Quantifying volcanic ash fall hazard to electricity infrastructure     

Mark Bebbington  Shane J. Cronin  Ian Chapman  Michael B. Turner 《Journal of Volcanology and Geothermal Research》2008

Quantifying the potential ash fall hazards from re-awakening volcanoes is a topic of great interest. While methods for calculating the probability of eruptions, and for numerical simulation of tephra dispersal and fallout exist, event records at most volcanoes that re-awaken sporadically on decadal to millennial cycles are inadequate to develop rigorous forecasts of occurrence, much less eruptive volume. Here we demonstrate a method by which eruption records from radiocarbon-dated sediment cores can be used to derive forecasting models for ash fall impacts on electrical infrastructure. Our method is illustrated by an example from the Taranaki region of New Zealand. Radiocarbon dates, expressed as years before present (B.P.), are used to define an age-depth model, classifying eruption ages (with associated errors) for a circa 1500–10 500 year B.P. record at Mt. Taranaki (New Zealand). In addition, data describing the youngest 1500 years of eruption activity is obtained from directly dated proximal deposits. Absence of trend and apparent independence in eruption intervals is consistent with a renewal model using a mix of Weibulls distributions, which was used to generate probabilistic forecasts of eruption recurrence. After establishing that interval length and tephra thickness were independent in the record, a thickness–volume relationship (from [Rhoades, D.A., Dowrick, D.J., Wilson, C.J.N., 2002. Volcanic hazard in New Zealand: Scaling and attenuation relations for tephra fall deposits from Taupo volcano. Nat. Hazards, 26:147–174]) was inverted to provide a frequency–volume relationship for eruptions. Monte Carlo simulation of the thickness–volume relationship was then used to produce probable ash fall thicknesses at any chosen site. Several critical electrical infrastructure sites in the Taranaki Region were analysed. This region, being the only gas and condensate-producing area in New Zealand, is of national economic importance, with activities in and around the area depending on uninterrupted power supplies. Forecasts of critical ash thicknesses (1 mm wet and 2 mm dry) that may cause short-circuiting, surges or power shutdowns in substations show that the annual probabilities of serious impact are between ~ 0.5% and 27% over a 50 year period. It was also found that while large eruptions with high ash plumes tend to affect “expected” areas in relation to prevailing winds, the direction impacts of small ash falls are far less predictable. In the Taranaki case study, areas out of normal downwind directions, but close to the volcano, have probabilities of impact for critical thicknesses of 1–2 mm of around half to 60% of those in downwind directions and therefore should not be overlooked in hazard analysis. Through this method we are able to definitively show that the potential ash fall hazard to electrical infrastructure in this area is low in comparison to other natural threats, and provide a quantitative measure for use in risk analysis and budget prioritisation for hazard mitigation measures.  相似文献   

地下流体数字化改造中几个技术性问题的探讨   总被引：3，自引：0，他引：3  

许秋龙  陈华静 《地震》2006,26(1):107-114

总结了地下流体前兆台站数字化改造中遇到的问题, 对出现的问题进行分析研究并探索解决方法。 介绍了井口、 脱气、 集气装置的原理和制作方法。 对比分析了数据传输中几种不同方法的优缺点, 为“十五”地下流体前兆台网数字化改造和未来地下流体台网的建设提供了科学依据。  相似文献   

虚拟专用网技术在远程数据传输中的应用   总被引：1，自引：0，他引：1  

蒋宁 《地质与资源》2007,16(3):234-236,182

野外地质调查工作者作为远程用户需要与其所在的地质调查研究机构进行数据的安全传输.应用虚拟专用网络技术可以在使用公用网络进行数据传输时保证其安全.本文讨论了虚拟专用网的分类、关键技术,通过分析某地质研究所的网络拓扑,给出了一个虚拟专用网的解决方案,对其中的基于Windows Server 2003的虚拟专用网服务器进行了详细配置.  相似文献   

Seismic analysis of underground tunnels by the 2.5D finite/infinite element approach     

《Soil Dynamics and Earthquake Engineering》2016

A procedure for the seismic analysis of underground tunnels using recorded free-field earthquakes based on the 2.5D finite/infinite element approach is presented. The near and far fields of the half space are modeled by finite and infinite elements, respectively. Using the 1D wave theory, the nodal force and displacement on the near-field boundary are computed for each spectral frequency of the earthquake. Then, equivalent seismic forces are computed for the near-field boundary for the earthquake spectrum. By assuming the soil-tunnel system to be uniform along the tunnel axis, the 2.5D approach can account for the wave transmission along the tunnel axis, which reduces to the 2D case for infinite transmission velocity. The horizontal and vertical components of the 1999 Chi-Chi Earthquake (TCU068) are adopted as the free-field motions in the numerical analysis. The maximal stresses and distribution patterns of the tunnel section under the P- and SV-waves are thoroughly studied by the 2.5D and 2D approaches, which should prove useful to the design of underground tunnels.  相似文献   

Higher harmonics induced by a submerged horizontal plate and a submerged rectangular step in a wave flume     

J. Brossard  G. Perret  L. BlonceA. Diedhiou 《Coastal Engineering》2009

The decomposition of a monochromatic wave over a submerged plate is investigated experimentally in a wave flume. Bound and free higher harmonic modes propagating upstream and downstream the structure are discriminated by means of moving resistive probes. The first-order analysis shows a resonant behaviour linked to the ratio of the plate's width and the fundamental mode wavelength over the plate. The second-order analysis shows an energy transfer from the fundamental mode towards free harmonics propagating downstream the structure. This transfer is linked to the ratio of the width of the plate and the bound harmonic wavelength over the plate. We also performed experiments with a submerged step to compare the efficiency of both structures. The submerged plate is shown to be a more efficient breakwater than the step, at the first as well as the second-order.  相似文献   

Velocity potential formulations of highly accurate Boussinesq-type models     

Harry B. Bingham  Per A. Madsen  David R. Fuhrman 《Coastal Engineering》2009

The highly accurate Boussinesq-type equations of Madsen et al. (Madsen, P.A., Bingham, H.B., Schäffer, H.A., 2003. Boussinesq-type formulations for fully nonlinear and extremely dispersive water waves: Derivation and analysis. Proc. R. Soc. Lond. A 459, 1075–1104; Madsen, P.A., Fuhrman, D.R., Wang, B., 2006. A Boussinesq-type method for fully nonlinear waves interacting with a rapidly varying bathymetry. Coast. Eng. 53, 487–504); Jamois et al. (Jamois, E., Fuhrman, D.R., Bingham, H.B., Molin, B., 2006. Wave-structure interactions and nonlinear wave processes on the weather side of reflective structures. Coast. Eng. 53, 929–945) are re-derived in a more general framework which establishes the correct relationship between the model in a velocity formulation and a velocity potential formulation. Although most work with this model has used the velocity formulation, the potential formulation is of interest because it reduces the computational effort by approximately a factor of two and facilitates a coupling to other potential flow solvers. A new shoaling enhancement operator is introduced to derive new models (in both formulations) with a velocity profile which is always consistent with the kinematic bottom boundary condition. The true behaviour of the velocity potential formulation with respect to linear shoaling is given for the first time, correcting errors made by Jamois et al. (Jamois, E., Fuhrman, D.R., Bingham, H.B., Molin, B., 2006. Wave-structure interactions and nonlinear wave processes on the weather side of reflective structures. Coast. Eng. 53, 929–945). An exact infinite series solution for the potential is obtained via a Taylor expansion about an arbitrary vertical position z = zˆ. For practical implementation however, the solution is expanded based on a slow variation of zˆ and terms are retained to first-order. With shoaling enhancement, the new models obtain a comparable accuracy in linear shoaling to the original velocity formulation. General consistency relations are also derived which are convenient for verifying that the differential operators satisfy a potential flow and/or conserve mass up to the order of truncation of the model. The performance of the new formulation is validated using computations of linear and nonlinear shoaling problems. The behaviour on a rapidly varying bathymetry is also checked using linear wave reflection from a shelf and Bragg scattering from an undulating bottom. Although the new models perform equally well for Bragg scattering they fail earlier than the existing model for reflection/transmission problems in very deep water.  相似文献   

基于NS2的TCPW性能改进算法研究     

邢苏珍  吴卫东 《中国海洋大学学报(自然科学版)》2008,(Z1)

TCP Westwood(TCPW)和Vegas都是基于测量的TCP New-Reno增强算法。TCPW针对ACK流直接估算可用带宽,在慢启动和线性递增部分依然采用传统Reno的盲目递增的机制,导致发送端较为频繁的重传。对这几种算法原理进行分析阐述,并提出1种改进方法,更精确的测量估计带宽,通过网络仿真工具NS2进行验证,明显去除TCP全局同步现象,增强网络性能。  相似文献   

The ecology and phylogeny of cyanobacterial symbionts in sponges     

Kayley M. Usher 《Marine Ecology》2008,29(2):178-192

Cyanobacteria have flexible photosynthetic apparatus that allows them to utilise light at very low levels, making them ideal symbionts for a wide range of organisms. Sponge associations with cyanobacteria are common in all areas of the world, but little is known about them. Recent research has revealed new cyanobacterial symbionts that may be host specific and two major clades, ' Candidatus Synechococcus spongiarum ' and Oscillatoria spongeliae , that occur in widely separated geographic locations in unrelated sponge hosts. These clades may represent a cluster of closely related symbiont species, or may be single species that are maintained by periods of horizontal transmission over large distances. Erroneous assumptions regarding the importance of cyanobacterial symbionts to the survival of individual sponges or species may arise from cyanosponges being deemed to be phototrophic or mixotrophic without studies of their photophysiology. This review brings together recent and past research on cyanobacterial associations with sponges, including their biogeography, phylogeny, host specificity, and ecology.  相似文献   

高频电力线信息传输的电机模型与仿真     

赵晖  何波 《中国海洋大学学报(自然科学版)》2008,38(5)

研究在电机驱动系统中,电力线通信的建模问题,着重讨论在高频时电机输入阻抗的特性下,电机模型的建立.通过实验测量得到电机和电力线在频率100 kHz～40 MHz的输入阻抗特性曲线,并分析高频输入阻抗的谐振特点.在Matlab中,提出基于阻抗公式的分析法、最小均方值误差估计法以及最优化方法进行模型的参数识别,将得到的参数代入模型中可以得到电机的阻抗模型.电机模型的精确度可以通过仿真曲线和测量曲线的逼近程度看出,从结果看仿真得到的阻抗曲线跟实际测量的阻抗曲线走向基本一致.  相似文献   

无线VPN技术在数字前兆台网中的应用     

郑树平  翦大西 《大地测量与地球动力学》2009,29(Z1):147-150

VPN技术提供了一种通过公用网络安全地对企业内部专用网络进行远程访问的连接方式。介绍了VPN的技术和原理，并以湖北省数字前兆台网为例，提出了一种无线VPN技术的连接设置方式。它具有运行成本低、使用方便、无线发送、有线接入等特点。  相似文献