How To Make Clean Model Out Of Mesh Surface In Rhino 6

The objective of this article is to requite some insights on how to prepare and extend a terrain using Rhino, in order to obtain a model ready for simulation in the Pedestrian Current of air Comfort (PWC) analysis type in the SimScale platform.

Background

When doing a Pedestrian Wind Comfort analysis, it is known that the topology cannot be ignored, and should be included in the analysis. SimScale requires that the topology needs to extend beyond the limits of the simulated region. This is for 2 main reasons, firstly information technology prevents flow from moving under the surface, and secondly, information technology ensures that there is a defined floor to the simulation, even if it is uneven. You lot tin can read more about why it is necessary to have the topology extended hither. However, it is common that nosotros only do not have whatsoever more of the topology to extend this far. For this reason, nosotros propose that terrain is extended artificially in software such as Rhino, and in the post-obit commodity, we describe the workflow and present an instance.

Overview

When preparing geometry for the PWC analysis, the user should get-go by defining the main Region of Interest in the project, which will be referred to by ROI. The importance of this is to ensure that the ROI is kept at the center of the geometry, and we can make sensible limits based upon the center of the region (usually where a new complex or edifice is proposed to exist developed).

Note

It might be useful to kickoff turn all the unnecessary layers off, normally leaving only the buildings and the topography visible.

Solution

Depending on the topography and the surroundings of the ROI, a circle should be defined with a sensible radius, centered on the epicenter of our ROI. This circle will define the region of inclusion, significant the region containing the ROI and the surroundings that may be interesting to study with a PWC analysis. If this area is missing some material that volition generate future problems in the mesh, there is a need to identify and eliminate those gaps or anomalies. In order to simplify the model and optimize its efficiency, the components not inside the area of inclusion should be removed. As a rule of thumb, the ROI radius plus 500 \(m\) could exist used as the radius for this inclusion circle, however, this can exist altered with the best judgment from the user.

At this point, you will have buildings, context, and terrain centered on the ROI. However, we at present need to extend that beyond the simulation limits. To start extending the terrain, a new circumference should be created once again using the ROI heart equally the reference point. This new circle added, determines the limits of the final model and, for that reason, its diameter should be wider than the one previously defined.

Every bit a rule of thumb, y'all can extend to a radius of 2500 \(m\), this is, however, much larger than required in most cases, and usually, a more sensible radius is the radius of the ROI, plus xx times the tallest building height. Hence, if a building was 100 \(m\) tall from the lowest point, and the ROI radius was 300 \(m\) then your extension radius could exist 2300 \(m\) or two.3 \(km\).

Worked Case

This example is from a Terrain CAD File from the area of Wellington, New Zealand, extracted from an online source named CADMAPPER.

wellington city of new zealand uncleaned model — Figure 1: CAD file of the terrain of Wellington, New Zealand extracted from CADMAPPER.

There is a lot of unnecessary information in the model, so all the unnecessary layers should exist turned off. Actress data like lost lines or points is removed using the delete function on the Command-Box.

Some small manual preparation is normally needed, for example, when dealing with gaps, betwixt buildings and the terrain, it is recommended to extrude the building floors for a minor distance to ensure that period cannot movement nether the buildings and negatively touch on the condolement. However, in detail cases with complicated geometries, there is a need for different approaches. In the example, there is as well a surface missing on the model that should be added at the coast. Since the sea is expected to be apartment and on one airplane, a unmarried surface was used.

this picture shows the model after a surface was added to eliminate a gap — Figure 2: New surface added to the model representation to eliminate the gap in the CAD

The objective, as described before, is to create a terrain extension, with no holes or gaps, that extend beyond the limits of the simulation, and keeping merely the recommended amount of particular. It's important to recognize that nosotros can't include everything in a simulation, or at to the lowest degree you could just it's non necessary. With that in heed, later creating a circumvolve including the environs of the ROI, all the buildings outside of that should be eliminated.

The Trim, MeshTrim, and Change layer function is useful in this process. To use the Trim functions, a cylinder that intersects the model's topology surface needs to exist created using the function ExtrudeCrv. For this function, the reference selected is the circle and the extrusion distance tin vary. There is but a demand to brand sure that the cylinder generated surrounds the area desired to be preserved.

using trim functions in rhino to trim cylinder — Effigy three: Model representation afterwards creating the cylinder and later applying the trim function

In order to generate the limits of the concluding model, a circumvolve can exist divers and, to simplify the next steps, the circles previously made should be hidden since they have already served their purpose.

the picture shows how the model looks like after hiding the old circle and generating the new limits — Figure 4: Later hiding the old circle and generating the new limits

Using the function Divide bend by the number of segments, the points from the new circle line should be extracted. To collect the points that define the topography, the model should be selected and the function ExtractPt should be executed. If extra points appear between the limit circle and the model, they should be removed past simply deleting them.

the picture shows the points defining the model — Figure v: All points extracted from the new circle line that define topography from the model

To finalize and generate the desired model, the role MeshPatch needs to be executed with all the points selected. In order to obtain the most simple and efficient model, all the points should be removed by selecting all the points with the function SelPt and erasing them with the Delete function. The relevant layers should be visible to obtain and visualize the final model.

the pictures shows the final and cleaned model — Figure six: Terminal model generated using the *MeshPatch* function with all the points selected

At present the model can be uploaded to the SimScale platform every bit an STL. You lot can find how to upload and save a model as an STL from Rhino into SimScale in this link. Under, you will find a video that demonstrates step-by-stride instructions presented during this commodity.

Video 1: Pace-past-step guide on cleaning a terrain model

It is important to call back that in that location are multiple possibilities to achieve a like model in Rhino nevertheless this particular method seems to be very efficient and robust.

Note

If none of the above suggestions solved your problem, and so delight mail service the issue on our forum or contact us.