scholarly journals Dynamic Analysis of Noncontacting Face Seals

1982 ◽  
Vol 104 (4) ◽  
pp. 460-468 ◽  
Author(s):  
I. Etsion
Keyword(s):  
Dynamic Behavior ◽  
Degrees Of Freedom ◽  
Approximate Expression ◽  
Operating Conditions ◽  
Design Parameters ◽  
Seal Ring ◽  
Critical Stability ◽  
Dimensionless Groups ◽  
Stability Maps ◽  
Metal Bellows

The dynamic behavior of a noncontacting coned face seal is analyzed for the case of a rigidly mounted rotating seat and a flexibly mounted stationary ring taking into account various design parameters and operating conditions. The primary seal ring motion is expressed by a set of nonlinear equations for three degrees of freedom. These equations, which are solved numerically, allow identification of two dimensionless groups of parameters that affect the seal dynamic behavior. Stability maps for various seals are presented. These maps contain a stable-to-unstable transition region in which the ring wobbles at half the shaft frequency. The effect of various parameters on seal stability is discussed and an approximate expression for critical stability is offered. The theoretical model assumes frictionless flexible mounting of the seal ring such as in metal bellows. However, the results for critical stability can also be used as an upper limit for cases when friction in the secondary seal is present.

Bearings Influence on the Dynamic Behavior of HSM Spindle

2012 ◽  
Author(s):  
David Noel ◽  
Mathieu Ritou ◽  
Sebastien Le Loch ◽  
Benoit Furet
Keyword(s):  
Dynamic Behavior ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Experimental Tests ◽  
Operating Conditions ◽  
Design Parameters ◽  
Mechanics Model ◽  
Bearing Stiffness ◽  
Rough Milling ◽  
The Impact

The aeronautic industry requires high speed and high power spindles to obtain high material removal rates during long rough milling operations. The weakness of HSM spindle is the bearings, although high precision hybrid ball bearings have been developed to achieve this critical application. Inadequate use of spindles inevitably leads to shortened lifetimes. Choosing the operating conditions is a required step before machining applications. It can be achieved through either experimental tests or numerical modeling that leads to stability lobe diagrams. Stability of cuts relies on the dynamic behavior of the spindle, which is particularly due to the eigenfrequencies of the tool-shaft assembly. The frequencies depend on bearing stiffness that can change under operating conditions. That is why the impact of cutting conditions and bearing parameters on its stiffness are studied in the paper. A five degrees of freedom model of angular ball bearing is briefly presented. A complete bearing model is introduced. The originality of the approach is the complete technological modeling, notably of the radial expansions of inner and outer rings of bearing. A non-linear expression is established from continuum mechanics model. The influence of geometry of bearing, operating conditions and design parameters of spindle on the bearing stiffness are established and analysed. Then, modal analyses of the tool-spindle assembly are carried out in relation to the varying bearing stiffness. Finally, significance of the approach is demonstrated through the analyses of Frequency Response Function.

scholarly journals Influence of the main operating parameters on the DRPSA process design based on the equilibrium theory

Adsorption ◽  
2020 ◽  
Author(s):  
Ester Rossi ◽  
Giuseppe Storti ◽  
Renato Rota
Keyword(s):  
Pressure Swing Adsorption ◽  
Degrees Of Freedom ◽  
Pressure Ratio ◽  
Complete Separation ◽  
Operating Conditions ◽  
Equilibrium Theory ◽  
Design Parameters ◽  
Reflux Ratio ◽  
Gaseous Mixtures ◽  
Pressure Swing

Abstract Among the adsorption-based separation processes for gaseous mixtures, those exploiting pressure variations, so-called Pressure Swing Adsorption (PSA) processes, are the most popular. In this work, we focus on the specific PSA configuration known as Dual Reflux-Pressure Swing Adsorption (DR-PSA) given its ability to achieve sharp separations. In the case of binary mixtures, an analytical approach based on Equilibrium Theory has been proposed to identify the operating conditions for complete separation under the assumption of linear isotherms. This same approach is not available when the separation is not complete. Accordingly, in this work we study the features of non-complete separations by solving numerically a general DR-PSA model with parameter values suitable to approach equilibrium conditions (no mass transport resistances, no axial mixing, isothermal conditions and no pressure drop), thus reproducing the analytical solution when complete separations are examined. Even for non-complete separations, triangularly shaped regions at constant purity can be identified on a plane whose axes correspond to suitable design parameters. Moreover, we found a general indication on how to select the lateral feed injection position to limit the loss in product purities when complete separation is not established, whatever is the composition of the feeding mixture. Finally, a sensitivity analysis with respect to pressure ratio, light reflux ratio and heavy product flowrate is proposed in order to assess how to recover product purities according to the specific degrees of freedom of a DR-PSA apparatus.

Modeling of a New Crank-Less Rotary Heat Engine Concept for Solar Power Utilization

2018 ◽  
Author(s):  
Muhammad I. Rashad ◽  
Hend A. Faiad ◽  
Mahmoud Elzouka
Keyword(s):  
Degrees Of Freedom ◽  
Unit Cost ◽  
Heat Engine ◽  
Structure Design ◽  
Operating Conditions ◽  
Design Parameters ◽  
Working Fluid ◽  
Heat Engines ◽  
And Performance ◽  
Engine Concept

This paper presents the operating principle of a novel solar rotary crank-less heat engine. The proposed engine concept uses air as working fluid. The reciprocating motion is converted to a rotary motion by the mean of unbalanced mass and Coriolis effect, instead of a crank shaft. This facilitates the engine scaling and provides several degrees of freedom in terms of structure design and configuration. Unlike classical heat engines (i.e. Stirling), the proposed engine can be fixed to the ground which significantly reduce the generation unit cost. Firstly, the engine’s configuration is illustrated. Then, order analysis for the engine is carried out. The combined dynamics and thermal model is developed using ordinary differential equations which are then numerically solved by Simulink™. The resulting engine thermodynamics cycle is described. It incorporates the common thermodynamics processes (isobaric, isothermal, isochoric processes). Finally, the system behavior and performance are analyzed along with studying the effect of various design parameters on operating conditions such as engine speed, output power and efficiency.

scholarly journals Complex Bogie Modeling Incorporating Advanced Friction Wedge Components

2009 ◽  
Author(s):  
Brian Sperry ◽  
Corina Sandu ◽  
Brent Ballew
Keyword(s):  
Dynamic Behavior ◽  
Degrees Of Freedom ◽  
Model Simulation ◽  
Surface Friction ◽  
Rigid Bodies ◽  
Operating Conditions ◽  
Normal Operation ◽  
Contact Points ◽  
Modeling Software ◽  
Simulation Results

This research focuses on the dynamic behavior of the three-piece bogie that supports the freight train car bodies. While the system is relatively simple, in that there are very few parts involved, the behavior of the bogie is somewhat more complex. Our research focuses primarily on the behavior of the friction wedges under different operating conditions that are seen under normal operation. The Railway Technologies Laboratory (RTL) at Virginia Tech has been developing a model to better capture the dynamic behavior of friction wedges using 3-D modeling software. In previous years, a quarter-truck model, and half-truck variably damped model have been developed using MathWorks MATLAB®. This year, research has focused on the development of a half-truck variably damped model with a new (curved surface) friction wedge, and a half-truck constantly damped model, both using the MATLAB® based software program. Currently a full-truck variably damped model has been created using LMS Virtual.Lab. This software allows for a model that is more easily created and modified, as well as allowing for a much shorter simulation time, which became a necessity as more contact points, and more complex inputs were needed to increase the accuracy of the simulation results. The new model consists of seven rigid bodies: the bolster, two sideframes, and four wedges. We have also implemented full spring nests on each sideframe, where in previous models equivalent spring forces were used. The model allows six degrees-of-freedom for the wedges and bolster: lateral, longitudinal, and vertical translations, as well as pitch, roll, and yaw. The sideframes are constrained to two degrees-of-freedom: vertical and longitudinal translations. The inputs to the model are vertical and longitudinal translations or forces on the sideframes, which can be set completely independent of each other. The model simulation results have been compared with results from NUCARS®, an industrially-used train modeling software developed by the Transportation Technology Center, Inc. (TTCI), a wholly owned subsidiary of the Association of American Railroads (AAR), for similar inputs, as well as experimental data from warping tests performed at TTCI.

Parametric Optimization of Structures Under Combined Base Motion Direct Forces and Static Loading

1998 ◽  
Vol 124 (1) ◽  
pp. 132-140 ◽  
Author(s):  
Izhak Bucher
Keyword(s):  
Degrees Of Freedom ◽  
Structural Parameters ◽  
Operating Conditions ◽  
Design Parameters ◽  
Power Spectral ◽  
Loading Patterns ◽  
The Cost ◽  
Selection Of ◽  
Eigenvectors And Eigenvalues

This paper deals with the optimization of vibrating structures as a mean for minimizing unwanted vibration. Presented in this work is a method for automatic determination of a set of preselected design parameters affecting the geometrical layout or shape of the structure. The parameters are selected to minimize the dynamic response to external forcing or base motion. The presented method adjusts the structural parameters by solving an optimization problem in which the constraints are dictated by engineering considerations. Several constraints are defined so that the static deflection, the stress levels and the total weight of the structure are kept within bounds. The dynamic loading acting upon the structure is described in this work by its power spectral density, with this representation the structure can be tailored to specific operating conditions. The uncertain nature of the excitation is overcome by combining all possible spectra into one PSD encompassing all possible loading patterns. An important feature of the presented method is its numerical efficiency. This feature is essential for any reasonably sized problem as such problems are usually described by thousands of degrees of freedom arising from a finite-element idealization of the structure. In this paper, efficient, closed form expressions, for the cost function and its gradients are derived. Those are computed with a partial set of eigenvectors and eigenvalues thus increasing the efficiency further. Several numerical examples are presented where both shape optimization and the selection of discrete components are illustrated.

scholarly journals Reactor network synthesis with guaranteed robust performance

2017 ◽  
Author(s):  
Xiao Zhao
Keyword(s):  
Degrees Of Freedom ◽  
Dynamic Properties ◽  
Dynamic Performance ◽  
Parametric Uncertainty ◽  
Fixed Number ◽  
Operating Conditions ◽  
Design Parameters ◽  
Network Synthesis ◽  
Reactor Network ◽  
Reactor Network Synthesis

In this work a systematic model-based approach for reactor network synthesis problem with guaranteed robust dynamic performance will be presented. The work is based on the superstructure approach and aims to find an optimal process flowsheet with determined connection patterns of reactors, reactor types, design parameters and operating conditions. In comparison to the classical design methods, certain specified dynamic properties are guaranteed simultaneously under parametric uncertainty. Structural alternatives in the flowsheet, i.e., how reactors are interconnected, as well as in the control system, i.e., how controlled and manipulated variables are paired, are subject to design degrees of freedom. It is allowed that idle reactors and controllers can appear in the reactor network superstructure, so that a fixed number of non-idle reactors and controllers does not have to be assumed as a priori. The optimal reactor network design in either open- or closed-loop is determined by solving...

scholarly journals Analyses of Dynamic Behavior of Vertical Axis Wind Turbine in Transient Regime

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Bacem Zghal ◽  
Imen Bel Mabrouk ◽  
Lassâad Walha ◽  
Kamel Abboudi ◽  
Mohamed Haddar
Keyword(s):  
Wind Turbine ◽  
Dynamic Behavior ◽  
Degrees Of Freedom ◽  
Vertical Axis ◽  
Transient Regime ◽  
Design Parameters ◽  
Vertical Axis Wind Turbine ◽  
Gear Mesh ◽  
Internal Sources ◽  
Aerodynamic Torque

In this paper, the dynamic behavior of a one-stage bevel gear used in vertical axis wind turbine in transient regime is investigated. Linear dynamic model is simulated by fourteen degrees of freedom. Gear excitation is induced by external and internal sources which are, respectively, the aerodynamic torque caused by the fluctuation of input wind speed in transient regime and the variation of gear mesh stiffness. In this study, the differential equations governing the system motion are solved using an implicit Newmark algorithm. In fact, there are some design parameters, which influence the performance of vertical axis wind turbine. In order to get the appropriate aerodynamic torque, the effect of each parameter is studied in this work. It was found that the rotational speed of the rotor shaft has a significant effect on the aerodynamic torque performance.

Dynamic analysis of a helical gear reduction by experimental and numerical methods

2020 ◽  
Vol 68 (1) ◽  
pp. 48-58
Author(s):  
Chao Liu ◽  
Zongde Fang ◽  
Fang Guo ◽  
Long Xiang ◽  
Yabin Guan ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Dynamic Analysis ◽  
Dynamic Behavior ◽  
Fourth Order ◽  
Numerical Models ◽  
Helical Gear ◽  
Operating Conditions ◽  
Dynamic Responses ◽  
Lumped Mass ◽  
Gear Mesh

Presented in this study is investigation of dynamic behavior of a helical gear reduction by experimental and numerical methods. A closed-loop test rig is designed to measure vibrations of the example system, and the basic principle as well as relevant signal processing method is introduced. A hybrid user-defined element model is established to predict relative vibration acceleration at the gear mesh in a direction normal to contact surfaces. The other two numerical models are also constructed by lumped mass method and contact FEM to compare with the previous model in terms of dynamic responses of the system. First, the experiment data demonstrate that the loaded transmission error calculated by LTCA method is generally acceptable and that the assumption ignoring the tooth backlash is valid under the conditions of large loads. Second, under the common operating conditions, the system vibrations obtained by the experimental and numerical methods primarily occur at the first fourth-order meshing frequencies and that the maximum vibration amplitude, for each method, appears on the fourth-order meshing frequency. Moreover, root-mean-square (RMS) value of the acceleration increases with the increasing loads. Finally, according to the comparison of the simulation results, the variation tendencies of the RMS value along with input rotational speed agree well and that the frequencies where the resonances occur keep coincident generally. With summaries of merit and demerit, application of each numerical method is suggested for dynamic analysis of cylindrical gear system, which aids designers for desirable dynamic behavior of the system and better solutions to engineering problems.

Stability of Ring-Type MEMS Gyroscopes Subjected to Stochastic Angular Speed Fluctuation

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Samuel F. Asokanthan ◽  
Soroush Arghavan ◽  
Mohamed Bognash
Keyword(s):  
Angular Velocity ◽  
Degrees Of Freedom ◽  
Microelectromechanical Systems ◽  
Damping Ratio ◽  
Operating Conditions ◽  
System Stability ◽  
System Response ◽  
Ring Type ◽  
Mems Gyroscopes ◽  
The Stability

Effect of stochastic fluctuations in angular velocity on the stability of two degrees-of-freedom ring-type microelectromechanical systems (MEMS) gyroscopes is investigated. The governing stochastic differential equations (SDEs) are discretized using the higher-order Milstein scheme in order to numerically predict the system response assuming the fluctuations to be white noise. Simulations via Euler scheme as well as a measure of largest Lyapunov exponents (LLEs) are employed for validation purposes due to lack of similar analytical or experimental data. The response of the gyroscope under different noise fluctuation magnitudes has been computed to ascertain the stability behavior of the system. External noise that affect the gyroscope dynamic behavior typically results from environment factors and the nature of the system operation can be exerted on the system at any frequency range depending on the source. Hence, a parametric study is performed to assess the noise intensity stability threshold for a number of damping ratio values. The stability investigation predicts the form of threshold fluctuation intensity dependence on damping ratio. Under typical gyroscope operating conditions, nominal input angular velocity magnitude and mass mismatch appear to have minimal influence on system stability.

Workspace, dexterity and dimensional optimization of microhexapod

2015 ◽  
Vol 35 (4) ◽  
pp. 341-347 ◽  
Author(s):  
E. Rouhani ◽  
M. J. Nategh
Keyword(s):  
Degrees Of Freedom ◽  
Optimization Problem ◽  
Screw Theory ◽  
Design Parameters ◽  
Dimensional Synthesis ◽  
Content Type ◽  
Workspace Analysis ◽  
The Difference ◽  
Flexure Joints ◽  
6 Degrees Of Freedom

Purpose – The purpose of this paper is to study the workspace and dexterity of a microhexapod which is a 6-degrees of freedom (DOF) parallel compliant manipulator, and also to investigate its dimensional synthesis to maximize the workspace and the global dexterity index at the same time. Microassembly is so essential in the current industry for manufacturing complicated structures. Most of the micromanipulators suffer from their restricted workspace because of using flexure joints compared to the conventional ones. In addition, the controllability of micromanipulators inside the whole workspace is very vital. Thus, it is very important to select the design parameters in a way that not only maximize the workspace but also its global dexterity index. Design/methodology/approach – Microassembly is so essential in the current industry for manufacturing complicated structures. Most of the micromanipulators suffer from their restricted workspace because of using flexure joints compared to the conventional ones. In addition, the controllability of micromanipulators inside the whole workspace is very vital. Thus, it is very important to select the design parameters in a way that not only maximize the workspace but also its global dexterity index. Findings – It has been shown that the proposed procedure for the workspace calculation can considerably speed the required calculations. The optimization results show that a converged-diverged configuration of pods and an increase in the difference between the moving and the stationary platforms’ radii cause the global dexterity index to increase and the workspace to decrease. Originality/value – The proposed algorithm for the workspace analysis is very important, especially when it is an objective function of an optimization problem based on the search method. In addition, using screw theory can simply construct the homogeneous Jacobian matrix. The proposed methodology can be used for any other micromanipulator.

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