Uncertainty in risk of highway bridges assessed for integrated seismic and flood hazards

Probabilistic risk assessment for bridges under natural hazards is of great interest to engineers for the development of risk mitigation strategies and implementation plans. The present study evaluates risk of an existing highway bridge in California, USA, under the integrated impact of regional seismic and flood hazards. A sensitivity study combining tornado diagram and first-order second moment reliability analyses is conducted to screen significant uncertain parameters to which bridge response is mostly sensitive. A rigorous uncertainty analysis, employing random sampling and Monte Carlo simulation techniques, is performed to obtain variations in fragility and risk curves of the bridge. Observed variations in risk curves at various risk levels are quantified through 90% confidence intervals and coefficients of variation (COV) of risk. It is observed that uncertainty in the estimated risk increases due to the presence of flood hazard at the bridge site, although mean risk does not vary with flood hazard level. Research outcome signifies that the variation in risk due to parameter uncertainty and varied flood hazard level should not be ignored to ensure bridge safety under the stated multi-hazard condition.     

Reliability-based settlement analysis of embankments over soft soils reinforced with T-shaped deep cement mixing piles

This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing (TDM) pile-supported embankments over soft soils. The uncertainties of the mechanical properties of the in-situ soil, pile, and embankment, and the effect of the pile shape are considered simultaneously. The analyses are performed using Monte Carlo Simulations in combination with an adaptive Kriging (using adaptive sampling algorithm). Individual and system failure probabilities, in terms of the differential and maximum settlements (serviceability limit state (SLS) requirements), are considered. The reliability results for the embankments supported by TDM piles, with various shapes, are compared and discussed together with the results for conventional deep cement mixing pile-supported embankments with equivalent pile volumes. The influences of the inherent variabilities in the material properties (mean and coefficient of variation values) on the reliability of the piled embankments, are also investigated. This study shows that large TDM piles, particularly those with a shape factor of greater than 3, can enhance the reliability of the embankment in terms of SLS requirements, and even avoid unacceptable reliability levels caused by variability in the material properties.     

通道不一致性对GPS天线自适应算法的影响

GPS信号到达地面终端时通常非常微弱,极易受到传输环境和去其他信号的干扰。功率反演(Power-Inversion)算法应用于GPS自适应天线阵可以很好地抑制干扰信号,但由于阵列天线通道存在幅相不一致,这会对自适应抗干扰算法产生很大影响。通过对自适应天线阵列及通道不一致性进行建模,经过理论分析和计算机仿真,以QRD-SMI算法为例,验证了自适应算法在一定条件下能够克服天线通道不一致,从而有效地抑制干扰信号,所得结论有利于指导工程应用。     

不确定随机变时滞神经网络的全局渐进稳定性

采用It(o)'s微分公式和不等式分析技巧,研究了一类不确定随机变时滞神经网络的全局渐进稳定性问题.该模型同时考虑了神经网络模型的两种扰动因素,即随机扰动与不确定性扰动.不确定性参数是时变且范数有界的.通过构造适当的Lyapunov泛函,以线性矩阵不等式形式给出了平衡点在均方根意义下的全局渐进稳定性判据,能够利用LMI工具箱很容易地进行检验.此外,仿真示例证明了结论的有效性.     

Two-stage Combinatory Planning Method for Efficient Wind Power Integration in Smart Distribution Systems Considering Uncertainties

—A crucial factor that may hinder the usage of renewable energies is the mismatch to load demand in the temporal dimension. In the smart-grid environment, demand response is regarded as a feasible solution to mitigate such a problem. In this study, a combinatory planning method is proposed for efficient integration of wind generation. The problem is formulated as a two-stage fuzzy chance-constrained programming model, which co-optimizes the installation of distributed wind generation along with network transformation and determination of optimal real-time prices to achieve the minimization of the total cost over planning horizons. The impact of both aleatory and epistemic uncertainties associated with wind generation, load growth, and responsive behaviors of customers has been considered. Results of the case study demonstrate the effectiveness of the proposed method and the necessity of considering different uncertainties in the planning.     

失配不确定性系统的局部调节器设计

提出了局部调节等概念，研究了一种新的调节器──局部调节器，在各种失配不确定性因素的作用下保证其输出等关键状态变量稳态无误差地收敛于零。最后给出算例验证了所得结论。     

Efficient shape optimization for certain and uncertain aerodynamic design

In this paper, we present novel developments in aerodynamic shape optimization based on shape calculus as well as the proper treatment of aleatoric uncertainties in the field of aerodynamic design.     

Nuclear data requirements for the ADS conceptual design EFIT: Uncertainty and sensitivity study

In this paper, we assess the impact of activation cross-section uncertainties on relevant fuel cycle parameters for a conceptual design of a modular European Facility for Industrial Transmutation (EFIT) with a “double strata” fuel cycle. Next, the nuclear data requirements are evaluated so that the parameters can meet the assigned design target accuracies. Different discharge burn-up levels are considered: a low burn-up, corresponding to the equilibrium cycle, and a high burn-up level, simulating the effects on the fuel of the multi-recycling scenario.     

Effect of in situ annealing on highly-mismatched In0.75Ga0.25As on InP grown using molecular beam epitaxy

We demonstrate that the electrical quality of junctions fabricated in lattice-mismatched In_0.75Ga_0.25As on InP grown by molecular beam epitaxy can be improved with the addition of in situ anneals in the buffer layer that separates the substrate from the In_0.75Ga_0.25As device layers. Near infrared photodetectors fabricated using this material had dark current densities of approximately 2.5 mA/cm² at a reverse bias of 1 V, which is more than one order of magnitude smaller than commercially available photodetectors grown using vapor phase epitaxy. Transmission electron microscopy revealed that dislocations due to the lattice mismatch between the substrate and the epitaxial layer are confined primarily to the buffer layer for all samples studied. No significant differences in x-ray diffraction spectra or dislocation distribution were observed on samples with and without in situ annealing. Atomic force microscopy indicated that all samples had a crosshatch pattern, and that the average surface roughness of the sample that contained in situ anneals is a factor of three greater than the sample without in situ anneals.     

Mismatched disturbance attenuation control for static var compensator with uncertain parameters

The use of a static var compensator (SVC) as a component of flexible alternating current transmission system (FACTS) devices to control power systems has been investigated for decades. Its aim is to regulate the system voltage and improve the stability and loadability of power systems. A typical assumption in such a system is that the parameters of the controlled system are known accurately, which is rarely satisfied in practice. This paper explores the development of a simple but effective controller for a single-machine infinite-bus power system with SVC subjected to both matched and mismatched disturbances where the controller derivation is based on the assumption that all parameters used in the system modeling are unknown, but bounded in size. The research in this paper illustrates how an indirect robust control can be incorporated with a modified disturbance observer-based feedforward term to attenuate the influence of parameter variations and disturbances from the outputs of the system. Simulation results are presented to confirm the effectiveness of the proposed scheme.