In order to deal with the "vicinity efiect" in the damage localization of plate structures, this paper proposes a method based on the modifled modal strain energy. Firstly, the relative strain change at adjacent points are used to calculate the weight coe-cients, Then the strain energy in the corresponding area is redistributed according to the weight coe-cients. By deflning a damage difierentiation degrees index, the influences of the noise on the damage localization can be evaluated. To verify the feasibility and the efiectiveness of the proposed method, a four edge simply supported plate is used as a numerical example. It is shown that the proposed method can realize an accurate damage localization in dot, block and strip damage cases, with a good anti-noise capability.
Combining two books by overlapping alternately their sheets, the integrated structure generates a great friction between the paper sheets when both spines are under horizontal tensile force. The correlation between the length of overlapping and the number of sheets of overlapping is obtained by experiments. A semitheoretical and semi-empirical friction calculation formula is obtained by the MATLAB numerical simulation and the predictions are in good agreement with the experimental data. The formula could provide a reasonable and reliable prediction of the ultimate bearing capacity for the integrated structure.
The astrodynamics software is a bridge between the astrodynamics theory and the engineering application, which can evidently improve the e-ciency and the ability of the space mission design and analysis. There are many mature software systems in the world, but many of them are not available in our country. In recent years, great progress has been made in the fleld of the national astrodynamics research and the engineering applications, but the mature astrodynamics software remains almost a blank area. The development of the international astrodynamics software is surveyed and sorted into two kinds:the space mission analysis and the spacecraft trajectory optimization. The representative open-source and commercial software systems are introduced, including JAT, STK, Freeflyer, POST and ASTOS. Additionally, the development of the Chinese astrodynamics software is also reviewed. At last, the technical characteristics of difierent astrodynamics softwares are summarized, and preliminary suggestions for the development of a mature astrodynamics software in China are given.
In this paper, the response of the spherical cavity expansion theory is used to analyze the penetration of the target under the impact of the missile, and a general form of the penetration similarity is established based on the dimension theory. The analysis of the existing experimental data of the projectile shows that the non-dimensional penetration depth curve is deflected and shifted for difierent penetration speeds. With the strain-rate efiect and the damage evolution of the material, the geometric similarity laws do not hold true for the brittle materials such as the concretes. It is necessary to introduce a correction of the geometric similarity law to account for the strain-rate efiect and the damage evolution of the material.
This paper studies the optimal control of the nonholonomic motion planning for the free-floating space robot with prismatic joint. A hybrid optimization strategy based on the Gauss pseudospectral method (GPM) and the direct shooting method (DSM) is proposed. First, a dynamics model for the space robot is established based on the multibody dynamics theory. For a given initial and flnal conflgurations, the motion planning problem is described as an optimal control problem in the Bolza form. Then, the continuous optimal control problem is transformed into a nonlinear programming problem based on the GPM. With fewer Legendre-Gauss (LG) points, the feasible solution of the state variables and the control variables can be obtained. Finally, the control variables are discretized at the LG points and used as the initial values of the DSM, the optimal trajectory and the optimal control inputs are obtained by the sequential quadratic programming (SQP) algorithm. As shown by the numerical simulation, the optimal trajectory of the system is stable with no detours, and the control inputs match the various constraints under actual conditions. The results indicate that the hybrid optimization strategy is efiective with a good robustness.
The discontinuity between two adjacent sine signals and the poor control precision are two di-cult problems in the multiple input multiple output (MIMO) swept sine vibration test. This paper proposes a new method to smooth the discontinuous signal segments of sinusoid waves at difierent frequencies, to guarantee the test time requirement and the phase tolerance requirement of the reference. The compression impedance control method (CICM) is proposed to solve the over correction problem of the excited signals. The impacts on the rate of convergence and the control precision are analyzed, and the threshold of the frequency response function matrix (FRFM) is set to avoid the over excitation of the singular FRFM at some special frequencies. Finally the paper establishes the test conditions for the multiple axis vibration test, and tests the algorithm for the multiple axis swept sine test. It is shown that the amplitude and phase responses could be controlled within the tolerance range of the reference values by the 5 times correction, when the compression factor value is 0.4, and the control algorithm is shown to be reliable.
To improve the interface vibration environment of the satellite and the rocket, a six-pole vibration isolation platform is built, with the magnetorheological damper as the semi-active control device. The magnetorheological damper for the whole vibration isolation platform is tested to obtain the experimental data for the damping characteristics of the magnetorheological damper. The BP (back propagation) neural network with two hidden layers is established to model the damper for predicting the damping characteristics of the magnetorheological damper and for the design of the control system. A sequential algorithm is proposed to optimize the network structure, the weight and the threshold to ensure that the network has a better generalization ability and the stability of the network training. The simulation results show that compared with the parametric model, the proposed neural network model has less training error and higher generalization ability, and can well predict the damping characteristics of the damper.
An inverse analysis model for identifying internal defects (inclusions) in the structure using a combined method of the extended flnite element method (XFEM) and the genetic algorithm (GA) is proposed. The discontinuous displacement mode introduced in the displacement function of the XFEM makes it possible to generate a grid independent of the discontinuous interface of the structure. The locations and the size of defects are determined by a modiflcation of the level set function in the study. The GA has a global and local optimization ability in each iteration process. The fltness value of the response determines whether the iteration should continue or not. Two numerical examples including a single circular defect and multiple defects are analyzed, and the locations of the response measuring points in the structure are also discussed. Results indicate that the inversion model presented in the paper can accurately identify the locations and the size of a single defect or multiple defects in the structure.
The nonlinear attenuation and acceleration creep stage of the rock cannot be well described by the traditional Bingham rheological model, which is valid in the stable stage. So, an action function and a nonlinear viscous element are added to characterize the two stages, which transform the traditional linear formulation into a nonlinear one, in the form of an improved Bingham model. The green rock and sandstone creep experimental data are obtained by rheological tests and the parameters of the model are obtained by a nonlinear fltting method. Compared the theoretical curves with the experimental curves, the results show that the improved model is efiective and rational.