Impact identification and localization using a sample-force-dictionary - General Theory and its applications to beam structures

Ginsberg, Daniel,Fritzen, Claus-Peter Techno-Press 2016 Structural monitoring and maintenance Vol.3 No.3

Monitoring of impact loads is a very important technique in the field of structural health monitoring (SHM). However, in most cases it is not possible to measure impact events directly, so they need to be reconstructed. Impact load reconstruction refers to the problem of estimating an input to a dynamic system when the system output and the impulse response function are usually known. Generally this leads to a so called ill-posed inverse problem. It is reasonable to use prior knowledge of the force in order to develop more suitable reconstruction strategies and to increase accuracy. An impact event is characterized by a short time duration and a spatial concentration. Moreover the force time history of an impact has a specific shape, which also can be taken into account. In this contribution these properties of the external force are employed to create a sample-force-dictionary and thus to transform the ill-posed problem into a sparse recovery task. The sparse solution is acquired by solving a minimization problem known as basis pursuit denoising (BPDN). The reconstruction approach shown here is capable to estimate simultaneously the magnitude of the impact and the impact location, with a minimum number of accelerometers. The possibility of reconstructing the impact based on a noisy output signal is first demonstrated with simulated measurements of a simple beam structure. Then an experimental investigation of a real beam is performed.

Sparsity-constrained Extended Kalman Filter concept for damage localization and identification in mechanical structures

Ginsberg, Daniel,Fritzen, Claus-Peter,Loffeld, Otmar Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.21 No.6

Structural health monitoring (SHM) systems are necessary to achieve smart predictive maintenance and repair planning as well as they lead to a safe operation of mechanical structures. In the context of vibration-based SHM the measured structural responses are employed to draw conclusions about the structural integrity. This usually leads to a mathematically illposed inverse problem which needs regularization. The restriction of the solution set of this inverse problem by using prior information about the damage properties is advisable to obtain meaningful solutions. Compared to the undamaged state typically only a few local stiffness changes occur while the other areas remain unchanged. This change can be described by a sparse damage parameter vector. Such a sparse vector can be identified by employing $L_1$-regularization techniques. This paper presents a novel framework for damage parameter identification by combining sparse solution techniques with an Extended Kalman Filter. In order to ensure sparsity of the damage parameter vector the measurement equation is expanded by an additional nonlinear $L_1$-minimizing observation. This fictive measurement equation accomplishes stability of the Extended Kalman Filter and leads to a sparse estimation. For verification, a proof-of-concept example on a quadratic aluminum plate is presented.

Operational modal analysis for Canton Tower

Yan Niu,Claus-Peter Fritzen,Peter Kraemer 국제구조공학회 2012 Smart Structures and Systems, An International Jou Vol.10 No.4

The 610 m high Canton Tower (formerly named Guangzhou New Television Tower) is currently considered as a benchmark problem for structural health monitoring (SHM) of high-rise slender structures. In the benchmark study task I, a set of 24-hour ambient vibration measurement data has been available for the output-only system identification study. In this paper, the vector autoregressive models (ARV) method is adopted in the operational modal analysis (OMA) for this TV tower. The identified natural frequencies, damping ratios and mode shapes are presented and compared with the available results from some other research groups which used different methods, e.g., the data-driven stochastic subspace identification (SSIDATA) method, the enhanced frequency domain decomposition (EFDD) algorithm, and an improved modal identification method based on NExT-ERA technique. Furthermore, the environmental effects on the estimated modal parameters are also discussed.

Operational modal analysis for Canton Tower

Niu, Yan,Kraemer, Peter,Fritzen, Claus-Peter Techno-Press 2012 Smart Structures and Systems, An International Jou Vol.10 No.4

The 610 m high Canton Tower (formerly named Guangzhou New Television Tower) is currently considered as a benchmark problem for structural health monitoring (SHM) of high-rise slender structures. In the benchmark study task I, a set of 24-hour ambient vibration measurement data has been available for the output-only system identification study. In this paper, the vector autoregressive models (ARV) method is adopted in the operational modal analysis (OMA) for this TV tower. The identified natural frequencies, damping ratios and mode shapes are presented and compared with the available results from some other research groups which used different methods, e.g., the data-driven stochastic subspace identification (SSI-DATA) method, the enhanced frequency domain decomposition (EFDD) algorithm, and an improved modal identification method based on NExT-ERA technique. Furthermore, the environmental effects on the estimated modal parameters are also discussed.

자서전적 서사와 일본만화(mangá) : 『맨발의 겐(Gen Pés Descalços)』 에 대한 분석

( Ana Cristina Gonçalves ),( Celdon Fritzen ) 한국포르투갈-브라질학회 2007 포르투갈-브라질 연구 Vol.4 No.1

21 세기 들어, 자서전적 서사는 문학이론과 문학사와 같은 인문과학연구에 있어서 주요 연구대상이 되어왔다. 또한 자서전적 서사는 본 연구조사의 다음과 같은 이론의 틀을 제공해주었다. 즉, 자서전적 서사가 집단 혹은 개인적 기억의 회상 과정에서 어떠한 중요성을 지니고 있느냐 하는 것이었다. 본 연구는 바로 이러한 의문점에서 출발했으며, 가장 전통적인 서사형태라 할 수 있는 자서전적 서사가 어떻게 새로운 언어와 표현장르를 지닌 현대화된 서사형태로 거듭날 수 있었는지에 대한 것을 밝혀내고자 한다. 이러한 방식으로 본 연구는 히로시마 원자폭탄 투하 때 피폭을 당한 주인공의 이야기를 통해 주인공 자신의 개인적 기억을 넘어 그가 속한 집단적 기억의 회상을 다루고 있는 나카자와 케이지(Keiji Nakazawa)의 『맨발의 겐(Gen Pés Descalços)』 을 분석하여 새로운 예술장르 라 할 수 있는 일본만화 - ‘망가’(mangá) - 에 대해 살펴보았다. A narrativa autobiográfica tem sido, no último século, objeto de estudos das ciências humanas, da Teoria Literária e da História em particular. É ela também que nos serve de horizonte para a proposição de nosso problema de pesquisa: qual a importância que essa forma de discurso assume nos processos de elaboração da memória, seja ela coletiva ou particular? Essa questão motivou a realização deste trabalho, cujo intuito era poder aclarar como essa forma de comunicação tão primitiva se apresentava contemporaneamente, tendo em vista os novos suportes e linguagens que a modernização disponibilizou. Desse modo, propusemo-nos desenvolver essa problemática a partir da abordagem de um novo gênero da arte seqüencial - o mangá - por meio da investigação da obra de Keiji Nakazawa, Gen Pés Descalços que a partir do episódio da bomba de Hiroshima constrói uma memória que é tanto referência de um sujeito como também da coletividade em que ele se insere.

Computational aspects of guided wave based damage localization algorithms in flat anisotropic structures

Moll, Jochen,Torres-Arredondo, Miguel Angel,Fritzen, Claus-Peter Techno-Press 2012 Smart Structures and Systems, An International Jou Vol.10 No.3

Guided waves have shown a great potential for structural health monitoring (SHM) applications. In contrast to traditional non-destructive testing (NDT) methodologies, a key element of SHM approaches is the high process of automation. The monitoring system should decide autonomously whether the host structure is intact or not. A basic requirement for the realization of such a system is that the sensors are permanently installed on the host structure. Thus, baseline measurements become available that can be used for diagnostic purposes, i.e., damage detection, localization, etc. This paper contributes to guided wave-based inspection in anisotropic materials for SHM purposes. Therefore, computational strategies are described for both, the solution of the complex equations for wave propagation analysis in composite materials based on exact elasticity theory and the popular global matrix method, as well as the underlying equations of two active damage localization algorithms for anisotropic structures. The result of the global matrix method is an angular and frequency dependent wave velocity characteristic that is used subsequently in the localization procedures. Numerical simulations and experimental investigations through time-delay measurements are carried out in order to validate the proposed theoretical model. An exemplary case study including the calculation of dispersion curves and damage localization is conducted on an exemplary unidirectional composite structure where the ultrasonic signals processed in the localization step are simulated with the spectral element method. The proposed study demonstrates the capabilities of the proposed algorithms for accurate damage localization in anisotropic structures.

Computational aspects of guided wave based damage localization algorithms in flat anisotropic structures

Jochen Moll,Miguel Angel Torres-Arredondo,Claus-Peter Fritzen 국제구조공학회 2012 Smart Structures and Systems, An International Jou Vol.10 No.3

Guided waves have shown a great potential for structural health monitoring (SHM) applications. In contrast to traditional non-destructive testing (NDT) methodologies, a key element of SHM approaches is the high process of automation. The monitoring system should decide autonomously whether the host structure is intact or not. A basic requirement for the realization of such a system is that the sensors are permanently installed on the host structure. Thus, baseline measurements become available that can be used for diagnostic purposes, i.e., damage detection, localization, etc. This paper contributes to guided wave-based inspection in anisotropic materials for SHM purposes. Therefore, computational strategies are described for both, the solution of the complex equations for wave propagation analysis in composite materials based on exact elasticity theory and the popular global matrix method, as well as the underlying equations of two active damage localization algorithms for anisotropic structures. The result of the global matrix method is an angular and frequency dependent wave velocity characteristic that is used subsequently in the localization procedures. Numerical simulations and experimental investigations through time-delay measurements are carried out in order to validate the proposed theoretical model. An exemplary case study including the calculation of dispersion curves and damage localization is conducted on an exemplary unidirectional composite structure where the ultrasonic signals processed in the localization step are simulated with the spectral element method. The proposed study demonstrates the capabilities of the proposed algorithms for accurate damage localization in anisotropic structures.