Return named result fields for creeping flow and the beam (#106)

solve() now also returns `fields` for models with more than one unknown
per node, each a Float64Array with one value per mesh node:
- creeping flow: velocityMagnitude, u, v, p (the pressure, solved at the
  corner nodes, is interpolated linearly to the mid-side and centre nodes)
- Euler–Bernoulli beam: w, theta

The plotting functions take a `field` option (plotSolution and
plotInterpolatedSolution in the options argument, the vtk.js functions
in renderOptions) and default to velocityMagnitude and w, so the result
of solve() can be plotted directly. solutionVector is unchanged, and
FEAScriptWorker.solve() passes the fields through.

The private _creepingFlowMetadata and _eulerBernoulliBeamMetadata
properties are removed.

Tests: check the fields against the solution vector in the creeping flow
and beam regression tests. Examples: use the fields.

Closes #106

Author: nikoscham

dist/feascript-worker.esm.js

@@ -34,9 +34,11 @@ model.addBoundaryCondition("3", ["constantVelocity", 0, 0]); // Right
 
 // 4. Solve
 model.setSolverMethod("lusolve");
-const { solutionVector, nodesCoordinates } = model.solve();
+const { nodesCoordinates, fields } = model.solve();
 
-// 5. Print the results
+// 5. Print the results (one value per mesh node for each field)
 console.log(`Number of nodes in mesh: ${nodesCoordinates.nodesXCoordinates.length}`);
 console.log("Node coordinates:", nodesCoordinates);
-console.log("Solution vector:", solutionVector);
+console.log("x-velocity u:", fields.u);
+console.log("y-velocity v:", fields.v);
+console.log("Pressure p:", fields.p);

dist/feascript-worker.esm.js.map

@@ -39,20 +39,16 @@ model.addBoundaryCondition("3", [
 
 // 4. Solve
 model.setSolverMethod("lusolve");
-const { solutionVector } = model.solve();
+const { nodesCoordinates, fields } = model.solve();
 
 // 5. Print the results
-const flatSolution = solutionVector.map((entry) => (Array.isArray(entry) ? entry[0] : entry));
-
-const nodeXCoordinates = [0, 5, 10];
+const { nodesXCoordinates } = nodesCoordinates;
 console.log("\nNode |    x (m) | Deflection w (m) | Rotation theta (rad)");
 console.log("-----|----------|-------------------|----------------------");
-for (let nodeIndex = 0; nodeIndex < nodeXCoordinates.length; nodeIndex++) {
-  const w = flatSolution[2 * nodeIndex];
-  const theta = flatSolution[2 * nodeIndex + 1];
+for (let nodeIndex = 0; nodeIndex < nodesXCoordinates.length; nodeIndex++) {
   console.log(
-    `  ${nodeIndex + 1}  | ${nodeXCoordinates[nodeIndex].toFixed(2).padStart(8)} | ${w
+    `  ${nodeIndex + 1}  | ${nodesXCoordinates[nodeIndex].toFixed(2).padStart(8)} | ${fields.w[nodeIndex]
       .toExponential(4)
-      .padStart(17)} | ${theta.toExponential(4).padStart(20)}`,
+      .padStart(17)} | ${fields.theta[nodeIndex].toExponential(4).padStart(20)}`,
   );
 }