From: boris petkovic
Date: Wed, 28 Mar 2001 05:36:46 -0800 (PST)
Subject: Re: [TSSP] Remaining CW problems & next stage of the project
Hi Paul, > Boris wrote: > > > Maybe this will be just repeating but I don't seem > to > > remember we got straigthened completely out the > > following: > > You're right. > > > 1) Problems of the coils at high elevation. > > Why so noticable discrepancy between mesured and > > simulated reso freqs. > > Still an open question. Kurt's measurements on his > small coil showed > that small features of the real coil, un-accounted > for by the model, > can introduce errors large enough to account for the > discrepancies, > but we don't know whether this kind of thing > accounts for all the > problems. --- Yes,this kinda of problems are called discretition demons in computer modelling .Powerful dynamic field softwares like EMAS meet the same problems . It is a true art to decide on right mathematical function of "step by step getting closer" in a vicinity of given geometry and be sure that error is enough small not to spoil all the work latter. If we add presence of fedding wire extending to the coil base it can alter resonance almost like much fatter metalic pole put there (logarithmic properties). ---- > > > Is the only reason suspicious external capacities > of > > elevated system with attached wire to it and > signal > > generator or there's perhaps more behind it? > > There may still be something wrong with the model, > either theoretical, > eg not accounting for dielectrics, or in > implementation, eg a coding > error which only shows up at small radius. I'm > hoping that someone > will supply Fres measurements on a small coil with > an additional tube > inside, in order to see the rough size of dielectric > effects. ---- Implementation should be in a first place. Problems ,if they were existing with dielectrics, should mmanifested themselfes in earlier simulations as well.But the simulations of coils placed just a little above ground plane were quite successful and in agreement with measurments. ---- > > > 2) > > I've noticed possibility for the difference > between > > reso > > frequencies of the coil structure excited by > voltage > > source (typical msm with signal generator),and > > corresponding "current source" frequency > (theoretical > > case of the current wave being pushed in a > bottom). > > In the first case the bottom of the coil is at > small > > potential but I haven't registered that in voltage > > graphs displays on tssp web pages. > > The voltage is too small to see on the graphs. ---- Hmm,for Q=70 little part should be there. But forget it .It's not as important anyway. ---- The > profile graphs in > all the documentation apply to isolated resonators > driven by a perfect > source. --- by voltage source,or by current source producing same reso effect ? For voltage source case ,as far as i remember,the result was something like "turning point" over the lenght of the resonator expressed aproximately by ratio 1/sqrt(Q). ---- I have an 'extended' version of tsim which > models the coil > plus the additional interactions of a realistic > external circuit, --- You mean walls,celling etc? --- and > this model reproduces the observed features, eg > splitting of the > resonance into a more complicated response, eg for > Terry's probed > small coil, I get > > 311.850 Max Ibase (Measured) > 312.920~ Ibase 90 deg to Vtop (Predicted) --- > 313.020 Max Vtop (Measured) by mutual agreement this should be what we call "resonance frequency " of the coil. ---- > 314.500~ Ibase in phase with Vbase (Predicted) > > which is an altogether more complicated picture. The > predicted > values above are based on guesses of various circuit > reactances, ---- I see.This depends on what radious of loop filament one takes into account when calculates inductivity,cross section of wire and nonlinear flow of current thru it etc? ---- > so they're not likely to be too accurate. > > > 3) > > Next stage of TSSP: When and how to approach to > > transient simulations modelling (time domain). > > More alternaives.. > > I've been busy revising documentation to match the > latest code > changes, and working on the next installment of > 'theory notes'. > Nothing much to report yet. A few items...the latest > simulator code > will model base feed, primary feed (incorporating > acmi's code), center > feed, and top feed (this latter is useful for > looking at output > admittances). This is for v0.9, to be released > shortly. ---- I will be looking forward to see any of these new changes. Even small ones. --- A major > revision of the tech notes, pn1205, is necessary to > describe all these > changes, and I'm still plodding on with that tedious > job. --- I know. It's not easy to systematicaly and concisely compose such document. -- As a bit of > light entertainment I managed to combine the (real) > functions > Cext(x), Cint(x,y), and M(x,y) into a single > (complex) function F(x,y) > which completely describes the physical coupling of > the solenoid. It > acts as a linear operator on the voltage profile > 'vector'. I've yet > to compute the eigenvectors of F but I think these > will turn out to be > the voltage profiles for each of the overtones, with > the corresponding > eigenvalues being inversely proportional to the > frequencies. > It remains to be seen where this leads to (if > anywhere), but it might > provide a more direct way to obtain the resonant > frequencies (as > opposed to the heuristics and trial solutions done > by tsim). ---- Yes! Every progress in this direction may lead to significant shotcuts in simulus,and to much more elegant methods for further exploring of the resonator behaviour.You're striving, in a sort of speaking , towards Bodlovic's way but using coupled qudruple network instead of coupled lattice of tx lines I guess. ----- > Presumably the eigenvectors of F(x,y) form a > complete orthogonal set, > so any particular voltage profile is then a vector > in the space > spanned by these basis vectors. It might be possible > to obtain from > F(x,y) an operator which is an infinitesimal > generator of the time > evolution of the basis vectors, which means that we > could explore the > time domain behaviour by just computing the > amplitude of each basis > vector, rather than having to compute the entire > V(x) for each delta t. ---- That would be valuable benefit of using eigenvectors method here. ---- > All falls apart of course when the load impedance is > a function of top > voltage. ---- Will you be more specific here? --- > > More realistically, I have a time domain model which > is just a basic > brute force iterative method. It has a tendency to > explode after a > few tens of cycles, and it uses too few elements to > be considered > quantitative, but it will cope very nicely with > non-linear elements > in the circuit. ---- arcs and nonlinearities don't have to bother us (yet). Regards, Boris __________________________________________________ Do You Yahoo!? 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