Wyniki wyszukiwania - Biblioteka Nauki

1

Advanced modelling of flexible multibody systems using virtual bodies

100%

Goncalves J. , Ambrosio J.

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tom Vol. 9, No. 3

374-390

EN

When new formulations for the description of flexible multibody systems are proposed, often they imply the use of new sets of generalized coordinates, even if the finite element method is used to describe the system flexibility. The adoption of such formulations implies that an additional effort must be made to describe the kinematic constraints that involve flexible bodies. The commercial multibody codes generally have good kinematic joint libraries for rigid bodies, but they are limited in the type of joints available in what flexible bodies are concerned. This work proposes and demonstrates that such limitations can be overcome by using virtual rigid bodies. The idea is to develop a single kinematic joint that restricts all relative degrees of freedom between one or more nodes of the flexible body and a rigid body. The designation of virtual body derives from assuming that it is a massless rigid body. In this form any of the kinematic joints between rigid bodies available in the multibody code libraries, can be used. In the process it is shown that the interaction of the user with the multibody code is much simpler. The numerical problems resulting from ill-conditioned mass matrix, due to the null inertias of the virtual bodies, are avoided by using a sparse matrix solver for the solution of the equations of motion. The proposed formulation is applied to a complex flexible multibody system, represented by the model of a road vehicle with flexible chassis, the results are presented and the discussion on the relative virtues and drawbacks of the current methodologies is made with emphasis on the models and algorithms used.

2

Nordsieck form of multirate integration method for flexible multibody dynamic analysis

88%

Kim S. S.

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tom Vol. 9, No. 3

391-403

EN

A Nordsieck form of multirate integration scheme has been proposed for flexible multibody dynamic systems of which motions are represented by large gross motion coupled with small vibration. Based on the conventional flexible multibody dynamics formulation, vibrational modal coordinates with floating reference frame and relative joint coordinates are employed to describe the motion in this research. In the multirate integration, the fast variables of the flexible multibody system are integrated with smaller stepsize, whereas the slow variables are integrated with larger stepsize. It is assumed that vibrational modal coordinates are treated as fast variables, whereas the relative joint coordinates are treated as slow variables to apply multirate integration method. A method that decomposes the equations of motion for flexible multibody systems into a fast system with flexible coordinates and a slow system with joint relative coordinates has been also proposed. The proposed multirate integration method is based on the Adams-Bashforth-Moulton predictor-corrector method and implemented in the Nordsieck vector form. The Nordsieck form of multirate integration method provides effective step-size control and at the same time, inherits the efficiency from the Adams integration method. Simulations of a flexible gun and turret system of a military tank have been carried out to show the effectiveness and efficiency of the proposed method.

3

Dynamics of sprayer with large flexible boom

75%

Gofron M.

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tom Vol. 9, No. 3

359-371

EN

The quality of spraying chemicals in a field depends on the distance between the boom of the sprayer and the canopy. Keeping that distance relatively constant enables even distribution of chemicals over the field. However, because the boom has a significant moment of inertia due to its length, (commonly 30 [m] and above) the vehicle has a tendency to roll. The excessive rolling significantly decreases the quality of spraying and can even cause damage to the boom if the tip of the boom hits the ground. The boom itself deflects significantly due to its flexibility and can increase the total amplitude of the boom tip point movement during spraying operation. In this study the effect of the boom flexibility on vehicle rolling, boom rolling and boom reaction forces is evaluated. Also the effect of number of modes selected to represent flexible model, on the boom tip point deflection is analyzed. The simulation model of the sprayer is developed in DADS multibody code and mode shapes of the boom are obtained from I-DEAS code. The simulation model of the sprayer is driven over a ramp and a numerical representation of the NATC (Nevada Automotive Test Center) track.

4

Structural performance of reinforced concrete interior beam-column joints with high-strength bars

63%

Kim S.-W. , Chang H.-J.

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tom Vol. 21, no. 3

200--213

EN

This study evaluates the structural performance of reinforced concrete interior beam–column joints having high-strength screw-type steel bars mechanically connected with couplers. A total of six full-scale specimens were cast and subjected to repeated cyclic lateral loads. High-strength screw-type reinforcing bars, with a yield strength of 690 MPa, were used as longitudinal reinforcement of the specimens. The main test variables were designed with and without couplers and the longitudinal reinforcement ratio of the beam. The couplers were applied to the plastic hinge zones of columns and beams to maximize their impact. The experiment confirmed that the flexural cracks generated near the couplers slightly influenced the initial stiffness, the yielding point of the longitudinal reinforcement of the beams, and the displacement at peak load of the specimens. However, the load versus story drift relationship, the peak load, and the ductility capacity of the specimens were not significantly affected. In addition, the analytical results obtained using the current structural design codes and finite element analysis were similar to the experimental results.

5

Flexibility of structure as a criterion of glass formation and stability.

63%

Stoch L.

Optica Applicata

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2000

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tom Vol. 30, nr 4

657-662

EN

The flexibility of structure and internal factors which prevent the ordering of structure randomness, as the indispensable condition of existence of the kinetically stable glasses, have been indicated. Based on the analysis of atomic interactions in solid structures, criteria of the formation of glass of different chemistry, including metallic and molecular glasses, are formulated.