Strong Feller Property for SDEs with Super-linear Drift and Hölder Diffusion Coefficients

In this paper,we investigate the strong Feller property of stochastic differential equations(SDEs)with super-linear drift and Hölder diffusion coefficients.By utilizing the Girsanov theorem,coupling method,truncation method and the Yamada-Watanabe approximation technique,we derived the strong Feller property of the solution.

Singular Stabilization and H_∞ Control of Nonlinear Systems with Ordinary Homogeneous Properties

In this paper, the nonlinear singular stabilization, H∞ control problem of systems with ordinary homogeneous properties is considered. At first, we discuss the stabilization problems of nonlinear systems with homogeneous. Secondly, by vitue of Hamilton-Jacobi-Isaacs equations or inequalities, we solve regular H∞ of nonlinear systems with homogeneous properties. To overcome the H∞ problem of singular nonlinear system, we try to transform inputs of the singular nonlinear system into two parts： regular part input and singular part input. Following the previous results, we solve the singular nonlinear system H∞ control, we give the Lyapunov function and the state feedback controller of the singular nonlinear systems with homogeneous properties.

Solvability Condition for Robust Stabilization Problem of Control Systems with Parameter Uncertainties

Aim The solvability condition for robust stabilization problem associated with a plant family P(s,δ) having parameter uncertainty δ was considered. Methods Using Youla parameterization of the stabilizers this problem was transformed into a strong stabilization problem associated with a related plant family G (s, δ). Results A necessary solvability condition was established in terms of the parity interlacing property of each element in G(s,δ). Another apparently necessary solvability condition is that every element in P(s,δ) must be stabilizable. Conclusion The two conditions will be compared with each other and it will be shown that every element in G(s,δ) possesses parity interlacing property if P(s,δ) is stabilizable.

基于HVSR方法的上海市典型场地特征研究

上海市强震台网获取了2020年5月3日日本九州6.0级地震等多次强震记录。通过对地震记录进行分析处理,分别计算了每个强震台站的H/V谱比曲线,结合上海市地质调查研究院的基岩埋深分布图,得到了每个台站的基阶共振频率与沉积层厚度。结果表明:H/V谱比曲线峰值与沉积层厚度存在明显相关性,并且通过数据拟合建立了上海市沉积层厚度与基阶共振频率的经验公式,绘制了上海市场地基本周期分布图,可以为上海市抗震设防提供一定的参考;厚沉积层场地上地震记录的谱比曲线会出现多个峰值,第二个峰值代表了沉积层的高阶共振频率;通过数据拟合得到上海地区剪切波速与沉积层厚度的经验公式。

h型双排桩在山地建筑边坡工程中应用

针对山地建筑边坡受用地限制而常用挡墙不太适用的问题,提出了h型双排桩结构形式,其由冠梁、腰梁、盖板、前排桩及后排桩组成。首先,假定h型双排桩的上部山体为滑裂体,采用传递系数法计算剩余下滑力,与双排桩抗滑力进行比较,判断边坡整体稳定性;假定h型双排桩为悬臂二阶柱结构,计算结构变形,判断变形是否满足正常使用要求。其次,依托某边坡工程进行实例论证,该工程竣工已近两年,监测数据表明边坡处于安全稳定可控状态。最后,h型双排桩解决了山地建筑边坡用地受限的难题,双排桩强有力的结构形式提高了悬臂式挡土高度,且双排桩盖板可兼作山地建筑的室外用地使用。

10℃条件下纳米C-S-H掺量对水泥早期水化的影响

目的探究10℃条件下不同掺量纳米C-S-H对水泥早期水化进程及强度发展的影响,并分析其早强剂作用机理。方法通过溶液共沉淀法制备纳米C-S-H悬浮液,将其掺入到普通硅酸盐水泥中,在10℃条件下进行养护,分析其对水泥凝结时间、抗折强度、抗压强度的影响;通过XRD、TG等检测手段分析水泥的水化进程及对水化产物的影响。结果掺入0.05%纳米C-S-H,可使水泥初凝时间缩短9.9%,终凝时间缩短10.4%;24 h时抗折强度和抗压强度分别提高了34%和33.5%。纳米C-S-H的掺入造成水泥3 d抗折强度略有降低。水化产物中Ca(OH)2质量分数在12 h、16 h和24 h时较参比样分别提高了17.6%、21.3%和29.6%。结论在10℃条件下,纳米C-S-H的加入能够有效促进C 3S和C 2S的水化过程,形成更多的水化产物,从而缩短水泥凝结时间,提高24 h内水泥砂浆强度,28 d强度没有显著降低。

Design and Comparison of H∞/H2 Controllers for Frigate Rudder Roll Stabilization

Roll motion of ships can be distinguished in two parts:an unavoidable part due to their natural movement while turning and an unwanted and avoidable part that is due to encounter with waves and rough seas in general.For the attenuation of the unwanted part of roll motion,ways have been developed such as addition of controllable fins and changes in shape.This paper investigates the effectiveness of augmenting the rudder used for rejecting part of the unwanted roll,while maintaining steering and course changing ability.For this purpose,a controller is designed,which acts through intentional superposition of fast,compared with course change,movements of rudder,in order to attenuate the high-frequency roll effects from encountering rough seas.The results obtained by simulation to exogenous disturbance support the conclusion that the roll stabilization for displacement can be effective at least when displacement hull vessels are considered.Moreover,robust stability and performance is verified for the proposed control scheme over the entire operating range of interest.

Analysis of a Strong-Inhibition Polyamine Drilling Fluid

Drilling technologies based on oil-based drillingfluids and strong inhibitory saltwaterfluids are affected by draw-backs such as downhole accidents where sticking and wellbore instabilities occur.Existing polyamine drillingfluids also exhibit problems such as easy decomposition and poor inhibition performances.In order to mitigate these issues,additives can be used,such as polyamine inhibitors and the synthesis of nanometerfiltrate reducers.Tests conducted in the frame of this study with a polyamine drillingfluid and such additives show that thisfluid has the same inhibitory,plugging,lubricating,and wellbore-stability performances as oil-based drillingfluids.However,it has long-term anti-wear performances even better than those of oil-based drillingfluids.The out-comes of a series of comparisons with other sample cases(other wells)are reported and the advantages related to the proposedfluid discussed in detail.

Delay-dependent robust stability and H_∞ analysis of stochastic systems with time-varying delay

This paper investigates the robust stochastic stability and H∞ analysis for stochastic systems with time-varying delay and Markovian jump. By using the freeweighting matrix technique, i.e., He＇s technique, and a stochastic Lyapunov-Krasovskii functional, new delay-dependent criteria in terms of linear matrix inequalities are derived for the the robust stochastic stability and the H∞ disturbance attenuation. Three numerical examples axe given. The results show that the proposed method is efficient and much less conservative than the existing results in the literature.

Evaluation of survival stow position and stability analysis for heliostat under strong wind

Heliostats are sensitive to the wind load, thus as a key indicator, the study on the static and dynamic stability bearing capacity for heliostats is very important. In this work, a numerical wind tunnel was established to calculate the wind load coefficients in various survival stow positions. In order to explore the best survival stow position for the heliostat under the strong wind, eigenvalue buckling analysis method was introduced to predict the critical wind load theoretically. Considering the impact of the nonlinearity and initial geometrical imperfection, the nonlinear post-buckling behaviors of the heliostat were investigated by load-displacement curves in the full equilibrium process. Eventually, combining B-R criterion with equivalent displacement principle the dynamic critical wind speed and load amplitude coefficient were evaluated. The results show that the determination for the best survival stow position is too hasty just by the wind load coefficients. The geometric nonlinearity has a great effect on the stability bearing capacity of the heliostat, while the effects of the material nonlinearity and initial geometrical imperfection are relatively small. And the heliostat is insensitive to the initial geometrical imperfection. In addition, the heliostat has the highest safety factor for wind-resistant performance in the stow position of 90-90 which can be taken as the best survival stow position. In this case, the extreme survival wind speeds for the static and dynamic stability are 150 m/s and 36 m/s, respectively.

Robust stabilization and disturbance attenuation for a class of underactuated mechanical systems

The robust control problem for a class of underactuated mechanical systems called acrobots is addressed. The goal is to drive the acrobots away from the straight-down position and balance them at the straight-up unstable equilibrium position in the presence of parametric uncertainties and external disturbance. First, in the swing-up area, it is shown that the time derivative of energy is independent of the parameter uncertainties, but exogenous disturbance may destroy the characteristic of increase in mechanical energy. So, a swing-up controller with compensator is designed to suppress the influence of the disturbance. Then, in the attractive area, the control problem is formulated into a H~ control framework by introducing a proper error signal, and a sufficient condition of the existence of Hoo state feedback control law based on linear matrix inequality （LMI） is proposed to guarantee the quadratic stability of the control system. Finally, the simulation results show that the proposed control approach can simultaneously handle a maximum ±10% parameter perturbation and a big disturbance simultaneously.

ABSOLUTE STABILIZATION RELATED TO CIRCLE CRITERION: AN LMI-BASED APPROACH

A method is proposed for synthesizing output feedback controllers for nonlinear Lur' e systems . The problem of designing an output dynamic controller for uncertain-free systems and systems subject to multiplicative norm-bounded perturbations in the linear part were proposed respectively. The procedure is based on the use of the absolute stability, through the circle criterion, and a linear matrix inequalities (LAI) formulation. The controller existence conditions are given in terms of existence of suitable solutions to a set of parameter-dependent LMIs.

A Strong Stability Preserving Analysis for Explicit Multistage Two-Derivative Time-Stepping Schemes Based on Taylor Series Conditions

High-order strong stability preserving(SSP)time discretizations are often needed to ensure the nonlinear(and sometimes non-inner-product)strong stability properties of spatial discretizations specially designed for the solution of hyperbolic PDEs.Multi-derivative time-stepping methods have recently been increasingly used for evolving hyperbolic PDEs,and the strong stability properties of these methods are of interest.In our prior work we explored time discretizations that preserve the strong stability properties of spatial discretizations coupled with forward Euler and a second-derivative formulation.However,many spatial discretizations do not satisfy strong stability properties when coupled with this second-derivative formulation,but rather with a more natural Taylor series formulation.In this work we demonstrate sufficient conditions for an explicit two-derivative multistage method to preserve the strong stability properties of spatial discretizations in a forward Euler and Taylor series formulation.We call these strong stability preserving Taylor series(SSP-TS)methods.We also prove that the maximal order of SSP-TS methods is p=6,and define an optimization procedure that allows us to find such SSP methods.Several types of these methods are presented and their efficiency compared.Finally,these methods are tested on several PDEs to demonstrate the benefit of SSP-TS methods,the need for the SSP property,and the sharpness of the SSP time-step in many cases.

Strong-Stability-Preserving, K-Step, 5- to 10-Stage, Hermite-Birkhoff Time-Discretizations of Order 12

We construct optimal k-step, 5- to 10-stage, explicit, strong-stability-preserving Hermite-Birkhoff (SSP HB) methods of order 12 with nonnegative coefficients by combining linear k-step methods of order 9 with 5- to 10-stage Runge-Kutta (RK) methods of order 4. Since these methods maintain the monotonicity property, they are well suited for solving hyperbolic PDEs by the method of lines after a spatial discretization. It is seen that the 8-step 7-stage HB methods have largest effective SSP coefficient among the HB methods of order 12 on hand. On Burgers’ equations, some of the new HB methods have larger maximum effective CFL numbers than Huang’s 7-step hybrid method of order 7, thus allowing larger step size.

Enforcing Strong Stability of Explicit Runge-Kutta Methods with Superviscosity

A time discretization method is called strongly stable(or monotone),if the norm of its numerical solution is nonincreasing.Although this property is desirable in various of contexts,many explicit Runge-Kutta(RK)methods may fail to preserve it.In this paper,we enforce strong stability by modifying the method with superviscosity,which is a numerical technique commonly used in spectral methods.Our main focus is on strong stability under the inner-product norm for linear problems with possibly non-normal operators.We propose two approaches for stabilization:the modified method and the filtering method.The modified method is achieved by modifying the semi-negative operator with a high order superviscosity term;the filtering method is to post-process the solution by solving a diffusive or dispersive problem with small superviscosity.For linear problems,most explicit RK methods can be stabilized with either approach without accuracy degeneration.Furthermore,we prove a sharp bound(up to an equal sign)on diffusive superviscosity for ensuring strong stability.For nonlinear problems,a filtering method is investigated.Numerical examples with linear non-normal ordinary differential equation systems and for discontinuous Galerkin approximations of conservation laws are performed to validate our analysis and to test the performance.

顺北1-7H超深水平井钻井液技术

顺北1-7H井位于顺托果勒低隆北缘,设计井深7726.51m,是四开制超深开发水平井。该井地质结构复杂,钻进过程中穿越多套地层,施工中钻井液井壁稳定技术难度大。针对不同井段及不同地层岩性,采用不同的钻井液体系,配合相应的现场钻井液维护处理工艺,保证了施工的顺利进行,施工中井壁稳定,井身质量好,取得了优快钻井的良好效果。

基于切换拓扑的量化时滞网络有限时间H∞控制

为了研究引入量化器的基于切换拓扑的动态时滞网络的有限时间H∞控制问题,通过设计量化控制器和状态依赖切换信号的方法,利用微分包含理论、矩阵理论、稳定性理论,经过严格的推导,得到了基于切换拓扑的具有量化的动态时滞网络在无外界干扰时有限时间稳定,并且在有外界干扰时具有有限L2增益的结论,最后通过一个数值仿真验证定理的有效性。

同步发电机调速系统附加H_∞鲁棒分散控制

发电机与系统之间的关联有功功率波动ΔPe 是危害发电机稳定性的主要扰动 ,同时ΔPe 代表着电力系统的非线性和耦合特征 ,在调速系统中用它作为控制器的一个输入变量 ,将避免非线性和耦合问题。该文利用H∞ 控制理论的干扰抑制方法 ,针对汽轮机和水轮机模型 ,提出了一种调速系统附加鲁棒分散控制 (GAHDC)策略。单机无穷大系统的仿真结果验证了GAHDC可提高汽轮发电机和水轮发电机稳定性的效果 ,GAHDC实现了发电机的分散稳定控制。

H_∞混合灵敏度控制在液压伺服系统中的应用

运用 H∞ 混合灵敏度控制理论 ,针对液压伺服系统的特点 ,通过仿真 ,总结了一般加权阵的选取规律和方法 ,提出采用线性矩阵不等式设计典型电液位置伺服系统 H∞ 控制器的计算方法 ,并设计了控制器 ,使系统在保证鲁棒稳定性的同时可以确保系统的瞬态性能指标。通过设计举例说明了控制器的设计方法 ,并通过与原系统参数摄动时系统特性的比较 ,验证了 H∞控制器不仅可以提高系统的频宽 ,改善系统的响应速度 ,而且可以改善参数变化对系统性能的影响 ,从而说明了 H∞ 控制器的有效性。

Delta算子系统的状态反馈鲁棒镇定与鲁棒H_∞控制

研究Delta算子描述的线性不确定离散系统的鲁棒镇定与H∞ 控制问题 .提出了“Delta算子系统二次稳定与二次可镇定”的概念 ,推导出Delta算子不确定系统鲁棒二次可镇定的充要条件及其状态反馈控制律 .基于Delta算子界实引理 ,给出闭环不确定系统具有H∞ 范数界的充分条件和状态反馈设计 .所得结论将连续与离散系统的有关结果统一于Delta算子框架 .