What is Dynamic Analysis?
Dynamic analysis is used to verify the maximum and minimum loads on all belt conveyor
components during all possible transient conditions of stopping and starting.
It is also used to develop and test the control algorithms necessary to safely and
reliability stop and start the load.
Proper dynamic analysis requires a time based, FEA solver which considers the elasticity
of the belting and all the masses which make us the conveyance system.
Hoe Does dynamic analysis work?
When performing starting and stopping calculations per CEMA or DIN 22101 (static analysis),
it is assumed all masses are accelerated at the same time and rate; in other words the belt is
a rigid body (non-elastic). In reality, drive torque transmitted to the belt via the drive pulley
creates a stress wave which starts the belt moving gradually as the wave propagates along the belt.
Stress variations along the belt (and therefore elastic stretch of the belt) are caused by these
longitudinal waves while being dampened by resistances to motion. It is, therefore, important a
mathematical model of the belt conveyor that takes belt elasticity into account during stopping
and starting be considered in these critical, long applications. A model of the complete conveyor
system can be achieved by dividing the conveyor into a series of finite elements. Each element has
a mass and rheological spring.
Many methods of analyzing a belt’s physical behavior as a rheological spring have been studied
and various techniques have been used. An appropriate model needs to address:
- Elastic modulus of the belt longitudinal tensile member
- Resistances to motion which are velocity dependent (i.e. idlers)
- Viscoelastic losses due to rubber-idler indentation
- Apparent belt modulus changes due to belt sag between idlers
Since the mathematics necessary to solve these dynamic problems are very complex, it is not the
goal of this presentation to detail the theoretical basis of dynamic analysis. Rather, the purpose
is to stress that as belt lengths increase and as horizontal curves and distributed power becomes
more common, the importance of dynamic analysis taking belt elasticity into account is vital
to properly develop control algorithms during both stopping and starting.