From: Philip R. <ph...@ph...> - 2015-02-21 18:20:28
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I am hoping that qucs can model a moderately complex transient non-linear component in a problem that I have in mind. What I want to do is model an circuit in which a thin wire explodes when a large current is passed through it (aka an exploding wire problem in the literature). It is bit like hugely overdriving a fuse in a circuit. The resistance of the wire changes significantly altering the current flow (obviously). The real question is, what capacitor energy is required to hard-fire the wire element (they vary in material, diameter and length). I include the simple LCR circuit doing the driving. In this case Rb is the resistance that changes (is is fixed at the moment because I am stuck). Now for the tricky bit. The resistance of the wire is highly non-linear, is not monotonic and depends on a function of the integral of i^2 dt where i is the current through the wire and t is time. This is called burst action in the literature. I have looked at the various equation driven elements in qucs and it is not obvious how to store a ‘history variable’, that is the burst action value up to the current point in the simulation. If I had that, I could add the next increment of burst action each calculation cycle and have what I need. Is this possible, or am I doing things the hard way? The second problem I see is that the controlling curves are of wire resistance vs burst action are not well matched to analytical fits. What would be easiest is a look-up table of burst action vs resistance. Alternatively, I could do a piecewise fit using the if:then structure that does seem to be in QUCS. I see that I can create a file-driven voltage source. Is there a way of using this since it appears to be designed for voltage vs time, not as an arbitrary look-up table? Again, am I doing thing the hard way? Many thanks Philip |
From: Guilherme B. T. <gui...@gm...> - 2015-02-22 18:54:37
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On 2/21/15 7:20 PM, Philip Rae wrote: > I am hoping that qucs can model a moderately complex transient non-linear component in a problem that I have in mind. What I want to do is model an circuit in which a thin wire explodes when a large current is passed through it (aka an exploding wire problem in the literature). It is bit like hugely overdriving a fuse in a circuit. The resistance of the wire changes significantly altering the current flow (obviously). The real question is, what capacitor energy is required to hard-fire the wire element (they vary in material, diameter and length). > > I include the simple LCR circuit doing the driving. In this case Rb is the resistance that changes (is is fixed at the moment because I am stuck). > > Now for the tricky bit. The resistance of the wire is highly non-linear, is not monotonic and depends on a function of the integral of i^2 dt where i is the current through the wire and t is time. This is called burst action in the literature. I have looked at the various equation driven elements in qucs and it is not obvious how to store a ‘history variable’, that is the burst action value up to the current point in the simulation. If I had that, I could add the next increment of burst action each calculation cycle and have what I need. Is this possible, or am I doing things the hard way? > > The second problem I see is that the controlling curves are of wire resistance vs burst action are not well matched to analytical fits. What would be easiest is a look-up table of burst action vs resistance. Alternatively, I could do a piecewise fit using the if:then structure that does seem to be in QUCS. I see that I can create a file-driven voltage source. Is there a way of using this since it appears to be designed for voltage vs time, not as an arbitrary look-up table? Again, am I doing thing the hard way? > > > Many thanks > > Philip Hi Philip Exploding wires sound like fun! Note that the list strips attachments above 50KB. Either copy and paste the schematic into the body of the message or post to the forum. As I understand you need to model a nonlinear resistor that depends on the integral (history) of another node. Perhaps the EDD (equation defined device) might be helpful for you. See http://qucs.sourceforge.net/docs/tutorial/equations.pdf The EDD supports the ternary if operator ( condition ? a : b ) and it may also give you the integration behavior depending on how you set it up. You can also build and ideal 'analog' integrator converging current to voltage with a 1F capacitor. In this case you might want to introduce some controlled sources to convert signals as appropriate and to decouple sections of the circuit. I am not sure we have support for look-up tables. I hope it helps. Regards. Guilherme |