Minimizing sequences of variational problems with small parameters

A class of variational problems with small parameters is studied. Their zeroth-order asymptotic solutions are constructed. It is shown that the zeroth-order asymptotic solution is just the minimizing sequence of variational problems as the small parameter approaches to zero.     

分布式光纤裂缝检测的有限元分析及试验

对分布式光纤裂缝检测技术中光纤-混凝土复合体的微观力学行为进行了分析. 考虑了涂覆-护套、护套-混凝土双界面的状态非线性,混凝土采用双线性各向同性强化模型以消减局部应力集中,避免护套-混凝土之间的过度穿透. 采用试验确定的接触对力学参数,用ANSYS进行了数值模拟,得到了光纤-混凝土复合体的微观应力分布及光纤的曲率分布. 定量分析了缝宽与弯曲损耗的关系,计算结果与试验结果符合较好,从理论上验证了光纤布置方式、护套厚度对传感灵敏度和动态范围的影响,为分布式光纤裂缝检测技术提供了修正的微观力学分析理论和方法.      

RESPONSE ANALYSIS OF PIEZOELECTRIC SHELLS IN PLANE STRAIN UNDER RANDOM EXCITATIONS

The random response of a piezoelectric thick shell in plane strain state under boundary random excitations is studied and illustrated with a piezoelectric cylindrical shell. The differential equation for electric potential is integrated radially to obtain the electric potential as a function of displacement. The random stress boundary conditions are converted into homogeneous ones by transformation,which yields the electrical and mechanical coupling differential equation for displacement under random excitations. Then this partial differential equation is converted into ordinary differential equations using the Galerkin method and the Legendre polynomials,which represent a random multi-degree-of-freedom system with asymmetric stiffness matrix due to the electrical and mechanical coupling and the transformed boundary conditions. The frequency-response function matrix and response power spectral density matrix of the system are derived based on the theory of random vibration. The mean-square displacement and electric potential of the piezoelectric shell are finally obtained,and the frequency-response characteristics and the electrical and mechanical coupling properties are explored.     

Control of flight forces and moments by flapping wings of model bumblebee

The control of flight forces and moments by flapping wings of a model bumblebee is studied using the method of computational fluid dynamics.Hovering flight is taken as the reference flight:Wing kinematic parameters are varied with respect to their values at hovering flight.Moments about(and forces along)x,y,z axes that pass the center of mass are computed.Changing stroke amplitude(or wingbeat frequency)mainly produces a vertical force.Changing mean stroke angle mainly produces a pitch moment.Changing wing angle of attack,when down-and upstrokes have equal change,mainly produces a vertical force,while when down-and upstrokes have opposite changes,mainly produces a horizontal force and a pitch moment.Changing wing rotation timing,when dorsal and ventral rotations have the same timing,mainly produces a vertical force,while when dorsal and ventral rotations have opposite timings,mainly produces a pitch moment and a horizontal force.Changing rotation duration has very small effect on forces and moments.Anti-symmetrically changing stroke amplitude(or wingbeat frequency)of the contralateral wings mainly produces a roll moment.Anti-symmetrically changing angles of attack of the contralateral wings,when down-and upstrokes have equal change,mainly produces a roll moment,while when down-and upstrokes have opposite changes,mainly produces a yaw moment.Anti-symmetrically changing wing rotation timing of the contralateral wings,when dorsal and ventral rotations have the same timing,mainly produces a roll moment and a side force,while when dorsal and ventral rotations have opposite timings,mainly produces a yaw moment.Vertical force and moments about the three axes can be separately controlled by separate kinematic variables.A very fast rotation can be achieved with moderate changes in wing kinematics.     

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主要基于三维弹性力学和状态空间法给出了四边简支各向同性矩形层合板自由振动和 强迫振动问题的精确解. 首先基于三维弹性力学建立了层合板的基本方程,利用状态空间法 解决了层合板的自由振动问题,然后根据Lagrange动力学方程求解了层合板受到横向冲击时 的强迫振动响应.     

倾转旋翼过渡状态的尾迹及气动力特性计算与分析

建立了倾转旋翼机倾转过渡状态旋翼尾迹和气动力的计算方法.该方法中,桨叶的气动模型采用Weissinger-L升力面理论模拟,尾迹的控制方程考虑了旋翼倾转运动对速度分量的影响,并采用时间步进方法求解旋翼自由尾迹,为提高计算精度,使用了4阶Adams-Moulton预测-校正数值算法.同时,该方法中还推导了能适用于倾转过渡状态的旋翼桨叶挥舞运动方程,并结合了旋翼配平模型.利用所建立的方法,首先计算了悬停和前飞状态时的旋翼自由尾迹几何形状,并通过与可得到的实验结果对比,验证了计算方法的有效性.然后,计算和分析了旋翼在不同倾转状态下的尾迹滞后及弯曲特征,以及倾转旋翼的拉力、俯仰和滚转力矩随时间的变化,在此基础上,得出了一些有意义的结论.     

孔周弹塑性变形与疲劳循环次数的相关性

应用白光散斑相关技术研究了孔周弹塑性变形与疲劳循环次数的相关性,以便探索疲劳寿命的预测方法.疲劳实验在单边带缺口的拉伸板状试件上进行,试件由GH4169材料制成,试件表面上喷涂了白光散斑图.疲劳加载采用0→Pmax→0的循环加载方式,加载波形为正弦波,加载频率为10Hz.实验中,按一定的疲劳循环周次在零载及最大载荷两种状态下停机、采图.应用数字图像相关技术求出孔周附近的残余位移场,并应用逐点最小二乘法求出应变场.实验中获得了一些对于疲劳寿命研究很有意义的结果.     

A Novel Deterministic Quantum Communication Scheme Using Stabilizer Quantum Code

Exploiting the encoding process of the stabilizer quantum code [[n, k, d]], a deterministic quantum communication scheme, in which n - 1 photons are distributed forward and backward in two-way channel, is proposed to transmit the secret messages with unconditional security. The present scheme can be implemented to distribute the secret quantum （or classical） messages with great capacity in imperfect quantum channel since the utilized code encodes k-qubit messages for each scheme run.     

Two-Mode Excited Squeezed Vacuum State and Its Properties

In this paper, the two-mode excited squeezed vacuum state (TESVS) is studied by using the statistical method. By calculating the normalization of the TESVS, a new form of Jacobi polynomials and some new identities are obtained. The photon number distribution of the TESVS is given and it is a simple form of Jacobi polynomials. Using the entangled state representation of Wigner operator, the Wigner function of the TESVS is obtainded and the variations of the Wigner function with the parameters m, n, and r are discussed. Here from the phase space point of view the TESVS can be well interpreted and described.     

Husimi Function of Excited Squeezed Vacuum State

The q-p phase-space distribution function is a popular tool to study semiclassical physics and to describe the quantum aspects of a system. In this paper by using the pure state density operator formula of the Husimi operator Δ_h(q,p;κ)=|p,q〉_κκ〈p,q| we deduce the Husimi function of the excited squeezed vacuum state. Then we study the behavior of Husimi distribution graphically.