Institute Of Mechanics,Chinese Academy of Sciences
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A compressed sensing based framework for surface pressure field reconstruction from sparse measurement
No full textTraditional experimental methods usually measure the aerodynamic load characteristics of an object by deploying a large number of pressure sensors on its surface, which are often challenging to economically and efficiently obtain accurate surface pressure distribution due to limitation imposed by experimental space, the complexity of geometry, and the cost of measurement instruments. To address this, a compressed sensing (CS) based framework has been proposed in this paper to investigate the reconstruction of the original surface pressure field from extremely sparse measurement data. The proposed framework integrates the generalized proper orthogonal decomposition method for flow field dimensionality reduction, the CS technique for accurate reconstruction of the original signal, and the improved particle swarm optimization algorithm for optimizing sensor placement strategies. Unlike image and unsteady flow field reconstructions, the method presented in this paper has been successful in reconstructing surface pressure fields of high-speed train under various conditions. Based on the accurate reconstruction of surface pressure fields, further aerodynamic load data can be obtained. Additionally, this paper optimizes the traditional pressure sensor layout using a particle swarm optimization method, which not only improves reconstruction accuracy but also significantly reduces the deployment of redundant sensors. Moreover, traditional point selection strategies based on experience can still be incorporated into the pressure sensor layout scheme and effectively reduce reconstruction errors under crosswind conditions. Comparison of the results showed that the proposed framework can accurately and efficiently reconstruct the surface flow field of three-dimensional complex-shaped objects from sparse measurement
Ultra-sensitive magnetic nanomechanical array sensor based on graphene oxide for single bacterial cell detection
No full textPathogenic bacterial infections pose major health threats and economic burdens. Rapid and highly sensitive biochemical sensors are essential for bacterial detection in food safety and clinical applications. Here, we introduce a graphene oxide (GO)-based magnetic nanomechanical array sensor that utilizes the large surface area of GO to bind more magnetic nanoparticles (MNPs) and aptamers. Rapid and ultra-sensitive detection can be achieved even at extremely low target concentrations. This approach can directly detect a single Escherichia coli cell without time-consuming bacterial culture, and sensor showed good specificity, reproducibility, stability, and stance to interference, and could detect 1 CFUmL(-1) Escherichia coli in milk. Moreover, we realized the simultaneous detection of two bacteria at extremely low concentrations, which proved that the sensor had the potential for high-throughput detection. In addition, for extremely low-concentration samples (mL(-1)), we controlled the magnetic force at the tip of the microcantilever, greatly enhancing its deflection and sensitivity. This method provides a novel and ultrasensitive method for the timely detection of pathogenic bacteria, and can also be applied to the highly sensitive detection of other targets such as DNA, small molecules, proteins, and viruses by using different probes. Our research provides a promising tool for effective, rapid and highly sensitive detection in the field of public health and food safety
Evaluation of the random sweeping hypothesis for the Reynolds normal stress fluctuation spectra
No full textThe space-time spectra of streamwise velocity fluctuations and streamwise Reynolds normal stress (SRNS) fluctuations in turbulent channel flows, as well as the spectral relationships between these two fluctuations based on the random sweeping hypothesis (RSH), are investigated. We demonstrate that the RSH is capable of predicting the space-time spectra of these fluctuations when the corresponding spatial spectra and appropriate convection and sweeping velocities are employed. However, when the RSH is applied to the spectral relationship between streamwise velocity fluctuations and SRNS fluctuations, discrepancies between the RSH-based predictions and the results from direct numerical simulation are observed. We propose that the inaccuracy arises from the frequency and amplitude modulations of the SRNS spectra, which are induced by streamwise velocity fluctuations but are not accounted for by the RSH. Theoretical expressions for the convection velocity and spectral bandwidth of the SRNS fluctuations are derived, highlighting the significant influence of the frequency and amplitude modulations on the space-time spectra of the SRNS fluctuations. Furthermore, a rescaling approach is proposed to improve the RSH-based space-time spectral relationship for large-scale structures, particularly in matching the spectral bandwidth and spectral peak
Mechanism on failure of cooled infrared detector illuminated by CW laser
No full textCooled infrared detectors with high sensitivity and high performance are widely applied in many fields. However, environmental disturbances such as intense light may cause a decline in their performance and even lead to permanent damage. In this study, the multi-physical behaviors and the performance degradation processes of typical cooled infrared detectors under the illumination of high-power density lasers are investigated to evaluate their survivability under extreme conditions. The experimental results reveal the electrical and thermomechanical responses of the detectors under the illumination of continuous-wave lasers, and the main thermomechanical failure modes that have not been revealed before are discovered. The theoretical results obtained through a newly established three-dimensional multi-physical numerical model of the detectors under laser illumination clarify the thermomechanical mechanism of the failure of the main components of the detectors. Moreover, the dependence of the thermomechanical results on relevant parameters is discussed, providing a scientific basis for the development and optimization of related systems
The deformation evolution and the formation pattern of hot regions of particle cloud with cavity under shock impact
No full textThe formation of hotspots and ignition phenomena in cavitated explosive particle clouds under shock wave impacts have garnered widespread attention. However, at the mesoscale, under shock wave impact, there is a notable scarcity of research on the deformation, temperature rise patterns, and heat transfer mechanisms of particle clouds. Most studies focus on loading methods such as drop hammer and falling tests. In our study, we introduce a particle motion elastoplastic contact model based on the discrete element method, enabling precise analysis of particle motion and collision behavior. Furthermore, we consider bidirectional coupling between the particle and gas phases, optimizing momentum and energy equations for the particle phase. This approach allows for a detailed analysis of the dynamics and thermodynamics between particles, systematically considering the elastoplastic collision and shear history between particles. Friction, rolling resistance, plastic dissipation, inter-particle heat transfer, and heat transfer between particles and the fluid are regarded as source terms in the energy equation. In this investigation, the deformation behavior and temperature rise process of particle clouds under shock wave impacts are thoroughly discussed. The temporal evolution of particle cloud temperature under shock wave impacts represents a spatiotemporal correlation phenomenon, delineated into two stages: accelerated temperature rise and steady temperature rise, resulting in the formation of symmetric critical high-temperature regions near the cavity perpendicular to the incoming shock wave direction. Notably, during the accelerated temperature rise stage, plastic dissipation, and two-phase heat transfer jointly contribute, whereas during the steady temperature increase stage, heat is primarily provided by two-phase heat transfer. Sustained heat transfer from the high-temperature shock-impacted gas phase to the particle phase acts as the primary mechanism triggering the formation of wide-range high-temperature regions. The role of plastic dissipation is mainly evident in the plastic collisions of particles near the cavity in the early stages. Additionally, we analyze the influence of incoming shock wave Mach numbers on temperature evolution and hot region formation patterns: stronger shock waves lead to quicker completion of the impact process and higher stable average temperatures. Under shock wave impact, the spatiotemporal characteristics of particle clouds differ from the results of the falling process. Prolonged two-phase heat transfer and intense plastic contact among particles near the cavity in the initial stages are factors triggering critical high-temperature regions
Tuning mechanics of metallic glasses via<i> in</i><i> silico</i> microalloying
No full textDuctilizing amorphous metals without sacrificing strength is challenging due to unclear plasticity carriers. This study attempts to mimic the microalloying strategy of physical metallurgy in computer simulations by selectively pinning a small fraction of typical atoms in metallic glass, which is targeted to efficiently optimize the mechanical properties. We found that pinning atoms with high participation in the low-frequency vibrational modes are more effective in strengthening, attributing to a mechanism of scale-dependent pinning effect. By pinning only 2 % atoms in the unstable glassy samples, one can achieve shear modulus comparable to samples prepared with cooling rates that are eight orders of magnitude slower, highlighting the validity of microalloying over thermal treatment. Moreover, this microalloying approach not only control elastic properties, but also mitigates the failure mode of metallic glass. It demonstrates that restricting the motion of atoms in regions external to the shear band plays a critical role in inhibiting the propagation of the shear band
Research on Left Ventricular Contraction Mechanism Based on Digital Cardiac Technology
No full text心血管疾病是我国居民的首要死因，深入探究其病理机制对临床诊疗具有重大意义。左心室作为心脏泵血功能的核心执行单元，其收缩舒张特性与心肌纤维独特的双螺旋空间构型密切相关。然而，心脏系统固有的多尺度结构特征与力-电多物理场耦合特性，使得传统研究方法在解析其复杂功能机制时面临显著局限。为此，本研究创新性地运用数字心脏技术，通过构建理想化半椭球体几何模型，采用规则化算法建立心肌纤维排布体系，并整合力-电耦合模型模拟心脏的电生理活动与机械行为，系统解析了心肌纤维结构特征对左心室收缩功能的调控机制。主要研究成果如下：
1. 心肌纤维螺旋角度的调控效应。通过调节心内膜至心外膜的心肌纤维螺旋角度分布，发现纤维角度与左心室射血分数呈显著负相关。具体而言，当纤维角度从20°增至90°时，射血分数由61.5%骤降至15.9%。这一发现首次量化证实了心肌纤维空间排布是调控心室收缩功能的关键结构参数。
2. 心肌纤维化病变的力学效应。心肌纤维化病变会改变纤维排列和力学刚度，通过模拟局部心肌纤维随机化排布，发现纤维排列紊乱区域的体积比与左心室收缩功能呈显著负相关，当纤维完全随机分布时，射血分数从47.7%跌至7.7%；纤维刚度增加导致心室顺应性降低，整体刚度提升十倍时射血分数下降32.5%，而当40%体积占比的心肌刚度增至十倍时，左心室射血分数下降23.6%。
3. 心室几何参数对左心室收缩功能的影响。研究了心肌肥厚和扩张型心肌病两类心脏几何参数的影响，发现单纯几何参数对左心室收缩功能的影响有限，表明临床观察到的左心室功能异常应该主要源于心肌纤维结构的重塑。这一发现为理解心室重构过程中的功能代偿机制提供了新视角。
本研究通过数字心脏技术首次系统量化了心肌纤维结构参数与左心室收缩功能的定量关系，不仅为心脏泵血机制的基础研究提供了创新理论框架，更为临床心肌纤维化疾病的病理机制阐释和治疗策略优化提供了重要科学依据。</p
Molecular Dynamics Simulations of Force Regulated Focal Adhesion Kinase Structure and Function
No full text 黏着斑激酶（FAK，Focaladhesionkinase）是细胞内重要的力学敏感多结构 域蛋白，其通过结构域间的相互协同发挥激酶和支架双重功能，在细胞的增殖、 迁移等过程中发挥重要作用。FAK从N-末端到C-末端依次含有FERM、Kinase 与FAT等三个主要结构域，并分别在FERM与Kinase之间，以及Kinase与FAT 之间含有linker1 与linker2 无序区。目前对FAK结构-功能关系的研究主要集中 在其FERM和Kinase两结构域之间自抑制机理的调控，强调了细胞内膜磷脂分 子PIP2以及FAK自身寡聚在其激活中的作用。但是，作为桥接细胞内膜与细胞 骨架的桥梁分子，细胞骨架重组或者细胞变形势必产生外力进而作用在FAK分 子上，此力如何调控FAK的生物学功能尚不清楚。另外，FAK的C端FAT结构 域一方面通过其与paxillin等骨架相关蛋白的相互作用行使支架功能，另一方面 其磷酸化位点Y925的磷酸化将启动胞内MAPK/ERK信号通路。而外力如何调 控FAT的结构-功能关系也不清楚。基于此，本论文利用多尺度分子动力学模拟 方法结合理论建模系统探究了外力作用下全分子FAK及其FAT结构域的结构响 应，及对其功能的调控。具体工作如下：
1) 全分子FAK结构在外力下的结构响应。首先本文基于AlphaFold2预测 的人源全分子FAK结构进行平衡分子动力学模拟，结合聚类以及构象自由能形 貌分析确定FAK代表性结构。接着基于FAK代表性结构进行力致去折叠模拟， 通过FAK各结构域端到端距离以及骨架粒子的RMSD变化，表征外力作用下全 分子FAK各结构域的去折叠时序和构象动力学。结果显示：外力作用下，FAT 结构域最不稳定，最先发生去折叠。而且FAT的去折叠过程呈现明显的中间态 特征。
2) 力致FAT结构域去折叠动力学及其功能。全分子FAK力致去折叠过程 中FAT呈现去折叠中间态。进一步基于FAT单体以及FAT-paxillin复合物进行 FAT的力致去折叠模拟，得到三个典型去折叠中间态I，II，III。而FAT的不同去 折叠中间态将产生两方面功能：一是通过分子对接及结合自由能计算，发现FAT 的去折叠I态会增强其与paxillin的相互作用，该相互作用的增强源于FATN端 的N916-D918，以及paxillin 中 LD2和LD4的E4；二是FAT的去折叠I态到II 态的转换会显著增加其磷酸化位点Y925周围的水分子数，增强其暴露程度，更 容易发生磷酸化。
3) 调控FAT去折叠动力学及其生物学功能的最优力值区间预测。上述模拟 结果显示：力致FAT去折叠在I态可以增强与paxillin的相互作用，而II态和 III 态可以暴露Y925增强其磷酸化。而外力大小则会通过调控FAT去折叠动力 学进而调控其功能。那么是否存在最优的力值作用区间来有序调控这两方面的 功能呢？基于此，本论文进一步利用分子动力学模拟数据，结合态转移方程和受 体-配体相互作用动力学，在去折叠I态维持的时间尽可能长，从I态到II态的转换时间尽可能短的假设下，预测出FAT在外力作用下实现功能的最优力值区 间是1.5-41.3 pN。
综上，本论文通过多尺度分子动力学模拟与理论建模相结合的策略，系统考察了黏着斑激酶FAK及其FAT结构域在外力作用下的动态构象变化与功能调控 机制。这些发现深化了对FAK力学敏感特性的认识，为进一步理解FAK分子的 结构-功能关系提供基础数据。</p
Global Stability Analysis of Flow-Induced Vibrations in a Forced Rotating Cylinder and Flexible Flag System
No full text流致振动是自然界和工业生产中一种常见的流固耦合现象，它将导致浸没在流体中的物体产生显著的位移或变形，对海上工作平台和能量收集装置等有重要影响。本文作者基于离散流函数浸入边界法，开发了适用于流固耦合系统的全局线性稳定性分析求解器，利用全局稳定性分析方法研究了受到强迫旋转作用的圆柱和沿着来流方向倒置的柔性细丝这两类典型的流致振动问题。结合非线性数值模拟和稳定性分析的结果，揭示了这两类流致振动发生的物理机制。本文的主要创新性工作如下：
1、针对浸没在流体中物体的流致振动问题，基于离散流函数浸入边界法，开发了可用于刚体和柔性体流固耦合系统的全局稳定性分析求解器。分别使用弹簧振子系统和非线性欧拉-伯努利梁方程来描述刚体位移和柔性体变形，以非线性方程的定常解作为基本流。在浸入边界法的框架下推导了扰动量的控制方程，通过显式构造雅可比矩阵的方法构建流固耦合系统的广义特征值方程，求解该方程以进行稳定性分析。
2、针对受到强迫旋转作用的圆柱流致振动问题，本文使用稳定性分析方法展开了研究。针对前人的非线性数值模拟结果，本文就多种运动自由度和不同雷诺数设置，在较宽的旋转速度和约化速度范围内开展稳定性分析。稳定性分析结果可以很好地解释非线性数值模拟预测的现象和规律。通过稳定性分析方法，研究了不同运动自由度设置下，强迫旋转圆柱涡激振动和驰振现象的内在机理；通过分析线性模态的变化趋势指出了强迫旋转作用对圆柱涡脱落的抑制作用；阐述了雷诺数对于圆柱流固耦合系统主导模态的重要性；揭示了强迫旋转作用在不同参数条件下对圆柱流致振动的影响效果，为使用强迫旋转作为控制手段控制圆柱流致振动现象提供指导思路。
3、针对沿着来流方向倒置的柔性细丝的流致振动问题，本文结合非线性数值模拟方法和线性稳定性分析展开了系统性的研究。通过非线性数值模拟方法，本文发现了倒置柔性细丝流固耦合问题中的五种不同振动模式，阐述了每种振动模式的流场特征和参数范围。针对不同的振动模式，本文使用线性稳定性分析方法展开了进一步的研究，通过分析不同模式对应的主导模态稳定性性质，揭示了控制倒置柔性细丝流致振动发生的潜在物理机制。指出了线性稳定性分析的作用与局限性。最后本文在柔性细丝临界振动参数范围，研究了刚度系数和质量比对主导模态稳定性的影响效果。</p
Rotational Effects on Multiscale Dynamics and Structures in Turbulent Flows
No full text
旋转湍流作为自然界与工程领域中广泛存在的复杂流动现象，其研究对深入理解地球物理、天体物理及工业流动中的输运机理与结构演化具有重要的科学价值与应用意义。在旋转效应主导的流动中，湍流呈现出各向异性、多尺度特性及手性破缺等特征，传统理论框架在描述此类流动时存在显著局限性。尤其在可压缩性、壁面约束与旋转效应耦合的复杂场景下，湍流的能量、螺旋度输运规律及其与涡结构的关联仍亟待系统研究。本文通过理论推导与高精度直接数值模拟相结合的研究方法，围绕均匀旋转湍流、旋转槽道湍流及可压缩旋转环管湍流，探究了旋转对湍流多尺度动力学与流动结构的影响，重点解析了能量与螺旋度的多尺度输运特性、流动结构变化规律及其内在物理机制，为旋转湍流的建模与流动控制提供了理论支撑。
主要研究内容及成果如下：
1. 针对均匀旋转湍流，本研究提出了谱空间新的螺旋度输运表达式，并与已有理论进行比较，揭示了由于谱空间中微分算符可交换性引起的差异。研究发现，螺旋度的注入对非线性作用具有显著影响，其通过抑制二维模式及跨手性能量通量，进而削弱能量的反向级串，抑制大尺度能量的增长。同时，能量的二维化与反向能量级串过程密切相关。跨手性螺旋度输运会引起手性极化，进一步增强了正负螺旋度分量的幅值。此外，旋转效应总体上对分解后的螺旋度通量起到了抑制作用，并且正同手性及负异手性螺旋度通量与相应正向各向异性输运密切相关。
2. 本部分针对流向旋转槽道这一典型多尺度非均匀流动开展研究，通过基本湍流统计、二阶结构函数及广义Kolmogorov方程分析，揭示了旋转对空间动量交换的强化作用及伪耗散抑制效应。研究发现，在快速旋转条件下，小尺度涡结构的倾角显著大于大尺度。随着旋转效应的增强，此特性更加明显。而当摩擦 Reynolds 数增大时，边界层变薄和尺度范围的拓宽导致倾角减弱。通过对小尺度强倾斜涡的生成机制进行细致剖析，明确了压力-速度关联项对小尺度倾斜涡的直接促进作用以及科氏力的双重效应，即科氏力直接抑制倾斜涡但又通过非零展向剪切产生间接激发作用。本研究进一步通过发夹涡模型阐释了这些效应对涡结构的具体影响。
3. 由于在流向旋转槽道中科氏力不直接对湍动能平衡产生影响，却直接作用于脉动螺旋度的平衡，因此螺旋度可作为揭示流动内在演化过程的重要特征量。研究中推导并验证了脉动螺旋度在近壁区的平衡行为及其对应的广义Kolmogorov方程，详细探讨了螺旋度在空间和尺度上的分布特征。结果显示，在近壁区域脉动螺旋度呈现正值，而在对数律层上方则转为负值，小尺度螺旋度先发生正负转换。尽管压力项以输运形式存在，但由于螺旋度的非正定性，此项实际上充当了源项的角色。随着湍流削弱或旋转效应的加强，脉动螺旋度峰值向壁面迁移，这不仅影响边界层结构，还对湍流转捩具备潜在影响。同时，本研究还探讨了螺旋度与流场涡结构之间的内在联系，表明在缓冲层以下，螺旋度与涡的直接对应关系较弱，但与条带演化及湍流脉动增强密切相关；而在对数律层中，旋转抑制展向涡的形成，进而阻碍了结构破碎和正向级串过程。
4. 为了进一步探索旋转与可压缩效应之间的耦合作用，本部分开展了可压缩旋转环管湍流的直接数值模拟，并推导了可压缩壁湍流中脉动螺旋度的平衡方程。在本部分研究中，详细讨论了曲率效应、可压缩效应以及旋转耦合作用对平均流、脉动流、湍动能及螺旋度平衡的影响。结果表明，旋转效应显著改变了外壁处平均流向速度的对数律特性，同时增强了对数律层的湍流脉动，并诱发了非零的展向二次流，其机理可通过惯性波解予以解释。受离心力影响，外壁附近的密度和压力均明显高于环管内部；此外，旋转还通过促进换热降低了主流温度。旋转与可压缩效应联合作用通过平均流向速度梯度加强了湍动能，同时通过压力项的增强促进了外壁处脉动螺旋度的空间输运，并导致了倾斜涡结构的出现。</p