What ASCEND IV Can and Cannot Do
From ASCEND
The purpose for this page is to provide guidance that will allow you to determine if ASCEND IV can be useful for your modeling needs. After you have read this page, you may wish to visit the page ASCEND IV Features.
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[edit] ASCEND IV is really good at
- Creating models as one might do now in a spreadsheet but where (1) the model involves solving simultaneous equations and/or (2) where one wishes to discover the value for several inputs so the spreadsheet model computes specified values for several of its outputs.
- Creating and debugging complex highly structured models (built out of parts which themselves are built out of parts, etc.) expressed in terms of algebraic equations.
- Setting up and solving initial value dynamic models involving a few tens of ODEs and thousands of algebraic equations - if it is your time to create the model that matters and not the final computation, our approach to solving initial value differential algebraic equation (DAE) models is good enough.
- Setting up and solving dynamic optimization problems involving a few ODEs and hundreds of algebraic equations - the problem becomes a two point boundary value problem that ASCEND IV is good at expressing and solving. To solve optimization problems, you will have to license the [[ConOpt|CONOPT]] optimizer we have coupled to ASCEND.
- Using superior debugging capabilities to "create with understanding" new building block submodels to include in other modeling systems - yes, we have found it faster to get the new model right in ASCEND IV and then rewrite it for the other system.
- Correctly handling models involving mixed units (ft, m, kg, ounces, pascals, ...). ASCEND IV knows all about dimensionality and units. It reports equations written with incorrect dimensionality or variables expressed with incorrect units.
- Solving many undergraduate homework problems - the tools allow students to play. (One of our developers uses ASCEND extensively in his chemical engineering classroom. To quote him: "For cubic equations of state, ASCEND is easier to use." - Krishnan. Our message here is only that you might find ASCEND to be quite good for students to use on small, solve from scratch, homework problems.
- Doing the one-off modeling for a thesis project - we have had students cut times from months to weeks.
[edit] ASCEND IV also okay at BUT
- Creating a one-off model that solves without iteration in a spreadsheet - a spreadsheet would be better (unless those unit conversions worry you).
- Simulating a conventional engineering system for which a commercial simulator exists. Hey, this is their specialty. They know how to "hammer home" a solution and have all sorts of nice input and display options you would not want to create in ASCEND IV. (However, from a pedagogical viewpoint, we might again quote Krishnan "If I could, I'd BAN commercial simulators from undergraduate hands - AT LEAST watch them like a hawk when they use them - have them use ASCEND." The implication: often the understanding of what is in the model is as important as the answers for students.)
[edit] ASCEND IV is not so good for
- Solving large DAE problems where solve time matters - others have better solvers than we do for that problem.
[edit] ASCEND IV cannot
- Carry out symbolic manipulations.
- Compute eigenvalues and eigenvectors.
- Solve integer (IP, MILP, MINLP) optimization problems (we need the solvers).
- Solve higher-order DAEs and ODEs directly (you need to reduce the order manually, a straight forward activity).
- Perform index reduction on systems of DAEs. Having said that, with tools available, ASCEND can guide one in how to change degrees of freedom to eliminate an index problem.
[edit] Broken functionality
- Solve 'conditional models' in which certain equations are used or not used depending on the values of boolean variables in the system - we are working on reinstating this functionality. It requires CONOPT (license required).
- Integration with IDA solver for DAEs (still under development).
- Export models to other formats (e.g., GAMS).
[edit] Examples of specific uses of ASCEND IV
- Performing heat and material balances using rigorous physical property calculations for a miniature hydrogen plant.
- Optimizing a system of distillation columns to separate azeotropic mixtures.
- Solving homework problems for undergraduate chemical engineering courses ("Far easier in ASCEND to solve Bubble Point T calculations when liquid is non-ideal!" - Krishnan).
- Generating and analyzing alternative architectural structures.
- Analysing batch distillation processes.
You might benefit from reading more about ASCEND IV Features.
