From ed99546b8a493cf5553686d712d890838d7d4877 Mon Sep 17 00:00:00 2001
From: Kutalmis Bercin <kutalmis.bercin@esi-group.com>
Date: Wed, 18 Dec 2024 15:00:57 +0000
Subject: [PATCH] ENH: tabulated6DoFMotion: add optional linear interpolation
 scheme

---
 .../tabulated6DoFMotion/tabulated6DoFMotion.C | 48 ++++++++++++++++---
 .../tabulated6DoFMotion/tabulated6DoFMotion.H | 18 ++++++-
 2 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.C b/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.C
index e9668c8044..5e880c5be1 100644
--- a/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.C
+++ b/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.C
@@ -31,6 +31,7 @@ License
 #include "Tuple2.H"
 #include "IFstream.H"
 #include "interpolateSplineXY.H"
+#include "interpolateXY.H"
 #include "unitConversion.H"
 
 
@@ -51,6 +52,17 @@ namespace solidBodyMotionFunctions
 }
 
 
+const Foam::Enum
+<
+    Foam::solidBodyMotionFunctions::tabulated6DoFMotion::interpolationType
+>
+Foam::solidBodyMotionFunctions::tabulated6DoFMotion::interpolationTypeNames
+({
+    { interpolationType::SPLINE, "spline" },
+    { interpolationType::LINEAR, "linear" }
+});
+
+
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 Foam::solidBodyMotionFunctions::tabulated6DoFMotion::tabulated6DoFMotion
@@ -90,12 +102,28 @@ Foam::solidBodyMotionFunctions::tabulated6DoFMotion::transformation() const
             << exit(FatalError);
     }
 
-    translationRotationVectors TRV = interpolateSplineXY
-    (
-        t,
-        times_,
-        values_
-    );
+    translationRotationVectors TRV;
+    switch (interpolator_)
+    {
+        case interpolationType::SPLINE:
+        {
+            TRV = interpolateSplineXY(t, times_, values_);
+            break;
+        }
+        case interpolationType::LINEAR:
+        {
+            TRV = interpolateXY(t, times_, values_);
+            break;
+        }
+        default:
+        {
+            FatalErrorInFunction
+                << "Unrecognised 'interpolationScheme' option: "
+                << interpolationTypeNames[interpolator_]
+                << exit(FatalError);
+            break;
+        }
+    }
 
     // Convert the rotational motion from deg to rad
     TRV[1] *= degToRad();
@@ -155,6 +183,14 @@ bool Foam::solidBodyMotionFunctions::tabulated6DoFMotion::read
 
     SBMFCoeffs_.readEntry("CofG", CofG_);
 
+    interpolator_ =
+        interpolationTypeNames.getOrDefault
+        (
+            "interpolationScheme",
+            SBMFCoeffs_,
+            interpolationType::SPLINE
+        );
+
     return true;
 }
 
diff --git a/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.H b/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.H
index cd583521a1..50fbe81de0 100644
--- a/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.H
+++ b/src/meshTools/solidBodyMotionFunctions/tabulated6DoFMotion/tabulated6DoFMotion.H
@@ -61,7 +61,23 @@ class tabulated6DoFMotion
 :
     public solidBodyMotionFunction
 {
-    // Private data
+    // Private Enumerations
+
+        //- Options for the interpolation algorithm
+        enum class interpolationType : char
+        {
+            SPLINE = 0, //!< "Spline interpolation method"
+            LINEAR      //!< "Linear interpolation method"
+        };
+
+        //- Names for interpolationType
+        static const Enum<interpolationType> interpolationTypeNames;
+
+
+    // Private Data
+
+        //- Interpolation algorithm
+        interpolationType interpolator_;
 
         //- Time data file name read from dictionary
         fileName timeDataFileName_;