Getting started

Getting started#

To install FatigueDS, use pip:

$ pip install FatigueDS

Importing the package#

import FatigueDS

Creating a Spectrum object#

To calculate the Extreme Response Spectrum (ERS) and Fatigue Damage Spectrum (FDS), a Spectrum object must be created. The object is created by providing the frequency range and damping ratio. Frequency range freq_data is defined by a tuple (f0_start, f0_stop, f0_step) in Hz and sets the frequency points where the ERS and FDS will be calculated. Alternatively, a frequency vector (array) can be passed as input. Damping ratio damp is a float value between 0 and 1.

load_spectrum = FatigueDS.Spectrum(freq_data=(f0_start, f0_stop, f0_step), damp)

# or

load_spectrum = FatigueDS.Spectrum(freq_vector, damp)

Setting the load signal#

Load signal is defined with different methods, depending on the type of signal.

Random signal (PSD)#

For the random signal defined by the Power Spectral Density, the following parameters must be provided:

  • signal_data : A tuple (PSD array, frequency array),

  • unit : unit of the PSD (ms2 or g)

  • T : time duration in seconds

load_spectrum.set_random_load((PSD, freq), unit, T)

Random signal (time history)#

For the random signal defined by the time history, the following parameters must be provided:

  • signal_data : A tuple (time history array, time step)

  • unit : unit of the time history (ms2 or g)

  • method : method of calculation.

Available methods are:

  • convolution : Directly from time history

  • psd_averaging : Conversion to PSD, then to ERS and FDS from PSD

load_spectrum.set_random_load((time_history, dt), unit, method)

Sine signal#

For the sine signal; frequency, amplitude, total time of the signal and an excitation type must be provided.

load_spectrum.set_sine_load(sine_freq, amp, t_total, exc_type)

Sine-sweep signal#

For the sine-sweep signal; amplitude, frequency range, excitation type, time step, sweep type and sweep rate must be provided.

load_spectrum.set_sine_sweep_load(const_amp, const_f_range, exc_type, dt, sweep_type, sweep_rate)

Calculating the ERS and FDS#

After the load signal is set, the ERS and FDS can be calculated.

ERS is calculated by:

load_spectrum.get_ers()

FDS calculation requires additional material fatigue parameters: k, C and p. It is calculated by:

load_spectrum.get_fds(k, C, p)

The results are stored in the ers and fds attributes of the Spectrum object.

Accessing the results:

load_spectrum.ers

load_spectrum.fds

load_spectrum.f0_range  # frequency array

Plotting the results#

The results can be plotted by:

load_spectrum.plot_ers()

load_spectrum.plot_fds()
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