Zhaohui (George) Qin, Ph.D.https://works.bepress.com/george_qin/Recent works by Zhaohui (George) Qin, Ph.D.en-usCopyright (c) 2019 All rights reserved.Tue, 01 Sep 2015 07:00:00 +00003600Use of Computational Fluid Dynamics to Model Free Surface Effects on Hydrofoil Systemshttps://works.bepress.com/george_qin/17/Tue, 01 Sep 2015 07:00:00 +0000https://works.bepress.com/george_qin/17/Conference ProceedingsUse of Athena Vortex Lattice for Preliminary Hydrofoil Designhttps://works.bepress.com/george_qin/16/Tue, 01 Sep 2015 07:00:00 +0000https://works.bepress.com/george_qin/16/Conference ProceedingsA Statistical Model of Pressure Drop Increase with Deposition in Granular Filtershttps://works.bepress.com/george_qin/15/<p>As deposits accumulate in a granular filter, pressure drop across the filter bed required to maintain a constant fluid flow rate may increase. Two pressure drop increase patterns had been observed. In slow sand filters pressure drop remains unchanged for a certain period of time then increases exponentially with the volume of filtrate; in granular aerosol filters pressure drop increases linearly with the amount of deposits from the beginning of the filtration process. New concepts of homogeneous and heterogeneous depositions were introduced in this paper. A statistical model based on these new concepts was developed. This non-linear model was able to reproduce both observed pressure drop increase patterns, including the linear one. Excellent agreements between the present model and experimental measurements were obtained. It was concluded that the two pressure drop increase patterns were indeed caused by different deposit distributions rather than different pressure drop increase mechanisms.</p>
Sat, 23 Aug 2014 07:00:00 +0000https://works.bepress.com/george_qin/15/Peer-Reviewed PublicationsUsing Computational Fluid Dynamics to Predict Drag on a Boat Hullhttps://works.bepress.com/george_qin/14/For many years Cedarville University’s Solar Boat team has been designing and creating boat hulls. One of the key elements in designing a hull is to decrease the amount of drag or resistance the boat has when moving through the water. Previous mechanical engineering seniors at Cedarville University have attempted to use computational fluid dynamics or CFD to predict the drag on the Solar Boat hull with software called Fluent produced by Ansys. However, they have been unsuccessful due to the complexity when trying to model two phases of flow, e.g. air and water. The project however, was successful in predicting the hull drag of our current Solar Boat design using Fluent. To approach this problem I first needed to create a model of the boat in another program also produced by Ansys called ICEM. This software allowed me to import the 3D model of the Solar Boat from SolidWorks 2013 and create a mesh around it. This mesh is crucial for Fluent to simulate the fluid flow of both the air and water as it interacts with the Solar Boat. Using a two phase volume of fluid, VOF, and k-omega viscous model I was able to reproduce the fluid flow experienced by the boat in real life conditions. The implications of my work are that future Solar Boat teams will be able to use my CFD work to accurately predict hull drag on the Solar Boat before having to create the actual boat which can be very costly. With a little bit of work and time the Solar Boat team will now be able to design a new hull and predict hull drag to check for improvements. Additional gains have been made in the way of modeling two phase flow in Fluent which will be critical when analyzing hydrofoils which may be used on the Solar Boat in the future.Wed, 16 Apr 2014 20:20:00 +0000https://works.bepress.com/george_qin/14/Conference PresentationsParticle Impact Theory Including Surface Asperity Deformation and Recoveryhttps://works.bepress.com/george_qin/5/<p>A new particle impact theory was proposed, which incorporated plastic deformation and elastic recovery of surface asperities into the overall energy balance of the impact process. Asperity heights were assumed to follow a truncated Gaussian distribution. The energy transfer associated with the deformation and recovery of asperities was derived based on the previous theoretical treatments of thermal contact resistance. It was found that even nanometer level roughness had significant effects on the rebound of micron size particles. The energy loss thus caused could explain the mysterious strong power–law dependence on particle size of critical velocity. Measurements of Wall et al. were compared with the theory. Good agreement had been reached between the theory and experiments for both coefficients of restitution and particle size dependence of critical velocity.</p>
Thu, 01 Dec 2011 08:00:00 +0000https://works.bepress.com/george_qin/5/Peer-Reviewed PublicationsOn the Apparent Particle Dispersion in Granular Mediahttps://works.bepress.com/george_qin/4/<p>The apparent particle dispersion in a granular medium due to the combined effects of random granular arrangements and interstitial fluid flow was studied. The particle motion was a two-dimensional random walk on the transverse plane. The corresponding dispersion coefficient was found by sampling all possible trajectories with the aid of two granular media models. The theoretical results were verified by numerical simulation data obtained with commercial CFD software. Reasonably good agreement between the theory and simulation suggests that the present theory may be applied to practical granular system applications.</p>
Tue, 01 Nov 2011 07:00:00 +0000https://works.bepress.com/george_qin/4/Peer-Reviewed PublicationsOn an Integral Related to Two-dimensional Random Walkhttps://works.bepress.com/george_qin/10/Sat, 01 Jan 2011 08:00:00 +0000https://works.bepress.com/george_qin/10/Book ChaptersA Flow Intensification Model for Granular Filter Applicationshttps://works.bepress.com/george_qin/6/<p>A flow intensification model was proposed for calculation of the initial collector efficiency of a granular filter. In this model, the flow acceleration within voids of granular media is taken into account with an intensification factor β. Simple physical argument gives an estimation of β, which should be close to 1/ɛ. Creeping flow is assumed and Happel model is used to represent the granular media. After obtaining the flow field, the initial collector efficiency η0 is calculated from trajectory analysis and compared with experimental data. The reasonably good agreement between the theory and experiments suggests that the current model is physically plausible and potentially useful for granular filter performance prediction if further theoretical development is implemented.</p>
Zhaohui (George) QinMon, 01 Mar 2010 00:00:00 +0000https://works.bepress.com/george_qin/6/Peer-Reviewed PublicationsA Flow Intensification Model for Granular Filter Applicationshttps://works.bepress.com/george_qin/1/<p>A flow intensification model was proposed for calculation of the initial collector efficiency of a granular filter. In this model, the flow acceleration within voids of granular media is taken into account with an intensification factor β. Simple physical argument gives an estimation of β, which should be close to 1/ɛ. Creeping flow is assumed and Happel model is used to represent the granular media. After obtaining the flow field, the initial collector efficiency η0 is calculated from trajectory analysis and compared with experimental data. The reasonably good agreement between the theory and experiments suggests that the current model is physically plausible and potentially useful for granular filter performance prediction if further theoretical development is implemented.</p>
Zhaohui (George) QinSun, 01 Nov 2009 00:00:00 +0000https://works.bepress.com/george_qin/1/Conference PresentationsThe Velocity Field and Instability of Rotating Duct Flowhttps://works.bepress.com/george_qin/11/<p>The velocity field and instability of the flow in a rotating square duct was investigated. The velocity field was obtained for Ekman numbers less than 1/16 by combining a linear Stewartson layer solution, a nonlinear Ekman layer solution, and a local similarity assumption. The transition of the secondary-flow pattern from one pair of vortices to two pairs of vortices was studied with linear stability analysis. The resultant eigenvalue problem was solved numerically. The onset of the instability of the Ekman layer was also studied and found to be relevant to the type A and type B waves. The present theory was compared with the experimental results of Smirnov and Yurkin [Mekh. Zh. Gaza (Fluid Mechanics) 6, 24 (1983)]. The critical rotation numbers for marginal stability of both the Stewartson layer and the Ekman layer were found to be in good agreement with the measurements. The experiments of Döbner [Ph.D. dissertion, Technische Huchschule, Dormstadt (1959)] also revealed a boundary in the parameter space corresponding to the sudden change of the slopes of the drag curves, which was found at least partially related to the wavy instability of the Stewartson layer. A quasigeostrophic method was used to include the effects of Ekman friction in the instability formula. The critical rotation numbers obtained were in qualitative agreement with experimental data. Another phenomenon the experiments discovered was the pulsation of the four-vortex pattern as a certain critical Reynolds number was exceeded. This phenomenon has not yet been explained by the present analysis.</p>
Mon, 01 Oct 2007 07:00:00 +0000https://works.bepress.com/george_qin/11/Peer-Reviewed Publications