Sven Oliver Klinkel

Experimental identification of an elasto-mechanical multi-degree-of-freedom-system using stochastic signals

The determination of dynamic parameters are the central points of the system identification of civil engineering structures under dynamic loading. This paper first gives a brief summary of the recent developments of the system identification methods in civil engineering and describes mathematical models, which enable the identification of the necessary parameters using only stochastic input signals. Relevant methods for this identification use Frequency Domain Decomposition (FDD), Autoregressive Moving Average Models (ARMA) and the Autoregressive Models with eXogenous input (ARX). In a first step an elasto-mechanical mdof-system is numerically modeled using FEM and afterwards tested numerically by above mentioned identification methods using stochastic signals. During the second campaign, dynamic measurements are conducted experimentally on a real 7-story RC-building with ambient signal input using sensors. The results are successfully for the relevant system identification methods.

Experimental Incremental System Identification Method Using Separate Time Windows on Basis of Ambient Signals

Experimental system identification methods, such as Frequency Domain Decomposition (FDD), Autoregressive Moving Average Model (ARMA), Autoregressive Models with eXogenous input (ARX), Kalman Filter and Stochastic Subspace Identification (SSI), are commonly used in civil engineering to determine dynamic parameters of existing structures. Basis for these methods are in-situ measurements, which can be very time-consuming and cost-intensive depending on the complexity of the structure. This paper investigates the possibility to reduce the in-situ measurement effort by introducing a new method, which bases on incremental measurements by using only a single sensor in separate time windows. The proposed incremental identification method (IIM) requires stationary ergodic response signals of the structure induced by ambient vibrations with white noise density. Therefore, after each incremental measurement a quality-check of the response signal should be conducted to verify the applicability of the theory. This approach ensures the comparability of the input signals with each other and thus the reproducibility of the identified dynamic behavior. For this purpose, a signal evaluation criterion is defined. For low-quality data, which cannot satisfy this criterion, special signal processing methods have to be applied. With the signals, which already accomplish the evaluation criterion, the identification of the system parameter can then be carried out by using one of the above mentioned system identification methods, such as FDD. The IIM is applied so far both on numerical and experimental examples. In this paper the validation of the IIM is reached by identifying the parameters of the IASC-ASCE Structural Health Monitoring Benchmark Problem for different ambient simulated input signals.

A method for the elimination of shear locking effects in an isogeometric Reissner-Mindlin shell formulation

This contributions discusses the simulation of magnetothermal effects in superconducting magnets as used in particle accelerators. An iterative coupling scheme using reduced order models between a magnetothermal partial differential model and an electrical lumped-element circuit is demonstrated. The multiphysics, multirate and multiscale problem requires a consistent formulation and framework to tackle the challenging transient effects occurring at both system and device level.Micro Abstract Shell elements for slender structures based on a Reissner-Mindlin approach struggle in pure bending problems. The stiffness of such structures is overestimated due to the transversal shear locking effect. Here, an isogeometric Reissner-Mindlin shell element is presented, which uses adjusted control meshes for the displacements and rotations in order to create a conforming interpolation of the pure bending compatibility requirement. The method is tested for standard numerical examples.Powered by TCPDF (www.tcpdf.org) This material is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. Niiranen, Jarkko; Khakalo, Sergei; Balobanov, Viacheslav

An isogeometric Reissner-Mindlin shell element for dynamic analysis considering geometric and material nonlinearities

The present approach deals with the dynamical analysis of thin structures using an isogeometric Reissner-Mindlin shell formulation. Here, a consistent and a lumped mass matrix are employed for the implicit time integration method. The formulation allows for large displacements and finite rotations. The Rodrigues formula, which incorporates the axial vector is used for the rotational description. It necessitates an interpolation of the director vector in the current configuration. Two concept for the interpolation of the director vector are presented. They are denoted as continuous interpolation method and discrete interpolation method. The shell formulation is based on the assumption of zero stress in thickness direction. In the present formulation an interface to 3D nonlinear material laws is used. It leads to an iterative procedure at each integration point. Here, a J2 plasticity material law is implemented. The suitability of the developed shell formulation for natural frequency analysis is demonstrated in numerical examples. Transient problems undergoing large deformations in combination with nonlinear material behavior are analyzed. The effectiveness, robustness and superior accuracy of the two interpolation methods of the shell director vector are investigated and are compared to numerical reference solutions.