scholarly journals Would an alternative gravity theory developed from an improved gravitational action approach includes negative kinetic energy dynamic degrees of freedom?

2018 ◽  
Vol 10 ◽  
pp. 145-149
Author(s):  
Veysel Binbay ◽  
F. Figen Binbay
2021 ◽  
Vol 11 (13) ◽  
pp. 6209
Author(s):  
Iwona Pajak ◽  
Grzegorz Pajak

This paper presents the usage of holonomic mobile humanoid manipulators to carry out autonomous tasks in industrial environments, according to the smart factory concept and the Industry 4.0 philosophy. The problem of transporting lengthy objects, taking into account mechanical limitations, the conditions for avoiding collisions, as well as the dexterity of the manipulator arms was considered. The primary problem was divided into three phases, leading to three different types of robotic tasks. In the proposed approach, the pseudoinverse Jacobian method at the acceleration level to solve each of the tasks was used. The redundant degrees of freedom were used to satisfy secondary objectives such as robot kinetic energy, the maximization of the manipulability measure, and the fulfillment mechanical and collision-avoidance limitations. A computer example involving a mobile humanoid manipulator, operating in an industrial environment, illustrated the effectiveness of the proposed method.


2021 ◽  
Vol 11 (5) ◽  
pp. 2346
Author(s):  
Alessandro Tringali ◽  
Silvio Cocuzza

The minimization of energy consumption is of the utmost importance in space robotics. For redundant manipulators tracking a desired end-effector trajectory, most of the proposed solutions are based on locally optimal inverse kinematics methods. On the one hand, these methods are suitable for real-time implementation; nevertheless, on the other hand, they often provide solutions quite far from the globally optimal one and, moreover, are prone to singularities. In this paper, a novel inverse kinematics method for redundant manipulators is presented, which overcomes the above mentioned issues and is suitable for real-time implementation. The proposed method is based on the optimization of the kinetic energy integral on a limited subset of future end-effector path points, making the manipulator joints to move in the direction of minimum kinetic energy. The proposed method is tested by simulation of a three degrees of freedom (DOF) planar manipulator in a number of test cases, and its performance is compared to the classical pseudoinverse solution and to a global optimal method. The proposed method outperforms the pseudoinverse-based one and proves to be able to avoid singularities. Furthermore, it provides a solution very close to the global optimal one with a much lower computational time, which is compatible for real-time implementation.


Author(s):  
Yanfei Zuo ◽  
Jianjun Wang ◽  
Weimeng Ma ◽  
Xue Zhai ◽  
Xinyu Yao

A method of selecting master degrees of freedom (DOFs) for rotating substructure is presented in this paper to obtain reduced 3D rotor models. Fixed modes of the substructure below thrice the operating frequency are analyzed. According to each mode shape, the DOFs at where main kinetic energy locates are selected as master DOFs to decrease missing of dynamic coupling. Additional DOFs may be selected based on traditional substructure method. In the stationary reference frame, frequency-dependent gyroscopic effects can be included as damping matrices changing with spin speed. Besides, by selecting appropriate substructure, localized damping and key parts of the rotor for analysis can be kept the same as the original model. A reduced model of a high pressure rotor amply demonstrated the capability of the method in reducing the model size and increasing the computational efficiency with less than two percent error.


2005 ◽  
Vol 1 (2) ◽  
pp. 135-142 ◽  
Author(s):  
Albert C. J. Luo

The numerical prediction of chaos and quasi-periodic motion on the homoclinic surface of a two-degree-of-freedom (2-DOF) nonlinear Hamiltonian system is presented through the energy spectrum method. For weak interactions, the analytical conditions for chaotic motion in such a Hamiltonian system are presented through the incremental energy approach. The Poincaré mapping surfaces of chaotic motions for this specific nonlinear Hamiltonian system are illustrated. The chaotic and quasi-periodic motions on the phase planes, displacement subspace (or potential domains), and the velocity subspace (or kinetic energy domains) are illustrated for a better understanding of motion behaviors on the homoclinic surface. Through this investigation, it is observed that the chaotic and quasi-periodic motions almost fill on the homoclinic surface of the 2-DOF nonlinear Hamiltonian system. The resonant-periodic motions for such a system are theoretically countable but numerically inaccessible. Such conclusions are similar to the ones in the KAM theorem even though the KAM theorem is based on the small perturbation.


2007 ◽  
Vol 22 (22) ◽  
pp. 1643-1649 ◽  
Author(s):  
INGEMAR BENGTSSON

We discuss a class of alternative gravity theories that are specific to four dimensions, do not introduce new degrees of freedom, and come with a physical motivation. In particular we sketch their Hamiltonian formulation and their relation with some earlier constructions.


1999 ◽  
Vol 121 (4) ◽  
pp. 482-487 ◽  
Author(s):  
P. Gardonio ◽  
S. J. Elliott

A theoretical study of the active control of structural vibration transmission in a multiple isolator system comprising a piece of equipment mounted on a base structure via active mounts is presented. Two types of problem have been studied with a common framework: first, the active isolation of vibration transmission from the equipment to the base structure and, second, the active isolation of vibration transmission from the base structure to the equipment. Four different control strategies using the measured axial velocity or/and axial force underneath or at the top of the mounts have been investigated and compared with the effectiveness of the reference control approaches of minimizing the total power transmitted from the equipment to the flexible base structure or minimizing the total kinetic energy of the suspended rigid equipment when driven by the base structure. For the first type of isolation problem the best control is achieved when a cost function which minimizes the weighted mm of the square values of the axial velocities and axial forces is implemented. For the second isolation problem the best control performance is given by the minimization of an estimate of the kinetic energy of the suspended equipment related to the translational degrees of freedom.


2002 ◽  
Vol 05 (04) ◽  
pp. 409-431 ◽  
Author(s):  
YANEER BAR-YAM

We derive a sum rule that constrains the scale based decomposition of the trajectories of finite systems of particles. The sum rule reflects a tradeoff between the finer and larger scale collective degrees of freedom. For short duration trajectories, where acceleration is irrelevant, the sum rule can be related to the moment of inertia and the kinetic energy (times a characteristic time squared). Thus, two nonequilibrium systems that have the same kinetic energy and moment of inertia can, when compared to each other, have different scales of behavior, but if one of them has larger scales of behavior than the other, it must compensate by also having smaller scales of behavior. In the context of coherence or correlation, the larger scale of behavior corresponds to the collective motion, while the smaller scales of behavior correspond to the relative motion of correlated particles. For longer duration trajectories, the sum rule includes the full effective moment of inertia of the system in space-time with respect to an external frame of reference, providing the possibility of relating the class of systems that can exist in the same space-time domain.


2021 ◽  
Vol 81 (8) ◽  
Author(s):  
Damianos Iosifidis ◽  
Lucrezia Ravera

AbstractWe study the cosmology of a quadratic metric-compatible torsionful gravity theory in the presence of a perfect hyperfluid. The gravitational action is an extension of the Einstein–Cartan theory given by the usual Einstein–Hilbert contribution plus all the admitted quadratic parity even torsion scalars and the matter action also exhibits a dependence on the connection. The equations of motion are obtained by regarding the metric and the metric-compatible torsionful connection as independent variables. We then consider a Friedmann–Lemaître–Robertson–Walker background, analyze the conservation laws, and derive the torsion modified Friedmann equations for our theory. Remarkably, we are able to provide exact analytic solutions for the torsionful cosmology.


1992 ◽  
Vol 07 (19) ◽  
pp. 1757-1764 ◽  
Author(s):  
K.G. AKDENIZ ◽  
Ö.F. DAYI ◽  
A. KIZILERSÜ

A two-dimensional gravity theory which was studied before within the Lagrangian methods, in the conformal gauge is investigated in terms of the Hamiltonian methods. Although the reparametrization invariant and the conformal gauge fixed Lagrangians lead to different number of physical degrees of freedom, it is shown that on mass-shell they are equivalent.


2020 ◽  
Vol 05 (03) ◽  
pp. 2050010
Author(s):  
Sergey V. Dmitriev ◽  
Alexander S. Semenov ◽  
Alexander V. Savin ◽  
Marat A. Ilgamov ◽  
Dmitry V. Bachurin

Carbon nanotube (CNT) bundles exhibit unusual mechanical properties, but nonlinear dynamics and possible energy localization in such systems have not yet been analyzed. The dynamics of a rotobreather in the form of a CNT rotating around its axis and placed in an array of similar CNTs is analyzed using a molecular dynamics model with a reduced number of degrees of freedom. The height of the Peierls–Nabarro potential associated with the discreteness of CNTs is estimated. It is found that if a CNT is given rotational kinetic energy not sufficient to overcome the Peierls–Nabarro potential, it does not rotate. Several resonant angular velocities are identified at which the rotating CNT loses its kinetic energy relatively quickly and eventually stops rotating. CNT with a sufficiently large, non-resonant angular velocity emits the rotational energy very slowly.


Sign in / Sign up

Export Citation Format

Share Document