| 1. |
- Björkenstam, Staffan C, 1981, et al.
(författare)
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Inverse Dynamics for Discrete Geometric Mechanics of Multibody Systems with Application to Direct Optimal Control
- 2018
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME International. - 1555-1423 .- 1555-1415. ; 13:10
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present efficient algorithms for computation of the residual of the constrained discrete Euler-Lagrange (DEL) equations of motion for tree structured, rigid multibody systems. In particular, we present new recursive formulas for computing partial derivatives of the kinetic energy. This enables us to solve the inverse dynamics problem of the discrete system with linear computational complexity. The resulting algorithms are easy to implement and can naturally be applied to a very broad class of multibody systems by imposing constraints on the coordinates by means of Lagrange multipliers. A comparison is made with an existing software package, which shows a drastic improvement in computational efficiency. Our interest in inverse dynamics is primarily to apply direct transcription optimal control methods to multibody systems. As an example application, we present a digital human motion planning problem, which we solve using the proposed method. Furthermore, we present detailed descriptions of several common joints, in particular singularity-free models of the spherical joint and the rigid body joint, using the Lie groups of unit quaternions and unit dual quaternions, respectively.
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| 2. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Experimental Validation of a Nonlinear Model Calibration Method Based on Multiharmonic Frequency Responses
- 2017
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME Press. - 1555-1415 .- 1555-1423. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- Correlation and calibration using test data are natural ingredients in the process of validating computational models. Model calibration for the important subclass of nonlinear systems which consists of structures dominated by linear behavior with the presence of local nonlinear effects is studied in this work. The experimental validation of a nonlinear model calibration method is conducted using a replica of the École Centrale de Lyon (ECL) nonlinear benchmark test setup. The calibration method is based on the selection of uncertain model parameters and the data that form the calibration metric together with an efficient optimization routine. The parameterization is chosen so that the expected covariances of the parameter estimates are made small. To obtain informative data, the excitation force is designed to be multisinusoidal and the resulting steady-state multiharmonic frequency response data are measured. To shorten the optimization time, plausible starting seed candidates are selected using the Latin hypercube sampling method. The candidate parameter set giving the smallest deviation to the test data is used as a starting point for an iterative search for a calibration solution. The model calibration is conducted by minimizing the deviations between the measured steady-state multiharmonic frequency response data and the analytical counterparts that are calculated using the multiharmonic balance method. The resulting calibrated model's output corresponds well with the measured responses.
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| 3. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Informative Data for Model Calibration of Locally Nonlinear Structures Based on Multi-Harmonic Frequency Responses
- 2016
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME Press. - 1555-1415 .- 1555-1423. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- In industry, linear FE-models commonly serve as baseline models to represent the global structural dynamics behavior. However, available test data may show evidence of significant nonlinear dynamic characteristics. In such a case, the baseline linear model may be insufficient to represent the dynamics of the structure. The causes of the nonlinear characteristics may be local in nature and the remaining parts of the structure may be satisfactorily represented by linear descriptions. Although the baseline model can then serve as a good foundation, the physical phenomena needed to substantially increase the model's capability of representing the real structure are most likely not modelled in it. Therefore, a set of candidate nonlinear property parameters to control the nonlinear effects have to be added and subjected to calibration to form a credible model. The selection of the calibration parameters and the choice of data for a calibration metric form a coupled problem. An over-parameterized model for calibration may result in parameter value estimates that do not survive a validation test. The parameterization is coupled to the test data and should be chosen so that the expected co-variances of the chosen parameter's estimates are made small. Accurate test data, suitable for calibration, is often obtained from sinusoidal testing. Because a pure mono-sinusoidal excitation is difficult to achieve during a test of a nonlinear structure, the excitation is here designed to contain sub and super harmonics besides the fundamental harmonic. The steady-state responses at the side frequencies are shown to contain valuable information for the calibration process that can improve the accuracy of the parameter estimates. The nonlinear steady-state solutions can be found efficiently using the multi-harmonic balance method. In this paper, synthetic test data from a model of a nonlinear benchmark structure are used for illustration. The model calibration and an associated K-fold cross-validation are based on the Levenberg-Marquardt and the undamped Gauss-Newton algorithm, respectively. Starting seed candidates for calibration are found by the Latin hypercube sampling method. The realization that gives the smallest deviation to test data is selected as a starting point for the iterative search for a calibration solution. The calibration result shows good agreement with the true parameter setting, and the K-fold cross validation result shows that the variance of the estimated parameters shrinks when adding sub and super harmonics to the nonlinear frequency response functions.
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| 4. |
- Chhabra, Robin, et al.
(författare)
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Reduction of Hamiltonian Mechanical Systems With Affine Constraints : A Geometric Unification
- 2017
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : The American Society of Mechanical Engineers (ASME). - 1555-1415 .- 1555-1423. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a geometrical approach to the dynamical reduction of a class of constrained mechanical systems. The mechanical systems considered are with affine nonholonomic constraints plus a symmetry group. The dynamical equations are formulated in a Hamiltonian formalism using the Hamilton-d'Alembert equation, and constraint forces determine an affine distribution on the configuration manifold. The proposed reduction approach consists of three main steps: (1) restricting to the constrained submanifold of the phase space, (2) quotienting the constrained submanifold, and (3) identifying the quotient manifold with a cotangent bundle. Finally, as a case study, the dynamical reduction of a two-wheeled rover on a rotating disk is detailed. The symmetry group for this example is the relative configuration manifold of the rover with respect to the inertial space. The proposed approach in this paper unifies the existing reduction procedures for symmetric Hamiltonian systems with conserved momentum, and for Chaplygin systems, which are normally treated separately in the literature. Another characteristic of this approach is that although it tracks the structure of the equations in each reduction step, it does not insist on preserving the properties of the system. For example, the resulting dynamical equations may no longer correspond to a Hamiltonian system. As a result, the invariance condition of the Hamiltonian under a group action that lies at the heart of almost every reduction procedure is relaxed
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| 5. |
- Nordenfelt, Anders
(författare)
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Selective Self-Excitation of Higher Vibrational Modes of Graphene Nano-Ribbons and Carbon Nanotubes Through Magnetomotive Instability
- 2013
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME International. - 1555-1423 .- 1555-1415. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate theoretically the feasibility of selective self-excitation of higher-mode flexural vibrations of graphene nano-ribbons and carbon nanotubes by the means of magnetomotive insta- bility. Apart from the mechanical resonator, the device consists only of a constant voltage source, an inductor, a capacitor, a gate electrode and a constant magnetic field. Numerical simluations were performed on both graphene and carbon nanotubes displaying an overall similar behaviour, but with some differences arising mainly due to the non-linear mechanical bending forces. The advantages and disadvanatges of both materials are discussed.
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| 6. |
- Orvnäs, Anneli, et al.
(författare)
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An Active Secondary Suspension Concept to Improve Lateral and Vertical Ride Comfort
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Ingår i: Journal of Computational and Nonlinear Dynamics. - 1555-1415 .- 1555-1423.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents an active secondary suspension conceptfor lateral and vertical ride comfort improvement in arail vehicle. Dynamic control of the lateral, yaw and verticalcarbody modes is achieved by means of actuators replacingthe conventional lateral and vertical dampers in the secondarysuspension. Active damping significantly improveslateral and vertical ride comfort compared to a passive system.Besides dynamic control, the actuators can generatequasi-static lateral and roll control of the carbody. This allowsfor higher speeds in curves, without negatively affectingride comfort. Furthermore, the active suspension concept reducesthe influence on ride comfort caused by the air springstiffness. This means that the total air spring volume can bereduced.
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| 7. |
- Wramner, Lina, 1979
(författare)
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Numerical Algorithms for Simulation of One-Dimensional Mechanical Systems With Clearance-Type Nonlinearities
- 2019
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME International. - 1555-1423 .- 1555-1415. ; 14:6
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Tidskriftsartikel (refereegranskat)abstract
- In many mechanical systems there are nonlinearities of clearance type. This type of nonlinearity often causes problems with convergence and accuracy in simulations, due to the discontinuities at impact. For systems with gap-activated springs connected to ground, it has been proposed in previous work to reformulate the problem as a linear complementary problem (LCP), which can be solved in a very efficient way. In this paper, a generalization of the LCP approach is proposed for systems with gap-activated springs connecting different bodies. The generalizations enable the LCP approach to be used for an arbitrary number of gap-activated springs connecting either different bodies or connecting bodies to ground. The springs can be activated in either compression or expansion or both and a gear ratio can be included between the bodies. The efficiency of the algorithm is demonstrated with an application example of a dual mass flywheel (DMF).
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