Adaptive multi‐rate interface: development and experimental verification for real‐time hybrid simulation

Real‐time hybrid simulation (RTHS) is a powerful cyber‐physical technique that is a relatively cost‐effective method to perform global/local system evaluation of structural systems. A major factor that determines the ability of an RTHS to represent true system‐level behavior is the fidelity of the numerical substructure. While the use of higher‐order models increases fidelity of the simulation, it also increases the demand for computational resources. Because RTHS is executed at real‐time, in a conventional RTHS configuration, this increase in computational resources may limit the achievable sampling frequencies and/or introduce delays that can degrade its stability and performance. In this study, the Adaptive Multi‐rate Interface rate‐transitioning and compensation technique is developed to enable the use of more complex numerical models. Such a multi‐rate RTHS is strictly executed at real‐time, although it employs different time steps in the numerical and the physical substructures while including rate‐transitioning to link the components appropriately. Typically, a higher‐order numerical substructure model is solved at larger time intervals, and is coupled with a physical substructure that is driven at smaller time intervals for actuator control purposes. Through a series of simulations, the performance of the AMRI and several existing approaches for multi‐rate RTHS is compared. It is noted that compared with existing methods, AMRI leads to a smaller error, especially at higher ratios of sampling frequency between the numerical and physical substructures and for input signals with high‐frequency content. Further, it does not induce signal chattering at the coupling frequency. The effectiveness of AMRI is also verified experimentally. Copyright © 2016 John Wiley & Sons, Ltd.     

The rosseland mean opacity of interstellar grains

We have calculated the opacity of interstellar grains in the temperature range 10–1500 K. Two composite grain models have been considered. One of them consists of silicate coated with an ice mantle and the second has a graphite core coated also with an ice mantle. These models are compared with isolated grain models. An exact analytical and computational development of Güttler's formulae for composite grain models has been used to calculate the extinction coefficient.It has been found that the thickness of the mantle affects the opacity of the interstellar grains. The opacity of composite models differs from that of the isolated models. The effect of the different species (ice, silicate, and graphite) is also clear.     

新疆南部地区暖冬年与春夏季降水的相关分析

利用春夏季(3~8月)12个站降水资料以及冬季(12~02月)温度资料,通过统计方法选取新疆南部地区温度异常年份与春夏季降水异常年份,并进行相关分析,结果表明:暖冬年份对应的来年春夏季总降水量偏多;反之,冷冬年对应的春夏季降水总量偏少。再利用NCEP/NCAR1960-2000年全球月平均网格点资料分析500 hPa高度场环流特征,结果表明:暖冬年前期环流特征为西低东高型,冷冬年前期环流特征为西高东低型,具有反位相关系。暖冬年后期才为西高东低型,与冷冬年前期相较起点晚,从而影响到来年的环流入夏时间,这可能就是导致暖冬年份来年降水增多的原因之一。     

基于多源遥感与再分析数据估算塔克拉玛干沙漠地表净辐射日变化

作为世界第二大流动性沙漠,塔克拉玛干沙漠独特的陆表水热交换过程直接影响中国乃至全球的大气环流运动。将静止气象卫星FY-2F地表温度产品、极地轨道卫星MODIS陆表产品与中国区域高时空分辨率地面气象要素驱动数据集（CMFD）结合,反演得到时间分辨率为3 h、空间辨率为0.1°的2017年塔克拉玛干沙漠地表净辐射,利用塔中气象站观测值验证反演结果,并分析地表净辐射的时空变化特征。结果表明：（1）利用卫星遥感与再分析资料获取的地表特征参数与实测值误差较小,决定系数R²均在0.8以上。（2）地表净辐射模拟值与地面实测值具有较好的一致性,决定系数R²为0.967,均方根误差RMSE为29.193 W·m^-2。（3）地表净辐射日变化呈现明显的单峰型特征：早晚值较低,正午值最高,并且夜间值基本为负且变化幅度不大。（4）地表净辐射夏季>春季>秋季>冬季。（5）沙漠边缘散布的绿洲和农田地区净辐射值最高,沙漠腹地次之,沙漠南缘的昆仑山和阿尔金山冰川覆盖地区净辐射值最低。     

Stability Analysis and Optimal Design of Ultimate Slope of an Open Pit Mine: A Case Study

Geotechnical and Geological Engineering - To avoid over-tailing and limit the risk of failure in open-pit mines, choosing an ideal and stable slope is critical. The major goal of this study was to...     

Application of the WEPP model to determine sources of run‐off and sediment in a forested watershed

This study investigates critical run‐off and sediment production sources in a forested Kasilian watershed located in northern Iran. The Water Erosion Prediction Project (WEPP) watershed model was set up to simulate the run‐off and sediment yields. WEPP was calibrated and validated against measured rainfall–run‐off–sediment data. Results showed that simulated run‐off and sediment yields of the watershed were in agreement with the measured data for the calibration and validation periods. While low and medium values of run‐off and sediment yields were adequately simulated by the WEPP model, high run‐off and sediment yield values were underestimated. Performance of the model was evaluated as very good and satisfactory during the calibration and validation stages, respectively. Total soil erosion and sediment load of the study watershed during the study period were determined to be 10 108 t yr^?1 and 8735 t yr^?1, respectively. The northern areas of the watershed with dry farming were identified as the critical erosion prone zones. To prioritize the subwatersheds based on their contribution to the run‐off and sediment production at the watershed's main outlet, unit response approach (URA) was applied. In this regard, subwatersheds close to the main outlet were found to have the highest contribution to sediment yield of the whole watershed. Results indicated that depending on the objective of land and water conservation practices, particularly, for controlling sediment yield at the main outlet, critical areas for implementing the best management practices may be identified through conjunctive application of WEPP and URA. Copyright © 2014 John Wiley & Sons, Ltd.     

3D numerical stability analysis of multi-lateral well junctions

The most important factors in multi-lateral well stability analysis are the magnitude of in situ stresses, the relation between the amount of in situ stresses and orientation of lateral wellbore. In this research, the stability analysis of multi-lateral junction is carried out using FLAC3D numerical code by considering seven varied stress regimes and different lateral wellbore orientations. The Normalized Yielded Zone Area (NYZA, ratio of surrounding yielded cross-sectional area to initial area of well) is determined for different junction mud pressures as well as diverse orientations of lateral wellbore. Then, the junction optimum mud pressure of each lateral wellbore orientation is calculated; hence, the optimum trajectory of lateral wellbore, in which the junction has got the lowest optimum mud pressure, is selected in each stress regime. The stability analysis of multi-lateral wells by means of finite difference method shows that in each stress regime the required mud pressure for the stability of junction is much more than that of the lateral branch and the main wellbore.     

Investigation of Effective Parameters on the Embankment Dam Filter Behavior in Simultaneous Cracking in the Core and Filter

Cracks in filter can develop as a result of earthquake deformations or post-construction settlement and in some cases cracks extended through both the core and filter. Hence, a test apparatus has been developed to investigate filter performance in the case of filter and core material cracking in the embankment dams. The apparatus allows testing of incomplete cylindrical test specimens of 10 cm diameter and height of 20 cm. If the filters work well and successfully, crack filling occur, also the flow rate decrease, and the head water pressure increase to the range of early pressure. In the failed filters case, the flow rate do not decrease and remain high, also a very low head water pressure take place. In this research, variations of pressure, fines contents of filter soils, compaction time, PI of the base material and amount of eroded materials was evaluated. Results showed that prime flow rate increased as hydraulic gradient increased, but decreased in a little time and reach to a stable value. Filter with 15% of non-plastic fine content, had ability to slump to fill the crack, but its coefficient of permeability decreased significantly, hence, cannot be used as a filter in embankment dams.     

Monte Carlo simulation of permeability fields and reservoir performance predictions with SVD parameterization in RML compared with EnKF

In a previous paper, we developed a theoretical basis for parameterization of reservoir model parameters based on truncated singular value decomposition (SVD) of the dimensionless sensitivity matrix. Two gradient-based algorithms based on truncated SVD were developed for history matching. In general, the best of these “SVD” algorithms requires on the order of 1/2 the number of equivalent reservoir simulation runs that are required by the limited memory Broyden–Fletcher–Goldfarb–Shanno (LBFGS) algorithm. In this work, we show that when combining SVD parameterization with the randomized maximum likelihood method, we can achieve significant additional computational savings by history matching all models simultaneously using a SVD parameterization based on a particular sensitivity matrix at each iteration. We present two new algorithms based on this idea, one which relies only on updating the SVD parameterization at each iteration and one which combines an inner iteration based on an adjoint gradient where during the inner iteration the truncated SVD parameterization does not vary. Results generated with our algorithms are compared with results obtained from the ensemble Kalman filter (EnKF). Finally, we show that by combining EnKF with the SVD-algorithm, we can improve the reliability of EnKF estimates.