Magnetic torque attitude control of a satellite using the state-dependent Riccati equation technique

A non-linear attitude control method for a satellite with magnetic torque rods using the state-dependent Riccati equation (SDRE) technique has been developed. The magnetic torque caused by the interaction with the Earth's magnetic field and the magnetic moment of torque rods plays a role of the control torque. The detailed equations of motion for this system are presented using angular velocity and quaternions. The SDRE controller is developed for the non-linear systems which can be formed in pseudo-linear representations using the state-dependent coefficient (SDC) method without linearization procedure. The aim of this control system is to achieve a stable attitude within 5°, and minimize the control effort. The stability regions for the SDRE controlled satellite system are estimated through the investigation of the stability conditions developed for pseudo-linear systems and the application of Lyapunov's theorem. For comparisons, the Linear Quadratic Regulator (LQR) method using the solution of the algebraic Riccati equation (ARE) is also applied to this non-linear system. The performance of the SDRE non-linear control system demonstrates more robustness and stability than the LQR control system when subjected to a wide range of initial conditions.     

Spin-orbit torques induced by spin Hall and spin swapping currents of a separate ferromagnet in a magnetic trilayer

Spin-orbit torques (SOTs) have been investigated most widely in normal metal/ferromagnet bilayers where the spin Hall effect of normal metal is a main source of spin currents. Recently, ferromagnets are found to also serve as spin-current sources through spin-orbit coupling. In this work, we theoretically investigate SOT acting on ferromagnet₂ in ferromagnet₁/normal metal/ferromagnet₂ trilayers, which is caused by the spin Hall and spin swapping effects of ferromagnet₁. Our result provides an analytical expression of SOT in the trilayers, which may be useful for quantifying the spin Hall and spin swapping effects of ferromagnets and also for designing and interpreting SOT experiments where a ferromagnet is used as a spin-current source instead of a normal metal.     

Interaction region of magnon-mediated spin torques and novel magnetic states

We determine the region in which the magnon-mediated spin torques exist. This region can be controlled by the spin waves. In terms of stability analysis of magnetization dynamics based on the spin-wave background, we obtain the instability conditions of spin waves. With these results, we find the relationship between unstable regions and the formation of Akhmediev breather, Kuznetsov–Ma breather and rogue waves. We establish the phase diagram of some novel magnetic excitaions.     

Investigation of Network Structure and Dynamic Mechanical Properties of Peroxide-Cured Ethylene Propylene Diene Rubber

The effect of peroxide and co-agent amount on the cure behavior, network structure, and dynamic mechanical properties of ethylene-propylene elastomers were studied by moving die rheometer, equilibrium swelling and dynamical mechanical measurements. The increase in peroxide and co-agent concentrations resulted in an increase in total cross-link density, C_tot. The model calculation results based on torque measurements considered the changes in C_tot as a function of peroxide and co-agent content; it linearly depended on initial peroxide content when the co-agent content was constant. The torque measurements were also carried out to investigate the cross-linking efficiencies of the peroxide and the co-agent triallyl isocyanurate (TAIC); the efficiencies were evaluated as 77–95% and 33%, respectively, but the use of TAIC didn't affect the scorch time and rate constants of EPDM compounds significantly. The incorporation of TAIC into the network enhanced the network heterogeneity, the glass transition temperature shifted towards higher temperature and the peak values of the loss factor gradually decreased, both of which were caused by restricted segmental mobility due to the increase in cross-link density.     

基于LabVIEW的旋转轮轴扭矩测试系统的设计

针对目前国内旋转动力机械动态扭矩测量中受环境因素影响大,精度低,稳定性差,操作使用不方便等问题,应用感应供电技术、无线通信技术、微功耗处理技术、虚拟仿真技术,设计了一种将WIFI无线传感器网络(WSNs)与虚拟仪器相结合的旋转轮轴扭矩测试系统,实现了动态扭矩参数的实时准确监测、在线校准、存储、分析、显示、预报预警及生成报表等功能,仿真和实测结果表明：该系统功耗低于0.05W,测量精度可达0.4%FS,动态响应好,操作简单,长时间运行稳定可靠。     

基于自抗扰控制器的力矩电机伺服系统控制

自抗扰控制器能将被控对象的内、外“总扰动”进行估计并用前馈补偿的方法将其抵消,适于力矩电机因直接驱动所带来干扰的补偿与控制。针对测量噪声对线性自抗扰控制器观测器带宽的限制,提出了二阶线性自抗扰的相似结构,并结合三阶积分链式微分器对其效果进行了对比仿真验证。力矩电机的控制仿真实验表明,与二阶线性自抗扰算法相比,基于相似结构的改进的力矩电机控制,能在有测量噪声情况下兼顾系统跟踪精度、突加负载时抗扰动性与抗噪性。     

气动负载虚拟加载系统设计

飞行器在飞行过程中,舵机将承受到空气动力的力矩载荷,气动负载虚拟负载模拟器是用于模拟空气力矩载荷变化规律的地面半实验设备。针对在地面试验过程中,传统负载模拟器与承载系统因机械结构耦合而产生的“多余力矩”问题,以磁粉离合器和力矩传感器为核心,构建虚拟负载模拟器,利用系统输出转矩的大小和方向分别只与励磁电流的大小和速度滑差的方向有关的特性,较彻底地解决“多余力矩”的问题,提高力矩加载试验设备的性能,从而进一步提高飞行器虚拟试验的水平。     

On the dynamic vibrations of an elastic beam in frictional contact with a rigid obstacle

Existence and uniqueness results are established for weak formulations of initial-boundary value problems which model the dynamic behavior of an Euler-Bernoulli beam that may come into frictional contact with a stationary obstacle. The beam is assumed to be situated horizontally and may move both horizontally and vertically, as a result of applied loads. One end of the beam is clamped, while the other end is free. However, the horizontal motion of the free end is restricted by the presence of a stationary obstacle and when this end contacts the obstacle, the vertical motion of the end is assumed to be affected by friction. The contact and friction at this end is modelled in two different ways. The first involves the classic Signorini unilateral or nonpenetration conditions and Coulomb's law of dry friction; the second uses a normal compliance contact condition and a corresponding generalization of Coulomb's law. In both cases existence and uniqueness are established when the beam is subject to Kelvin-Voigt damping. In the absence of damping, existence of a solution is established for a problem in which the normal contact stress is regularized.The work of the last two authors was supported in part by Oakland University Research Fellowships.     

On the control of n-dimensional thermoelastic system

In this article, we consider n-dimensional thermoelastic system with a nonlinear weak frictional damping. We establish an explicit and general decay rate result, using some properties of the convex functions. Our result is obtained without imposing any restrictive growth assumption on the damping term.     

Spin-transfer induced ultrafast precessional switching enhanced by interface anisotropy in a ferromagnetic nanopillar

Spin-transfer induced ultrafast precessional switching of magnetization in a Co/Cu/Co nanopillar device is studied. Micromagnetic calculations show that precessional magnetization switching occurs above a threshold current. The presence of interface uniaxial anisotropy in the Co-thin film free layer influences heavily the current and the energy required to initiate the switching in the device, and the speed of the precessional switching. The threshold current and the precessional switching time are significantly reduced by this effect.