Wrong calculation result when using imported user module?

ArnoldH

Hello,

I am trying to develop a script to do some fatigue calculations, but I noticed something weird and wanted to investigate further.

Hi,

I noticed when I use a function from an imported user module, the result is for some reason different than if I run the same function from the module itself.

I have following code which is a part of a module I will import into the main script:

```
from module_base import * #This will import the Ansys.Mechanical.DataModel.Enums items

import math #another modules you are using in the project

def Initialize(MyExtAPI, MyAnsys):
global ExtAPI; global Ansys
ExtAPI = MyExtAPI; Ansys = MyAnsys

def CalculateFatigueLife_DNV_Test(stress_range, SN_Curve,thickness,SCF=1,ref_thickness=25):
m1=3
log_a1=12.192
m2=5
log_a2=16.32
k=0.05
trans=1000000

log_N=log_a1-m1*math.log10(stress_range*SCF*math.pow(thickness/ref_thickness,k))
N = math.pow(10,log_N)
if(N>trans):
    log_N=log_a2-m2*math.log10(stress_range*SCF*math.pow(thickness/ref_thickness,k))    
    N = math.pow(10,log_N)
return N

print(CalculateFatigueLife_DNV_Test(334.7,"C CP",30,1,25))

import math
import Ansys.ACT.Math as math_ACT
import mech_dpf
import Ans.DataProcessing as dpf
import sys
CodePath = r"D:\ANSYS Scripts"
if not CodePath in sys.path:
sys.path.append(CodePath)

import FatigueFunctions as FF #module with fatigue calculations functions
reload(FF)

FF.Initialize(ExtAPI, Ansys)

print(FF.CalculateFatigueLife_DNV(334.7,"C CP",30,1,25))
print("Test: "+repr(FF.CalculateFatigueLife_DNV_Test(334.7,"C CP",30,1,25)))

FF.Initialize(ExtAPI, Ansys)

print("Test: "+repr(FF.CalculateFatigueLife_DNV_Test(334.7,"C CP",30,1,25)))
```
The code above prints: "Test: 41498.544"

I don't understand why when I call the function from the main code I get the different result from running the same function from the imported module. Is this a bug? Did anyone come across this before? My end plan here is to develop a module I can import into other scripts to carry out calculations etc.

Thanks

Running the main script yields the following message

ArnoldH

Something went wrong with the formatting in my post, I apologise, please see the below for clarity.

Imported module:

from module_base import * #This will import the Ansys.Mechanical.DataModel.Enums items

import math #another modules you are using in the project

def Initialize(MyExtAPI, MyAnsys):
global ExtAPI; global Ansys
ExtAPI = MyExtAPI; Ansys = MyAnsys

def CalculateFatigueLife_DNV_Test(stress_range, SN_Curve,thickness,SCF=1,ref_thickness=25):
m1=3
log_a1=12.192
m2=5
log_a2=16.32
k=0.05
trans=1000000

print(CalculateFatigueLife_DNV_Test(334.7,"C CP",30,1,25))

The above produces message: "40379" (and some extra digits

Main code:

import math
import Ansys.ACT.Math as math_ACT
import mech_dpf
import Ans.DataProcessing as dpf
import sys
CodePath = r"D:\ANSYS Scripts"
if not CodePath in sys.path:
sys.path.append(CodePath)

import FatigueFunctions as FF #module with fatigue calculations functions
reload(FF)

FF.Initialize(ExtAPI, Ansys)


print("Test: "+repr(FF.CalculateFatigueLife_DNV_Test(334.7,"C CP",30,1,25)))

The above produces following message: "Test: 41498" (and again, some extra digits)

Landon Mitchell Kanner

The issue is that the thickness and ref_thickness arguments are both being defined as integers, which causes thickness/ref_thickness to evaluate as 1 (an integer) instead of 1.2. I am not sure why we don't see this behavior when running the function directly in Mechanical, but luckily this allowed you to catch the bug.

A quick fix is to add this line to your function:

def CalculateFatigueLife_DNV_Test(stress_range, SN_Curve,thickness,SCF=1,ref_thickness=25):
    thickness = float(thickness)
...

Landon Mitchell Kanner

I did a little more digging. The Mechanical scripting environment seems to always return a float from integer division. This is not the default behavior for IronPython 2.7 (which is what Mechanical runs). I suspect that the Mechanical initialization scripts include something like:

from __future__ import division

An alternative solution is to add the above line to the top of your FatigueFunctions.py file.

Mike.Thompson

I have had issues myself with using integers to do math operations and not remembering that they are different from a float. It would be best practice to code your math functions with a float(SomeVal) function to ensure the input values are actually float numbers and not integers when appropriate.

ArnoldH

@Landon Mitchell Kanner , casting thickness as float seems to have solved this issue, The results are now matching the calculations. I will add some comments into the code to remember about this behaviour in the future. Thanks for help.