I would like to formalise this problem with system dynamics: I have a stock of raw materials and one of finished goods, among them I have a production flow that has a certain value (e.g 1000 units per day). My goal is to calculate the manufacturing cost, so I create a flow that feeds a stock "manufacturing cost" and within the flow I have the product of:
Manufacturing_cost_flow = Unit_variable_cost * production_rate [$/unit] * [unit/time]
Now, I would like to enter the fixed costs. In particular, if I have a shortage of raw materials (so RM = 0 --> production_rate = 0) the manufacturing_cost_flow will be 0 but, in fact, I have to sustain a fixed cost. Taking into account the fact that fixed costs are in $, how can i add them in the "manufacturing_cost_flow" ?
Picture of the problem: problem