A mechanistic insight into the shaft resistance of vertically vibrating piles

A mechanism for the dynamic shaft resistance of vertically vibrating single end-bearing and infinitely long piles is proposed through the use of elastodynamics. The generalized expression for the shaft resistance is obtained by means of Hamilton's principle. The shaft resistance is divided analytically into three parts, namely, the Winkler spring, the membrane and the participating mass of the surrounding soil. In light of the contributions of these three components of shaft resistance, a physical model is presented for the nature of single piles subjected to dynamic loading. The three components are obtained as explicit forms. The first is linear to the pile settlement. The second is related to the derivative of the second order of the pile settlement. The third involves the participating mass of the surrounding soil. The effect of the properties of the soil-pile system on the dynamic responses of the characteristic coefficients of the shaft resistance is investigated. The results indicate that the Winkler spring contributes the most to the shaft resistance. The contributions of the membrane and the participating mass of the surrounding soil are negligible for cases of high incident frequency.     

Vibration velocity control standard of buried pipeline under blast loading of adjacent tunnel

With the rapid development and construction of China’s transportation system, more and more projects are being conducted near existing buried pipelines, which will inevitably influence the safety of the pipelines. Among the safety issues related to buried pipelines, blasting during the construction of an adjacent tunnel is one of the most adverse factors for existing pipelines. To ensure the safety and normal operation of the pipelines, a method for determining the peak vibration velocity control standard for buried pipelines under blast loading is established in this study. The acceleration time-history function that acts on the rock mass under the blasting seismic wave is derived as external excitation acting on the pipeline. By using the acceleration time-history function as input and combining it with a dynamic and static analysis of the pipeline, the critical vibration velocity of pipelines under the action of blast loading can be determined by the von Mises yield criterion of the buried pipeline material. Using the Dashanpi No. 1 tunnel project in Shenzhen, China as a background, the critical velocity control standard for buried pipelines under tunnel blast loading can be set at 190 mm/s without considering either the initial defects or the corrosion conditions during the operation.     

Transducer invariant multi-class fault classification in a rotor-bearing system using support vector machines

Faults in a rotor-bearing system due to bearings and unbalance have been classified using support vector machines (SVMs). Vibration signals on a rotor-bearing system were measured simultaneously at five different rotating speeds using seven transducers. The most sensitive feature of the vibration signals has been determined using compensation distance evaluation technique. Multi-class SVMs classification algorithm was then implemented for classification of the faults by considering SVMs created by the possible combinations of the most two sensitive features for each type of fault. By using optimal SVM parameters, the effective location of transducer among seven transducers for best classification of the faults has been investigated and found that any transducer provides a classification of 75% or better and this classification rate increases when more transducers are considered. This paper provides a robust SVM based technique using only time domain data without any additional preprocessing for classifying bearing and unbalance faults.     

Boundary Stabilization of a Cosserat Elastic Body

Boundary stabilization of vibrating three‐dimensional Cosserat elastic solids are studied using mathematical tools, such as operator theory and semigroup techniques. The advantages of the boundary control laws for both boundary stabilization problems are investigated. The boundary stabilization problems are studied using a Lyapunov stability method and LaSalle's invariant set theorem. Numerical simulations are provided to illustrate the effectiveness and performance of the designed control scheme.     

Identification and characterization of solids in sand-water two-phase flows via vibration multi-sensor approaches

The monitoring of tiny particles in multiphase pipe flow is widely encountered in industry. In this paper, the identification and characterization of solid particles suspended in sand-water flow were developed based on vibration multi-sensor approaches. Verification experiments were conducted, and good agreement was found between the concentrations (0–0.1 wt% with an interval of 0.02 wt%) of varisized sands (from 86 to 180 μm) and the monitored vibration signal characteristics by multi-sensor approaches. A quadratic relationship between the particle concentration and vibration energy was obtained. In sand-carrying flow measurement experiments, the sand’s characteristic frequency bands were found at 22–23.6 kHz and 24.8–26.6 kHz. Additionally, the sand particle identification effect was evaluated from two positions at bends, that is, the outer wall of the 45-degree bend on the elbow and the exit of the 90-degree bend. Compared with these two monitor positions, the sand vibration energy from the outlet of the elbow had a higher signal-to-noise ratio with obvious energy variations. In addition, the accuracies of the detected sand vibration features were mutual confirmation. Consequently, the above methods are applicable for little solid detection in sand-water flow, which lays the foundation for particles monitoring in the complexed multiphase flow.     

Distance Estimation and Material Classification of a Compliant Tactile Sensor Using Vibration Modes and Support Vector Machine

Many animals possess actively movable tactile sensors in their heads, to explore the near-range space. During locomotion, an antenna is used in near range orientation, for example, in detecting, localizing, probing, and negotiating obstacles. A bionic tactile sensor used in the present work was inspired by the antenna of the stick insects. The sensor is able to detect an obstacle and its location in 3D (Three dimensional) space. The vibration signals are analyzed in the frequency domain using Fast Fourier Transform (FFT) to estimate the distances. Signal processing algorithms, Artificial Neural Network (ANN) and Support Vector Machine (SVM) are used for the analysis and prediction processes. These three prediction techniques are compared for both distance estimation and material classification processes. When estimating the distances, the accuracy of estimation is deteriorated towards the tip of the probe due to the change in the vibration modes. Since the vibration data within that region have high a variance, the accuracy in distance estimation and material classification are lower towards the tip. The change in vibration mode is mathematically analyzed and a solution is proposed to estimate the distance along the full range of the probe.     

微电路模块灌封工艺研究

针对某款微电路模块在组装过程中存在的质量隐患以及在试验中存在的振动、散热、短路等质量可靠性问题,调整微电路模块的灌封方案,通过对比三种灌封-元器件焊接组合,得到最优灌封方案,确定灌封胶制备、灌胶填充和灌封胶固化等核心步骤的工艺条件。在灌封胶量确定和灌封工艺过程控制中,通过筛选和鉴定检验的典型试验,验证该微电路模块灌封工艺方案的可靠性。实验结果表明,利用灌封胶改善了绝缘、散热、耐温、防震作用,解决了该微电路模块在组装过程中存在的质量隐患及产品可靠性问题。     

Exact solution for free vibration of coupled double viscoelastic graphene sheets by viscoPasternak medium

Based on nonlocal theory, this article discusses vibration of CDVGS¹ systems. The properties of each single layer graphene sheet (SLGS) are assumed to be orthotropic and viscoelastic. The two SLGSs are simply supported and coupled by an enclosing viscoelastic medium which is simulated as a Visco-Pasternak layer. This model is aimed at representing dynamic interactions in nanocomposite materials with dissipation effect. By considering the Kirchhoff plate theory and Kelvin–Voigt model, the governing equation is derived using Hamilton's principle. The equation is solved analytically to obtain the complex natural frequency. The parametric study is thoroughly performed, concentrating on the series effects of viscoelastic damping structure, aspect ratio, visco-Pasternak medium, and mode number. In this system, in-phase (IPV) and out-of-phase (OPV) vibrations are investigated. The numerical results of this article show a perfect correspondence with those of the previous researches.     

Modified continuum model for stability analysis of asymmetric FGM double-sided NEMS: Corrections due to finite conductivity,surface energy and nonlocal effect

Finite conductivity, surface energy and nonlocal effect can influence the electromechanical performance of micro/nano-electromechanical systems (MEMS/NEMS). However, these factors are yet ignored on stability analysis of MEMS/NEMS fabricated from functionally graded materials (FGM). In this paper, dynamic stability of double-sided NEMS fabricated from non-symmetric FGM is investigated incorporating finite conductivity, surface energy and nonlocal effect. The Gurtin–Murdoch model and Eringen's elasticity are employed to consider the surface energy and nonlocal effect, respectively. Effect of finite conductivity of FGM on electrostatic and Casimir attractions is incorporated via relative permittivity and plasma frequency of the material. The stability analysis of the nanostructure is conducted by plotting time history and phase portraits. Moreover, bifurcation analysis is conducted to investigate the stability of the fixed points of the nano-structure. The validity of the proposed model is examined by comparing the results of the present study with those reported in the literature. The impact of various parameters i.e. finite conductivity, nonlocal parameter, surface stresses and material characteristics on the dynamic instability of the NEMS are addressed.     

Performance evaluation of spaceborne cryocooler micro-vibration isolation system employing pseudoelastic SMA mesh washer

A spaceborne cryocooler produces undesirable micro-vibration disturbances during its on-orbit operation, which is one of the main sources of degradation of the image quality of high-resolution observation satellites. Therefore, to comply with the strict mission requirement for the acquisition of high-quality images, micro-vibration disturbances induced by cryocooler operation need to be isolated. In this study, we proposed a spaceborne cryocooler micro-vibration isolator that employs a pseudoelastic shape memory alloy (SMA) mesh washer, which guarantees vibration isolation performance in a severe launch vibration environment while effectively isolating the micro-vibrations from the cryocooler on-orbit. Basic characteristics of the cryocooler assembly integrated with the proposed isolators were measured through static tests and free vibration tests. The effectiveness of the isolator design was demonstrated by the micro-vibration measurement tests under qualification temperature limits.