scholarly journals Implementation of A Geometric Constraint Regularization For Multibody System Models

2014 ◽  
Vol 61 (2) ◽  
pp. 365-383 ◽  
Author(s):  
Andreas Müller
Keyword(s):  
Multibody System ◽  
Time Integration ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Computational Performance ◽  
Kinematic Loops ◽  
Computationally Expensive ◽  
Technical Systems ◽  
Loop Constraints

Abstract Redundant constraints in MBS models severely deteriorate the computational performance and accuracy of any numerical MBS dynamics simulation method. Classically this problem has been addressed by means of numerical decompositions of the constraint Jacobian within numerical integration steps. Such decompositions are computationally expensive. In this paper an elimination method is discussed that only requires a single numerical decomposition within the model preprocessing step rather than during the time integration. It is based on the determination of motion spaces making use of Lie group concepts. The method is able to reduce the set of loop constraints for a large class of technical systems. In any case it always retains a sufficient number of constraints. It is derived for single kinematic loops.

Semialgebraic Regularization of Kinematic Loop Constraints in Multibody System Models

2011 ◽  
Vol 6 (4) ◽  
Author(s):  
Andreas Müller
Keyword(s):  
Multibody System ◽  
Dynamics Simulation ◽  
Time Step ◽  
Kinematic Loops ◽  
Low Dimensional ◽  
Kinematic Loop ◽  
Value Decomposition ◽  
Loop Constraints ◽  
Simulation Time

Redundant constraints in multibody system (MBS) models, reflected by a singular constraint Jacobian, impair the efficient dynamics simulation. In particular, kinematic loop constraints are often found to be permanently redundant. This problem is commonly attacked numerically by decomposing the constraint Jacobian either at every simulation time step or beforehand in an admissible assembly (assuming that the redundancy is permanent). This paper presents a method for the elimination of permanently redundant loop closure constraints, which, instead of numerically decomposing the constraints, relies on the geometric characterization of kinematic loops comprising lower kinematic pairs. In particular, the invariant vector space of velocities of a kinematic loop is taken into account, which can be determined as the sum of Lie (screw) algebras of two subchains of a kinematic loop. The actual reduction is achieved by restricting the constraints to this space. The presented method does not interfere with the actual generation of constraints but can be considered as a preprocessing step of MBS models. It is numerically robust and only uses a geometrically exact model. The method is able to completely eliminate redundant loop constraints for “nonparadoxical” single-loop mechanisms and applies conservatively to multiloop MBS. The presented method only requires information (vectors, matrices) that is readily available in any MBS simulation package. The only numerical operations involved are cross products and a singular value decomposition of a low dimensional matrix.

scholarly journals The Structure and Crystallizing Process of NiAu Alloy: A Molecular Dynamics Simulation Method

2021 ◽  
Vol 5 (1) ◽  
pp. 18
Author(s):  
Dung Nguyen Trong ◽  
Van Cao Long ◽  
Ştefan Ţălu
Keyword(s):  
Heating Rate ◽  
Atomic Number ◽  
Crystallization Process ◽  
Amorphous State ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Glass Temperature ◽  
Structural Units ◽  
The Common ◽  
Moving Process

This paper studies the influence of factors such as heating rate, atomic number, temperature, and annealing time on the structure and the crystallization process of NiAu alloy. Increasing the heating rate leads to the moving process from the crystalline state to the amorphous state; increasing the temperature (T) also leads to a changing process into the liquid state; when the atomic number (N), and t increase, it leads to an increased crystalline process. As a result, the dependence between size (l) and atomic number (N), the total energy of the system (Etot) with N as l~N−1/3, and −Etot always creates a linear function of N, glass temperature (Tg) of the NiAu alloy, which is Tg = 600 K. During the study, the number of the structural units was determined by the Common Neighborhood Analysis (CNA) method, radial distribution function (RDF), size (l), and Etot. The result shows that the influencing factors to the structure of NiAu alloy are considerable.

Femtosecond photoelectron spectroscopy of the I2− anion: A semiclassical molecular dynamics simulation method

1999 ◽  
Vol 110 (8) ◽  
pp. 3736-3747 ◽  
Author(s):  
Victor S. Batista ◽  
Martin T. Zanni ◽  
B. Jefferys Greenblatt ◽  
Daniel M. Neumark ◽  
William H. Miller
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Photoelectron Spectroscopy ◽  
Simulation Method ◽  
Dynamics Simulation

Self-diffusion of lignite/water under different temperatures and pressure: A molecular dynamics study

2016 ◽  
Vol 30 (01) ◽  
pp. 1550253 ◽  
Author(s):  
Xinjian Liu ◽  
Yu Jin ◽  
Congliang Huang ◽  
Jingfeng He ◽  
Zhonghao Rao ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Water System ◽  
Simulation Method ◽  
The Self ◽  
Dynamics Simulation ◽  
Low Rank ◽  
Self Diffusion ◽  
Change Mechanism ◽  
Different Temperatures ◽  
Temperature And Pressure

Temperature and pressure have direct and remarkable implications for drying and dewatering effect of low rank coals such as lignite. To understand the microenergy change mechanism of lignite, the molecular dynamics simulation method was performed to study the self-diffusion of lignite/water under different temperatures and pressure. The results showed that high temperature and high pressure can promote the diffusion of lignite/water system, which facilitates the drying and dewatering of lignite. The volume and density of lignite/water system will increase and decrease with temperature increasing, respectively. Though the pressure within simulation range can make lignite density increase, the increasing pressure showed a weak impact on variation of density.

THE "FOLDING" BEHAVIORS OF HOMOPOLYMERS WITH ONE END FIXED

2004 ◽  
Vol 18 (15) ◽  
pp. 2123-2139 ◽  
Author(s):  
BIN XUE ◽  
JUN WANG ◽  
WEI WANG
Keyword(s):  
Molecular Dynamics ◽  
Chain Length ◽  
Conformational Changes ◽  
Canonical Ensemble ◽  
Interaction Strength ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Radius Of Gyration ◽  
Native Conformation ◽  
Collapse Temperature

We study the "folding" behaviors of homopolymers with one end fixed. By using canonical ensemble molecular dynamics simulation method, we observe the conformational changes during folding processes. Long chains collapse to the helical nuclei, then regroup to helix from the free-end to form the compact conformations through the middle stages of helix-like coil and helix-like cone, while short chains do not apparently have the above mentioned middle stages. Through simulated annealing, the native conformation of homopolymer chain in our model is found to be helix. We show the relations between specific heat C v (T) and radius of gyration R g (T) as functions of temperature, chain length and the interaction strength, respectively. We find that these two quantities match well and can be combined to interpret the "folding" process of the homopolymer. It is found that the collapse temperature Tθ and the native-like folding temperature T f do not change with the chain length in our model, however the interaction strength affects the values of Tθ and T f .

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