| 1 | SUBROUTINE iniorbit |
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| 2 | $ (papoastr,pperiastr,pyear_day,pperi_day,pobliq) |
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| 3 | |
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| 4 | USE planete_mod, only: apoastr, periastr, year_day, obliquit, |
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| 5 | & peri_day, e_elips, p_elips, timeperi |
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| 6 | use comcstfi_mod, only: pi |
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| 7 | IMPLICIT NONE |
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| 8 | |
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| 9 | !======================================================================= |
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| 10 | ! Initialisation of orbital parameters (stored in planete_h module) |
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| 11 | !======================================================================= |
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| 12 | |
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| 13 | c Arguments: |
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| 14 | c ---------- |
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| 15 | |
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| 16 | REAL,INTENT(IN) :: papoastr,pperiastr,pyear_day,pperi_day,pobliq |
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| 17 | |
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| 18 | c Local: |
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| 19 | c ------ |
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| 20 | |
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| 21 | REAL zxref,zanom,zz,zx0,zdx |
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| 22 | INTEGER iter |
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| 23 | |
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| 24 | c----------------------------------------------------------------------- |
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| 25 | |
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| 26 | pi=2.*asin(1.) |
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| 27 | |
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| 28 | apoastr =papoastr |
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| 29 | periastr=pperiastr |
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| 30 | year_day=pyear_day |
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| 31 | obliquit=pobliq |
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| 32 | peri_day=pperi_day |
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| 33 | |
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| 34 | PRINT*,'iniorbit: Periastron in AU ',periastr |
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| 35 | PRINT*,'iniorbit: Apoastron in AU ',apoastr |
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| 36 | PRINT*,'iniorbit: Obliquity in degrees :',obliquit |
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| 37 | |
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| 38 | |
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| 39 | e_elips=(apoastr-periastr)/(periastr+apoastr) |
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| 40 | p_elips=0.5*(periastr+apoastr)*(1-e_elips*e_elips) |
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| 41 | |
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| 42 | print*,'iniorbit: e_elips',e_elips |
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| 43 | print*,'iniorbit: p_elips',p_elips |
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| 44 | |
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| 45 | !----------------------------------------------------------------------- |
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| 46 | ! compute polar angle and distance to the Sun: |
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| 47 | ! ------------------------------------------------------- |
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| 48 | |
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| 49 | ! compute mean anomaly zanom |
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| 50 | |
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| 51 | zz=(year_day-pperi_day)/year_day |
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| 52 | zanom=2.*pi*(zz-nint(zz)) |
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| 53 | zxref=abs(zanom) |
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| 54 | PRINT*,'iniorbit: zanom ',zanom |
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| 55 | |
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| 56 | ! solve equation zx0 - e * sin (zx0) = zxref for eccentric anomaly zx0 |
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| 57 | ! using Newton method |
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| 58 | |
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| 59 | zx0=zxref+e_elips*sin(zxref) |
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| 60 | DO iter=1,100 |
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| 61 | zdx=-(zx0-e_elips*sin(zx0)-zxref)/(1.-e_elips*cos(zx0)) |
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| 62 | if(abs(zdx).le.(1.e-12)) exit |
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| 63 | zx0=zx0+zdx |
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| 64 | ENDDO |
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| 65 | |
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| 66 | zx0=zx0+zdx |
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| 67 | if(zanom.lt.0.) zx0=-zx0 |
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| 68 | PRINT*,'iniorbit: zx0 ',zx0 |
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| 69 | |
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| 70 | timeperi=2.*atan(sqrt((1.+e_elips)/(1.-e_elips))*tan(zx0/2.)) |
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| 71 | PRINT*,'iniorbit: Perihelion solar long. Ls (deg)=', |
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| 72 | & 360.-timeperi*180./pi |
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| 73 | |
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| 74 | END |
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