| Author | Message | ||
     yang (gymwyy) New member Username: gymwyy Post Number: 1 Registered: 05-2006 |
Mr. Nelson: I am a novice of flexpde5.0.8, and I need your help.I present a photoconductor device model in 2D that is based on time-dependent convective/diffusive continuity and transport equatations. For simplified the equations,I consider the outer electric field Ex in script as constant.The source in script is the Gausse pulse laser which excited the photoconducted semiconductor. Only the hole continuity equation is listed blow. The equations seems to be an easy problem. However, the program that I wrote cannot give a meaningful result. Could you give me some advices? Thank you very much for your patience and answer. TITLE 'photoconductive semiconductor' { the problem identification } COORDINATES cartesian2 { coordinate system, 1D,2D,3D, etc } VARIABLES { system variables } p(threshold=1) DEFINITIONS { parameter definitions } up=400 ni=1.1e7 Ex=10 L=0.2 {PCSS(photoconductive semiconductor) length cm} W=0.15 {PCSS width cm} h=6.625e-28 Sp=1.5e-6 Sn=1.5e-6 Lambda=0.532 {wavelength of laser um} c=3e8 I0=0.01 {energy of laser uJ} Dp=1e-3 tp=1e3 Twidth=0.1000 Sigma=Twidth/(2*sqrt(2)) t0=1 ndelay=0.05 Alpha=2.1 R=0.35 g0=(1-R)*I0*Alpha/(sqrt(2*pi)*L*W*h*c/Lambda*Sigma) vin=2500 Ld=0.3614 u0=38.4615 t00=0.1306 R0=8.422e7 source=10*exp(-((t/t00-t0)/ndelay)^2-(x-L/2)^2/Ld^2-Alpha*y/Ld){with normalize} {source=g0*exp(-((t-t0)/ndelay)^2-Alpha*y)} {without normalize} INITIAL VALUES p=0 EQUATIONS { PDE's, one for each variable } div(Dp*grad(p)) + source-p/tp/R0-up/u0*Ex*dx(p)= dt(p){with normalize} {div(Dp*grad(p)) + source-p/tp-up*Ex*dx(p)= dt(p)} {without normalize} ! CONSTRAINTS { Integral constraints } BOUNDARIES { The domain definition } REGION 1 { For each material region } START(0,0) NATURAL(p)=Sp*p/Dp LINE TO (L,0) NATURAL(p)=Sp*p/Dp LINE TO (L,W) VALUE(p)=0 LINE TO (0,W) NATURAL(p)=Sp*p/Dp LINE TO FINISH ! TIME 0 TO 1 { if time dpendent } time 0 to 30 by 0.1 MONITORS { show progress } for t = 0 by 0.1 to 30 elevation(p) from (L/2,0) to (L/2,W) as "p " elevation(p) from (0,0) to (0,W) as "p left" elevation(p) from (L,0) to (L,W) as "p right" elevation(p) from (0,W/2) to (L,W/2) as "p hengxiang" {surface(p)} PLOTS { save result displays } surface(source) CONTOUR(p) histories { history(p) at (0,0) (0.1,0) (0.2,0) (0.1,0.075) (0.1,0.15)} history(p) at (L/2,W/2) (L/4,W/4) (3*L/4,3*W/4) (L/4,W/2) END | ||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 613 Registered: 06-2003 |
1. Your THRESHOLD is fourteen times larger than the maximum value of P. This says you don't care about the accuracy of the solution (see THRESHOLD in the Help Index). However, changing this to 0.001 doesn't entirely cure the difficulty. 2. You have specified the inward normal flux of P on three boundaries as Dp*dn(p)=(Sp/Dp)*p. Equivalently, the outward normal derivative of p is (Sp/Dp^2)*p. This says that the larger P is, the more flux comes in through the boundary. Is that what you wanted? (See "Natural boundary conditions" in the Help Index). | ||
| yang (gymwyy) New member Username: gymwyy Post Number: 2 Registered: 05-2006 |
Mr.Nelson,I'm so grateful for your reply.Thank you for your answer. Firstly,I have specified the THRESHOLD as 0.001. However,as you said,the difficulty didn't been cured entirely. Second,I have also read the help index and checked boundaries carefully.I have changed the boundaries as dn(p)=(Sp/Dp)*p.I think the boundary condition is reasonable.For in the 3 boundaries of semiconductor,the carriers are recombined through surface recombinations.And also,when the Ex was specified as zero,i.e.,only the diffusive effect was considered,the result was ideal. Mr.Nelson,could you give me a farther advice?Thank you very much! TITLE 'photoconductive semiconductor' { the problem identification } COORDINATES cartesian2 { coordinate system, 1D,2D,3D, etc } VARIABLES { system variables } p(threshold=0.001) DEFINITIONS { parameter definitions } up=400 ni=1.1e7 Ex=10 L=0.2 {PCSS(photoconductive semiconductor) length cm} W=0.15 {PCSS width cm} h=6.625e-28 Sp=1.5e-6 Sn=1.5e-6 Lambda=0.532 {wavelength of laser um} c=3e8 I0=0.01 {energy of laser uJ} Dp=1e-3 tp=1e3 Twidth=0.1000 Sigma=Twidth/(2*sqrt(2)) t0=1 ndelay=0.05 Alpha=2.1 R=0.35 g0=(1-R)*I0*Alpha/(sqrt(2*pi)*L*W*h*c/Lambda*Sigma) vin=2500 Ld=0.3614 u0=38.4615 t00=0.1306 R0=8.422e7 source=10*exp(-((t/t00-t0)/ndelay)^2-(x-L/2)^2/Ld^2-Alpha*y/Ld){with normalize} {source=g0*exp(-((t-t0)/ndelay)^2-Alpha*y)} {without normalize} INITIAL VALUES p=0 EQUATIONS { PDE's, one for each variable } div(Dp*grad(p)) + source-p/tp/R0-up/u0*Ex*dx(p)= dt(p){with normalize} {div(Dp*grad(p)) + source-p/tp-up*Ex*dx(p)= dt(p)} {without normalize} ! CONSTRAINTS { Integral constraints } BOUNDARIES { The domain definition } REGION 1 { For each material region } START(0,0) NATURAL(p)=Sp*p LINE TO (L,0) NATURAL(p)=Sp*p LINE TO (L,W) VALUE(p)=0 LINE TO (0,W) NATURAL(p)=Sp*p LINE TO FINISH ! TIME 0 TO 1 { if time dpendent } time 0 to 30 by 0.1 MONITORS { show progress } for t = 0 by 0.1 to 30 elevation(p) from (L/2,0) to (L/2,W) as "p " elevation(p) from (0,0) to (0,W) as "p left" elevation(p) from (L,0) to (L,W) as "p right" elevation(p) from (0,W/2) to (L,W/2) as "p hengxiang" {surface(p)} PLOTS { save result displays } surface(source) CONTOUR(p) histories { history(p) at (0,0) (0.1,0) (0.2,0) (0.1,0.075) (0.1,0.15)} history(p) at (L/2,W/2) (L/4,W/4) (3*L/4,3*W/4) (L/4,W/2) END | ||
| Elhanafi Shamseldin (hanafi) New member Username: hanafi Post Number: 1 Registered: 06-2006 |
I am trying to use fexpde to solve my equations hover after the program run for a long time it stops by it self, have repeated that several time but still it will stop and close Any one can give me a clue | ||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 621 Registered: 06-2003 |
The FlexPDE scripting languages allows an enormous flexibility in what you can say and how you build your equations. It is impossible for me to guess what is wrong merely from the fact that the evolution runs into trouble. If you send me the script that fails, I will try to see what is happening. Send to support@pdesolutions.com |