新型迅捷弹箭动力学建模与姿态控制

为大幅度提高弹箭的超大角度机动能力,提出一种新型迅捷弹箭动力学建模与姿态控制方法。通过在传统直接力/气动力复合控制敏捷弹箭尾部加装一类柔性可控圆伞,设计一种新型弹箭的几何构型,并划分新型迅捷转向的三个阶段。为回避牛顿欧拉力学在多体动力学建模过程中求解复杂约束力带来的一系列问题,以拉格朗日力学为基础,选取弹箭的位置、姿态和伞的姿态作为广义坐标,推导系统的动能,求解系统的广义力,建立以弹箭为主体的铅垂平面4自由度动力学模型。针对具有快时变性、强不确定性、强非线性等特点的柔性力/直接力/气动力复合控制律设计问题,建立系统姿态跟踪误差的状态方程,基于非奇异终端滑模面和双幂次趋近律设计具有有限时间收敛特性的姿态控制器,利用扩张状态观测器消除内外扰动对系统造成的负面影响,抑制抖振。通过仿真验证了新方法的合理性和有效性,并与传统敏捷弹箭进行仿真对比,验证了新方法有利于减小转弯半径、缩短转弯时间、减少能量消耗。

008004型多层片式陶瓷电容器制作工艺研究

该文以国产的X7R特性瓷粉、镍内电极浆料及铜外电极浆料为原材料制备了008004尺寸多层片式陶瓷电容器(MLCC)。对高精密微小图形印刷技术、微小尺寸切割技术、圆控技术及其端电极形成技术等关键制备工艺进行了研究。并通过试验发现,采用30°编角的网版进行印刷,电极图案饱满,边缘平直。将弧形单刃刀和热敏性树脂片作为切割垫材,切后008004尺寸胚片直角性和分散性均较好。采用适合的电极宽度/胚片宽度比例,配合立式行星球磨,圆控后008004产品引出效果良好。采用不锈钢板和热剥离胶带进行单面端铜,配合使用适宜的铜浆,芯片外观平整性好。用离心镀机电镀镍、纯锡,最后制得的00800410V X5R 101M成品电性能良好,可靠性高。

Azimuthal cement evaluation with an acoustic phased-arc array transmitter:numerical simulations and field tests

We developed a novel cement evaluation logging tool,named the azimuthally acoustic bond tool（AABT）,which uses a phased-arc array transmitter with azimuthal detection capability.We combined numerical simulations and field tests to verify the AABT tool.The numerical simulation results showed that the radiation direction of the subarray corresponding to the maximum amplitude of the first arrival matches the azimuth of the channeling when it is behind the casing.With larger channeling size in the circumferential direction,the amplitude difference of the casing wave at different azimuths becomes more evident.The test results showed that the AABT can accurately locate the casing collars and evaluate the cement bond quality with azimuthal resolution at the casing-cement interface,and can visualize the size,depth,and azimuth of channeling.In the case of good casingcement bonding,the AABT can further evaluate the cement bond quality at the cementformation interface with azimuthal resolution by using the amplitude map and the velocity of the formation wave.

Fluid Flow Past a Circular Cylinder with Tandem Rod and Staggered Rod at Low Reynolds Number

The flow past a primary cylinder with one tandem control rod and one staggered control rod is simulated in this paper through solving the Navier-Stokes equations. Two examples are simulated to validate the model, and the results matched well with those of previous researches. The Reynolds number based on the diameter of the primary cylinder is 500. The diameter ratio between the control rod and the primary cylinder （d/D） is 0.25. It was found that the effect of the combination of one upstream tandem control rod and one staggered control rod on the hydrodynamics of the primary cylinder is a linear superposition of the effect of a corresponding single control rod, and the effect of the upstream tandem control rod is dominant at larger spacing ratios such as G/D=2. For the combination of a downstream tandem control rod and a staggered control rod, the effect of the control rods is different from that of the corresponding single control rod in the region of 0.2〈G/D〈0.5 ＆ 30°〈a〈120° and 0.9〈G/D〈1.4 ＆ 30°〈a〈50°, where the additional effect is obvious. In this case, the effect of the downstream tandem control rod is dominant at small spacing ratios （such as G/D=0.1）. At moderate spacing ratios such as G/D=0.4, the effects of the tandem control rod and the staggered control rod are comparable in both cases.

Taper Angle Correction in Cutting of Complex Micro-mechanical Contours with Ultra-Short Pulse Laser

The objective of this work was to investigate the possibility of taper angle correction in cutting of complex micro-mechanical contours using a TruMicro ultra-short pulse laser in combination with the SCANLAB precSYS micro machining sub system. In a first step, the influence of the process parameters on the kerftaper angle of metallic alloys was systematically investigated without beam inclination. A set of base parameters was derived for the subsequent investigations. In a second step, the kerftaper angle was controlled by static beam inclination. In a third step, the same optics was used in its dynamic precession mode to fabricate micro-mechanical components of complex contours with perpendicular 0~ taper angles. It was found that taper angle adjustments of up to 7.5~ are possible with the used setup for cutting applications. Taper angle control is possible both in the static beam inclination mode and in the dynamic precession mode. The static mode could be interesting for contours with sharp inner radii and for achieving faster cutting times similar to results with fixed optics, but would require excellent synchronization of beam inclination and axis motion. The dynamic precession mode would allow an easier integration of the optics into a laser machine but will result in longer cutting times and limitations with respect to achievable inner radii.

Active Control of Structurally Radiated Sound from an Elastic Cylindrical Shell

A numerical and experimental study was presented on active control of structurally radiated sound from an elastic cylindrical shell.An analytical model was developed for the active structural acoustic control (ASAC) of the cylindrical shell.Both global and local control strategies were considered.The optimal control forces corresponding to each control strategy were obtained by using the linear quadratic optimal control theory.Numerical simulations were performed to examine and analyze the control performance under different control strategies.The results show that global sound attenuation of the cylindrical shell at resonance frequencies can be achieved by using point force as the control input of the ASAC system.Better control performance can be obtained under the control strategy of minimization of the radiated sound power.However,control spillover may occur at off-resonance frequencies with the control strategy of structural kinetic energy minimization in terms of the radiated sound power.Considerable levels of global sound attenuation can also be achieved in the on-resonance cases with the local control strategy,i.e.,minimization of the mean-square velocity of finite discrete locations.An ASAC experiment using an FXLMS algorithm was implemented,agreement was observed between the numerical and experimental results,and successful attenuation of structural vibration and radiated sound was achieved.

A review on single-pass grinding processes

The most important grinding processes were realized in a single pass of the grinding wheel,such as continuous path controlled grinding (CPCG/Peelgrinding/HSP),CPCG with reduced contact of the grinding wheel (Quickpoint),single-pass longitudinal internal grinding,creep feed grinding (CFG),longitudinal cylindrical grinding with grinding wheels made of conventional abrasive materials and longitudinal internal cylindrical grinding using grinding wheels with zone-diversified structure.

Design and Evaluation of CRDMAC： Circular RTR Directional MAC Protocol for WANETs

Using directional antennas in Wireless Ad hoc Networks (WANETs) offers great potential of reducing the radio interference, and improving the communication throughput. Directional antennas, however, introduces new problems in the wireless Media Access Control (MAC), that is, the deafness and new hidden terminal problem, which may cause severe performance degradation. To solve the problems, we propose an effective Circular RTR Directional MAC (CRDMAC) protocol for WANETs by using a sub-transmission channel and Ready to Receive (RTR) packets, which modifies the IEEE 802.11 Distributed Coordinated Function (DCF). The sub-channel avoids collisions to other ongoing transmission, and the RTR packets notify the neighbor nodes that the mutual transmission has been finished. We evaluate the CRDMAC protocol through simulations and the results show that the proposed protocol outperforms existing DMAC (directional MAC) protocol and the CRCM (Circular RTS and CTS MAC) protocol in terms of throughput and packet drop rate.

Study on Position Control System with Programmable Logic Controller

To solve the problems of mechanical cam, tracking in an automatic welding machine, a new method of programmable logic controller ( PLC) tracking is presented. Based on analyzing the forming of welding tracking, a mathematical model of position control is set up. The experiments show that using a modified machine, PLC makes little welding positional error and can meet the product requirements.

Li^+-templated complexation of cylindrical macrotricyclic host with naphthalene diimide:Cation-controlled switchable complexation processes

Anthracene-based cylindrical macrotricyclic polyether (1) containing two dibenzo-30-crown-10 cavities has been proved to be an efficient host for the templated complexation with N,N'-dipropyl-1,4,5,8-naphthalenetetracarboxylic diimide in the presence of lithium ions in both solution and solid state. Host 1 could also form 1:1 complex with the bispyridinium salt with two β-hydroxyethyl groups in solution and in the solid state. Moreover, it was also found that the switchable complexation processes between the macrotricyclic host and two different kinds of guests could be chemically controlled by the addition and removal of lithium ions.

Experimental investigation on control of vortex shedding mode of a circular cylinder using synthetic jets placed at stagnation points

Control of flow around a circular cylinder by synthetic jets has been experimentally investigated in a water tunnel with particle image velocimetry(PIV) technique.The synthetic jets are positioned at both the front and rear stagnation points.With power spectrum analysis,proper orthogonal decomposition(POD) method and other techniques for data processing,particular attention is paid to the control of vortical structures around the circular cylinder,in which the excitation frequency f e is one to three times of the natural frequency f0 and the cylinder Reynolds number and the excitation amplitude are fixed.The influenced-scope of the synthetic jet enlarges as the excitation frequency increases,and thus the synthetic jet dominates the global flow field gradually.For the natural case and the control case at fe/f0=1,the distributions of the first two POD modes and the power spectra for their POD coefficients all exhibit the characteristics of the natural shedding with antisymmetric mode.For fe/f0=2 and fe/f0=3,the variations in the third and fourth POD modes and the corresponding power spectra indicate that the wake vortex shedding mode changes and the dominant frequency becomes the excitation frequency.For fe/f0=2,the wake vortex sheds downstream with either the antisymmetric or the symmetric mode;for fe/f0=3,the synthetic jet vortex pair interacts with the near wake shear layers from both sides to induce a pair of the symmetric wake vortices,which is gradually converted into an antisymmetric mode when shedding downstream.

Suppression of vortex-induced vibration of a circular cylinder by Lorentz force

The electro-magnetic control of vortex-induced vibration (VIV) of a circular cylinder is investigated numerically in the exponential-polar coordinates attached on the moving cylinder for Re=150 in the paper. Compared with the fixed cylinder, the vibration of cylinder leads to the shift of stagnation point, the shear layer strength and the inertial force, which affects the hydrodynamic forces on the cylinder. The effects of the instantaneous wake geometries and the corresponding cylinder motion on the hydrodynamic forces for one entire period of vortex shed are discussed in the drag-lift phase diagram. The Lorentz force for controlling the vibration cylinder is classified into the field Lorentz force and the wall Lorentz force. The field Lorentz force decreases the lift oscillation, and in turn, suppresses the VIV, whereas the wall Lorentz force has no effect on the lift.

Active control of circular cylinder flow by affiliated rotating cylinders

This study puts forward an active control method for circular cylinder flow by placing two small affiliated rotating cylinders adjacent to the main cylinder, and their effects on the drag and lift forces acting on the main cylinder as well as the heat trans- fer effectiveness are numerically investigated. According to the diameter of the main cylinder the Reynolds number is chosen as Re=200. The well-proven finite volume method is employed for the calculation. The code is validated by comparing the present computed results of flow passing an isolated rotating cylinder with those available from the literature. To describe the present control model, two parameters are defined： the rotation direction of the two small cylinders （including co-current rota- tion and counter-current rotation） and the dimensionless rotation rate a. In the simulation, the rotation rate a varies from 0 to 2.4. The results indicate that the optimum rotation direction of the subsidiary cylinders, which is beneficial to both drag reduc- tion and beat transfer enhancement, is the co-current rotating （the upper affiliated cylinder spins clockwise and the lower affili- ated cylinder spins counter-clockwise）. We observe noticeable suppression of the vortex shedding and favorable reduction of the fluid forces acting on the main cylinder as the rotation rate increases. Besides, the pressure and viscous components of the drag force are analyzed. Energy balance between energy cost for activating the rotating cylinders and energy saving by the momentum injection is considered. In addition, the influence of the affiliated rotating cylinders on heat transfer is also investi- gated. The average Nusselt number is found to increase with the rotation rate.

Phase control of ellipsometric interferometer for nanometric positioning system

Development in industry is asking for improved resolution and higher accuracy in dimensional metrology. In this paper,we proposed a control displacement method based on a polarization ellipsometirc interferometer and phase-locked loop technique. The proposed principle was set up. The experimental results of step and step displacements with a step value of 5 nm were presented. We also analyzed the resolution,the potential minimal displacement of the established system. The results show that the position error induced by the ellipticty deviation of the light beam becomes negligible thanks to our signal processing circuit with high-order filter. This method could be useful for many applications in nano dimensional metrology and semiconductor industry.

Superconvergence of RT1 mixed finite element approximations for elliptic control problems

In this paper,we investigate the superconvergence property of the numerical solution to a quadratic elliptic control problem by using mixed finite element methods.The state and co-state are approximated by the order k=1 Raviart-Thomas mixed finite element spaces and the control variable is approximated by piecewise constant functions.We prove the superconvergence error estimate of h3/2 in L2-norm between the approximated solution and the average L2 projection of the control.Moreover,by the postprocessing technique,a quadratic superconvergence result of the control is derived.

Wafer-level site-controlled growth of silicon nanowires by Cu pattern dewetting

An approach for the wafer-level synthesis of size- and site-controlled amorphous silicon nanowires （α-SiNWs） is presented in this paper. Microscale Cu pattern arrays are precisely defined on SiO2 films with the help of photolithography and wet etching. Due to dewetting, Cu atoms shrink to the center of patterns during the annealing process, and react with the SiO2 film to open a diffusion channel for Si atoms to the substrate, α-SiNWs finally grow at the center of Cu patterns, and can be tuned by varying critical factors such as Cu pattern volume, SiO2 thickness, and annealing time. This offers a simple way to synthesize and accurately position a SiNW array on a large area.

An alternating direction method of multipliers for elliptic equation constrained optimization problem

We propose an alternating direction method of multipliers(ADMM)for solving the state constrained optimization problems governed by elliptic equations.The unconstrained as well as box-constrained cases of the Dirichlet boundary control,Robin boundary control,and right-hand side control problems are considered here.These continuous optimization problems are transformed into discrete optimization problems by the finite element method discretization,then are solved by ADMM.The ADMM is an efficient first order algorithm with global convergence,which combines the decomposability of dual ascent with the superior convergence properties of the method of multipliers.We shall present exhaustive convergence analysis of ADMM for these different type optimization problems.The numerical experiments are performed to verify the efficiency of the method.

Pressure-controlled elliptical cavity expansion under anisotropic initial stress: Elastic solution and its application

This paper presents an elastic solution to the pressure-controlled elliptical cavity expansion problem under the anisotropic stress conditions. The problem is formulated by the assumption that an initial elliptical cavity is expanded under a uniform pressure and subjected to an in-plane initial horizontal pressure Kσ_0 and vertical pressure σ_0 at infinity. A conformal mapping technique is used to map the outer region of the initial elliptical cavity in the physical plane onto the inner region of a unit circle in the phase plane. Using the complex variable theory, the stress functions are derived; hence, the stress and displacement distributions around the elliptical cavity wall can be obtained. Furthermore, a closed-form solution to the pressure-expansion relationship is presented based on the elastic solution to the stress and displacement. Next, the proposed analytical solutions are validated by comparing with the Kirsch's solution and the finite element method(FEM). The solution to the presented pressure-controlled elliptical cavity expansion can be applied to two cases in practice. One is to employ the solution to the interpretation of the shear modulus of the soil or rocks and the in-situ stress in the pre-bored pressuremeter test under the lateral anisotropic initial stress condition. The other is the interpretation of the membrane expansion of a flat dilatometer test using the pressure-controlled elliptical cavity expansion solution. The two cases in practice confirm the usefulness of the present analytical solution.

L∞-ESTIMATES OF MIXED FINITE ELEMENT METHODS FOR GENERAL NONLINEAR OPTIMAL CONTROL PROBLEMS

This paper investigates L∞--estimates for the general optimal control problems governed by two-dimensional nonlinear elliptic equations with pointwise control constraints using mixed finite element methods. The state and the co-state are approximated by the lowest order Raviart-Thomas mixed finite element spaces and the control is approximated by piecewise constant functions. The authors derive L∞--estimates for the mixed finite element approximation of nonlinear optimal control problems. Finally, the numerical examples are given.

Investigation of thermal radiation effect on optical dome of sapphire coated yttrium oxide

Compared to traditional optical domes, domes of sapphire coated with films can effectively reduce emissivity and increase transmittance. The purpose of this work is to investigate the thermal radiation effect on sapphire optical dome coated with yttrium oxide by a radio frequency mag- netron sputtering method. The emissivity of sapphire coated with Y203 films is studied by both numerical and experi- mental methods. The results indicate that the emissivity of sapphire substrate is reduced effectively with increasing the thickness of the Y203 film. In addition, a finite element model is developed to simulate the radiation intensity of the optical dome. The thermal responses indicate that the max- imum temperature is reduced apparently compared with the uncoated sapphire as Y203 film thicknesses increase. The average irradiance distribution at different film thicknesses with time shows that the self-thermal radiation disturbance of sapphire optical dome delays 0.93 s when the thickness of Y203 film is 200μm, which can guarantee the dome works properly and effectively even in a harsh environment.