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Modal Analysis

Dewesoft provides an efficient solution for the modal test, time for setup and measurement is very short. Import or draw the geometry, perform the measurement and animate the structure.

Strain / Stress
Strain / Stress
High-speed video
High-speed video

Main Features

  • FREQUENCY RESPONSE FUNCTION (FRF): describe the ratio between input and output of any system in the frequency domain
  • EXCITATION AND RESPONSE SPECTRA, WINDOWING: separately adjust the window length of excitation and response in order to reduce the influence of noise appearing after the event of interest
  • IMPACT HAMMER OPERATION MODE:  impulse signal is used for excitation (wide frequency spectrum )
  • SHAKER OPERATION MODE: the structure is excited by a shaker which sweeps through the frequencies
  • OPERATING DEFLECTION SHAPES:  ODS is the simplest way to see how a machine or structure moves during its operation, at a specific frequency or moment in time
  • SISO, SIMO, MISO, RESPONSE GROUP ALIGNMENT: single input - single output, single input - multiple output, multiple input - single output
  • MULTI-REFERENCE MODAL TESTAdd multiple excitations and multiple response channels at the same time
  • GEOMETRY ANIMATION AND PROJECTIONS: animate the geometry in all three directions and with different projections
  • MODE INDICATOR FUNCTION (MIF): calculate the MIF for each axis (X, Y, Z) separately
  • MODAL CIRCLE: calculate damping factor (viscous or structural) with circle fit method
  • MERGE DATAFILES: combine data files from separate measurements
  • EXPORT TO MEscope: export time domain or frequency domain signals to MEscope for advanced modal analysis (OMA, time domain ODS)

Multireference Modal Test

Multi-reference testing is required in cases where the structure has more modes with the same resonance frequency. This is often referred to as ‘repeated roots’, where ‘roots’ refer to the solutions to the characteristic equation giving the frequency and damping values of the structure. This is, for example, the case for certain symmetrical structures.

Add multiple excitations and multiple response channels at the same time (example: triaxial responses and excitation in all three directions in one data file).

Autofill for Fast Input and Setup

In case of a high number of channels, the adding and removing of the excitation and response channels is easy and fast with autofill setup.

  • Autofill for uniaxial and triaxial sensors (response channels)
  • Start node index and index increment selection
  • Define the direction and sign of added channels
  • Group the sensors and define the number of groups

Auto-generated Screens

For an easier start, Dewesoft X software offers auto-generated displays, which already come with the most often used instruments and an arrangement that makes sense according to the type of application. 

One screen is generated for the acquisition and one is generated especially for analysis

Geometry Animation and Projection

In Dewesoft X software, you can quickly draw simple structures, as well as import more complex ones (UNV file format). Cartesian and cylindrical coordinate system are supported, which is great for drawing circular objects.

The FRF animation is done by putting sine functions with the amplitudes and phases from the measurement into the geometry model points. You can animate the structure for a single frequency, which can be chosen in the 2D graph.  

Animation can be done at a selected frequency in all three directions. During the measurement, the color of the points is changing, for easier identification of excitation point and response points.

The structure can be shown in different projections (3D perspective, 3D orthographic and several 2D projections).


Merge Several Data Files

Record one data file for each point or group. You can easily merge separate data files into one and animate the structure and observe the behavior.

Each transfer function contains information about response node, response direction, reference node and reference direction.


Operating Deflection Shapes (ODS)

In ODS analysis the structure is only excited by the machine, like in real operation, whenever it is not possible to vary the excitation frequency. Operating Deflection Shape (ODS) is the simplest way to see how a machine or structure moves during its operation, at a specific frequency or moment in time. There are only accelerometers used.

Inside Dewesoft X modal test module, one of the acceleration sensors has to be defined as excitation (this one is the reference, normalized to 1), the others as a response. Animation can be displayed as usual but only makes sense in areas with good coherence.

Exporting Data

After the measurement is done the data can be exported to a lot of different file formats, e.g. UNV/UFF, Diadem, Matlab, Excel, Text... The transfer function can be separately exported by Real, Imag, Ampl or Phase part.

The Universal File Format (also known as UFF or UNV format) is very common in modal analysis. Depending on the header, it can contain either transfer functions, coherence, geometry, ... or various other data. We modified the  UNV/UFF export, especially for the modal test.

Advanced Modal Analysis

With ME’scope, you can import or directly acquire multi-channel time or frequency data from a machine or structure, and post-process it. Its industry-leading interactive 3D animation allows you to observe order-related operating deflection shapes from running machinery, resonant vibration and mode shapes from real structures, acoustic shapes, and engineering shapes directly from acquired data. 

OMA - Operational Modal Analysis

The operational modal analysis is used for large civil engineering structures, operating machinery or other structures, making use of their output response only. These structures are always loaded by natural loads that cannot easily be controlled and measured, for instance, waves load (offshore structures), the wind loads (buildings) or traffic loads (bridges).

It is very difficult to excite large structures by artificial means. So OMA is more economical and fast and endowed by nature with characteristics of multiple-input/multiple-output (MIMO). It could be used to distinguish closely coupled modes. Moreover, all the measured responses come under an operational state of structures, and their real dynamic characteristics in operation could be revealed, so OMA is very suitable for health monitoring and damage detection of large-scale structures.

Free Online Training

You can learn more about modal testing at Dewesoft PRO online training by navigating to the Modal Test PRO training course.

Dewesoft PRO training is a free online training for measurement professionals. Learn how to measure signals, data processing and how to use Dewesoft products. Online PRO training is completely free.

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