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Laminar flow between solid boundaries
Published in Bernard S. Massey, John Ward-Smith, Mechanics of Fluids, 2018
Bernard S. Massey, John Ward-Smith
A dashpot is essentially a device for damping vibrations of machines, or rapid reciprocating motions. This aim may readily be achieved by making use of a fluid of fairly high viscosity. A dashpot of the simplest kind is illustrated in Fig. 6.12. A piston P, connected to the mechanism whose movement is to be restrained, may move in a concentric cylinder C, the diameter of which is only slightly greater than that of the piston. The cylinder contains a viscous oil, and the quantity of oil should be sufficient to cover the top of the piston. If the piston is caused to move downwards, oil is displaced from underneath it. This displaced oil must move to the space above the piston and its only route is through the small annular clearance between the piston and the wall of the cylinder. If the viscosity of the oil is great enough, its flow upwards through the clearance space is laminar and occurs simply as a result of the pressure developed underneath the piston. The more viscous the oil and the smaller the clearance between the piston and the cylinder, the greater is the pressure required to produce a particular movement of oil; thus the greater is the resistance to the motion of the piston.
Constitutive relations
Published in Roderic S. Lakes, Viscoelastic Solids, 2017
Exponential response functions arise in simple discrete mechanical models composed of springs, which are perfectly elastic (σs= Eɛs); and dashpots, which are perfectly viscous (σd = ηdɛd/dt, with η as viscosity). The dashpot may be envisaged as a piston-cylinder assembly in which motion of the piston causes a viscous fluid to move through an aperture. Some people find spring-dashpot models to be useful in visualizing how viscoelastic behavior can arise; however, they are not necessary in understanding or using vis-coelasticity theory.
Formulation and Solutions of Fractional Continuously Variable-Order Mass-Spring Damper Systems
Published in Santanu Saha Ray, Subhadarshan Sahoo, Generalized Fractional Order Differential Equations Arising in Physical Models, 2018
Santanu Saha Ray, Subhadarshan Sahoo
The damping on a linear spring-mass system usually occurred due to the dashpot. A dashpot is considered as a mechanical device, which resists motion via viscous friction. As a result, the obtained force, which is also known as resulting force is directly proportional to the velocity and acts to the opposite direction of motion. Due to the force acting in the opposite direction, it absorbs energy and impedes the motion of the system. When the damping force is considered as viscoelastic, it follows the viscous and elastic characteristic to prevent or damp the oscillation of the system. When the system achieves a pure viscous friction at high speed and viscoelastic friction at low speed the damping force is called “viscous-viscoelastic”. Similarly, when the system achieves a pure viscoelastic friction at high speed and viscous friction at low speed the damping force is called “viscoelastic-viscous”. The damping force is expressed in the form of fractional derivative of position [340,364–368], with damping constant c. In this chapter, the order of fractional derivative is taken as q, which varies continuously with position on the guide where the body moves. This forms a continuously variable-order viscosity (or friction) mass-spring damper system. The damping force (or frictional force) is given by Fd=−cDtqx(t), where the order of fractional derivative is varying continuously.
Parabolic effects of viscosity on dispersion and stability of millimeter-scale W1/O/W2 double droplets for ICF polymer shells
Published in Journal of Dispersion Science and Technology, 2022
Qiang Chen, Yong Huang, Meifang Liu, Zhanwen Zhang, Qiang Yin
To investigate the interactions (collision) between the solid particles during the movement and dispersion inside the rotating shear flow field, the DEM based soft sphere model is introduced. The particle–particle and particle–wall interactions are obtained by a viscoelastic model containing a spring, a dashpot and a friction slider. The spring and the dashpot are adopted to model the deformation of the particles and the damping effects during the collisions, respectively. The friction slider is introduced to model the sliding frictions between particles. Moreover, the particle–particle contact force caused by the collision is decomposed into normal and tangential forces (Fnij and Ftij). The normal and tangential forces can be respectively written as:
Evaluation of the effect of cone geometry on spouted bed fluid dynamics by CFD-DEM simulation
Published in Drying Technology, 2022
The spring-dashpot collision law requires the definition of a spring constant (K), as in the spring collision law, along with a coefficient of restitution () for the dashpot term: in which: where is a loss factor, and are the masses of particles 1 and 2, respectively, is the so-called “reduced mass”, is the collision time scale, and are the velocities of particles 1 and 2, respectively, is the relative velocity, and is the damping coefficient.
Fatigue life estimation of continuous girder bridges based on the sequence of loading
Published in Structure and Infrastructure Engineering, 2021
Anjaly J Pillai, Sudip Talukdar
The dynamic response of the bridge was found to be significantly affected by road surface roughness in several bridge-vehicle interaction studies. Schenk and Bergman (2003) evaluated the response of a continuous system subjected to a moving load over randomly varying road surface which did not depend on ideal white noise function. Coussy, Said, and van Hoove (1989) analysed the dynamic response of the bridge subject to moving loads carrying shock absorber, spring and dashpot. The dynamic behaviour of multi-span continuous bridges was studied by various researchers using numerical and analytical techniques (Chatterjee, Datta, & Surana, 1994; De Salvo, Muscolino, & Palmeri, 2010; Ichikawa, Miyakawa, & Matsuda, 2000; Johansson, Pacoste, & Karoumi, 2013). Marchesiello, Fasana, Garibaldi, and Piombo (1999) solved the dynamic response of continuous bridges by modelling the bridge as a multi-span continuous orthotropic plate. The dynamic analysis of a two-span continuous beam considering road surface irregularities were studied by Shin, An, Sohn, and Yun (2010), and Kwark, Choi, Kim, Kim, and Kim (2004). Stancioiu, Ouyang, Mottershead, and James (2011) experimentally studied a four-span continuous flexible structure. The dynamic response of three span continuous bridge is addressed by Mu and Choi (2014) wherein bridge-vehicle interaction is taken into account and was solved combining both Newmark Method and Newton–Raphson Method.