time,the energy efficiency ratio decreases by about 0.07.A square meter decline in the effective heat collecting area pushes an increase in the heating capacity of 5.75 MJ.Meanwhile,the cumulative heating capacity of collector increases by 5 MJ,and the ASHP energy consumption decreases by 0.54 kWh.The dynamic changes of the ambient temperature and instantaneous solar radiation are the main reasons of the heat balance errors.Therefore,both the developed system and model are feasible and reliable in different climate regions.
基金supported by Arc Research Huh for Integrated Energy Storage Solutions(IH180100020).
文摘Integration of renewable energy generators has greatly altered both static and dynamic characteristics of the system.Combined with the uncertainties it introduced,the risk of a system being transient instable is significantly alleviated.This paper proposes a multi-objective coordinated post-contingency control method.It aims to increase post-contingency system security with emergence control(EC)while minimizing the total control cost.Two ECs are adopted in this paper:energy storage systems(ESSs)and emergency load shedding(ELS).ESSs are immediately connected to the network after contingency occurrence to provide both active and reactive power support.ELS will be triggered when the support from ESSs is insufficient to stabilize the system to prevent further deterioration of system security.Performance of the proposed method was evaluated on a modified New England 39-bus benchmark system.The results indicate that the proposed method can find solutions to stabilize the system against credible contingencies and optimally balance between system stability and economy.
