Papers by Keyword: Singularity

Abstract: Solutions for many rigid/plastic models are singular in the vicinity of maximum friction surfaces. In particular, the magnitude of the equivalent strain rate near such surfaces is controlled by the strain rate intensity factor. This factor is the coefficient of the leading singular term is a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. Since the equivalent strain rate has a great effect of material properties, it is of important to reveal the dependence of the strain rate intensity factor on parameters characterizing material models. In the present paper, quite a general model of anisotropic plasticity under plane strain conditions is adopted. Then, using an analytic solution for instantaneous compression of a layer of plastic material between two parallel plates the effect of the shape of the yield locus on the asymptotic behavior of the equivalent strain rate in the vicinity of the friction surface is demonstrated.

Abstract: Using the method of composite material complex and constructing new stress functions with complex singularity exponents, the problem of singularities near interface crack tip for mode II of orthotropic bi-material is studied. Boundary value problems of generalized bi-harmonic equations can be solved with the help of boundary conditions, then four kinds of stress singularities are deduced, respectively, such as the constant singularity at λ=-1/2, the non-constant singularity at λ=-1/2+ε , the constant oscillation singularity at λ=-1/2+iε, and non-constant oscillation singularity at λ=-1/2+c+iε. For each case, the analytic expressions for stress intensity factors near the central-penetrated interface crack tip for mode II of orthotropic bi-material are obtained.

Abstract: Singularity problem in attitude estimation of small tail-sitter aircraft with traditional algorithm is researched. According to the flight characteristics of small tail-sitter aircraft, a new algorithm is proposed. Vertical Euler angles whose singularity points are away from standard Euler angles are introduced. Only one set of angles are used in horizontal or near-vertical state to avoid singularity. Simulation results show that attitude angles can vary continuously and have high accuracy under the condition of a large tilting angle.

Abstract: A Planar Parallel Manipulator (PPM) with non-planar links overcomes most of the shortcomings in conventional manipulators. Due to cantilever action, the links of a PPM develop bending stress. When the links are non-planar (having inclination with the horizontal plane), this cantilever action reduces and the same manipulator can have higher payload capacity. In this project, a planar 3-RRR manipulator with non-planar links is investigated for rectifying singularity at home configuration, and a novel method of position feedback of the motor is designed, fabricated and tested with rest of the motion control components.

Abstract: A novel parallel mechanism which enlarges the workspace by singularity-free mode change is proposed. The proposed mechanism is inherited the design of Linear DELTA which has three degree-of-freedom translational moving plate driven by three linear actuators, in addition, extended it by redundantly actuation by four linear actuators and asymmetric design. New criterions about redundancy and singularity of redundantly actuated parallel mechanism using summation and product of determinants of minor matrices of the transposed Jacobian matrix are proposed. Redundantly actuation and asymmetric design enables singularity-free mode changes with loss redundancy but maintain non-singularity, that are evaluated by the proposed criterions. Numerical simulations demonstrate the singularity-free mode changes of the proposed mechanism.

Abstract: Hull structure has sharp corners with singularity which tends to produce fatigue cracks and cause structural damages. Its not straightforward to assess FE analysis results of stiffened plating structures because of the stress singularities that are inherent in the overall geometry. This paper concentrates on the analysis of a simple planar right angled cruciform corner and a 135-degree sheet corner through a series of FE analyses using ANSYS. The aim is to try and provide an understanding of the nature of the singularities. Through the understanding a simple method is proposed to estimate the singular stress at the corners using as named as singularity strength which is based on notch-stress intensity factor theory. Finally the estimation methods of as are given for the 2D corners.

Abstract: In this paper, kinematics and singularity of a 2-RPU&SPR parallel mechanism are analyzed by algebraic method. Firstly, the inverse kinematics of the parallel mechanism is derived. Secondly, the Jacobian matrix of the parallel mechanism is obtained and the singularity of the mechanism is analyzed. Finally, the correctness of singularity analysis of the mechanism is verified by numerical simulations.

Abstract: Mode I crack for an example, this paper conducts the introduction and analysis of the use of finite element software ANSYS to calculate the stress intensity factor approaches. Compared the stress intensity factor values with the analytic solution, it shows that the finite element method to calculate the stress intensity factor has a very high precision, and easy to operate.

Abstract: The basic principle of the wavelet analysis method to extract the mineral spectral absorption characteristics is summarized and different wavelet bases,wavelet decomposition scale extraction effect are analyzed in this paper. Then, the algorithm of mineral spectral absorption characteristics based on wavelet spectral analysis is provided and a large number of experiments are carried out using the spectrums of field rock mineral. Experimental result shows that such a method is less affected by original signal noise and depict the parameters of the mineral spectral absorption feature more precise, which is an ideal spectral feature extraction method compared with the traditional mineral spectral absorption feature extraction method.

Abstract: This paper devotes to address the problem of the singularity of the Stewart platform, which is different from the serial mechanism. An algorithm has been constructed; also, by solving a minimum problem, it finds a alternative path to instead the preliminary path, in which there are several singular configurations. At the end of this paper, a numerical case has been developed and gives two points on the preliminary path. By applying this algorithm, a singularity-free path can be found to avoid the singularities in the preliminary path and ill-condition. So, this algorithm can be proven practical.