Modeling Hydraulic Pressure Changes
Peter Nachtwey’s outstanding tutorials in Hydraulics & Pneumatics have covered a wide range of fluid power challenges. One area that has evolved in Nachtwey’s time, as he noted in a recent article, was the calculations involved in modeling pressure changes in hydraulic systems.
“Back in the early 2000s, I used a spreadsheet to simulate a customers’ system which had been designed incorrectly. At that time, my spreadsheet program could only handle 32,768 rows,” writes Nachtwey, president of Delta Computer Systems and a member of the IFPS Hall of Fame. “But at 100 microseconds for each row, I could only simulate 3.2 sec., which fortunately was long enough.
“Each column was an equation for calculating position, velocity, acceleration, net force, cap side and rod side pressure. Once the first row was complete, the formulas were copied to the rest of the rows. Pressure changes depend on these values, so they had to be calculated for each row or in 100 microsecond iterations. It worked but was limited by the speed and memory capacity of personal computers back then.”
A Deeper Dive into Calculations
Today, the process for doing those calculations are more automated, but no less important, Nachtwey notes. “Obviously, the equations for calculating pressure changes are complicated and depend on many factors that are constantly changing. Hydraulic simulators use the current state to calculate the next state in small time increments. Usually increments of 100 microseconds are sufficient.
“The reason for using small time increments is that pressure changes quickly when an obstruction is hit, as in a press,” he adds. “Plus, the smaller the time increments, the better and smoother the simulation will likely be. The tradeoff is the additional calculation time needed and the large amount of data generated.”
A look at the formulas involved and a deeper dive into the calculations can be found here.
