# Monitor

*This document describes how to set up and use monitors in Flow360 simulations. Monitors allow you to track flow field variables at specific locations during the simulation, providing real-time feedback on how your solution is developing.*

## Available Options

| *Option* | *Description* |
|------------|-----------------|
| **Total Forces** | Integrated forces and moments over all surfaces |
| **Forces by surface** | Force and moment distribution over individual surfaces |
| **Heat transfer by surface** | Heat transfer distribution over surfaces |
| **BET Forces and Moments** | Blade Element Theory forces and moments for rotors |
| **BET Sectional Loading** | Blade Element Theory radial distribution of forces and moments for rotors |
| **Force distribution (Y)** | Force distribution along the y-axis |
| **Force distribution (X)** | Force distribution along the x-axis |
| **Actuator Disk** | Forces and moments for actuator disk models |

## Detailed Descriptions

### Total Forces

*Total Forces monitor calculates the integrated forces and moments over all surfaces in the computational domain.*

**Axis settings:**

| *Axis* | *Available Values* |
|----------|----------------------|
| **X-axis** | `pseudo step` (for steady state simulation)<br>`physical step` (for unsteady simulation) |
| **Y-axis** | `CL`<br>`CD`<br>`CFx`<br>`CFy`<br>`CFz`<br>`CMx`<br>`CMy`<br>`CMz`<br>`CLPressure`<br>`CDPressure`<br>`CFxPressure`<br>`CFyPressure`<br>`CFzPressure`<br>`CMxPressure`<br>`CMyPressure`<br>`CMzPressure`<br>`CLSkinFriction`<br>`CDSkinFriction`<br>`CFxSkinFriction`<br>`CFySkinFriction`<br>`CFzSkinFriction`<br>`CMxSkinFriction`<br>`CMySkinFriction`<br>`CMzSkinFriction` |

**Notes:** 
  - Provides overall aerodynamic performance metrics
  - Calculates lift, drag, and moment coefficients
  - Available for both steady and unsteady simulations

### Forces by surface

*Forces by Surface monitor provides detailed force and moment distribution over individual surfaces.*

**Axis settings:**
  
| *Axis* | *Available Values* |
|----------|----------------------|
| **X-axis** | `pseudo step` (for steady state simulation)<br>`physical step` (for unsteady simulation) |
| **Y-axis** | `CL`<br>`CD`<br>`CFx`<br>`CFy`<br>`CFz`<br>`CMx`<br>`CMy`<br>`CMz`<br>`CLPressure`<br>`CDPressure`<br>`CFxPressure`<br>`CFyPressure`<br>`CFzPressure`<br>`CMxPressure`<br>`CMyPressure`<br>`CMzPressure`<br>`CLSkinFriction`<br>`CDSkinFriction`<br>`CFxSkinFriction`<br>`CFySkinFriction`<br>`CFzSkinFriction`<br>`CMxSkinFriction`<br>`CMySkinFriction`<br>`CMzSkinFriction` |
| **Series** | Available wall-type surfaces |

**Notes:**
  - Useful for analyzing contribution of different components
  - Provides local force and moment coefficients
  - Supports both steady and unsteady simulations

### Heat transfer by surface

*Heat Transfer by Surface monitor calculates heat transfer distribution over surfaces.*

**Axis settings:**

| *Axis* | *Available Values* |
|----------|----------------------|
| **X-axis** | `pseudo step` (for steady state simulation)<br>`physical step` (for unsteady simulation) |
| **Y-axis** | `HeatTransferRate` |
| **Series** | Available wall-type surfaces |

**Notes:**
  - Provides local heat flux and heat transfer coefficients
  - Useful for thermal analysis
  - Available for both steady and unsteady simulations

### BET (Blade Element Theory) Analysis

BET analysis provides two types of monitors for rotor analysis:

- **Forces and Moments**
  - Calculates forces and moments for each blade element
  - Provides detailed rotor performance metrics
  - Available for both steady and unsteady simulations
  
  **Axis settings:**
  | *Axis* | *Available Values* |
  |----------|----------------------|
  | **Disk** | Available BET disks |
  | **X-axis** | `pseudo step` (for steady state simulation)<br>`physical step` (for unsteady simulation) |
  | **Y-axis** | `Force_x`<br>`Force_y`<br>`Force_z`<br>`Moment_x`<br>`Moment_y`<br>`Moment_z` |

- **Sectional Loading**
  - Shows radial distribution of forces and moments
  - Useful for analyzing blade loading
  - Provides insight into rotor performance across the span

  **Axis settings:**
  | *Axis* | *Available Values* |
  |----------|----------------------|
  | **Disk** | Available BET Disks |
  | **X-axis** | `radius` |
  | **Y-axis** | `ThrustCoeff`<br>`TorqueCoeff` |
  | **Series** | Blades available for selected Disk |

### Force distribution

Force distribution monitors provide spanwise and chordwise force distributions:

- **Y-Direction distribution**
  - Shows force distribution along the y-axis
  - Useful for analyzing spanwise loading
  - Provides sectional force coefficients

  **Axis settings:**
  | *Axis* | *Available Values* |
  |----------|----------------------|
  | **X-axis** | `Y` |
  | **Y-axis** | `CMy_per_span`<br>`CFx_per_span`<br>`CFz_per_span` |
  | **Series** | Available wall-type surfaces |

- **X-Direction distribution**
  - Shows force distribution along the x-axis
  - Useful for analyzing chordwise loading
  - Provides sectional force coefficients

  **Axis settings:**
  | *Axis* | *Available Values* |
  |----------|----------------------|
  | **X-axis** | `X` |
  | **Y-axis** | `CD_per_length`<br>`Cumulative_CD_Curve` |
  | **Series** | Available wall-type surfaces |

### Actuator Disk

*Actuator Disk monitor calculates forces and moments for actuator disk models.*

**Axis settings:**
| *Axis* | *Available Values* |
|----------|----------------------|
| **X-axis** | `pseudo step` (for steady state simulation)<br>`physical step` (for unsteady simulation) |
| **Y-axis** | `Power`<br>`Force`<br>`Moment` |
| **Series** | Available actuator disks |

**Notes:**
  - Provides integrated forces and moments
  - Useful for simplified rotor modeling
  - Available for both steady and unsteady simulations

## Available Output Fields

The following table lists all available output fields that can be monitored in Flow360, along with their descriptions and units:

| *Output* | *Description* |
|------------|-----------------|
| **Force Monitors** |
| `CD` | Drag coefficient (force parallel to freestream direction) |
| `CL` | Lift coefficient (force perpendicular to freestream direction) |
| `CS` | Side force coefficient (force perpendicular to lift and drag) |
| `CMx` | Rolling moment coefficient (moment about x-axis) |
| `CMy` | Pitching moment coefficient (moment about y-axis) |
| `CMz` | Yawing moment coefficient (moment about z-axis) |
| `CFx` | Force coefficient in x-direction (body-fixed coordinate system) |
| `CFy` | Force coefficient in y-direction (body-fixed coordinate system) |
| `CFz` | Force coefficient in z-direction (body-fixed coordinate system) |
| **Heat Transfer Monitors** |
| `HeatTransferRate` | Heat flux through surface |
| **BET Analysis** |
| `ThrustCoeff` | Thrust coefficient (normalized axial force on rotor) |
| `TorqueCoeff` | Torque coefficient (normalized moment about rotation axis) |
| **Force Distribution** |
| `CMy_per_span` | Sectional pitching moment coefficient per unit span |
| `CFx_per_span` | Sectional force coefficient in x-direction per unit span |
| `CFz_per_span` | Sectional force coefficient in z-direction per unit span |
| `CD_per_length` | Sectional drag coefficient per unit length |
| `Cumulative_CD_Curve` | Integrated drag coefficient from leading edge to current position |
| **Actuator Disk** |
| `Power` | Power generated/consumed by actuator disk |
| `Force` | Force vector generated by actuator disk |
| `Moment` | Moment vector generated by actuator disk |

These outputs are dimensionless in the case of coefficients, while others use our own unit system. To learn more about non-dimensional outputs, refer to [Non-Dimensional Outputs](../../../user_guide/NonDimensionalization/NonDimOutputs/NonDimOutputs).

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<details>
<summary><h3 style="display:inline-block"> 💡 Tips</h3></summary>

- Use force monitors to track convergence of aerodynamic coefficients
- Monitor heat transfer for thermal analysis and cooling system design
- BET analysis provides detailed insight into rotor performance
- Force distribution monitors help identify critical loading regions
- Actuator disk monitors are useful for simplified rotor modeling

<details style="padding-left:20px">
<summary><h4 style="display:inline-block"> Best Practices for Force Analysis</h4></summary>

- Monitor both total and component-specific forces
- Use force distribution monitors to identify critical regions
- Monitor forces at key operating conditions
- Compare results with experimental data when available

</details>
</details>

---

<details>
<summary><h3 style="display:inline-block"> ❓ Frequently Asked Questions</h3></summary>

- **What is the difference between Total Forces and Forces by Surface?**  
  > Total Forces provides overall aerodynamic performance metrics, while Forces by Surface gives detailed distribution over individual components.

- **How do I interpret BET analysis results?**  
  > BET analysis provides both integrated forces/moments and sectional loading, helping understand rotor performance at both global and local scales.

- **What monitors should I use for thermal analysis?**  
  > Use Heat Transfer by Surface monitor to track heat flux and heat transfer coefficients over surfaces.

- **How do I analyze force distributions?**  
  > Use X and Y direction force distribution monitors to understand spanwise and chordwise loading patterns.

</details>

---

<details>
<summary><h3 style="display:inline-block"> 🐍 Python Example Usage</h3></summary>

Below is a Python code example showing how to access force monitors:

```python
import flow360 as fl

case = fl.Case(id="case-XXXXX") # provide a valid case id
case.wait() # wait for the case to finish running
results = case.results

# Force monitor
total_forces = results.total_forces
print(total_forces)

# Surface force monitor
surface_forces = results.surface_forces
print(surface_forces)

# BET monitor
bet_forces = results.bet_forces
print(bet_forces)
```

</details>