Institute Of Mechanics,Chinese Academy of Sciences
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Constraints on covariant Horava-Lifshitz gravity from precision measurement of planetary gravitomagnetic field
No full textAs a generalization of Einstein's theory, Horava-Lifshitz gravity has attracted significant interest owing to its healthy ultraviolet behavior. In this paper, we analyze the impact of the Horava-Lifshitz corrections on the gravitomagnetic field. We propose a new measurement method for the planetary gravitomagnetic field based on space-based laser interferometry, which is further used to constrain the Horava-Lifshitz parameters. Our analysis shows that high-precision laser gradiometers can indeed limit the parameters in Horava-Lifshitz gravity and improve the results by one or two orders of magnitude compared with the existing theories. Our novel method also provides insights into how to constrain the parameters in the modified gravitational theory to gain deeper understanding of this complex framework and pave the way for potential technological advancements in the field
Linear stability analysis on flow-induced vibration of an elastically mounted rotating cylinder
No full textIn this paper, we present a linear stability analysis on flow-induced vibration of an elastically mounted cylinder subjected to forced rotation. Four series of cases, with different combinations of degrees of freedoms in oscillation and Reynolds number are investigated. For each series of cases, a wide range of reduced velocity at various rotation rates are considered. The variations of growth and frequency with reduced velocity for the leading modes are presented. Some phenomena observed in previous numerical studies are interpreted by using the results of linear stability analysis. The supressing of vortex shedding at moderate rotation rate is explained by the absence of unstable fluid mode. The amplitude enhancement in high range of rotaton rate is explained by the emergence of unstable elastic mode. The stability properties of the leading modes provide some new insight into the influences of forced rotation on flow-induced vibration. The results of the current study have important implications in the design of offshore structures and energy-harvesting devices.</p
Investigation of thermal behavior and fluid dynamics within molten pool during quasi-continuous-wave laser directed energy deposition
No full textThe quasi-continuous-wave laser directed energy deposition (QCW-DED), a form of directed energy deposition (DED), has garnered growing interest in recent years due to its ability to reduce thermal deformation and improve the performance of manufactured components. However, the interaction between the quasi-continuouswave (QCW) laser and the molten pool surface, and its subsequent effects on the dynamics and morphology of the molten pool, is still not clear. In this work, a coupled ray-tracing computational fluid dynamics (CFD) model, which integrates a laser-powder interaction model and material deposition model, is developed to study the multi-physics coupling characteristics in QCW-DED process. The incident angle between the laser rays and molten pool surface was quantified and the corresponding laser absorptivity was analyzed. After accounting for the influence of laser-surface interaction, the heat transfer and fluid dynamics within the molten pool were subsequently investigated. Several dimensionless numbers, including the Fourier number (Fo), Peclet number (Pe), Marangoni number (Ma), and Grashof number (Gr), were employed to elucidate the physical mechanisms underlying the evolution of the molten pool. The results show that the heat transfer within the molten pool is controlled alternately by thermal convection and thermal conduction during the QCW-DED process. Furthermore, the Marangoni effect and buoyancy effect are weaker in the QCW-DED process compared to the continuous-wave laser directed energy deposition (CW-DED) process. However, the molten pool has a stronger heat dissipation capability in the QCW-DED process. Finally, the calculated molten pool geometry shows good agreement with the experimental results with the relative error less than 14.5%. This work provides a deeper insight into laser-surface interaction and the dynamics behavior within the molten pool during the QCW-DED process. The developed model can also serve as a fundamental tool for understanding the forming mechanism, predicting the deposition quality and optimizing the process of QCW-DED
Effect of curvature on the hypersonic turbulent boundary over the curved compression ramp
No full textDirect numerical simulation of the shock wave/turbulent boundary layer interaction on a compression ramp and curved compression ramps with different radii of the curvature at the Mach number Ma=5.0 and Reynolds number Re=16 800/mm is performed, and the purpose of the study is to investigate the impact of different radii of the curvature on the development of the flow. The flow structure and turbulence properties are analyzed. As the curved angle radius increases, the range of flow deceleration and the impact of the shock wave interaction on the turbulent boundary layer gradually decrease, and the peak value of turbulent pulsation amplification in the interaction zone becomes smaller. Mean skin friction decomposition is carried in upstream undisturbed region and reattachment region. The skin friction coefficient in the upstream is primarily composed of the viscous dissipation term C-f,C-V and the turbulent kinetic energy production term C-f,C-T. While in the reattachment zone, it is mainly balanced by the term C-f,C-T and the spatial growth term C-f,C-G. Bidimensional empirical mode decomposition is applied to further study the contribution of the turbulent motion at different scales to C-f,C-T, and the result shows that for the compression ramp, C-f,C-T is mainly contributed by the large-scale vortex structure generated in the interaction zone, while for the curved compression ramp, it is mainly contributed by the rapid amplification of turbulent pulsations caused by the shock wave interaction. This study is not only a new parametric study of the shock wave/turbulent boundary interaction but also provides a reference for the aerodynamic design of hypersonic vehicles
Online Measurement of Water Entry Cavity Using Outward Electrical Capacitance Tomography
No full textOnline measurement of water entry cavities is important for the stable manipulation of high-speed underwater vehicles. However, there are almost no feasible methods to track and measure the cavity online when the vehicles are moving. For this purpose, an online measurement method using outward electrical capacitance tomography (Outward-ECT) is proposed to obtain the circumferential cavity profile on the outer surface of an axisymmetric blunt body during water entry. An Outward-ECT physical model is developed to incorporate the effect of finite boundaries on the cavity measurement in laboratory tests. Based on this physical model, simulation is conducted and a cavitator equipped with Outward-ECT electrodes is designed and fabricated, enabling the reconstruction of the cavity profile during water entry. Experiments were carried out to verify the proposed method, where images taken by a high-speed camera are used as references. It is found that the cavity profiles reconstructed by the Outward-ECT are consistent with their references when the cavitation enters the water in different attitudes, where the relative measurement errors of the cavity diameter are less than 5.9%. Analyzing the boundary measurements by the Outward-ECT sensor shows that the global capacitance is related to the water entry stages and attitudes of the cavitator as well as the initial entry velocity. Overall, the success of this approach would provide a feasible method for the online measurement of the water entry cavity when high-speed underwater vehicles are moving, which is essential for their online control to maintain a stable cavity
Online Measurement of Water Entry Cavity Using Outward Electrical Capacitance Tomography
No full textOnline measurement of water entry cavities is important for the stable manipulation of high-speed underwater vehicles. However, there are almost no feasible methods to track and measure the cavity online when the vehicles are moving. For this purpose, an online measurement method using outward electrical capacitance tomography (Outward-ECT) is proposed to obtain the circumferential cavity profile on the outer surface of an axisymmetric blunt body during water entry. An Outward-ECT physical model is developed to incorporate the effect of finite boundaries on the cavity measurement in laboratory tests. Based on this physical model, simulation is conducted and a cavitator equipped with Outward-ECT electrodes is designed and fabricated, enabling the reconstruction of the cavity profile during water entry. Experiments were carried out to verify the proposed method, where images taken by a high-speed camera are used as references. It is found that the cavity profiles reconstructed by the Outward-ECT are consistent with their references when the cavitation enters the water in different attitudes, where the relative measurement errors of the cavity diameter are less than 5.9%. Analyzing the boundary measurements by the Outward-ECT sensor shows that the global capacitance is related to the water entry stages and attitudes of the cavitator as well as the initial entry velocity. Overall, the success of this approach would provide a feasible method for the online measurement of the water entry cavity when high-speed underwater vehicles are moving, which is essential for their online control to maintain a stable cavity
Cryogenic 3D printing of damage tolerant hierarchical porous ceramics
No full textFabricating damage tolerant porous ceramics with efficient energy absorption and impact-resistant capability has been a challenge because of the brittle nature of ceramic materials. In nature, mineralized tissues or organisms such as cuttlebones and diatoms have evolved with hierarchical porous structures to overcome this difficulty. A bioinspired design of ceramic lattice structure with pores at multiple length scales, ranging from few nanometers to hundreds of micrometers, is proposed in the present work. These ceramic lattices with hierarchical porous structures were successfully fabricated via 3D cryogenic printing. Under quasi-static compressions, the printed ceramic lattices showed unprecedented long plateau strain (similar to 60%) and a specific energy absorption of similar to 10 kJkg-1 with a porosity of similar to 90%. The resulting energy absorption capability was comparable with most composites and metals, thus overcoming the brittle nature of traditional porous ceramics. This was attributed to the delayed destruction of the lattice structure, as well as the gradual collapse of pores at multiple length scales. Similar trends have also been observed under split Hopkinson pressure bar (SHPB) tests, indicating excellent energy absorption under high strain-rate impacts. The proposed 3D printing technique that produces hierarchical pores was also demonstrated to apply to other functional materials, such as silicon carbide, barium titanate, hydroxyapatite, and even titanium alloy, thus opening up new possibilities for fabricating bioinspired hierarchical porous structures.
A distinctive hierarchical architectural design strategy of porous ceramics was proposed and realized via cryogenic 3D printing technique.The hierarchically porous ceramics showed unprecedented long plateau strain (similar to 60%) and a specific energy absorption of similar to 10 kJkg-1.Similar trends have also been observed under split Hopkinson pressure bar (SHPB) tests, indicating excellent energy absorption under high strain-rate impacts.The energy absorption mechanisms include gradual destruction of ceramic lattices layer-by-layer and collapse of pores with different sizes
Study on damage initiation mechanism of rubber/cord composites and the structure optimization
No full textIn this paper, a novel experimental equipment was developed to conduct stretch bending and compression bending load on rubber/cord composites, and its damage mechanism was studied. Macroscopic analysis revealed that the application of compression bending loads significantly accelerates the degradation of bending stiffness in the specimens. Microscopic characterization demonstrated the formation of numerous micro gaps between fibers during cyclic loading, with their population density being markedly increased under compression bending conditions. Through finite element analysis at the microscopic scale, these micro gaps were identified as stress-induced defects resulting from plastic strain accumulation in cord fibers. These defects, termed as "acquired defects", were found to exacerbate the stress state within the micro structure, serving as the primary initiation sites for composite damage. Based on the study of the damage initiation mechanism, a quantitative methodology was established to correlate fiber plastic strains with the dimensions of these acquired defects, enabling the prediction of defect size and their impact on the composite's stress state. This approach provides valuable insights for micro structure optimization and material performance enhancement in rubber/cord composite systems.</p
HPRNA: Predicting synergistic drug combinations for angina pectoris based on human pathway relationship network algorithm
No full textOver the years, synergistic drug combinations therapies have attracted widespread attention due to its advantages of overcoming drug resistance, increasing treatment efficacy and decreasing toxicity. Compared to lengthy medical drugs experimental screening, mathematical models and algorithms show great potential in synergistic drug combinations prediction. In this paper, we introduce a novel mathematical algorithm, the Human Pathway Relationship Network Algorithm (HPRNA), which is designed to predict synergistic drug combinations for angina pectoris. We first reconstruct a novel angina pectoris drug dataset, which include drug name, drug metabolism, chemical formula, targets and pathways, then construct a comprehensive human pathway network based on the genetic similarity of the pathways which contain information about the targets. Finally, we introduce a novel indicator to calculate drug pair scores which measure the likelihood of forming synergistic drug combination. Experimental results on angina pectoris drug datasets convincingly demonstrate that the HPRNA makes efficient use of target and pathway information and is superior to previous algorithms
TRPML1 ion channel promotes HepaRG cell differentiation under simulated microgravity conditions
No full textStem cell differentiation must be regulated by intricate and complex interactions between cells and their surrounding environment, ensuring normal organ and tissue morphology such as the liver1. Though it is well acknowledged that microgravity provides necessary mechanical force signals for cell fate2, how microgravity affects growth, differentiation, and communication is still largely unknown due to the lack of real experimental scenarios and reproducibility tools. Here, Rotating Flat Chamber (RFC) was used to simulate ground-based microgravity effects to study how microgravity effects affect the differentiation of HepaRG (hepatic progenitor cells) cells. Unexpectedly, the results show that RFC conditions could promote HepaRG cell differentiation which exhibited increased expression of Alpha-fetoprotein (AFP), albumin (ALB), and Recombinant Cytokeratin 18 (CK18). Through screening a series of mechanical receptors, the ion channel TRPML1 was critical for promoting the differentiation effect under RFC conditions. Once TRPML1 was activated by stimulated microgravity effects, the concentration of lysosomal calcium ions was increased to activate the Wnt/beta-catenin signaling pathway, which finally led to enhanced cell differentiation of HepaRG cells. In addition, the cytoskeleton was remodeled under RFC conditions to influence the expression of PI (3,5) P2, which is the best-known activator of TRPML1. In summary, our findings have established a mechanism by which simulated microgravity promotes the differentiation of HepaRG cells through the TRPML1 signaling pathway, which provides a potential target for the regulation of hepatic stem/progenitor cell differentiation and embryonic liver development under real microgravity conditions