Institute Of Mechanics,Chinese Academy of Sciences
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太极计划激光链路辅助功能方案设计及验证
No full text太极计划是由中国科学院主导的空间引力波探测任务，其目标是在深空中探测0.1 mHz至1 Hz频段的引力波信号。在太极计划中，激光链路的辅助功能是实现星间激光通信测距和时钟噪声传递。为实现引力波探测辅助功能在激光干涉链路中的集成，拟对同一激光干涉链路进行边带倍频时钟噪声传递（以消除时钟噪声）和伪随机码扩频调制（以实现星间激光通信）。本文介绍了太极计划通过激光链路实现星间时钟噪声传递及激光通信的需求、原理、方法，分析了二者的耦合关系。搭建光学激光链路，对实验现象及性能进行评估，确定相关实验参数，以确保倍频时钟噪声传递方案耦合星间激光通信方案整体可靠，满足太极计划需求。实验结果表明，在0.1 Hz至1 Hz、0.1 mHz至0.5 mHz频段内，时钟噪声抑制效果达到了优于2π×10-5 rad/Hz1/2的精度水平，同时通信误码率低于10-6。这说明激光链路辅助功能的集成方案有效，为未来太极计划实现干涉仪辅助功能整体化集成奠定了实验和理论基础
Fatigue-induced microstructural deformation and multimode defect-assisted cracking of laser powder bed fused superalloy at 650 °C
No full textMulti-scale characterization was conducted to investigate the interior failure behavior of a laser powder bed fused (LPBF) nickel-based superalloy under fatigue cyclic loading at operating temperature of 650 degrees C. The results reveal a shift in crack nucleation sites with increasing fatigue life-from additive manufacturing defects to crystallographic facets. Six distinct interior fatigue failure modes were identified, each involving defect-assisted crack nucleation surrounded by faceted features. Microcracks preferentially propagated in a transgranular fracture mode under localized shear stress, leading to grain fracture and facet formation. Variations in grain orientation influenced local fracture behavior, resulting in the formation of highly uneven facets. Competition between surface, subsurface and interior crack nucleation modes was observed, particularly at lower stress levels, indicating a transition in dominant fatigue mechanisms. At elevated temperatures, facet cracking was driven by a synergistic mechanism involving anti-phase boundary shearing, precipitate bypassing, and stacking fault shearing. These findings advance the understanding of defect-microstructure interactions and provide a basis for improving fatigue life prediction and design strategies for high-temperature LPBF components
Imaging simulation of light scattering signals in atmospheric disturbance density fields
No full textDuring flight operations, aircraft induces atmospheric disturbances in the surrounding environment through aerodynamic interactions between its geometric configuration and ambient air medium, resulting in spatially distinct density distribution characteristics that are significantly different from natural background scenario. Considering the positive correlation between atmospheric medium density and light scattering intensity, theoretical analysis shows that detecting the light scattering intensity signals in disturbed regions can map density distributions, thereby extracting the features of aircraft-induced atmospheric disturbance density fields. Based on the concept of long-range aircraft detection through atmospheric disturbance density field characterization, a novel remote sensing method for aircraft detection is proposed in this work. Specifically, a three-dimensional tomographic imaging detection mode for scattered light in an atmospheric disturbance region is designed, and a comprehensive simulation framework covering the entire process of disturbance optical signal generation, transmission, and response is constructed. The study accomplishes the following tasks: 1) the critical challenges in estimating the imaging modulation transfer function under short-exposure conditions subjected to laser pulse secondary scattering effects are resolved, and a photon scattering echo imaging simulation model for aircraft-induced disturbance density fields is established; 2) the scattering echo signal images from active light sources in disturbed density fields and the differential images obtained under disturbed background and non-disturbed background are simulated, with simulation results under varying system parameters analyzed systematically. The research demonstrates that this simulation model can be used to optimize detection system parameters, develop signal processing methods, and assess long-range detection capabilities, thus providing both theoretical foundations and technical support for advancing aircraft detection technologies based on density disturbance characteristics
Biomechanical Effects of Partial Decortication on All-Suture and Conventional Suture Anchors in Different Bone Densities
No full textWhile biomechanical testing has shown a correlation between decortication and anchor failure load, the effects of partial decortication on the biomechanical properties of all-suture anchors remain unclear. We aimed to evaluate the biomechanical effects of partial decortication on all-suture anchors and conventional suture anchors in Sawbones of varying densities. Suture anchors were tested in nondecorticated, partially decorticated, and completely decorticated Sawbones. Two types of all-suture anchors and one type of conventional anchor were evaluated. Two types of biphasic polyurethane foam were used to mimic normal bone: 0.32 g/cm3 density (20 pounds per cubic foot, pcf 20) and osteoporotic bone: 0.16 g/cm3 density (10 pounds per cubicfoot, pcf 10). Cyclicloadingswere applied, and peakdisplacementwas recorded. After cyclic loading tests, surviving anchors were subjected to pull-to-failure tests. The number of cycles, peak displacement, ultimate failure loads, and failure modes were determined. First, peak displacement was significantly influenced by bone density and anchor type: normal bone models exhibited lower peak displacement than osteoporotic models, and conventional screw-type anchors consistently demonstrated reduced peak displacement compared to all-suture anchors. In contrast, the extent of bone decortication-whether non-decorticated, partially decorticated, or completely decorticated-showed no significant effect on peak displacement. Second, in osteoporotic bone models (10 pounds per cubic foot), no significant difference in failure load was observed between the partially and non-decorticated groups, but both exhibited significantly higher values than the completely decorticated group
Centrifugal Pressurization Process in the Near Critical Region for Supercritical CO<sub>2</sub> Brayton Cycle
No full textThe starting point for the pressurization process of a supercritical CO2 Brayton cycle is near the critical point, which may lead to a liquid hammer if the inlet pressure fluctuates. It is important to judge whether the phase change of working fluid occurs during the pressurization process. With CO2 as the working fluid, the pressurization process for a centrifugal pressurization component is attention considered and analyzed. Specifying the inlet temperature, inlet pressure and outlet pressure as 32 degrees C, 7.4 MPa and 24 MPa, respectively, the thermodynamic parameters of key state points of a centrifugal pressurization component are obtained. At the entrance of the impeller, a phase change of CO2 may occur, especially when the inlet points are close to the critical point. A method using enthalpy difference and exergy difference to express the possibility CO2 phase change is proposed. Furthermore, the risk degree of CO2 phase change is represented visibly. In view of the power consumption and efficiency of compressors under different working conditions, the changes of power consumption, isentropic efficiency and internal efficiency of compression components were analyzed under the conditions of constant outlet pressure and constant pressurization ratio. The power consumption is affected by the specific volume of the working fluid and the pressure difference. With the same inlet conditions, the isentropic efficiency under constant pressurization ratio is higher than that under a constant outlet pressure due to the lower power consumption; the internal efficiency is higher than the isentropic efficiency, and the trend is similar. This method can contribute to the setting of safe conditions for pressurization components
Chemical energy accommodation of atomic oxygen recombination on silica surfaces under high-temperature nonequilibrium flow environments: Insights from atomistic-scale simulations
No full textThe energy transfer and accommodation for the catalytic recombination of atomic oxygen (O) on silica surfaces, a key process to be understood for the accurate prediction of aerothermal heating of hypersonic vehicles, are studied using a combination of the density functional theory (DFT) and reactive molecular dynamics calculations. The key elementary reactions are determined by the DFT calculations, along with the barriers and changes of free energy for each reaction. The energy carried by the recombined oxygen molecules ( O-2) and its partition into different internal modes for various reactions are obtained by averaging the corresponding molecular information from a significant number of molecular dynamics trajectories. The chemical energy accommodation (CEA) coefficients, for various reactions, internal modes, and surface structures, are then computed based on the free energy changes and energies carried by the recombined O-2. Moreover, the detailed energy distributions of O-2 are also provided. It is found that CEA for the recombination of O on the silica surfaces depends greatly on the reaction type and internal energy mode but is less profoundly influenced by the surface structures. The results of the present study offer better insights into the mechanisms of chemical energy transfer and accommodation for the catalytic recombination of O on silica surfaces and can help improve the modeling of the relevant gas-surface interactions for more reliable aerothermal heating prediction.</p
Effects of interfacial rheology on solutocapillary convection near the air-liquid interface
No full textThe roles of interfacial rheology in solutocapillary convection near the air-liquid interface driven by a point mass source are investigated. First, the assumption of the conically similar viscous flow is successfully extended to treat the effects of interfacial rheology on solutocapillary convection near the air-liquid interface. By taking the surface viscosity as a small parameter, the steady solutocapillary convection is analyzed by applying the matched asymptotic expansion method. For small Re numbers and small/large Sc numbers, the exact solutions of the solutocapillary convection are shown. It is found that, to generate the first-order surface tension, the interfacial rheology related to the leading order solution is more dominant than the first-order concentration gradient of surfactant. Moreover, for general physical parameters, the governing equations of the solutocapillary convection for the perturbation solutions are numerically solved by applying the shooting method. In comparison with basic solutions for the solutocapillary convection near the air-liquid interface without the interfacial rheology, the interfacial rheology enhances both the divergent flow near the interface and the convergent flow far from the interface. Its effects on the distribution of surfactant depend on Pe number. For small/large Pe numbers, the interfacial rheology slightly/greatly increases the distribution of the surfactant near the interface and slightly/greatly decreases the distribution of the surfactant near the symmetric axis
Hierarchical modeling of strain-concentrating effect in notched ceramic-matrix composite laminates
No full textThis study presents a hierarchical analysis framework to examine the stress-strain distributions in notched fiber-reinforced ceramic-matrix composite (CMC) laminates and correlates microstructural variability with macroscopic mechanical responses. Hierarchical models are employed, including a finite element (FE) model incorporating an inelastic constitutive model for CMC laminates, an analytical model that captures inelastic deformation resulting from matrix cracking and a micro-mechanical model developed to assess fiber break displacement due to fiber failure, accounting for the interfacial shear response between fibers and the matrix. Both the analytical and FE models produce accurate stress predictions; however, the results are non-conservative. The strain predictions are validated against digital image correlation data under moderate strain conditions, with the analytical model providing more conservative strain estimates. A domain map of the elastic-inelastic transition near the notch edge, as a function of applied stress and notch size, is presented to assist in predicting stress and strain distributions. Simultaneous analysis of stress and strain distributions reveals that inelastic strains in the concentration region reduce peak stresses, thus mitigating stress concentration. Quantitative analysis of microstructural features using X-ray tomography demonstrates a strong correlation between microstructural variations and the stress state in the stress concentration region of the notched CMCs. The results indicate that hierarchical analytical modeling correlates stress distributions with the microstructure ahead of notches, offering new insights into the behavior of the notched CMCs
Effects of air-core vortex on the hydraulic instability of a bulb turbine
No full textAt low operating water levels, an air-core vortex can form at the turbine inlet, resulting in two-phase, highly swirling inflows and unit damage. We coupled the vortex field with the turbine's inlet boundary using bilinear interpolation and employed large-eddy simulation to replicate the unstable flow phenomena. The presence of the air-core vortex leads to a notable reduction in output and efficiency. As the air-core vortex disintegrates in the inlet channel, it transforms into an air-water mixture that travels along the upper wall without forming an air pocket. The air-core vortex increases the helical vortex pitch and expands the stalled region of the vortex rope. An air entrainment rate of 1.35% results in a 7.41% rise in entropy production, mainly occurring in the inlet channel. The amplitude of pressure pulsations increases at the precession frequency, while decreases at the high-frequency. The baroclinic torque budget is significant, reflecting the inhibitory effect of air-water interaction on small-scale vortices
Effects of air-core vortex on the hydraulic instability of a bulb turbine
No full textAt low operating water levels, an air-core vortex can form at the turbine inlet, resulting in two-phase, highly swirling inflows and unit damage. We coupled the vortex field with the turbine's inlet boundary using bilinear interpolation and employed large-eddy simulation to replicate the unstable flow phenomena. The presence of the air-core vortex leads to a notable reduction in output and efficiency. As the air-core vortex disintegrates in the inlet channel, it transforms into an air-water mixture that travels along the upper wall without forming an air pocket. The air-core vortex increases the helical vortex pitch and expands the stalled region of the vortex rope. An air entrainment rate of 1.35% results in a 7.41% rise in entropy production, mainly occurring in the inlet channel. The amplitude of pressure pulsations increases at the precession frequency, while decreases at the high-frequency. The baroclinic torque budget is significant, reflecting the inhibitory effect of air-water interaction on small-scale vortices