Krzysztof Mendrok

Experimental verification of the damage localization procedure based on modal filtering

Modal filtering has numerous applications in the analysis of object dynamics. One possible use of this technique, recently presented in the literature, is damage detection. The method has several advantages but one major disadvantage — it does not provide any information about damage location. This article presents a solution that eliminates this drawback. The proposed method is tested first on a numerical example. Next, it is verified on the laboratory measurement data, and finally, it is applied to a real structure — a footbridge over a street in Krakow.

Load Identification Using a Modified Modal Filter Technique

In this paper the authors propose a modification to the known force identification procedure based on modal filtration. The modification consists of replacing the modal vectors with the Ritz vectors. The latter seem to be more accurate because they take into account the static deformation of the structure and are less sensitive to truncation error. After the main idea- the algorithm modification- is presented, it is verified and then compared with the original solution. Two sets of data are used for this purpose, firstly simulation data from the numerical model, and then physical data recorded during a laboratory experiment.

SHM System Based on Modal Filtration

The modal filter has various applications, among the others for damage detection. It was shown, that a structural modification (e.g. drop of stiffness due to a crack) causes an appearance of peaks on the output of the modal filter. This peaks result from not perfect modal filtration due to system local structural changes. That makes it a great indicator for damage detection, which has fallowing advantages: low computational afford due to the data reduction, the structural health monitoring system based on it, is easy to automate. Furthermore the system is theoretically insensitive to environmental changes as temperature or humidity variation (global structural changes do not cause a drop of modal filtration accuracy). In the paper the practical implementation of the presented technique is shown. The developed structural health monitoring (SHM) system is described as well as results of its extensive simulation and laboratory testing. Finally the application of the system for the structural changes detection on the airplane parts is presented..

An application of operational modal analysis in modal filtering

Modal filtration in the field of damage detection has many advantages, including: its autonomous operation (without the interaction of qualified staff), low computational cost and low sensitivity to changes in external conditions. However, the main drawback of this group of damage detection methods is its limited applicability to operational data. In this paper a method of modal filter formulation from the in-operational data is described. The basis for this approach is FRFs synthesis using knowledge of the operational modal model. For that purpose a method of operational mode shape scaling is described. This is based on the measurements of several FRFs of the object. The method is then applied to the construction of modal filters and modal filtration. Additionally, the study presents verification of the method using data obtained from simulation and laboratory experiments. Verification consisted of comparing the results of modal filtering based on classical experimental modal analysis with the results of the approach proposed in the work.

Modal Analysis of Bridges for the SHM Purposes

The paper presents problems of modal testing of large civil engineering objects like bridges or viaducts. Authors placed here the practical information, which need to be taken into account while planning and performing this type of measurements. Descriptions of 3 modal experiments with their results are shown. All measurements and analysis were performed for the structural health monitoring and damage assessment purposes. Particularly interesting is the third case, where authors tried to assess a damage level in the road viaduct without undamaged structure model.

Spatial Filter for Operational Deflection Shape Component Filtration

Modal filtration in the field of damage detection has many advantages, including: its autonomous operation (without the interaction of qualified staff), low computational cost and low sensitivity to changes in external conditions. However, the main drawback of this group of damage detection methods is its limited applicability to operational data. The modal filtration of the responses spectra (in place of FRFs), proposed in the literature, often does not give the expected results, working properly only for excitation in the form of white noise, or an ideal impulse. In other cases, for example in rotational machines, when in the response spectrum the rotational velocity harmonics dominate it can give wrong results. For such cases authors propose to use a new type of spatial filter, similar to modal filter with the difference that it has ability to filter the operational deflection shape components from the system response. Its application together with classical modal filter allows for damage detection using operational data with other type of excitation. The main assumption of the new spatial filter is the orthogonality of the filter coefficient vector to the operational deflection shape vector, it is then similar to the classical modal filter.

Applicaton of Modal Filtration for Damage Detection of Rotating Shaft

The paper describes a modification of the method which uses the modal filtration for damage detection [11] to make it suitable for rotating machinery. Authors have formulated a diagnostic procedure which is based on the output only data measured during object operation. The measurement can be performed both by accelerometers placed on the shaft bearing cages and directly on the shaft with use of the laser vibrometer. The procedure was verified on the experimental data. For the experimental verification authors have used the laboratory stand which allows simulation of different faults.

Operational Forces Identification From Helicopter Model In-Flight Data With Use of Inverted Regressive Parametric Models

The paper presents an attempt to identify forces acting on the control unit of a helicopter model during flight. The helicopter model will, according to the project assumptions, operate as an inspection robot i.e. it will autonomously fly in selected regions and monitor them with an embedded camera. It could be used for visual inspection of high masts or chimneys. Autonomous flying requires a sophisticated control system. The control unit is placed in an additional box hung under the fuselage. One of the stages of the unit development was examination of in-flight forces acting on the box and if it was necessary, a vibroinsulation selection. For this reason, an experiment was conducted. During the test, forces in the box suspension and accelerations in selected locations of the object were recorded. Having both, forces and responses in the form of vibrations accelerations, enabled to verify a force identification procedure. It is a procedure based on regressive parametric models inversion. The paper presents this method’s description and an attempt to apply it to the described forces identification.Copyright

Direct and Indirect Vibro-Acoustic Measurements for Road Noise NVH Predictions

This paper describes vibro-acoustic direct and indirect measurements for road noise NVH predictions from a complete car. Attention is devoted to the dynamic response of the structure and interior pressure field toward tire patch displacement inputs. The direct measurements exploited the Team Corporation CUBE™ high frequency 6 degree-of-freedom (DOF) shaker recently installed at the KULeuven Vehicle Technologies Laboratory; the input was provided directly at the tire contact patch, while the responses were measured as accelerations and pressures on the structure. In the indirect measurements a low-mid frequency volume velocity source (LMFVVS) was used to acoustically excite the structure in the reverse path direction from the inside of the interior car cavity, while accelerations on the car and forces/torques where acquired by a 6-DOF dynamometer at the tire patch. From both types of excitations Frequency Response Functions (FRF) were calculated in the frequency range [0–500 Hz]. The non-linearity of the full car system was investigated with different direct and indirect measurement tests, in order to assess the feasibility of the reciprocity principle in such a complex structure. Measurement set-ups, results and comparisons are described and discussed in detail.© 2005 ASME

Comparison of Different Methods of Ritz Vectors Extraction

Ritz vectors are parameters, which describe object dynamics in similar way as modal vectors. Their advantage with respect to modal vectors is a fact, that less number of them is required to estimate object response. It is also proofed, that Ritz vectors are more sensitive for damage detection then modal vectors. The problem which arises, when one wants to use Ritz vectors for damage assessment is that there are no many methods to extract Ritz vectors from operational data. In addition, the methods require knowledge of analytical mass matrix or state a space model matrix, which makes them rather complicated. In the paper two Ritz vectors extraction methods are taken into account. First bases on flexibility matrix and second is related with state space model. Both of them are evaluated with respect to analytical procedure of Ritz vectors calculation. For the vectors evaluation, a simulation data from theoretical model were used. In next step Ritz vectors were extracted from data measured on a real structure. On the structure damage was simulated. The Ritz vectors extracted with use of both tested methods were used to detect damage.