Institute Of Mechanics,Chinese Academy of Sciences
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Waveform reconstruction of core-collapse supernova gravitational waves with improved multisynchrosqueezing transform
No full textGravitational waves (GWs) from core-collapse supernovae (CCSNe) have been proposed as a means to probe the internal physical properties of supernovae. However, due to their complex time-frequency structure, effectively searching for and extracting GW signals from CCSNe remains an unsolved challenge. In this paper, we apply the improved multisynchrosqueezing transform (IMSST) method to reconstruct simulated GW data based on the advanced LIGO (aLIGO) and Einstein Telescope (ET) detectors. These data are generated by the rotational and neutrino-driven mechanisms, and we use the match score as the criterion for evaluating the quality of the reconstruction. To assess whether the reconstructed waveforms correspond to true GW signals, we calculate the false alarm probability of reconstruction (FAPR). For GW sources located at 10 kpc and data sets where the waveform amplitudes are normalized to 5x10(-21) observed by aLIGO, FAPR are 2.1x10(-2) and 6.2x10(-3), respectively. For GW sources at 100 kpc and with waveform amplitudes normalized to 5x10(-21) observed by ET, FAPR are 1.3x10(-1) and 1.5x10(-2), respectively. When the GW strain reaches 7x10(-21) and the match score threshold is set to 0.75, the IMSST method achieves maximum reconstruction distances of approximately 37 and 317 kpc for aLIGO and ET, respectively. Finally, we compared the performance of IMSST and STFT in waveform reconstruction based on the ET. The results show that the maximum reconstructable distance using STFT is 186 kpc
Wall heat flux analysis in a hypersonic turbulent boundary layer over a compression ramp
No full textThe wall heat flux (WHF) in a hypersonic turbulent boundary layer over a 24 degrees compression ramp at Mach 6.0 is studied based on direct numerical simulation with the grid point number up to 3.5 billion and the Reynolds number based on momentum thickness of 8200. An apparent spanwise non-homogeneity of the mean WHF is observed on the compression ramp, caused by large-scale G & ouml;rtler-type streamwise vortices. The pre-multiplied spanwise energy spectra of the fluctuating WHF reveal two energetic spanwise length scales in the interaction region, which are associated with the elongated streaky structures and G & ouml;rtler-type vortices, respectively. The probability density functions of the fluctuating WHF in the interaction region are much more negatively skewed than that in the upstream flat-plat boundary layer, and the probability that the extremely high WHF occurs is significantly increased, both of which are found to be caused by the spanwise large-scale vortical structures via applying the low (high)-wavenumber-pass filter technique. The mean WHF in the interaction region is significantly increased, and two local maximum peaks are obtained. The upstream one lies just downstream of the reattachment position, arising from the significantly increased temperature peak value nearby and the strong downward motion that transports the relatively high-temperature fluid toward the wall. The other one is associated with the combined influence of the strong mean convection and turbulent mixing as well as the high viscous dissipation. The Reynolds analogy factor reveals an obvious variation in the interaction region, and its streamwise distribution downstream of the reattachment position is similar to the ratio of the total viscous dissipation and its component related to the wall-normal gradient of the streamwise velocity
Direct numerical simulation of hypersonic boundary layer transition over a lifting body at different angles of sideslip
No full textHypersonic boundary layer transition on a hypersonic transition research vehicle model lifting body by direct numerical simulations under typical hypersonic conditions is investigated. The simulations analyze the model at three angles of sideslip: 0 degrees, 2 degrees, and 4 degrees. The freestream Mach number is 6, the unit Reynolds number is 1x10(-7)m(-1), with a fixed 2 degrees angle of attack. The result indicates that asymmetric transition occurs on the lifting body's surface between the sideslip windward and leeward sides, due to the side incoming flow. Five distinct transition regions are identified: the shoulder crossflow-vortex region, the shoulder vortex region, the lower surface vortex region, the lower surface crossflow region, and the top crossflow-vortex region. The shoulder crossflow-vortex region (windward) shows forward-shifting transition and expanding ranges as the angle of sideslip increases, with two different modes in the head of transition. The transition of the shoulder vortex region (leeward) moves forward and shifts spanwisely toward the attachment line; at the angle of sideslip of 4 degrees, the transition mode induced by the secondary instability of the stationary crossflow occurs. In the lower surface vortex region, transition moves forward, accompanied by localized turbulence spots and altered disturbance patterns at the high angle of sideslip. The lower surface crossflow-vortex (windward) region exhibits a transition region including two zones, while lower surface crossflow-vortex region (leeward) dissipates. The top crossflow-vortex region experiences intensified crossflow effects and localized turbulence spots as the angle of sideslip increases, with the appearance of the distinct topline similar to the attachment line
超低轨道卫星气动特性分析与优化设计
No full text超低地球轨道(VLEO)卫星在提升对地观测平台性能和降低观测成本方面具有显著优势.然而,在超低轨道环境下,大气分子与卫星表面碰撞所产生的气动阻力与气动热载荷给卫星的在轨运行寿命和安全带来了巨大挑战不可忽视.首先采用直接模拟蒙特卡洛(DSMC)方法,对100～300 km高度范围内超低轨卫星的气动阻力、气动力矩与气动热特性进行了分析,系统研究了轨道高度、表面适应系数和飞行迎角等条件对卫星气动力和气动热特性的影响规律.随后,基于平板外形与旋成体外形的减阻优化分析,提出了两种超低轨卫星减阻优化方案,分别为基于表面特性的侧面光滑设计与基于遗传算法的头部外形优化.通过DSMC计算评估了两种优化方案的可行性,结果表明,在100 km的轨道高度下,侧面光滑设计的减阻效果可达40%,头部外形优化的减阻效果可达26%.两种优化方案均有效降低了超低轨卫星的气动阻力,对超低轨卫星的气动优化设计具有重要的参考和指导意义
微重力环境电解制氧系统临界运行条件与供水优化研究
No full text电解制氧系统的稳定运行关系载人航天器内部氧气的稳定连续供应，电解系统临界运行条件是系统安全稳定运行的基础。研究微重力条件下电解制氧芯体单池和电解堆运行时的临界供水量和临界工作电流，并通过改进电解堆局部结构提出了供水优化方案。利用流体动力学模拟软件开展数值模拟，采用气-液混合两相流动模型描述电解芯体内的流动过程。研究结果表明，无论对于电解池单体还是电解堆，当工作电流一定时，存在极限供水量，当供水量小于该值时，芯体内部出现局部缺水现象。对于特定的供水量，存在临界工作电流，当电流大于临界值时，芯体内部局部缺水。通过增加供水管径可明显改善多层芯体流量分配的均匀性，随着直径的增加，最小水流量与平均流量的比值线性增加，最大流量与平均流量的比值线性减小，直径增加75%时，最小流量与平均流量的比值增加约39%,最大流量与平均流量的比值降低约30%。进出口在电解堆同侧时水量分配的均匀性更好，相同供水量时，最大水量与平均水量之比可降低30%以上。研究工作可为载人航天器电解槽的安全运行提供参数建议，为系统优化设计提供依据
超薄不锈精密带钢力学性能的实验表征与数值仿真
No full text新型材料不锈精密带钢的使用逐渐广泛,但现有的关于这种材料的力学性能的实验测试还比较少。本文中通过设计非标准实验测试了不同厚度下304H不锈精密带钢材料的力学性能,利用DIC技术计算得到了不同厚度材料的断裂韧性JIC,并利用有限元模拟验证了实验测试结果的准确性。结果显示,随着厚度的减小,材料的弹性模量逐渐增大,而塑性与断裂韧性先减少后增大。利用晶体塑性模型对此现象进行了定性的解释,即在轧制到更薄的过程中,因晶粒在轧制方向被拉伸而出现了各向异性,进而导致了轧制方向弹性模量逐渐增大;同时在此过程中随着加工硬化,材料的塑性与断裂韧性逐渐降低,而晶粒细化到纳米级后增多的晶界阻碍了裂纹扩展,导致材料的断裂韧性上升
Effect of Transcatheter Edge-to-Edge Repair on Left Ventricular Flow Features
No full textPurpose This study aims to investigate the effects of transcatheter edge-to-edge repair (TEER) on left ventricular hemodynamics and its potential implications for patient health. Methods An in vitro experimental platform was designed to replicate the anatomical and functional characteristics of the left ventricle (LV). This platform integrates native porcine mitral and aortic valves with a patient-specific 3D-printed silicone LV. The LV hemodynamics after TEER is assessed using echocardiography and particle image velocimetry, focusing on critical indices such as vorticity, Reynolds shear stress (RSS), viscous shear stress (VSS), and energy dissipation rate (epsilon). Results TEER effectively reduces the degree of mitral regurgitation (MR); however, it significantly increases RSS, VSS, and epsilon due to the formation of numerous small-scale vortices in the LV. Conclusion These hemodynamic changes may lead to adverse left ventricular remodeling, red blood cell damage, and reduced cardiac pumping efficiency, which have to be taken into consideration to optimize the TEER procedure and improve patient outcomes
Quantitative macro and micro analysis on enhanced oil recovery (EOR) mechanisms of multi-component composite steam flooding<i> (MCCSF</i>) based on image recognition algorithm
No full textMulti-component composite steam flooding (MCCSF) has emerged as a promising method for enhancing oil recovery (EOR) in heavy oil reservoirs. However, its complex EOR mechanisms remain unclear, and a quantitative evaluation method for production performance in the process has not been established. In this paper, one dimensional (1D) displacement experiments were conducted to measure the oil displacement efficiency (ODE), and the optimal composite mode of multi-components was selected. This was coupled with two dimensional (2D) visualization experiments to investigate the macroscopic and microscopic EOR mechanisms during the process of MCCSF. Image recognition algorithms and image segmentation techniques were introduced to quantitatively analyze the volume of remaining oil (VORO) and the sweep efficiency at different locations during the different displacement stages. The results indicated that the integration of foams and viscosity reducer (VR) significantly improved both sweep efficiency and ODE. Finally, the effective oil production period was obviously extended. The ODE in the 1D experiments reached 76.3%, and the overall sweep efficiency in the 2D visualization experiments reached 97.97%. During pure steam flooding (PSF), the swept area was mainly targeted the near-well zone and the main flow channel. However, after adding foams and a VR for along with steam flooding, the remaining oil in the side channels and corner zones was effectively mobilized, and the ODE in the central swept areas and the displacement front were significantly enhanced, resulting in a final oil recovery factor (ORF) of 74.72%, which was 46.71% higher than that of PSF. This study primarily investigated the EOR mechanisms of MCCSF from two perspectives: improving ODE and sweep efficiency. These findings provided valuable insights and offer a quantitative method for the development effect evaluation