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70 lines
1.9 KiB
70 lines
1.9 KiB
2 years ago
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C Copyright(C) 1999-2020 National Technology & Engineering Solutions
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C of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with
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C NTESS, the U.S. Government retains certain rights in this software.
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C
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C See packages/seacas/LICENSE for details
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SUBROUTINE PRINC3(SK1, SK2, SK3, SK4, SK5, SK6, EV, INFO)
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REAL EV(3)
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REAL I1, I2, I3
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INTEGER INFO
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PARAMETER (THIRD = 0.33333 33333 33333 33333 33333)
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SQRT3 = SQRT(3.0)
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INFO = 0
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C Find principal trial stresses and directions -
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I1 = ( SK1 + SK2 + SK3 )
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I2 = ( (SK1-SK2)**2 + (SK1-SK3)**2 + (SK2-SK3)**2 ) / 6.0
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* + SK4**2 + SK5**2 + SK6**2
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S1 = ( (SK1 - SK2) + (SK1 - SK3) ) * THIRD
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S2 = (-(SK1 - SK2) + (SK2 - SK3) ) * THIRD
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S3 = (-(SK1 - SK3) - (SK2 - SK3) ) * THIRD
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I3 = S1 * S2 * S3 + 2.*SK4 * SK5 * SK6
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* - S1 * SK5**2 - S2 * SK6**2
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* - S3 * SK4**2
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C Calculate constants for Malvern Method (p92)
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C .... This sign trick does not work on Ultrix (and others?) with IEEE
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C since IEEE has a signed 0...........
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CC FI2 = I2 + (SIGN (0.5, I2) + SIGN (0.5, -I2))
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IF (I2 .EQ. 0.0) THEN
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FI2 = 1.0
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ELSE
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FI2 = I2
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END IF
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COS3AL = SQRT3 * 1.5 * I3 / FI2 / SQRT(FI2)
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COS3AL = SIGN( MIN( 1.0, ABS(COS3AL) ),COS3AL )
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C ... TRIG FUNCTION USED
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CALPHA = COS( ACOS(COS3AL) / 3.0)
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SALPHA = SQRT(1.0 - CALPHA**2)
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T = SQRT3 * SQRT(I2)
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P1 = (I1 + T * 2. * CALPHA ) * THIRD
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P2 = (I1 - T * (CALPHA + SALPHA * SQRT3)) * THIRD
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P3 = (I1 - T * (CALPHA - SALPHA * SQRT3)) * THIRD
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C ... Sort Into Correct Position (ev1 < ev2 < ev3)
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EV(1) = MIN(P1, P2, P3)
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EV(3) = MAX(P1, P2, P3)
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C ... This is bad from a round-off perspective, but we don't use the
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C value in algebra. Be warned if use where you need an accurate
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C ev(2).....
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EV(2) = P1 + P2 + P3 - EV(1) - EV(3)
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RETURN
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END
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