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REXS V1.6

Load spectra

See "load_spectrum" object.

Problem

  • A load spectrum calculation corresponds to variation of the load and environmental data (external torque, speed, gear, temperature, etc.).

  • Each expression of the variation corresponds to a load case (load_case).

  • Much of the gear information (geometry, etc.) remains unchanged over the entire calculation.

  • The varied input values and the corresponding calculation values must be represented for every load case. Furthermore, values accumulated via the load spectrum must be recorded.

  • Consequently, a load spectrum consists of multiple load cases as well as the values accumulated across all of the load cases.

Solution

  • The load spectrum is represented by a master model (containing the data and the relations that remain unchanged) and multiple sub-models (containing only the varied data).

  • Each load case corresponds to a sub-model. Therefore, the load_case term has been selected for sub-models.

  • The load cases of a load spectrum are summarized in a load_spectrum.

  • Only the varied data in the load spectrum is included in a load_case (sub-model). The following applies:

  • The corresponding attributes are structured in components, as in the master model.

  • The (unique) component ID is used to associate a component in the master model and a component in the sub-model.

  • All sub-models must include the same number of attributes.

  • Attributes that are specified in the sub-models may not be reused in the master model.

  • The master model only becomes a complete model that can be calculated when it is combined with a sub-model.

  • Values accumulated via the load spectrum are stored in a separate sub-model of the load spectrum named "accumulation."

  • Initially, only one load spectrum is permitted per model.

  • A model with load spectrum is represented in the .xml format as follows:

<model>
	<relations>
	<components>
	<component id="1">
	<component id="4">
	<component id="6">
	<!-- further components -->
	</components>
	<load_spectrum id="1">
		<load_case id="1">
		<load_case id="2">
		<load_case id="3">
			<component id="4">
			<component id="6">
		</load_case>
		<accumulation>
			<component id="4">
			<component id="6">
		</accumulation>
	</load_spectrum>
</model>

A possible extension to include other calculus of variations (e.g., design variations such as bearing types or different gear qualities) may be considered once the concept for representing load spectra has been proven in practice.

Time periods and load durations

The duration of load cases may be specified absolutely or relatively.

  • Absolute specification is made via the operating_time attribute of the gear unit (in hours) for each load case.

  • Relative specification is made via the operating_time_fraction attribute of the gear unit as a percent for each load case. On the other hand, an (optional) total duration of the load spectrum can be specified via the operating_time attribute of the gear unit in the master model.

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