17 A Framework for Dynamic Simulation of Interconnected …
587
• number and composition of phases;
• total number and composition of compounds;
• set of distributed parameters.
Material stream interacts closely with the materials database (see Sect. 7). Thus,
in addition to data, which is based on the general structure of the material stream,
some additional MDB-related information is always available. In accordance with a
given stream structure, various compound-related properties can be obtained for:
• Each individual material available in the database. The specific value is taken
directly from the database (for constant properties) or calculated in accordance
with the current stream temperature and pressure (for temperature- and pressure
dependent properties).
• Each phase mixture indicated in the stream. The calculation method usually
depends on the type of the phase (solid/liquid/vapor).
• Overall mixture of all available phases in the stream. Only possible for a limited
set of properties.
The calculation of mixtures can be performed either on the basis of mass flow or
on the basis of the molar amount of substance.
To describe continuous changes of material parameters through time, a discretized
representation is used. All variations that occur in the material stream during the entire
modelling interval [t START ; t END ] are presented in the form of separate discrete states,
which are called time points. Each time point describes the state of the material at that
particular moment in time. Thus, in order to describe dynamic changes, the material
stream is represented as a sequence of time points with the same structure given
in Fig. 2. Wherein, access to data should be provided over the entire time interval,
regardless of whether a particular time point was directly stored in the structure of
the material stream. To do so, linear data interpolation is used to access data between
points. At the same time, to represent the dynamic process with a given accuracy, the
interval between neighbouring points should depend on the rate of change of material
parameters and the user-specified tolerance. For more details on time integration, see
Sect. 3.
In dynamic modelling, units can have an internal time-dependent state. In this
case, in the simulation system Dyssol, the so-called holdup is used to describe the
material inside the unit. Its structure is completely analogous to the structure of
the material stream, except for the fact that the mass flow parameter in this case is
replaced by the mass of the internal material.
2.3 Structure of Unit
The proposed structure of the unit (Fig. 3) was developed, on the one hand, to
support the calculation algorithm for the dynamic simulation and, on the other hand,
to provide interaction between the model, the simulation system and the user.
587
• number and composition of phases;
• total number and composition of compounds;
• set of distributed parameters.
Material stream interacts closely with the materials database (see Sect. 7). Thus,
in addition to data, which is based on the general structure of the material stream,
some additional MDB-related information is always available. In accordance with a
given stream structure, various compound-related properties can be obtained for:
• Each individual material available in the database. The specific value is taken
directly from the database (for constant properties) or calculated in accordance
with the current stream temperature and pressure (for temperature- and pressure
dependent properties).
• Each phase mixture indicated in the stream. The calculation method usually
depends on the type of the phase (solid/liquid/vapor).
• Overall mixture of all available phases in the stream. Only possible for a limited
set of properties.
The calculation of mixtures can be performed either on the basis of mass flow or
on the basis of the molar amount of substance.
To describe continuous changes of material parameters through time, a discretized
representation is used. All variations that occur in the material stream during the entire
modelling interval [t START ; t END ] are presented in the form of separate discrete states,
which are called time points. Each time point describes the state of the material at that
particular moment in time. Thus, in order to describe dynamic changes, the material
stream is represented as a sequence of time points with the same structure given
in Fig. 2. Wherein, access to data should be provided over the entire time interval,
regardless of whether a particular time point was directly stored in the structure of
the material stream. To do so, linear data interpolation is used to access data between
points. At the same time, to represent the dynamic process with a given accuracy, the
interval between neighbouring points should depend on the rate of change of material
parameters and the user-specified tolerance. For more details on time integration, see
Sect. 3.
In dynamic modelling, units can have an internal time-dependent state. In this
case, in the simulation system Dyssol, the so-called holdup is used to describe the
material inside the unit. Its structure is completely analogous to the structure of
the material stream, except for the fact that the mass flow parameter in this case is
replaced by the mass of the internal material.
2.3 Structure of Unit
The proposed structure of the unit (Fig. 3) was developed, on the one hand, to
support the calculation algorithm for the dynamic simulation and, on the other hand,
to provide interaction between the model, the simulation system and the user.