Institute Of Mechanics,Chinese Academy of Sciences
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Dynamics of bubble collapse near rigid boundaries with different curvatures
No full textUnderstanding the bubble dynamics near a curved boundary is crucial for evaluating the cavitation impacts, as well as advancing the beneficial use of cavitation in real-world applications such as biofilm cleaning and environmental treatment. This study employs a high-fidelity multiphase flow model to analyze the dynamics of bubble collapse near rigid curves of varying curvatures. The numerical model employs a second-order-accurate solver within a two-dimensional axisymmetric coordinate system to solve the 5-equation model (Kapila's model). After being validated by three bubble collapse experiments, the model is applied to examine the bubble morphology and jet characteristics near different curved boundaries at varying standoff distances. The results reveal that as curvature increases, the jet momentum decreases due to the decrease in the jet volume, while the bubble jet velocity gradually increases in scenarios of downward jetting. Smaller standoff distances lead to bubbles with higher transverse to longitudinal ratio, insufficient longitudinal contraction, and reduced jet velocity. Finally, we summarize the changes in bubble morphology, jet velocity, jet momentum, and peak pressure with curvatures and standoff distances and fit the boundary for different bubble collapse patterns. This study establishes a clear correlation between bubble jet momentum and bubble type, finding that downward jetting can enhance jet momentum
Dynamics of bubble collapse near rigid boundaries with different curvatures
No full textUnderstanding the bubble dynamics near a curved boundary is crucial for evaluating the cavitation impacts, as well as advancing the beneficial use of cavitation in real-world applications such as biofilm cleaning and environmental treatment. This study employs a high-fidelity multiphase flow model to analyze the dynamics of bubble collapse near rigid curves of varying curvatures. The numerical model employs a second-order-accurate solver within a two-dimensional axisymmetric coordinate system to solve the 5-equation model (Kapila's model). After being validated by three bubble collapse experiments, the model is applied to examine the bubble morphology and jet characteristics near different curved boundaries at varying standoff distances. The results reveal that as curvature increases, the jet momentum decreases due to the decrease in the jet volume, while the bubble jet velocity gradually increases in scenarios of downward jetting. Smaller standoff distances lead to bubbles with higher transverse to longitudinal ratio, insufficient longitudinal contraction, and reduced jet velocity. Finally, we summarize the changes in bubble morphology, jet velocity, jet momentum, and peak pressure with curvatures and standoff distances and fit the boundary for different bubble collapse patterns. This study establishes a clear correlation between bubble jet momentum and bubble type, finding that downward jetting can enhance jet momentum
火箭发动机燃烧室和喷管强动载试验装置的工况评估方法
No full text本发明公开了火箭发动机燃烧室和喷管强动载试验装置的工况评估方法，包括步骤：预先计算模拟形成基本数据库之后，提炼获得数据信息表；基于基本数据库和数据信息表建立工况评估模型；对工况评估模型的计算数据与实际试验的实验数据对比获取差异，并计算分析获得修正系数，以修正并更新工况评估模型。本发明采用循环更新模型的方式，预先计算模型形成基本数据库后提炼获取数据信息表，并基于基本数据库和数据信息表建立工况评估模型，利用工况评估模型获取计算数据对运行状态进行评估，并对比实际试验的实验数据获取修正系数，利用修正系数对工况评估模型进行修正更新，以逐步提高工况评估模型的准确度，从而准确反映实际的强动载工况
一种内燃机表面催化多孔涂层及其制备方法
No full text本发明实施例公开了一种内燃机表面催化多孔涂层及其制备方法，包括：将待加工件表面进行清洗和干燥，得到预处理后的待加工件；将待加工件置于电解液中，采用等离子体微弧氧化进行操作，在待加工件表面镀覆形成致密层；向电解液中加入纳米催化材料分散，在等离子体微弧氧化操作的条件下，至等离子体光谱的强度达到不低于峰值的2/5，完成过渡层的镀覆；调节等离子体微弧氧化操作的加工参数，继续进行等离子体微弧氧化操作，至离子发射光谱的强度达到峰值的7/10～4/5时，完成内燃机表面催化多孔涂层的制备。本发明最终制备的涂层载体兼备高强度、高孔隙率以及大量蜂巢孔洞的属性，解决了目前内燃机催化载体比表面积不足的问题
用于同轴柱面爆燃驱动装置的弹性弯曲式高压电极
No full text本发明公开了用于同轴柱面爆燃驱动装置的弹性弯曲式高压电极，包括导电芯极、绝缘套、螺纹压帽、密封压环；导电芯极包括第一导电芯极部、第二导电芯极部和第三导电芯极部；第三导电芯极部远离第二导电芯极部一侧开设有中心孔，点火丝贯穿中心孔，中心孔与爆燃驱动段的轴心位于同一水平面上；第三导电芯极部上设置有弹性件，弹性件具有第一弹性部和第二弹性部，第二弹性部与第三导电芯极部之间具有空隙；第二弹性部远离第二导电芯极部一侧设置有凹槽，且凹槽与中心孔相对应，凹槽的底面靠近第三导电芯极部一侧；绝缘套具有第一包覆部、第二包覆部和第三包覆部。本发明不仅便于安装或更换点火丝，而且能够保证点火丝与爆燃驱动段1之间精确同轴
Nonlinear dynamic analysis and vibration reduction of two sandwich beams connected by a joint with clearance
No full textThe dynamics and vibration reduction characteristics of the clamped-clamped two sandwich beams jointed with clearance is studied theoretically and experimentally. A transverse and torsional spring system with clearance is used to equivalent the joint model. The homogenization method is used to equivalent the core layer and Rayleigh-Ritz method is utilized to derive the mode function of the interconnected sandwich beam by using a sequence of orthogonal polynomials. The nonlinear motion equation of the two jointed sandwich beam structure with clearance is derived by the application of the Hamilton principle and then solved using an improved Newmark integration approach. In order to validate the accuracy of the natural frequency and vibration mode, the finite element model is established. This paper examines the impact of clearance on the amplitude frequency response and vibration transmission of the two jointed sandwich beam structure, it is found the jointed sandwich beams show obvious nonlinear characteristics and intermittent vibration transmission phenomenon due to the clearance. Moreover, the vibration transmission analysis reveals that the existed clearance demonstrates significant vibration reduction effect, for which an experiment is conducted to validate the results. In general, this work proposes a novel approach for modeling sandwich structures with clearance with improved vibration reduction performance
Superior tensile properties induced by triple-level heterogeneous structures in the CoNiV-based medium-entropy alloy
No full textThe strength-ductility trade-off was evaded by deploying a triple-level heterogeneous structure into a CoNiV-based medium-entropy alloy (THS MEA). The innovative hetero-structures comprise chemical short-range ordering (CSRO) at the atomic level, B2 precipitates at the nanoscale level, and heterogeneous grains at the microscale level. The THS MEA exhibits superior mechanical properties, displaying a yield strength from 1.1 GPa to 1.5 GPa alongside a uniform elongation of 18 %-35 %. Compared with its coarse-grained (CG) counterpart, the THS MEA demonstrates the pronounced up-turn phenomenon and enhanced hardening behavior attributed to hetero-deformation-induced (HDI) hardening. The detailed microstructural characterizations reveal that CG MEA primarily accommodates deformation through extensive planar dislocations and Taylor lattices. However, the THS MEA exhibits a more complex deformation profile, characterized by planar and waved dislocations, deformation twins, stacking faults, and Lomer-Cottrell locks. Additionally, the interactions between dislocations and B2 nanoprecipitates play a pivotal role in dislocation entanglements and accumulations. Furthermore, the CSRO within the matrix effectively retards the dislocation motion, contributing to a substantive hardening effect. These findings underscore the potential of a heterogeneous microstructure strategy in enhancing strain hardening for conquering the strength-ductility dilemma. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology
Determining pressure from velocity via physics-informed neural network
No full textThis paper describes a physics-informed neural network (PINN) for determining pressure from velocity where the Navier-Stokes (NS) equations are incorporated as a physical constraint, but the boundary condition is not explicitly imposed. The exact solution of the NS equations for the oblique Hiemenz flow is utilized to evaluate the accuracy of the PINN and the effects of the relevant factors including the boundary condition, data noise, number of collocation points, Reynolds number and impingement angle. In addition, the PINN is evaluated in the twodimensional flow over a NACA0012 airfoil based on computational fluid dynamics (CFD) simulation. Further, the PINN is applied to the velocity data of a flying hawkmoth (Manduca) obtained in high-speed schlieren visualizations, revealing some interesting pressure features associated with the vortex structures generated by the flapping wings. Overall, the PINN offers an alternative solution for the problem of pressure from velocity with the reasonable accuracy and robustness
The oxidation of NH<sub>3/</sub>CO/O<sub>2</sub>/H<sub>2</sub>O system in a plug flow reactor: Experimental and kinetic modeling study
No full textAmmonia, as a carbon-free fuel, is easier to store and transport than hydrogen. Due to the high ignition energy and low reactivity of ammonia, adding hydrogen or carbon-based fuels as combustion aids may improve the ignition and burnout of ammonia. CO is an important intermediate product in the co-combustion process of ammonia and carbon-based fuels. Research on NH3/CO co-combustion will further promote the application of such co-fuel in propulsion systems and power generation. In this work, experimental results were supplemented with novel flow reactor results on the effect of NH3 on CO oxidation in the absence of NO, and explained based on a detailed chemical kinetic model. The effects of temperature (1023-1223 K), NH3 concentration (250-1500 ppm), and water content (1 %-10 %) on CO oxidation, NH3 conversion, and NO generation were analyzed. In the NH3/CO system, the properties of CO always dominate. As the NH3 content increases, NH3 gradually inhibits the oxidation of CO by seizing free radicals (O, H, OH) and converting into NH2. NH2 further interacts with free radicals to convert into NH or HNO, and ultimately into NO. An increase in temperature will decrease the release of NO and CO and gradually decrease the conversion of NO from NH3. However, ammonia concentration had little effect on the ratio of ammonia conversion to NO. When H2O increases from 1 % to 2 %, it has a significant inhibitory effect on the production of NO and promotes the oxidation of CO. When the water concentration increases from 5 % to 10 %, the inhibitory effect reaches saturation. The present work evaluates the amine subset of the reaction mechanism under the studied conditions and provides experimental data under different NH3/CO ratios, which can be used to construct and verify the reaction mechanism of mixed fuels of carbon-based fuels and ammonia
Graphical models of dominant topologies of polymer-substrate adhesive-interfacial strength and toughness
No full textIt is a challenge to determine the dominant topological characteristics of mechanical properties of adhesive interfaces. In this paper, we used graph theory and molecular dynamics simulation to investigate the influence of topological characteristics on the strength and toughness of highly cross-linked polymer interface systems. Based on the microstructure of the adhesive system, we extracted the dominant topological characteristics, including the connectivity degree (D) that determines the yield strength, and the average node-path (P) and the simple cycles proportions (R) that determine the deformability and load-bearing capacity during the void propagation respectively, which co-determine the toughness. The influence of the wall-effect on the dominant topological characteristics was also analyzed. The results showed that the interfacial yield strength increases with the increase of D, while the toughness increases with the increase of P and R. The wall-effect has a significant influence on D, P, and R. The strong wall-effect causes the enrichment of amino groups near the wall and insufficient cross-linking away from the wall, leading to the lower D and R, i.e., the lower yield strength and load-bearing capacity during the void propagation. With the attenuation of the wall-effect, the D increases gradually, while the P and the R first increase and then decrease, showing an optimized wall-effect for the toughness of the adhesive interface. This paper reveals the dominant topological characteristics of adhesive interfacial strength and toughness, providing a new way to modulate the mechanical properties of polymer adhesive interface systems