Papers by Keyword: Modal Identification

Abstract: In this paper, there are built new composite bars with different core: with the core made of polypropylene honeycomb and polystyrene reinforced with fiber-glass. Starting from the theoretical background the modal parameters identification, there will be established an experimental method used to determine the eigenparameters of the sandwich bars. In the end, some comparisons between the eigenparameters will be made.

Abstract: Mass distribution of floating structures will change due to such factors as ballast water management during ship sailing or inward and outward port, crane movement during construction, and the loading and unloading of cargoes on the offshore platform structures, which will then make its natural frequency change with time. While traditional modal identification cannot deal with the issues of non-stationary of time-varying system, Hilbert-Huang transform is quite effective for the processing and analysis of non-stationary signal. Therefore, this paper investigates the identification of linear time-varying system using the Hilbert-Huang transform, and conducts a numerical simulation of the two degrees-of-freedom time-varying system. In addition, this paper designs a cantilever beam subjected to a moving mass, and then makes a comparison of the identification results between the present identification method and those from finite element method (FEM) and eigensystem realization algorithm (ERA), which shows a higher accuracy of the present method for modal identification of time-varying system.

Abstract: A new kind of human-imitate shooting platform is needed, so that the automation and standardization of small arm experiment could be realized. And the main part of shooting platform design is the modeling of human-gun interaction system. The main object of this paper is modeling human-gun interaction system by testing the model of the system. Firstly, the testing scheme is promoted for testing interaction between gun and human shoulder, and high quality test data is collected. Then, the model parameter of human-gun system is calculated by the method of model parameter identification. 3D model of human-gun system is built. At last, the dynamic simulation is made by ADAMS. And human-gun model built by experiment method is verified.

Abstract: The concept of Smart City (SC) has been introduced to categorize the vast area of activities to enhance the life quality of citizen, which are characterised by a pervasive use of Information and Communication Technologies (ICT), to help cities, with various urban domains, making better use of their resources. Monitoring the structural behaviour of strategic buildings and monuments may be desirable for citizens, which have recently experienced a destructive earthquake in their own town, such as the case of L’Aquila. The paper deals with the design of a distributed structural monitoring network for a selected set of strategic structures belonging to the city of L’Aquila. Preliminary design criteria are discussed on the basis of previous authors’ experiences in this context. Specific attention has been dedicated to analyse the expected acceleration response measurements induced by small seismic excitations for the general purpose of monitoring.

Abstract: This paper focus on the model updating of civil structural systems. Traditional modal test method can identify the frequency of the civil structure accurate, but it is difficult to identify the mass-normalized mode shape. By adding a series of known masses to the structure, measuring the frequency of this mass-modified system, and only using this set of frequency data, the mass-normalized mode shape of the structure can be identified. And the model updating method was developed, which constructed an objective function through the frequency of the measurement and the FE model, corrected the FE model's parameters to minimize the objective function. The example was included to show the capabilities of the technique. The finite element model of the fixed-free beam was updated by the dynamic characteristics which was identified from the modal test, the results show that updated results coincided with the experience of the analyst.

Abstract: The paper discusses the basic principle of blind source separation algorithm applying in structural modal identification. By improving the signal-whitening method, a robust second-order blind identification (RSOBI) algorithm is established on the basis of second-order statistics. The modal responses and mode shapes can be obtained using the RSOBI algorithm from the observed data of structures in time domain. Frequency and damping are estimated from the modal responses by traditional single degree of freedom methods. The simulation results show that the RSOBI algorithm has good performance in modal identification of structures.

Abstract: The paper discusses the basic principles of blind source separation and modal identification of structures, analyses the feasibility that using blind source separation techniques for modal parameter identification. According to the noisy features of the measured data in experiments, a second-order blind identification algorithm based on moving average method is proposed. By moving average method the noises are efficiently eliminated. It greatly improves the separation performance of this algorithm. The cantilever experiments verify the stability and the applicability of the algorithm.

Abstract: This paper makes a brief characterisation of some aspects related with the extensive research activity of the Laboratory of Vibrations and Structural Monitoring (ViBest) of the Faculty of Engineering of the University of Porto (FEUP) in the field of Continuous Dynamic Monitoring of Bridges and Special Structures, selecting four examples where large high quality databases have been created since 2007, namely Infante D. Henrique bridge, Pedro e Inês footbride, FEUP Campus stress-ribbon footbridge and Trezói railway bridge.

Abstract: Research on the dynamic characteristics of gravity dam was carried out by adopting ARX model using the seismic response data of concrete gravity dam at Shui-Kou hydropower station. The applicability and effectiveness of single-output-multiple-input ARX model were deduced and verified. A corresponding computer program was developed, and performed to identify the modal parameters of the system. The identified natural frequencies and damping ratios were basically same with the results by traditional peak point pick-up method, and also close to the finite element method (FEM) results. It is indicated that the structure natural frequencies and damping ratios are determined by the characteristics of the structure, the dynamic characteristics identified by ARX model are correct, and ARX model can avoid frequency leakiness when smoothing processing and Fourier transform are conducted in solving process of the peak point pick-up method. The modal identification can be applied to other structures.

Abstract: According to characteristics of frequency-intensive on spatial truss structures, maximum isolation each modal is a good solution to this question. Considering this idea, calculating modal weighting coefficients of spatial truss structures through dynamic response expression, mode vector and objection vector can be obtained. An objection function was established based on euclidean distance. When the euclidean distance between mode vector and objection vector minimize, the optimal excitation position can be also received.