沉积岩中波速、衰减及渗透率随压力的变化

在三轴围压容器内对泥岩、粉砂岩、砂岩和杂砂岩中的弹性波速度、衰减和渗透率进行了测量,并对样品作了显微组构分析。实验发现,由于砂岩的孔隙率大,矿物颗粒的分选度和磨圆度较好,颗粒间孔隙的连通性很好,其渗透率最高;粉砂岩中晶体颗粒尺寸比砂岩的小,颗粒间的孔隙也较小,连通性受到影响,因此渗透率比砂岩的低;泥岩的渗透率更低,因为它的矿物颗粒更细小且固结性较差,很容易将连通的孔隙堵塞;杂砂岩是由分选性差、未经磨圆的碎砾通过基质胶结形成的,孔隙间的连通性很低,它的渗透率最小。随着围压和轴向差异应力的变化,四种样品中的波速、衰减和渗透率均发生不同形式的变化,反映了岩样组构特别是微裂隙的变化情况。     

水下目标圆偏振成像及最远 成像距离的计算

报道了用圆偏振技术进行水下目标成像结果并分析了用圆偏振技术提高图像清晰度的原因:推导了水下目标最远成像距离的计算公式,在衰减常数α为0.5的水体中,目标放在1.5m处,测量出用圆偏振成像系统成像所得图像对比度C为4.1,通过r0和C可计算出圆偏振成像系统的最远成像距离r为1.92m,与实测距离相差0.08m,相对误差为4%。     

紧凑式SCR净化消声装置设计与性能分析

紧凑式SCR净化消声装置能够实现柴油机尾气净化和排气噪声控制双重功能，使用Fluent软件DPM模型对SCR净化消声装置内的气体流动、水溶液喷射雾化过程进行数值模拟，使用Sysnoise软件中的有限元法计算SCR净化消声装置的声学性能，研究不同进口方式和穿孔管对阻力损失和传递损失的影响。     

Effect of Channel Restoration on Flood Wave Attenuation

Stream channel restoration can increase flow storage and energy dissipation of passing flood waves. Elements of restoration design that can enhance attenuation include remeandering, which reduces channel slope and increases channel length relative to the floodplain; restoring channel-floodplain connectivity; and revegetating banks and the floodplain. Reestablishment of floodplain hydraulic function is increasingly a goal of restoration programs, yet the approximate magnitude of possible change to attenuation due to reach-scale restoration remains poorly quantified. We examined the efficacy of channel restoration on flood attenuation using restored reaches and synthetic reaches representing median dimensions of channel restoration projects in North Carolina (e.g., ～ 1?km in length). We applied an industry standard dynamic flood routing model (UNET in HEC-RAS) to route floods in impaired and restored reach models. Floods routed through field-based reach models either exhibited very small increases in attenuation, largely due to assumed increases in floodplain roughness, or a decrease in attenuation. Analysis demonstrated that attenuation of peak discharge is overall most sensitive to channel and valley slope, channel and floodplain roughness, and channel and valley length in decreasing order, but is dependent on flood magnitude. Restoration most impacted floods of intermediate magnitude (between 2- and 50-year return interval), particularly those confined to the channel under the impaired morphology but able to access the floodplain under the restored morphology. Restoration may rehabilitate a channel’s ability to attenuate small to intermediate floods by augmenting flood access to the floodplain, changing channel geometry, and enhancing channel and floodplain roughness over time. However, our study shows that the predominantly small scale of current channel restoration will provide minimally quantifiable enhancement to flood attenuation.     

基于超声波衰减法煤泥水浓度检测的研究

针对目前选煤厂煤泥水的浓度检测多采用伽马射线方式,使用过程中存在诸多不便的问题,通过引入超声波技术用于检测煤泥水浓度,研究了超声波在煤泥水中的衰减规律及影响声波衰减的因素,并提出了影响超声波衰减检测的解决办法。     

Determination of attenuation rates of recycled water disinfection by‐products in a natural reservoir system using a laboratory‐based approach

A batch test approach was used to assess the in situ attenuation by natural reservoir systems of selected disinfection by‐products (DBPs). The aim was to determine which natural attenuation processes (volatilisation, photolysis and biodegradation) dominated for selected trihalomethanes (THMs) and N‐nitrosodimethylamine (NDMA), common DBPs present in reclaimed water which could be used to potentially augment drinking water supplies. Attenuation rates for THMs were found to be all very similar, with half‐lives ranging from 1.5–1.6 days for open batch tests. The dominant attenuation mechanisms for THMs were volatilisation with hydrolysis and biodegradation of potentially minor importance. NDMA had a half‐life of 3.5–4.3 days for vials exposed to light. The most important attenuation mechanism for NDMA was photolysis with volatilisation and biodegradation of minor importance. The results indicate that the selected DBPs could be effectively attenuated by a natural reservoir system such as a surface water reservoir.     

Damage Characterisation of Inhomogeneous Materials: Experiments and Numerical Simulations of Wave Propagation

Abstract: Elastic waves are commonly used for characterisation of concrete. To produce reliable results, wave propagation needs a lot of understanding. Therefore, combined study through experiments and simulations is deemed essential. In the present paper, the case of concrete with flakey inclusions, serving as micro‐cracks, is investigated both in laboratory experiments and computer simulation. The results suggest new wave features suitable for characterisation. Parameters like wave dispersion and frequency dependent attenuation prove to be more sensitive to damage than the traditionally used pulse velocity and can improve characterisation when employed in situ. The monitoring of a cracked concrete bridge before and after repair is discussed as a case study.     

Performance and robustness trade-offs in PID control

Control design is a rich problem which requires consideration of many issues such as load disturbance attenuation, set-point tracking, robustness with respect to process variations and model uncertainty, and effects of measurement noise. The purpose of this paper is to provide insight into the trade-offs between performance and robustness explicitly. This is accomplished by introducing plots that show the trade-offs for PI and PID control. These also provide valuable understanding of design compromises used for common PI design methods.     

Development of a mathematical model for optimizing a heliostat field layout using differential evolution method

In this study, differential evolution was employed to perform optimization of a heliostat field. A complete mathematical code was developed for this purpose, which generates a heliostat field and calculates the optimum spacing between heliostats through differential evolution optimization technique. The optimization was executed for two sets of two cases and compared with an un‐optimized case. In the first case, only the optical performance was optimized, whereas in the second case, the normalized ratio of the optical performance to the land area covered by the heliostat field was maximized. In the first set of cases, the extra security distance between the heliostats was neglected, whereas in the second set of cases, the extra security distance was taken into account. To apply and examine the application of the optimization algorithm developed, 3 days of the year were selected: March 21, June 21, and December 21, considering Dhahran, Saudi Arabia as an illustrative example. For June 21, when the extra security distance between the heliostats is neglected, the optical efficiency of the un‐optimized case was 0.6026, while for the first optimized case, it was 0.6395, and for the second optimized case, it was 0.6033. However, when the extra security distance was considered, the optical efficiency of the un‐optimized case was 0.6167; while for the first optimized case, it was 0.6241, and for the second optimized case, it was 0.6167. Similar observations were realized for the other cases selected. Copyright © 2015 John Wiley & Sons, Ltd.     

Static output‐feedback for Takagi–Sugeno systems with delays

A practical methodology to design controllers for Takagi–Sugeno discrete‐time systems with unknown delays is proposed, based on using Linear Matrix Inequalities. More precisely, the design of discrete‐time output‐feedback stabilizing controllers in the presence of bounded delays is solved, when values of the disturbance attenuation and decay‐rate are imposed. A numerical example is provided to illustrate the proposed approach. Copyright © 2010 John Wiley & Sons, Ltd.