About mixed forced, parametric and self-oscillations by limited excitation and delayed elasticity

PNRPU Mechanics Bulletin ◽

10.15593/perm.mech/2020.3.02 ◽

2020 ◽

pp. 12-19

Author(s):

A. A Alifov

Keyword(s):

Energy Source ◽

Metal Cutting ◽

Amplitude Curve ◽

Labor Costs ◽

Oscillation System ◽

System A ◽

Oscillation Modes ◽

Final Design ◽

Limited Power ◽

The Stability

Mixed forced, parametric, and self-oscillations are considered if there is a delay in the elastic force in the system. A dynamic model is a friction self-oscillation system describing the frictional self-oscillations that occur in many technical systems for various purposes (metal-cutting machines, textile equipment, brakes and a number of other engineering objects). The operation of the system is supported by the energy source of limited power. For the analysis we used the method of straight linearization which is easier than the known methods of analysis of nonlinear systems, has no time-consuming and complex approximations of different orders, provides an opportunity to obtain the final design ratios regardless of the specific type and degree of nonlinearity, thus reducing labor costs and time by several orders of magnitude. By using this method, we obtained solutions of a nonlinear system of differential equations describing the system's motion. The equations of non-stationary and stationary movements are derived. To analyze the stability of stationary movements, the stability conditions based on the Routh-Hurwitz criteria are compiled. Calculations were performed to obtain information about the effect of delay on the oscillation modes. It is shown that the delay affects both the magnitude of the amplitude and the location of the amplitude-frequency curve in the frequency range depending on the magnitude of the delay, the amplitude curve is shifted to the region of lower frequencies. The stability of stationary oscillations depends both on the energy source characteristics and lag value. The interaction of the oscillating system and the energy source leads to a number of effects, both in the presence and absence of the lag. However, their course may be different depending on the lag value.

Download Full-text

Gait Planning and Stability Control of a Quadruped Robot

Computational Intelligence and Neuroscience ◽

10.1155/2016/9853070 ◽

2016 ◽

Vol 2016 ◽

pp. 1-13 ◽

Cited By ~ 8

Author(s):

Junmin Li ◽

Jinge Wang ◽

Simon X. Yang ◽

Kedong Zhou ◽

Huijuan Tang

Keyword(s):

Stability Control ◽

Quadruped Robot ◽

Oscillation System ◽

Hip Joints ◽

Gait Planning ◽

Reduced Order ◽

System A ◽

The Stability ◽

Real Time Computing ◽

Speed Adjustment

In order to realize smooth gait planning and stability control of a quadruped robot, a new controller algorithm based on CPG-ZMP (central pattern generator-zero moment point) is put forward in this paper. To generate smooth gait and shorten the adjusting time of the model oscillation system, a new CPG model controller and its gait switching strategy based on Wilson-Cowan model are presented in the paper. The control signals of knee-hip joints are obtained by the improved multi-DOF reduced order control theory. To realize stability control, the adaptive speed adjustment and gait switch are completed by the real-time computing of ZMP. Experiment results show that the quadruped robot’s gaits are efficiently generated and the gait switch is smooth in the CPG control algorithm. Meanwhile, the stability of robot’s movement is improved greatly with the CPG-ZMP algorithm. The algorithm in this paper has good practicability, which lays a foundation for the production of the robot prototype.

Download Full-text

NPLs — The Solution Recipe for Albania

European Journal of Economics and Business Studies ◽

10.26417/ejes.v3i1.p48-57 ◽

2015 ◽

Vol 3 (1) ◽

pp. 48

Author(s):

Elona Shehu ◽

Elona Meka

Keyword(s):

Interest Rate ◽

Negative Relationship ◽

Banking System ◽

Gdp Growth ◽

System A ◽

Analysis Technique ◽

Recent Financial Crisis ◽

The Stability ◽

Asset Quality ◽

Macroeconomic Determinants

The quality of the loan portfolio in Albanian banking system is facing many obstacles during the last decade. In this paper we look at possible determinants of assets quality. During the recent financial crisis commercial banks were confronted with deteriorating asset quality that threatened not only the banking industry, but also the stability of the entire financial system. This study aims to examine the correlation between non-performing loans and the macroeconomic determinants in Albania during the last decade. NPLs are considered to be of a high importance as they represent the high risk exposure of banking system. A solid bank with healthy assets increases the market efficiency. Our approach is based on a panel data regression analysis technique from 2005-2015. Within this methodology this study finds robust evidence on the existing relationship between lending interest rate, real GDP growth and NPLs. We expect to find a negative relationship between lending interest rate and asset quality. Further we assume an inverse relationship between GDP growth and non-performing loans, suggesting that NPLs decrease if the economy is growing. Furthermore this study proposes a solution platform, which looks deeper into the possibility of creating a secondary active market for troubled loans, restructuring the banking system or implementing the Podgorica model. This research paper opens a new lieu of discussion in terms of academic debates and decision-making policies.

Download Full-text

Towards a new design with generic modeling and adaptive control of a transformable quadrotor

The Aeronautical Journal ◽

10.1017/aer.2021.54 ◽

2021 ◽

pp. 1-31

Author(s):

S.H. Derrouaoui ◽

Y. Bouzid ◽

M. Guiatni

Keyword(s):

Adaptive Control ◽

Control Strategy ◽

Experimental Tests ◽

Generic Model ◽

System Control ◽

System A ◽

Viable Solution ◽

Generic Modeling ◽

Adaptive Control Strategy ◽

The Stability

Abstract Recently, transformable Unmanned Aerial Vehicles (UAVs) have become a subject of great interest in the field of flying systems, due to their maneuverability, agility and morphological capacities. They can be used for specific missions and in more congested spaces. Moreover, this novel class of UAVs is considered as a viable solution for providing flying robots with specific and versatile functionalities. In this paper, we propose (i) a new design of a transformable quadrotor with (ii) generic modeling and (iii) adaptive control strategy. The proposed UAV is able to change its flight configuration by rotating its four arms independently around a central body, thanks to its adaptive geometry. To simplify and lighten the prototype, a simple mechanism with a light mechanical structure is proposed. Since the Center of Gravity (CoG) of the UAV moves according to the desired morphology of the system, a variation of the inertia and the allocation matrix occurs instantly. These dynamics parameters play an important role in the system control and its stability, representing a key difference compared with the classic quadrotor. Thus, a new generic model is developed, taking into account all these variations together with aerodynamic effects. To validate this model and ensure the stability of the designed UAV, an adaptive backstepping control strategy based on the change in the flight configuration is applied. MATLAB simulations are provided to evaluate and illustrate the performance and efficiency of the proposed controller. Finally, some experimental tests are presented.

Download Full-text

Study on Self-Excited Vibration Mechanism of Wheel-Rail Lateral Contact System

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.427-429.257 ◽

2013 ◽

Vol 427-429 ◽

pp. 257-261

Author(s):

Li Xia Sun ◽

Jian Wei Yao ◽

Fu Guo Hou ◽

Xin Zhao

Keyword(s):

Feedback Mechanism ◽

Point Of View ◽

Contact System ◽

Vibration System ◽

Lateral Contact ◽

System A ◽

Vibration Model ◽

Excited Vibration ◽

Vibration Mechanism ◽

The Stability

In order to investigate self-excited vibration mechanism of wheel-rail lateral contact system, a two DOF elasticity position wheelset lateral vibration model is established which considers the dry friction; the mechanism of the wheelset lateral self-excited vibration is investigated from the energy point of view. It shows that: the bifurcation diagram of this wheel-rail lateral contact system has a supercritical Hopf bifurcation. The energy of self-excited vibration derives from a part of traction energy; the creep rate in the wheel-rail system act as a feedback mechanism in the wheelset lateral self-excited vibration system. The stability of the wheelset self-excited vibration system depends mainly on the total energy removed from and imported into the system.

Download Full-text

Solving Vlasov-Poisson-Fokker-Planck Equations using NRxx method

Communications in Computational Physics ◽

10.4208/cicp.220415.080816a ◽

2017 ◽

Vol 21 (3) ◽

pp. 782-807 ◽

Cited By ~ 1

Author(s):

Yanli Wang ◽

Shudao Zhang

Keyword(s):

Splitting Method ◽

Linear Convergence ◽

Mass Conservation ◽

System A ◽

Spectral Convergence ◽

The Stability ◽

The Moment ◽

Stability And Accuracy ◽

Fokker Planck Equations ◽

Fokker Planck

AbstractWe present a numerical method to solve the Vlasov-Poisson-Fokker-Planck (VPFP) system using the NRxx method proposed in [4, 7, 9]. A globally hyperbolic moment system similar to that in [23] is derived. In this system, the Fokker-Planck (FP) operator term is reduced into the linear combination of the moment coefficients, which can be solved analytically under proper truncation. The non-splitting method, which can keep mass conservation and the balance law of the total momentum, is used to solve the whole system. A numerical problem for the VPFP system with an analytic solution is presented to indicate the spectral convergence with the moment number and the linear convergence with the grid size. Two more numerical experiments are tested to demonstrate the stability and accuracy of the NRxx method when applied to the VPFP system.

Download Full-text

Socio-Political Aspects of Russian Muslim Pilgrimage to Mecca in the XIX-Th Century

Cuestiones Políticas - Conflictividad política, pandemia de COVID-19 y nuevos paradigmasConflictividad política, pandemia de COVID-19 y nuevos paradigmas ◽

10.46398/cuestpol.382e.03 ◽

2020 ◽

Vol 38 (Especial II) ◽

pp. 47-57

Author(s):

Anvar Ajratovich Gafarov ◽

Mariam Arslanovna Galeeva

Keyword(s):

19Th Century ◽

Special Role ◽

System A ◽

Russian State ◽

Holy Places ◽

Expert Assessments ◽

Confessional Identity ◽

The Stability ◽

Political Economic ◽

The 19Th Century

Starting from the middle of the 16-th century, during the foreign policy expansion increase, the ethno-confessional diversity of the Russian state was steadily increasing. The imperial policy aimed at assimilating non-Russian peoples sharply raised the issue of their identity preservation. For domestic Muslims, an important factor in cultural and confessional identity provision was the preservation and development of their traditional ties with the Islamic world. Various political, economic, cultural, and other contacts maintained with the countries of the Muslim East have become the basis for the stability of the Muslim community in Russia under imperial pressure. In this system, a special role was originally played by the Hajj (Muslim pilgrimage to the holy places in the Hejaz), which the official administration had to reckon with. The aim of the proposed study is to identify socio-political aspects, socio-political conditions, and the specifics of the Hajj implementation in the 19th century. After the analysis of office documentation, travel notes of Muslim pilgrims, and expert assessments of orientalists, the authors concluded that, despite the increasing opposition from the authorities, the significance of the Hajj intensifies in the 19th century. Hajj became not only the factor of opposition to imperial acculturation, but also a channel for presentation the ideas of renewal.

Download Full-text

Glymphatic System in the Central Nervous System, a Novel Therapeutic Direction Against Brain Edema After Stroke

Frontiers in Aging Neuroscience ◽

10.3389/fnagi.2021.698036 ◽

2021 ◽

Vol 13 ◽

Author(s):

Xiangyue Zhou ◽

Youwei Li ◽

Cameron Lenahan ◽

Yibo Ou ◽

Minghuan Wang ◽

...

Keyword(s):

Brain Edema ◽

Brain Tissue ◽

Molecular Mechanisms ◽

Glymphatic System ◽

System A ◽

Function Recovery ◽

The Central Nervous System ◽

The Stability ◽

The Brain

Stroke is the destruction of brain function and structure, and is caused by either cerebrovascular obstruction or rupture. It is a disease associated with high mortality and disability worldwide. Brain edema after stroke is an important factor affecting neurologic function recovery. The glymphatic system is a recently discovered cerebrospinal fluid (CSF) transport system. Through the perivascular space and aquaporin 4 (AQP4) on astrocytes, it promotes the exchange of CSF and interstitial fluid (ISF), clears brain metabolic waste, and maintains the stability of the internal environment within the brain. Excessive accumulation of fluid in the brain tissue causes cerebral edema, but the glymphatic system plays an important role in the process of both intake and removal of fluid within the brain. The changes in the glymphatic system after stroke may be an important contributor to brain edema. Understanding and targeting the molecular mechanisms and the role of the glymphatic system in the formation and regression of brain edema after stroke could promote the exclusion of fluids in the brain tissue and promote the recovery of neurological function in stroke patients. In this review, we will discuss the physiology of the glymphatic system, as well as the related mechanisms and therapeutic targets involved in the formation of brain edema after stroke, which could provide a new direction for research against brain edema after stroke.

Download Full-text

Target Optimization Design of Cam Curve in Zoom System

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.552.44 ◽

2013 ◽

Vol 552 ◽

pp. 44-51

Author(s):

Chen Wei Ning ◽

Cao Jian Zhong ◽

Yang Hong Tao ◽

Zhang Jian ◽

Fan Zhe Yuan ◽

...

Keyword(s):

Optimization Design ◽

Rotation Angle ◽

Optical Design ◽

Zoom Lens ◽

Pressure Angle ◽

Cam Design ◽

System A ◽

Cam Follower ◽

Optimization Function ◽

The Stability

Zoom lens has been widely applied in all kinds of fields, and its cam optimization is the key to actualizing the performance of its optical design and the zooming process, while the smoothness and speediness of zooming movement must be considered for military and civilian use. With the incremental use of environmental requirements, it puts forward higher requests to the cam performance of lens. In order to guarantee that the cam has good stiffness in the case of vibration and shock environment, in the process of cam design, it not only requires curve optimal, but also needs to consider influence on the performance which is caused by reduced cam stiffness of the zoom system. A fine curve can ensure that the cam pressure angle α is smaller, and to ensure the cam follower maintains the uniform velocity and smaller acceleration in zooming process, and make the zoom system produce little impact, and whole zooming process smooth and fluent, it can reduce the zoom systems driving moment M, and can ensure the stability imaging of the zoom system. Good cam stiffness K can make the zoom lens have good stability in vibration environment, and make sure that the image quality. M and K respectively up to the pressure angle α of zoom curve and the rotation angle θ of zoom curve in cam. In the new cam design process, considering the whole influence on the performance that is caused by K and M to cam, we construct the function expressions K = f (α, θ) and M = f (α, θ), and then, build target optimization function with K and M, optimize the relationship between pressure angle α of zoom curve and rotation angle θ, looking for the optimal value for the stiffness K and the cam system driving moment M , and improve overall performance of the zoom cam .

Download Full-text