From b9389a1331f0fd2f89decaa51f9fc724639f4aa1 Mon Sep 17 00:00:00 2001
From: Jukka Aho <ahojukka5@gmail.com>
Date: Mon, 15 Dec 2025 13:31:43 +0200
Subject: [PATCH] test(solvers): add modal analysis test

New 110-line test file for modal analysis:
- Tests modal analysis with Tet4 element (eigenvalue computation)
- Tests with and without geometric stiffness
- Tests Poisson problem modal analysis (heat equation)
- Uses legacy Element/Problem API
- Contains commented-out test for mesh tie (future work)

Validates eigenvalue computation for structural and thermal modal analysis.
---
 test/solvers/test_modal_analysis.jl | 110 ++++++++++++++++++++++++++++
 1 file changed, 110 insertions(+)
 create mode 100644 test/solvers/test_modal_analysis.jl

diff --git a/test/solvers/test_modal_analysis.jl b/test/solvers/test_modal_analysis.jl
new file mode 100644
index 0000000..4248994
--- /dev/null
+++ b/test/solvers/test_modal_analysis.jl
@@ -0,0 +1,110 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+using JuliaFEM, Test
+
+X = Dict(
+    1 => [2.0, 3.0, 4.0],
+    2 => [6.0, 3.0, 2.0],
+    3 => [2.0, 5.0, 1.0],
+    4 => [4.0, 3.0, 6.0])
+u = Dict(
+    1 => [0.0, 0.0, 0.0],
+    2 => [0.0, 0.0, 0.0],
+    3 => [0.0, 0.0, 0.0],
+    4 => [0.25, 0.25, 0.25])
+element1 = Element(Tet4, (1, 2, 3, 4))
+element2 = Element(Tri3, (1, 2, 3))
+update!((element1, element2), "geometry", X)
+update!((element1, element2), "displacement", 0.0 => u)
+update!(element1, "youngs modulus", 96.0)
+update!(element1, "poissons ratio", 1.0/3.0)
+update!(element1, "density", 420.0)
+update!(element2, "displacement 1", 0.0)
+update!(element2, "displacement 2", 0.0)
+update!(element2, "displacement 3", 0.0)
+problem1 = Problem(Elasticity, "test problem", 3)
+problem1.properties.finite_strain = false
+problem1.properties.geometric_stiffness = false
+problem2 = Problem(Dirichlet, "boundary condition", 3, "displacement")
+add_elements!(problem1, element1)
+add_elements!(problem2, element2)
+analysis = Analysis(Modal)
+analysis.properties.which = :LM
+add_problems!(analysis, problem1, problem2)
+
+# test eigenvalues for single tet4 element
+run!(analysis)
+@test isapprox(analysis.properties.eigvals, [4/3, 1/3])
+
+# test eigenvalues for single tet4 element, with geometric stiffness
+problem1.properties.geometric_stiffness = true
+analysis.properties.geometric_stiffness = true
+run!(analysis)
+@test isapprox(analysis.properties.eigvals, [5/3, 2/3])
+
+# test poisson problem modal analysis without tie
+X = Dict(
+    1 => [0.0, 0.0],
+    2 => [1.0, 0.0],
+    3 => [1.0, 3.0],
+    4 => [0.0, 3.0],
+    5 => [0.0, 3.0],
+    6 => [1.0, 3.0],
+    7 => [1.0, 9.0],
+    8 => [0.0, 9.0])
+element1 = Element(Quad4, (1, 2, 3, 4))
+element2 = Element(Quad4, (4, 3, 7, 8))
+element3 = Element(Seg2, (1, 2))
+element4 = Element(Seg2, (7, 8))
+update!((element1, element2, element3, element4), "geometry", X)
+update!((element1, element2), "density", 6.0)
+update!((element1, element2), "thermal conductivity", 36.0)
+update!((element3, element4), "temperature 1", 0.0)
+problem1 = Problem(PlaneHeat, "combined body", 1)
+problem2 = Problem(Dirichlet, "fixed ends", 1, "temperature")
+add_elements!(problem1, element1, element2)
+add_elements!(problem2, element3, element4)
+analysis = Analysis(Modal)
+add_problems!(analysis, problem1, problem2)
+run!(analysis)
+@test isapprox(first(analysis.properties.eigvals), 1.0)
+
+#=
+@testset "test poisson modal problem with mesh tie" begin
+    X = Dict{Int64, Vector{Float64}}(
+        1 => [0.0, 0.0],
+        2 => [1.0, 0.0],
+        3 => [1.0, 3.0],
+        4 => [0.0, 3.0],
+        5 => [0.0, 3.0],
+        6 => [1.0, 3.0],
+        7 => [1.0, 9.0],
+        8 => [0.0, 9.0])
+    el1 = Element(Quad4, [1, 2, 3, 4])
+    el2 = Element(Quad4, [5, 6, 7, 8])
+    el3 = Element(Seg2, [1, 2])
+    el4 = Element(Seg2, [7, 8])
+    el5 = Element(Seg2, [3, 4])
+    el6 = Element(Seg2, [5, 6])
+    update!([el1, el2, el3, el4, el5, el6], "geometry", X)
+    update!([el1, el2], "density", 6.0)
+    update!([el1, el2], "thermal conductivity", 36.0)
+    update!([el3, el4], "temperature 1", 0.0)
+    update!(el5, "master elements", [el6])
+    p1 = Problem(PlaneHeat, "body 1", 1)
+    add_elements!(p1, [el1])
+    p2 = Problem(PlaneHeat, "body 2", 1)
+    add_elements!(p2, [el2])
+    p3 = Problem(Dirichlet, "fixed ends", 1, "temperature")
+    add_elements!(p3, [el3, el4])
+    p4 = Problem(Mortar2D, "interface between bodies", 1, "temperature")
+    add_slave_elements!(p4, [el5])
+    add_master_elements!(p4, [el6])
+
+    solver = Solver(Modal)
+    push!(solver, p1, p2, p3, p4)
+    solver()
+    @test isapprox(solver.properties.eigvals[1], 1.0)
+end
+=#