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 Author Comment/Response DSolve Piecewise Replacement 05/16/12 10:54am Hello! I just started using Mathematica two days ago. I'm having some trouble with the following: I have two differential equations, where I want to use the solution of the first one to solve the second one. Then I get errors regarding replacement . I've spent a lot of time trying and failing and I thought it was time two ask for help. The input is as follows and I use Wolfram 8 Trial version. wallThickness = 0.2 wallArea = 2.2*2.2 c1 = c2 = 1.1 v1 = v2 = wallArea*4.4 p1 = p2 = 1.15 emissivity = 0.9 stefan = 5.6704*10^(-8) hAir = 100 kWall = 10^(-1.4) R1 = R3 = 1/(hAir*wallArea) R2 = wallThickness/(kWall*wallArea) R = 6 (R1 + R2 + R3) a = p1*v1*c1 b = p2*v2*c2 fullyTime = 358.4 decayTime = 636 extTime = 1100 growCoef = 0.0029 decayCoef = 0.00003 grow[t_] = growCoef*t^2 fully[t_] = grow[fullyTime] decay[t_] = grow[fullyTime]*Exp[-((t - decayTime)^2)*decayCoef] heatRate[t_] = 2*1000*Piecewise[{ {grow[t], 0 <= t < fullyTime}, {fully[t], fullyTime <= t < decayTime}, {decay[t], decayTime <= t < extTime} }] Plot[heatRate[t], {t, 0, 1100}] heat[t_] = Integrate[heatRate[t], t] Plot[heat[t], {t, 0, 1100}] sol1 = DSolve[{Derivative[1][q][t] + q[t]/(R*b) == ( heat[t] - 5*q[t])/(R*a), q[0] == 0}, q, t] Plot[q[t]/1000 /. sol1, {t, 0, 1100}] j = q[t] /. sol1[[1]]; sol2 = DSolve[{Derivative[1][w][t] = j - w[t]/(6*R*b), w[0] == 0}, w, t] Plot[Evaluate[q[o] /. sol2], {o, 0, 1100}] URL: ,

 Subject (listing for 'DSolve Piecewise Replacement') Author Date Posted DSolve Piecewise Replacement DSolve Piece... 05/16/12 10:54am Re: DSolve Piecewise Replacement Bill Simpson 05/17/12 1:12pm Re: DSolve Piecewise Replacement Peter Pein 05/20/12 07:40am
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