Influence of discrete step size on wind setup component of storm surge

Open coast storm surge water levels consist of wind setup due to wind shear at the water surface; a wave setup component caused by wind induced waves transferring momentum to the water column; an atmospheric pressure head component due to the atmospheric pressure deficit over the spatial extent of the storm system; a Coriolis forced setup or setdown component due to the effects of the rotation of the earth acting on the wind driven alongshore current at the coast; a possible seiche component due to resonance effects initiated by moving wind system, and, if astronomical tides are present, an astronomical tide component (although the tide is typically considered to be a forced astronomical event and not really a direct part of the external wind-driven meteorological component of storm surge). Typically the most important component of a storm surge is the wind setup component, especially on the U.S. East Coast and the Gulf of Mexico shorelines. In many approaches to storm surge modeling, a constant depth approximation is invoked over a limited step size in the computational domain. The use of a constant depth approximation has received little attention in the literature although can be very important to the resulting magnitude of the computed storm surge. The importance of discrete step size to the wind setup storm surge component is considered herein with a simple case computation of the wind setup component on a linear slope offshore profile. The present study findings show that the constant depth approximation to wind setup storm surge estimation is biased on the low side (except in extremely shallow water depths) and can provide large errors if discrete step size is not sufficiently resolved. Guidance has been provided on the error that one might encounter for various step sizes on different slopes.     

我国乳品工业区位分析

工业区位问题是工业地理学研究的核心问题之一。近年来我国乳品工业发展迅速,布局面貌变化很大,探讨适合我国国情的乳品工业区位问题,对于合理地开发利用乳品工     

A design method for plastic tube cast-in-place concrete pile considering cavity contraction and its validation

Bearing capacity calculation method and field static load test (SLT) program were carried out simultaneously to study the bearing characteristics of individual Plastic Tube Cast-in-Place Concrete Pile (TC pile), which are increasingly being employed for support of embankments in southeast China. The bearing capacity calculation method considering pile setup (i.e., setup calculation method) was built up according to the cylindrical cavity contraction and horizontal consolidation theories. A series of SLTs on different dates were applied to study the bearing behavior of TC pile and to verify the validity of the established setup calculation method. During TC piles installation, there is about 45% contraction in cylindrical volume due to the extraction of steel casing. Both theoretical and experimental results show that the calculated outcomes considering cylindrical cavity contraction agree well with measured ones. The difference value between them is not more than 12%. On the other hand, if the cylindrical cavity contraction is ignored, the calculated bearing capacities of TC piles are overestimated by 160–300%. The setup of TC pile is mainly due to the increment of pile shaft resistance with time elapsed. Cylindrical cavity contraction accompanied by TC pile installation causes much loss of pile shaft resistance.     

Is the instrumental drift of superconducting gravimeters a linear or exponential function of time?

The instrumental drift of the superconducting gravimeter in Membach, Belgium, is estimated using 9 years of co-located and episodic absolute gravity measurements. We show that the best model of the long-term drift of the SG-C021 is an exponential. The thermal levelers used to compensate tilts are unlikely to induce the observed drift. Rather, the capacitance bridge, magnetic variations, gas adsorption on the levitating sphere, or helium gas pressure variations around it are most likely the possible combined causes of the observed instrumental drift. In practice, either linear or exponential drift models are equivalent as long as the record duration does not exceed 10 years. For longer records, this study demonstrates that an exponential models the drift better than a simple linear trend.