Index
Time-dependence
Ver: 1
 

DESCRIPTION

In the context of time-dependent tasks, material parameters or boundary condition parameters can be a function of time (e.g. changing flow rate).

In Polyflow version 3, any problem parameter can be defined as an algebraic function of time t .

When the task setup is of the transient type, the "Time-dependence" menu appears after the definition of parameters which might be a function of time.

During the time-marching process, the value of a specific parameter will be calculated as the product of its nominal value and the function of time selected for that particular parameter.

Implemented functions are as follows :

  OPTIONS
 
 -1 
 Upper level menu
0
 F(S) = User Defined Function
Allows the user to enter the index his own function of time. This function will be evaluated at run-time by CLIPS interpreter. (cfr 'User Defined Functions' chapter of the User's Manual).
1
 Time-independent
This is the default setup
2
 f(t) = t
Linear function of time.
Frequently used for flow rates changing with time.
3
 f(t) = 1/t
Inverse function of time.
Not available if tinit = 0.0
4
 f(t) = a + b*t + c*t**2 + d*t**3 
Third order polynomial
5
 f(t) = ramp function
This is a function with 4 parameters (a,b,c,d) representing the corner values of a ramp function as follows:


 
6
 f(t) = a * cos( b*t + c ) + d + e*t
A cosine function
7
 f(t) = a * t**b + c * t**d
Rational exponents of t
8
 f(t) = a * exp( b*t ) + c + d*t
Exponential function (e-base)
9
 f(t) = double ramp function
This is a function with 7 parameters (a,b,c,d,e,f,g) representing the corner values of a double ramp function as follows:


 
10
 f(t) = trapezoidal wave
This is a function with 6 parameters (a,b,c,d,e,f) representing a 'trapezoidal wave' as follows:


 
11
 f(t) = H step function
This is a function with 4 parameters (a,b,c,d) increasing or decreasing step by step as follows:


 
12 Multi-Ramp Function
This is a multi-linear function : the user gives a series of n ( ti , f(ti ) ) pairs.
f(t) = f(t1)                                                                if  t < t1
f(t) = f(ti ) + ( f(ti+1) - f(ti ) ) * (t-ti )/(ti+1-ti )      if  ti < t < ti+1
f(t) = f(tn)                                                                if  t  > tn
13
 Modify the value of a
To enter the "a" parameter in laws (4 to 11)
14
 Modify the value of b
To enter the "b" parameter in laws (4 to 11)
15
 Modify the value of c
To enter the "c" parameter in laws (4 to 11)
16
 Modify the value of d
To enter the "d" parameter in laws (4 to 11)
 17
 Modify the value of e
To enter the "e" parameter in laws (6, 9 and 10)
18
 Modify the value of f
To enter the "f" parameter in laws (9 to 10)
19
 Modify the value of g
To enter the "g" parameter in laws (9)
EXAMPLES For an transient problem starting at a low flow rate and ending at a flow rate of Q, enter :
Q as the flow rate; select function 2.
The calculation will start at a flow rate = Q * (tinit + Dtinit) SEE ALSO