post_processing.rst

Post processing

Besides plotting the result, it is also possible to query numerical results. We'll go through them with a simple example.

from anastruct import SystemElements
import matplotlib.pyplot as plt
import numpy as np

ss = SystemElements()
element_type = 'truss'

# create triangles
x = np.arange(1, 10) * np.pi
y = np.cos(x)
y -= y.min()
ss.add_element_grid(x, y, element_type=element_type)

# add top girder
ss.add_element_grid(x[1:-1][::2], np.ones(x.shape) * y.max(), element_type=element_type)

# add bottom girder
ss.add_element_grid(x[::2], np.ones(x.shape) * y.min(), element_type=element_type)

# supports
ss.add_support_hinged(1)
ss.add_support_roll(-1, 2)

# loads
ss.point_load(node_id=np.arange(2, 9, 2), Fy=-100)

ss.solve()
ss.show_structure()

Node results system

anastruct.fem.system.SystemElements.get_node_results_system

Example

We can use this method to query the reaction forces of the supports.

print(ss.get_node_results_system(node_id=1)['Fy'], ss.get_node_results_system(node_id=-1)['Fy'])

output :

199.9999963370603 200.00000366293816

Node displacements

anastruct.fem.system.SystemElements.get_node_displacements

Example

We can also query node displacements on a node level (So not opposite, as with the system node results.) To get the maximum displacements at node 5 (the middle of the girder) we write.

print(ss.get_node_displacements(node_id=5))

output :

{'id': 5, 'ux': 0.25637068208810526, 'uy': -2.129555426623823, 'phi_y': 7.11561178433554e-09}

Range of node displacements

anastruct.fem.system.SystemElements.get_node_result_range

Example

To get the deflection of all nodes in the girder, we use the get_node_result_range method.

deflection = ss.get_node_result_range('uy')
print(deflection)
plt.plot(deflection)
plt.show()

output :

[-0.0, -0.8704241688181067, -1.5321803865868588, -1.9886711039126856, -2.129555426623823, -1.9886710728856773, -1.5321805004461058, -0.8704239570876975, -0.0]

Element results

anastruct.fem.system.SystemElements.get_element_results

Example

Axial force, shear force and extension are properties of the elements and not of the nodes. To get this information, we need to query the results from the elements.

Let's find the value of the maximum axial compression force, which is in element 10.

print(ss.get_element_results(element_id=10)['N'])

output :

-417.395490645013

Range of element results

anastruct.fem.system.SystemElements.get_element_result_range

Example

We can of course think of a structure where we do not know where the maximum axial compression force will occur. So let's check if our assumption is correct and that the maximum force is indeed in element 10.

We query all the axial forces. The returned item is an ordered list. Because Python starts counting from zero, and our elements start counting from one, we'll need to add one to get the right element. Here we'll see that the minimum force (compression is negative) is indeed in element 10.

print(np.argmin(ss.get_element_result_range('axial')) + 1)

output :

10