Structural Damage Detection Robust Against Time Synchronization Errors

Structural Damage Detection based on Wireless Sensor Networks Can Be Affected Significantly by Time Synchronization Errors among Sensors. Precise Time Synchronization of Sensor Nodes Has Been Viewed as Crucial for Addressing This Issue. However, Precise Time Synchronization over a Long Period of Time is Often Impractical in Large Wireless Sensor Networks Due to Two Inherent Challenges. First, Time Synchronization Needs to Be Performed Periodically, Requiring Frequent Wireless Communication among Sensors at Significant Energy Cost. Second, Significant Time Synchronization Errors May Result from Node Failures Which Are Likely to Occur during Long-Term Deployment over Civil Infrastructures. in This Paper, a Damage Detection Approach is Proposed that is Robust Against Time Synchronization Errors in Wireless Sensor Networks. the Paper First Examines the Ways in Which Time Synchronization Errors Distort Identified Mode Shapes, and Then Proposes a Strategy for Reducing Distortion in the Identified Mode Shapes. Modified Values for These Identified Mode Shapes Are Then Used in Conjunction with Flexibility-Based Damage Detection Methods to Localize Damage. This Alternative Approach Relaxes the Need for Frequent Sensor Synchronization and Can Tolerate Significant Time Synchronization Errors Caused by Node Failures. the Proposed Approach is Successfully Demonstrated through Numerical Simulations and Experimental Tests in a Lab. © 2010 IOP Publishing Ltd

Response Surface Method based on Radial Basis Functions for Modeling Large-Scale Structures in Model Updating

The Response Surface (RS) Method based on Radial Basis Functions (RBFs) is Proposed to Model the Input-Output System of Large-Scale Structures for Model Updating in This Article. as a Methodology Study, the Complicated Implicit Relationships between the Design Parameters and Response Characteristics of Cable-Stayed Bridges Are Employed in the Construction of an RS. the Key Issues for Application of the Proposed Method Are Discussed, Such as Selecting the Optimal Shape Parameters of RBFs, Generating Samples by using Design of Experiments, and Evaluating the RS Model. the RS Methods based on RBFs of Gaussian, Inverse Quadratic, Multiquadric, and Inverse Multiquadric Are Investigated. Meanwhile, the Commonly Used RS Method based on Polynomial Function is Also Performed for Comparison. the Approximation Accuracy of the RS Methods is Evaluated by Multiple Correlation Coefficients and Root Mean Squared Errors. the Antinoise Ability of the Proposed RS Methods is Also Discussed. Results Demonstrate that RS Methods based on RBFs Have High Approximation Accuracy and Exhibit Better Performance Than the RS Method based on Polynomial Function. the Proposed Method is Illustrated by Model Updating on a Cable-Stayed Bridge Model. Simulation Study Shows that the Updated Results Have High Accuracy, and the Model Updating based on Experimental Data Can Achieve Reasonable Physical Explanations. It is Demonstrated that the Proposed Approach is Valid for Model Updating of Large and Complicated Structures Such as Long-Span Cable-Stayed Bridges. © 2012 Computer-Aided Civil and Infrastructure Engineering

Existence of Multiple Positive Periodic Solutions of Delayed Predator-Prey Models with Functional Responses

AbstractIn this paper, by applying the continuation theorem of coincidence degree theory, we establish some new criteria for the existence of multiple positive periodic solutions for the delayed predator-prey model.x′(t)=x(t)(r(t)−a(t)x(t))−b(t)f(x(t))y(t),y′(t)=y(t)(c(t)f(x(t−τ))−d(t)),when functional response function f is monotonic or nonmonotonic

Review of Aircraft Vibration Environment Prediction Methods

AbstractAircraft vibration response environment prediction, which is adopted in aircraft initial vehicle development, has not been got enough attention and wide application yet. This paper briefly reviews theoretical and engineering significance of aircraft vibration response environment prediction firstly. Then the paper summarizes the main aircraft vibration response environment prediction methods and indicates their advantages, disadvantages and applicability scopes, including extrapolation of similar structure, theory analysis and analytical solution of differential dynamical equation, statistical parameter modeling, simulation calculation modeling and machine learning. Finally, the paper points out that uncertainty and non-linear structures, nonstationary signal analysis and complex vibration environment response prediction are major problems for aircraft vibration response prediction and directions for future research work

On Internal Resonance Analysis of a Double-Cable-Stayed Shallow-Arch Model with Elastic Supports at Both Ends

In previous research on the nonlinear dynamics of cable-stayed bridges, boundary conditions were not properly modeled in the modeling. In order to obtain the nonlinear dynamics of cable-stayed bridges more accurately, a double-cable-stayed shallow-arch model with elastic supports at both ends and the initial configuration of bridge deck included in the modeling is developed in this study. The in-plane eigenvalue problems of the model are solved by dividing the shallow arch (SA) into three partitions according to the number of cables and the piecewise functions are taken as trial functions of the SA. Then, the in-plane one-to-one-to-one internal resonance among the global mode and the local modes (two cables\u27 modes) is investigated when external primary resonance occurs. The ordinary differential equations (ODEs) are obtained by Galerkin\u27s method and solved by the method of multiple time scales. The stable equilibrium solutions of modulation equations are obtained by using the Newton-Raphson method. In addition, the frequency-/force-response curves under different vertical stiffness are provided to study the nonlinear dynamic behaviors of the elastically supported model. To validate the theoretical analyses, the Runge-Kutta method is applied to obtain the numerical solutions. Finally, some interesting conclusions are drawn

Damage Localization in Ambient Vibration by Constructing Proportional Flexibility Matrix

Damage Localization Approaches based on Changes of Flexibilities Constitute an Important Technique for Damage Detection. However, the Unavailability of Flexibility Matrix with Output-Only Data Makes Flexibility-Based Approaches Not Really Applicable in the Very Important Cases of Ambient Vibrations. an Algorithm is Presented to Construct a Proportional Flexibility Matrix (PFM) from a Set of Arbitrarily Scaled Tested Modal Shapes and Modal Frequencies. the Constructed PFM is Just within a Scalar Multiplier to the Real Flexibility Matrix, and the Scalar Multiplier is Theoretically the First Modal Mass, Which is Undetermined Before the Mode is Properly Scaled. Instead of Real Flexibilities, the PFMs Are Incorporated into the Damage Locating Vectors (DLV) Method for Damage Localizations in Ambient Vibrations. PFMs for the Pre- and Post-Damaged Structure Need to Be Comparable Before Being Integrated into the DLV Procedure. This Requirement is Guaranteed When There is at Least One Reference Degree with Unchanged Mass after Damage. Two Numerical Examples Show that a Small Number of Measured Modes Can Produce PFMs with Sufficient Accuracy to Correctly Locate the Damages by the DLV Method from Output-Only Data. © 2004 Elsevier Ltd. All Rights Reserved

An Improved Optimal Elemental Method for Updating Finite Element Models

The Optimal Matrix Method and Optimal Elemental Method Used to Update Finite Element Models May Not Provide Accurate Results. This Situation Occurs When the Test Modal Model is Incomplete, as is Often the Case in Practice. an Improved Optimal Elemental Method is Presented that Defines a New Objective Function, and as a Byproduct, Circumvents the Need for Mass Normalized Modal Shapes, Which Are Also Not Readily Available in Practice. to Solve the Group of Nonlinear Equations Created by the Improved Optimal Method, the Lagrange Multiplier Method and Matlab Function Fmincon Are Employed. to Deal with Actual Complex Structures, the Float-Encoding Genetic Algorithm (FGA) is Introduced to Enhance the Capability of the Improved Method. Two Examples, a 7-Degree of Freedom (DOF) Mass-Spring System and a 53-DOF Planar Frame, Respectively, Are Updated using the Improved Method. the Example Results Demonstrate the Advantages of the Improved Method over Existing Optimal Methods and Show that the Genetic Algorithm is an Effective Way to Update the Models Used for Actual Complex Structures

Revealing Bluff-Body Aerodynamics on Low-Rise Buildings under Tornadic Winds using Numerical Laboratory Tornado Simulator

Tornadoes result in death and property loss in communities around the world. To quantify the actions of tornadoes on civil structures, researchers have built physical laboratory tornado simulators to simulate tornadoes in the lab environment and tested building models in the simulated tornadic wind field, which is similar to wind tunnel testing when quantifying the wind effects induced by straight-line winds. Unfortunately, physical tornado simulators are much less common than straight-line wind tunnels, leading to the lack of research on bluff-body aerodynamics on civil structures under tornadic winds. Considering that it is expensive to conduct experimental testing in physical tornado simulators, numerical models of physical tornado simulator has been developed using computational fluid dynamics (CFD) simulations. However, they have not been validated at the level of pressure distribution on the structural surface of the testing model. In this study, the numerical model developed for the large-scale tornado simulator of the Missouri University of Science and Technology (Missouri S&T), which is based on the numerical simulation of the entire process of the physical testing in tornado simulator, will be validated by the measured data on the building model tested in the physical tornado simulator. Then, through the validated numerical simulation model, the bluff-body aerodynamics of buildings under tornadic winds will be revealed. To be specific, CFD simulation is first applied to model the entire process of experimental testing of a low-rise building model in the physical tornado simulator. Then, the obtained results are compared with laboratory-measured data to evaluate the effects of the building model on the wind field and the surface pressure on the building model. Then, the bluff-body aerodynamics on low-rise buildings under tornadic winds will be revealed based on the data obtained from numerical simulations using the relationship between streamline pattern change and velocity magnitude change (mass continuity theorem) and using the relationship between the velocity magnitude change and the pressure change (Bernoulli\u27s theorem), as well as the flow separation and vortex shedding