Recognition: unknown
Mixed Finite Elements for Geometrically Exact Beams using Discontinuous Rotations and Discrete Curvature
Pith reviewed 2026-05-08 16:15 UTC · model grok-4.3
The pith
A mixed finite-element formulation for geometrically exact beams treats moments as independent variables to allow discontinuous rotations per element.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is that a mixed variational formulation for geometrically exact beams, obtained by introducing the moment vector as an independent field, enables an element-local discontinuous approximation of rotations while remaining consistent through the notion of discrete curvature. Objectivity is retained by interpolating relative rotations via a multiplicative split, and path independence follows directly from the total Lagrangian description.
What carries the argument
mixed variational principle with moment vector as independent field and discrete curvature to accommodate discontinuous rotations
Load-bearing premise
The Legendre transform of the curvature strain energy produces a stable and consistent discrete system for every slenderness ratio and every element order.
What would settle it
A benchmark computation on a highly slender beam with the lowest-order element that exhibits locking or suboptimal convergence rates would falsify the claims.
read the original abstract
We propose a novel mixed finite-element formulation for geometrically exact (Simo--Reissner) beams that introduces the moment vector as additional independent field. The specific mixed form allows for an element-local, discontinuous approximation of rotations, which is key to a simple and efficient discretization framework. The concept of discrete curvature provides a mathematically consistent treatment of rotation discontinuities. For linear constitutive laws, the mixed form is derived via a Legendre transform of the curvature-related strain energy. Objectivity is retained at the discrete level by interpolating relative rotations through a multiplicative split of the rotation field; path-independence is inherent to the total Lagrangian setting and verified numerically. Several benchmarks demonstrate optimal rates of convergence and accuracy, irrespective of the beam's slenderness and order of approximation. Notably, the lowest-order element entirely avoids rotation interpolation by employing element-constant rotations only.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes a novel mixed finite-element formulation for geometrically exact Simo-Reissner beams. It introduces the moment vector as an independent field, derived for linear constitutive laws via a Legendre transform of the curvature strain energy. This enables element-local discontinuous rotation approximations, with discrete curvature providing consistent treatment of rotation jumps. Objectivity is retained via multiplicative interpolation of relative rotations, and the total Lagrangian setting ensures path-independence. Numerical benchmarks are presented to demonstrate optimal convergence rates independent of beam slenderness and polynomial order, including a lowest-order element with element-constant rotations only.
Significance. If the stability and convergence properties hold as indicated by the benchmarks, the formulation would offer a practical simplification for discretizing geometrically exact beams by avoiding continuous rotation fields and associated interpolation complexities. The approach could be particularly useful for slender beams and varying element orders. The paper credits the total Lagrangian framework and multiplicative split for preserving key properties, and the numerical evidence for optimal rates across slenderness is a positive aspect, though the lack of supporting analysis limits the strength of the claims.
major comments (2)
- [Abstract and formulation derivation] The central claim that the method achieves optimal convergence 'irrespective of the beam's slenderness and order of approximation' rests on numerical benchmarks, but the mixed formulation obtained via Legendre transform lacks an explicit discrete inf-sup condition or uniform stability estimate. This is load-bearing for the assertion of robustness in the slender limit and for arbitrary orders, as the discontinuous rotations and discrete curvature are introduced precisely to enable the mixed form.
- [Numerical benchmarks] The lowest-order element, which employs element-constant rotations only, is highlighted as avoiding rotation interpolation; however, the paper does not provide a specific analysis or additional tests confirming that this element remains stable and accurate for extreme slenderness ratios without introducing locking or other pathologies.
minor comments (2)
- [Abstract] The abstract could more explicitly reference the specific benchmarks (e.g., number of test cases, range of slenderness ratios, and polynomial orders tested) to better support the convergence claims.
- Notation for the discrete curvature and the multiplicative split of the rotation field should be introduced with a brief reminder of their relation to the continuous fields to improve readability for readers unfamiliar with the Simo-Reissner model.
Simulated Author's Rebuttal
We thank the referee for the careful and constructive review. The comments correctly identify that our convergence claims rest primarily on numerical evidence rather than a full theoretical stability analysis. We address each major comment below, indicate planned revisions, and note where we cannot provide additional analysis within the current scope.
read point-by-point responses
-
Referee: [Abstract and formulation derivation] The central claim that the method achieves optimal convergence 'irrespective of the beam's slenderness and order of approximation' rests on numerical benchmarks, but the mixed formulation obtained via Legendre transform lacks an explicit discrete inf-sup condition or uniform stability estimate. This is load-bearing for the assertion of robustness in the slender limit and for arbitrary orders, as the discontinuous rotations and discrete curvature are introduced precisely to enable the mixed form.
Authors: We acknowledge that the manuscript provides no discrete inf-sup condition or uniform stability estimate for the mixed formulation. The claims of optimal convergence independent of slenderness and polynomial order are supported exclusively by the numerical benchmarks in Section 5, which include multiple slenderness ratios (from thick to very slender) and approximation orders up to cubic, with the lowest-order element showing no degradation or locking. The mixed moment field and discrete curvature are introduced precisely to permit stable discontinuous rotations while preserving objectivity via multiplicative interpolation. In the revised manuscript we will (i) rephrase the abstract and introduction to state that robustness is demonstrated numerically rather than proven theoretically, and (ii) add a short discussion paragraph in the formulation section that explicitly notes the absence of an inf-sup analysis and identifies it as future work. This is a partial revision because a complete theoretical proof lies beyond the present scope. revision: partial
-
Referee: [Numerical benchmarks] The lowest-order element, which employs element-constant rotations only, is highlighted as avoiding rotation interpolation; however, the paper does not provide a specific analysis or additional tests confirming that this element remains stable and accurate for extreme slenderness ratios without introducing locking or other pathologies.
Authors: The lowest-order element is already included in the convergence studies of Section 5 and exhibits optimal rates across the tested slenderness range. To strengthen the evidence, the revised manuscript will contain additional targeted numerical experiments using this element at extreme slenderness ratios (L/h up to 10^6) under both bending and torsion loads. These tests will explicitly monitor for locking, spurious modes, or loss of accuracy. We therefore accept the referee's suggestion and will incorporate the new results. revision: yes
Circularity Check
No circularity: derivation rests on standard Legendre transform and total Lagrangian setting
full rationale
The core mixed weak form is obtained by applying the Legendre transform to the curvature strain energy for linear constitutive laws, then introducing the moment as independent field. This algebraic step is independent of the subsequent discrete choices (discontinuous rotations, discrete curvature) and of the numerical benchmarks. Path-independence follows directly from the total Lagrangian formulation. No self-citations are invoked as load-bearing uniqueness theorems, no fitted parameters are relabeled as predictions, and no ansatz is smuggled via prior work. The convergence rates are reported from numerical experiments rather than being presupposed by the derivation equations themselves.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption The beam kinematics follow the Simo-Reissner geometrically exact model
- domain assumption Constitutive response is linear so that a Legendre transform yields the mixed form
invented entities (2)
-
Moment vector as independent field
no independent evidence
-
Discrete curvature
no independent evidence
Reference graph
Works this paper leans on
-
[1]
Marc-Michel Bousquet et Soc., Lausanne (1744)
Euler, L.: Methodus Inveniendi Lineas Curvas Maximi Minimive Proprietate Gaudentes, Sive Solutio Problematis Isoperimetrici Lattissimo Sensu Accepti. Marc-Michel Bousquet et Soc., Lausanne (1744)
-
[2]
Kirchhoff, G.: Ueber das Gleichgewicht und die Bewegung eines unendlich dünnen elastischen Stabes. Journal für die reine und angewandte Mathematik 1859(56), 285–313 (1859) https: //doi.org/10.1515/crll.1859.56.285
-
[3]
On the correction for shear of the differential equation for transverse vibrations of prismatic bars
Timoshenko, S.P.: LXVI. On the correction for shear of the differential equation for transverse vibrations of prismatic bars. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 41(245), 744–746 (1921) https://doi.org/10.1080/14786442108636264
-
[4]
On one-dimensional finite-strain beam theory: The plane problem
Reissner, E.: On one-dimensional finite-strain beam theory: The plane problem. Zeitschrift für angewandte Mathematik und Physik (ZAMP) (1972) https://doi.org/10.1007/BF01602645
-
[5]
Studies in Applied Mathematics 52(2), 87–95 (1973) https://doi.org/10.1002/sapm197352287
Reissner, E.: On One-Dimensional Large-Displacement Finite-Strain Beam Theory. Studies in Applied Mathematics 52(2), 87–95 (1973) https://doi.org/10.1002/sapm197352287
-
[6]
Reissner, E.: On finite deformations of space-curved beams. ZAMP Zeitschrift für angewandte Mathematik und Physik 32(6), 734–744 (1981) https://doi.org/10.1007/BF00946983
-
[7]
Antman, S.S.: The Theory of Rods. In: Truesdell, C. (ed.) Linear Theories of Elasticity and Thermoelasticity vol. VIa/2, pp. 641–703. Springer, Berlin Heidelberg (1973). https: //doi.org/10.1007/978-3-662-39776-3_6
-
[8]
A finite strain beam formulation. The three-dimensional dynamic problem. Part I
Simo, J.C.: A finite strain beam formulation. The three-dimensional dynamic problem. Part I. Computer Methods in Applied Mechanics and Engineering 49(1), 55–70 (1985) https: //doi.org/10.1016/0045-7825(85)90050-7 25
-
[9]
part II: Computational aspects
Simo, J.C., Vu-Quoc, L.: A three-dimensional finite-strain rod model. part II: Computational aspects. Computer Methods in Applied Mechanics and Engineering 58(1), 79–116 (1986) https://doi.org/10.1016/0045-7825(86)90079-4
-
[10]
Journal of Applied Mechanics 53(4), 849–854 (1986) https://doi
Simo, J.C., Vu-Quoc, L.: On the Dynamics of Flexible Beams Under Large Overall Motions— The Plane Case: Part I. Journal of Applied Mechanics 53(4), 849–854 (1986) https://doi. org/10.1115/1.3171870
-
[11]
Journal of Applied Mechanics 53(4), 855 (1986) https://doi.org/ 10.1115/1.3171871
Simo, J.C., Vu-Quoc, L.: On the Dynamics of Flexible Beams Under Large Overall Motions— The Plane Case: Part II. Journal of Applied Mechanics 53(4), 855 (1986) https://doi.org/ 10.1115/1.3171871
-
[12]
Acta Mechanica 224(7), 1493–1525 (2013) https://doi.org/10.1007/s00707-013-0818-1
Humer, A.: Exact solutions for the buckling and postbuckling of shear-deformable beams. Acta Mechanica 224(7), 1493–1525 (2013) https://doi.org/10.1007/s00707-013-0818-1
-
[13]
Acta Mechanica (2019) https://doi.org/ 10.1007/s00707-019-02472-1
Humer, A., Pechstein, A.S.: Exact solutions for the buckling and postbuckling of a shear- deformable cantilever subjected to a follower force. Acta Mechanica (2019) https://doi.org/ 10.1007/s00707-019-02472-1
-
[14]
Bathe, K.-J., Bolourchi, S.: Large displacement analysis of three‐dimensional beam structures. International Journal for Numerical Methods in Engineering 14(7), 961–986 (1979) https: //doi.org/10.1002/nme.1620140703
-
[15]
Cardona, A., Geradin, M.: A beam finite element non‐linear theory with finite rotations. International Journal for Numerical Methods in Engineering 26(11), 2403–2438 (1988) https: //doi.org/10.1002/nme.1620261105
-
[16]
Ibrahimbegović, A., Frey, F., Kožar, I.: Computational aspects of vector‐like parametriza- tion of three‐dimensional finite rotations. International Journal for Numerical Methods in Engineering 38(21), 3653–3673 (1995) https://doi.org/10.1002/nme.1620382107
-
[17]
Computer Methods in Applied Mechanics and Engineering 149(1-4), 49–71 (1997) https://doi.org/10.1016/ S0045-7825(97)00059-5
Ibrahimbegovic, A.: On the choice of finite rotation parameters. Computer Methods in Applied Mechanics and Engineering 149(1-4), 49–71 (1997) https://doi.org/10.1016/ S0045-7825(97)00059-5
1997
-
[18]
Meier, C., Popp, A., Wall, W.A.: Geometrically Exact Finite Element Formulations for Slen- der Beams: Kirchhoff–Love Theory Versus Simo–Reissner Theory. Archives of Computational Methods in Engineering 26(1), 163–243 (2019) https://doi.org/10.1007/s11831-017-9232-5
-
[19]
Proceedings of the Royal Society of London
Crisfield, M.A., Jelenić, G.: Objectivity of strain measures in the geometrically exact three- dimensional beam theory and its finite-element implementation. Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences 455(1983), 1125–1147 (1999) https://doi.org/10.1098/rspa.1999.0352
-
[20]
Jelenić, G., Crisfield, M.A.: Geometrically exact 3D beam theory: implementation of a strain- invariant finite element for statics and dynamics. Computer Methods in Applied Mechanics and Engineering 171(1-2), 141–171 (1999) https://doi.org/10.1016/S0045-7825(98)00249-7
-
[21]
Wehage, R.A.: Quaternions and Euler Parameters — A Brief Exposition. In: Haug, E.J. (ed.) Computer Aided Analysis and Optimization of Mechanical System Dynamics, pp. 147–180. Springer, Berlin, Heidelberg (1984). https://doi.org/10.1007/978-3-642-52465-3_5
-
[22]
Nikravesh, P.E., Wehage, R.A., Kwon, O.K.: Euler Parameters in Computational Kinematics and Dynamics. Part 1. Journal of Mechanisms, Transmissions, and Automation in Design 107(3), 358–365 (1985) https://doi.org/10.1115/1.3260722 26
-
[23]
Zupan, E., Saje, M., Zupan, D.: The quaternion-based three-dimensional beam theory. Computer Methods in Applied Mechanics and Engineering 198(49-52), 3944–3956 (2009) https://doi.org/10.1016/j.cma.2009.09.002
-
[24]
Acta Mechanica 224(8), 1709–1729 (2013) https://doi.org/10.1007/s00707-013-0824-3
Zupan, E., Saje, M., Zupan, D.: On a virtual work consistent three-dimensional Reissner– Simo beam formulation using the quaternion algebra. Acta Mechanica 224(8), 1709–1729 (2013) https://doi.org/10.1007/s00707-013-0824-3
-
[25]
A projection-based quaternion discretization of the geometrically exact beam model
Wasmer, P., Betsch, P.: A projection‐based quaternion discretization of the geometrically exact beam model. International Journal for Numerical Methods in Engineering 125(20), 7538 (2024) https://doi.org/10.1002/nme.7538
-
[26]
Sonneville, V., Cardona, A., Brüls, O.: Geometrically exact beam finite element formulated on the special Euclidean group. Computer Methods in Applied Mechanics and Engineering 268, 451–474 (2014) https://doi.org/10.1016/j.cma.2013.10.008
-
[27]
Sonneville, V., Brüls, O., Bauchau, O.A.: Interpolation schemes for geometrically exact beams: A motion approach. International Journal for Numerical Methods in Engineering 112(9), 1129–1153 (2017) https://doi.org/10.1002/nme.5548
-
[28]
International Journal for Numerical Methods in Engineering 124(13), 2965–2994 (2023) https://doi.org/10.1002/ nme.7236
Harsch, J., Sailer, S., Eugster, S.R.: A total Lagrangian, objective and intrinsically locking- free Petrov–Galerkin SE (3) Cosserat rod finite element formulation. International Journal for Numerical Methods in Engineering 124(13), 2965–2994 (2023) https://doi.org/10.1002/ nme.7236
2023
-
[29]
Noor, A.K., Peters, J.M.: Mixed models and reduced/selective integration displacement mod- els for nonlinear analysis of curved beams. International Journal for Numerical Methods in Engineering 17(4), 615–631 (1981) https://doi.org/10.1002/nme.1620170409
-
[30]
Nukala, P.K.V.V., White, D.W.: A mixed finite element for three-dimensional nonlinear anal- ysis of steel frames. Computer Methods in Applied Mechanics and Engineering 193(23-26), 2507–2545 (2004) https://doi.org/10.1016/j.cma.2004.01.029
-
[31]
Herrmann, M., Castello, D., Breuling, J., Garcia, I.C., Greco, L., Eugster, S.R.: A mixed Petrov-Galerkin Cosserat rod finite element formulation. arXiv. arXiv:2507.01552 [math] (2026). https://doi.org/10.48550/arXiv.2507.01552
-
[32]
International Journal of Solids and Structures 26(8), 887–900 (1990) https://doi.org/10
Saje, M.: A variational principle for finite planar deformation of straight slender elastic beams. International Journal of Solids and Structures 26(8), 887–900 (1990) https://doi.org/10. 1016/0020-7683(90)90075-7
1990
-
[33]
Computers & Structures 39(3-4), 327–337 (1991) https://doi.org/10.1016/0045-7949(91) 90030-P
Saje, M.: Finite element formulation of finite planar deformation of curved elastic beams. Computers & Structures 39(3-4), 327–337 (1991) https://doi.org/10.1016/0045-7949(91) 90030-P
-
[34]
Computers & Structures 225, 106109 (2019) https://doi.org/10.1016/j.compstruc.2019
Neunteufel, M., Schöberl, J.: The Hellan–Herrmann–Johnson method for nonlinear shells. Computers & Structures 225, 106109 (2019) https://doi.org/10.1016/j.compstruc.2019. 106109
-
[35]
Neunteufel, M., Schöberl, J.: A voiding membrane locking with Regge interpolation. Computer Methods in Applied Mechanics and Engineering 373, 113524 (2021) https://doi.org/10.1016/ j.cma.2020.113524
-
[36]
Acta Mechanica 27 (2025) https://doi.org/10.1007/s00707-025-04255-3
Platzer, S., Pechstein, A., Humer, A., Krommer, M.: Viscoelastic Kirchhoff–Love shells at finite strains: constitutive modeling and mixed low-regularity finite elements. Acta Mechanica 27 (2025) https://doi.org/10.1007/s00707-025-04255-3
-
[37]
ISSS Journal of Micro and Smart Systems (2025) https://doi.org/10.1007/s41683-025-00138-w
Platzer, S., Pechstein, A., Humer, A., Krommer, M.: A low-regularity finite element approach for dielectric viscoelastic Kirchhoff–Love shells. ISSS Journal of Micro and Smart Systems (2025) https://doi.org/10.1007/s41683-025-00138-w
-
[38]
Computational Mechanics 66(6), 1377–1398 (2020) https://doi.org/10.1007/s00466-020-01907-0
Steinbrecher, I., Mayr, M., Grill, M.J., Kremheller, J., Meier, C., Popp, A.: A mortar-type finite element approach for embedding 1D beams into 3D solid volumes. Computational Mechanics 66(6), 1377–1398 (2020) https://doi.org/10.1007/s00466-020-01907-0
-
[39]
Cambridge university press, Cambridge, GB (1998)
Shabana, A.A.: Dynamics of Multibody Systems, 2nd ed edn. Cambridge university press, Cambridge, GB (1998)
1998
-
[40]
Wiley, Chichester Weinheim (2001)
Géradin, M., Cardona, A.: Flexible Multibody Dynamics: a Finite Element Approach. Wiley, Chichester Weinheim (2001)
2001
-
[41]
2: Advanced Topics, Repr
Crisfield, M.A.: Non-linear Finite Element Analysis of Solids and Structures. 2: Advanced Topics, Repr. with corr edn. Wiley, Chichester (2003). Num Pages: 494
2003
-
[42]
Computational Mechanics 57(5), 817–841 (2016) https://doi.org/10
Sander, O., Neff, P., Bîrsan, M.: Numerical treatment of a geometrically nonlinear planar Cosserat shell model. Computational Mechanics 57(5), 817–841 (2016) https://doi.org/10. 1007/s00466-016-1263-5
2016
-
[43]
Computer Graphics Forum 25(3), 547–556 (2006) https://doi.org/10.1111/ j.1467-8659.2006.00974.x
Grinspun, E., Gingold, Y., Reisman, J., Zorin, D.: Computing discrete shape operators on general meshes. Computer Graphics Forum 25(3), 547–556 (2006) https://doi.org/10.1111/ j.1467-8659.2006.00974.x
-
[44]
Koschnick, F., Bischoff, M., Camprubí, N., Bletzinger, K.-U.: The discrete strain gap method and membrane locking. Computer Methods in Applied Mechanics and Engineering 194(21- 24), 2444–2463 (2005) https://doi.org/10.1016/j.cma.2004.07.040
-
[45]
Journal of Structural Mechanics 11(2), 153–176 (1983) https://doi.org/ 10.1080/03601218308907439
Stolarskl, H., Belytschko, T., Carpenter, N.: Bending and Shear Mode Decomposition in C ◦ Structural Elements. Journal of Structural Mechanics 11(2), 153–176 (1983) https://doi.org/ 10.1080/03601218308907439
-
[46]
Meier, C., Popp, A., Wall, W.A.: A locking-free finite element formulation and reduced mod- els for geometrically exact Kirchhoff rods. Computer Methods in Applied Mechanics and Engineering 290, 314–341 (2015) https://doi.org/10.1016/j.cma.2015.02.029
-
[47]
Finite element formulations for constrained spatial nonlinear beam theories
Harsch, J., Capobianco, G., Eugster, S.R.: Finite element formulations for constrained spatial nonlinear beam theories. Mathematics and Mechanics of Solids 26(12), 1838–1863 (2021) https://doi.org/10.1177/10812865211000790
-
[48]
Multibody System Dynamics 20(1), 51–68 (2008) https://doi.org/10.1007/s11044-008-9105-7
Romero, I.: A comparison of finite elements for nonlinear beams: The absolute nodal coordi- nate and geometrically exact formulations. Multibody System Dynamics 20(1), 51–68 (2008) https://doi.org/10.1007/s11044-008-9105-7
-
[49]
Eugster, S.R., Hesch, C., Betsch, P., Glocker, Ch.: Director-based beam finite elements relying on the geometrically exact beam theory formulated in skew coordinates. International Journal for Numerical Methods in Engineering 97(2), 111–129 (2014) https://doi.org/10.1002/nme. 4586 28
work page doi:10.1002/nme 2014
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.