vpasolve returns empty syms 0x1
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I'm not able to figure out what is going on with this system. My other systems are getting solved but not this one. Can anyone help me figure this one out?
rho = 0.289018; % [lb/in^3]; density of material
Sy = 30000; % [psi]; yield strength of material
E = 27992280; % [psi]; Youngs modulus of material
V = 2158.689078; % [in^3]; volume of ENTIRE structure with solid legs, from SolidWorks
L = 118.25; % [in]; length of box structure, perpendicular to truck pulling force
w = 26; % [in]; width of box structure
l = 36; % [in]; height of legs
h = 9.1; % [in]; height of box structure only
Dl = 4; % [in]; outer diameter of legs
W = rho*V; % [lbf]; weight load of structure (conservative, treats legs as solid)
P = 16*20*2 + W; % [lbf]; centroidal load due to weight and PTDs w/ safety factor
Ry = 1250; % [lbf]; rxn in dir of pulling
Mx1 = (2500*2)*(l+h)/4 - P*w/8;
My1 = P*L/8;
MR1 = sqrt(Mx1^2 + My1^2); %total moment
syms I A t1x tau sigz R1 R3 %Leg 1, x-max
%Leg 1, x-max
eqns = [I == (pi/64)*(Dl^4 - (Dl-2*t1x)^4), A == (pi/4)*(Dl^2 - (Dl-2*t1x)^2), ...
tau == (3/2)*Ry/A, sigz == R1/A + My1*(Dl/2)/I, R1 == (P/2)-R3, ...
R3 == P/2 - (P*(w/2) + 5000*(l+h))/(2*w), Sy == sqrt(sigz^2 + 3*tau^2)];
S1 = vpasolve(eqns, [I,A,t1x,tau,sigz,R1,R3]);
采纳的回答
Star Strider
2018-11-29
One option is to use solve first rather than vpasolve, then use vpa later.
Example —
S1 = solve(eqns, [I,A,t1x,tau,sigz,R1,R3]);
I_num = vpa(S1.I)
A_num = vpa(S1.A)
producing:
I_num =
-1.5809251179322542233857232451522
-1.5809251179322542233857232451522
1.5598335563826831618612834229733
1.5598335563826831618612834229733
1.2534178213176158442695309403285
1.2534178213176158442695309403285
-1.2380191890238977904464145042831
-1.2380191890238977904464145042831
A_num =
-0.76705210311723380012877421564178
-0.76705210311723380012877421564178
0.80574886841346695683272432220417
0.80574886841346695683272432220417
24.489573101112048426635864036903
24.489573101112048426635864036903
25.737212591028410232062479989006
25.737212591028410232062479989006
Do the same for the others.
2 个评论
Shrikrishna Basude
2018-11-29
Star Strider
2018-11-29
As always, my pleasure!
The only explanationi I can offer is that it’s just the way the Symbolic Math Toolbox works. Other symbolic engines, such as Maple, might provide more direct results.
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