An introductory presentation on OpenMI in my department.

1. Open Modelling Interface and Environment
[OpenMI]
Narayan Kumar Shrestha [nashrest@vub.ac.be]
Vrije Universiteit Brussel
Department of Hydrology and Hydraulic Engineering

2. Presentation Layout
1. Introduction
2. Model Linking Approaches
3. OpenMI Data Exchange Mechanism
4. Migrating an existing model to OpenMI
5. Advantages and Drawbacks of OpenMI
6. Conclusions

3. Introduction
• Integrated interacting system
Rainfall • A standard for linking models
Module • A standard for data exchange
• Enables Model Linking/Coupling
Precipitation
Rainfall- River
Runoff Runoff Model
Model ex: SWMM
ex: SWAT

4. Introduction
• Another standard USB
• Provides freedom of choice
to the users

5. Model Linking Approaches
File Based Altogether OpenMI Way
RR Model RR Model
+
Write RR Model River Model
River Model
Write Write
Output File Write
Output File Output File
Read Output File
River Model
Write
Output File

6. Data Exchange Mechanism
Model „A‟ requires data from Model „B‟
Model „A‟ Model „B‟ Model „A‟ Model „B‟
Model „A‟ runs Data from Model „A‟ is passed to Model B
Model „B‟ runs

7. Data Exchange Mechanism
Model „A‟ runs on a 5 minute time step
Model „B‟ runs on a 15 minute time step
Model „A‟ Model „B‟ • Data from Model „A‟ is passed to Model B
√ when Model „B‟ requests.
• Standardized data exchange [What,
where and when?].
• Request-Reply mechanism.
√
5 minute 15 minute

8. Data Exchange Mechanism
• Request Reply Mechanism
• Pull-Driven System
• „GetValues‟ function is the essence of the OpenMI data exchange mechanism.
RR Model: inflow
River Model: SWMM [NonNav]
Run GetValues()
Trigger Discrete Quality Model
Reply with data

9. Migrating an existing Model to OpenMI
• Existing Model: Migrating the model
• New Model: Development of the complaint model
Why migration?
• Many hydrological models results of years of development
• Significant amount of money has already been invested
Typical Scenario
OpenMI Framework
(.NET)
Model Wrapper
(.NET)
Model Core
(FORTRAN)

10. Migrating an existing Model to OpenMI
Step-1. Changes to the Engine Core: “.exe to .dll” so that it can be complied into a DLL

11. Migrating an existing Model to OpenMI
Step- 2. Wrapping the Model Engine
- OpenMI standard are develpoed in C# but most model engines are in FORTRAN, C,
C++ etc.
- To reduce the gap between two technologies and to minimize the changes to engine
core, wrapper is needed.
- to change calling convention, to communicate internally to Engine core.
<<Linkable Engine>> Wrapper Engine Core

12. Advantages of OpenMI
• Making integrated modelling feasible at operational level
• Allows data exchange at run time.
• Constructing a single model of all catchment processes is not a
feasible option.
• Makes use of existing model and provides the flexibility to try
alternative model of individual process.
• Not limited to models only.
• Growing number of users and becoming a standard.
• Not limited to models running on different dimension, different
calculation time step, different scale, different platform, different
projection, different spatial representation.

13. Drawbacks of OpenMI
• The usefulness of the OpenMI standard relies on the availability of
compliant models.
• Existing models need to migrate to OpenMI compliant models,
which requires some work. But OpenMI association provides
“Software Development Kit”.
• New model components can be coded in OpenMI way.
• Calculation time overhead [Standalone vs Combined/Integrated].

14. Conclusions
• Becoming more and more popular.
• Many known models are made OpenMI complaint:
SWAT, SWMM, MIKE11, InfoWorks, Sobek, Delft3D, ISIS etc.
• Becoming a standard interface for integrated modelling.

15. References
This presentation is based on series of documents “The OpenMI Series
– for the OpenMI version 1.4) released by OpenMI association.
Documents can be downloaded from: http://www.openmi.org/

16. Thank You
&
Questions??