On the hydrodynamic theory of a magnetic liquid II. Hydrodynamic modes in the Heisenberg fluid

1996 ◽  
Vol 234 (1-2) ◽  
pp. 129-150 ◽  
Author(s):  
I.M. Mryglod ◽  
R. Folk
Keyword(s):  
Hydrodynamic Theory ◽  
Magnetic Liquid ◽  
Hydrodynamic Modes

Unconventional relaxation of hydrodynamic modes in anharmonic chains under strong pressure fluctuations

2021 ◽  
Author(s):  
Da Ke ◽  
Wei Zhong ◽  
Sergey V Dmitriev ◽  
Daxing Xiong
Keyword(s):  
Thermal Transport ◽  
Numerical Scheme ◽  
Pressure Fluctuations ◽  
Hydrodynamic Theory ◽  
Hydrodynamic Modes ◽  
Large Pressure

Abstract We develop an effective numerical scheme to capture hydrodynamic modes in general classical anharmonic chains. This scheme is based on the hydrodynamic theory suggested by Ernst-Hauge-van Leeuwen, which takes full role of pressure fluctuations into account. With this scheme we show that the traditional pictures given by the current nonlinear fluctuating hydrodynamic theory are valid only when the system's pressure is zero and the pressure fluctuations are weak. For nonvanishing pressure, the hydrodynamic modes can, however, respond to small and large pressure fluctuations and relax in some distinct manners. Our results shed new light on understanding thermal transport from the perspective of hydrodynamic theory.

scholarly journals A holographic superfluid symphony

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
Daniel Areán ◽  
Matteo Baggioli ◽  
Sebastian Grieninger ◽  
Karl Landsteiner
Keyword(s):  
Constitutive Relations ◽  
Quasinormal Modes ◽  
Role Reversal ◽  
Hydrodynamic Theory ◽  
Hydrodynamic Dispersion ◽  
Complex Frequency ◽  
Hydrodynamic Modes ◽  
Weakly Coupled ◽  
Reversal Phenomenon ◽  
Theory Framework

Abstract We study the hydrodynamic excitations of backreacted holographic superfluids by computing the full set of quasinormal modes (QNMs) at finite momentum and matching them to the existing hydrodynamic theory of superfluids. Additionally, we analyze the behavior of the low-energy excitations in real frequency and complex momentum, going beyond the standard QNM picture. Finally, we carry out a novel type of study of the model by computing the support of the hydrodynamic modes across the phase diagram. We achieve this by determining the support of the corresponding QNMs on the different operators in the dual theory, both in complex frequency and complex momentum space. From the support, we are able to reconstruct the hydrodynamic dispersion relations using the hydrodynamic constitutive relations. Our analysis rules out a role-reversal phenomenon between first and second sound in this model, contrary to results obtained in a weakly coupled field theory framework.

scholarly journals MAGNETIC LIQUID IN HYDRODYNAMIC LUBRICATION MODE OF SPHERICAL SURFACES

2016 ◽  
Vol 2016 (3) ◽  
pp. 90-93 ◽  
Author(s):  
Али Албагачиев ◽  
Ali Albagachiev ◽  
Владимир Данилов ◽  
Vladimir Danilov
Keyword(s):  
Hydrodynamic Lubrication ◽  
Point Contact ◽  
Hydrodynamic Theory ◽  
Magnetic Liquid ◽  
Magnetic Forces ◽  
Spherical Surfaces ◽  
Lubrication Layer ◽  
Lubrication Mode ◽  
Hydrodynamic Lubrication Theory ◽  
The Magnetic Field

From the position of the hydrodynamic lubrication theory are considered the peculiarities of magnetoliquid lubrication in a point contact determined with a complicated character of the interaction of hydrodynamic and magnetic forces in a lubrication layer. The pressure distribution in a lubrication layer of magnetic liquid is considered as a superposition of the augend and addend pr and pm induced with hydrodynamic and magnetic forces. The contribution of the constituent pr is described by Reynolds equation in accordance with the classic hydrodynamic theory. At the saturation of magnetic liquid the constituent pm is presented as a function of the magnetic field strength, saturation magnetization of magnetic liquid and its viscosity and also velocity of rolling. As a result of the solution of a hydrodynamic problem through a numerical method there are defined conditions under which a lubrication layer loses its stability that is followed with the loss of carrying capacity in areas with negative pressure. The dependences of resistance to rolling forces, and sliding ones in a contact of spherical surfaces.

scholarly journals Double Closed-Loop Compound Control Strategy for Magnetic Liquid Double Suspension Bearing

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1195
Author(s):  
Jianhua Zhao ◽  
Yongqiang Wang ◽  
Xuchao Ma ◽  
Sheng Li ◽  
Dianrong Gao ◽  
...  
Keyword(s):  
Control Strategy ◽  
Electromagnetic Force ◽  
Closed Loop ◽  
Static Characteristic ◽  
Magnetic Liquid ◽  
Initial Current ◽  
Electromagnetic System ◽  
Initial Flow ◽  
Hydrostatic Force ◽  
Position Feedback

As a new type of suspension bearing, the magnetic liquid double suspension bearing (MLDSB) is mainly supported by electromagnetic suspension and supplemented by hydrostatic support. At present, the MLDSB adopts the regulation strategy of “electromagnetic-position feedback closed-loop, hydrostatic constant-flow supply” (referred to as CFC mode). In the equilibrium position, the external load is carried by the electromagnetic system, and the hydrostatic system produces no supporting force. Thus, the carrying capacity and supporting stiffness of the MLDSB can be reduced. To solve this problem, the double closed-loop control strategy of “electromagnetic system-force feedback inner loop and hydrostatic-position feedback outer loop” (referred to as DCL mode) was proposed to improve the bearing performance and operation stability of the MLDSB. First, the mathematical models of CFC mode and DCL mode of the single DOF supporting system were established. Second, the real-time variation laws of rotor displacement, flow/hydrostatic force, and regulating current/electromagnetic force in the two control modes were plotted, compared, and analyzed. Finally, the influence law of initial current, flow, and controller parameters on the dynamic and static characteristic index were analyzed in detail. The results show that compared with that in CFC mode, the displacement in DCL mode is smaller, and the adjustment time is shorter. The hydrostatic force is equal to the electromagnetic force in DCL mode when the rotor returns to the balance position. Moreover, the system in DCL mode has better robustness, and the initial flow has a more obvious influence on the dynamic and static characteristic indexes. This study provides a theoretical basis for stable suspension control and the safe and reliable operation of the MLDSB.

scholarly journals Impact-Rubbing Dynamic Behavior of Magnetic-Liquid Double Suspension Bearing under Different Protective Bearing Forms

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1105
Author(s):  
Jianhua Zhao ◽  
Lanchun Xing ◽  
Sheng Li ◽  
Weidong Yan ◽  
Dianrong Gao ◽  
...  
Keyword(s):  
Dynamic Behavior ◽  
Ball Bearing ◽  
Magnetic Liquid ◽  
Electromagnetic System ◽  
Fixed Ring ◽  
Deep Groove ◽  
Deep Groove Ball Bearing ◽  
Protection Devices ◽  
Hydrostatic System ◽  
The Impact

The magnetic-liquid double suspension bearing (MLDSB) is a new type of suspension bearing, with electromagnetic suspension as the main part and hydrostatic supports as the auxiliary part. It can greatly improve the bearing capacity and stiffness of rotor-bearing systems and is suitable for a medium speed, heavy load, and frequent starting occasions. Compared with the active electromagnetic bearing system, the traditional protective bearing device is replaced by the hydrostatic system in MLDSB, and the impact-rubbing phenomenon can be restrained and buffered. Thus, the probability and degree of friction and wear between the rotor and the magnetic pole are reduced drastically when the electromagnetic system fails. In order to explore the difference in the dynamic behavior law of the impact-rubbing phenomenon between the traditional protection device and hydrostatic system, the dynamic equations of the rotor impact-rubbing in three kinds of protection devices (fixed ring/deep groove ball bearing/hydrostatic system) under electromagnetic failure mode are established, and the axial trajectory and motion law of the rotor are numerically simulated. Finally, the dynamic behavior characteristics of the rotor are compared and analyzed. The results show that: Among the three kinds of protection devices (fixed ring/deep groove ball bearing/hydrostatic system), the hydrostatic system has the least influence on bouncing time, impact-rubbing force, and impact-rubbing degree, and the maximum impact-rubbing force of MLDSB is greatly reduced. Therefore, the protective bear is not required to be installed in the MLDSB. This study provides the basis for the theory of the “gap impact-rubbing” of MLDSB under electromagnetic failure, and helps to identify electromagnetic faults.

scholarly journals Exploring the Distribution of Traffic Flow for Shared Human and Autonomous Vehicle Roads

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3425
Author(s):  
Huanping Li ◽  
Jian Wang ◽  
Guopeng Bai ◽  
Xiaowei Hu
Keyword(s):  
Traffic Flow ◽  
Autonomous Vehicles ◽  
Flow Model ◽  
Road Traffic ◽  
Autonomous Vehicle ◽  
Transformation Model ◽  
Hydrodynamic Theory ◽  
Traffic Flow Model ◽  
Traffic System ◽  
The Stability

In order to explore the changes that autonomous vehicles would bring to the current traffic system, we analyze the car-following behavior of different traffic scenarios based on an anti-collision theory and establish a traffic flow model with an arbitrary proportion (p) of autonomous vehicles. Using calculus and difference methods, a speed transformation model is established which could make the autonomous/human-driven vehicles maintain synchronized speed changes. Based on multi-hydrodynamic theory, a mixed traffic flow model capable of numerical calculation is established to predict the changes in traffic flow under different proportions of autonomous vehicles, then obtain the redistribution characteristics of traffic flow. Results show that the reaction time of autonomous vehicles has a decisive influence on traffic capacity; the q-k curve for mixed human/autonomous traffic remains in the region between the q-k curves for 100% human and 100% autonomous traffic; the participation of autonomous vehicles won’t bring essential changes to road traffic parameters; the speed-following transformation model minimizes the safety distance and provides a reference for the bottom program design of autonomous vehicles. In general, the research could not only optimize the stability of transportation system operation but also save road resources.

Sign in / Sign up

Export Citation Format

Share Document