Problem in continuum mechanics module.

[Alejandro Martín Hernán]

Hi everyone!

I has been testing the continuum mechanics module in order to understand how it works for the gsoc2020, but I found a problem.

I was trying to calculate the reaction forces of the following beam to validate the module, knowing that the reactions are R_0 = -2801.2 N and R_8.3 = -7198.8 N.

However, the results obtained are: {R_0: -2500.00000000000, R_8.30000000000000: -7500.00000000000}. This is not correct since if we calculate the equilibrium of moments about a point it is not zero because the beam must be in equilibrium. The code used was:

>>>from __future__ import print_function, division

>>>from sympy import *

>>>from sympy.external import import_module

>>>numpy = import_module('numpy', import_kwargs={'fromlist':['arange']})

>>>from sympy.physics.continuum_mechanics.beam import Beam

>>>from sympy import symbols, Piecewise

>>>init_printing(use_unicode=True, wrap_line=False)

>>>E, I = symbols('E, I')

>>>R_0, R_8 = symbols('R_0, R_8.30000000000000')

>>>b = Beam(8.3, E, I)

>>>b.apply_support(0,'pin')

>>>b.apply_support(8.3, 'roller')

>>>b.apply_load(-1250, 2, -2)

>>>b.apply_load(4000, 4.3, -1)

>>>b.apply_load(3000, 6.3, 0, 8.3)

>>>b.solve_for_reaction_loads(R_0, R_8)

>>>b.reaction_loads

>>>b.draw().show()

The sketch looks well. I do not know if I am making someting wrong, but I will try to solve the problem.

[Jashan]

Hello Alejandro,

The issue is with the sign convention you used for the moment at x=2m. Changing its sign will give you the correct answer:

>>> b.apply_load(1250, 2, -2)

>>> b.apply_load(4000, 4.3, -1)

>>> b.apply_load(3000, 6.3, 0, 8.3)

>>> b.solve_for_reaction_loads(R_0, R_8)

>>> b.reaction_loads

{R₀: -2801.20481927711, R_8.30000000000000: -7198.7951807229}

[Alejandro Martín Hernán]

Hi Jashan, 

Thank you for your answer, but then the b.draw() method uses a different sign criteria since in the sketch provided above if the moment is negative means counterclockwise which is the desired sense and if we introduce the moment positive the plot shows the moment in the clockwise direction as it is shown here:

[Jason Moore]

There may be a sign convention inconsistently in the new draw() method. Please submit and issue on github about this.

Thanks,

Jason

moorepants.info
+01 530-601-9791

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