Displacement barrier heights from experimental nucleation rate data

Nucleation phenomena have a great importance in many areas of science. However, the main theoretical tool to analyse these phenomena, the classical nucleation theory (CNT), has known weaknesses. A decade ago a nucleation theorem based correction to CNT was developed [McGraw, R., Laaksonen, A., 1996. Scaling properties of the critical nucleus in classical and molecular-based theories of vapor–liquid nucleation. Phys. Rev. Lett. 76, 2754–2757]. We have analysed experimental nucleation rate data of two homologous series of molecular fluids in terms of this scaling relation. Our first results suggest possible universal functional form for correction to the temperature dependence of CNT.     

Use of geosynthetics for performance enhancement of earth structures in cold regions

Earth structures, such as roadways, embankments and slopes, and earth retaining walls, have been commonly used in cold regions for transportation and other applications. In addition to typical design c...     

中国边缘海及邻区地壳和上地幔速度结构特征

本文利用中国地震台网和世界地震台网1 222个地震台记录到的27 909个研究区内地震的479 707条P波到时数据和4 995个研究区外远震事件的90 530条P波到时数据,采用多波多震相地震层析成像法重建了中国边缘海及其邻近地区（10°~45°N,105°~145°E,深至1 061 km）的三维速度图像,揭示了中国边缘海及其邻近地区地壳和上地幔三维速度结构特征.     

一种利用双源反激的随钻声波测井方法

随钻单极子纵波测井时存在很强的钻铤波的干扰.针对这一问题,提出了一种双源反激随钻声波测井方法,从数据采集环节对钻铤波进行压制;在后续数据处理中结合声波干涉法,从而实现一种无需隔声装置的随钻声波测井方法.理论模拟表明双源反激方法可以有效压制钻铤波,地层波的信噪比也能得到相对增强.对钻铤波压制后的数据进一步用声波干涉法处理可以从中提取地层纵波信息.设计了实验样机,并在空气中进行了实验.结果表明不同工作频率下该方法对钻铤波均有明显的压制效果,即使在5kHz低频情况下钻铤波也能压制到原来的25%.验证了该方法的可行性.应用该方法的好处是可以避免对钻铤强度的破坏,并能扩展现有随钻声波测井仪纵波测量的工作频带范围.     

Pile response subjected to rock blasting induced ground vibration near soil-rock interface

Blasting has been widely used in mining and construction industries for rock breaking. Ground vibration induced by blasting is an inevitable side effect that may cause damage to nearby structures, if not properly controlled. In this study, response and possible damage of rock-socketed pile near soil-rock interface subjected to ground shock excitations are investigated and quantified with coupled SPH-FEM method. Results indicate that the base of the pile is relatively vulnerable and that the soil properties significantly influence on response of pile subjected to a specific blast load. Furthermore, based on the numerical results, ground vibration attenuation equation is proposed.     

Numerical investigation of oscillations induced by submerged sliding masses within a harbor of constant slope

Oscillations within a rectangular harbor of constant slope induced by submerged sliding masses are investigated numerically based on Boussinesq-type equations and results are used to reveal the characteristics of the generated oscillations. The numerical result of each transverse eigenfrequency is very close to the theoretical prediction and the spatial structure of each mode of the oscillations may also be well captured by the existing analytical solutions based on shallow water equations. The investigation shows that relatively small-scale sliding masses whose width is small compared with the harbor width may induce obvious transverse oscillations. The predominant transverse components are those with small mode numbers when the solid slides start moving from the backwall. In comparing the oscillations induced by the slides of constant velocity and those accelerated by gravity force with bottom friction, it is observed that the movements accelerated by gravity force may facilitate the development of very low transverse oscillation modes while those with constant velocity may also be in favor of the higher ones. The augmentation of the sliding velocity along the constant slope may shift the amplitudes of the oscillation components to smaller values, which corresponds to the physical understandings of the waves generated by underwater sliding masses or landslides. While the sliding masses may not act on an isolated point of the bottom but follow a certain trajectory along the harbor, the transverse oscillations induced by them are sensitive to their position of departure in both the cross-harbor direction and the offshore direction. Longitudinal oscillations may be induced by relatively large sliding masses of harbor width on a constant slope within the harbor. Although the longitudinal oscillations may not reach a steady state without forcing terms at the entrance of the harbor, some patterns of several low-mode ones occur and wavelet spectra are used to analyze their evolutions and comparisons are made with theoretical predictions. It is revealed that the longitudinal oscillations are also sensitive to the moving velocity and initial location of the sliding masses.     

Experimental and numerical investigations on hydrodynamic and aerodynamic characteristics of the tunnel of planing trimaran

The planing trimaran possesses distinctive hybrid hydrodynamic and aerodynamic performance due to the presence of tunnel. The research described in this paper was carried out based on the observation of wave characteristics of a planing trimaran model in towing tests, in which the resistance drops as soon as the wave surface separates from tunnel roof. In order to gain a deeper insight into the relationship between wave flow and forces in tunnel region, a comprehensive series of viscous CFD simulations considering free-surface and 2-DOF motion of the hull (heave and pitch) have been performed for the tested model at the volume based Froude numbers ranging from 3.16 to 5.87. The calculated results were validated by comparison with experimental data and showed good agreement. Numerical results of wave contours, longitudinal wave cuts and lifting force distributions at the calculated speeds were presented for the analysis of ventilation process in tunnel region and the corresponding variation of tunnel forces. It is found that, for the speeds higher than Froude number of 4.52, the aerodynamic forces provide major tunnel lift and mainly act on the straight section of the tunnel. And, therefore, numerical simulations of two modified models have also been performed for the analysis of influence of straight section length on the hydrodynamic and aerodynamic performance of planing trimaran.     

Investigations on 3D effects and correlation between wave height and lip submergence of an offshore stationary OWC wave energy converter

Understanding the hydrodynamic interactions between ocean waves and the oscillating water column (OWC) wave energy converter is crucial for improving the device performance. Most previous relevant studies have focused on testing onshore and offshore OWCs using 2D models and wave flumes. Conversely, this paper provides experimental results for a 3D offshore stationary OWC device subjected to regular waves of different heights and periods under a constant power take–off (PTO) damping simulated by an orifice plate of fixed diameter. In addition, a 3D computational fluid dynamics (CFD) model based on the RANS equations and volume of fluid (VOF) surface capturing scheme was developed and validated against the experimental data. Following the validation stage, an extensive campaign of computational tests was performed to (1) discover the impact of testing such an offshore OWC in a 2D domain or a wave flume on device efficiency and (2) investigate the correlation between the incoming wave height and the OWC front wall draught for a maximum efficiency via testing several front lip draughts for two different rear lip draughts under two wave heights and a constant PTO damping. It is found that the 2D and wave flume modelling of an offshore OWC significantly overestimate the overall power extraction efficiency, especially for wave frequencies higher than the chamber resonant frequency. Furthermore, a front lip submergence equal to the wave amplitude affords maximum efficiency whilst preventing air leakage, hence it is recommended that the front lip draught is minimized.     

Michell and Hogner models of far-field ship waves

The far-field waves, and the related far-field wave drag, predicted by the Michell or Hogner theories are considered. These two classical theories are found to predict nearly identical transverse waves for all practical cases. However, the Michell and Hogner models predict divergent waves—dominant at high Froude numbers—that can differ significantly. Differences between the far-field waves predicted by the Michell and Hogner models are much smaller for catamarans, for which lateral interferences between the twin hulls overwhelm lateral interferences between the port and starboard sides of the hulls, than for monohull ships. Moreover, differences between the divergent waves predicted by the Michell and Hogner theories are larger for higher Froude numbers, bigger beam/length ratios, smaller draft/length ratios, or larger separation distances between the twin hulls of a catamaran.