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The present article investigates the quality factor of thermoelastic damping in micro-beam resonator from the standpoint of a very recent thermoelasticity theory proposed by Quintanilla (2011). In recent years, significant attention is being paid to micro- and nano-resonators due to their wide applications in micro- and nano-electromechanical systems (MEMS/NEMS). The quality performance of a micro-beam resonator is usually measured by the quality factor and thermoelastic damping is considered to be the most important intrinsic dissipative mechanism in micro and nanoscale devices. In the present article, we consider the heat conduction model with a single delay term given by Quintanilla (2011) and derive an expression for thermoelastic damping by applying complex frequency approach. The variation of thermoelastic damping versus normalized frequency and thickness of Silicon micro-beam resonator for different aspect ratios have been studied. We compare the results of present model with the corresponding results of thermoelasticity theories of type GN-III, three-phase-lag (TPL), and Lord-Shulman (LS) models and investigate that the new model with a single delay term (NMSDT) gives high Q-factor of the micro-beam resonator’s sensitivity in comparison to LS and TPL models and the results under this model have more similarity to the results of GN-III model. 相似文献
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Numerical simulations have been carried out to investigate the liquid atomization and spray process using the Discrete Phase
Model of the commercial CFD code combined with the Wall-Film boundary conditions. The effects of spray parameters on droplets
Sauter mean diameter (SMD), droplet collision speed, the thickness of liquid-film, the surface temperature and its uniformity
were analyzed in the present study. The simulation results and the experimental data obtained in the available literature
agree within 13.8%. The computational results show that the spray pressure is the main factor to realize the atomization.
Increasing the mass flux and the spray pressure, the droplet collision speed increases while the corresponding maximum film
thickness on the heated surface declines. The surface temperature changes indistinctively with the increase of the spray distance,
but the temperature distribution tends to be uniform. 相似文献
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建立了蒸汽喷射器热力学模型,并验证了该模型性能及结构计算的可靠性。并针对实际情况中,对该模型进行了动态模拟。结果显示:当工作流体的温度升高时,工质流体的质量流量都会增加,引射系数存在峰值,峰值所对应温度为热力学模型设定温度值;当引射流体的温度升高时,其质量流量也会随之增大,而工作流体的质量流量则较稳定,因此引射流体温度与压力的升高可以改善喷射器的性能;当背压升高时,在一定压力范围内,工质流体的质量流量都趋于稳定,而当背压超过热力学模型设定背压值时,引射流体的质量流量便随背压的升高而急剧下降,喷射器性能严重恶化,故认为该压力值为喷射器的临界背压。本文研究结果对喷射器的设计计算具有一定的指导作用。
关键词:蒸汽喷射器;热力学模型;数值模拟;引射系数 相似文献
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Fluent软件是用于模拟和分析在复杂几何区域内的流体流动与热交换问题的专用CFD软件。将k-e模型与多相流技术Mixture模型相结合,借助Fluent软件进行多相流分析,对喷嘴处的气穴流场进行了数值模拟,并计算了模型内二维轴对称气穴流场的液态水的体积分数分布及压力分布。 相似文献
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The authors have been developing an empirical mathematical model to predict the dynamic behaviour of a polymer electrolyte membrane fuel cell (PEMFC) stack. Today there is a great number of models, describing steady-state behaviour of fuel cells by estimating the equilibrium voltage for a certain set of operating parameters, but models capable of predicting the transient process between two steady-state points are rare. However, in automotive applications round about 80% of operating situations are dynamic. To improve the reliability of fuel cell systems by model-based control for real-time simulation dynamic fuel cell stack model is needed. Physical motivated models, described by differential equations, usually are complex and need a lot of computing time. To meet the real-time capability the focus is set on empirical models. Fuel cells are highly nonlinear systems, so often used auto-regressive (AR), output-error (OE) or Box-Jenkins (BJ) models do not accomplish satisfying accuracy. Best results are achieved by splitting the behaviour into a nonlinear static and a linear dynamic subsystem, a so-called Uryson-Model. For system identification and model validation load steps with different amplitudes are applied to the fuel cell stack at various operation points and the voltage response is recorded. The presented model is implemented in MATLAB environment and has a computing time of less than 1 ms per step on a standard desktop computer with a 2.8 MHz CPU and 504 MB RAM. Lab tests are carried out at DaimlerChrysler R&D Centre with DaimlerChrysler PEMFC hardware and a good agreement is found between model simulations and lab tests. 相似文献
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INTRODUCTIONBasalt is natural rock with multi-compositions containing SiOZ about 55% and A12O3 about 13% etc.It can be processed illto fiber through melting, wiredrawing etc. Wiredrawn basalt fiber is a new kind ofnon metal fiber material. It can be used in variousfields because of its superior properties, i.e. incombustibility, corrosion resistance, high strength, goodthermal and soulld ins.lation[1]. However at present,the production and research on the basalt fiber israther limited[2… 相似文献
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Application and comparison of SST model in numerical simulation of the axial compressors 总被引:1,自引:0,他引:1
<正>The shear-stress transport(SST)turbulence model is incorporated into Navier-Stokes equations to simulate a turbomachinery flowfield.A staggered finite volume method is used to make the mean flow equations and turbulence model equations strongly coupled and enhance the stability of the numerical computation.The implicit treatment of the source terms is applied to the SST model.A steady state solution is obtained using five-stage Runge-Kutta time-stepping scheme with local time stepping and residual smoothing to accelerate convergence. The wall distance d,a key parameter in the SST model,is solved by a partial differential equation.The validations of the code are conducted on rotor 37,wp11 at design and off-design conditions by comparison with measurements and the Spalart-Allmaras(SA)turbulence model.The flow within the tip is calculated with a multi-block grid. 相似文献
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ANSYS Fluent提供的焦炭燃烧模型中,忽略了碳粒燃烧过程中灰层累积的影响,导致模拟焦炭燃烧速率偏大。为此,基于Fluent原始模型,结合碳粒燃烧过程中灰层积累对燃烧的抑制原理,利用Fluent中User Defined Functions(UDF)模块,提出一种基于灰层累积的焦炭燃烧缩核数学模型,称为“基于灰层累积的动力/扩散控制”燃烧模型。计算结果表明,相比于原始模型,改进模型中炉膛速度与温度分布更符合热力计算值,模拟得到的飞灰含碳量与实际测值基本一致,说明改进模型更加合理,且模拟结果相对准确。 相似文献
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Zhijun Zhang Jun Chai Hanyu Zhang Liting Guo 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2021,43(2):252-265
ABSTRACT The product distribution and reaction mechanism of steam pyrolysis of Longkou oil shale kerogen was researched by molecular dynamics simulation. Molecule structural model used in the simulation was constructed according to the analysis results of a series of detection about kerogen extracted from Longkou oil shale. Reactive force field molecular dynamics (ReaxFF MD) was used to simulate both steam pyrolysis and direct pyrolysis process of the kerogen at the temperature of 1600, 2000, 2400 and 2800 K. The results show that temperature is a critical factor affecting product distribution in steam pyrolysis, and 2000 K is a proper set temperature for studying steam pyrolysis via molecular simulation method. Besides that, adding the H2O molecules during steam pyrolysis can form complexes with heterogeneous atoms, thus destroying the intermolecular interactions in kerogen. Moreover, as the hydrogen radicals come from H2O molecules can inhibit cross-linking reactions between small fractions, it can reduce the average molecular weight of organic molecules product. These conclusions could be helpful for rational use of oil shale. 相似文献
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《International Journal of Hydrogen Energy》2020,45(50):26413-26425
The research on wave energy systems has been ongoing for decades. However, there are not many operational wave energy converters in use. The hydrogen energy systems also have a great potential. The proposed solution is to combine wave energy system with hydrogen energy system. The study provides details of simulation models and related simulation results. It is environmentally friendly, safe, feasible and effective. The results indicate that the proposed system model has a very high potential. With the use of low to medium energy density sea states, it is appears to be possible to generate (for DS1, DS2 and DS3, mH2 = 350.8 kg, 623.9 kg and 2124 kg, respectively) a considerable amount of hydrogen in 20-min. The presented results include WEC motion properties, instantaneous and moving average value of other system parameters. The future promising simulations results indicate that next generation wave energy converter systems could be accompanied by hydrogen generation and storage systems. 相似文献
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《International Journal of Hydrogen Energy》2023,48(43):16445-16456
In this paper, computational fluid dynamics (CFD) numerical simulation is used to analyze and discuss the horizontal propagation process of premixed hydrogen flame with obstacles. A total of three different obstacle channel arrangements at the blocking ratio of 0.5, which will affect the explosion flame and pressure development. The results show that the premixed flame is affected by flow instabilities and vortices when propagating through the obstacle channel, thereby distorting the flame. The vortices outside the flame boundary are more conducive to the acceleration of the flame. The continuous acceleration and synergistic promotion of the flame is more prominent due to the existence of the channel in the central axis of flame propagation, and the maximum velocity even achieved 307.91 m/s. The degree of the wrinkle of flame increases with the number of obstacle channels. The flame propagation process is always accompanied by pressure variations, and the dynamic pressure builds up at the flame front and intensifies periodically. But the downstream pressure gradually increases as the number of obstacle channels increases. CFD simulation of the explosion process clearly reveals the changing trends and interactions of explosion characteristic factors. 相似文献
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J. Yáñez A. KotchourkoA. Lelyakin A. GavrikovA. Efimenko M. ZbikowskiD. Makarov V. Molkov 《International Journal of Hydrogen Energy》2011,36(3):2613-2619
In order to ensure the public acceptance of the newly introduced technologies, such as e.g., exponentially growing hydrogen utilization, the risk management of them must be brought at the corresponding height. As a part of modern risk assessment procedure, CFD modeling of the accident scenario development must provide reliable data on the possible pressure loads resulting from explosion processes. The expected combustion regimes can be ranged from slow flames to deflagration-to-detonation transition and even to detonation. In the last case, the importance of the reliability of the simulation is particularly high since detonation is usually considered as a worst case scenario. A set of large-scale detonation experiments performed in Kurchatov Institute on RUT facility was selected as a benchmark. Due to the fact that RUT facility has typical industry-relevant characteristic dimensions, the capabilities of several CFD codes to correctly describe detonation in such scales for different hydrogen-air mixtures were surveyed. Two detonation tests were selected with uniform hydrogen-air mixtures and concentrations of 20.0% and 25.5% vol. Three CFD codes with different detonation models were used to simulate those experiments. A thorough inter-comparison between the models and the simulated process characteristics was performed. The obtained results allow improving the predictive capabilities of detonation models, providing a basis for the models validation and for future code development. 相似文献
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Cryocoolers are devices that are capable of achieving and maintaining cryogenic temperatures for a number of applications such as high‐energy physics, cooling of superconducting magnets, sensors, high‐vacuum production, cryotronics, cryonics, and so on. All the above applications need coolers with high reliability, efficiency, low maintenance, and low cost. The absence of moving parts at the cryogenic temperatures makes the pulse tube (PT) coolers quite suitable for the above applications. In spite of considerable developments in the area of PT cryocoolers, many of the fundamental processes responsible for the cold production are not fully understood. In this work, we present the results of numerical simulations of two‐stage pulse tube refrigerators (PTR) using adiabatic flow of gas through the pulse tube system. A two‐stage PTR is the improved version of single‐stage system to achieve temperature close to 4 K. Assuming adiabatic gas flow through PTs, the algebraic equations for pressure, mass flow, and volumes at different locations have been derived and solved by a MATLAB based program. Using the above, the performance of PTR has been optimized for different operational parameters. The cooling powers predicted by the model have been compared with the experimental data, and they are in good agreement with each other. 相似文献
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Zhou Bing Cui Guixiang Chen Naixiang 《Frontiers of Energy and Power Engineering in China》2007,1(4):468-472
Current dynamic procedures in large-eddy simulation treat the two subgrid-scale stresses in the Germano identity with the
same subgrid base model. Thus to get the base model coefficient, the coefficient must be assumed to be constant for test filter
operation. However, since the coefficient has sharp fluctuations, this assumption causes some inconsistence. A new dynamic
procedure was developed in which these two stresses are modeled by the base model and the scale-similarity hypotheses respectively.
Thus the need for the assumption is removed and consistence is restored. The new procedure is tested in the large-eddy simulation
of a lid-driven cavity flow at Reynolds number of 10,000. The results show that the new procedure can both improve the prediction
of statistics of the flow and effectively relieve the singularity of subgrid-scale (SGS) model coefficient.
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Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(8): 1 438–1 446 [译自: 清华大学学报] 相似文献
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Understanding the detailed dynamics of wind turbine wakes is critical to predicting the performance and maximizing the efficiency of wind farms. This knowledge requires atmospheric data at a high spatial and temporal resolution, which are not easily obtained from direct measurements. Therefore, research is often based on numerical models, which vary in fidelity and computational cost. The simplest models produce axisymmetric wakes and are only valid beyond the near wake. Higher‐fidelity results can be obtained by solving the filtered Navier–Stokes equations at a resolution that is sufficient to resolve the relevant turbulence scales. This work addresses the gap between these two extremes by proposing a stochastic model that produces an unsteady asymmetric wake. The model is developed based on a large‐eddy simulation (LES) of an offshore wind farm. Because there are several ways of characterizing wakes, the first part of this work explores different approaches to defining global wake characteristics. From these, a model is developed that captures essential features of a LES‐generated wake at a small fraction of the cost. The synthetic wake successfully reproduces the mean characteristics of the original LES wake, including its area and stretching patterns, and statistics of the mean azimuthal radius. The mean and standard deviation of the wake width and height are also reproduced. This preliminary study focuses on reproducing the wake shape, while future work will incorporate velocity deficit and meandering, as well as different stability scenarios. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献