B-COPNA resin formation from ethylene tar light fractions:Process development and mechanical exploration by molecular simulation

An efficient utilization strategy of ethylene tar(ET),the main by-product of the ethylene cracking unit,is urgently required to meet demands for modern petrochemical industry.On the other hand,condensed polynuclear aromatic resin of moderate condensation degree(B-COPNA)is a widely used carbon material due to its superb processability,the production of which is,however,seriously limited by the high cost of raw materials.Under such context,an interesting strategy was proposed in this study for producing B-COPNA resin using crosslinked light fractions of ethylene tar(ETLF,boiling point<260℃)facilitated by molecular simulation.1,4-Benzenedimethanol(PXG)was first selected as the crosslinking agent according to the findings of molecular simulation.The effects of operating conditions,including reactions temperature,crosslinking agent,and catalyst content on the softening point and yield of B-COPNA resin products were then investigated to optimize the process.The reaction mechanism of resin production was studied by analyzing the molecular structure and transition state of ETLF and crosslinking agents.It was shown that PXG exhibited a superior capacity of withdrawing electrons and a higher electrophilic reactivity than other crosslinking agents.In addition to the highest yield and greatest heat properties,PXG-prepared resin contained the most condensed aromatics.The corresponding optimized conditions of resin preparation were 180℃,1:1.9(PXG:ETLF),and 3%(mass)of catalyst content with a resin yield of 78.57%.It was the electrophilic substitution reaction that occurred between the ETLF and crosslinking agent molecules that were responsible for the resin formation,according to the experimental characterization and molecular simulation.Hence,it was confirmed that the proposed strategy and demonstrated process can achieve a clean and high value-added utilization of ETLF via B-COPNA resin preparation,bringing huge economic value to the current petrochemical industry.

Deglacial change of Antarctic Bottom Water in transient simulations

本文利用气候瞬变模拟试验TraCE21k分析了末次冰消期南极底层水(Antarctic Bottom Water,AABW)的演变特征及物理机制.TraCE21k的全强迫试验复现了观测记录里现代大西洋AABW相对于冰期时变薄的特征,其强迫敏感性试验进一步指出冰期-现代AABW的差异主要由大气温室气体的升高及大陆冰川的退缩二者共同驱动.冰消期气候强迫下海洋和大气温度升高,南大洋海冰逐渐消融,后者直接调控了AABW强度和形态的演变.本文还从绝热翻转环流的观点出发,认为冰消期南大洋的气候变化潜在影响了北大西洋深层水的演变.

The steady-state and dynamic simulation of cascade distillation system for the production of oxygen-18 isotope from water

Accurate simulation of water distillation system for oxygen-18(18O) isotope separation is necessary to guide industrial practice, since both deuterium(D) and oxygen-18 isotope get enriched and interfere with each other. In the present work, steady-state and dynamic distillation models are established based on a classic method and a cascade distillation system with 5 towers is introduced to test the models. The theoretical expressions of separation factor αH/Dfor protium/deuterium and separation factor α^(16)O/^(18) O.for oxygen-16/oxygen-18 were derived,with the existence of deuterium and oxygen-18, respectively. The results of the steady-state simulation by the classical method proposed in the present work agreed well with the results of the lumping method. The dynamic process could be divided into 5 stages. Impressively, a peak value of product withdraw was observed before the final steady state, which was resulted from the change of ^(16)O/^(18) O separation factor and isotope distribution. An interesting low concentration zone in the towers of T2–T5 existed at the beginning of the dynamic process and it required industrial evidence.

Equivalent Method of Integrated Power Generation System of Wind, Photovoltaic and Energy Storage in Power Flow Calculation and Transient Simulation

针对工程实际开展风光储联合发电系统在潮流计算和机电暂态仿真中的等值方法研究，旨在为大容量风光储联合发电系统的并网仿真分析奠定基础。将潮流计算的等值分为单元机组和集电系统2部分来研究。单元机组等值采用根据不同控制模式选取不同节点类型的方法，针对集电系统等值提出基于损耗不变原则的方法。等值模型和详细模型的算例结果表明，潮流计算等值方法具有较好的精度。在机电暂态仿真动态等值中，基于实际工程计算的最严重工况分析原则，提出运行在满出力点的单机“倍乘”等值模型，为工程计算中的风光储联合发电系统动态等值提供了一种解决方案。

Impact of Typical Steady-state Conditions and Transient Conditions on Flow Ripple and Its Test Accuracy for Axial Piston Pump

The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy of flow ripple is above 93.07%. The model constructed in this research proposes a method to determine the flow ripple characteristics of pump and its attainable test accuracy under the large-scale and time-variant working conditions. Meanwhile, a discussion about the variation of flow ripple and its obtainable test accuracy with the conditions of the pump working in wide operating ranges is given as well.

Numerical Simulation of Transient Thermal Stress Field for Laser Metal Deposition Shaping

To decrease thermal stress during laser metal deposition shaping(LMDS)process,it is of great importance to learn the transient thermal stress distribution regularities.Based on the“element life and death”technique of finite element analy- sis(FEA),a three-dimensional multi-track and multi-layer numerical simulation model for LMDS is developed with ANSYS parametric design language(APDL)for the first time,in which long-edge parallel reciprocating scanning paths is introduced. Through the model,detailed simulations of thermal stress during whole metal cladding process are conducted,the generation and distribution regularities of thermal stress are also discussed in detail.Using the same process parameters,the simulation results show good agreement with the features of samples which fabricated by LMDS.

Dynamic phasor-based hybrid simulation for multi-inverter grid-connected system

To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient and dynamic phasors. Based on a demonstration of the concepts and properties of dynamic phasors, the models of single-phase and three-phase inverters described by dynamic phasors are established first. Considering the numerical compatibility problem between dynamic phasors and instantaneous values, an interface scheme between dynamic phasors and instantaneous values is designed, and the efficiency and precision differences of various transformation methods are compared in detail.Finally, by utilizing MATLAB/Simulink, a hybrid simulation platform of a multi-inverter grid-connected system is built, and the efficiency and accuracy of the hybrid simulation are validated via comparison with the full electromagnetic transient simulation.

Three-dimensional transient numerical simulation for intake process in the engine intake port-valve-cylinder system

This paper presents a KIVA-3 code based numerical model for three-dimensional transient intake flow in the intake port-valve-cylinder system of internal combustion engine using body-fitted technique, which can be used in numerical study on internal combustion engine with vertical and inclined valves, and has higher calculation precision. A numerical simulation (on the intake process of a two-valve engine with a semi-sphere combustion chamber and a radial intake port) is provided for analysis of the velocity field and pressure field of different plane at different crank angles. The results revealed the formation of the tumble motion, the evolution of flow field parameters and the variation of tumble ratios as important information for the design of engine in-take system.

Numerical simulation of transient flow performance during different periods in centrifugal pumpNumerical simulation of transient flow performance during different periods in centrifugal pump

The instantaneous variations of the hydraulic characteristics take place in centrifugal pumps during their start-up,shutdown and other variable speed operations.In this paper,the variable speed method was proposed to simulate the transient internal flow field and the external performance of the pump during starting and stopping periods.The terms of accelerations due to variable speeds in the flow governing equations were analyzed in a multiple reference of frame(MRF).A transient CFD simulation was performed for a typical centrifugal pump by using ANSYS-CFX with the standard k-εturbulence model.The entire simulation process was composed of four stages:start-up,normal run,shutdown and post-shutdown.The function of rotating speed with regard to time was set by CEL language directly into the impeller domain in the pre-processor of the software to conduct variable speed simulation.The variations of the flow field in the centrifugal pump were obtained from the transient simulation.The changing laws of flow rate,head and other performance parameters over time were also analyzed and summarized.

Simulations of the Transient Flow Generated from a Started Flat Plate

Transient operations are commonly founded in fluid machineries such as the starting, stopping, and variations of rotor speeds, etc. Flow generated from a started fiat plate is of fundamental importance. Experiments have been done to observe the flow evolution in current researches. And in order to explore the flow in more detailed scale, some vortex methods with high resolution and other numerical methods were developed to solve various related problems by some researchers. But the promotion of vortex method to engineering application is rare due to its complexity and difficulty in specifying the boundary conditions. In order to build up a method of numerical study for such problems, a simplified model is built up with a flat plate. The development of two-dimensional viscous incompressible flow generated from an impulsively started and uniformly accelerated infinitesimally thin flat plate is simulated numerically. A dynamic mesh（DM） method based on the spring analogue and local remeshing is applied to realize the mesh motion caused by the started plate. Researches show that the mesh quality will decline under large grid shear force during the updating process. To conquer this problem, a region near the plate is separated to guarantee the mesh quality at location of interest which is the innovation of the present paper. All computations at least cover a period during which the plate translates 6 times its length. The simulated instantaneous velocity profiles, flow structures and drag coefficients under several Reynolds numbers （20 ≤ Re ≤ 126） and accelerations （20 m/s2≤ a ≤ 152 m/s2） are presented and compared with existing results in literatures. Comparisons are found to be satisfactory, confirming the validity of the current proposed method（region separated DM）. The proposed DM method is firstly used to study the transient flow generated from a started flat plate and can be used in further study of transient characteristics during transient operations of turbo machineries.

A Unique Modelling Strategy to Dynamically Simulate the Performance of a Lobe Pump for Industrial Applications

The performance of a newly designed tri-lobe industrial lobe pump of high capacity is simulated by using commercial CFD solver Ansys Fluent. A combination of user-defined-functions and meshing strategies is employed to capture the rotation of the lobes. The numerical model is validated by comparing the simulated results with the literature values. The processes of suction, displacement, compression and exhaust are accurately captured in the transient simulation. The fluid pressure value remains in the range of inlet pressure value till the processes of suction and displacement are over. The instantaneous process of compression is accurately captured in the simulation. The movement of a particular working chamber is traced along the gradual degree of lobe’s rotation. At five different degrees of lobe’s rotation, pressure contour plots are reported which clearly shows the pressure values inside the working chamber. Each pressure value inside the working chamber conforms to the particular process in which the working chamber is operating. Finally, the power requirement at the shaft of rotation is estimated from the simulated values. The estimated value of power requirement is 3.61 BHP FHP whereas the same calculated theoretically is 3 BHP FHP. The discrepancy is attributed to the assumption of symmetry of blower along the thickness.

Transient simulation and analysis of current collapse due to trapping effects in AlGaN/GaN high-electron-mobility transistor

In this paper, two-dimensional （2D） transient simulations of an A1GaN/GaN high-electron-mobility transistor （HEMT） are carded out and analyzed to investigate the current collapse due to trapping effects. The coupling effect of the trapping and thermal effects are taken into account in our simulation. The turn-on pulse gate-lag transient responses with different quiescent biases are obtained, and the pulsed current-voltage （l-V） curves are extracted from the transients. The experimental results of both gate-lag transient current and pulsed I-V curves are reproduced by the simulation, and the current collapse due to the trapping effect is explained from the view of physics based on the simulation results. In addition, the results show that bulk acceptor traps can influence the gate-lag transient characteristics of A1GaN/GaN HEMTs besides surface traps and that the thermal effect can accelerate the emission of captured electrons for traps. Pulse transient simulation is meaningful in analyzing the mechanism of dynamic current collapse, and the work in this paper will benefit the reliability study and model development of GaN-based devices.

PHOTOCONDUCTIVE PROPERTIES OF PVK:Alq_3 BLEND FILMS STUDIED BY STEADY-STATE AND TIME-RESOLVED TRANSIENT PHOTOCURRENT SPECTRA

The carrier transport properties of the blends of the hole transport material poly(N-vinylcarbazole) (PVK) and the electron transport material tris (8-hydroxyquinolinolato) aluminumⅢ(Alq_3) are investigated at room temperature using steady-state and time-resolved transient photocurrent measurements as a function of doping concentration of Alq_3.Due to lower LUMO and higher HOMO energy level of Alq_3 than those of PVK,Alq_3 molecules may act as carrier trap states in PVK films at low concentration.However,at...

Nonlinear Switching Transient Field Simulation of Cable Joint without Residual Charge

The analysis of the impulse voltage on the internal electric field of the cable joint plays a key role in studying the breakdown of the joint. Based on the finite element method, a three-dimensional electromagnetic field simulation model of the cable joint is established in this paper. Simulation results show that the voltage at the head of the cable joint reaches about twice the impulse voltage. The increase of the conductivity of semi-conductive material also leads to the increase of electric field intensity. Then, several points and curves at different positions are selected for further analysis in this paper. Among them, the electric field distortion at the edge of the high voltage shield is the most serious and the electric field in the air gap is the least.

On Transient Simulation of Field Equations

We investigate under what conditions transient simulation could be used to integrate backward in time so that the initial field could be recovered from later histories. In this paper we use realistic examples and find that, in long histories, traces of the initial field would be present only in the exact analytical solutions. We conclude that the recovery of initial field is possible only if the equations could be solved analytically or only short time periods are involved. In practice, it is not possible to detect those traces by measurements or observations. If numerical procedures are used, truncation and discretization errors are always present. Fine-tuning of system parameters used or transforming time into another pseudo time frame may allow numerical integration to be carried out backward in time. But numerical instability is still a problem. Large spurious increases found by numerical procedures are most likely due to numerical inaccuracy and instability.

Discussion on the application prospect of the transient electromagnetic method based on the dual launcher and mine advanced detection

The dual transmitter implements the equivalent anti-magnetic flux transient electromagnetic method, which can effectively reduce the scope of the transient electromagnetic detection blind area. However, this method is rarely reported in the detection of pipelines in urban geophysical exploration and the application of coal mines. Based on this, this paper realizes the equivalent anti-magnetic flux transient electromagnetic method based on the dual launcher. The suppression effect of this method on the blind area is analyzed by physical simulation. And the detection experiment of underground pipelines is carried out outdoors. The results show that the dual launcher can significantly reduce the turn-off time, thereby effectively reducing the impact of the blind area on the detection results, and the pipeline detection results verify the device’s effectiveness. Finally, based on the ground experimental results, the application prospect of mine advanced detection is discussed. Compared with other detection fields, the formation of blind areas is mainly caused by the equipment. If the dual launcher can be used to reduce the blind area, the accuracy of advanced detection can be improved more effectively. The above research results are of great significance for improving the detection accuracy of the underground transient electromagnetic method.

The Analysis of the Differences between Electromechanical Transients Simulation and Electromagnetic Transients Simulation

The paper firstly interprets the differences between electromechanical transients program BPA and electromagnetic transients program EMTDC in the field of principle, model and algorithm. Then the authors carry out the simulation based on single-machine infinite-bus system and draw some conclusions. The time consumption of the simulation using EMTDC is much longer than the simulation using BPA under the same length of time. The results of BPA are close to those of EMTDC under steady conditions. The fundamental frequency component of the EMTDC results seems closer to the BPA results than its original value, but they still away from completely consistent. In this simulation of single-machine infinite-bus system, the transient stability results of BPA and EMTDC are close, but the results of BPA are apt to be more conservative. All the conclusions above have a certain reference value to both hybrid simulation and comprehensive analysis method in the study of the AC/DC digital simulation of large power grid.

Modeling and Simulation for Transient Thermal Analyses Using a Voltage-in-Current Latency Insertion Method

This article presents a modeling and simulation method for transient thermal analyses of integrated circuits(ICs)using the original and voltage-in-current(VinC)latency insertion method(LIM).LIM-based algorithms are a set of fast transient simulation methods that solve electrical circuits in a leapfrog updating manner without relying on large matrix operations used in conventional Simulation Program with Integrated Circuit Emphasis(SPICE)-based methods which can significantly slow down the solution process.The conversion from the thermal to electrical model is performed first by using the analogy between heat and electrical conduction.Since electrical inductance has no thermal equivalence,a modified VinC LIM formulation is presented which removes the requirement of the insertion of fictitious inductors.Numerical examples are presented,which show that the modified VinC LIM formulation outperforms the basic LIM formulation,in terms of both stability and accuracy in the transient thermal simulation of ICs.

Simulation research and application on response characteristics of detecting water-filled goaf by transient electromagnetic method

Water inrush disasters poses a great threat to the safe exploitation of coal resources.To solve this problem,the transient electromagnetic method(TEM)was proposed to accurately detect the water accumulation in the goaf.The electromagnetic response characteristics of diferent water-flled goaves were studied by electromagnetic feld theory,numerical simulation and feld verifcation.Through the models of 100%water accumulation,50%water accumulation,0%water accumulation,100%water accumulation with collapsed rock,50%water accumulation with collapsed rock and 0%water accumulation with collapsed rock goaf,the characteristics of induced voltage attenuation curves were studied.Meanwhile,the relationship between the attenuation voltage value and area of the transmitting coil,the depth of the goaf,the background resistivity,and the delay time were also simulated.The results illustrate that the attenuation curve of induced voltage presented a regular exponential decay form in the 0%water accumulation model but existed abnormal exaltation for voltage in water-flled model.Through the linear ftting curve,it can be seen that the abnormal intensity of the induced voltage becomes stronger as the distance between the measuring point and the center of the target decrement.Moreover,the abnormal amplitude of the induced voltage increases with the rise of the water accumulation and collapsed rock will weakly reduce the low-resistivity anomalous efect on the water-accumulated goaf.In addition,the response value of the attenuation voltage increased as the area of the transmitting coil increases,but decreased with increasing delay time and increasing background resistivity and depth of the target body.The feld detection results of the Majiliang coal mine also confrmed the theoretical analysis and the numerical simulation.

Transient Simulation and Optimization of Regional Integrated Energy System

A modeling method of regional integrated energy system based on bus method and transient simulation is proposed,and the system optimization is based on the dynamic balance of supply and demand in the whole year energy supply cycle.A CCHP systemof gas turbine coupled with ground source heat pump and electric refrigeration unit is constructed.The energy relationship of the systemis described by bus structure,and the transient calculationmodel is built on TRNSYS platform.The weighted sum of annual total cost saving rate,primary energy saving rate and environmental pollutant shadow cost saving rate is taken as the optimized objective function,and on the basis of annual dynamic balance,the Hooke-Jeeves algorithm is used for optimization of the system configuration.A complex commercial area in Beijing is taken as an example,and different weighting coefficients are set for optimization of the system configuration.The results show that,from the perspective of economy,environmental benefit and primary energy consumption,performance of the system increases and then decreases with rise of gas turbine power;under the simulated cooling/heating load,the maximum number of optimum configuration is seen in the combination of 35 kW gas turbine+723 kW GSHP and 1178 kW electric chiller;in comparison with traditional distributed system,the annual cost saving rate,primary energy saving rate and environmental pollutant shadow cost saving rate of the system are 29.4%,49.6%and 58.2%,respectively.