• Korea-Australia Rheology Journal
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• v.19 no.4
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• pp.201-209
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• 2007

The present paper is concerned with non-isothermal spherical Couette flow of Oldroyd-B fluid in the annular region between two concentric spheres. The inner sphere rotates with a uniform angular velocity while the outer sphere is kept at rest. Moreover, the two spherical boundaries are maintained at fixed temperature values. Hence, the fluid is effect by two heat sources; namely, the viscous heating and the temperature gradient between the two spheres. The viscoelasticity of the fluid is assumed to dominate the inertia such that the latter can be neglected. An approximate analytical solution of the energy and momentum equations is obtained through the expansion of the dynamical fields in power series of Nahme number. The analysis show that, the temperature variation due to the external source appears in the zero order solution and its effect extends to the fluid velocity distribution up to present second order. Viscous heating contributes in the first and second order solutions. In contrast to isothermal case, a first order axial velocity and a second order stream function fields has been appeared. Moreover, at higher orders the temperature distribution depends on the gap width between the two spheres. Finally, there exist a thermal distribution of positive and negative values depend on their positions in the domain region between the two spheres.

• Structural Engineering and Mechanics
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• v.59 no.3
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• pp.403-430
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• 2016

This paper studies the dynamics of the lineal-located time-harmonic moving-with-constant-velocity load which acts on the hydro-elastic system consisting of the elastic plate, compressible viscous fluid - strip and rigid wall. The plane-strain state in the plate is considered and its motion is described by employing the exact equations of elastodynamics but the plane-parallel flow of the fluid is described by the linearized Navier-Stokes equations. It is assumed that the velocity and force vectors of the constituents are continuous on the contact plane between the plate and fluid, and impermeability conditions on the rigid wall are satisfied. Numerical results on the velocity and stress distributions on the interface plane are presented and discussed and the focus is on the influence of the effect caused by the interaction between oscillation and moving of the external load. During these discussions, the corresponding earlier results by the authors are used which were obtained in the cases where, on the system under consideration, only the oscillating or moving load acts. In particular, it is established that the magnitude of the aforementioned interaction depends significantly on the vibration phase of the system.

• Steel and Composite Structures
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• v.19 no.3
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• pp.713-733
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• 2015

In this paper, viscous fluid induced nonlinear free vibration and instability analysis of a functionally graded carbon nanotube-reinforced composite (CNTRC) cylindrical shell integrated with two uniformly distributed piezoelectric layers on the top and bottom surfaces of the cylindrical shell are presented. Single-walled carbon nanotubes (SWCNTs) are selected as reinforcement and effective material properties of FG-CNTRC cylindrical shell are assumed to be graded through the thickness direction and are estimated through the rule of mixture. The elastic foundation is modeled by temperature-dependent orthotropic Pasternak medium. Considering coupling of mechanical and electrical fields, Mindlin shell theory and Hamilton's principle, the motion equations are derived. Nonlinear frequency and critical fluid velocity of sandwich structure are calculated based on differential quadrature method (DQM). The effects of different parameters such as distribution type of SWCNTs, volume fractions of SWCNTs, elastic medium and temperature gradient are discussed on the vibration and instability behavior of the sandwich structure. Results indicate that considering elastic foundation increases frequency and critical fluid velocity of system.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.379-386
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• 2001

Fluid viscous dampers have been used as energy dissipators or STU's (Shock Transmission Unit) in earthquake resistant designs for bridges. Viscous dampers have many advantages compared to other friction type or visco-elastic type of dampers. They do neither increase internal pier forces due to their out of phase response, nor produce reaction forces at the low velocities associated with thermal movements. Therefore, they anable the super structure to restore itself perfectly after a severe movement dut to seismic excitations. This paper investigates the response of bridges designed with viscous dampers in regard to damping coefficients, properties of dampers, and arrangements of dampers. For this purpose, time-history dynamic analyses have been performed using a very simple model relevant to a typical bridge example. Based on the results, it presents some design duidelines on how to determine a proper damping ratio and on how to arrange dampers. In usual cases, damping coefficients corresponding to about 0.2-0.3 of damping ratios seem to be very effective in bridge designs.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.198-203
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• 2000

In this paper, a numerical analysis is carried out to show the effect of friction farce on the dynamic characteristics of a flow divider valve. The continuity equations and the equation of motion fur spool are numerically solved. The viscous friction force acting on the spool is considered analyzing the Reynolds equation which governs the viscous flow in the clearance gap between the spool and sleeve. Dynamic characteristics are highly affected by the viscous friction farce whose magnitude is relatively small compare with other fluid forces. Therefore present theoretical formulation and numerical scheme can be used generally in designing and performance evaluation of all the hydraulic spool valve.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.246-251
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• 2003

This paper presents an experimental study on the energy dissipation characteristics of viscous damping wall (VDW). VDW is consisted of a plate floating in a thin case made of steel plated filled with highly viscous silicone oil. Because VDW demonstrates both viscous damping and stiffness characteristics, the viscous resisting force can be expressed as the sum of velocity dependant viscous damping force and displacement dependant restoring force. The viscous resisting force and energy absorbing capacity can be easily adjusted by changing three factors, i.e. viscosity of the fluid, gap distance and area of the wall plates. VDW was tested using a series of harmonic (sinusoidal) displacement history having different frequency and amplitude and the force-displacement relationship was recorded. The relationship between dissipated energy with three factors and the influence of exciting frequency on resisting force were Investigated

• Structural Monitoring and Maintenance
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• v.5 no.1
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• pp.151-171
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• 2018

Transmission tower-line systems are commonly slender and generally possess a small stiffness and low structural damping. They are prone to impulsive excitations induced by cable rupture and may experience strong vibration. Excessive deformation and vibration of a transmission tower-line system subjected to cable rupture may induce a local destruction and even failure event. A little work has yet been carried out to evaluate the performance of transmission tower-line systems in mountain areas subjected to cable rupture. In addition, the control for cable rupture induced vibration of a transmission tower-line system has not been systematically conducted. In this regard, the dynamic response analysis of a transmission tower-line system in mountain areas subjected to cable rupture is conducted. Furthermore, the feasibility of using viscous fluid dampers to suppress the cable rupture-induced vibration is also investigated. The three dimensional (3D) finite element (FE) model of a transmission tower-line system is first established and the mathematical model of a mountain is developed to describe the equivalent scale and configuration of a mountain. The model of a tower-line-mountain system is developed by taking a real transmission tower-line system constructed in China as an example. The mechanical model for the dynamic interaction between the ground and transmission lines is proposed and the mechanical model of a viscous fluid damper is also presented. The equations of motion of the transmission tower-line system subjected to cable rupture without/with viscous fluid dampers are established. The field measurement is carried out to verify the analytical FE model and determine the damping ratios of the example transmission tower-line system. The dynamic analysis of the tower-line system is carried out to investigate structural performance under cable rupture and the validity of the proposed control approach based on viscous fluid dampers is examined. The made observations demonstrate that cable rupture may induce strong structural vibration and the implementation of viscous fluid dampers with optimal parameters can effectively suppress structural responses.

• Journal of applied mathematics & informatics
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• v.25 no.1_2
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• pp.51-66
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• 2007

A layer of compressible, rotating, elastica-viscous fluid heated & soluted from below is considered in the presence of vertical magnetic field to include the effect of Hall currents. Dispersion relation governing the effect of viscoelasticity, salinity gradient, rotation, magnetic field and Hall currents is derived. For the case of stationary convection, the Rivlin-Erickson fluid behaves like an ordinary Newtonian fluid. The compressibility, stable solute gradient, rotation and magnetic field postpone the onset of thermosolutal instability whereas Hall currents are found to hasten the onset of thermosolutal instability in the absence of rotation. In the presence of rotation, Hall currents postpone/hasten the onset of instability depending upon the value of wavenumbers. Again, the dispersion relation is analyzed numerically & the results depicted graphically. The stable solute gradient and magnetic field (and corresponding Hall currents) introduce oscillatory modes in the system which were non-existent in their absence. The case of overstability is discussed & sufficient conditions for non-existence of overstability are derived.

• Journal of applied mathematics & informatics
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• v.18 no.1_2
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• pp.393-403
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• 2005

We study the isothermal flow of a dusty viscous incompressible conducting fluid between two types of boundary motions- oscillatory and non-oscillatory, under the influence of gravitational force. Within the frame work of some physically realistic approximations and suitable boundary conditions, closed form solutions were obtained for the velocity profiles and the skin friction of the particulate flow. These results show that for a constant pressure gradient, only the velocity profile of the fluid and the skin friction are unaffected by gravity, while magnetic field is seen to affect both the fluid, particle velocities and the skin friction. Thus, our results are extension of previous results in literature, and graphical demonstration of some these solutions have been presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.153-159
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• 2002

This paper deals with the measurement of the fluid viscosity by using the torsional vibration of a circular red excited by a torsional vibrator at one end. The effect of an adjacent viscous fluid on the torsional vibration of the rod has been studied theoretically and expressed in terms of the mechanical impedance. The theoretically-obtained trend that the mechanical impedance is proportional to the square root of the viscosity times the density of the fluid has been confirmed by the impedance measurement. The paper demonstrates that a torsionally-vibrating rod can be used as a sensor to measure the viscosity of a fluid.