Upcoming New Module – Experimental Modal Analysis
In ARTeMIS Modal 6.0, planned for a release in the second quarter of 2018, we are introducing a new module for Experimental Modal Analysis (EMA). The new module will support both hammer and shaker tests that deploy Frequency Response Functions (FRFs) obtained in one of the following ways:
- Direct uploading of the FRF’s from Universal File Format. In this case, some of ARTeMIS Modal tasks are either hidden or simplified. This also count for the Prepare Data Task as there is no signal processing to do.
- Upload of simultaneously measured input and output time histories into the Manage Measurement Task, then followed by the estimation of the FRF’s using either H1, H2 or Hv estimators. This is accomplished in the Prepare Data Task.
- Use the ARTeMIS Modal data acquisition plugins to measure input and output simultaneously then followed by the estimation of the FRF’s using either H1, H2 or Hv estimators as in (2).
Below a preview of this new module can be seen.
Experimental Modal Analysis of an Audi TT Car Body
The experimental tests presented here has been conducted at TH Ingolstadt, Faculty of Mechanical Engineering, Germany under the guidance of Professor J. Bienert, who is gratefully acknowledged.
The experimental campaign consist of impact (hammer) testing of an Audi TT car body, see a picture depicted below.
The car body was mounted free on four air cushions. Four references respectively impact points were excited with 14 accelerometers as responses. The data acquisition and processing of the FRF’s were made with a 24-channel data acquisition system. The FRF’s were stored in the four separate Universal File Format Files (Audi_TT_FRF_runX.unv) along with a test geometry in its own file (Audi_TT.unv).
Importing FRF’s into ARTeMIS Modal
Importing the FRF’s into ARTeMIS Modal starts with creating a new project using Universal File Format, which is illustrated in the picture below.
Once the files are uploaded, the geometry and FRF’s can be seen in the simplified Prepare Data task. The Data Organizer contains all four impact tests listed below each other, and the Geometry window visualize the positions and the directions of the response and reference channels. All the impact positions can be viewed by selecting the first item, All Test Setup, in the Data Organizer, illustrated below.
The 14 response accelerometers are seen in blue, and the impact positions, indicated by a hammer symbol, are colored green.
Estimating Modes using Rational Fraction Polynomial – Z Domain
The modal parameters of the car body are computed with a Rational Fraction Polynomial estimator working in Z-domain. This estimator has been developed in cooperation with Politecnico di Torino, Dynamics and Identification Research Group (DIRG) at Department of Mechanical and Aerospace Engineering, Italy, the I4S Team at Inria, France and Aalborg University, Department of Civil Engineering, Denmark.
The estimator has been adapted, so it is operated in nearly the same way as the Stochastic Subspace Identification methods used for Operational Modal Analysis in ARTeMIS Modal.
The work flow is as follows:
- Select a maximum model order to initialize the estimation of the system matrices of the highest dimension for the subsequent computation of a lower model orders.
- Select the desired frequency band.
- Select a specific range of the model orders by dragging the mouse down on the stabilization diagram, or simply click the Estimate Models button to estimate all the model orders.
- Stable modes are found by a study of the natural frequencies, damping ratios and mode shapes (MAC and maximum modal complexity).
- Global modes are estimated based on the stable modes.
The figure below illustrates the analysis of the experimental test of the Audi TT in the frequency range from around 4 Hz up to 140 Hz. Maximum model order was set to 80, however only models up to 60 were estimated.
Validating Modes with Other Estimators
The modes obtained from the RFP-Z estimator are validated using the standard tools available in ARTeMIS Modal. By selecting the Validation Task, the modes can be compared with the other estimators as well as imported results from any other modal analysis tools. Below we are comparing the RFP-Z modes with the modes obtained with a simple peak-picking tool already available in ARTeMIS Modal. It is based on the peak picking on the Complex Mode Indicator Function (CMIF).
We would appreciate your help!
If you are interested in helping us with testing the new EMA module, please contact us at firstname.lastname@example.org.
International Modal Analysis Conference (IMAC XXXVI)
We will be presenting the new RFP-Z estimator at the International Modal Analysis Conference (IMAC XXXVI) on February 12-15, 2018 in Orlando, Florida. See you in booth 213!
Next User Training Course – Sign Up Deadline is March 1, 2018
The next user training course will take place in Lisbon, Portugal, on May 7-8, 2018.
This 2-day course is for the new as well as experienced users that would like to be updated on Operational Modal Analysis technology as well as the latest features of ARTeMIS Operational Modal Analysis software.
The course will be held on May 7-8, 2018 at Hotel SANA Rex in Lisbon, Portugal. Both days we start at 9.30 and end at 17.00 on the first day and at 16.00 on the second. There will be lunch and coffee breaks during the day and free WiFi internet access. The course instructor is Dr. Palle Andersen, CEO at Structural Vibration Solutions A/S.
On day 1, you will get a comprehensive introduction to Operational Modal Analysis technology in general. During this introduction, the differences to the well-known input/output modal analysis will be described. Also the procedures for acquiring high quality measurements will be discussed in detail. We will help each other acquiring good measurements of different demo structures. The introduction is followed by a presentation of the user-friendly Frequency Domain Decomposition (FDD) technique, and we will analyze the acquired measurements as hands-on exercises. Finally, the two other FDD related techniques of ARTeMIS (Enhanced Frequency Domain Decomposition and Curve-fit Frequency Domain Decomposition) are introduced, and we will continue with hands-on exercises using these techniques.
You will get course material as well as a 1-month free demo version of the ARTeMIS Modal Pro which we invite you to install on your own laptop for use during the hands-on exercises of the course.
Attending the course will cost 750 EUR per person. Students get 50% discount.