Do you want to open multiple 3D models in a 3D viewer for a more comprehensive visualization experience? Here's how you can do it.

1. Choose a 3D Viewer: First, you need to select a 3D viewer that supports opening and viewing multiple models simultaneously. There are various 3D viewer applications available, both free and paid, that offer this functionality.

2. Import Models: Once you have selected a 3D viewer, you can start by importing the 3D models you want to view. Most 3D viewers allow you to import models in common 3D file formats such as .obj, .fbx, .stl, or .dae.

3. Arrange Models: After importing the models, you can arrange them in the 3D viewer according to your preferences. Some 3D viewers provide tools for positioning, rotating, and scaling the models to create an optimal viewing environment.

4. Explore and Analyze: With multiple models open in the 3D viewer, you can explore and analyze them together to gain a better understanding of their interrelationships, structures, or design aspects. This can be particularly useful for architects, engineers, designers, and anyone working with complex 3D designs or assemblies.

5. Utilize Viewing Tools: Many 3D viewers offer a variety of viewing tools such as cross-sectioning, measurement, annotations, and markup capabilities. These tools can enhance your ability to inspect and analyze multiple models simultaneously.

6. Save and Share: Once you have finished viewing and analyzing the multiple 3D models, you may want to save your workspace or share it with colleagues or clients. Some 3D viewers allow you to save the arrangement of multiple models for future reference or collaboration.

By opening multiple 3D models in a 3D viewer, you can gain a more comprehensive understanding of complex designs, assemblies, or objects. This approach can streamline your workflow and provide valuable insights for various industries and applications.