Preliminaries

When using the interface, there are four important points to handle carefully

• units,

• sign conventions,

• implicit variables (when using Simcenter Amesim from Adams),

• numerical aspects.

With reasonable care these points can be solved without any problem.

The problem of different units in Adams and Simcenter Amesim often leads to the need for the interfacing variables to be adjusted with some unit conversion factor.

What we mean by a sign convention is the significance of the signs of forces, displacements and velocities in both Simcenter Amesim and Adams. It is almost always necessary to reverse the sign of displacements and velocities when they are imported into Simcenter Amesim if hydraulic jacks or hydraulic pumps, motors or rotary actuators are used. Since the sign convention depends on the interfacing of components and variables it is necessary to use caution regarding the sign. This is another good reason for creating two separate sub-system models. The single software simulation results will give good insight into the system behavior and make any sign errors in the combined simulation apparent.

As explained in the Simcenter Amesim manual, Simcenter Amesim can solve two kinds of systems of differential equations: ordinary differential equations (ODEs) and differential algebraic equations (DAEs). The latter uses implicit variables. The interface between Simcenter Amesim and the General State Equation in Adams supports only ODEs. It is therefore impossible to use any submodel in Simcenter Amesim that uses implicit variables when exporting the model into Adams. It may also be necessary to modify the Simcenter Amesim model to eliminate any implicit variables that may be created to resolve algebraic loops.

When working from Adams, numerical problems arise due to the fact that the interface uses the Adams integrator, which is tuned to work well with the equations governing multi-body systems. The numerical characteristics of a fluid power system are different. Another source of numerical problems is that a Simcenter Amesim model when run with the Simcenter Amesim integrators can employ some special tricks to deal with discontinuities. This is not possible when using the Adams integrator. In fact, the documentation of the AdamsGSE facility, states that the imported system of ODEs must be continuous. It is therefore recommended to avoid hard discontinuities completely in the  Simcenter Amesimmodel. By a hard discontinuity we mean that there are jump changes in the values of state variables. Fortunately very few Simcenter Amesim submodels employ hard discontinuities. Avoid the following hydraulic actuator icons that have an integral mass as the corresponding submodels employ hard discontinuities.

It is not impossible to use these submodels but if you do, make sure that the jack never hits its end-stops. However, submodels associated with alternative icons employ elastic end-stops, which do not have hard discontinuities. Hence it is preferable to use these.

USE THESE ICONS

DO NOT USE THESE ICONS

Similarly if you use the mechanical icons, , use MAS21 not MAS005.

Looking at the input and output requirements of these preferred submodels and at the requirements of hydraulic pumps and motors, a second general rule becomes apparent.

The Adams model normally calculates position and velocity, (or angle and angular velocity) and passes them to the Simcenter Amesim model, which calculates the corresponding force (or torque).

Again it is possible to think of exceptions but this rule is very useful.

In the same way when working from Simcenter Amesim numerical problems can arise when importing a large Adams system. The Simcenter Amesim integrator is not designed to solve such problems, and simulation times may rise significantly.

In these cases the co-simulation interface can be a solution if no workaround is found to make the full import facility efficient.