Code documentation

The FRF class

class pyFRF.FRF(sampling_freq, exc=None, resp=None, exc_type='f', resp_type='a', window='none', resp_delay=0.0, weighting='linear', fft_len=None, nperseg=None, noverlap=None, archive_time_data=False, frf_type='H1', copy=True, **kwargs)

Perform Dual Channel Spectral Analysis

__init__(sampling_freq, exc=None, resp=None, exc_type='f', resp_type='a', window='none', resp_delay=0.0, weighting='linear', fft_len=None, nperseg=None, noverlap=None, archive_time_data=False, frf_type='H1', copy=True, **kwargs)

Initiates the Data class:

Parameters:

• sampling_freq (int, tuple(int), list[int]) – Sampling frequency of excitation and response signals. int - same sampling frequency for both excitation and response signals. tuple, list - different sampling frequencies for excitation and reponse signals. First element represents excitation, second element represents response sampling frequency.

• exc (ndarray) – Excitation array. A 3D, 2D or 1D ndarray: 3D (general shape, allows multiple inputs (MIMO, MISO)): (number_of_measurements, excitation_DOFs, time_series). 2D (multiple measurements, single input): (number_of_measurements, time_series). 1D (single measurement, single input): (time_series).

• resp (ndarray) – Response array. A 3D, 2D or 1D ndarray: 3D (general shape, allows, multiple outputs): (number_of_measurements, response_DOFs, time_series). 2D (multiple measurements, single output): (number_of_measurements, time_series). 1D (single measurement, single output): (time_series).

• exc_type (str) – Excitation type, see _EXC_TYPES.

• resp_type (str) – Response type, see _RESP_TYPES.

• window (str, tuple(str), list[str]) – Scipy window used for cross power spectral desnity computation or excitation and reponse signals. see _WINDOWS. str - used for csd. tuple, list - first element is excitation signal window, second element is response signal window

• resp_delay (float) – Response time delay (in seconds) with regards to the excitation.

• weighting (str) – weighting type used for averaging with continous measurements - see _WGH_TYPES. If exponential weighting is used, specify the number of averages - example: ‘exponential:5’

• fft_len (int) – The length of the FFT (zero-padding if longer than length of data), If None, freq length matches time length.

• nperseg (int) – Optional segment length, by default one segment (data length) is analyzed.

• noverlap (int) – Optional segment overlap, by default noverlap = nperseg // 2.

• archive_time_data (bool) – Archive the time data (this can consume a lot of memory).

• frf_type (str) – Default frf type returned at self.get_frf(), see _FRF_TYPES.

• copy (bool) – If true the excitation and response arrays are copied (if data is not copied the applied window affects the source arrays).

add_data(exc, resp)

Adds new data - called at object creation if excitation and response signals are given. Used also for continous data adding.

Parameters:

• exc – Excitation array.

• resp – Response array.

Returns:

True if data is added.

is_data_ok(exc, resp, overflow_samples=3, double_impact_limit=0.001, verbose=0)

Checks the data for overflow and double-impacts.

Parameters:

• exc – Excitation array.

• resp – Response array.

• overflow_samples (int) – Number of samples that need to be equal to max for overflow identification.

• double_impact_limit (float) – Ratio of freqency content of the double vs single hit. Smaller number means more sensitivity

• verbose (int) – Prints overflow and double impact status. 0 or 1.

Returns:

True if data is ok, False if there is overflow or double impact present.

Return type:

bool

get_f_axis()

Get frequency series.

Returns:

Frequency ndarray in Hz.

Return type:

ndarray

get_w_axis()

Get angular freqency series.

Returns:

Frequency ndarray in rad/s.

Return type:

ndarray

get_df()

Get delta frequency.

Returns:

Delta frequency in Hz.

Return type:

float

get_t_axis()

Get time axis.

Returns:

Time axis ndarray.

Return type:

ndarray

get_ods_frf()

Operational deflection shape averaged estimator.

Numerical implementation of Equation (6) in [1].

Literature:

[1] Schwarz, Brian, and Mark Richardson. Measurements required for displaying

operating deflection shapes. Presented at IMAC XXII January 26 (2004): 29.

Returns:

ODS FRF estimator.

Return type:

ndarray

get_resp_spectrum(amplitude_spectrum=True)

Get response amplitude/power spectrum.

Parameters:

amplitude_spectrum – True - get amplitude spectrum, False - power spectrum.

Returns:

Response spectrum.

Return type:

ndarray

get_exc_spectrum(amplitude_spectrum=True)

Get excitation amplitude/power spectrum.

Parameters:

amplitude_spectrum – True - get amplitude spectrum, False - power spectrum.

Returns:

Excitation spectrum.

Return type:

ndarray

get_H1()

Get H1 FRF averaged estimator (receptance), preferable call via get_FRF().

Returns:

H1 FRF estimator matrix (ndarray) of shape (response DOF, excitation DOF, freqency points).

Return type:

ndarray

get_H2()

H2 FRF averaged estimator (receptance), preferable call via get_FRF().

Returns:

H2 FRF estimator matrix (ndarray) of shape (response DOF, excitation DOF, freqency points).

Return type:

ndarray

get_Hv()

Get Hv FRF averaged estimator (receptance), preferable call via get_FRF().

Literature:

[1] Kihong and Hammond: Fundamentals of Signal Processing for

Sound and Vibration Engineers, page 293.

Returns:

Hv FRF estimator matrix (ndarray).

Return type:

ndarray

get_FRF(type='default', form='receptance')

Returns the default FRF function set at init.

Parameters:

• type (str) – Choose default (as set at init) or H1, H2, Hv or ODS.

• form (str) – Choose receptance, mobility, accelerance.

Returns:

FRF estimator matrix (ndarray).

Return type:

ndarray

get_coherence()

Get coherence.

Returns:

Coherence ndarray of shape (response DOF, freqency points).

Return type:

ndarray

get_archive()

Returns the time archive. If not available, it returns None.

Returns:

(excitation, response) time archive.