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:

  • Contibutions
    • 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.