From 60d6df337ac4c9b542bf67b515b1fc05e81779d3 Mon Sep 17 00:00:00 2001
From: Lennart Karstensen <lennart.karstensen@ipa.fraunhofer.de>
Date: Wed, 29 Apr 2026 16:34:46 +0200
Subject: [PATCH] [RodStraightSection] Fix rest shape double-offset for
 non-first sections (#223)

x_used is the global curvilinear abscissa; adding x_start again placed
the rest node at 2*x_start + local_offset instead of x_used. For wires
with two or more RodStraightSections this produced enormous elastic
restoring forces at every timestep, causing simulation explosion.

Fix: use x_used directly, consistent with RodSpireSection and RodMeshSection.
---
 src/BeamAdapter/component/model/RodStraightSection.inl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/BeamAdapter/component/model/RodStraightSection.inl b/src/BeamAdapter/component/model/RodStraightSection.inl
index e74851ca0..a6c247eab 100644
--- a/src/BeamAdapter/component/model/RodStraightSection.inl
+++ b/src/BeamAdapter/component/model/RodStraightSection.inl
@@ -53,7 +53,7 @@ bool RodStraightSection<DataTypes>::initSection()
 template <class DataTypes>
 void RodStraightSection<DataTypes>::getRestTransformOnX(Transform& global_H_local, const Real x_used, const Real x_start)
 {
-    global_H_local.set(type::Vec3(x_start + x_used, 0.0, 0.0), Quat());
+    global_H_local.set(type::Vec3(x_used, 0.0, 0.0), Quat());
 }