Profile response of a lacustrine multiple barred nearshore to a sequence of storm events

Profile change in a lacustrine multiple-barred nearshore was investigated over the ice-free season of 2001/2002 at Burley Beach on the southeastern shore of Lake Huron in order to identify the feedback mechanisms between the pre-existing morphology and the wave forcing and the consequence of those feedbacks to the behaviour of the nearshore environment. The characteristics of the offshore wave field were monitored using a Falmouth Scientific combined 3D-ACM wave recorder and pressure transducer. Supplemental wave data were downloaded from a 3-m discus buoy operated by the National Data Buoy Center, 75 km to the NW of the study site. The three nearshore bars were in a quasi-equilibrium state through a large part of the ice-free season, with dramatic changes occurring during relatively moderate storm events that followed much larger storms in late October. A comparison of the incident wave field with changes in the nearshore profile through canonical correlation analysis indicates that the morphology responds to the distribution of the significant, root-mean-square (rms) and average wave heights between surveys. The threshold between bar decay and onshore bar migration and growth is associated with the onset of breaking of the rms wave at the bar crest (H_rms h_cr⁻¹ ≈0.3–0.4). The threshold between onshore and offshore migration is associated with the onset of breaking of the average wave at the bar crest (H_avg h_cr⁻¹ ≈0.3–0.4), coincident with complete dissipation of the significant wave over the lakeward slope of the bar (H_s h_cr⁻¹ >0.6). Inshore wave data collected during an instrumented study at the same site revealed that the middle and inner bars remained at the threshold of onshore and offshore migration over a wide range of offshore significant wave heights (0.8 to 2.4 m) prior to the October storms. This self-organised equilibrium is a result of changes to the incident wave distribution through breaking on the outer bar. It is concluded that the prediction of bar response requires an understanding of the feedback between the bar and the local wave distribution in addition to an understanding of the feedback associated with the profile as a whole.     

无限终端线性二次调节器最优输出反馈律

线性二次调节器问题在现代控制理论中占有重要地位。该文针对状态调节器最优反馈律结构复杂、不便工程实现等问题，着重讨论了无限终端带有输出方程的状态调节器的最优输出反馈律，还跟踪讨论了无限终端输出调节器的最优反馈律。所得结论可降低调节器的复杂程度，便于工程实现。     

带有控制结构约束的次优状态反馈律的研究

研究了带有约束机制的次优状态反馈律，主要对终端时间tf=∞系统建立次优状态反馈的数学模型。通过简单控制结构约束的引入，消除状态变量不完全可测所造成的障碍，从而得到了带控制结构约束的次优必要条件及改进后的迭代算法。     

矿井瞬变电磁法中多匝回线电感对目标体探测的影响

线圈的自感耦合作用使瞬变电磁早期时间道信号严重失真.为研究瞬变电磁早期信号的特性,讨论了多匝线圈与单匝线圈的自感系数的关系,得出线圈自感信号振幅的理论表达式,推导了单匝和多匝回线的电感公式,分析了回线匝数和回线边长的变化对目标体响应曲线的影响.研究成果对进一步研究瞬变电磁早期场的附加效应打下了基础,同时为提取早期数据的研究提供参考.     

多匝回线的自感对瞬变电磁早期信号的影响特征

为了研究瞬变电磁早期信号的特性,这里讨论了多匝线圈与单匝线圈的自感系数的关系,同时也分析了瞬变电磁线圈等效回路的暂态过程,以及多匝线圈感应电动势的响应特征。最后,得出了影响早期信号的因素,为提取早期数据的研究提供参考。     

定回线源瞬变电磁三维异常特征反演

分析了实现定回线源瞬变电磁三维异常特征反演的可行性,简要地介绍了改进的广义逆反演方法基本原理,给出了定回线源瞬变电磁三维异常特征反演的流程。对正演模拟数据进行反演的实例表明,定回线源瞬变电磁三维异常特征反演已得到初步实现。     

静电反馈在重力测量中的应用

概述了两种不同类型的静电反馈装置的基本原理，介绍它们在区域重力测量、微重力测量、垂直梯度测量、固体潮观测和周期误差标定等方面的优越性及实际应用效果。根据四台仪器的标定实践，研究了反馈系统的线性度检测与调整和转换因子的标定问题。最后提出了还有待研究的几个问题。     

Pressure-related feedback processes in the generation of pseudotachylytes

Pseudotachylyte formation is typically viewed as a self-limiting process. Quantitative models have demonstrated that frictional melting is possible at seismic slip rates, but once a thin film of melt forms on a seismic fault plane, the dramatic decrease in fault friction is thought to suppress further melting. Volumes of melt-generated pseudotachylyte observed in field studies, however, are in many cases substantially larger than the amounts of frictional melt predicted by theoretical models. This suggests that previously unrecognized physical processes may enhance melting during seismic slip. Localized decompression at dilational jogs may be one such phenomenon. Transient unloading could play two important roles in the dynamics of pseudotachylyte generation. First, by setting up significant fluid pressure gradients, it would lead to rapid migration of the melt to sites of low pressure, thereby reestablishing frictional contact across the fault surface and favoring further melt generation. Second, at significant depths, sudden depressurization might lead to in situ decompression melting.     

Optimal displacement feedback control law for active tuned mass damper

Optimal displacement feedback control law is derived for a vibration control of a single‐degree‐of‐freedom structure with an active tuned mass damper (ATMD). Analytical expressions of the linear quadratic regulator (LQR) feedback gains for the ATMD are derived by solving the Ricatti equation straightforwardly. Based on these solutions, it is found that if the stiffness of the tuned mass damper (TMD) is calibrated to satisfy a certain condition, the control law is simplified to be composed of the feedback gains only for the displacement of the structure and the velocity of the auxiliary mass stroke, which is referred to as ‘optimal displacement feedback control’. The mean‐square responses of the structure as well as the auxiliary mass against Gaussian white noise excitations are evaluated by solving the Lyapunov equation analytically based on the stochastic optimal control theory. Using these analytical solutions, the optimal damping parameter for the auxiliary mass is also derived. Finally, the optimal displacement feedback control law is presented. Copyright © 2001 John Wiley & Sons, Ltd.     

渝怀铁路圆梁山隧道桐麻岭背斜东翼岩溶涌水突泥灾害与整治方案比选

圆梁山隧道是在建铁路重庆至怀化线的关键性控制工程,隧道全长11.068km,最大埋深约780m。隧道施工穿越桐麻岭背斜东翼时,遇到了水平循环带岩溶强烈发育地段,该地段岩溶十分发育,且连通性好;加之数次强降雨,DK361 764、DK360 873等段多次突发大规模的涌水突泥砂、块石灾害,造成部分施工机具掩埋损毁,施工掘进严重受阻,蒙受巨大的经济损失,初步分析认为涌水突泥与地下暗河或岩溶泉群的主管道网络发生较为密切的联系,可以直接接受大气降水补给。为了确保隧道施工和运营安全,针对背斜东翼段岩溶发育情况、涌水突泥特征及其降雨影响程度,进行了泄水洞排水、平导排水、封堵和堵排结合4个整治方案比选,最终采用了泄水洞方案;2003年5～9月雨季,背斜地区多次普降(特)大暴雨,DK361 764、DK360 873等地段又再次突发大规模的涌突水(泥、砂、块石),都通过兴修的泄水洞排泄掉了,隧道及其村砌结构安然无恙,表明采用泄水洞方案整治背斜东翼段的岩溶涌水突泥灾害是正确的选择。