Why doesn't the subtract function work with 3D DiscreteGeometry in R2024b?

10 次查看（过去 30 天）
Timothy
Timothy 2024-12-31
编辑： Walter Roberson 2025-1-4
% Why doesn't the subtract function work with 3D DiscreteGeometry in R2024b?
model = femodel(); % Create a Finite element analysis model object
% Define dimensions of the rectangular plate (width, height, thickness)
plateWidth = 10;
plateHeight = 6;
plateThickness = 1;
% Create the rectangular plate
rectPlate = multicuboid(plateWidth, plateHeight, plateThickness);
% Define dimensions of the circular hole (radius, height)
holeRadius = 1;
holeHeight = plateThickness;
% Create the cylinder for the hole
cylinderHole = multicylinder(holeRadius, holeHeight);
% Subtract the cylinder from the plate
plateWithHole = subtract(rectPlate, cylinderHole);
% The error message follows...
'subtract' is used in the following examples:
Outputs Defined for a Function
Outputs for Current Function
-----------------------------------------------------------
I have also tried to use:
plateWithHole = addVoid(rectPlate, cylinderHole);
and I get the following error message.
Error using pde.DiscreteGeometry/addVoid
Added cells must be located strictly inside a single cell of the original geometry.
In the error-generating case, the cylindrical void is the same thickness as the rectangular plate. If I make the cylindrical void ever so slightly shorter than the thickness of the plate, it works without error, but then I don't get a hole that goes completely through the plate.
-----------------------------------------------------------
What other Boolean functions will work with these DiscreteGeometry types that result in a hole going completely through the flat plate?
-----------------------------------------------------------
I’ve heard it said that subtract works in R2023, but I don't want to revert to that version.
Thank you,
Tim
  3 个评论
显示 1更早的评论
Paul
Paul 2025-1-1
If there was a "subtract" method for DiscreteGeometry objects in R2023 and there isn't now, perhaps that decision is discussed in the release notes for whatever version removed that method, perhaps pointing to an alternative method.
Don't know why the error message doesn't come with a link. But it looks like if "subtract" isn't found then Matlab does search through the documentation to find potential use-cases. I've never seen this type of message before (I've always seen "function not found" or something like that), perhaps it's a new feature.
Anyway, I did a search for "Outputs for Current Function" and found nargout, which does seem to be relevant to the error message but nothing the OP would care about (Outputs Defined for a Function is the other example at nargout).
DGM
DGM 2025-1-2
编辑：DGM 2025-1-2
I'm not sure, but the lack of links in the error message might just be a forum-only thing. I don't have the PDE toolbox, so I don't know.
Certainly, I found a lot of function() related docs links, but as much as those are relevant to function(), none are relevant to subtract().

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Timothy
Timothy 2025-1-2
编辑：Walter Roberson 2025-1-4
Ran in:
Walter et al,
I would like to thank all of you who helped me get to the answer for the problem I ran into. Your insights and suggestions really helped me to learn more about MATLAB and discover more of its nooks and crannies.
I will publish the complete Live Script for how I was able to solve the thermal FEA problem. It’s probably longer than the experts need, but it may be helpful to another non-expert like me.
Unfortunately for people like “DGM” I am using the PDE toolbox. There I generate a 2D shape and then within the Live Script I extrude it to the 3D block with holes that I need.
Again, thank you for your help.
-Tim
-----------------------------------------------------------------------------------------------------------------------------------------
Thermal FEA of a Three Dimensional (3-D) Object
Create the FEA Model Object
model = femodel();
Define Analysis Type
%model.AnalysisType = "thermalSteady";
model.AnalysisType = "thermalTransient";
Geometry 2-D: Get 2-D Geometry from PDE the Modeler App
%Note: "g" can be found in the attached file.
load g_b
model.Geometry = g; % This variable "g" comes from the PDE Modeler App using the "Boundary -> Export Decomposed Geometry..." command
pdegplot(g,"FaceLabels","on")
Geometry 3-D: Extrude 2-D Geometry to Make 3-D Object
%model = generateMesh(model,'Hmax',0.025,'GeometricOrder','quadratic','Hgrad',1.1); % 'Hmax' defines the maximum element size
extrudeDistance = 0.1;
model.Geometry = extrude(model.Geometry,extrudeDistance);
pdegplot(model.Geometry,"FaceLabels","on"); % Now I have 3-D geometry that works in an FEA model
xlim([-0.138 0.941])
ylim([-0.219 0.281])
zlim([-0.231 0.100])
view([30.300 49.623])
Face_Hot = 4;
Face_Cold = 6;
Generate Mesh:
model = generateMesh(model,'Hmax',0.05,'GeometricOrder','quadratic','Hgrad',1.1); % 'Hmax' defines the maximum element size
pdemesh(model);
xlim([-0.138 0.941])
ylim([-0.219 0.281])
zlim([-0.231 0.100])
view([30.300 49.623])
Define Physics: Material Properties:
E = 210e9; % Young's modulus: N/m^2
nu = 0.3; % Poisson's ratio: unitless
rho = 7850.0; % Density:kg/m³
k = 60.5; % Thermal Conductivity: W/m/K
Cp = 0.49; % Specific Heat Capacity: kJ/kg.K
cte = 12*10^-6; % Coefficient of Thermal Expansion : m/m/K
model.MaterialProperties = materialProperties(YoungsModulus=E, ...
PoissonsRatio=nu, ...
MassDensity=rho, ...
CTE=cte, ...
SpecificHeat=Cp, ...
ThermalConductivity=k);
Define Physics: Boundary Conditions & Loads:
model.FaceLoad(1,1:max(model.Geometry.NumFaces)) = faceLoad(ConvectionCoefficient=5.0, AmbientTemperature=350); % All the other faces
model.FaceLoad(1, Face_Hot).ConvectionCoefficient = [];
model.FaceLoad(1, Face_Hot).AmbientTemperature = [];
model.FaceLoad(1, Face_Cold).ConvectionCoefficient = [];
model.FaceLoad(1, Face_Cold).AmbientTemperature = [];
model.FaceBC(Face_Hot) = faceBC(Temperature=500);
model.FaceBC(Face_Cold) = faceBC(Temperature=200);
model.CellIC = cellIC(Temperature=300);
Solve FEA Problem:
time_start = -2; % starting exponent (e.g., 10^-1)
time_end = 1; % ending exponent (e.g., 10^2)
num_points = 10; % number of points in the vector
tlist = logspace(time_start, time_end, num_points);
%tlist = 0:0.1:10; %Time steps
thermalresults = solve(model,tlist); % Solve the problem for times in tlist.
%thermalresults = solve(model); % Solve the problem.
Postprocess Results: Plotting the Temperature Results:
% Plot the solution at different time steps
for i = 1:length(tlist)
pdeplot3D(thermalresults.Mesh.Nodes,thermalresults.Mesh.Elements,'ColorMapData',thermalresults.Temperature(:,i));
xlim([-0.138 0.941])
ylim([-0.219 0.281])
zlim([-0.231 0.100])
view([30.300 49.623])
title(['Temperature at t = ', num2str(tlist(i)), ' seconds. Steps to go: ',num2str(length(tlist) -i)]);
pause(0.001); % Pause to visualize each time step
end
Results: Plotting the heat flow results:
QnHot = evaluateHeatRate(thermalresults,Face=Face_Hot); % if the problem is specified in SI, the units of Qn are Watts/
QnCold = evaluateHeatRate(thermalresults,Face=Face_Cold);
semilogx(tlist,QnHot);
hold on;
semilogx(tlist,QnCold);
hold off;
% Set y-axis limits
%ylim([-50 50]);
xlabel("Time")
ylabel("Heat Flow Rate")
grid on
legend(["QnHotFace", "QnColdFace"], "Position", [0.7077 0.6853 0.1893, 0.0774])

更多回答（1 个）

Walter Roberson
Walter Roberson 2025-1-1
In R2023a, the methods available for DiscreteGeometry are
addCell addVertex cellEdges extrude facesAttachedToEdges nearestFace scale
addFace addVoid cellFaces faceEdges nearestEdge rotate translate
You can subtract() certain kinds of Antenna Toolbox shapes; https://www.mathworks.com/matlabcentral/answers/2092471-creating-solid-geometry-with-pde or some RF Toolbox shapes
For subtracting geometries with the PDE toolbox, you use decsg
  10 个评论
显示 8更早的评论
DGM
DGM 2025-1-2
编辑：DGM 2025-1-2
I'm the tangential simpleton here, but decsg() sounds terribly obtuse for object-level CSG, especially considering that I wouldn't have found out about it even after an hour's worth of dredging the docs for a toolbox I don't have. I'm going to re-suggest a comment I deleted earlier.
Is it possible or practical with your expected workflow to develop the composite geometry as a mesh and then convert it to a DiscreteGeometry object afterwards? I have seen that GPToolbox (FEX) has some CSG tools which I haven't tested, and there are any number of external tools that could do this. Even external tools can be exploited programmatically via system().
https://www.mathworks.com/matlabcentral/answers/2169008-are-there-matlab-functions-or-scripts-to-perform-boolean-operations-on-triangulated-solids
I don't have PDE toolbox and don't use DiscreteGeometry for anything, so I don't know if this is helpful. I'm just throwing this out there, since none of this seems like it's a satisfying resolution to the problem.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Structural Mechanics 的更多信息

标签

产品


版本

R2024b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by