Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 120-121). Also available via the Internet.

The wind-induced vibration of bridge stay cables has been a long studied and documented topic including a vast literature presenting experimental and numerical investigation results. There are several aerodynamic phenomena which can be associated with the wind-induced vibrations of bridge stay cables, such as vortex-induced vibration, rain-wind induced vibrations, buffeting phenomenon, dry cable galloping, and high-speed vortex excitation, to name a few. One of the most critical types of vibrations for slender structures exposed to wind is the galloping instability. This is typically not encountered for round structures, like circular cylinders or cables, due to their symmetrical nature, and therefore a lack of negative slope in the lift coefficient. However, vibrations of inclined cables of cable-stayed bridges have been noticed for several bridges, and were associated with partial damage of the cable stays, and damaged noted to cable anchors. It is still unclear if these cable vibrations are caused by dry inclined cable galloping, or by high speed vortex excitation. For this reason, stay cables construction guidelines (FHWA, 2005) have not been able to clearly identify the aerodynamic instability resulting in the recommended use of high structural damping, and high Scruton numbers used to limit bridge stay cable vibrations. The current research addresses these issues by performing numerical CFD (computational fluid dynamics) simulations of wind flow around inclined and yawed cables in order to identify the flow behaviour around the circumference and downstream of the cable. Such numerical models provide a new understanding regarding the flow conditions around an inclined cable and the beginning of dry galloping instability. The simulation was performed for full scale cables in the form of cylinder models with high aspect ratios. The arrangement for the cable was considered as a combination of the inclination and yaw angles, in such a way that it should match the experimental setting considered by Cheng et al (2003), based on which a validating comparison of results was performed. A LES (Large Eddy Simulation) model was developed with a constant Smagorinsky model for simulating the turbulent flow around the cylinders. Reynolds numbers (Re) ranging from 1.1 × 105 to 6.7 × 105 were investigated for various combinations of the inclination angles of 0° to 60° and yaw angles of 0° to 40°. The diameter of the circular cylinder was set to D = 0.089 m and the length of the cable was 2.67 m (30D). Pressure on the surface of the cylinder was monitored on 5 rings arranged along the circular cylinder at equal intervals and velocities were recorded for intervals of 0.1 – 0.5D downstream the cylinder. Also pressure, vorticity and streamlines distributions were recorded for several plans along and across the cylinder. The flow pattern visualisations were clearly established and wind speed profiles were presented. An axial flow along the leeward side of the cylinder was identified for inclined circular cylinders. The predominant axial flows were noted at intervals of 0.1D to 0.3D downstream of the cylinder. As the distance from the leeward side of the cylinder increased, the effect of the far field flow increased as well, for the flow around the leeward side of the cylinder. The drag crisis encountered as a sudden drop in the drag coefficient CD, with the increase of Re number, was confirmed. The preliminary results for inclined cylinders showed good agreement with the experimental results available in the literature. Slight discrepancies for the upper and lower branches of the drag crisis were found between the published data and results obtained in the current study. A new flow classification for inclined and/or yawed circular cylinders was proposed based on the velocity profiles, eddy viscosity, and swirl threads formations, as a combination of the TrSL and TrBL regimes similar with the ones defined by Zdravkovich (1997), for flow perpendicular to cylinders. Four cases showed a potential aerodynamic instability when results of the current study were employed into the theoretical aerodynamic damping equation derived by MacDonald and Larose (2006). Three of these cases demonstrated a similar flow phenomenon to the TrSL-Short flow phenomenon defined in this study, which occurs when the major axis of the ellipse is close to the direction of flow, and the turbulent shear layers detach almost on the leeward side of the cylinder. The coherence, cross-coherence and cross-bicoherence were calculated for the frequency components of the coefficient of lift, the pressure coefficient along the leeward side of the cylinder, and the total velocity along the leeward side of the cylinder, and it was found that three cases of low non-linear interaction, intermediate non-linear interaction, and high non-linear interaction could be identified. Also it was concluded that the interaction between the lift and pressure coefficients monitored for the cylinder and the variation of the total velocity component, did not have a significant influence on the flow regimes, or on the transition between the flow regimes. The high-nonlinear interactions relate more to the potential coupling between the frequencies of the parameters mentioned above, especially for the critical case of 60° relative angle.

Desalination plants are becoming essential due to the limited water resources in order to reduce the pressure of high demand of freshwater in many countries in recent decades. A concerning problem associated with desalination plants is the high concentration brine which has high risk to marine environments. Inclined dense jets are commonly used to treat brine produced by desalination plants or in industrial outfall discharges. They are produced when the brine is discharged at an upwardly inclined angle through a pipe or a diffuser system. Previous studies have mainly focused on jets on a horizontal bottom. In the present study, the influence of sloped bottom is investigated by numerical simulations using a modified solver in OpenFOAM (pisoFoam). Four different Reynolds Averaged Navier Stokes (RANS) turbulence models (Realizable k-ε, Standard k-ε, RNG k-ε and Nonlinear k-ε were employed to assess the accuracy of the selected turbulence models in predicting the jet behavior. Jets of inclination angle of 30° with four different initial conditions (Froude number=15, 20, 25, 30) on three different bed slope angles (2°, 5°, 10°) in stagnant water were conducted. Although inclined dense jets of the discharge angel of 60° are more common in discharge systems, sometimes they cannot be used in shallow waters in order to prevent surface pollution. In such cases, a relatively small jet inclining angle can be used to prevent the surface pollution and as shown in this thesis, bed slope can enhance the brine mixing and dilution. The results showed that Realizable k-ε model is more accurate among the turbulence models studied herein. The dilution at the impact point can be estimated based on the Froude number and initial conditions. After the impact point, the slope did enhance the dilution of the plume compared to the horizontal bed. The dilution was thus affected by the slope and the dilution after the impact point on the slope appeared to be linearly related to the distance to the source. Besides, the slope could enhance the jet dilution up to 20% compared with the horizontal bed after the impact point.

The 1/4£f dual-mode resonators made from c-axis-oriented aluminum nitride films grown on different conduction material have been studied in this thesis. The RF/DC sputter system is used to grow on layers of reflector. During the porcess, 3.5 pairs of Bragg reflector alternating with W and SiO2 are composed by Si substractor. To achieve 0.999 reflective rate, fabrication parameters are adjusted to make W films become £\-phase structurre. On the other hand, piezoelectric layers as well as reflective layers that using reactive RF magnetron sputtering system and means of off-axis are combined to deposite optimal resonators of shear mode quality factor (Q) resonatros. While changing the substract and target distance between various bottom electrode materials, including Si, W/Si, and Mo/Si could deposit AlN with various c-axis tilting angle which resulted in stimulating longitudinal and shear acoustic waves. Futhermore, the finding is used to discuss the growth mechanism of inclined AlN by TEM. The analysis of various distances of AlN films shows that column inclining angle and XRD-Rocking Curve £s will increase with distance. The quality of shear mode would be better when column and £s are highly shifed. About the influence on AlN deposites, AlN/Si was grown away from the center by 6 cm. AlN/Si column inclining angle is about 20 degree, and RMS could reach 2.63nm beneath. Uner AlN/W/Si, column incling angle is about 30 degree, and £s shift angle 4.14 degree, the shear mode quality factor of freaquency response is obtained to 262. Under AlN/Mo/W/Si, column incling angle would be 25.4 degree, and XRD are better-choosed c-aixsm, £s tilting angle shifs 6.72 degree, and the shear mode quality factor is obtained to 290. Film intersurface appears bigger misfit by TEM to obtain better shear mode.

When a bluff body is placed in flow, vortices are shed downstream of the body. For the case of a bluff body with a circular cross-section (a cylinder) attached to a spring and a damper, when the frequency of vortex shedding is close to the natural frequency of the structure, the cylinder oscillates in a direction perpendicular to the flow. This is called Vortex Induced Vibration (VIV) and is a canonical problem in fluid-structure interactions. The majority of studies on VIV of a flexibly mounted rigid cylinder are for the cases where the flow direction is perpendicular to the long axis of the structure. However, in many engineering applications, such as cable stays in bridges, mooring lines of floating offshore wind turbines and undersea pipelines, the flow direction may not be perpendicular to the structure. The hypothesis is that the VIV in inclined cylinders is similar to a normal-incidence case, if only the component of the free stream velocity normal to the cylinder axis is considered. This is called the Independence Principle (IP). The IP neglects the effect of the axial component of the flow, which is legit for small angles of inclination, but not for large angles. In this Thesis, a series of experiments have been conducted on a flexibly-mounted rigid cylinder placed inclined to the oncoming flow with various angles of inclination (0° < θ < 75°) in a subcritical Reynolds number range of 500 – 4,000 to investigate how the angle of inclination affects VIV. In these experiments, a rigid cylinder was mounted on springs, and air bearings were used to reduce the structural damping of the system. The system was placed in the test section of a recirculating water tunnel and crossflow displacements were measured. Even at high angles of inclination, large-amplitude oscillations were observed. The IP was found to be valid for angles of inclination up to 55°. While for all inclinations the onset of lock-in was observed to be at the same normalized flow velocity, for angles of inclination larger than 55°, the lock-in region (the range of dimensionless flow velocities for which the cylinder oscillates with a large amplitude) was smaller. These results show that the influence of the axial component of the flow is non-negligible for angles of inclination larger than 55°.

Steady two-dimensional natural convection in air-filled, regular and irregular inclined enclosures has been investigated numerically. The effect of various configurations of bidirectional temperature gradients on mode transition of thermal convection inside the cavity has been investigated. Numerical treatment of temperature discontinuity at the comer points of the cavity and its effect on the calculated Nusselt number has been discussed. Rayleigh numbers range between 103 and 104, aspect ratio (width/height) =1,2,4, and angle of inclination in the range between 0 and 90°. While the cavity bottom and top walls were kept at constant temperatures at Th (heated) and at Tc (cooled), respectively, thermal conditions of end walls were varied. In addition to the base case of insulated end walls, seven different configurations of thermal conditions of the two side walls have been studied. Results show that numerically predicted heat transfer rates strongly depend on the numerical treatment of temperature discontinuities at cavity comer points. Results also indicate that thermal conditions of cavity end walls have a significant effect on mode-transition of thermal convection flows; and hence, on heat transfer effectiveness inside the cavity, and on the Hysteresis phenomenon occurred as the cavity angle of inclination varied from zero (horizontal position) to 90 ° (vertical position) and back to zero. The effect of curved bottom is carried out by replacing flat bottom of the cavity with a curved one. Only insulated end walls were discussed in curved case. Results indicated that heat transfer rate and mode transition are strongly dependent on the height of curvature of the bottom wall, which offers more flexibility in controlling flow mode-transition, and hence, effectiveness of heat transfer inside the cavity. / Thesis / Master of Applied Science (MASc)

In recent years, the field of transportation engineering has witnessed the emergence of technological innovations linking several different application areas like human factors, computer science, communications and operations research. This research deals with automatic freeway traffic operations including ramp guidance and merging which is an important aspect of Intelligent Vehicle Highway Systems (VHS) Technology. An existing traffic flow model is utilized to generate a non-overtaking, continuous traffic stream with automatic acceleration/ deceleration characteristics of the smart cars to fulfill the needs of a high-speed flow under controlled headway and optimized density conditions. The orientation, shape, and geometry of such ramps on a high-speed highway system is investigated. It is proposed that the angle between the ramp and highway would be very acute and lane changes from acceleration lane to the cruising lane would follow a smooth trajectory. The curve would be composed of two circular curves of large radii of curvature or two spiral curves in succession. The adequacy of the existing geometric design specifications are questionable, not only for the merging section, but the entire stretch of the "smart highway”. The introduction of intelligent highway network extensively in rural areas could necessitate a complete rethinking about highway geometric design standards. An alternate method of geometric design requirements is undertaken to explore the applications of vehicle aerodynamics’ principles to the highway design, which is perceived to be essential under the high-speed conditions. The results obtained can be compared to those of the conventional geometric design formulae to yield a comparison. Though the principal aim of this research is to serve the highways, it has applicability to other forms of highspeed, controlled guideway transportation systems also. / Master of Science

This thesis presents the results of research into the potential of underground mining methods applicable to inclined thick seams (thickness greater than 3.5m, and seam dip of 15 - 35 degree) in the Quangninh coalfield, Vietnam. The primary objectives of this research are to investigate the most suitable underground methods applicable to inclined thick seams in the Quangninh coalfield and to improve understanding of the operational and geotechnical issues associated with the application of chosen methods in thick seams with steeply dipping conditions. From a risk and operational assessment, the Longwall Top Coal Caving (LTCC) method is considered most appropriate for inclined thick seams under the current mining conditions in Vietnam. The LTCC method offers great potential for the efficient extraction of thick seams by caving coal from the upper section during the mining of the lower section. This significantly reduces the development cost per tonne. Compared to High reach Single Pass Longwalling, the LTCC method offers a low extraction height, resulting in smaller and less expensive equipment and better face conditions. Results from this study identified that for extracting an inclined thick seam, the face retreating along the strike has better operational advantages and better cavability than the face retreating updip or downdip of the seam. The operational issues of the LTCC method when extracting inclined seams are: the stability of the support, transport in the mine, and the difficulties in roof control at the transition between face ends and the gateroads. In terms of geotechnical issues, better cavability of the top coal is anticipated for flat coal seams compared to inclined seams. In addition, the chain pillar for flat coal seams is subjected to a higher vertical stress distribution than that of inclined ones. An improved cavability assessment method for the categorisation of the cavability of the top coal with four categories, ranging from 1 (excellent cavability) to 4 (very poor cavability), was suggested to assist the feasibility and design stages of the LTCC application. The cavability assessment method was conducted by numerical analysis combined with back analysis from the database obtained from past LTCC practices.

Vortex induced vibration of a circular cylinder in an inclined flow is a major subject in this thesis, the interaction and effect between a moving cylinder and fluid is always focused and investigated. We used a finite differences method to get the forces on cylinder, and then combined a Runge-Kutta four order approximate method to get a new position of a cylinder at next time step, repeated above procedure and we will get the solutions of a time series of cylinder response for VIV simulations. Most of papers focus on the peak amplitude and its scale due to the shedding frequency of system is near or at the fs, where fs is the shedding frequency of a uniform flow past a stationary cylinder. Except the ¡§first resonance¡¨, we found the ¡§second resonance¡¨ in the VIV simulations. The ¡§second resonance¡¨ occurs due to the natural shedding frequency of system is near or at the twice of the reduced frequency of the oscillator ¡§fs=2F1¡¨. The natural shedding frequency of a body is a key parameter, it always be discussed its effect and importance, and its value is also presented the frequency of lift force (or displacement on Y direction) of a body. On the contrary, the frequency of in-line force (or displacement on X direction) and its effect is seldom be investigated and discussed. In this study, we will discuss the effect of frequency of in-line force and the scale of ¡§first resonance¡¨ and ¡§second resonance¡¨ for VIV simulations. In order to verify the accuracy of our numerical model, this study simulated four different types for the cases of uniform flow past a circular cylinder with stationary, streamwise, transversal and rotational oscillating, respectively. The simulation results are compared with the study results of other paper by experimental and numerical methods, and the comparison show good agreement and high accuracy in the range of the in-line and lift forces on the cylinder, the main wake size behind the cylinder, the vortex shedding mode and the streamline pattern of the flow field. Furthermore, this study investigates a uniform flow past an inclined oscillating cylinder which is forcing oscillation in a range of 00 ~ 900 for the inclined angle (with respect to the X-direction of the Cartesian coordinates system). The effects of giving the different forced frequencies of a cylinder were investigated and discussed. And the application and restriction of Morison¡¦s equation will also be studied and investigated in different input conditions.

This paper is divided into two parts, experiments and finite element simulations. In experiments, the effects of various rolling conditions such as roll rotational speed, reduction, upon entrance and exit axial velocities, entrance and exit rotational speeds, twisting angle of rolled products are investigated. Experiments with roll rotation and planetary rotation are carried out to check the validity of the results obtained by roll rotation only. In finite element simulations, DEFORM 3D is used to simulate planetary three-roll rolling. The rolling torque, the distance between spirals, and the shape are analyzed, and the analytical results are compared with experimental results.