Bearing Output

The bearing output dialog allows one to specify the request components generated during the simulation for post-processing. For the detailed method, in addition to the total bearing force, one can choose to report the stiffness and damping components separately. Also, from this dialog one can alter the default value of failure probability used in a service life prediction based on ISO/TS 16281. This equates to the percentage of bearings that can be expected to fail after the calculated service life duration. The service life duration can be interpreted as the predicted service life in hours for the bearing under the loading and rotational speed conditions at the given time step.

For the detailed modeling option only, Adams Machinery Bearing calculates a service life estimate at every output step which can be interpreted as the as the predicted service life in hours for the bearing under the loading and rotational speed conditions at that output step. See Bearing Output for details of the inputs to this calculation and Calculation of service life based on the bearing inner geometry (ISO/TS 16281) as for details of the life calculation method according to ISO/TS 16281.

Within Adams PostProcessor one can also generate a "duty cycle" style life output via the "Adams Machinery Bearing Duty-Cycle Service Life" tool. This tool can be launched by selecting "Bearing Life" from the "Tools" menu within Adams Postprocessor. The single-value service life estimate provided by the "Adams Machinery Bearing Duty-Cycle Service Life" tool aggregates the individual service life output values from each output step described above (known as Li in the formulation description, below) over the course of the duty-cycle specified in the dialog box. The formulation used to accomplish this amounts to an "equivalent life" calculation and is described below:

Where:

Such a calculation is useful when one is not interested in how long the bearing can survive at any single load condition (that is, some single Adams output step in, perhaps, a steady-state portion of the analysis) but instead is interested in what fraction of the bearing's available life is used up by being subjected to the conditions of some time range of the Adams analysis. As illustrated in the equation above this is done as follows:

What about the number of repeats? These values increase the length of time the bearing is assumed to be subjected to the loading conditions of any single Adams output step. Mathematically each ti is simply multiplied by its corresponding number of repeats (ri in the equation above). Practically speaking these values are often used when the length of the Adams analysis, or segments of it, does not match the actual physical length of time that the user is trying to represent. This is often the case when the Adams results would simply cyclically repeat or stay in a steady state if the analysis was run for a longer duration and the user has no need to spend all that computational time since they consider the Adams analysis (or segments of it) representative of the actual load spectrum the bearing will endure.

For example, a physical test in the lab might run at a given loading state for several hours whereas the Adams analysis representing that test was only a few seconds long. If one wants to know how many times the bearing could survive the physical lab test (as opposed to the Adams analysis test), then one would use a number of repeats in the duty cycle definition within Adams. That number of repeats would essentially be equal to the multiplier needed to scale the Adams analysis duration into the physical test duration. For example, if an Adams analysis was 10 seconds in duration, but the physical test it represents lasts for 60 hours, then the number of repeats should be 60/(10/3600) = 2.16e4. The resulting "duty cycle service life" would be a value in hours that is the calculated number of times the bearing can survive the 60 hour duty cycle multiplied by 60 hours thus providing a prediction of how long the bearing can survive in the application if we assume that it undergoes that 60 hour physical test continuously.

This means that if the same number of repeats are applied to each row in the duty cycle definition table, the service life calculation won't change if the number of repeats is changed, only the number of survivable duty cycles will change. This is because in such a condition the relative amount of time of any output steps' loading conditions compared to others has not changed and, thus, the load spectrum has not changed. So, the total time the bearing can survive remains constant. All one is really doing in uniformly adjusting the number of repeats is changing the duration of the duty cycle. So, only the number of survivable duty cycles would change.

A more typical and interesting usage for "number of repeats" is when the Adams results represent a number of loading conditions to which, in reality, the bearing will not be subjected in the same proportions. For example, a 10-second Adams analysis may represent 3 seconds of start-up followed by 4 seconds of steady state and finally 3 seconds of shut off. An engineer might know in reality that the system will run in the steady state condition 1000 times longer than start-up and shut-down. So, to represent this one would define the duty cycle in Adams like so: