Simulation and experimental studies of a vibro-impact capsule system driven by an external magnetic field

This paper studies the electromagnetic field used for driving a vibro-impact capsule prototype for small bowel endoscopy. Mathematical models of the electromagnetic field and the capsule system are introduced, and analytical solution of the magnetic force applied on the capsule is derived and verified by experiment. The impact force between the inner mass of the capsule and the capsule body is also compared via numerical simulation and experimental testing. By comparing the capsule’s progressions under different control parameters (e.g. the excitation frequency and duty cycle), the merits of using the vibro-impact propulsion are revealed. Based on the experimental results, the optimised speed of the prototype can achieve up to 3.85 mm/s. It is therefore that the potential feasibility of using the external electromagnetic field for propelling the vibro-impact capsule system is validated.

     

PIV measurements of the flow field inside an enclosed cubical cavity in natural convection

The natural convective velocity field in an enclosed air-filled cubical cavity with two opposing isothermal faces and the remaining four sides having a well-defined linear temperature rise from the cold to the hot face has been measured at different physical orientations and Rayleigh (Ra) numbers. In particular, two components of the velocity at the mid-plane have been measured by using particle image velocimetry (PIV) at Ra = 10⁶ and 6 × 10⁶ at each of two different physical orientations: heating-from-the-side (HFS), and heating-from-below (HFB). The 95% confidence limit uncertainties in the measured velocity vectors are about 2% for laminar flow. The accuracy and integrity of the experiments were validated by the comparison to some well-established CFD results at the HFS orientation at Ra = 10⁶. It was concluded that the experimental method is sound and so findings at other orientations and at other values of Ra should have an accuracy consistent with the findings of the uncertainty analysis. Therefore, the other results can be confidently used as benchmark data for testing CFD codes. The turbulence intensities at the mid-plane are also presented.     

Numerical and experimental study on parameters distribution inside a two-phase ejector

The two-phase flow process in an ejector was numerically and experimentally studied using R141b as a working fluid. A modified one-dimensional gas–liquid ejector model was proposed to remedy the defect in the traditional one. Gas–liquid boundary layer regions were discussed and used to close the model. Mac Cormack method is used to discrete controlling equations of gas–liquid two-phase flow in the ejector. The radial distribution of velocity and temperature, the variation of void fraction, the axial velocity variation and the influence of primary steam pressure on the mixing process were predicted with the numerical model. An experimental rig was set up to validate the model by comparing the experimental pressure distribution in the ejector with the calculating one.     

Numerical and experimental study of driven flow in a polar cavity

A numerical and an experimental study of the flow of an incompressible fluid in a polar cavity is presented. The experiments included flow visualization, in two perpendicular planes, and quantitative measurements of the velocity field by a laser Doppler anemometer. Measurements were done for two ranges of Reynolds numbers; about 60 and about 350. The stream function-vorticity form of the governing equations was approximated by upwind or central finite-differences. Both types of finite-difference approximations were solved by a multi-grid method. Numerical solutions were computed on a sequence of grids and the relative accuracy of the solutions was studied. Our most accurate numerical solutions had an estimated error of 0.1 per cent and 1 per cent for Re = 60 and Re = 350, respectively. It was also noted that the solution to the second order finite difference equations was more accurate, compared to the solution to the first order equations, only if fine enough meshes were used. The possibility of using extrapolations to improve accuracy was also considered. Extrapolated solutions were found to be valid only if solutions computed on fine enough meshes were used. The numerical and the experimental results were found to be in very good agreement.     

Investigation of the fluid temperature field inside a flat-plate solar collector

An experimental study was conducted to investigate fluid temperature fields inside a flat-plate solar collector tube. The results show the highest fluid temperature at the upper end of the tube which decreased gradually to the lowest value at the bottom end of the tube, whereas, the temperature field in the horizontal plane is symmetric about the centerline. The vertical temperature gradients vary with the axial distance. The local fluid temperature increased nonlinearly along the collector length and its magnitude decreased with an increase in the Reynolds number. The local Rayleigh number increased with the axial distance and at a given location, its magnitude increased with a decrease in the Reynolds number, whereas, the local Nusselt number trends in flat-plate collector tube are in general similar to that in the conventional laminar channel flows. The local fluid temperature increased with an increase in the incident heat flux at a given collector orientation but decreased for the inclined collectors. The results show that over the given Reynolds number range, the fluid in a flat-plate collector tube is stably stratified over most of the fluid cross-sectional domain and the convective currents are suppressed and restricted to a thin layer adjacent to the lower tube wall. The results from the present study provide the physical explanation for the heat transfer enhancement by insert devices. That is, the insert devices disrupt the stably stratified layer and induce mixing which enhances the heat transfer.     

Numerical and experimental study of the forced convection inside a rotating disk-cylinder configuration

In this paper, axisymmetric bulk flow patterns generated by moderate disk rotation and counter-rotation inside a coaxial disk-cylinder configuration with a fixed aspect ratio are obtained both experimentally and numerically. Experimental results are based on chronophotographic visualization and image processing techniques, while numerical results are computed using the full stationary Navier-Stokes equations assuming two different dynamic boundary conditions (no-slip and meridional free-slip) for all rigid walls. A comparative analysis between both numerical distributing and the patterns obtained experimentally is carried out in terms of streamfunction and vorticity meridional distributions.     

Numerical and experimental study of heat transfer in a tall vertical closed cavity

In this work the numerical and experimental results of heat transfer in a vertical tall closed cavity are presented. The cavity has an aspect ratio of 20, one of the vertical walls receive a constant and uniform heat flux, while the opposite wall is kept at a constant temperature. The remaining walls are assumed adiabatic. The cavity is full of air. The computational fluid dynamics software Fluent 6.3 was used for the simulation and an experimental prototype was built to obtain the heat transfer coefficients. The air temperature and the fluid velocity values are higher when emissivity (ε) is 0.03 (almost pure natural convection). The experimental total heat transfer coefficient increases between 119.9 and 159.9 % when the emissivity of the walls changes from 0.03 to 0.95.     

Numerical and experimental study of an innovative pipeline design in a granular pneumatic-conveying system

During gas–solid mixture conveying in a dense phase, material is conveyed in dunes on the bottom of the pipeline, or as a pulsating moving bed. This phenomenon increases the pressure drop and power consumption. We introduce a new technique to reduce the pressure drop, which is termed the perforated double tube. To validate this new model, the gas–solid flow pattern and pressure drop were studied numerically and experimentally. The power consumption was also studied experimentally. Numerical studies were performed by the Eulerian–Lagrangian approach to predict gas and particle movement in the pipeline. Comparisons between the numerical predictions and the experimental results for the gas–solid flow patterns and pressure drop show good agreement.     

Dynamic strain of a conducting half space with a cavity in a strong magnetic field

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 6, pp. 16–20, November–December, 1991.     

Further studies on the hrr field of a moving crack, an experimental analysis

An improved moire interferometry was used to record simultaneously both the vertical and horizontal displacements associated with stable crack growth in uniaxially loaded 5052H32 aluminum, single-edge-notched specimens. For stable crack growth up to 2 mm, the vertical displacement field showed the dominance of the HRR field. The HRR field was detected in the horizontal displacement only at the initial stage of loading. The far and near field J-integrals were path independent during this incremental crack extension period. These and previous results involving 2024-0 and 2024-T3 aluminum specimens indicate that J-characterization of a crack is not valid for these ductile materials in this specimen configuration.     

Numerical analysis of characteristic features of shallow and deep cavity in supersonic flow

Flow past open cavities are numerically simulated at a Mach number of 1.5, and Reynolds number, based on initial momentum thickness at the front lip of cavity, of 3333 for variable depths (D) with constant length (L). The dominant frequency of oscillation shows a sudden jump when there is a transition from shallow (L/D > 1) to deep cavity (L/D < 1). The vorticity thickness displays two different growth rates along the length of cavity: (1) initial lower spreading rate, followed by (2) higher spreading rate. The lower spreading rate of shear layer is dictated by the type of cavity (either shallow or deep), while the higher spreading rate is directly related to the amplitude of oscillations. Proper orthogonal decomposition (POD) is implemented to visualise the coherent structures based on their energy content. The first two POD spatial structures in the shallow cavity represent vortex shedding, while in the deep cavity, they comprise vortex pairing interactions as in mixing layer. The higher POD modes contain coherent structures at mixed frequencies. The behaviour of coherent structures associated with a temporal frequency is further investigated using dynamic mode decomposition (DMD). The higher DMD modes confirm the dominance of mixing layer behaviour in the deep cavity.     

Numerical and experimental studies on the hydrodynamic damping of a zero-thrust propeller

Fluid added mass and damping are significant parameters when predicting the dynamic response of a submerged structure. The hydrodynamic damping of underwater rotating machinery is numerically and experimentally investigated by a zero-thrust propeller in this paper. The lifting surface method(LSM) combined with forced vibration was introduced as the numerical method to compute the corresponding unsteady thrust, while the experimental method of measuring added damping was accomplished by a propeller undergoing rotation combined heave motion. Results of the theoretical method are in good agreement with the experimental results before cavitation occurs, as cavitation is regarded to weaken the unsteady response of the propeller partly. The calculation results also show that both the frequency ratio(vibration frequency divided by rotation frequency) and the blade angle have a significant influence on the hydrodynamic damping. Therefore, the effect of blade angle on hydrodynamic damping should be considered during the design phase.     

Trajectories of a ball moving inside a spherical cavity using first integrals of the governing nonlinear system

Nonlinear Dynamics - Analytical study of ball vibration absorber behavior is presented in the paper. The dynamics of trajectories of a heavy ball moving without slipping inside a spherical cavity...     

Design of an experimental set up for convective drying: experimental studies at different drying temperature

An experimental setup is designed to investigate the convective drying of moist object experimentally. All the design data, components of setup, materials and specifications are presented. Transient moisture content of a rectangular shaped potato slice (4 × 2 × 2 cm) is measured at different air temperatures of 40, 50, 60 and 70 °C with an air velocity of 2 m/s. Two different drying rate periods are observed. Results are compared with available results from literature.     

Numerical investigation of the temperature field in a reservoir with a hydraulic fracture

The temperature distribution in a reservoir with a hydraulic fracture is studied by numerical modeling of transient temperature fields taking into account the Joule–Thomson effect and the adiabatic effect. It is shown that the presence of a hydraulic fracture in the reservoir leads to a nonmonotonic change in the reservoir temperature: as the well pressure decreases, the temperature first decreases due to the adiabatic expansion of the fluid and then increases due to the Joule–Thomson effect. As the water–oil displacement front approaches the wellbore, the temperature decreases slightly due to heat exchange in the fracture–reservoir system.     

Numerical study of two-phase flow in a square cavity under magnetic field of parallel wires

Meccanica - In this paper, a two-phase model is administered to investigate natural convection of Fe3O4–water ferrofluid in a square cavity and under turbulent regime. Ferrofluid flow is...     

Unsteady phenomena of an oscillating turbulent jet flow inside a cavity: Effect of aspect ratio

Self-sustained oscillatory phenomena in confined flow may occur when a turbulent plane jet is discharging into a rectangular cavity. An experimental set-up was developed and the flow analysis has been made using mainly hot-wire measurements, which were complemented by visualisation data. Previous studies confirmed that periodic oscillations may occur, depending on the location of the jet exit nozzle inside the cavity, and also the distance between the side-walls. The present study deals with the symmetrical interaction between a turbulent plane jet and a rectangular cavity and the influence of the geometrical characteristics of the cavity on the oscillatory motion. The size and aspect ratio of the cavity were varied together with the jet width compared to that of the cavity. The study is carried out both numerically and experimentally. The numerical method solves the unsteady Reynolds averaged Navier–Stokes equations (URANS) together with the continuity equation for an incompressible fluid. The closure of the flow equations system is achieved using a two-scale energy-flux model at high Reynolds number in the core flow coupled with a wall function treatment in the vicinity of the wall boundaries. The fundamental frequency of the oscillatory flow was found to be practically independent of the cavity length. Moreover, the oscillations are attenuated as the cavity width increases, until they disappear for a critical value of the cavity width. Contour maps of the instantaneous flow field are drawn to show the flow pattern evolution at the main phases of oscillation. They are given for several aspect ratios of the cavity, keeping constant values for the cavity width and the jet thickness. The proposed approach may help to investigate further the oscillation mechanisms and the entrainment process occurring in pressure driven jet–cavity interactions.     

Scattering of a pulsed Rayleigh wave by a spherical cavity in an elastic half space

The time-dependent scattering by a spherical cavity in an elastic half space is considered. The incoming wave is a pulsed Rayleigh wave. The stationary part of the problem is solved by the T-matrix method, and an integration in frequency is performed with a modified gaussian weight function. The displacement components at some points on the surface of the half space are computed and shown in a number of plots.