Dynamic Load Identification For Tubular Inflatable Membrane Structure Based On Linear Vibration Discrete Equation In Time Domain

Dynamic load identification belongs to the second kind of inverse problem in structural dynamics.Research idea can be summed up as: how to obtain the excitation information accurately under the premise of knowing the structure's inherent characteristic and dynamic response.The tubular inflatable membrane structure(inflatable beam)is taken as research object in this paper.Dynamic excitation imposed on this structure is studied systematically and thoroughly.A series of load identification algorithms are proposed in time domain.The main research work consists of the following aspects:1.A step-by-step integration algorithm based on Taylor polynomial expansion is set up.The vibration convolution equation is decoupled and the linear discrete equation combining input load,output response and system characteristic is gained.All subsequent load identification algorithms are developed on the basis of this equation.With regard to concentrated force exciting on the inflatable beam,the excitation position and magnitude of the force are identified in time domain.Acceleration transmissibility theory is adopted to evaluate the number and position of loads.To reduce the ill-posed problem caused by response noise and inverse of transfer function matrix,truncated singular value decomposition is applied to reconstruct the amplitudes of input loads.Load amplitude dentification effect is verified by a single point excitation experiment of inflatable beam.2.After identifying concentrated force applied on the inflatable beam with fixed parameters,some physical parameters and size parameters of the inflatable beam are set as uncertain interval parameters.An algorithm combining interval model and second-order perturbation theory is set up to reconstruct the upper and lower boundaries of input loads.3.Based on the linear discrete equation obtained by step-by-step integration algorithm,the concentrated force is extended to more complex distributed force.A two-step ideology is put forward to identify the distributed load applied on the beam.Firstly,in order to overcome the ill-posed problem,L-curve method is improved to obtain more precise regularization parameter.And the distributed load amplitudes at the node position are computed by regularization technology.Secondly,the node amplitudes are used as control points,and cubic Catmull-Rom spline function is employed to interpolate the control points.As a result,the time history and space distribution of the distributed load on the whole beam is acquired.4.Aiming at the inflatable beam structure with uncertain interval parameters,an intelligent algorithm combining Latin hypercube sampling and genetic algorithm is built up to calculate the upper and lower bounds of the distributed force acting on the inflatable beam.In addition,all the load identification algorithms have corresponding numerical examples.The accuracy,robustness and noise resistance of the algorithms are analyzed in detail by means of numerical examples.