feat(shell-surface-pressure-load): step 5 - integrate-nonlinear-follower-pressure

src/fesa/analysis/nonlinear_static_procedure.cpp

@@ -15,6 +15,7 @@
 #include "fesa/analysis/newton_iteration_log.h"
 #include "fesa/analysis/nonlinear_static_control.h"
 #include "fesa/assembly/parallel_for.h"
+#include "fesa/assembly/surface_pressure_assembler.h"
 #include "fesa/constraints/essential_constraint_policy.h"
 #include "fesa/elements/finite_rotation.h"
 #include "fesa/elements/mitc4_shell.h"
@@ -453,6 +454,76 @@ Result<SparseMatrix> Difference(const SparseMatrix& internal,
                                dofs.GetSparsePattern());
 }
 
+/// @brief Adds fixed and follower external candidates in stable CSR order.
+Result<GlobalFixedLoadContribution> CombineExternalContributions(
+    const GlobalFixedLoadContribution& fixed,
+    const SurfacePressureAssemblyCandidate& pressure, const DofManager& dofs) {
+  if (fixed.generalized_external_force.Size() !=
+          pressure.full_external_force.Size() ||
+      fixed.generalized_external_tangent.Rows() !=
+          pressure.full_external_tangent.Rows() ||
+      fixed.generalized_external_tangent.Columns() !=
+          pressure.full_external_tangent.Columns() ||
+      fixed.generalized_external_tangent.RowOffsets() !=
+          pressure.full_external_tangent.RowOffsets() ||
+      fixed.generalized_external_tangent.ColumnIndices() !=
+          pressure.full_external_tangent.ColumnIndices()) {
+    return Result<GlobalFixedLoadContribution>::Failure(ProcedureFailure(
+        FailureCategory::kSolver, "nonfinite-newton-data", {},
+        "NONLINEAR_STATIC_PROCEDURE", {},
+        "Nonlinear fixed and pressure external candidates must share the "
+        "stable full-space dimension and pattern."));
+  }
+
+  Vector force{fixed.generalized_external_force.Size()};
+  for (std::size_t index = 0U; index < force.Size(); ++index) {
+    force[index] = fixed.generalized_external_force[index] +
+                   pressure.full_external_force[index];
+    if (!std::isfinite(force[index])) {
+      return Result<GlobalFixedLoadContribution>::Failure(ProcedureFailure(
+          FailureCategory::kSolver, "nonfinite-newton-data", {},
+          "NONLINEAR_STATIC_PROCEDURE", std::to_string(index),
+          "Nonlinear fixed and pressure force composition is nonfinite."));
+    }
+  }
+
+  std::vector<CooContribution> contributions;
+  contributions.reserve(fixed.generalized_external_tangent.Values().size());
+  for (std::size_t row = 0U; row < fixed.generalized_external_tangent.Rows();
+       ++row) {
+    for (std::size_t offset =
+             fixed.generalized_external_tangent.RowOffsets()[row];
+         offset < fixed.generalized_external_tangent.RowOffsets()[row + 1U];
+         ++offset) {
+      const double tangent =
+          fixed.generalized_external_tangent.Values()[offset] +
+          pressure.full_external_tangent.Values()[offset];
+      if (!std::isfinite(tangent)) {
+        return Result<GlobalFixedLoadContribution>::Failure(ProcedureFailure(
+            FailureCategory::kSolver, "nonfinite-newton-data", {},
+            "NONLINEAR_STATIC_PROCEDURE", std::to_string(row),
+            "Nonlinear fixed and pressure tangent composition is nonfinite."));
+      }
+      contributions.push_back(
+          {row, fixed.generalized_external_tangent.ColumnIndices()[offset],
+           tangent, row, offset});
+    }
+  }
+  Result<SparseMatrix> tangent =
+      SparseMatrix::FromCoo(fixed.generalized_external_tangent.Rows(),
+                            fixed.generalized_external_tangent.Columns(),
+                            std::move(contributions), dofs.GetSparsePattern());
+  if (!tangent.HasValue()) {
+    return Result<GlobalFixedLoadContribution>::Failure(tangent.GetStatus());
+  }
+
+  std::vector<Diagnostic> diagnostics = fixed.diagnostics;
+  diagnostics.insert(diagnostics.end(), pressure.diagnostics.begin(),
+                     pressure.diagnostics.end());
+  return Result<GlobalFixedLoadContribution>::Success(
+      {std::move(force), std::move(tangent.Value()), std::move(diagnostics)});
+}
+
 Vector SelectFreeComponents(const Vector& full, const DofManager& dofs,
                             const bool rotations) {
   std::size_t count = 0U;
@@ -670,6 +741,11 @@ NonlinearStaticProcedureExecutor::Execute(
   if (!dofs.HasValue()) {
     return Result<NonlinearStaticExecutionResult>::Failure(dofs.GetStatus());
   }
+  Result<AnalysisModel> analysis_model = AnalysisModel::Create(domain);
+  if (!analysis_model.HasValue()) {
+    return Result<NonlinearStaticExecutionResult>::Failure(
+        analysis_model.GetStatus());
+  }
   Result<NonlinearStateBaselineInput> baseline = BuildBaseline(domain);
   if (!baseline.HasValue()) {
     return Result<NonlinearStaticExecutionResult>::Failure(
@@ -732,14 +808,32 @@ NonlinearStaticProcedureExecutor::Execute(
       }
       record.last_completed_stage = NewtonIterationStage::kInternalAssembled;
 
-      Result<GlobalFixedLoadContribution> external =
+      Result<GlobalFixedLoadContribution> fixed =
           AssembleGlobalFixedLoadContribution(
               domain, dofs.Value(), trial.Value().generalized_coordinates,
               increment.load_factor);
+      if (!fixed.HasValue()) {
+        return Result<NonlinearStaticExecutionResult>::Failure(
+            RecordFailure(log, &record, fixed.GetStatus(),
+                          NewtonIterationStage::kExternalAssembled));
+      }
+      Result<SurfacePressureAssemblyCandidate> pressure =
+          AssembleSurfacePressure(
+              analysis_model.Value(), dofs.Value(),
+              trial.Value().generalized_coordinates, increment.load_factor,
+              SurfacePressureConfiguration::kCurrent, parallel_for_);
+      if (!pressure.HasValue()) {
+        return Result<NonlinearStaticExecutionResult>::Failure(
+            RecordFailure(log, &record, pressure.GetStatus(),
+                          NewtonIterationStage::kExternalAssembled));
+      }
+      Result<GlobalFixedLoadContribution> external =
+          CombineExternalContributions(fixed.Value(), pressure.Value(),
+                                       dofs.Value());
       if (!external.HasValue()) {
-        return Result<NonlinearStaticExecutionResult>::Failure(RecordFailure(
-            log, &record, external.GetStatus(),
-            NewtonIterationStage::kExternalAssembled));
+        return Result<NonlinearStaticExecutionResult>::Failure(
+            RecordFailure(log, &record, external.GetStatus(),
+                          NewtonIterationStage::kExternalAssembled));
       }
       record.last_completed_stage = NewtonIterationStage::kExternalAssembled;
 

tests/CMakeLists.txt

@@ -76,6 +76,7 @@ add_executable(
     fesa_integration_tests
     integration/analysis/linear_static_analysis_test.cpp
     integration/analysis/shell_surface_pressure_linear_test.cpp
+    integration/analysis/shell_surface_pressure_nonlinear_test.cpp
     integration/analysis/nonlinear_static_procedure_test.cpp
     integration/app/fesa_application_test.cpp
     integration/app/shell_surface_pressure_application_test.cpp

tests/integration/analysis/shell_surface_pressure_nonlinear_test.cpp

@@ -0,0 +1,430 @@
+#include <gtest/gtest.h>
+#include <hdf5.h>
+
+#include <algorithm>
+#include <array>
+#include <atomic>
+#include <chrono>
+#include <cmath>
+#include <filesystem>
+#include <fstream>
+#include <iterator>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include "fesa/app/fesa_application.h"
+#include "fesa/loads/shell_surface_pressure.h"
+
+namespace {
+
+class TempDirectory {
+ public:
+  explicit TempDirectory(const std::string& label) {
+    static std::atomic<unsigned long long> sequence{0U};
+    const auto tick =
+        std::chrono::steady_clock::now().time_since_epoch().count();
+    path_ =
+        std::filesystem::temp_directory_path() /
+        ("fesa-surface-pressure-nonlinear-" + label + "-" +
+         std::to_string(tick) + "-" + std::to_string(sequence.fetch_add(1U)));
+    std::error_code error;
+    if (!std::filesystem::create_directory(path_, error) || error) {
+      throw std::runtime_error{"Unable to create nonlinear pressure fixture."};
+    }
+  }
+
+  TempDirectory(const TempDirectory&) = delete;
+  TempDirectory& operator=(const TempDirectory&) = delete;
+
+  ~TempDirectory() {
+    std::error_code ignored;
+    std::filesystem::remove_all(path_, ignored);
+  }
+
+  const std::filesystem::path& Path() const noexcept { return path_; }
+
+ private:
+  std::filesystem::path path_;
+};
+
+class Hdf5File {
+ public:
+  explicit Hdf5File(const std::filesystem::path& path)
+      : handle_{H5Fopen(path.string().c_str(), H5F_ACC_RDONLY, H5P_DEFAULT)} {
+    if (handle_ < 0) {
+      throw std::runtime_error{"Unable to open nonlinear pressure results."};
+    }
+  }
+
+  Hdf5File(const Hdf5File&) = delete;
+  Hdf5File& operator=(const Hdf5File&) = delete;
+
+  ~Hdf5File() { (void)H5Fclose(handle_); }
+
+  hid_t Get() const noexcept { return handle_; }
+
+ private:
+  hid_t handle_;
+};
+
+void WriteText(const std::filesystem::path& path, const std::string& text) {
+  std::ofstream stream{path, std::ios::binary | std::ios::trunc};
+  stream.write(text.data(), static_cast<std::streamsize>(text.size()));
+  if (!stream) {
+    throw std::runtime_error{"Unable to write nonlinear pressure input."};
+  }
+}
+
+std::vector<char> ReadBytes(const std::filesystem::path& path) {
+  std::ifstream stream{path, std::ios::binary};
+  return {std::istreambuf_iterator<char>{stream},
+          std::istreambuf_iterator<char>{}};
+}
+
+std::string NonlinearPressureDeck(const bool include_pressure,
+                                  const bool collapsed) {
+  const std::string surface = include_pressure
+                                  ? "*Surface, TYPE=ELEMENT, NAME=Pressure\n"
+                                    "Shell-1.1, SPOS\n"
+                                  : "";
+  const std::string dsload =
+      include_pressure ? "*Dsload\nPressure, P, 4.0\n" : "";
+  const std::string node_three =
+      collapsed ? "3, 1., 0., 0.\n" : "3, 1., 1., 0.\n";
+  const std::string constraints =
+      "N1, 1, 6\n"
+      "N2, 1, 6\n"
+      "N3, 2, 6\n"
+      "N3, 1, 1, 1.0\n"
+      "N4, 1, 6\n";
+  return std::string{R"inp(*Part, name=ShellPart
+*Node
+1, 0., 0., 0.
+2, 1., 0., 0.
+)inp"} + node_three +
+         R"inp(4, 0., 1., 0.
+*Element, type=S4
+1, 1, 2, 3, 4
+*Elset, elset=ShellSet
+1
+*Shell Section, elset=ShellSet, material=Steel
+0.1
+*End Part
+*Assembly, name=Assembly
+*Instance, name=Shell-1, part=ShellPart
+*End Instance
+)inp" + surface +
+         R"inp(*Nset, nset=N1, instance=Shell-1
+1
+*Nset, nset=N2, instance=Shell-1
+2
+*Nset, nset=N3, instance=Shell-1
+3
+*Nset, nset=N4, instance=Shell-1
+4
+*End Assembly
+*Material, name=Steel
+*Elastic
+1000., 0.25
+*Boundary
+)inp" + constraints +
+         R"inp(*Step, name=Step-1, nlgeom=YES
+*Static
+0.1, 1., 0.001, 0.1
+)inp" + dsload +
+         "*End Step\n";
+}
+
+std::vector<double> ReadFrameDataset(const Hdf5File& file,
+                                     const std::uint32_t frame_index,
+                                     const std::string& suffix) {
+  const std::string path =
+      "/steps/Step-1/frames/" + std::to_string(frame_index) + suffix;
+  const hid_t dataset = H5Dopen2(file.Get(), path.c_str(), H5P_DEFAULT);
+  if (dataset < 0) {
+    throw std::runtime_error{"Unable to open nonlinear pressure dataset."};
+  }
+  std::vector<double> values(24U);
+  const herr_t read = H5Dread(dataset, H5T_NATIVE_DOUBLE, H5S_ALL, H5S_ALL,
+                              H5P_DEFAULT, values.data());
+  (void)H5Dclose(dataset);
+  if (read < 0 ||
+      !std::all_of(
+          values.begin(), values.end(),
+          [](const double value) { return std::isfinite(value); })) {
+    throw std::runtime_error{"Unable to read nonlinear pressure dataset."};
+  }
+  return values;
+}
+
+std::array<double, 6> ReadEquilibrium(const Hdf5File& file,
+                                      const std::uint32_t frame_index) {
+  const std::string path = "/steps/Step-1/frames/" +
+                           std::to_string(frame_index) + "/global/equilibrium";
+  const hid_t dataset = H5Dopen2(file.Get(), path.c_str(), H5P_DEFAULT);
+  if (dataset < 0) {
+    throw std::runtime_error{"Unable to open nonlinear equilibrium."};
+  }
+  std::array<double, 6> values{};
+  const herr_t read = H5Dread(dataset, H5T_NATIVE_DOUBLE, H5S_ALL, H5S_ALL,
+                              H5P_DEFAULT, values.data());
+  (void)H5Dclose(dataset);
+  if (read < 0) {
+    throw std::runtime_error{"Unable to read nonlinear equilibrium."};
+  }
+  return values;
+}
+
+double SumTranslation(const std::vector<double>& values,
+                      const std::size_t component) {
+  double result = 0.0;
+  for (std::size_t node = 0U; node < 4U; ++node) {
+    result += values[node * 6U + component];
+  }
+  return result;
+}
+
+double MaximumAbs(const std::array<double, 6>& values) {
+  double result = 0.0;
+  for (const double value : values) {
+    result = (std::max)(result, std::abs(value));
+  }
+  return result;
+}
+
+fesa::ShellSurfacePressureInput CurrentPressureInput(
+    const double node_three_x_displacement) {
+  return {
+      {{{0.0, 0.0, 0.0}, {1.0, 0.0, 0.0}, {1.0, 1.0, 0.0}, {0.0, 1.0, 0.0}}},
+      {{{0.0, 0.0, 0.0},
+        {0.0, 0.0, 0.0},
+        {node_three_x_displacement, 0.0, 0.0},
+        {0.0, 0.0, 0.0}}},
+      fesa::ShellSurfaceSide::kSpos,
+      4.0,
+      1.0,
+      fesa::SurfacePressureConfiguration::kCurrent,
+      {},
+      "unsymmetric"};
+}
+
+const Hdf5File RunNonlinearPressure(const std::filesystem::path& input,
+                                    const std::filesystem::path& output) {
+  testing::internal::CaptureStderr();
+  const int exit_code = fesa::FesaApplication{}.Run({input.string()});
+  const std::string standard_error = testing::internal::GetCapturedStderr();
+  EXPECT_EQ(exit_code, 0) << standard_error;
+  EXPECT_TRUE(std::filesystem::exists(output));
+  EXPECT_GT(H5Fis_hdf5(output.string().c_str()), 0);
+  return Hdf5File{output};
+}
+
+}  // namespace
+
+TEST(NonlinearShellSurfacePressure,
+     AssemblesFollowerForceFromCurrentTrialGeometry) {
+  TempDirectory directory{"current-force"};
+  const auto input = directory.Path() / "current-force.inp";
+  const auto output = directory.Path() / "current-force_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, false));
+
+  const Hdf5File file = RunNonlinearPressure(input, output);
+  const auto external =
+      ReadFrameDataset(file, 9U, "/nodal/generalized_external_force");
+
+  EXPECT_NEAR(SumTranslation(external, 2U), -6.0, 1.0e-12);
+}
+
+TEST(NonlinearShellSurfacePressure,
+     FormsResidualAndTangentWithApprovedExternalSigns) {
+  TempDirectory directory{"external-sign"};
+  const auto input = directory.Path() / "external-sign.inp";
+  const auto output = directory.Path() / "external-sign_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, false));
+
+  const Hdf5File file = RunNonlinearPressure(input, output);
+  const auto external =
+      ReadFrameDataset(file, 9U, "/nodal/generalized_external_force");
+  const auto residual =
+      ReadFrameDataset(file, 9U, "/nodal/generalized_residual");
+
+  EXPECT_NEAR(SumTranslation(external, 2U), -6.0, 1.0e-12);
+  EXPECT_NEAR(SumTranslation(residual, 2U), 6.0, 1.0e-12);
+}
+
+TEST(NonlinearShellSurfacePressure, AppliesIncrementFactorExactlyOnce) {
+  TempDirectory directory{"factor-once"};
+  const auto input = directory.Path() / "factor-once.inp";
+  const auto output = directory.Path() / "factor-once_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, false));
+
+  const Hdf5File file = RunNonlinearPressure(input, output);
+  const auto external =
+      ReadFrameDataset(file, 0U, "/nodal/generalized_external_force");
+
+  EXPECT_NEAR(SumTranslation(external, 2U), -0.42, 1.0e-12);
+}
+
+TEST(NonlinearShellSurfacePressure, UsesFullUnsymmetricTangentSolverPath) {
+  TempDirectory directory{"unsymmetric"};
+  const auto input = directory.Path() / "unsymmetric.inp";
+  const auto output = directory.Path() / "unsymmetric_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, false));
+
+  const Hdf5File file = RunNonlinearPressure(input, output);
+  const auto external =
+      ReadFrameDataset(file, 9U, "/nodal/generalized_external_force");
+  const auto residual =
+      ReadFrameDataset(file, 9U, "/nodal/generalized_residual");
+
+  EXPECT_NE(SumTranslation(external, 2U), 0.0);
+  EXPECT_NE(SumTranslation(residual, 2U), 0.0);
+
+  const auto central =
+      fesa::EvaluateShellSurfacePressure(CurrentPressureInput(1.0));
+  const auto forward =
+      fesa::EvaluateShellSurfacePressure(CurrentPressureInput(1.0 + 1.0e-6));
+  const auto backward =
+      fesa::EvaluateShellSurfacePressure(CurrentPressureInput(1.0 - 1.0e-6));
+  ASSERT_TRUE(central.HasValue());
+  ASSERT_TRUE(forward.HasValue());
+  ASSERT_TRUE(backward.HasValue());
+
+  bool has_antisymmetric_entry = false;
+  for (std::size_t row = 0U; row < 24U; ++row) {
+    const double finite_difference =
+        (forward.Value().force[row] - backward.Value().force[row]) / 2.0e-6;
+    EXPECT_NEAR(finite_difference,
+                central.Value().external_tangent[row * 24U + 12U], 1.0e-8)
+        << "row=" << row;
+    for (std::size_t column = row + 1U; column < 24U; ++column) {
+      has_antisymmetric_entry =
+          has_antisymmetric_entry ||
+          std::abs(central.Value().external_tangent[row * 24U + column] -
+                   central.Value().external_tangent[column * 24U + row]) >
+              1.0e-12;
+    }
+  }
+  EXPECT_TRUE(has_antisymmetric_entry);
+}
+
+TEST(NonlinearShellSurfacePressure,
+     ConvergesOpenPatchAndPreservesAntisymmetricEvidence) {
+  TempDirectory directory{"open-patch"};
+  const auto input = directory.Path() / "open-patch.inp";
+  const auto output = directory.Path() / "open-patch_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, false));
+
+  const Hdf5File file = RunNonlinearPressure(input, output);
+  const auto external =
+      ReadFrameDataset(file, 9U, "/nodal/generalized_external_force");
+
+  EXPECT_NEAR(SumTranslation(external, 2U), -6.0, 1.0e-12);
+  EXPECT_GT(H5Lexists(file.Get(), "/steps/Step-1/accepted_frames", H5P_DEFAULT),
+            0);
+}
+
+TEST(NonlinearShellSurfacePressure,
+     SatisfiesAcceptedFreeResidualAndFactorOneGlobalBalance) {
+  TempDirectory directory{"balance"};
+  const auto input = directory.Path() / "balance.inp";
+  const auto output = directory.Path() / "balance_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, false));
+
+  const Hdf5File file = RunNonlinearPressure(input, output);
+  const auto equilibrium = ReadEquilibrium(file, 9U);
+
+  EXPECT_LE(MaximumAbs(equilibrium), 1.0e-8);
+}
+
+TEST(NonlinearShellSurfacePressure,
+     IsObjectiveUnderRigidMotionAndTracksCurrentArea) {
+  fesa::ShellSurfacePressureInput input{
+      {{{0.0, 0.0, 0.0}, {1.0, 0.0, 0.0}, {1.0, 1.0, 0.0}, {0.0, 1.0, 0.0}}},
+      {{{0.0, 0.0, 0.0}, {0.0, 0.0, 0.0}, {0.0, -1.0, 1.0}, {0.0, -1.0, 1.0}}},
+      fesa::ShellSurfaceSide::kSpos,
+      4.0,
+      1.0,
+      fesa::SurfacePressureConfiguration::kCurrent,
+      {},
+      "objectivity"};
+
+  const auto contribution = fesa::EvaluateShellSurfacePressure(input);
+
+  ASSERT_TRUE(contribution.HasValue());
+  double force_x = 0.0;
+  double force_y = 0.0;
+  double force_z = 0.0;
+  for (std::size_t node = 0U; node < 4U; ++node) {
+    force_x += contribution.Value().force[node * 6U];
+    force_y += contribution.Value().force[node * 6U + 1U];
+    force_z += contribution.Value().force[node * 6U + 2U];
+  }
+  EXPECT_NEAR(force_x, 0.0, 1.0e-12);
+  EXPECT_NEAR(force_y, 4.0, 1.0e-12);
+  EXPECT_NEAR(force_z, 0.0, 1.0e-12);
+}
+
+TEST(NonlinearShellSurfacePressure,
+     ReducesSerialAndParallelContributionsDeterministically) {
+  TempDirectory directory{"deterministic"};
+  const auto first_input = directory.Path() / "first.inp";
+  const auto first_output = directory.Path() / "first_results.h5";
+  const auto second_input = directory.Path() / "second.inp";
+  const auto second_output = directory.Path() / "second_results.h5";
+  const std::string deck = NonlinearPressureDeck(true, false);
+  WriteText(first_input, deck);
+  WriteText(second_input, deck);
+
+  const Hdf5File first = RunNonlinearPressure(first_input, first_output);
+  const Hdf5File second = RunNonlinearPressure(second_input, second_output);
+  const auto first_force =
+      ReadFrameDataset(first, 9U, "/nodal/generalized_external_force");
+  const auto second_force =
+      ReadFrameDataset(second, 9U, "/nodal/generalized_external_force");
+
+  EXPECT_EQ(first_force, second_force);
+  EXPECT_NE(SumTranslation(first_force, 2U), 0.0);
+}
+
+TEST(NonlinearShellSurfacePressure,
+     InvalidTrialRollsBackCommittedFrameAndFinalOutput) {
+  TempDirectory directory{"rollback"};
+  const auto input = directory.Path() / "rollback.inp";
+  const auto output = directory.Path() / "rollback_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, true));
+  const std::vector<char> previous{'p', 'r', 'i', 'o', 'r'};
+  {
+    std::ofstream stream{output, std::ios::binary | std::ios::trunc};
+    stream.write(previous.data(),
+                 static_cast<std::streamsize>(previous.size()));
+  }
+
+  const int exit_code = fesa::FesaApplication{}.Run({input.string()});
+
+  EXPECT_NE(exit_code, 0);
+  EXPECT_EQ(ReadBytes(output), previous);
+}
+
+TEST(NonlinearShellSurfacePressure,
+     WritesSchemaOneExternalInternalResidualReactionAndEquilibrium) {
+  TempDirectory directory{"schema"};
+  const auto input = directory.Path() / "schema.inp";
+  const auto output = directory.Path() / "schema_results.h5";
+  WriteText(input, NonlinearPressureDeck(true, false));
+
+  const Hdf5File file = RunNonlinearPressure(input, output);
+  const std::string root = "/steps/Step-1/frames/9";
+  for (const std::string& suffix :
+       {"/nodal/generalized_internal_force",
+        "/nodal/generalized_external_force", "/nodal/generalized_residual",
+        "/nodal/reaction", "/global/equilibrium"}) {
+    EXPECT_GT(H5Lexists(file.Get(), (root + suffix).c_str(), H5P_DEFAULT), 0)
+        << suffix;
+  }
+  const auto external =
+      ReadFrameDataset(file, 9U, "/nodal/generalized_external_force");
+  EXPECT_NEAR(SumTranslation(external, 2U), -6.0, 1.0e-12);
+  EXPECT_EQ(H5Lexists(file.Get(), "/surface_pressure", H5P_DEFAULT), 0);
+}

tests/integration/app/shell_surface_pressure_application_test.cpp

@@ -101,6 +101,38 @@ All, 1, 6
          dsload + "*End Step\n";
 }
 
+std::string NonlinearShellDeck() {
+  return R"inp(*Part, name=ShellPart
+*Node
+1, 0., 0., 0.
+2, 1., 0., 0.
+3, 1., 1., 0.
+4, 0., 1., 0.
+*Element, type=S4
+1, 1, 2, 3, 4
+*Elset, elset=ShellSet
+1
+*Shell Section, elset=ShellSet, material=Steel
+0.1
+*End Part
+*Assembly, name=Assembly
+*Instance, name=Shell-1, part=ShellPart
+*End Instance
+*Nset, nset=All, instance=Shell-1
+1, 2, 3, 4
+*End Assembly
+*Material, name=Steel
+*Elastic
+1000., 0.25
+*Boundary
+All, 1, 6
+*Step, name=Step-1, nlgeom=YES
+*Static
+0.1, 1., 0.001, 0.1
+*End Step
+)inp";
+}
+
 }  // namespace
 
 TEST(ShellSurfacePressureApplication,
@@ -143,3 +175,21 @@ TEST(ShellSurfacePressureApplication,
             0);
   EXPECT_GE(H5Fclose(file), 0);
 }
+
+TEST(ShellSurfacePressureApplication,
+     InputWithoutPressureRetainsExistingNonlinearBehavior) {
+  TempDirectory directory{"nonlinear-no-pressure"};
+  const auto input = directory.Path() / "nonlinear-no-pressure.inp";
+  const auto output = directory.Path() / "nonlinear-no-pressure_results.h5";
+  WriteText(input, NonlinearShellDeck());
+
+  EXPECT_EQ(fesa::FesaApplication{}.Run({input.string()}), 0);
+  ASSERT_TRUE(std::filesystem::exists(output));
+  ASSERT_GT(H5Fis_hdf5(output.string().c_str()), 0);
+  const hid_t file =
+      H5Fopen(output.string().c_str(), H5F_ACC_RDONLY, H5P_DEFAULT);
+  ASSERT_GE(file, 0);
+  EXPECT_GT(H5Lexists(file, "/steps/Step-1/accepted_frames", H5P_DEFAULT), 0);
+  EXPECT_EQ(H5Lexists(file, "/surface_pressure", H5P_DEFAULT), 0);
+  EXPECT_GE(H5Fclose(file), 0);
+}

tests/unit/io/hdf5/nonlinear_hdf5_results_writer_test.cpp

@@ -478,6 +478,7 @@ TEST(NonlinearHdf5ResultsWriter,
   EXPECT_EQ(H5Lexists(file.Get(), "/steps/Step-1/frames/2", H5P_DEFAULT), 0);
   EXPECT_EQ(H5Lexists(file.Get(), "/steps/Step-1/trial_history", H5P_DEFAULT),
             0);
+  EXPECT_EQ(H5Lexists(file.Get(), "/surface_pressure", H5P_DEFAULT), 0);
 
   const std::string root = "/steps/Step-1/frames/1";
   for (const std::string& suffix :