### Load spectra

#### Using load spectra in the system calculation

To consider load spectra in the system calculation, "consider load spectrum" must be activated in the *calculations* tab under the gear unit.

**Number of points calculated in the load spectrum**

The system calculation is performed for each load and speed stage. Thus, the influences from the load (such as the face load distribution) and the speed (such as the lubricant film thickness) valid for these stages are taken into account in all stages of the load spectrum. In order to reduce the calculation time for large spectra, the number of operating points for which the system calculation is solved can be specified. These operating points are distributed evenly in the spectrum. For all other load spectrum levels, the loads and speeds are interpolated and the corresponding damage fractions and lifetimes are calculated. If the number of load points is greater than or equal to the number of stages selected in the load spectrum, all stages are calculated in the system calculation.

### Notice

When specifying only a speed spectrum, two different calculation options are available. If the torque is specified in the power flow definition of the gearbox, this is kept constant and only the speed is varied. If the gearbox power is specified, the torques in the load stages are adjusted so that the power remains constant.

**Specifying a load spectrum and time shares**

In the load spectrum calculation, an individual load spectrum can be specified for every gear in the gear unit. The required settings can be made in the *Power Flow* tab of the gear unit component.

Time shares are used to distribute the specified total service life of the gear to the individual gears. Weighting factors are specified, and a time share is calculated from the weighting factor divided by the sum of all weighting factors multiplied by the total service life. Thus, the time shares can be entered as percentages, factors, or hours. The following entries lead to the same result:

Total number of hours: 30,000 | ||||

Gear | Factor | Factor | Percent | Hours |
---|---|---|---|---|

Gear 1 | 0.1 | 2 | 10 | 3000 |

Gear 2 | 0.2 | 4 | 20 | 6000 |

Gear 3 | 0.7 | 14 | 70 | 21000 |

If existing percentage or hourly weighting factors are used, the sum does not need to correspond to 100 % or the total number of hours. If the specified total number of hours in the table above was not 30,000 h but rather 60000 h, the individual time shares would be internally converted to 6000 h (Gear 1), 12000 h (Gear 2) and 42,000 h (Gear 3).

##### Calculation options

Load spectra can be considered in the following calculations in the FVA-Workbench:

**Cylindrical gears**

Tooth flank & tooth root load carrying capacity acc. to ISO 6336 Part 6:

Safety factor (spectrum) acc. to Miner

Static safety

Continuous safety

Various damage accumulation hypotheses can be selected

Stress collectives and Woehler S-N curves

Maximum permissible scaled total number of load cycles

Gear excitation

Excitation level over the load

Tooth force level over the load

Force amplitudes over the load

Excitation amplitude level over the load

Transmission deviation amplitudes over the load

Maximum transmission deviation over the load

Mean transmission deviation over the load

**Bevel gears**

Standard bevel gear calculation (standard calculation acc. to ISO 10300 (2014))

Comparison of variants for local calculations

Mean specific gear tooth stiffness

Velocity level at 1000 U/min

Efficiency

Double amplitude of the total working variation

Minimum safety against scuffing

Maximum Hertzian contact stress

Maximum flash temperature

Maximum tooth root stress

Minimum safety against pitting of the pinion

Minimum safety against pitting of the gear

Local damage accumulation (tooth root/tooth flank damage sum)

**Rolling bearings**

Rolling bearing lifetime (accumulated lifetimes)

**Shafts**

Strength calculation acc. to FKM (2012)

#### Creating load spectra

Load spectra are saved as data records in the Global Database. Load spectra saved in the database can be then be added to any gearbox model as a database component.

##### Importing load spectra as .csv

Load spectra can be imported as .csv files (comma-separated values). These files can be created in Excel or another spreadsheet program. The step frequency must be specified in the first column. Load amplitudes for torque and speed can be specified in the second and third columns. The load spectra can be single or double column. Optionally, the title of the data row can be specified in the first row.

### Notice

Commas must be used as a decimal separator in the data series. The default decimal separator can be configured in Excel under *file *-> *options *-> *advanced*.

- Figure 7. Import the example file
- Figure 8. Define the type and units of the data series

##### Creating synthetic load spectra

Synthetic spectra can be useful in general investigations and preliminary design. They can be described mathematically using the three parameters spectrum scope H_{0}, highest value Ŝ_{a}, and shape parameter ν. The larger the shape parameter ν, the greater the damage content of the synthetic load spectra with the same scope H_{0} and highest value Ŝ_{a}.

- Figure 10. Create a load spectrum
- Figure 11. Start the load spectrum calculation
- Figure 12. Specify the load spectrum parameters