> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ntop.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How to use Max and Min Feature Size Constraints?

## **Objective**

Use feature size constraints to ensure manufacturability and correct feature disconnections in **Topology Optimization** results.

## **Applies to:**

**Topology Optimization** workflows.

![Bracket Example which has ribbed structures in it when using Feature Size Constraints](https://files.learn.ntop.com/help-articles/optimization/50598707101587.png)## **Procedure**

### 1. Optimize Your Mesh Size

To accurately capture feature size constraints, your mesh must be sufficiently refined.

* Ensure the **element edge length** of your FE mesh is at most **1/3** the size of your desired feature size specification.

***Note:** If your mesh is too coarse, nTop will issue a warning in the log panel.*

### 2. Apply the Constraints

Add the **Min Feature Size Constraint** and/or **Max Feature Size Constraint** blocks to your **Optimization Constraint List**.

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            <img alt="Topology Optimization Example with Min Feature Size Constraint" src="https://files.learn.ntop.com/help-articles/optimization/50598707138323.png" />
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            <img alt="Topology Optimization Example with Max Feature Size Constraint" src="https://files.learn.ntop.com/help-articles/optimization/50598707169683.png" />
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* **Min Feature Size:** Prevents feature disconnections and enforces manufacturing limits.
* **Max Feature Size:** Prevents the design from becoming too bulky or violating space constraints.
* **Domain Size:** Ensure your feature size input is less than the total thickness of your design domain.

![MinFS\_9.png](https://files.learn.ntop.com/help-articles/optimization/50598722454035.png)### 3. Configure other Constraints

For the most accurate results, use field-based constraints rather than traditional planar constraints.

* **Symmetry:** Use the **Remap Constraint** block instead of the **Planar Symmetry Constraint**. The **Remap Constraint** is mesh-independent and acts as the final step in the filtering sequence, preventing discrepancies from being amplified.

![MinFS\_3.png](https://files.learn.ntop.com/help-articles/optimization/50598707206163.png)- **Extrusion:** If using a [**Remap Constraint**](/help-articles/knowledge-base/optimization/how-do-i-use-the-remap-constraint-for-topology-optimization) for extrusion, embed the reference surface at least one element deep inside the design space to prevent disconnections at the boundaries.

* **Passive Region: I**t is recommended to limit the passive region thickness to half the feature size specification. Our solution already expands passive regions to achieve the defined minimum feature size. As a result, when defining thick passive regions, the final solutions may present unexpectedly oversized regions. When this undesired situation occurs with the **Max Feature Size Constraint** (using similar feature size inputs), it may lead to convergence problems, as the bulged passive region may not respect the chosen feature size.

![MinFS\_8.png](https://files.learn.ntop.com/help-articles/optimization/50598707230099.png)### 4. Set Algorithmic Parameters

Feature size constraints require more iterations to converge than standard optimizations.

* Set the **Max Iterations** to at least **250** (the default is 200).
* The goal is to ensure the **Min/Max Projection** filter (blue line in the convergence plot) meets the target (yellow dotted line).

![Convergence Plot: "A line graph showing the blue Min/Max Projection line meeting the yellow dotted target line over 250 iterations.](https://files.learn.ntop.com/help-articles/optimization/50598707258387.png)### 5. Monitor Convergence

Once the optimization begins, navigate to the **Display** tab in the **Topology Optimization** block.

* **Min/Max Projection:** Tracks the primary constraint filter.
* **Plot:** For the **Max Feature Size Constraint**, the value should always be below 1 (the yellow dotted line) to remain within the defined input.

**And that's it!** You've successfully applied feature size constraints to your **Topology Optimization**.

### Example Files

* [Download Simple Bracket Example](https://files.learn.ntop/Support%20Article%20Example%20Files/Knowledge%20Base/Optimization/SimpleBracket.ntop)

![Swing Arm Extrusion Example which has ribbed structures in it when using Feature Size Constraints](https://files.learn.ntop.com/help-articles/optimization/50598707292563.png)

* [Download Swing Arm Extrusion Example](https://files.learn.ntop.com/Support%20Article%20Example%20Files/Knowledge%20Base/Optimization/SwingArmExtrusion.ntop)

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## Keywords:

*topology optimization Min Feature Size Constraint Max Feature Size Constraint manufacturing constraint mesh refinement feature size disconnected features*