Institute Of Mechanics,Chinese Academy of Sciences
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Scaling Laws of the Drag-free Control System Between Ground Model and Space Prototype
No full textTo address issues in the construction of the ground test platform and closed-loop control performance evaluation of the drag-free system in space gravitational wave detection, this paper proposes a verification method based on a ground composite semi-physical drag-free simulation system. A ground simulator for drag-free simulation is innovatively designed based on the configuration of a drag-free satellite with two test masses. The scaling laws between the space prototype and the ground simulator are determined by using the Pi theorem. The scaling laws are used as the design guide for the ground simulator. According to the principle of the drag-free satellite in the science mode, the drag-free controller is designed using the active disturbance rejection control (ADRC) algorithm, and the control scaling laws are established for the controller design of the ground simulator. The closed-loop similarity of the two systems is studied, and the simulation results indicate that the two systems exhibit similar closed-loop dynamic behavior. The drag-free controller of the space prototype can be transferred to the ground simulator for verification using control scaling laws
Physics-informed neural networks for phase-based material defect identification
No full textThe accurate identification of material defects is critical for ensuring structural integrity and performance. Traditional computational methods often struggle to balance efficiency and physical fidelity in complex material systems. This paper presents a novel approach integrating physics-informed neural networks (PINNs) with the phase field method to address these challenges. Our approach leverages a phase field variable to delineate intact regions from voids, while a stress degradation model modifies mechanical responses at defect sites. Neural networks serve as surrogate forward solvers to predict displacement and stress fields, enabling rapid simulations. To ensure compatibility with physical laws, the framework embeds governing equations into the training loss function. Additionally, a data-driven term minimizes discrepancies between simulated and experimentally measured strain fields, enhancing defect localization precision. Numerical experiments validate the framework's robustness across diverse configurations, including circular, elliptical, irregular, and multiple voids, as well as material behaviors, extending from linear elastic to hyperelastic models. The results demonstrate superior accuracy in identifying void geometry, size, and spatial distribution compared to conventional methods. The proposed approach's adaptability to complex geometries and material nonlinearities highlights its broad applicability in aerospace, automotive, and biomedical industries
Linear stability analysis of a premixed flame in curved micro-combustors
No full textA micro-combustor is an attractive concept to enable a high-energy-density power supply for microelectromechanical applications. This work concerns the combustion instability in micro-combustors with curved geometries. We calculate the base-flame solutions and present a systematic linear stability analysis of anchored premixed flames suited in curvatured-affected flow fields with the focus on the so-called intrinsic thermoacoustic (ITA) modes. By varying the ratio of channel radius of curvature to channel height, R-c/H, the global eigen spectrum shows that the first ITA mode tends to destabilize with the growth of R-c/H and then stabilize at a very strong curvature where a significant flame bending is present. A flame-transfer function based on streamwise velocity perturbations confirms that the classical -pi phase-lag criterion remains valid even under strong curvature. To pinpoint the regions most responsible for mode growth or decay, we perform an adjoint-based structural sensitivity analysis. The resulting wavemaker maps reveal two key loci: one enveloping the flame front and another upstream in the inflow region, highlighting the critical role of convective velocity disturbances in ITA formation. Unlike straight channels, curved geometries support multiple ITA branches, each exhibiting dominant sensitivity to inlet perturbations. Our findings not only elucidate the physical origins of curved-channel ITA instabilities but also verify a rapid criterion-based prediction in non-planar ducts. The identified "safe" curvature intervals offer practical guidance for the geometry of micro-thermophotovoltaic combustors
Linear stability analysis of a premixed flame in curved micro-combustors
No full textA micro-combustor is an attractive concept to enable a high-energy-density power supply for microelectromechanical applications. This work concerns the combustion instability in micro-combustors with curved geometries. We calculate the base-flame solutions and present a systematic linear stability analysis of anchored premixed flames suited in curvatured-affected flow fields with the focus on the so-called intrinsic thermoacoustic (ITA) modes. By varying the ratio of channel radius of curvature to channel height, R-c/H, the global eigen spectrum shows that the first ITA mode tends to destabilize with the growth of R-c/H and then stabilize at a very strong curvature where a significant flame bending is present. A flame-transfer function based on streamwise velocity perturbations confirms that the classical -pi phase-lag criterion remains valid even under strong curvature. To pinpoint the regions most responsible for mode growth or decay, we perform an adjoint-based structural sensitivity analysis. The resulting wavemaker maps reveal two key loci: one enveloping the flame front and another upstream in the inflow region, highlighting the critical role of convective velocity disturbances in ITA formation. Unlike straight channels, curved geometries support multiple ITA branches, each exhibiting dominant sensitivity to inlet perturbations. Our findings not only elucidate the physical origins of curved-channel ITA instabilities but also verify a rapid criterion-based prediction in non-planar ducts. The identified "safe" curvature intervals offer practical guidance for the geometry of micro-thermophotovoltaic combustors
Wearable Pneumatic Soft Physiotherapy Device for Shoulder and Neck Acupoint Massage
No full textThe high reliance on traditional Chinese medicine (TCM) knowledge and practical skills has led to prolonged training cycles for therapists and a significant talent shortage, posing a severe challenge to the standardization of TCM physiotherapy in rehabilitation. Meanwhile, most physiotherapy robots based on rigid robotics technology suffer from insufficient safety and adaptability, resulting in unsatisfactory treatment effects. This paper presents a novel wearable pneumatic soft physiotherapy device, designed to achieve high-safety and personalized physiotherapy for shoulder and neck acupoint massage. The device integrates four soft massage actuators, four embedded thin-film stress sensors, two miniature airflow sources, and a power supply system, enhancing its portability. Additionally, a hybrid control strategy combining feedforward inverse compensation and PID feedback is proposed to regulate and customize the therapy intensity on human acupoints. Experimental results demonstrate that the developed device can apply therapeutic intensities ranging from 0 to 3.45 N to human acupoints, effectively adapting to the human shoulder and neck region to achieve good wearing comfort, and performing safe acupoint massage with customized physiotherapy intensities. This study explores and realizes the integration of emerging soft robotics technology with TCM, providing a paradigm for the development of more soft physiotherapy devices
Laser-Induced Visualization of Latent Fingerprints on Metal Surfaces
No full textLatent fingerprints (LFPs) are pivotal evidence in criminal investigations, yet their direct observation poses inherent challenges, necessitating advanced visualization techniques. Here, an innovative one-step laser-based methodology is presented for the rapid and accurate visualization of LFPs on metal surfaces. Gray value analysis is utilized to compare the optical contrast between the ridges and valleys of original and visualized fingerprints. Additionally, an orientation field method is employed to evaluate the texture quality of visualized fingerprints. The results demonstrate that laser irradiation significantly enhances the recognizability and pattern fidelity of LFPs by inducing differential oxide deposition: ridges, enriched in skin secretions, exhibit reduced oxide accumulation compared to valleys, thereby amplifying ridge-valley optical contrast. Furthermore, the visualized fingerprints exhibit excellent resistance to abrasion. Importantly, this method demonstrates broad applicability across surfaces with varying roughness levels and diverse metal types. This study establishes a robust and versatile tool for the rapid and accurate visualization of LFPs, offering transformative potential for forensic investigations
Optical images of the Kerr-Sen black hole and thin accretion disk
No full textThis paper investigates the observable properties of a Kerr-Sen black hole surrounded by a thin accretion disk, focusing on the impact of the black hole's spin and charge on the image. Using ray-tracing techniques, we conduct a detailed analysis of the black hole's image, redshift distribution, and intensity distributions at different observation frequencies. The results demonstrate that spin has a more significant effect on the distortion of the inner shadow than charge, and the observer's inclination angle plays a critical role in shaping the redshift distribution, especially near the innermost stable circular orbit. Additionally, the intensity is found to be higher at 86 GHz than at 230 GHz. This study highlights the crucial role of the accretion disk's geometry in determining the black hole's image and redshift effects, thereby providing a refined theoretical framework to guide future observational efforts targeting the Kerr-Sen black hole and its electromagnetic signals
A lubrication-based method for reconstructing the dynamic parameters of particle-wall collisions in liquids
No full textPrecise measurement or simulation of particle collisions in liquids typically requires prohibitively high spatiotemporal resolution. This study employs lubrication theory to develop a reconstruction technique for the collision parameters and process of spherical particles in liquids with known properties. Time series of collision behaviors under varying parameters are first obtained through direct numerical simulation level adaptive refinement fully resolved numerical simulations. The sequence to be enhanced is then derived through subsampling and noise addition. A simplified relationship is developed using lubrication theory to evaluate key parameters with constrained uncertainties, enabling the recovery of high-resolution temporal processes and the extraction of critical parameters such as the equivalent recovery coefficient and collision time. The approach is successfully applied to enhance experimental data of spherical inertial measurement unit particle collisions, significantly improving the accuracy of collision event measurements. This method shows promise for enhancing low-resolution experimental or numerical simulation data in similar collision problems
A novel photosensitive poly(amic acid) for reducing film thickness shrinkage after curing
No full textFilm thickness shrinkage negatively impacted product yield and device packaging performance. Photosensitive polyimides (PSPIs) without adding crosslinkers and photosensitizers had low film thickness shrinkage after curing, but this design limited the diversity of PSPIs. We devised photosensitive poly(amic acid) (PSPAA) that requires additional crosslinkers. After exposure, PSPAA had a high degree of crosslinking and high thermal property, resulting in low film thickness shrinkage after curing. Finally, a fine negative image with a resolution of about 4 mu m was printed in a film approximately 1.00 mu m thick after being exposured to i-line at 7.5 J/cm2 and developed with a 0.25 % TMAH aqueous solution. The film thickness shrinkage after curing was about 20 %
Phase transition and agglomeration characteristics of fine particles in humid flue gas flowing through perpendicular pipe arrangement
No full textThe excessive emission of particulate matter and the waste of residual heat are major issues in the flue gas emission process. By arranging perpendicular pipe turbulence heat exchange devices in the flue gas, it is possible to achieve flue gas heat recovery and fine particles agglomeration during water vapor phase change process. A numerical calculation model of the particle agglomeration process was established, involving turbulent agglomeration, Brownian agglomeration and vapor phase-change agglomeration. The influence of flue gas particle concentration, flue gas temperature, flue gas flow rate, flue gas humidity, heat exchange device wall temperature and structure on the agglomeration of particles was studied. The results indicate that an increase in particle concentration can enhance agglomeration efficiency, while excessively large or small particle sizes can reduce this efficiency. A decrease in flow velocity provides particles with more residence time within the heat exchanger, thereby improving agglomeration efficiency. A drop in flue gas temperature weakens convective heat transfer and vapor-phase condensation, leading to decreased agglomeration efficiency. Condensation of water vapor on particle surfaces promotes particle agglomeration efficiency. Lower wall temperatures and higher water vapor volume fractions increase the amount of vapor condensation, leading to more particles agglomeration under the influence of condensation. The use of staggered arrangements in the structure also helps improve particle agglomeration efficiency