Why is it so difficult to predict run times in 1D/2D models?

Why is it so difficult to predict run times?

Often we’re asked how long it will take to run a model with X number of pipes or manholes, a 2D area of Y, running on Z computer hardware. We completely understand why we are asked questions like this, but unfortunately it’s almost impossible to provide indicative runtimes. It’s very much like the “how long is a piece of string” question! Every model is different and runtimes are influenced by so many different factors.

Adding 2D analysis into the equation will usually increase runtimes, but for large piped models the 1D calculations can sometimes be the dominant factor, which adds further uncertainty. Models where flows constantly transition between a free-surface and surcharged condition will run more slowly than those where the majority of pipes maintain their hydraulic condition for long periods. Models with ancillary structures (particularly pump stations), will run more slowly than those without such devices, especially if overflows are constantly triggered or if pumps constantly turn on and off. Changes of state within a model force the software to use a lower time step. The smaller the time-step, the longer the run-times. 2D models tend to use time-steps of 10 seconds or less whereas 1D models usually run at around 60 seconds or more. This requirement alone will mean a 2D model is sometimes many times slower than a 1D model. 

The increase in 2D runtimes can be countered when using InfoWorks ICM by employing a GPU card for the 2D calculations. Even then, the speed gain is dependent on the proportion of time the 2D calculations take in the overall simulation (i.e. how many elements are wet during the simulation, and for how long) and the type of GPU card used. New PC hardware will run models considerably more quickly than hardware which is 4 or 5 years old. For example, todays Intel Core i5 and Core i7 processors are a lot quicker than the Intel Core2Duo and Core2Quad processors produced between 2006 and 2008.

If you want to remove the burden of running a model from your own machine then another option is to explore using InfoWorks ICM and configuring it to operate as part of a Workgroup.  This will allow you to schedule multiple concurrent simulations across a pool of connected Laptops, Desktop PC’s, Workstations or High-Powered Servers.

See the videos below for more information.

Configuring a workgroup in InfoWorks ICM


Running Multiple Simulations in InfoWorks ICM


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    About Andrew Walker

    Andrew Walker is a Senior Client Service Manager with Innovyze in the United Kingdom, specializing in the computerised analysis of drainage and flooding. He has over 30 years’ experience of modelling the key hydraulic processes involved in urban drainage design and analysis. He is one of the key members of staff tasked with supervising the roll-out and adoption of InfoWorks ICM throughout the UK and wider European marketplace.
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