Modal Testing and Modal Analysis​​​​​​​Structural dynamics testing and analysis solution

Modal Testing
Application Overview

Modal testing and the acquired test data are the basis for performing modal analysis and making conclusions on the structural dynamics of test objects. The natural frequencies of the system, modal damping ratios, and mode shapes of the object under test can be determined.

You can perform modal testing with either applied artificial excitation sources, to induce the test object to vibrate, or by having the test object running under operational conditions, and measure the in-situ vibration.

Modal testing is used for:

• Troubleshooting: To reduce excessive vibration levels or to ensure resonances are kept away from excitation frequencies.

• Simulation of “what if ” scenarios: Determination of forces or response to complex excitation.

• Structural assembly analysis: To predict the dynamic characteristics of assembled subcomponents.

• Refinement of Finite Element Model (FEM): Validation by testing on prototypes or refinement of the FE analytical model by inclusion of damping.

Applications
For Modal Testing and Analysis

Modal analysis is heavily used in civil engineering and industries such as aerospace and automotive, across a vast range of applications including:

• Ensuring that resonances are separated from excitation frequencies

• Prediction of the dynamic behavior of components and assembled structures

• Optimization of the structure’s dynamic properties (mass, stiffness, damping)

• Prediction of the responses due to complex excitation

• Inclusion of damping in Finite Element Models

• Damage detection and assessment

MIMO Method
Multi-input Multi-output

Multi-shaker tests are normally performed with many accelerometer sensors. Dewesoft modal testing suite allows you to excite complex structures by using multiple shakers and to measure and analyze on a virtually unlimited number of channels. 

MIMO measurement techniques are proven and well-established methods for collecting FRF data sets. They offer some distinct advantages for the measurement and extraction of basic modal parameters especially while testing larger structures. 

The main advantage of using multiple shakers is that the input-force energy is distributed over more locations on the structure. This provides a more uniform vibration response over the structure, especially in cases of large and complex structures and structures with heavy damping. 

Random, burst random and sine sweep excitation signals are configured directly in the Modal Test setup screen using the Function generator, and you can use MCOH (multiple coherence) to validate your shaker setting.

Instrumentation
Modal Testing Equipment

Several instruments are typically used to perform Modal Test and Modal Analysis:

• One or more exciters, such as modal shakers or an impact hammer

• Force transducers that acquire the input excitation signals

• Accelerometers that acquire the output response signals

• A data acquisition system (DAQ) device to record the test

• A computer with Modal Test and Analysis software to perform calculations, display the results and create reports

Dewesoft can provide turn-key modal testing and modal analysis solutions with all the components above. See the details of available modal testing hardware below.

Modal Shakers
Vibration Shakers for Modal Testing

If high-frequency excitation content or signal-controlled testing is desired, then modal shakers are the only excitation solution. Dewesoft modal shakers are lightweight and powerful. They can operate up to 15,000 Hz, and provide force levels up to 440N with a maximum 25mm stroke.

Advantages:

• Modal stinger can be easily adjusted by the through-hole armature

• Lightweight, durable, portable, and easy to use

• The adjustable trunnion base provides high flexibility

• Up to 25mm stroke and broad frequency range

Dewesoft modal shakers can be used for Modal testing and Structural Dynamics. The series of Dewesoft modal shakers covers a wide range of structures for dynamic characterization from electronic boards and sub-components to machinery, vehicles, and aircraft, even constructions

Simple Setup
Autofill Configuration

Whenever a high number of measured channels is used, adding and removing the excitation and response channels process is made simple with autofill setup functionality. 

Autofill functionality is enabled for:

• Autofill for uniaxial and triaxial sensors (response channels)

• Start node index and index increment selection

• Defining the direction and sign of added channels

• Grouping sensors and defining the number of groups

Stunning Visuals
3D Geometry With Animation

3D geometry with animation is perfectly integrated into both the Modal Test and Modal Analysis modules and provides everything needed to build a 3D model of your structures. 

With the geometry editor, you can quickly draw simple 3D structures as well as import more complex models using the UNV file format. The geometry of the measured structure is defined by objects, lines, or points. The geometry editor supports cartesian and cylindrical coordinate systems, ideal for drawing circular objects.

Structures can be animated at a single frequency in all three directions with the interpolation of non-measured points. You have the ability to animate different mode shapes and compare deflections with the non-excited structure shape. This gives a thorough visual representation of the structural dynamics.

The color of the points changes during the measurement for easier identification of the excitation and response points. The structure geometry can be rendered in different projections:

• 3D perspective

• 3D orthographic

• Several 2D projections

Post Processing
With Stored Raw Data

DewesoftX data acquisition software always stores raw values of the measured data. This enables offline calculations using the raw signals from the accelerometers and hammer (or shaker) excitation points.

This is very convenient if some additional calculations need to be performed without the need for repeating the entire modal test setup.

Export Data
For Further Analysis

All measured data can be exported to a variety of standard file formats. The most common and standard data formats available include UNV/UFF, Diadem, Matlab, Excel, and Text (CSV). But DewesoftX includes even more formats. 

Transfer functions 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, etc., or various other data. We include a modified UNV/UFF export made especially for modal tests.

See the complete list of supported export file formats.

Operating Deflection Shapes (ODS)

Operating Deflection Shapes (ODS) is a simple way to do dynamic analysis and see how a machine or a structure moves within its operational conditions. ODS tests have no applied artificial forces and only response vibration signals are measured. 

In ODS analysis the structure is only excited by the machine itself, as in real operation. Frequency ODS is the simplest method to see how a machine or structure moves during its operation, at a specific frequency.

The DewesoftX Modal suite supports ODS testing. With Frequency ODS one of the acceleration sensors has to be defined as an excitation reference signal and the other sensors as response sensors. Animation can be displayed as usual, but it works best only in areas with good coherence.

ODS is used successfully for machine conditioning monitoring and in civil engineering applications like bridges, buildings, and other structures that are difficult to excite with artificial forces.

Great Investment
Future-Proof Application

Dewesoft modal testing and modal analysis are a great investment in your future. Our solutions are constantly being improved, and new features are being added all the time. All updates to the modal testing software suite are free of charge.

Our industry-leading 7-year warranty on Dewesoft data acquisition systems means worry-free measurements for you. We are committed to ensuring that your investment in our measurement equipment was a good one - even when the unexpected occurs. 

Together with world-class data acquisition technology, Dewesoft provides the best Modal testing and modal analysis solution your money can buy.