Institute Of Mechanics,Chinese Academy of Sciences
Not a member yet
33838 research outputs found
Sort by
Droplet sliding on an inclined substrate with chemical defects
No full textWe numerically study the dynamics of a droplet sliding on an inclined and inhomogeneous substrate under gravity force using three-dimensional diffuse interface method. On the path of the sliding droplet, there are two transversely located defects with the shape of circle, and their wettability is different from the substrate. Our aim is to identify the regimes of the droplet motion and figure out the critical conditions between the different regimes. By varying the distance between the two defects, the inclination angle of the substrate, and the size of the defects, three regimes are found according to the status of the droplet: capture, breakup and release. By analyzing geometrical relationships, the shape of the contact line and the force balance of the droplet at rest, we derive critical conditions between each two regimes. The theoretical predictions of critical conditions agree well with our numerical simulations, which provide a comprehensive understanding of the underlying mechanisms of a droplet sliding on a chemical defect substrate
Wind farm fluid mechanics for high-penetration wind energy
No full textAdvancements in aerodynamics during the early 20th century laid the foundation for modern wind energy. The increasing penetration of wind power presents novel challenges in fluid mechanics, which stem from an incomplete understanding of the dynamics of wind turbine wakes and their interactions with the atmospheric flow. This article provides a comprehensive review of the current understanding of the mechanisms of wind turbine wakes and wake-atmosphere interactions. It summarizes existing models for wind turbine wakes and explores control strategies for mitigating wake losses and tracking power reference signals. Finally, it delves into research trends in the field and summarizes the review
Numerical simulation of droplet solidification on a cold plate
No full textWe proposed a solidification model based on the Front-Tracking method to simulate the freezing of liquid droplets on a cold substrate. The model is validated through comparison with existing numerical and experimental results, demonstrating agreement and improved mass conservation relative to previous approaches. Subsequently,the model is employed to investigate droplet solidification dynamics by varying key parameters, including the initial contact angle (theta 0), growth angle (theta gr), Stefan number (St), Bond number (Bo), solid-liquid density ratio (chi sl) and solid-liquid thermal conductivity ratio (kappa sl). The results reveal that, on hydrophobic surfaces, increasing the growth angle enhances circulation near the three-phase contact line, promoting upward liquid motion and yielding taller, more slender solidified morphologies. A higher Stefan number and kappa sl accelerate solidification by driving faster interface propagation, while an increased Bond number facilitates horizontal spreading, enlarging the solidification interface and improving heat transfer with the substrate. The solid-liquid density ratio is found to significantly influence both solidification rate and morphological development. These insights offer valuable guidance for controlling droplet solidification on hydrophobic surfaces and have direct implications for anti-icing technologies in power systems and aerospace applications
Numerical simulation of droplet solidification on a cold plate
No full textWe proposed a solidification model based on the Front-Tracking method to simulate the freezing of liquid droplets on a cold substrate. The model is validated through comparison with existing numerical and experimental results, demonstrating agreement and improved mass conservation relative to previous approaches. Subsequently,the model is employed to investigate droplet solidification dynamics by varying key parameters, including the initial contact angle (theta 0), growth angle (theta gr), Stefan number (St), Bond number (Bo), solid-liquid density ratio (chi sl) and solid-liquid thermal conductivity ratio (kappa sl). The results reveal that, on hydrophobic surfaces, increasing the growth angle enhances circulation near the three-phase contact line, promoting upward liquid motion and yielding taller, more slender solidified morphologies. A higher Stefan number and kappa sl accelerate solidification by driving faster interface propagation, while an increased Bond number facilitates horizontal spreading, enlarging the solidification interface and improving heat transfer with the substrate. The solid-liquid density ratio is found to significantly influence both solidification rate and morphological development. These insights offer valuable guidance for controlling droplet solidification on hydrophobic surfaces and have direct implications for anti-icing technologies in power systems and aerospace applications
Elevated-temperature fatigue behavior and microstructure based cumulative damage evaluation of additive manufacturing superalloy under variable amplitude loading
No full textFatigue properties under service conditions are a critical barrier to the reliable application of additive manufacturing (AM) metals. Yet, the associated damage mechanisms and life evaluation approaches, particularly at long term, elevated temperature and variable amplitude (VA) loading, are almost unclear. To address these, high and very-high cycle fatigue VA tests and meso-microscale analyses were performed to investigate damage mechanism of a laser powder bed fused superalloy with heat treatment at service temperature of 650 degrees C, and a microstructure based cumulative damage evaluation approach was proposed. Results show that interior failures characterized by defect-assisted faceted cracking are predominant. VA loading tends to sequentially activate multiple defects, resulting in competitive multi-site crack nucleation. Increased stress levels accelerate crack growth, leading to the formation of localized rough growth areas and crack deflection. Both primary and secondary cracks grow transgranularly, with crack paths showing negligible dependence on grain orientation. The interior crack nucleation and growth mechanisms under VA loading are elucidated. A cumulative damage evaluation model incorporating the remaining life factor, correlation function transformation, and a reconstructed stress-life relationship was developed, with the prediction results being in close accord with the experimental data under VA loading. These findings provide new insights into the interior crack nucleation and growth mechanisms in AM superalloys and offer a predictive framework for fatigue life estimation under realistic service conditions
纤维与橡胶复合结构抗拉压弯疲劳性能的测试装置及方法
No full text本发明提供了一种纤维与橡胶复合结构抗拉压弯疲劳性能的测试装置及方法,该测试装置包括导辊系统、杠杆加载系统、试样条带和挤压预紧装置；导辊系统包括固定导辊和滑动导辊；杠杆加载系统设置于滑动导辊水平方向一侧且一端与滑动导辊的转轴连接；杠杆加载系统对滑动导辊施加一个向上的力，以完成对试样条带的加载；挤压预紧装置设置于试样条带外侧，其与试样条带的外侧表面接触连接并对试样条带的外表面施加挤压力。本发明能够使纤维与橡胶复合结构试样产生拉伸、压缩、弯曲变形，并能控制试样条带中各个组分分别产生什么样的变形，特别是能够使纤维在试验过程中产生压缩应变，从而评价其包括耐压缩性能在内的各项疲劳寿命指标
Thermo-mechanically coupled compatibility conditions in orthogonal curvilinear coordinates: equivalent temperature variation of initially stressed elastomers
No full textThe initial stresses widely exist in elastic materials. While achieving a
continuum stress-free configuration through compatible unloading is desirable, mechanical unloading alone frequently proves insufficient, posing challenges in avoiding virtual stress-free configurations. In this paper, we introduce a novel concept of equivalent temperature variation to counteract the incompatible initial strain. Our focus is on initially stressed cylindrical and spherical elastomers, where we first derive the Saint-Venant, Beltrami-Michell, and Volterra integral conditions in orthogonal curvilinear coordinates using the exterior differential form theory. It is shown that for any given axially or spherically distributed initial stress, an equivalent temperature variation always exists. Furthermore, we propose two innovative initial stress forms based on the steady-state heat conduction. By introducing an equivalent temperature variation, the initial stress can be released through a compatible thermo-mechanical unloading process, offering valuable insights into the constitutive theory of initially stressed elastic materials.</p
Quantitative assessment of physical aging on dynamical heterogeneity of amorphous alloys: Insight from stress relaxation
No full textProbing the dynamical and structural heterogeneity is a critical issue for understanding the mechanical and physical properties of amorphous alloys. Here, the stress relaxation of a (La0.6Ce0.4)(65)Al10Co25 amorphous alloy is investigated to probe the evolution of dynamical and structural heterogeneity due to aging. The characteristics of amorphous alloys are time-dependent during stress relaxation due to the metastability; thus, the aging effect should be considered by modifying the classical Kohlrausch-Williams-Watts (KWW) function. We find that the fixed-parameter KWW function during prolonged stress relaxation is not valid due to aging. Furthermore, the parameters of the modified KWW function indicate that physical aging leads to an increase in the characteristic time tau and decrease in the stretched exponent beta KWW. The latter widens the instantaneous stress relaxation curve toward long-time end. The results demonstrated that the modified KWW function and the corresponding parameters conform to the conventional understanding of amorphous alloys
Revisiting GRACE Follow-On KBR Antenna Phase Center Calibration by Addressing Multipath Noise
No full textThe Gravity Recovery and Climate Experiment Follow-On (GRFO) mission precisely measures the inter-satellite range between the centers of mass of its twin satellites to map the earth's gravity field. The baseline ranging measurement is achieved using the K-band ranging (KBR) system, which is sensitive to satellite attitude variations caused by the offset between the satellite center of mass and the KBR antenna phase center. Accurate decoupling of the KBR range from attitude variations requires precise determination of the KBR's antenna offset vectors (AOVs). To address this, GRFO conducted eight KBR calibration maneuvers on 17 and 28 September 2020. However, these maneuvers exaggerated the impact of microwave multipath noise, complicating AOV estimation. Existing studies have not fully mitigated this noise. This study introduces a new frequency-domain method to estimate AOVs by leveraging double-difference signals and analyzing their spectral characteristics, along with those of the KBR range during calibration maneuvers, to suppress multipath noise. Our recalibrated AOVs achieve good alignment between the KBR and laser ranging interferometer (LRI) ranging signals. We validate our recalibrated AOVs by comparing the residuals between the LRI and KBR ranging signals corrected using both recalibrated AOVs and documented AOVs. The results show that, for the majority (58.4%) of the analyzed period (from January 2020 to June 2023), the residuals corrected by the recalibrated AOVs are closer to the LRI ranging signal. These findings demonstrate the effectiveness of the proposed method in addressing multipath noise and improving the accuracy of KBR range measurements. This work provides a framework for future gravity missions requiring precise calibration of multipath effects in inter-satellite ranging systems
旋流式气液分离器结构优化及试验研究
No full text为有效解决井下含气率在50%以上的高气液比油井电泵举升难题，本文设计了一种集重力及旋流原理于一体的旋流重力式井下气液分离器。采用数值模拟技术对分离器的结构进行了优化，并通过地面带压试验得到了带压条件下的分离规律。分离器的结构优化双对称环状转切向入口，入口位置居中，出气管向内筒插入30 mm