Manuel de Leon, Juan Carlos Marrero, David Martin de Diego
We develop a semi-discrete version of discrete variational mechanics with applications to numerical integration of classical field theories. The geometric preservation properties are studied.
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Finite-dimensional non-canonical Hamiltonian systems arise naturally from Hamilton's principle in phase space. We present a method for deriving variational integrators that can be applied to perturbed non-canonical Hamiltonian systems on manifolds based on discretizing this phase-space variational principle. Relative to the perturbation parameter $ε$, this type of integrator can take $O(1)$ time steps with arbitrary accuracy in $ε$ by leveraging the unperturbed dynamics. Moreover, these integrators are coordinate independent in the sense that their time-advance rules transform correctly when p…
An interesting family of geometric integrators for Lagrangian systems can be defined using discretizations of the Hamilton's principle of critical action. This family of geometric integrators is called variational integrators. In this paper, we derive new variational integrators for higher-order lagrangian mechanical system subjected to higher-order constraints. From the discretization of the variational principles, we show that our methods are automatically symplectic and, in consequence, with a very good energy behavior. Additionally, the symmetries of the discrete Lagrangian imply that mome…
This paper formulates variational integrators for finite element discretizations of deformable bodies with heat conduction in the form of finite speed thermal waves. The cornerstone of the construction consists in taking advantage of the fact that the Green-Naghdi theory of type II for thermo-elastic solids has a Hamiltonian structure. Thus, standard techniques to construct variational integrators can be applied to finite element discretizations of the problem. The resulting discrete-in-time trajectories are then consistent with the laws of thermodynamics for these systems: for an isolated sys…
For the linearized setting of the dynamics of complex bodies we construct variational integrators and prove their convergence by making use of BV estimates on the rate fields. We allow for peculiar substructural inertia and internal dissipation, all accounted for by a d'Alembert-Lagrange-type principle.
We present geometric numerical integrators for contact flows that stem from a discretization of Herglotz' variational principle. First we show that the resulting discrete map is a contact transformation and that any contact map can be derived from a variational principle. Then we discuss the backward error analysis of our variational integrators, including the construction of a modified Lagrangian. Throughout the paper we use the damped harmonic oscillator as a benchmark example to compare our integrators to their symplectic analogues.
Variational Collision Integrators for Nonholonomic Lagrangian Systems
本文提出非完整拉格朗日系统弹性碰撞的离散变分理论，基于拉格朗日-达朗贝尔-庞特里亚金原理推导离散方程，并构建了弹跳椭圆和圆柱内球摆等例子的碰撞积分器。
Variational integrators and time-dependent lagrangian systems
针对含时拉格朗日系统，提出一种构造变分积分器的方法，所得算法具有辛性、保持对称李群对应的动量映射并描述能量变化。
On converting any one-step method to a variational integrator of the same order
本文在约束力学形式下（如分子动力学中的SHAKE和RATTLE方法），提出一种算法，可将任意单步积分方法转换为同阶变分积分器，实现自动转换，为生成任意阶的新型变分积分器提供灵活强大的方法。
Optimal control problems for underactuated mechanical systems can be seen as a higher-order variational problem subject to higher-order constraints (that is, when the Lagrangian function and the constraints depend on higher-order derivatives such as the acceleration, jerk or jounces). In this paper we discuss the variational formalism for the class of underactuated mechanical control systems when the configuration space is a trivial principal bundle and the construction of variational integrators for such mechanical control systems. An interesting family of geometric integrators can be defined…
Geometric Formulation of Combined Conservative Dissipative Mechanics via Contact Hamiltonian Dynamics Symmetries, Reduction, and Variational Integrators
本文提出了一种基于接触哈密顿动力学的几何框架，用于统一描述混合保守耗散力学系统，并设计了结构保持的变分积分器以实现数值稳定性。
Variational Integrators for Nonvariational Partial Differential Equations
本文提出通过形式拉格朗日量构建变分积分器，扩展其应用范围至所有动力系统，以流体动力学中的对流扩散方程为例进行验证。
In this work, we present a new approach to the construction of variational integrators. In the general case, the estimation of the action integral in a time interval $[q_k,q_{k+1}]$ is used to construct a symplectic map $(q_k,q_{k+1})\to (q_{k+1},q_{k+2})$. The basic idea here, is that only the partial derivatives of the estimation of the action integral of the Lagrangian are needed in the general theory. The analytic calculation of these derivatives, give raise to a new integral which depends not on the Lagrangian but on the Euler--Lagrange vector, which in the continuous and exact case vanis…
Error analysis of variational integrators of unconstrained Lagrangian systems
通过放大离散变分原理（在零时间步长处具有奇点），并利用新的过去-未来对称性修复由时间步长除法导致的阶数损失，得到了变分积分器的完整误差分析。
By introducing an integration factor to the differential one-form of contact dynamics, equations of motion are derived variationally, and contact Poisson bracket and contact Lagrangian are formulated. Discrete symplectic integrator, named hybrid leap-frog method, is found to be a numerical solver of equations of motion for contact dissipative systems.
Higher Order Variational Integrators: a polynomial approach
本文提出一种新的变分积分器，即辛Galerkin方案，用于高阶准确地模拟机械系统，同时保持其结构特性，并应用于最优控制问题。
High-order geometric integrators for the local cubic variational Gaussian wavepacket dynamics
针对局部三次变分高斯波包动力学计算成本高的问题，提出高效的高阶几何积分器，具备辛、时间可逆和范数守恒等性质，并在多维不可分耦合Morse势上验证了其效率。
On the exact discrete Lagrangian function for variational integrators: theory and applications
本文提出精确离散拉格朗日函数的严格构造，适用于Lie群体和Lie余结构，用于分析变分积分器的误差。
Variational integrators are derived for structure-preserving simulation of stochastic forced Hamiltonian systems. The derivation is based on a stochastic discrete Hamiltonian which approximates a type-II stochastic generating function for the stochastic flow of the Hamiltonian system. The generating function is obtained by introducing an appropriate stochastic action functional and considering a stochastic generalization of the deterministic Lagrange-d'Alembert principle. Our approach presents a general methodology to derive new structure-preserving numerical schemes. The resulting integrators…
Projected Variational Integrators for Degenerate Lagrangian Systems
本文提出并比较了用于退化拉格朗日系统的投射方法，针对拉格朗日函数线性于速度的情况，改进了传统方法的长期稳定性，验证了投射积分器在能量守恒和长期精度方面的优越性。
Stochastic Discrete Hamiltonian Variational Integrators
本文提出了一种随机哈密顿系统的结构保持数值方法，通过构造随机离散哈密顿量来近似II型随机生成函数，统一了多种已有积分器并提出新的结构保持数值方案，所得积分器具有辛性、保持李群对称的守恒量，并包含随机辛龙格-库塔方法作为特例。
Variational Integrators in Plasma Physics
本文开发了适用于等离子体物理中粒子动力学、维拉索-泊松系统和理想磁流体力学的变分积分器，通过扩展理论至非变分微分方程，实现了更广泛系统的应用，并分析了守恒性质。
Multisymplectic geometry, variational integrators, and nonlinear PDEs
本文基于多辛几何与变分原理，提出统一框架以构造保持辛性与诺特对称性的连续及离散力学/场论模型，并给出非线性正弦-戈登方程的数值验证。
Variational integrators using forced discrete Hamiltonian systems
研究受外力的余切丛上离散哈密顿系统，由离散变分原理确定轨迹。分析辛结构演化等，构建精确离散类似物及近似方法，得到变分积分器，其近似解可达至少r阶精度。
In this paper, high-order numerical integrators on homogeneous spaces will be presented as an application of nonholonomic partitioned Runge-Kutta Munthe-Kaas (RKMK) methods on Lie groups. A homogeneous space $M$ is a manifold where a group $G$ acts transitively. Such a space can be understood as a quotient $M \cong G/H$, where $H$ a closed Lie subgroup, is the isotropy group of each point of $M$. The Lie algebra of $G$ may be decomposed into $\mathfrak{g} = \mathfrak{m} \oplus \mathfrak{h}$, where $\mathfrak{h}$ is the subalgebra that generates $H$ and $\mathfrak{m}$ is a subspace. Thus, varia…
Geometric integrators for adiabatically closed simple thermodynamic systems
本文提出了一种用于绝热封闭简单热力学系统的离散变分原理，以构建数值积分器，通过实例验证了方法的有效性。
Discretizing variational principles, as opposed to discretizing differential equations, leads to discrete-time analogues of mechanics, and, systematically, to geometric numerical integrators. The phase space of such variational discretizations is often the set of configuration pairs, analogously corresponding to initial and terminal points of a tangent vectors. We develop alternative discrete analogues of tangent bundles, by extending tangent vectors to finite curve segments, one curve segment for each tangent vector. Towards flexible, high order numerical integrators, we use these discrete ta…
In this paper we study, from a variational and geometrical point of view, second-order variational problems on Lie groupoids and the construction of variational integrators for optimal control problems. First, we develop variational techniques for second-order variational problems on Lie groupoids and their applications to the construction of variational integrators for optimal control problems of mechanical systems. Next, we show how Lagrangian submanifolds of a symplectic groupoid gives intrinsically the discrete dynamics for second-order systems, both unconstrained and constrained, and we s…
In this paper we provide a variational derivation of the Euler-Poincaré equations for systems subjected to external forces using an adaptation of the techniques introduced by Galley and others. Moreover, we study in detail the underlying geometry which is related to the notion of Poisson groupoid. Finally, we apply the previous construction to the formal derivation of the variational error for numerical integrators of forced Euler-Poincaré equations and the application of this theory to the derivation of geometric integrators for forced systems.
Compatible discretizations, such as finite element exterior calculus, provide a discretization framework that respect the cohomological structure of the de Rham complex, which can be used to systematically construct stable mixed finite element methods. Multisymplectic variational integrators are a class of geometric numerical integrators for Lagrangian and Hamiltonian field theories, and they yield methods that preserve the multisymplectic structure and momentum-conservation properties of the continuous system. In this paper, we investigate the synthesis of these two approaches, by constructin…
The purpose of this paper is to perform an error analysis of the variational integrators of mechanical systems subject to external forcing. Essentially, we prove that when a discretization of contact order $r$ of the Lagrangian and force are used, the integrator has the same contact order. Our analysis is performed first for discrete forced mechanical systems defined over $TQ$, where we study the existence of flows, the construction and properties of discrete exact systems and the contact order of the flows (variational integrators) in terms of the contact order of the original systems. Then w…
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