Component 131: Transient separator (with transfer function)

Specifications

Line connections
1	Signal input
2	Signal output

General User Input Values Results Characteristic Lines Physics Used Displays Example

General

The task of a transient separator is to represent transient processes by means of one or several coupled transfer functions without having to calculate a detailed physical model. The behaviour of many dynamic components can often be modelled e.g. using a simple PTn system. In contrast to the physically determined model, this results in a significantly lower calculating effort and thus expenditure of time. An approach from control theory is pursued by means of which a component is regarded as a signal transmitter. In this way it is possible to simulate a lot of components using a differential equation of following type:


	eqn. 1-1

This equations delivers the output/ answer signal y(t) using the parameters:

K: Proportional gain (Enhancing factor for input signal)
t: Time constant
n: Exponent
u(t): Input signal
Tt: Time of delay

The difference between present state and input signal generates the driving force for changing the output signal scaled by the time constant. The exponent is responsible for loading the driving force, while delay time fixes the period of input signal getting valid for the calculation. Even-numbered exponents are able to be solved analytically (n = 1 delivers PT1-Behaviour for example). Other exponents are going to be solved numerically. Discretisation of eqn 1-1 in time leads to following structure showing time step k:


	eqn. 1-2

In order to avoid errors due to fractional exponents, the absolute value of expression in brackets in eqn 1-1 will be taken for further calculations and hence rated by sgn function. Realization of delay time is carried out using a signal memory, which is able to feed back the signal into the calculation after a certain amount of time steps.
Delay time has not to be a multiple of the time step, if required sub steps will be added to the calculation.

With the FFU=2 mode, it is possible to calculate the input signal from the known output signal based on the same equations. This can be interesting, for example, if you have a time-damped measurement signal available and want to calculate the time characteristic of a non-damped value. The attenuation can be caused, for example, by the thick armor of a measured value sensor.
Note: Additional flag for calculating the output values of the transfer functions (FYOUT).

FYOUT serves to select between the value at the end of the time step, the moving average, and an arithmetic mean.

It is possible to calculate transfer functions with reaction times using non-equidistant time steps too.

Global Initialization of Transient Components

All transient components that possess the flag FINIT can be commonly controlled via one global flag.

For this, the flag FINIT has been expanded by the position GLOBAL: 0.

If it is set to this value, the control of the transient simulation will be handed over to the global variable “Transient mode“, which can be found under

Extras \Model Options\Simulation\Transient\ Combo Box "Transient mode".

This will then pass on the desired mode (first iteration or following iteration) to the components. This can be controlled from the time series dialog by means of the expression “@calcoptions.sim.transientmode“.

Component 131 has been expanded by 4 default values:

FOUTUS_M – used of outlet, mass flow
FOUTUS_H – used of outlet, enthalpy
FOUTUS_P – used of outlet, pressure
FDT - direction of transfer

The three flags FOUTUS_X can take two values. At FOUTUS_X=0, the calculated value (M, H, P) on Pin 2 from the current time step will be used, as before. This enables the highest precision. At FOUTUS_X=1, in contrast, the respective value from the last time step will be used. This has the advantage that this value does not change during the current time step, which leads to a better convergence of the calculation. However, the calculation will become less precise here.

The flag FDT controls the direction of transfer. For FDT=0, the value is transferred from Pin 1 to Pin 2. For FDT=1, the value is transferred from Pin 2 to Pin 1.

User Input Values


	General Properties
FINIT	Flag: Initializing state =0: Global, which is controlled via global variable "Transient mode" under Model Options: "Extras" ->"Model Options" -> "Simulation" -> "Transient" -> Combo Box "Transient mode" (See -> General-> Global Initialization of Transient Components ) =1: First run (TCOUNT set to 0) =2: Continuation run
FFU	Switch component on/off =0: Transient separator switched off (every input will be bypassed) =1: Transient separator active - Output signal is calculated from the known input signal =2: Transient separator active - Input signal is calculated from the known output signal
FSPEC	Type of transfer function =0: None =1: Only pressure =2: Only enthalpy =3: Pressure and enthalpy =4: Only mass flow =5: Mass flow and pressure =6: Mass flow and enthalpy =7: Mass flow, enthalpy and pressure
FDELAY	Switch calculation of delay time =0: Only transfer function =1: Only delay =2: Transfer function with delay
FYOUT	Calculation method of output =1: End of time step =2: Integral mean =3: Arithmetic average
	Parameters mass transfer
EXP_M	Exponent mass transfer function
FTAU0_M	Source of time constant for mass transfer =0: From specification value TAU0_M =1: Use function ETAU0_M
TAU0_M	Time constant mass transfer function
ETAU0_M	Function for TAU0_M function evalexpr:REAL; begin evalexpr:=60.0; // value interpreted as time [s] required end;
K_M	Gain factor mass transfer function
DELAY_M	Delay time mass transfer function
	Parameters enthalpy transfer
EXP_H	Exponent enthalpy transfer function
FTAU0_H	Source of time constant for enthalpy transfer =0: From specification value TAU0_H =1: Use function ETAU0_H
TAU0_H	Time constant eenthalpy transfer function
ETAU0_H	Function for TAU0_H function evalexpr:REAL; begin evalexpr:=60.0; // value interpreted as time [s] required end;
K_H	Gain factor enthalpy transfer function
DELAY_H	Delay time enthalpy transfer function
FOUTUS_H	Output value usage enthalpy = 0: from the current time step (highest accuracy) =1: From previous time step (highest convergence rate)
	Parameters pressure transfer
EXP_P	Exponent pressure transfer function
FTAU0_P	Source of time constant for pressure transfer =0: From specification value TAU0_P =1: Use function ETAU0_P
TAU0_P	Exponent pressure transfer function
ETAU0_P	Function for TAU0_P function evalexpr:REAL; begin evalexpr:=60.0; // value interpreted as time [s] required end;
K_P	Gain factor pressure transfer function
DELAY_P	Delay time pressure transfer function
FOUTUS_P	Output value usage pressure = 0: from the current time step (highest accuracy) =1: From previous time step (highest convergence rate)
FDT	Transfer direction =0: The value is transferred from connection 1 to connection 2 =1: The value is transferred from connection 2 to connection 1
	Miscellaneous
MACCU0	Mass stored previous time step
TPRE	Index previous time step
TIMEINT	Total integration time

Results

DIFFM	Actual difference input output mass flow
DIFFH	Actual difference input output enthalpy
DIFFP	Actual difference input output pressure
RTAU_M	Used value for TAU0_M
RTAU_H	Used value for TAU0_H
RTAU_P	Used value for TAU0_P
RMACCU	Mass stored end of time step
RTCURR	Index calculated time step
RTIMTOT	Total time at end of calculation

Characteristic curves

These "characteristic" curves doesn´t give any specifications or correlations to characterize the component. They are necessary to build up a memory for the signals.
Normally, there´s no need to set any values or give specifications, because the are transferred automatically by the time series calculations.

CINPUTM - History of input signal mass flow at line 1

This line stores the course of the input signal mass flow at line 1.