Acta Mechanica Sinica

Inflatable membrane antennas have been extensively applied in space missions; however, the simulation methods are not perfect, and many simulation methods still have many difficulties in accuracy, efficiency, and stability. Therefore, the extended position-based dynamics (XPBD) method is employed and improved for the simulation of folded inflatable structures in this paper. To overcome the problem that the original XPBD method with only geometric constraints does not contain any mechanical information and cannot reflect the mechanical characteristics of the structure, we improve the XPBD method by introducing the strain energy constraint. Due to the complicated nonlinear characteristics of the membrane structures, the results with the traditional finite element method (Abaqus) cannot converge, while the tension field theory (TFT) can, but some pretreatments are needed. Compared with them, the method in this paper is simple and has better stability to accurately predict the displacement, stress, and wrinkle region of the membrane structure. In addition, the present method is also compared with the experiment in the reference to verify the feasibility of the folded tube simulation. Finally, the present method is applied to simulate inflatable membrane antennas and analyze the deployable driving force and deployable process sequence of each component.

Micro air vehicles (MAV’s) have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV’s’ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV’s, including massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment (larger dimension) is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.

It has not been a simple matter to obtain a sound extension of the classical J 2 flow theory of plasticity that incorporates a dependence on plastic strain gradients and that is capable of capturing size-dependent behaviour of metals at the micron scale. Two classes of basic extensions of classical J 2 theory have been proposed: one with increments in higher order stresses related to increments of strain gradients and the other characterized by the higher order stresses themselves expressed in terms of increments of strain gradients. The theories proposed by Muhlhaus and Aifantis in 1991 and Fleck and Hutchinson in 2001 are in the first class, and, as formulated, these do not always satisfy thermodynamic requirements on plastic dissipation. On the other hand, theories of the second class proposed by Gudmundson in 2004 and Gurtin and Anand in 2009 have the physical deficiency that the higher order stress quantities can change discontinuously for bodies subject to arbitrarily small load changes. The present paper lays out this background to the quest for a sound phenomenological extension of the rateindependent J 2 flow theory of plasticity to include a dependence on gradients of plastic strain. A modification of the Fleck-Hutchinson formulation that ensures its thermodynamic integrity is presented and contrasted with a comparable formulation of the second class where in the higher order stresses are expressed in terms of the plastic strain rate. Both versions are constructed to reduce to the classical J 2 flow theory of plasticity when the gradients can be neglected and to coincide with the simpler and more readily formulated J 2 deformation theory of gradient plasticity for deformation histories characterized by proportional straining.

The round-off error introduces uncertainty in the numerical solution. A computational uncertainty principle is explained and validated by using chaotic systems, such as the climatic model, the Rossler and super chaos system. Maximally effective computation time (MECT) and optimal stepsize (OS) are discussed and obtained via an optimal searching method. Under OS in solving nonlinear ordinary differential equations, the self-memorization equations of chaotic systems are set up, thus a new approach to numerical weather forecast is described.

A novel approach is proposed in determining dynamic fracture toughness (DFT) of high strength steel, using the split Hopkinson tension bar (SHTB) apparatus, combined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors (DSIF) are obtained with the aid of 3D finite element analysis (FEA). In this approach, the dimensions of the specimen are not restricted by the connection strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the experimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.

This paper considers the dynamical behavior of a Duffing-Mathieu type system with a cubic single-well potential during the principal parametric resonance. Both the cases of constant and time-dependent excitation amplitude are used to observe the variation of the extent and the rate of the erosion in safe basins. It is evident that the appearance of fractal basin boundaries heralds the onset of the losing of structural integrity. The minimum value of control parameter to prevent the basin from erosion is given along with the excitation amplitude varying. The results show the time-dependence of excitation amplitude can be used to control the extent and the rate of the erosion and delay the first occurrence of heteroclinic tangency.