## Структурный анализ

# Main features

- Frequency response function (FRF)
- Coherence
- Excitation and response spectra, windowing
- Double hit detection
- Reject hits

- Averaging of hits
- SISO, MISO, SIMO, Response group alignment
- Mode indicator function (MIF)
- Circle-fit method for extracting modal
- parameters (to check with simulation)

## MODAL ANALYSIS, IMPACT TEST

DEWESoft provides an efficient solution, time for setup and measurement is very short. The structure can be imported or drawn in the geometry editor, hereby the points are defined. For measurement move the modal hammer or the response accelerometers, whatever you prefer. In analyse mode click on the resonant frequencies and check the animated shape.

MODAL ANALYSIS, SWEEP SINE

For a running FRF the structure is usually excited with a shaker. For bigger structures DEWESoft supports the generation of multiple shaker signals (amplitude, phase, waveform and frequency). Shaker control have to be done externally.

DEWESoft® offers an integrated function generator (OPT-FGEN), which is fully software controlled. Various time patterns like fixed, sweep, step sweep, burst, chirp, noise and arbitrary table are configurable. Alternatively the FRF also works when the shaker is remotely controlled.

LARGE STRUCTURES, HIGH CHANNEL COUNT

For a running FRF the structure is usually excited with a shaker. For bigger structures DEWESoft® supports the generation of multiple shaker signals (amplitude, phase, waveform and frequency). Shaker control have to be done externally.

DEWESoft® offers an integrated function generator, which is fully software controlled. Various time patterns like fixed, sweep, step sweep, burst, chirp, noise and arbitrary table are configurable. Alternatively the FRF also works when the shaker is remotely controlled.

OPERATING DEFLECTION SHAPES (ODS)

The spectral ODS measurement is useful wherever it‘s not possible to measure the excitation source, and the structure is excited by the machine and it‘s operation state(s).

SHOCK AND DROP TESTS (SRS)

The Shock response spectrum (SRS) shows the maximum responses of a series of uniformly damped single degree-of-freedom (SDOF) systems caused by a shock waveform applied on the structure. After setting damping, resolution (1/3, 1/6, 1/12, 1/24, 1/48 octave) and primary section, the spectra are calculated out of the time domain signals. After the time domain signals are recorded, the data is analysed by the DEWESoft® SRS plugin. The simple user interface offers a convenient straight forward procedure for fast results.

BUMP TEST

This is a quick test done to determine the resonance (natural) frequencies of a structure. No modal hammer is need- ed, only one accelerometer, just knock on the structure. Of course the impact tip influences the usable frequency range, but for a quantification measurement this is fine.

With the FFT Analyser the FFT spectra over a certain time window (impact +/- pre/post time) can be averaged.

SHORT-TIME FFT

High frequency bursts are almost impossible to accurately analyse by standard FFT, because the calculation takes too long (during calculation the signal is quickly changing). For this reason DEWESoft® mathematics offers the STFT - short term Fourier transform, which can have smaller blocks but still the same resolution as standard FFT. Therefore it’s much faster.

FINITE ELEMENT ANALYSIS

For further investigation and analysis in modal packages, like ME-Scope, the FRF complex data (Real/Imag/Ampl/ Phase), coherence, excitation and responses can be exported to the UFF (Universal File Format).

# DS-MODAL: advanced modal analysis

**DS-MODAL** is a powerful post-processing software for big and more complex structures with highly dedicated algorithms for easy automatic modal parameter identification. It features **OMA** (Operational Modal Analysis), **MIMO** (Multiple references) and **ODS** (Operational Deflection Shapes) modal analysis.

# Main applications

In addition to the existing DSA package, which covers basic hammer/shaker EMA and ODS, DEWESoft now offers a powerful, but easy-to-use advanced modal analysis software. The data is acquired in DEWESoft, then exported to DS-MODAL by the Universal File Format (UFF).

This enables you to analyse more complex structures like car chas- sis, ship hulls or any freeform surfaces with mode shapes in dif- ferent axis, by the use of multiple references.

Big structures, such as ships, planes, bridges and buildings, where artificial excitation is not possible, can be analysed using the OMA principle.

For exciting large structures a high number of response channels is needed. With the modular concept of DEWESoft, synchronisation of multiple systems is very easy.

From 8 channel instruments with USB interface up to 128 channels with a high performance industrial computer integrated in one box and data transferred over Ethernet (OPT-NET).

**Engines, turbines, compressors, pumps** or any other mechanical components need to be validated experimentally before to guarantee safe operation. Critical resonances are best identified in early stage, along with the development process.

With the compact, mobile form factor of our instruments applications also reach into **diagnostics, troubleshooting and on-site tests**.

# Features

## GEOMETRY EDITOR

The mechanical structure is drawn by use of the geometry modelling interface. You can create lines, cubes, ellipses, cylinders, spheres, ... or enter coordinates in a table. Select from different coordinate systems like cartesian, cylindrical and spherical. Points can be linked by equations. It is also possible to import structures (UFF or IGES format).

## ODS

The Operational Deflection Shape measurement is useful wherever it‘s not possible to measure the excitation force, and the structure is excited by the machine operation.

With time-domain ODS the natural movement of the structure can be replayed, in frequency-domain ODS the MIF identifies resonances.

## DETECT CLOSE SPACED, REPEATED MODES

When dealing with a symmetric structure, e.g. the left and right wing of an airplane, close spaced modes (also repeated modes) will appear.

Multiple references, as used in MIMO or OMA technique, and special algorithms are need- ed to separate them and get the full picture of movement behaviour.

# Mode identification & validation

## EMA & OMA BROADBAND

**Operational Modal Analysis (OMA)** is performed whenever the structure is too big to excite, e.g. a bridge or a ship. The excitation is done naturally, by wind or waves, it is a pure "output-only" measurement. The raw data of the accelerometers is stored with Dewesoft X Software for e.g. 20 minutes, then analysis is done in DS-MODAL-OMA.

**Experimental Modal Analysis (EMA)** can be done by using a shaker or impact hammer. The impact force and the output response is measured. In addition to the SIMO (single input multiple output), which is already possible in the Dewesoft X Software, the advanced MIMO (multiple input multiple output) technique allows to identify all modes, and animation in x-y-z direction.

## The implemented algorithms belong to following category:

**MDOF methods**

Based on the assumption that each resonance peak in the measured frequency response functions can be viewed as the summed contribution of a number of modes in a particular frequency band.

**Global methods**

Use a formulation where all frequency response functions are considered simultaneously. Global methods deliver superior results compared to local methods. But global estimation method requires reasonably high quality measurement data. Indeed these methods are sensitive to small variations in the data.

**Frequency domain methods**

Based on a model formulation in the frequency domain. These methods distinguish physical (structural) modes from computational (noise) modes more easily than time domain methods. For application to real-world structure, locate structural modes reliably is the most important task of a modal analysis.

## CMIF

**The Complex Modal Indicator Function (CMIF)** is based on Singular Value Decomposition of the FRF or PSD matrix. It determines all the main modes observed in the set of measurements.

# STABILITY DIAGRAM AND CURVE FITTING

The stability diagram works in a way, that extracted poles from the increasing order mathematical model will repeat as the order is increased, if the pole is a global characteristic of the system. The curve-fitting (synthesised FRF) is done on all single FRFs, and you can check the result by browsing through them.

# MAC, COMAC

The **Modal Assurance Criterion (MAC)** is a good tool to verify the results (extracted modes) from two different algorithms (e.g. Narrowband and Broadband) on the same test data. It can also be used to check the orthogonality of the mode shapes when weighted by the mass matrix.

The **Coordinate Modal Assurance Criterion (COMAC)M** is used to identify which measurement degrees of freedom contribute negatively to a low value of MAC. With the possibility to **import/export mode tables**, simulation and experimental test can be overlapped.

# ADDITIONAL FUNCTIONS

Various plots can be configured for detailed analysis, i.e. Magnitude, Phase, Imag, Real part, Coherence ...

Among the import and export functionality, there is also the ability to generate a video file of the single structural mode shapes animation for documentation.

# COMPATIBILITY AND MODEL UPDATING

DS-MODAL is a good complementary tool to Finite Element Analysis software (FEM), and compatible with e.g. NX Nastran or DDS FEMTools.

These software environments can addition- ally provide static and dynamic simulation, validation and updating, and design optimization.

# Algorithms

METHOD | ALGORITHM | TECHNIQUE | ADVANTAGES | LIMITS |
---|---|---|---|---|

EMA SIMO | Rational Fraction Polynomial of transfer function |
Special case of MIMO2 with only one reference (single shaker / single reference for hammer impact) | As the similar features as ist MIMO counterpart | Only measurements with one reference |

EMA/OMA Narband | Narrowband MIMO algorithm | Complex Mode Indicator Function (CMIF); one mode at a time | Easy to use | Requires the mass matrix uniformity assumption and consequently modal vector orthogonality, which is not the case for more complex structures |

EMA MIMO1 | Frequency Domain Poly-Reference (FDPR) | Selected-band MIMO: The modes within the user-selected band are identified at once | Optimised for 3 or more references | Use singular-value decomposition (SVD) of FRF data to separate structural modes from noise modes. Number of measurements should be larger than number of modes |

EMA MIMO2 | Rational Fraction Polynomial of transfer function. To improve the result, orthogonal polynomial is adopted instead of power polynomial | Selected-band MIMO: The modes within the user-selected band are identified at once | Can be applied with only a few response measurements | Recommended for up to two reference DOFs |

EMA/OMA Broband | Polyreference Least Squares Complex Frequency (p-LSCF) | Selected-band MIMO: The modes are identified in a wide frequency range (e.g. full band) | The stability diagram separates structural modes from noise modes. All modes are found at once | Eeds good data (less noise), not adequate for exact calculation of damping |

# Feature matrix

DEWESoft X DSA | DS-MODAL-MIMO | DS-MODAL-OMA | DS-MODAL-FULL | |||
---|---|---|---|---|---|---|

Data acquisition | ||||||

STRUCTURAL MODELLING | ||||||

Interactive Geometric Modelling | ||||||

UFF geometry import | ||||||

IGES geometry import | ||||||

DATA INPUT / OUTPUT | ||||||

Time- and frequency-domain data import | ||||||

Time- and frequency domain data and 2D graphics output | ||||||

Modal frequency and damping tabular output | ||||||

Mode shapes animation AVI output | ||||||

SIGNAL PROCESSING | ||||||

Trend removal | ||||||

Signal extraction | ||||||

Windowing (Hanning, exponential, power windows, etc.) | ||||||

ODS RESPONSE MODAL ANALYSIS | ||||||

Time ODS | ||||||

Frequency ODS | ||||||

EMA EXPERIMENTAL MODAL ANALYSIS | ||||||

Single-point hammering / multi-point response | ||||||

Single-point response / point-by-point hammering | ||||||

Single shaker excitation / multi-point response | ||||||

SIMO Circle-Fit estimation | ||||||

SIMO algorithm: EMA SelBand | ||||||

SIMO FRF estimate | ||||||

SIMO FRF curve fitting | ||||||

Multi reference point hammering MRIT | separate measurements | |||||

Multi shaker excitation / multi-point response | ||||||

MIMO frequency response estimate | ||||||

MIMO frequency response curve fitting | ||||||

Narrow Band: MIMO algorithm (FSDD) | ||||||

Selective Band: SelBand1 MIMO Algorithm 1 (FDPR) | ||||||

Selective Band: SelBand2 MIMO Algorithm 2 (FDPR) | ||||||

Broadband: BroBand MIMO algorithm (p-LSCF) | ||||||

Wideband frequency/damping Automatic Identification | ||||||

Modal stabilisation diagram | ||||||

Wideband curve fitting | ||||||

OMA OPERATIONAL MODAL ANALYSIS | ||||||

Narrowband OMA NarBand Full (FSDD) | ||||||

Environmental excitation at full power spectral density estimation | ||||||

Broadband OMA BroBand (p-LSCF) | ||||||

Semi-h-PSD power spectral density estimation | ||||||

Wideband h-PSD curve fitting | ||||||

Wideband frequency/damping Automatic Identification | ||||||

Mode indicator factor MIF | ||||||

Modal Animation | ||||||

MAC modal correlation matrix technology | ||||||

MAC dimensional and three-dimensional graphics display | ||||||

MAC table shows |