Stability Analysis of Spools with Imperfect Sealing Gap Geometries

2021 ◽  
Author(s):  
Rituraj Rituraj ◽  
Rudolf Scheidl
Keyword(s):  
Stability Analysis ◽  
Analytical Model ◽  
Ritz Method ◽  
Lateral Force ◽  
Graphical Analysis ◽  
Numerical Results ◽  
Design Parameters ◽  
Analytical Expression ◽  
Parametric Studies ◽  
The Stability

Spools in hydraulic valves are prone to sticking caused by unbalanced lateral forces due to geometric imperfections of their sealing lands. This sticking problem can be related to the stability of the coaxial spool position. Numerical methods are commonly used to study this behaviour. However, since several parameters can influence the spool stability, parametric studies become significantly computationally expensive and graphical analysis of the numerical results in multidimensional parameter space becomes difficult. To overcome this difficulty, in this work, an analytical approach for studying the stability characteristics of the spool valve is presented. A Rayleigh-Ritz method is used for solving the Reynolds equation in an approximate way in order to determine an analytical expression for the lateral force on the sealing lands. This analytical expression allows stability analysis of the spool via analytical means which finally results in the expression of critical axial velocity which demarcates the regions of stable behaviour. Simplicity of the expression allows an immediate insight into the role of design parameters in the stability of the spool. To verify the analytical model, a numerical model for spool dynamics is developed in this work and the numerical results are found to match the analytical model in terms of the stability behaviour of the spool.

Stability Analysis of High-Speed Railway Vehicle Based on Multibody Dynamics Analysis

2013 ◽  
Vol 392 ◽  
pp. 156-160
Author(s):  
Ju Seok Kang
Keyword(s):  
Stability Analysis ◽  
Multibody Dynamics ◽  
High Speed ◽  
Equations Of Motion ◽  
Contact Forces ◽  
Design Parameters ◽  
Railway Vehicle ◽  
Dynamics Analysis ◽  
Contact Points ◽  
The Stability

Multibody dynamics analysis is advantageous in that it uses real dimensions and design parameters. In this study, the stability analysis of a railway vehicle based on multibody dynamics analysis is presented. The equations for the contact points and contact forces between the wheel and the rail are derived using a wheelset model. The dynamics equations of the wheelset are combined with the dynamics equations of the other parts of the railway vehicle, which are obtained by general multibody dynamics analysis. The equations of motion of the railway vehicle are linearized by using the perturbation method. The eigenvalues of these linear dynamics equations are calculated and the critical speed is found.

Stability and Vibrations of Geometrically Nonlinear Cylindrically Orthotropic Circular Plates

1984 ◽  
Vol 51 (2) ◽  
pp. 354-360 ◽  
Author(s):  
D. Shilkrut
Keyword(s):  
Stability Analysis ◽  
Qualitative Methods ◽  
Dynamic Method ◽  
Numerical Results ◽  
Geometrically Nonlinear ◽  
Circular Plates ◽  
Different Types ◽  
The Stability ◽  
Thermal Influence ◽  
Cylindrically Orthotropic

The stability analysis of axisymmetrical equilibrium states of geometrically nonlinear, orthotropic, circular plates that are deformed by multiparameter loading, including thermal influence, is presented. The dynamic method (method of small vibrations) is used to accomplish this purpose. The behavior of the plate in different cases is revealed. In particular, it is shown that two different types of snapping processes can occur. The values of frequencies of small eigenvibrations from various cases have been calculated. These investigations are realized by numerical and qualitative methods. Here only the numerical results are presented.

scholarly journals Stability analysis of cylindrical shells subjected to complex loads

2001 ◽  
Vol 23 (4) ◽  
pp. 247-256
Author(s):  
Ngo Huong Nhu
Keyword(s):  
Cylindrical Shell ◽  
Stability Analysis ◽  
Composite Shell ◽  
Laminated Composite ◽  
Numerical Results ◽  
Load Pressure ◽  
Combined Loads ◽  
Analytical Result ◽  
The Stability ◽  
Good Agreement

The paper deals with stability analysis of shell on the basis FEM via Castem 2000. The numerical results of stability problems of cylinders subjected to different loads as compress load, pressure, concentrated and combined loads are compared with analytical result and give a good agreement. The influence of changing radius of the cylindrical shell on the unstable forms and the influence of angles of fibers on unstable behaviour of laminated composite shell are considered. Numerical results and corresponding programs by languages Gibian given in the paper to realize software Castem 2000 can be applied in the design and in the stability analysis of the shell with more complex conditions

Automated Stability Analysis of a Vehicle in Combined Pitch and Roll

2002 ◽  
Author(s):  
James K. Sprague ◽  
Shyi-Ping Liu
Keyword(s):  
Stability Analysis ◽  
Rigid Body ◽  
Contact Forces ◽  
Design Parameters ◽  
Spherical Coordinates ◽  
Stability Boundaries ◽  
Overturning Stability ◽  
Heading Angle ◽  
The Stability ◽  
Six Degree Of Freedom

This paper presents a rigid body modeling approach using ADAMS™ for an overturning stability analysis of a vehicle stopped at an arbitrary heading angle on a steep grade. The vehicle is modeled as a six-degree-of-freedom rigid body with multiple contact forces acting on the ground. A gravity vector bounded by sets of spherical coordinates is applied to the vehicle to represent the physics of a vehicle stopped on a grade with any arbitrary combination of pitch and roll angles. A design of experiments study is performed to locate the overturning stability boundaries within given levels of design parameters. Results are output using two effective graphical means of depicting the stability regions and magnitude of contact forces.

Stability and Dynamical Analysis of Generalized Tumor-Immune Interaction Model with Conformable Fractional Derivative

2021 ◽  
Author(s):  
Rimpi Pal ◽  
Afroz ◽  
Ayub Khan ◽  
MOHMAD AUSIF PADDER
Keyword(s):  
Stability Analysis ◽  
Fixed Points ◽  
Fractional Order ◽  
Interaction Model ◽  
Tumor Model ◽  
Graphical Analysis ◽  
Dynamical Analysis ◽  
Complex Behaviour ◽  
The Stability ◽  
Two Parameters

Abstract Fractional order tumor-immune interaction models are being frequently used for understanding the complex behaviour of immune system and tumor growth. In this paper, a generalized fractional order tumor-immune interaction model has been developed by introducing immunotherapy (IL2) as third variable in the model. The study of generalized model is done by using conformable fractional order derivative. The stability analysis is done for both fractional order tumor model and its conformable fractional order version. By considering some biological fixed points for both versions of the model, the stability analysis around these fixed points shows that both the systems are stable at some fixed point under some stability conditions, which are defined in the model analysis. The numerical and graphical analysis is also done for both the systems by varying two parameters and keeping other parameters fixed for better understanding the dynamics of proposed model.

Linear Stability Analysis of a Waveboard Multibody Model With a Minimal Set of Equations

2021 ◽  
Author(s):  
A. G. Agúndez ◽  
D. García-Vallejo ◽  
E. Freire ◽  
A. M. Mikkola
Keyword(s):  
Stability Analysis ◽  
Multibody System ◽  
Equations Of Motion ◽  
Nonholonomic Constraints ◽  
Design Parameters ◽  
Multibody Model ◽  
Aspect Ratios ◽  
Holonomic And Nonholonomic Constraints ◽  
The Stability ◽  
Nonlinear Equations Of Motion

Abstract In this paper, the stability of a waveboard, the skateboard consisting in two articulated platforms, coupled by a torsion bar and supported of two caster wheels, is analysed. The waveboard presents an interesting propelling mechanism, since the rider can achieve a forward motion by means of an oscillatory lateral motion of the platforms. The system is described using a multibody model with holonomic and nonholonomic constraints. To perform the stability analysis, the nonlinear equations of motion are linearized with respect to the forward upright motion with constant speed. The linearization is carried out resorting to a novel numerical linearization procedure, recently validated with a well-acknowledged bicycle benchmark, which allows the maximum possible reduction of the linearized equations of motion of multibody systems with holonomic and nonholonomic constraints. The approach allows the expression of the Jacobian matrix in terms of the main design parameters of the multibody system under study. This paper illustrates the use of this linearization approach with a complex multibody system as the waveboard. Furthermore, a sensitivity analysis of the eigenvalues considering different scenarios is performed, and the influence of the forward speed, the casters’ inclination angle and the tori aspect ratios of the toroidal wheels on the stability of the system is analysed.

Non-linear stability analysis of floating ring bearings using Hopf bifurcation theory

2011 ◽  
Vol 225 (12) ◽  
pp. 2804-2818 ◽  
Author(s):  
A Amamou ◽  
M Chouchane
Keyword(s):  
Stability Analysis ◽  
Hopf Bifurcation ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Limit Cycles ◽  
Critical Speed ◽  
Design Parameters ◽  
Stable Limit ◽  
Non Linear ◽  
The Stability

Floating ring bearings are used to support and guide rotors in several high-speed rotating machinery applications. They are usually credited for lower heat generation and higher vibration suppressing ability. Similar to conventional hydrodynamic bearings, floating ring bearings may exhibit unstable behaviour above a certain stability critical speed. Linear stability analysis is usually applied to predict the stability threshold speed. Non-linear stability analysis, however, is needed to predict the presence and the size of stable limit cycles above the stability threshold speed or unstable limit cycles below the stability critical speed. The prediction of limit cycles is an important step in bearing stability analysis. In this article, a non-linear dynamic model is derived and used to investigate the stability of a perfectly balanced symmetric rigid rotor supported by two identical floating ring bearings near the critical stability boundaries. The fluid film hydrodynamic reactions of the floating ring bearings are modelled by applying the short bearing theory and the half Sommerfeld solution. Hopf bifurcation theory is then utilized to determine the existence and the approximate size of stable and unstable limit cycles in the neighbourhood of the stability critical speed depending on the bearing design parameters. Numerical integration of the non-linear equations of motion is then carried out in order to compare the trajectories obtained by numerical integration to those obtained analytically using Hopf bifurcation analysis. Stability boundary curves for typical bearing design parameters have been decomposed into boundaries with supercritical stable limit cycles and boundaries with subcritical unstable limit cycles. The shape and size of the limit cycles for selected bearing parameters are presented using both analytical and numerical approaches. This article shows that floating ring stability boundaries may exhibit either stable supercritical limit cycles or unstable subcritical limit cycles predictable by Hopf bifurcation.

scholarly journals Solving Volterra Integrodifferential Equations via Diagonally Implicit Multistep Block Method

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Nur Auni Baharum ◽  
Zanariah Abdul Majid ◽  
Norazak Senu
Keyword(s):  
Stability Analysis ◽  
Numerical Solution ◽  
Numerical Method ◽  
Numerical Computation ◽  
Numerical Solutions ◽  
Numerical Results ◽  
Integrodifferential Equations ◽  
Block Method ◽  
The Stability ◽  
Predictor Corrector

The performance of the numerical computation based on the diagonally implicit multistep block method for solving Volterra integrodifferential equations (VIDE) of the second kind has been analyzed. The numerical solutions of VIDE will be computed at two points concurrently using the proposed numerical method and executed in the predictor-corrector (PECE) mode. The strategy to obtain the numerical solution of an integral part is discussed and the stability analysis of the diagonally implicit multistep block method was investigated. Numerical results showed the competence of diagonally implicit multistep block method when solving Volterra integrodifferential equations compared to the existing methods.

Stability Analysis of a Flexible Rotor Supported by Plain Circular Bearings with Micropolar Fluid

2014 ◽  
Vol 592-594 ◽  
pp. 1381-1385
Author(s):  
Pankaj Bhatia ◽  
Jaideep Gupta
Keyword(s):  
Stability Analysis ◽  
Micropolar Fluid ◽  
Hydrodynamic Lubrication ◽  
Tangential Direction ◽  
Design Parameters ◽  
Flexible Rotor ◽  
Basic Principles ◽  
Operating Variables ◽  
The Stability ◽  
Micropolar Lubrication

This paper describes the stability analysis of a flexible rotor supported by two horizontal identical plain circular bearings lubricated with Non-Newtonian fluid as micropolar fluid. The basic principles of hydrodynamic lubrication are also discussed here to study the dynamics of rotor bearing system. The mechanisms of hydrodynamic film generation and the effects of operating variables such as velocity, load, design parameters etc., on the performance of such films are outlined. The effects in hydrodynamic lubrication of rotor system using Non-Newtonian lubricant found some undesirable vibrations, undergoes periodic and quasi-periodic motion is described and their influence on bearing performance assessed. The numerical solution of modified Reynolds equation under micropolar lubrication with the usual lubrication assumptions is considered which yield the pressure distribution to find the couple of resulting forces in radial as well as in tangential direction.

A Scalabale Microfluidic Device for Switching of Microparticles Using Dielectrophoresis

2018 ◽  
Author(s):  
Waqas Waheed ◽  
Anas Alazzam ◽  
Bobby Mathew ◽  
Eiyad Abu Nada ◽  
Ashraf N. Al Khateeb
Keyword(s):  
Red Blood Cells ◽  
Microfluidic Device ◽  
Blood Cells ◽  
Element Model ◽  
Microfluidic System ◽  
Numerical Results ◽  
Design Parameters ◽  
Glass Wafer ◽  
Parametric Studies ◽  
Cell Trajectories

In this paper, we have introduced a negative Dielectrophoresis based microfluidic system using a novel arrangement of microelectrodes to perform switching of micro objects. Both the experimental and numerical results are presented. Two sets of interdigitated electrodes, extending slightly into the microchannel from each sidewall, are embedded on the bottom of the microchannel. A finite element model in COMSOL Multiphysics 5.2a was developed to demonstrate switching of Red Blood Cells in the microchannel followed by multiple parametric studies to study the effect of several parameters on cell trajectories and optimize the design parameters. To verify numerical results, a PDMS-based microfluidic device on glass wafer was fabricated. The switching of Red Blood Cells in the microfluidic device with a single inlet and three outlets was also demonstrated.

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