CFD modelling of pressure and shear rate in torsionally vibrating structures using ANSYS CFX and COMSOL multiphysics

This paper discusses numerical methodologies to simulate micro vibrations on a nontrivial torsionally oscillating structure. The torsional structure is the tip of a viscosity-density sensor using micro vibrations to measure the fluid properties. A 2D transient simulation of the fluid domain surrounding the tip of the sensor has been conducted in ANSYS CFX and COMSOL Multiphysics software. ANSYS CFX uses a frame of reference to induce the micro vibration whereas a moving wall approach is used in COMSOL Multiphysics for the full Navier-Stokes equation as well as their linearized form. The shear rate and pressure amplitude have been compared between the different numerical approaches. The obtained results show good agreement for both pressure and shear rate amplitudes in all models

FSI of viscosity measuring mechanical resonators : theoretical and experimental analysis

Measuring viscosity online in processes is crucial to maintaining the quality of many chemical and biological processes. The damping induced by the liquid around the resonator is used to determine the viscosity of the liquids. Typical viscosity sensors are probe style and obstruct the piping system, disturbing the flow and creating a potential source of contamination in critical processes. The eventual goal is to design a non-intrusive sensor capable of accurately measuring the viscosity of the liquids without influencing the flow within the pipe. In order to get a deeper insight into the functionality of such a device, a mathematical model has been developed describing the mechanical vibration coupled with the fluid-structure interaction (FSI) models. The shear stresses at the wall have been analysed using the computational fluid dynamics tool OpenFOAM and have been integrated into the derived model. For validation, the model has been tested against the samples. The model is capable of accurately predicting the response of the sensor and can be used as an optimization and design tool

Numerical Modelling of Melt Behaviour in the Lower Vessel Head of a Nuclear Reactor

Acknowledgements The authors would like to thank the EPSRC MEMPHIS multi-phase programme grant, the EPSRC Computational modelling for advanced nuclear power plants project and the EU FP7 projects THINS and GoFastR for helping to fund this work.Peer reviewedPublisher PD

Application of the penalty coupling method for the analysis of blood vessels

Due to the significant health and economic impact of blood vessel diseases on modern society, its analysis is becoming of increasing importance for the medical sciences. The complexity of the vascular system, its dynamics and material characteristics all make it an ideal candidate for analysis through fluid structure interaction (FSI) simulations. FSI is a relatively new approach in numerical analysis and enables the multi-physical analysis of problems, yielding a higher accuracy of results than could be possible when using a single physics code to analyse the same category of problems. This paper introduces the concepts behind the Arbitrary Lagrangian Eulerian (ALE) formulation using the penalty coupling method. It moves on to present a validation case and compares it to available simulation results from the literature using a different FSI method. Results were found to correspond well to the comparison case as well as basic theory

A semi transient methodology for dual time stepping of particle and flow field simulations of an Eulerian-Lagrangian multiphysics solver

Many industrial applications involve particles transported by a carrier fluid flow with additional multi-physical effects such as electromagnetics. The simulation of such processes is computationally expensive especially because of the diverse dimensional and time scales involved. In this study, the time scale for the fluid flow to be stably simulated is shown to be up to 2 orders of magnitude higher than the time scale for a spherical particle to assume carrier flow velocity. A semi-transient solution methodology has been devised, utilizing a dual time stepping approach for the flow and particle simulations. In this methodology, first the flow field is simulated with the larger time step, saving the resultant fields at regular intervals serving as snap shots of the flow. Then between each snap shot, the flow is treated as steady state, facilitating the calculation of the particle trajectory based on the resultant forces. This approach is especially suitable for applications where the particle cloud density is low enough not to have a significant effect on the flow field warranting a one way coupling. The accuracy of the method is established by comparing key performance parameters such as coating transfer efficiency and the homogeneity of the coating obtained from a fully transient simulation. The saving potential in terms of computational resources is also quantifie

Finite Element Modeling and Design of a Pneumatic Braided Muscle Actuator with Multi-functional Capabilities

This paper reports the concept, design and development of a pneumatic braided muscle actuator, able to produce bi-directional force and motion. Such a capability can simplify the design and enhance the capabilities of robotic/automation systems using pneumatic muscles as actuators. Finite element modeling is utilized as a design tool in order to study the feasibility of the concept, where a single braid structure is deformed to produce both contraction and elongation. A 3D-finite element model of the actuator is developed and a number of non-linear quasi-static simulations are performed using the explicit dynamic solver LS-Dyna$\circledR$, to measure the blocked force and free displacement of the actuator. The effect of varying the end-fittings diameter and the length of the inner chamber, on the mechanical characteristics of the actuator is also analyzed. The simulation results are validated through mechanical experimentation performed on the functional prototype. With an actuation pressure of 1 bar, the actuator is able to produce a contraction force of around 80 N, extension force of around 40 N and an overall stroke of >40% of the total length of the actuator. Moreover, the novel actuator has been utilized as main driver for a one degree of freedom variable stiffness joint, as a case study, to demonstrate the usability of the actuator

Impact of fouling on mechanical resonator-based viscosity sensors : comparison of experiments and numerical models

Monitoring fluid properties such as viscosity is crucial in many industrial processes. Viscosity sensors based on mechanical vibrations can offer a solution to monitor the fluid viscosity online. However, such sensors’ sensitivity drop due to fouling and it is a common problem in industrial processes. The goal of the presented study is to investigate the effects of a purely elastic fouling layer on the sensing element of a viscosity sensor using experiments and numerical models. The sensor used in this study is a probe style torsional resonator. The measuring principle of this sensor is correlating the damping of the resonating system to the viscosity-density product of the surrounding fluid. In case of fouling, the characteristics of the resonator are affected by the fouling layer. In the given study, the impact on the damping due to the fouling layer is investigated by conducting the experiments and comparing it with three different numerical models. In experiments, the sensor has been coated with metal in the sensing area. Then, the sensor has been immersed into different fluids to determine the impact of the metal layer on the viscous induced damping. To understand the physical implications of the deposit on the resonating system three different numerical models have been developed. These models describe the resonator with increasing degree of detail. First model is using single mass spring system, second model is two masses with three springs system, and third model is 3D structural model solved in COMSOL® Multiphysics. In all of the above models, the fluid-structure interaction is weakly coupled with an analytical solution for the flow field. These models are compared and tested against the experiments