Analysis of the Instability for Two Nano-Scale Liquid Threads Coexisting in a Periodic Fundamental Cell

2011 ◽  
Author(s):  
Chun-Lang Yeh
Keyword(s):  
Stability Criterion ◽  
Md Simulation ◽  
Density Field ◽  
Stability Criteria ◽  
Stable Domain ◽  
Nano Scale ◽  
Critical Wavelength ◽  
Molecular Scale ◽  
Vaporization Process ◽  
Simulation Results

This paper investigates the vaporization process of two nano-scale liquid threads coexisting in a periodic fundamental cell by molecular dynamics (MD) simulation. The influences of liquid thread radius, fundamental cell length, and relative position of the two threads are discussed. Snapshots of molecules, the number of liquid particles formed, and density field are analyzed. Two linear stability criteria, namely, Rayleigh’s stability criterion and Kim’s stability criterion, are accessed for their validity in molecular scale. It is found that more liquid particles are formed when the separation of the two threads is larger. Moreover, vaporization is slower when the two liquid threads are close to each other. It is also found that the trends of Rayleigh’s stability criterion and Kim’s stability criterion agree with MD simulation results. However, when the two threads coalesce into a single thread and remain intact, the critical wavelength of perturbation may be increased and the stable domain is broadened. Under such a situation, Rayleigh’s stability criterion and Kim’s stability criterion underpredict the stable domain.

scholarly journals Stability Criterion for Dynamic Gaits of Quadruped Robot

2018 ◽  
Vol 8 (12) ◽  
pp. 2381 ◽  
Author(s):  
Yan Jia ◽  
Xiao Luo ◽  
Baoling Han ◽  
Guanhao Liang ◽  
Jiaheng Zhao ◽  
...  
Keyword(s):  
Dynamic Stability ◽  
Stability Criterion ◽  
Quadruped Robot ◽  
Stability Criteria ◽  
Irregular Terrain ◽  
Quadruped Robots ◽  
Simulation Results ◽  
Zero Moment ◽  
The Stability ◽  
Dynamic Gait

Dynamic-stability criteria are crucial for robot’s motion planning and balance recovery. Nevertheless, few studies focus on the motion stability of quadruped robots with dynamic gait, none of which have accurately evaluated the robots’ stability. To fill the gaps in this field, this paper presents a new stability criterion for the motion of quadruped robots with dynamic gaits running over irregular terrain. The traditional zero-moment point (ZMP) is improved to analyze the motion on irregular terrain precisely for dynamic gaits. A dynamic-stability criterion and measurement are proposed to determine the stability state of the robot and to evaluate its stability. The simulation results show the limitations of the existing stability criteria for dynamic gaits and indicate that the criterion proposed in this paper can accurately and efficiently evaluate the stability of a quadruped robot using such gaits.

Intrinsic Thermal Stability of Anisotropic Thin-Film Superconductors

1990 ◽  
Vol 112 (1) ◽  
pp. 10-15 ◽  
Author(s):  
M. I. Flik ◽  
C. L. Tien
Keyword(s):  
Thin Film ◽  
Thermal Stability ◽  
Stability Criterion ◽  
High Temperature Superconductors ◽  
Stability Criteria ◽  
Anisotropic Thermal Conductivity ◽  
Operating Current ◽  
Released Energy ◽  
The Stability ◽  
Thermal Stability Of

Intrinsic thermal stability denotes a situation where a superconductor can carry the operating current without resistance at all times after the occurrence of a localized release of thermal energy. This novel stability criterion is different from the cryogenic stability criteria for magnets and has particular relevance to thin-film superconductors. Crystals of ceramic high-temperature superconductors are likely to exhibit anisotropic thermal conductivity. The resultant anisotropy of highly oriented films of superconductors greatly influences their thermal stability. This work presents an analysis for the maximum operating current density that ensures intrinsic stability. The stability criterion depends on the amount of released energy, the Biot number, the aspect ratio, and the ratio of the thermal conductivities in the plane of the film and normal to it.

Evaluation of the Dynamic-Response-Based Intact Stability Criterion for Floating Wind Turbines

2015 ◽  
Author(s):  
Marco Masciola ◽  
Xiaohong Chen ◽  
Qing Yu
Keyword(s):  
Wind Speed ◽  
Dynamic Response ◽  
Wind Turbines ◽  
Stability Criterion ◽  
Area Ratio ◽  
Operating Conditions ◽  
Dynamic Responses ◽  
Stability Criteria ◽  
Intact Stability ◽  
Overturning Moment

As an alternative to the conventional intact stability criterion for floating offshore structures, known as the area-ratio-based criterion, the dynamic-response-based intact stability criteria was initially developed in the 1980s for column-stabilized drilling units and later extended to the design of floating production installations (FPIs). Both the area-ratio-based and dynamic-response-based intact stability criteria have recently been adopted for floating offshore wind turbines (FOWTs). In the traditional area-ratio-based criterion, the stability calculation is quasi-static in nature, with the contribution from external forces other than steady wind loads and FOWT dynamic responses captured through a safety factor. Furthermore, the peak wind overturning moment of FOWTs may not coincide with the extreme storm wind speed normally prescribed in the area-ratio-based criterion, but rather at the much smaller rated wind speed in the power production mode. With these two factors considered, the dynamic-response-based intact stability criterion is desirable for FOWTs to account for their unique dynamic responses and the impact of various operating conditions. This paper demonstrates the implementation of a FOWT intact stability assessment using the dynamic-response-based criterion. Performance-based criteria require observed behavior or quantifiable metrics as input for the method to be applied. This is demonstrated by defining the governing load cases for two conceptual FOWT semisubmersible designs at two sites. This work introduces benchmarks comparing the area-ratio-based and dynamic-response-based criteria, gaps with current methodologies, and frontier areas related to the wind overturning moment definition.

Thermal Transport in Nanocrystalline Materials

2005 ◽  
Author(s):  
Zhanrong Zhong ◽  
Xinwei Wang
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Thermal Transport ◽  
Nanocrystalline Materials ◽  
Large Scale ◽  
Md Simulation ◽  
Fundamental Physics ◽  
Grain Sizes ◽  
Simulation Results ◽  
Thermal Phenomena

In this work, thermal transport in nanocrystalline materials is studied using large-scale equilibrium molecular dynamics (MD) simulation. Nanocrystalline materials with different grain sizes are studied to explore how and to what extent the size of nanograins affects the thermal conductivity and specific heat. Substantial thermal conductivity reduction is observed and the reduction is stronger for nanocrystalline materials with smaller grains. On the other hand, the specific heat of nanocrystalline materials shows little change with the grain size. The simulation results are compared with the thermal transport in individual nanograins based on MD simulation. Further discussions are provided to explain the fundamental physics behind the observed thermal phenomena in this work.

Thermal Expansion and Isotopic Composition Effects on Lattice Thermal Conductivities of Crystalline Silicon

2006 ◽  
Author(s):  
Yunfei Chen ◽  
Guodong Wang ◽  
Deyu Li ◽  
Jennifer R. Lukes
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Md Simulation ◽  
Lattice Thermal Conductivity ◽  
Mass Difference ◽  
Dynamics Simulation ◽  
Temperature Range ◽  
Simulation Results ◽  
Callaway Model ◽  
Thermal Conductivities

Equilibrium molecular dynamics simulation is used to calculate lattice thermal conductivities of crystal silicon in the temperature range from 400K to 1600K. Simulation results confirmed that thermal expansion, which resulted in the increase of the lattice parameter, caused the decrease of the lattice thermal conductivity. The simulated results proved that thermal expansion imposed another type resistance on phonon transport in crystal materials. Isotopic and vacancy effects on lattice thermal conductivity are also investigated and compared with the prediction from the modified Debye Callaway model. It is demonstrated in the MD simulation results that the isotopic effect on lattice thermal conductivity is little in the temperature range from 400K to 1600K for isotopic concentration below 1%, which implies the isotopic scattering on phonon due to mass difference can be neglected over the room temperature. The remove of atoms from the crystal matrix caused mass difference and elastic strain between the void and the neighbor atoms, which resulted in vacancy scattering on phonons. Simulation results demonstrated this mechanism is stronger than that caused by isotopic scattering on phonons due to mass difference. A good agreement is obtained between the MD simulation results of silicon crystal with vacancy defects and the data predicted from the modified Debye Callaway model. This conclusion is helpful to demonstrate the validity of Klemens' Rayleigh model for impurity scattering on phonons.

PID Control Strategy of Vehicle Active Suspension Based on Considering Time-Delay and Stability

2013 ◽  
Vol 706-708 ◽  
pp. 901-906
Author(s):  
Guang Hui Yan ◽  
Shao Hua Wang ◽  
Zhi Wei Guan ◽  
Chen Fu Liu
Keyword(s):  
Time Delay ◽  
Pid Control ◽  
Stability Criterion ◽  
Control Method ◽  
Critical Time ◽  
Active Suspension ◽  
Vertical Acceleration ◽  
Hurwitz Stability ◽  
Critical Instability ◽  
Simulation Results

The stability conditions of 1/4 vehicle active suspension with time-delay were deduced by the theory of Routh-Hurwitz stability criterion and the critical instability time-delay was discussed and calculated. Compared with PID control method of without time-delay the simulation results show that when the critical time-delay is 0.153s, the amplitude range and its root mean square value of spring load quality vertical acceleration were increased 1.2 times or so and the system was being on the critical stability. The calculation and simulation results proved that the theory of Routh-Hurwitz stability criterion laid a foundation for the design and instability mechanism of active suspension.

A scale-up nanoporous membrane centrifuge for reverse osmosis desalination without fouling

TECHNOLOGY ◽  
2018 ◽  
Vol 06 (01) ◽  
pp. 36-48 ◽  
Author(s):  
Qingsong Tu ◽  
Tiange Li ◽  
Ao Deng ◽  
Kevin Zhu ◽  
Yifei Liu ◽  
...  
Keyword(s):  
Angular Velocity ◽  
Reverse Osmosis ◽  
Large Scale ◽  
Md Simulation ◽  
Scale Up ◽  
Scale Separation ◽  
Nanoporous Membrane ◽  
Micron Size ◽  
Simulation Results ◽  
Reverse Osmosis Desalination

A scale-up nanoporous membrane centrifuge is designed and modeled. It can be used for nanoscale scale separation including reverse osmosis desalination. There are micron-size pores on the wall of the centrifuge and nanoscale pores on local graphene membrane patches that cover the micron-size pores. In this work, we derived the critical angular velocity required to counter-balance osmosis force, so that the reverse-osmosis (RO) desalination process can proceed. To validate this result, we conducted a large scale (four million atoms) full atom molecular dynamics (MD) simulation to examine the critical angular velocity required for reverse osmosis at nanoscale. It is shown that the analytical results derived based on fluid mechanics and the simulation results observed in MD simulation are consistent and well matched. The main advantage of such nanomaterial based centrifuge is its intrinsic anti-fouling ability to clear [Formula: see text] and [Formula: see text] ions accumulated at the vicinity of the pores due to the Coriolis effect. Analyses have been conducted to study the relation between osmotic pressure, centrifugal pressure, and water permeability.

New stability criteria for a class of systems arising in neural network control and fuzzy systems

2000 ◽  
Vol 214 (1) ◽  
pp. 1-8
Author(s):  
Y Fang ◽  
T G Kincaid ◽  
S Li
Keyword(s):  
Neural Network ◽  
Stability Criterion ◽  
Fuzzy Systems ◽  
Neural Control ◽  
Network Control ◽  
Neural Network Control ◽  
Stability Criteria ◽  
Simple Derivation ◽  
The Stability

In this paper, the stability of a class of systems arising from neural control and fuzzy systems is studied. A new unifying stability criterion is presented using a very simple derivation. This result generalizes some previous results; some easily testable conditions are obtained.

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