Structures are always exposed to the surrounding environment. The environmental variability (especially fluctuation in temperature) creates noticeable variations in structural modal properties. Two major mechanisms from temperature can cause uncertainties in natural frequency and mode shape measurements: i) the changes of material properties (elastic modulus) by temperature variation, and ii) the stress stiffening effects by temperature induced axial loading. Also, changes of boundary condition may cause variation in modal properties as well. In model updating, not considering these environmental effects may cause false identification on structural damage, thus compromises the accuracy of the updating results. This study presents a finite element model updating technique which can address the issue of varying environment including temperature variation and boundary condition changes. Temperature and boundary condition information is incorporated into the stiffness formulation of the finite element model. A numerical study on updating a bridge model subjected to damage and environmental changes is presented to demonstrate the effectiveness of the proposed method.
Changes in environmental conditions (such as temperature and humidity) and boundary conditions have been observed to have significant impact on structure's dynamic properties [1-6]. In general, environmental factors affect structures in a complicated manner such that it may result in support movement to strengthen or weaken the constraints [6]. Such changes of boundary conditions also can lead to significant variation of structure’s modal properties. However, few studies have considered the existence of both temperature and boundary condition as the combined contributing factors in changing structure’s dynamic properties.
This paper proposes a numerical study to analyze structure’s dynamic properties under combined influence of temperature and boundary condition. A beam finite element model that can consider the changes in both temperature and boundary condition is established. Numerical study is conducted to reveal the relationship between the variation of the beam’s dynamic properties and the changes of its boundary condition as well as ambient temperature. The obtained conclusion will provide insights of the influence of these two factors on future dynamic based structural health monitoring studies.
In performing an effective structural analysis for wind turbine, the simulation of turbine aerodynamic loads is of great importance. The interaction between the wake flow and the blades may impact turbine blades loading condition, energy yield and operational behavior. Direct experimental measurement of wind flow field and wind profiles around wind turbines is very helpful to support the wind turbine design. However, with the growth of the size of wind turbines for higher energy output, it is not convenient to obtain all the desired data in wind-tunnel and field tests. In this paper, firstly the modeling of dynamic responses of large-span wind turbine blades will consider nonlinear aeroelastic effects. A strain-based geometrically nonlinear beam formulation will be used for the basic structural dynamic modeling, which will be coupled with unsteady aerodynamic equations and rigid-body rotations of the rotor. Full wind turbines can be modeled by using the multi-connected beams. Then, a hybrid simulation experimental framework is proposed to potentially address this issue. The aerodynamic-dominant components, such as the turbine blades and rotor, are simulated as numerical components using the nonlinear aeroelastic model; while the turbine tower, where the collapse of failure may occur under high level of wind load, is simulated separately as the physical component. With the proposed framework, dynamic behavior of NREL’s 5MW wind turbine blades will be studied and correlated with available numerical data. The current work will be the basis of the authors’ further studies on flow control and hazard mitigation on wind turbine blades and towers.
Identification of the changes in the properties of a structure are a potential indication of damage in that structure. In
nonlinear systems, hysteretic models are often used to represent structural deterioration as well. Thus, the updating of
such nonlinear hysteretic models using measured responses from a monitoring system is one approach to identify
structural properties and thus damage. Nonlinear observer theory provides the tools to update such models, potentially
online and in real-time. This paper examines several nonlinear observers that can be applied as online hysteretic model
updating tools, and compares the results by using a Bouc-Wen model updating case. The online updating feature also
demonstrates the potential application in providing state feedback to nonlinear structural control.
Civil engineering structural systems exhibit hysteretic behavior when under extreme loading conditions as well as when
energy dissipation devices are employed. To investigate the optimal control strategy for reducing the system response
under random excitations (earthquakes, wind gust or sea waves), a general control solution is proposed in this paper.
The approach considers the solution of the Hamilton-Jacobi-Bellman equation for general nonlinear stochastic systems,
under the assumption that the evolution of the state of the stochastic system can be described by a Markov diffusion
process. Several numerical examples are provided to verify the efficacy of the optimal control solution obtained from the
proposed method. First, a linear oscillator is used to verify that the obtained solution is indeed the optimal solution by
comparing it to the closed form solution. Then the proposed method is applied to several nonlinear systems including
Van der Pol and Duffing oscillators and a Bouc-Wen system. In each case, optimality is demonstrated by comparing the
system responses and costs under optimal control with the ones obtained using linearized optimal control.
Conference Committee Involvement (8)
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2023
13 March 2023 | Long Beach, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
7 March 2022 | Long Beach, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
22 March 2021 | Online Only, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
27 April 2020 | Online Only, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
4 March 2019 | Denver, Colorado, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
5 March 2018 | Denver, Colorado, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
26 March 2017 | Portland, Oregon, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
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