Software for Fluid Power Technology

From Editor

The purpose of the Software Review section of the Journal is to present information to the reader about engineering software, including simulation programs, to highlight their specific features and their "fitness to purpose" in the unique field of fluid power and motion control. It is, of course, impossible to establish evaluation criteria matching the needs of all readers, therefore readers should not look for absolute ratings but more or less "fuzzy" opinions of the reviewer. A software program is like a wrench, just a tool to solve problems. It is good to solve some problems and not so good for others and this depends on both the nature of the problem and the users' attitude - and generally when we review software we do not know either. A software tool can be highly specialised and great for a some applications but not so well suited for others, on the other hand another software tool can be more flexible and generally applicable but without outstanding features. It is impossible, and even misleading, to say which one is better. What we hope to accomplish is to give the reader information necessary to take his/her own decision.

ITI-SIM®
Modelling and Simulation Environment for Fluid Power Components and Systems


The purpose of this review is on one hand to introduce the simulation tool ITI®-SIM (from ITI GmbH in Dresden, Germany) and on the other hand to provide the reader with some relevant issues for the evaluation of fluid power simulation software.

1 General Concept

The overall concept of ITI®-SIM is based on the following principles:
Complex fluid power systems combine not only hydraulic and pneumatic components, but also several devices from different physical domains (mechanical, thermal, electrical etc.) ITI®-SIM offers model libraries which cover a wide range of physics and application areas (e.g. hydraulics, pneumatics, thermics, mechanics, motors and couplings, electromechanical drives, signal blocks). Most of these predefined model objects combine several options, which can be turned on or off in order to adapt the model to a specific technical device (e.g. hydraulic accumulator: choice of different construction types, different gases, heat transfer mechanisms, ideal/real gas behaviour etc.)
In ITI®-SIM, the way of model construction has been adapted to the most common description for each engineering discipline, which means circuit diagrams for fluid power components, functional diagrams for mechanical devices and block diagrams for control structures. Figure 1 shows a typical structure of such a model, combining hydraulic and mechanical components as well as control blocks.
The parameter concept of ITI®-SIM strongly relates to the actual technical device. Figure 2 shows the parameter dialog for the model object Hydraulic Hose Line. The user has access to the dialog box by clicking on the component symbol in the model window.


Fig. 1: ITI®-SIM allows quick and easy model construction due to the large library set of predefined model objects from many physical domains and application areas

 
Fig. 2: Parameter specification in ITI®-SIM strongly relates to catalog data of the real device (example: Hydraulic Hose Line)

 

Many people have become familiar with the standards of Windows and their Office applications. With ITI®-SIM as a native Windows-Application, the user can work in the common way. Model libraries, dialogs, menus, tool tips, tool bars and online help have been designed to give a maximum of ergonomic comfort and intuitive-ness. As a result, users without any preliminary simulation experience become familiar with the program very quickly.

2 Creation of User-Defined Models

Even the most-comprehensive model library will not be able to cover the full range of technical devices and components. For this reason, the possibilities to con-struct user-specific model components should be considered as an important feature of the simulation software. In ITI®-SIM, the user has several opportunities to build its own model components:

a) Parameter Input Using Expressions:

For any parameter in ITI®-SIM, the user can input variables combined with functional/boolean ex-pressions instead of constant values. This way, ar-bitrary dependencies between parameters and re-sult variables can be realized.

b) Parameter Input Using Data Tables:

For a lot of parameters (especially in the Hydraulics Library), the user can alternatively specify data tables. This option allows easily to include data which has been obtained from measurements (or CFD-Simulations) into ITI®-SIM. As an example, Fig. 3 shows the relevant dialogs for the model object Throttle Valve.


Fig. 3: For many model parameters (here: pressure- flow characteristics of throttle valve) the user can input curves / data tables

 

c) Definition of Additional Connectors:

A higher degree of flexibility to realize arbitrary dependencies between result variables and input parameters can be obtained using the feature Connection Assistant. To any pre-defined model object, the user can easily add one or more inputs or outputs. A special wizard will guide the user to accomplish this task.

d) User-Defined Elements:

For each library of model objects, ITI®-SIM provides so-called User-Defined Elements. The behaviour of these elements (in hydraulics and pneumatics the relationship between flow and pressure drop) can be specified by the user. A number of input parameters can be created for this task.

e) Macro-Objects (Sub-Models):

Existing model structures can be grouped together to build one Macro-Object (sub-model). Such a Macro-Object can be stored in a Macro Library for subsequent use. The technique can be used to built up hierarchical models - any number of levels is possible.
For example, arbitrary valve models can be constructed very fast from the library of Basic Hy-draulic Components (Orifice, Nozzle, Gap, Inertia, Piston Area etc.) Figure 4 shows the Macro Model for a 4/3 switching valve.


Fig. 4: Macro Objects allow the fast creation of models for special components, like hydraulic valves from basic elements

 

f) User-Defined Algorithms:

Another option to model special components with non-standard behaviour is to include a user-specific algorithm. For this purpose, ITI®-SIM provides a special model object called User-DLL. The only parameter of this model object is a link to an ex-isting Windows-DLL file (Dynamic Link Library). The DLL-file can be created by any external compiler, such as Microsoft C++, Delphi, but also by Real-Time Workshop® of MATLAB®/Simu-link®. The last option allows to include existing MATLAB® models for control structures into ITI®-SIM. Figure 5 shows the model for a Pressure Control Valve using the model object User-DLL. The DLL-file was created from a C++ algorithm.


Fig. 5: User-defined algorithms (here C++) can be used to describe non-standard components and functions

 

g) Co-Simulation:

For certain applications, it might be favorable to simulate parts of the system by an external simu-lation tool. One possible reason for this approach could be, that existing models from other simulation packages are to be used (e.g. models for control structures in MATLAB®/Simulink®). Another reason could be to include additional domains, which are not covered by ITI®-SIM (e.g. 3D-mechanics).
ITI®-SIM provides special model objects to realize a co-simulation with external simulation tools. Examples for this option are shown in Fig. 6 and 7. Both simulation programs communicate with each other at certain time intervals and exchange their data.


Fig. 6: Online-coupling of MATLAB®/Simulink® and ITI®-SIM. The model of the controller is realized in MATLAB® , the model of the hydraulic circuit in ITI®-SIM


Fig. 7: Online-coupling of ADAMS (3D model of excavator) and ITI®-SIM (model of hydraulic circuit)

 

3 Library of Hydraulic and Pneumatic Elements

ITI®-SIM offers a large set of pre-defined model objects for fluid power applications (see Fig. 8 for the Hydraulics Library). These libraries include the following features:


Fig. 8: ITI®-SIM offers a comprehensive set of pre- defined model objects for fluid power applications (here: Hydraulics Library) Online-coupling of ADAMS (3D model of excavator) and ITI®-SIM (model of hydraulic circuit)

  To select a hydraulic fluid (for the Hydraulics Library), the user has access to a pre-defined database. He can choose among the available fluids, but he can also eas-ily define its own fluid. The following properties are built-in functions of each fluid:

Special emphasis was given to ensure a great variety of available model descriptions. It means, the user can choose between alternative modelling approaches, in order to specify the necessary input parameters based on

Such a variety is quite useful, especially since different application fields demand different modelling strategies (e.g. component/system simulation) and different levels of abstraction as well as accuracy. Figure 9 shows the parameter dialog for the model object 2-Way Proportional Edge. The user can select the kind of flow description, the cross section shape as well as the kind of input parameter (value/expression/function or table).


Fig. 9: In ITI®-SIM the user can select different model descriptions, depending on the available input parameters as well as on the preferred model quality (example: parameter dialog of the model object "2-Way Proportional Edge")

  In summary, ITI®-SIM is a tool for engineers and scientists, who want to analyze and optimize the dynamic behaviour of systems combining hydraulic, pneumatic, mechanical, electrical and thermal components together with control structures. It does not require a deep theoretical knowledge about numerical algorithms, mathematical and physical description of the systems as well as experience in modelling and simulation. The ergonomic and intuitive graphical user interface lets the modelling and simulation process to become very efficient. It is, however, also a tool open for specialists, due to the vast variety of available model descriptions and the flexible features to build user-defined models of non-standard components.

Facts about ITI®-SIM

Internet Site http://www.itisim.com
Vendor  ITI GmbH
Location Gostritzer Str. 63
01217 Dresden, Germany
Contact Person Andreas Klein, Dr.-Ing.
Educational Version Yes
Telephone number +49 351 871 7239
Telefax number +49 351 871 7255
E-mail klein@iti.de
fluid@iti.de
Platforms WinNT, Win2000

 

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