Atomizer/studies/uav_arm_optimization/NX_FILE_MODIFICATIONS_REQUIRED.md

NX File Modifications Required for Drone Gimbal Arm Study

Overview

The study uses the same beam model as simple_beam_optimization but requires modifications to:

1. Add modal analysis (frequency extraction)
2. Update loading conditions for the 850g camera payload
3. Ensure material properties match Al 7075-T6

Critical Modifications

1. Simulation File (Beam_sim1.sim)

REQUIRED: Add Modal Analysis Solution

You need to add a second solution for modal analysis:

1. Open Beam_sim1.sim in NX Simcenter

2. Create New Solution:

   • Solution Type: SOL 103 - Normal Modes
   • Name: modal_analysis
   • Number of modes: 10 (we only need the first, but calculate more for safety)
   • Frequency range: 0-500 Hz

3. Use Same Mesh as the static solution

   • Link to existing FEM file: Beam_fem1.fem

4. Boundary Conditions: Use same constraints as static analysis

   • Fixed constraint at base (same as static)
   • No loads needed for modal (it finds natural frequencies)

2. Static Analysis Modifications

Update Load Magnitude:

The existing static analysis load needs to represent the 850g camera payload:

1. Open Solution 1 (static analysis)
2. Modify Force Magnitude:
   • Old value: (whatever is currently there)
   • New value: 8.34 N (850g × 9.81 m/s²)
   • Direction: Downward (negative Y or Z depending on your coordinate system)
   • Location: Tip of beam (where camera attaches)

Note: 120 MPa stress limit provides safety factor of 2.3 on 6061-T6 yield strength (276 MPa)

3. Material Properties

Verify Material is Al 6061-T6:

1. Open Part File: Beam.prt

2. Check Material Assignment:

   • Material: Aluminum 6061-T6
   • Yield Strength: ~276 MPa
   • Young's Modulus: ~68.9 GPa
   • Density: ~2700 kg/m³
   • Poisson's Ratio: ~0.33

3. If not Al 6061-T6, update material assignment to match drone application requirements

4. Results Configuration

Ensure these results are requested:

For Static Solution (Solution 1):

• Displacement (VECTOR, all components)
• von Mises Stress
• Mass properties

For Modal Solution (Solution 2):

• Natural frequencies
• Mode shapes (optional, for visualization)

What You DON'T Need to Change

The parametric design variables are already set up correctly in the beam model:

• beam_half_core_thickness (20-30mm)
• beam_face_thickness (1-3mm)
• holes_diameter (180-280mm)
• hole_count (8-14)

These parameters will be automatically updated by the optimization loop.

Verification Steps

Before running optimization, verify:

1. Two Solutions Exist:

   Solution 1: Static Analysis (SOL 101) - displacement and stress
   Solution 2: Modal Analysis (SOL 103) - natural frequencies
   

2. Load is Correct:

   • Static load = 8.34 N downward at tip

3. Material is Al 7075-T6

4. Both solutions solve successfully with baseline parameters:

   beam_half_core_thickness = 25mm
   beam_face_thickness = 2mm
   holes_diameter = 230mm
   hole_count = 11
   

Quick Test

Run a manual solve with baseline parameters to verify:

Expected Results (approximate):

• Mass: ~140-150g
• Max Displacement: ~1-2 mm
• Max Stress: ~80-100 MPa
• First Frequency: ~120-140 Hz

If these are wildly different, check your setup.

Extraction Configuration

The optimization engine will extract:

• Mass: From Solution 1 mass properties
• Displacement: Maximum displacement magnitude from Solution 1
• Stress: Maximum von Mises stress from Solution 1
• Frequency: First natural frequency (mode 1) from Solution 2

All extraction is automated - you just need to ensure the solutions are configured correctly.

Optional Enhancements

If you want more realistic results:

1. Add Gravity Load:

   • Apply -9.81 m/s² gravity in addition to tip load
   • Represents arm's own weight during flight

2. Add Damping to modal analysis:

   • Structural damping ratio: ~0.02 (2%)
   • More realistic frequency response

3. Refine Mesh at stress concentrations:

   • Around holes
   • At base constraint
   • Better stress accuracy

But these are NOT required for the optimization to run successfully.