Do you need a slam dunk test?

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Static
studies assume loads are constant or applied very slowly until they reach their
full values. Because of this assumption, velocity and acceleration of each
particle of model is assumed zero. As a result, static studies neglect inertial
and damping forces.

For many
practical cases, loads are not applied slowly or they change with time or
frequency. For such cases we use a dynamic study. The software calculates
response of model by accumulating the contribution of each mode to loading
environment. In most cases, only lower modes contribute significantly to the
response. The contribution of a mode depends on load’s frequency content,
magnitude, direction, duration and location.

To test the
effect of slam dunk on a basket ball rim we need a linear dynamic test. Let’s
say it takes 0.5 seconds for a player to dunk the ball. We will solve this
problem using linear dynamic analysis in COSMOS or SOLIDWORKS Simulation and
then solve again using Linear Static analysis.

For load case we will consider, slam dunk force
to be 260lb. For a static test we will consider the load to be constant. For
linear dynamic, we will apply the load over 0.5 seconds and calculate upto 10
seconds duration. Also, we will include material damping effects, hopefully
making it a realistic simulation.
1_4

1_3
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Stress from Dynamic Test                    Stress from Static Test

1_7

Displacement
from Static Test               Displacement from Dynamic Test

From the
stress and displacements plots, it is obvious if we use static analysis for
this problem our results would be inaccurate. Static tests shows a stress and
displacement value of 83443 psi and 0.83 in respectively. Dynamic tests on the
other hand indicate stress value of 1284 psi and 0.006 in respectively. If we
were to go by static tests we would be severely over designing the rim, making
it more expensive.

A time based
test is needed to accurately slam dunk a basket!

Rajat Trehan

Product
Manager – Design Validation

Computer
Aided Technology Inc.