bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Automotive Hydrobushing in Off-Axis Vibration
Authors: Lu Min , Ari-Gur Judah , Garety John
Published: November 2021

A model was developed for the dynamic behavior of a misaligned hydrobushing, which is forced to oscillate in directions that are not aligned with the axis of the fluid chambers. It was found that the displacement of the fluid in the inertia track and of the equivalent piston peak at the fluid resonant frequency, but they decrease when the off-axis angle increases. Similarly, the fluid pressure difference between the chambers peaks at the fluid resonant frequency and it decreases when the off-axis angle increases. The dynamic stiffness and loss angle are functions of the off-axis angle and become less and less sensitive to the frequency when the off-axis angle increases. At high frequencies, the dynamic stiffness is the sum of the static stiffness and the equivalent volumetric stiffness. A comparison of the measured and calculated equivalent volumetric stiffness shows good correlation. But further work is needed to improve the accuracy of the dynamic stiffness and loss angle prediction.
The Generalized Shooting Arc-Length Method for Periodic Solutions and the Corresponding Periods of Nonlinear Dynamical Systems
Authors: Li Dexin , Xu Jianxue
Published: November 2021

In this paper, a generalized shooting/arc-length method for determining periodic orbit and its period of nonlinear dynamical system is presented. At first, by changing the time scale the period value of periodic orbit of the nonlinear system is drawn into the governing equation of this system. Then, by using the period value as a parameter, the shooting/arc-length procedure is taken for seeking such a periodic solution and its period simultaneously. The value of increment changed in iteration procedure is selected by using optimization method. The procedure involves the detennining of periodic orbit and its period value of the system. Thereby, the periodic orbit and period value of the system can be sought out rapidly and precisely. At last, the validity of such method is verified by determining the periodic orbit and period value for van der pol equation and nonlinear rotor-bear system.
Combination Resonance of a Magnet Over a High-TC Superconductor Excited Vertically
Authors: Sugiura Toshihiko , Kondo Masayuki
Published: November 2021

This research deals with nonlinear dynamics of a permanent magnet freely levitated above a high-Tc superconductor (HTSC) excited in the vertical direction. Magnetic force and torque can be evaluated analytically by the advanced mirror image method as nonlinear functions of both displacement and roll angle of the magnet. Equations of 3 d.o.f. motion show that the magnet has two oscillation modes due to linear coupling of the horizontal and roll motions. The both modes can be excited by nonlinear coupling with vertical motion when the superconductor is exited vertically in the neighborhood of the sum of the natural frequency of each mode. Frequency response of this combination resonance was numerically simulated. This resonance was also observed in experiments.
Nonlinear Vibration and Periodicity Analysis of Timoshenko Beams Under Harmonic Base Excitation
Authors: Jalili Nader , Esmailzadeh Ebrahim
Published: November 2021

The parametric response of a cantilever thick beam with a tip mass subjected to harmonic axial support motion is investigated. The governing non-linear equation of motion is derived for an arbitrary axial support motion. To formulate a simple, physically correct dynamic model for the stability and periodicity analyses, the governing equation is truncated to the first characteristic mode of vibration. Using Green’s function and Schauder’s fixed point theorem, the necessary and sufficient conditions for the existence of periodic oscillatory behavior of the beam are established. The influence of the harmonic base excitation parameters, i.e., the excitation amplitude and frequency, on the steady-state amplitude of vibration are determined. Depending on the values of the excitation amplitude and frequency in the stable and unstable regions, the solution exhibits many shapes besides the transition periodic shapes. Numerical results indicate that for a given beam under a known excitation, increasing the tip mass would usually reduce the stable periodic region. To show the effect of rotary inertia and shear deformation, the beam model is reduced to the Euler-Bernoulli and purely flexural beam theories, respectively. The results show that using purely flexural or even Euler-Bernoulli model rather than Timoshenko, would produce an incorrect periodic region.
Experiments on the Active Control of Circular Disk Vibration
Authors: Qiu J. B. , Huang X. Q. , Wang D. Q.
Published: November 2021

Circular disk is a basic mechanical element, which is used widely in industry such as turbine machine, circular saw, and computer memory. Considering the requirements for the actuator to control the transverse vibration of circular disk, the non-contact electromagnetic actuator which can produce large actuating force is used, and a whole set of control system that is composed of analog components is built. The good experimental results are obtained by using the control system to control the transverse vibration of circular disk.
Vibration of Free-Free Two Member Open Frames With End and Elbow Masses
Authors: Heppler G. R. , Oguamanam D. C. D. , Hansen J. S.
Published: November 2021

The vibration of an, in general, unrestrained two member open frame structure undergoing both in- and out-of-plane motion is examined. The frames are modeled using the Euler-Bernoulli beam theory and are further generalized by permitting an arbitrary angle between the beams and the attachment of point masses at the ends and joint (elbow) of the beams. The equations of motion are derived using Hamilton’s principle and the orthogonality conditions are presented. It is shown that the in-plane and out-of-plane motions can be decoupled by including the axial deformation components in the assumed displacement fields. The natural frequencies of the system and the contribution of each member into the system potential energy are examined via numerical examples.
The Bifurcation Behaviors for a 5D Magnetic Levitation Control System
Authors: Yao Hong , Xu Jian-Xue
Published: November 2021

This study concerns the local and global bifurcation behaviors for the 5D magnetic levitation flex-rotator control system. A five dimension dynamic model of the system is constructed and appropriate equations of the nonlinear control system are developed. The co-dimension two local bifurcation is discussed. An analytical method was formulated and used to directly yield two dimension normal forms, and universal unfolding for the case with the non-semisimple double zero eigenvalue about the system; by Melnikov method, global homoclinic bifurcation behaviors are discussed. The conditions of bifurcation for various parameters, bifurcation curve, parameters plane, are obtained. A safe domain for selection of the parameters of the system is given. Finally, the theoretic analysis is proved by simulating for a 5D control system. Hopefully, the breath of the application will indicate the potential of the theoretic analysis.
Robust Stability and Dynamic Analysis of a Special Type of Floating Offshore Structure
Authors: Esmailzadeh E. , Goodarzi A.
Published: November 2021

A comprehensive dynamic model of a catenary anchor leg mooring system has been developed and the governing equations of notion were derived. The equations of motion are found to be nonlinear parametric ordinary differential ones of the order two. The necessary and sufficient conditions, for the existence of a stable periodic response of this system, were found using the Green’s function and Schauder’s fixed-point theorem. The validity of the assumptions has been fully demonstrated with a few case studies. Results obtained from the dynamic modeling reiterate the presence of inherently nonlinear and time-varying characteristics of the system and hence a stability condition in terms of the physical and environment parameters of the system must be sought.
On the Suppression of Flow-Induced Vibration With a Simple Control Algorithm
Authors: Carbonell Pablo , Wang Xiaodong , Jiang Zhong-Ping
Published: November 2021

We present a study on the suppression of flow-induced vibration using a simple control algorithm with an assumption that the disturbance as well as the system parameters are bounded variables. By introducing three different control signals, we explore three schemes, namely, robust control, sliding mode, and adaptive control. The control schemes are implemented numerically with a few illustrative examples, which includes a bounded chaotic system. It is demonstrated that all three schemes can be effectively used for fluid-structure interaction systems. In addition, with these numerical examples, we also illustrate various advantages and disadvantages of different control schemes. In general, robust control and adaptive control schemes are (globally) ultimately uniformly bounded, whereas sliding mode scheme is (globally) asymptotically stable. Thus, as we further reduce the integration time step, the residual of robust control and adaptive control schemes will approach to a bounded (finite) asymptotic function, and the residual of sliding mode scheme will approach to zero. Furthermore, due to self-tuning, the gain of adaptive control scheme is relatively small, yet, the computation cost is higher because of the excessively small time step requirement for the numerical integration. With respect to sliding mode scheme, the control signal is discontinuous due to the sign function and consequently, the practical implementation has fast switching fluctuations (chattering).
Vibration Analysis of Multifunctional Satellite Structure
Authors: Nayeb-Hashemi H. , Vaziri A.
Published: November 2021

Natural frequencies and damping ratios of doubly clamped and cantilever alviminum pipes filled with high pressure gas (Argon or, Xenon fuel) or high pressure liquid (Water) were measured using shaker and hammer test techniques. The results show that natural frequencies and damping are a little sensitive to the pipe internal pressure. The damping ratios were slightly affected by the pipe filler material. However, the natural frequencies of the pipe filled with water was lower compared to those filled with Argon and Xenon fuel. The damping ratios measured using a shaker were almost two orders of magnitude lower than those measured using hammer tests. This could be due to the extra damping induced to the system from the magnetic field of the shaker.
Enhancement for Frequency Domain Based Tool Breakage Detection System
Authors: Hamidieh Youssef A. , Seth Brij B. , Sridhara Raghunandan
Published: November 2021

Effective monitoring of machining operations, for tool breakage and wear in automotive powertrain manufacturing, has proven difficult despite significant activity in industry and universities. Various monitoring schemes have been tried with different sensing strategies and algorithms. Despite these efforts, results have been mixed, with systems working in some operations and not in others or systems requiring too much attention on the plant floor. All this, while the need for reliable monitors, due to emphasis on productivity and quality, continues to increase. Some of the reasons for the limited success of monitoring systems include changing machine condition, variability of cutting edge on tools due to regrind, the variability of incoming part material together with different possible failure modes for the tools. The shortcoming of existing monitoring systems has been even more apparent in multi-spindle and spindle cluster stations whereby a number of tools operate simultaneously, therefore adding to the complexity. The frequency and time domain vibration1 based monitoring strategy described in this paper for breakage detection addresses some of the shortcomings of the available systems by concentrating on discriminants which produce high signal to noise ratio. Also, by recognizing that the tool failure signatures may vary on different machines while performing the same machining operations with similar tools. This can be attributed to different structural characteristics of the spindles and other elements of the machine tools. Therefore, in this paper for the first time, a pre-characterization2 scheme is proposed to capture this vital information and to utilize it for adding further robustness to tool monitoring.
On Axisymmetric Vibration of Annular Plate of Parabolic Thickness Variation by Factorization of Differential Equation
Authors: Caruntu Dumitru I.
Published: November 2021

In the present paper an analytic solution of free axisymmetric vibration of a class of annular plates of parabolic thickness variation is obtained by factorization of the fourth-order differential equation. Poisson’s ratio is taken v = 1/3, applicable to many materials.
Inverse Dynamics of a Planar Flexible-Link Manipulator With Revolute-Prismatic Joints
Authors: Farid M. , Salimi I.
Published: November 2021

This paper proposes an inverse dynamic approach to determie the required actuating torque and force for a planar flexible-link manipulator with revolute-prismatic joints such that its end-point follows a given trajectory. The formulation includes all of the non-linear terms due to large rotation of the links. Since one of the joints is prismatic, the resulting system of equations is time varying too. The results show that by applying actuating loads found by the proposed algorithm, the tracking error becomes smaller than that resulting from actuating loads obtained based on rigid link modeling.
A Solution for the Interior Sound Field With a Nonuniform Temperature Distribution in the Vehicle Passenger Room
Authors: Wu Jiuhui , Chen Hualing
Published: November 2021

A non-linear wave equation in a nonuniform sound space is deduced to determine the coupling relation between sound field and temperature field. Adopting Poisson’s integral a formula for calculating the interior sound field with uneven temperature field and certain initial conditions is developed. This establishes the corresponding theoretical foundation for studying the heat and vibroacoustic comfortability in a vehicle passenger room.
The Vibration Control of a Flexible Linkage Mechanism With Impact
Authors: Jin Chunmei , Qiu Yang , Fan Ling
Published: November 2021

An combined control methodology for suppressing elastic vibration and impact effects in clearance pairs are developed by employing active control of structural vibration and passive control concepts of clearance pairs in the structures. Numerical simulation is performed to evaluate the combined control effect of elastic vibration and impact effects. The analytical results indicate that the elastodynamic response in the mechanism with clearance connections can not be well controlled by using a single control method. Only through using combined control method the elastodynamic response can be controlled favorably and so the feasibility of combined control method is proved.
Dynamic Analysis of a Slider-Crank Mechanism With Flexible Connecting Rod and Viscous Friction
Authors: Zhang Jinfu , Xu Qingyu , Zhang Ling
Published: November 2021

The equation of motion for the slider-crank mechanism with flexible connecting rod and viscous friction are formulated using Lagrange equation. Viscous friction and coupling effect between rigid body motion and elastic deformation are considered in the formulation. Numerical results show that viscous friction and flexibility of connecting rod have effects on motion of the mechanism.
Reliable Subjective Assessment of Vehicle Handling by Drivers: Is it an Elusive Goal?
Authors: Crolla D. A. , Whitehead J. P.
Published: November 2021

Much progress has been made over recent years in understanding many aspects of driver-vehicle interactions, for example, linked to ergonomics/comfort of the cabin, influence of improved safety systems, interactions with ITS systems etc. However, in more dynamic situations, similar levels of understanding have not been achieved. Such dynamic events range from whole body motions such as vehicle handling and ride to component behaviour including, in particular, steering wheel feel and gearshift quality.
Nonlinear Active Rollover Prevention Control Strategies for a 5-Axle Tractor/Semitrailer
Authors: Lewis A. Scott , El-Gindy Moustafa
Published: November 2021

This paper presents new active control strategies to prevent heavy vehicle rollover and focuses mainly on cases of maneuver-induced rollover such as rollover in cornering and lane-change maneuvers. Two performance measures as control strategies are explored: the lateral load transfer ratio and the trailer lateral acceleration. A nonlinear 75,000 pound 5-axle tractor/semitrailer computer simulation model has been used to demonstrate the effectiveness of the proposed active control system. A new non-linear sliding mode controller has been designed and found to be effective in improving the dynamic performance and roll stability, regardless of parameter uncertainties, such as tires or suspension characteristics. The controller torque requirement is limited by the differential dynamic braking forces that the tractor drive axles are able to produce as a function of the applied dynamic loads and road surface condition. The results show that with this new controller, the vehicle lateral acceleration can be controlled to prevent rollover without significant change of the vehicle trajectory when active yaw torque is applied to the tractor drive axles. Also, simulation results indicate that the vehicle rollover might be prevented using either the lateral load transfer ratio or the lateral acceleration at the trailer centre of gravity as control strategies.
The Use of Modeling and Simulation in Ground Vehicle Analysis
Authors: Letherwood Michael D. , Gunter David D.
Published: November 2021

In support of Department of Defense (DOD) mandated acquisition reform initiatives to reduce vehicle related life cycle costs and timelines, the Tank-automotive and Armaments Research, Development and Engineering Center (TARDEC) is using simulation-based acquisition strategies to investigate the dynamic performance of wheeled and tracked ground vehicles. These strategies are used throughout the vehicle development, testing, and fielding life cycle process. The paper will describe how modeling and simulation (M&S) is applied to answer a wide variety of design and performance evaluation questions. It will also depict a series of simulation-based engineering projects that build on the Army’s simulation investments as a tool to investigate and answer real-world vehicle design, acquisition, and engineering support questions.
Utilising the Potential of Individual Wheel Control on a 6x6 Off-Road Vehicle
Authors: Jackson Andrew , Brown Michael , Crolla David , Woodhouse Adrian , Parsons Michael
Published: November 2021

This paper will present a form of mobility control for a 6x6 Hybrid Electric Vehicle (HEV). The vehicle concerned is a series configured HEV utilising Hub Mounted Electric Drives (HMED) at each of the six wheel stations to provide Individual Wheel Control (IWC). Whereas a conventional vehicle needs individual brake actuators or bulky differentials to vary individual wheel torques, IWC can be realised in this hybrid configuration through software control of each HMED, making it potentially more accurate, responsive and flexible than a mechanically implemented version.

Direct Yaw-moment Control (DYC) is a method of regulating individual wheel torque to control vehicle yaw motion, providing greater stability in cornering. By varying the torque applied to the left and right wheels, tyre forces can be controlled to produce a desired yaw moment. Not only can this be used to aid cornering, but also to reject disturbances, such as side winds, in straight line running. When combined with a Traction Control System (TCS), optimisation of these tyre forces are considered, ensuring that the vehicle handling characteristics remain stable while acceleration performance is improved. When integrating these two systems, consideration is given to the torque demands of each controller. This co-ordinated control ensures that the vehicle takes full advantage of the torque capabilities associated with the electric motor to provide improved vehicle handling, acceleration and stability.

The proposed control algorithms are implemented in MATLAB/SIMULINK on a basic non-linear vehicle handling model utilising a Dugoff tyre model to determine longitudinal and lateral tyre forces. The torque of each individual wheel is controlled to maintain a desired yaw rate and/or wheel slip. The model is then simulated on a number of road surfaces, undertaking a variety of test manoeuvres to assess the potential improvements that the combined controller can offer over a vehicle with fixed-torque distribution. The paper shows how the resultant controller offers a robust method of improving vehicle mobility, providing good stability under varying conditions.
Numerical Simulations of Resonant Heat Transfer Augmentation at Low Reynolds Numbers
Authors: Greiner Miles , Fischer Paul F. , Tufo Henry
Published: November 2021

The effect of flow rate modulation on low Reynolds number heat transfer enhancement in a transversely grooved passage was numerically simulated using a two-dimensional spectral element technique. Simulations were performed at subcritical Reynolds numbers of Rem = 133 and 267, with 20% and 40% flow rate oscillations. The net pumping power required to modulate the flow was minimized as the forcing frequency approached the predicted natural frequency. However, mixing and heat transfer levels both increased as the natural frequency was approached. Oscillatory forcing in a grooved passage requires two orders of magnitude less pumping power than flat passage systems for the same heat transfer level. Hydrodynamic resonance appears to be an effective method of increasing heat transfer in low Reynolds number systems where pumping power is at a premium, such as micro heat transfer applications.
On Low-Dimensional Galerkin Modeling of Confined Twin-Jet Flow and Heat Transfer
Authors: Gunes H. , Gocmen K. , Kavurmacioglu L.
Published: November 2021

The two-dimensional incompressible non-isothermal confined twin-jet flow has been numerically studied in the transitional flow regime by a finite volume technique. Results have been obtained for the velocity and temperature distributions close to the onset of temporal oscillations. Next, the proper orthogonal decomposition (POD) is applied to the instantaneous flow and temperature data to obtain POD-based basis functions for both velocity and temperature fields. These basis functions are capable to identify the coherent structures in the velocity and temperature fields. The low-dimensional Galerkin models of the full Navier-Stokes and energy equations are constructed by the Galerkin projection onto basis functions. Since the low-dimensional Galerkin models are much easier to analyze than the full governing equations, basic insights into important mechanisms of dynamically complex flow and heat transfer (e.g. flow instabilities) can be easily studied by these models. The numerical implications, the validity of the models and their performance characteristics are discussed.
Experimental Flow Field and Heat Transfer Study of a Slot Jet Reattaching Onto a Flat Plate
Authors: Narayanan V. , Seyed-Yagoobi J. , Page R. H.
Published: November 2021

Detailed heat transfer, impingement surface pressure and flow field measurements on a submerged slot jet reattachment nozzle are presented. The nozzle is comprised of a rectangular region of aspect ratio 20:1, with circular ends. The jet exits the nozzle parallel to an adjacent flat impingement surface and reattaches onto it. Contours of local heat transfer exhibit three-dimensionality within the recirculation and reattachment regions with increase in nozzle-to-surface spacing. Mean and time averaged fluctuating surface pressure distribution at the center plane of the nozzle along the minor indicate that the location of peak fluctuating pressure occurs upstream of the peak mean pressure. Flow field measurements are presented for a nozzle-to-surface spacing of 3.85 exit hydraulic diameters from the surface, at a turbulent exit Reynolds number of 10 500. Surface pressure and flow field observations are used to explain heat transfer results in the recirculation and reattachment regions.
Fundamental Heat Transfer Correlations for Natural Convection From a Uniformly Heated Vertical Plate
Authors: Aydın Orhan , Guessous Laila
Published: November 2021

The problem of natural convection from a uniformly heated vertical plate has long been investigated due to its relevance to many industrial applications. Attempts have been made over the years to develop generalized heat transfer correlations that would cover a large range of Prandtl numbers. Here we introduce, on fundamental grounds, a new dimensionless parameter for the correlation of natural convection induced by a vertical plate subject to a constant wall heat flux. This dimensionless parameter, which depends on the Prandtl number, Pr, and the modified Rayleigh number, Ra*, is used to correlate the heat transfer over the entire Prandtl number domain. The development is based on physical and dimensional arguments and leads to correlations relating the laminar Nusselt number to the new parameter. Comparison with published empirical, numerical, and theoretical results leads to excellent agreement over the Prandtl number domain studied, which spans the range between 0.001 and 1000.
Particle Image Velocimetry Measurements of Confined Co-Rotating Vortices in a Square Duct
Authors: Langford Heather M. , Beasley Donald E.
Published: November 2021

The axial development of a paired co-rotating vortex system is experimentally studied in a square duct. The duct confines the vortex system. The co-rotating vortices are shed from a pair of NACA 0012 airfoils in a split-wing configuration. Lateral velocity fields are measured using particle image velocimetry. Time-averaged lateral velocity and axial vorticity fields are used to document the location of the vortices in the lateral flow field. The present study examines the effect of Reynolds number, lateral spacing, and angle attack on the development of the vortex system in a confined geometry.
Single-Phase Turbulent Rod Bundle Heat Transfer
Authors: Armfield Mary V. , Langford Heather M. , Beasley Donald E. , Conner Michael E.
Published: November 2021

The present study investigates single-phase heat transfer coefficients in a 5 × 5 horizontal rod bundle representing a water-cooled nuclear reactor. The rod bundle assembly consists of a square array of parallel rods held in place by support grids. Flow-enhancing features such as disc blockage or split-vane pairs are often added to the downstream edge of the support grids in an attempt to improve the heat transfer performance of the rod bundle assembly. The effects on the local heat transfer coefficients of several support grid designs are examined in the present study.

The local, average heat transfer coefficients are measured using a heated copper sensor for standard, disc, and split-vane pair grid designs. In addition, lateral flow fields are obtained for the split-vane pair grid design using Particle Image Velocimetry (PIV) measurements. Results indicate that the local heat transfer coefficient is enhanced just downstream of the support grids. This enhancement decays to the fully-developed value of heat transfer by five hydraulic diameters downstream of the support grid for all of the grid designs. Heat transfer measurements of the split-vane pair grid design indicate a region of decreased heat transfer below the fully-developed value. Identification of swirl migration and weak exchange of fluid between subchannels in the lateral flow fields of the split-vane pair grid design provides insight into the decreased region of heat transfer.
Numerical Simulations and Experimental Investigations of the Flow Field and Heat Transfer of Fin-and-Tube Heat Exchangers
Authors: Bender Jens K. , Schmidt Roland K. , Koehler Juergen
Published: November 2021

The investigation of the flow field and heat transfer of fin-and-tube heat exchangers is presented. The numerical simulation is focused on the heat transfer, whereas the emphasis of the experimental investigation is put on the flow field.

The numerical calculations are carried out with the CFD-Code “Fluent”. The highly complex geometry of the heat exchanger is modelled by CAD, covered by a hybrid mesh, and simulated using finite-volume-technique. The results of the overall pressure drop and heat transfer are compared with measurements made by the authors as well as with other experimental data available in the literature.

For the experimental set-up a heat exchanger model was designed using perspex that allows measurements with PIV technique. The investigations concentrate on the influence of different geometries (tube diameters, tube distances, etc.).
A Numerical Study of the Effect of Subcooling on Natural Convection in a Densified Cryogenic Propellant
Authors: Akyuzlu K. M. , Antoniou A. , Manalo L. , Nguyen K.
Published: November 2021

A numerical study is conducted to investigate the effect of subcooling on natural convection in a densified cryogenic propellant. It is assumed that the cryogenic propellant (liquid oxygen in this study) is subcooled through a densification unit and then stored in a cryogenic tank which is pressurized with helium. Natural circulation in the propellant is initiated by the heat leak through the walls of the cryogenic tank that sets up a thermal stratification in the liquid with time. A two dimensional (radial and axial) single domain (liquid) mathematical model is adopted to investigate this transient phenomenon. The physics based mathematical model consists of conservation of mass, momentum, and energy equations for the liquid subjected to prescribed temperature (saturation temperature for the ullage pressure) at the vapor-liquid interface and constant wall heat flux boundary condition at the walls of the container. The density of the propellant is assumed to be temperature dependent only in the buoyancy term of the momentum equation (Boussinesq approximation.) The transport properties of the fluid are assumed temperature dependent in all of the equations. The resulting nonlinear governing equations are solved by an explicit finite-difference technique to predict the transient velocity and temperature fields inside the propellant. Finally, numerical simulations are carried out to study the effect of subcooling on thermal stratification using the proposed model.
A Numerical Study of the Development of Unsteady Three-Dimensional Natural Convective Flow in a Horizontal Enclosure With a Uniform Heat Flux on the Lower Surface
Authors: Oosthuizen Patrick H.
Published: November 2021

Flow in a rectangular enclosure with a square horizontal cross-section and with a uniform heat flux applied across the lower horizontal surface and with the upper horizontal surface cooled to a uniform low temperature has been considered. The vertical side-walls of the enclosure are adiabatic. It has been assumed that the flow is laminar and that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces. In this situation, there is no flow in the enclosure at low Rayleigh numbers, steady flow in the enclosure at intermediate Rayleigh numbers and an unsteady flow in the enclosure at high Rayleigh numbers. The conditions under which unsteady flow develops have been numerically investigated in the present study. The unsteady form of the governing equations, written in terms of the vector potential and vorticity vector functions and expressed in dimensionless form, have been solved using a finite-difference procedure. The solution was started with no flow in the enclosure. The solution, in general, has the following parameters: the heat flux Rayleigh number Raq, the Prandtl number and the aspect ratio A of the enclosure, i.e. the ratio size of the height of the enclosure to the size of the square cross-sectional shape of the enclosure. Results have only been obtained for a Prandtl number of 0.7. Results for values of A between 1.25 and 3 for various values of Rayleigh number (up to 80000) have been obtained. The results have been used to determine the effect of A on the value of Rayleigh number above which there is unsteady fluid motion in the enclosure.
Stochastic Modelling of Scalar Transport in Turbulent Flows Based on Conditional Moment Closure
Authors: Klimenko A. Y. , Wandel Andrew P. , Smith Nigel S. A.
Published: November 2021

The difficulties of modelling transport of scalar properties (such as temperature and concentrations) in physical space are well-known. It is conventional to call the turbulent scalar transport as turbulent diffusion. However, if a strict mathematical definition of the term “diffusion” is to be used, this stochastic process is not a diffusion process since its characteristic time is quite long. That is why the gradient-based approximations of the turbulent fluxes, which are precise for the diffusion transport, may have some difficulties when dealing with a turbulent flow. In the present work, we investigated an alternative formulation of the turbulent scalar transport: the transport of one scalar with respect to another scalar. Using DNS data, we demonstrated that this transport can be much better approximated by a diffusion process than the turbulent scalar transport in physical space. This property is effectively used in Conditional Moment Closure (CMC) which deals with turbulent transport of reactive scalers (i.e. scalars participating in chemical reactions) with respect to the conserved scalar.

The similarity with diffusion processes can be used to numerically simulate this process by stochastic differential equations. Although solving such equations would be much easier than using DNS to predict characteristics of the turbulent scalar transport, the idea needs a proper theoretical analysis due to the complicated structure of CMC equations which have, in their conserved form, both forward and inverse parabolic terms. In the present work, we also demonstrated how the CMC equations can be properly represented by a stochastic model.
Swirling Effect on Thermal-Fluid Transport Phenomena in a Strongly Heated Concentric Annulus
Authors: Torii Shuichi , Yang Wen-Jei
Published: November 2021

A numerical study is performed to investigate thermal transport phenomena in circular Couette flow in a concentric annulus, in which an axially rotating inner cylinder and stationary outer cylinder are strongly heated under the same heat flux condition. The anisotropic t 2 ¯ - ε t heat-transfer model together with the anisotropic k-ε turbulence model is employed to determine thermal eddy diffusivity. When the inner cylinder is at rest, the turbulent kinetic energy and temperature variance substantially diminish over the whole annular cross-section along the flow, resulting in laminarization, i.e., a deterioration in heat-transfer performance at the inner and outer cylinder walls. In contrast, a substantial reduction in the turbulent kinetic energy and temperature variance in the laminarizing flow is suppressed in the presence of inner core rotation. In other words, inner core rotation contributes to the suppression of laminarization in a strongly heated gas flow. These characteristics in thermal fluid flow with temperature-dependent thermal property are summarized in the form of dimensionless heat flux parameter versus inlet Reynolds number with the Taylor number, as the parameter.
Chracteristics of Dehumidifying Fin and Tube Heat Exchangers for Various Wettability Surfaces
Authors: Ahn S. P. , Lee H. U. , Ha S. C.
Published: November 2021

Generally, the air-side pressure drop is known to be dependent on the wetting surface of fin and tube heat exchanger (coil) in an air-conditioning system. Filmwise condensation occurs in good hydrophilic surface having a smaller contact angle on the fin. Thus, many hydrophilic coated materials were developed and applied to heat exchangers to decrease pressure drop in wet condition. This experimental study investigated the characteristics of dehumidifying fin and tube heat exchangers for various wetting surfaces and durabilities. This study proposed that the air-side wet/dry pressure drop ratio (ΔPwet/ΔPdry) can be correlated with the advancing dynamic contact angle and the water droplet diameter. Also, the heat exchangers were accelerated with 200 cycles in which they were dipped into distilled water for 60 minutes and dried with a fan for another 60 minutes consecutively for evaluating the wetting durability performance.
A Microdevice for Measuring Thermophysical Properties of Nanowires and Nanotubes
Authors: Shi Li , Kim Philip , McEuen Paul L. , Majumdar Arunava
Published: November 2021

Nonotubes and nanowires are expected to have interesting thermophysical properties. For example, unusually high thermal conductivity and possibly low-temperature quantized thermal conductance have been predicted for carbon nanotubes (Berber et al. 2000). Meanwhile, other nanowires, such as Bi wires, may have suppressed thermal conductivity and high thermoelectric figure of merit (Volz and Chen). However, there lacks of experimental proof of these predictions because there are no established methods to measure the thermophysical properties of nanotubes and nanowires. Up to date, there are very few measurement data of thermal properties of nanotubes as well as nanowires (Hone et al. 1998, 1999, and 2000; Mizel et al., 1999). To provide a platform for concurrently measuring thermal conductivity and Seebeck coefficient of nanotubes and nanowires, a microdevice has been designed and used for measuring multiwall carbon nanotubes (MWCNs). Figure 1 shows the scanning electron micrographs of the microdevice. The device is a suspended structure consisting of two adjacent 10 μm × 10 μm silicon nitride (SiNx) membranes or islands suspended with three (or four) 200-μm long and 2 μm wide silicon nitride beams. One 30 nm thick, 200 nm wide, and 150 μm long platinum (Pt) heater/thermometer coil was built on each island. The heater coil is connected to contact pads with 200 μm long and 1μm wide Pt lines.
Two-Dimensional Nanoscale Heat Conduction Using Ballistic-Diffusive Equations
Authors: Yang Ronggui , Chen Gang
Published: November 2021

It is well recognized that heat conduction in micro- and nanoscale and in ultrafast processes may deviate from the predictions of the Fourier law, due to boundary and interface scattering and the finite relaxation time of heat carriers. The Boltzmann equation is often used with the relaxation time approximation to study classical size effect. However, the solution of Boltzmann equation has been limited to few simple geometrical configurations such as thin films and superlattices. In this paper, we apply the transient ballistic-diffusive equation (BDE) to study the two-dimensional nonlocal phonon transport phenomena. The numerical calculation strategies developed in this paper can be promising for incorporating into commercial device simulator.
Rotation of Laser Opto-Microactuator With Low-Heat-Conductivity Material
Authors: Ota Masahiro , Noguchi Atsunobu
Published: November 2021

A laser opto-microactuator with four flat blades made of aluminum or Pyrex glass plates is proposed in this paper. The effects of the heat conductivity of the actuator materials on rotation phenomena are discussed. Through molecular gas dynamics effects, the actuator is rotated upon irradiation by an argon-ion laser beam. The blade surfaces of the actuator were coated with carbon black powder to absorb laser beam power and heat the surfaces. Three kinds of blades, noncoated, single-side-coated and both-sides-coated blades, were manufactured.

The rotation rate of the actuator with both surfaces of one blade coated with the powder is faster than that of the actuator with only one surface coated with the powder because the total amount of radiation from the both-sides-coated surface is greater than that of a single-side-coated surface.
Compressible Gas Flow Through Smooth and Rough Microchannels
Authors: Turner Stephen E. , Gregory Otto J.
Published: November 2021

This paper presents an experimental investigation on compressible gas flow through microchannels with a constant area, rectangular cross-section. The microchannels are etched into silicon wafers, capped with smooth glass, and have hydraulic diameters between 4 and 100 μm. All measurements were made in the laminar flow regime with Reynolds numbers ranging from 0.02 to 1000. Smooth channels were obtained by etching (100) silicon wafers with potassium hydroxide (KOH) solution. Rough channel surfaces were obtained by etching (110) silicon wafers with KOH. The investigation shows that the friction factor for both smooth and rough microchannels compares closely with continuum theory.
Analytical Investigation of the Effect of Thermal Dispersion on Forced Convection in Heterogeneous Porous Media
Authors: Kuznetsov A. V.
Published: November 2021

This paper presents a new analytical solution of a problem of forced convection in a heterogeneous channel filled with two different layers of isotropic porous media. The Brinkman-Forchheimer-extended Darcy equation is utilized to describe the fluid flow in the porous layers, and the effect of transverse thermal dispersion is accounted for in the energy equations. Three momentum boundary layers are identified in the channel: a boundary layer at the solid wall and two boundary layers at the interface between the porous media. The dependence of the Nusselt number on the Darcy numbers, Forchheimer coefficients, and particle Reynolds numbers in different parts of the channel is investigated. This study demonstrates that thermal dispersion has a strong effect on the Nusselt number in the channel for large particle Reynolds numbers.
Numerical Simulation for the Process of Recovery of a Planar Reservoir With Non-Newtonian Petroleum
Authors: Zhu Zuojin , Wu Qingsong , Gao Chunfu
Published: November 2021

The numerical simulation has been carried out for the process of the recovery of a reservoir with non-Newtonian Petroleum in terms of the stablized bi-conjugate gradient approach. To propose the governing equations for the problem on hand, the traditional Darcy law for flow in porous media is used to describe the flow behavior of water as the driving fluid, and the rheological relation for the so-called Bingham fluid is employed to describe the flow behavior of the driven non-Newtonian petroleum. The pressure potential and the water saturation are used as the primary variables. The two phase fluids system is considered to be a subsurface immiscible and micro compressible one. The solutions of the transient planar two phase flow problem in porous media have been sought with the corresponding outer and inner boundary conditions. The finite difference scheme has been used to approximate the governing equations for the problem considered. To keep the approximation physically effective, the upwind weighted treatment for the relative permeability at mesh surface is provided. Newton-Raphson iteration is used in view of the existence of non-linearity. And finally, the stablized bi-conjugate gradient approach is applied to seek the solutions of the corresponding algebraic equations required. A good agreement is obtained between the results of non-Newtonian model and production data, but results of the Newtonian model were unable to yield good agreement with the data.
Forced Convection in a Channel Limited by Permeable Boundaries
Authors: Segrilo Leonardo M. , Martins-Costa Maria Laura
Published: November 2021

A mixture theory model is employed in a local description of the energy transfer in a channel with permeable boundaries which is simulated by considering two distinct flow regions, one consisting of a Newtonian incompressible fluid and the other represented by a binary (solid-fluid) mixture. Compatibility conditions at the interface (pure fluid-mixture) for momentum and energy transfer are considered. The simulations are carried out by using an iterative procedure with a finite difference approach, in which the fluid (in the pure fluid region) and the fluid constituent (in the mixture region) inlet temperatures are the only boundary conditions prescribed on the flow direction.
Some New Approaches to Bubble Plume Modelling Using CFD
Authors: Milelli Massimo , Smith Brian L. , Lakehal Djamel
Published: November 2021

The paper describes some advancements made in using Computational Fluid Dynamics (CFD) techniques in a generic study of venting of gases to liquid pools. The work focusses on the role played by turbulence in promoting pool mixing and, in particular, explores the application of Large Eddy Simulation (LES) methodology to capture bubble-induced turbulence effects. In the first part of the paper, a study is reported involving two-dimensional simulations of a simple, vertical shear layer containing bubbles for which some turbulence data are available from experiments. This work demonstrates particularly the importance of grid size, and its relation to the ratio of the cut-off filter to the bubble diameter. Optimum model parameters derived from this study are then used in a three-dimesional simulation of a free bubble plume, for which the flow is buoyancy-driven rather than shear-induced. Points of similarity (and difference) between the two analyses are discussed and some general conclusions drawn regarding the applicability of using LES techniques for this class of flow.
Experimental Verification of the Performance of a Droplet Injection System for Use in a Rod Bundle Test Facility
Authors: Ireland A. J. , Rosal E. , Hochreiter L. E. , Cheung F. B.
Published: November 2021

A droplet injection system has been developed for use in a rod bundle heat transfer test facility designed specifically for the study of dispersed flow film boiling during reflood transients in a nuclear reactor. Three different injectors having various pitch configurations and hole patterns were tested. The drop field produced by each was characterized using a laser-assisted size measurement technique. Appropriate mean diameter and drop size distributions that closely simulate the drop field encountered in a reactor bundle assembly under reflood conditions was obtained. The drop injection system developed can readily be employed in the rod bundle test facility to investigate the droplet heat transfer in the dispersed flow film boiling regime.
A Fully-Coupled Transient Model for Predicting Interface Contamination in Product Pipelines
Authors: de Freitas Rachid Felipe Bastos , Carneiro de Araujo José Henrique , Baptista Renan Martins
Published: November 2021

This work presents a coupled fluid transient model to describe the mixing phenomenon arising in batch transfers in petroleum pipelines. The concentration evolution described by the dispersion of matter at the products’ interface is properly taken into account on the mass and momentum balance equations for the mixture as a whole. The resulting mathematical problem is formed by a system of non-linear partial differential equations which is solved by means of an operator splitting technique, combined with a Glimm’s scheme and predictor-corrector method. The influence of stopping the line during a batch transfer on the mixing volume is preliminarily analyzed for a particular batch.