How to get simulations running in Collimator
The continuous and discrete portions of a hybrid system require different solvers to advance them in time, and produce the simulation results. Because these portions require different solvers, it is important that Collimator assign the blocks of a model into continuous and discrete sets.
These blocks require a continuous solver.
These can be isolated in the library browser by filtering with the keyword
discrete. These blocks require a discrete solver.
Most blocks in the library are neither continuous nor discrete by design, they can be either. These are gain, lookup table, saturation, etc. Before Collimator can run a simulation, each of these blocks in the model is assigned to either continuous or discrete sets, such that the appropriate solver is applied. Collimator creates the Continuous and Discrete sets by applying some simple steps to propagate the
time_modefrom blocks which have
time_modedefined by design, to blocks which do not. The rules applied are:
- 1.For all unassigned blocks for which all upstream blocks are Discrete, the block is assigned Discrete. When a block’s
time_modeis changed, revisit all blocks downstream to see if they need to be changed. Once there are no more blocks to visit, this step is done.
- 2.Any remaining unassigned blocks are assigned Continuous.
With the blocks of the model all assigned to either Continuous or Discrete
time_mode, the simulation may begin.
The pseudo code below illustrates how Continuous and Discrete portions are advanced in time.
while time < stop_time
major_step_end_time = time + next_discrete_update_time
# presently, next_discrete_update_time == discrete_update_interval (a.k.a sample_time)
update discrete portion of the model
store signal results to memory at beginning of major_step
while time < major_step_end_time
perform continuous solver step to update continuous portion
time += solver_step_dt
if solver_step_dt > interpolation
interpolation_time = time - solver_step_dt
while interpolation_time < time
compute interpolated results
store signal results to memory at interpolation_time
interpolation_time += interpolation
store signal results to memory at end of solver step
The outer loop iterations are referred to as
major_steps, this is when discrete solver is at work. The middle loop iterations are referred to as
minor_steps, this is where the continuous solver is at work. The inner loop iterations are referred to as continuous result interpolation, this is where, if needed, the continuous solver interpolant can be used to produce results that are higher resolution in time than just the steps taken by the solver.
The continuous portion is a set of ordinary differential equations (ODE). Some systems that can be modeled with ODEs include some discontinuities, like contact between two objects. The discontinuities can be modeled using blocks with
events, e.g. the comparator block, so that numerical integration of the ODEs progresses correctly before and after the discontinuity. To configure Collimator to do this, set
normal. If you know that your model does not need any events handling, then select
none, as this will be most efficient. More granular user controls of events handling may be available in the future.