The present study aims to explore dynamical behavior of the single cylinder and the staggered cylinder arrays in shear flow by numerical simulations. The results are compared with the case in uniform flow. After the observation of the fluid-elastic vibration in the staggered cylinder arrays in the two flows. This paper investigates the effects of the spacing(P/D), mass ratio and the shear parameter on the trajectories, oscillation amplitudes among the different cylinders. Continuity equation and momentum equations are used to solve the aforementioned problems alternatively by PISO method. Dynamic meshing techniques together with the cylinder motion equations are employed in the simulation. Under the different conditions, flow types and cylinder motion models, lock-in and fluid-elastic vibration are studied when the flow crosses the staggered cylinder arrays. The results show that the motion and the flow field around the single cylinder is consistent with the literature. In terms of the staggered cylinder arrays in uniform flow, the oscillation is dominated by the vortex shedding, and the lock-in area in the downstream cylinders is greater than the upstream cylinders. Fluid elastic vibration occurs in the small spacing between cylinders. In shear flow, when the shear parameters are larger or the spacing between cylinders are smaller, the more likely the fluid elastic vibration of the cylinders will occur.

In this study, a cylindrical near-field electrospining (CNFES) process will be used to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF) piezoelectric fibers, and a piezoelectric fiber harvesting device with parallel electrode was fabricated to capture ambient energy. First, the PVDF powder was mixed in acetone solution uniformly and the dimethyl sulfoxide (DMSO) was mixed with fluorosurfactant to prepare PVDF macromolecular solution. The PVDF macromolecular solution was filled in a metals needle injector and contacted a high power supply, after the PVDF drops in the needle was subjected to high electric field, the drops became a Taylor cone and overcame surface tension of the solution itself, extremely fine PVDF fiber was formed and jetted out. The fibers were collected numerous and quickly by homemade cylindrical collector and the diameter of fiber could be controlled easily by adjusting the rotating speed of the cylinder and the electric field. From the observation of XRD (X-ray diffraction), it reveals a high diffraction peak at 2£c=20.7¢X of piezoelectric crystal £]-phase structure by adjusting PVDF concentrations and DC voltage. By providing 7Hz shake and 0.23% strain, the piezoelectric fiber harvesting device with parallel electrode could generate 76mV; by providing 7Hz shake and 0.14% strain, the device could generate 1.1nA.

A new type of heterogeneous carbon fiber bunch bipolar plate developed in our lab is applied to portable pure hydrogen proton exchange membrane fuel cell stacks. Several different types of bipolar plate structures have been designed, and the voltages and currents of these fuel cell stacks are measured to compare their performance. The new type of heterogeneous carbon fiber bunch bipolar plate is well in low contact resistance, weight low, small volume and the flexible geometry shape. Due to its flexible structure of carbon fiber bunch, the compressing pressure is small while assembling stack so that the electrode can not be over compressed and out of shape. Therefore the high porosity of diffusion layer can be keep and reaction gas can enter and distribute to all reaction areas easily. For using to portable equipments, a small 6-cell flat type of fuel cell stack are developed firstly. The total weight is about 75g and the total volume is about 68cm . The second stack is cylinder-type(I) fuel cell stack. The total weight is about 60g and the total volume is about 71cm . The third stack is cylinder-type (II). The total weight has been reduced to about 20g and the total volume has been reduced to about 30cm . Above three kinds of the 6-cell stacks the total electrode area is 13.5cm . Using Nafion, the catalyst content anode Pt 0.4mg/cm , cathode Pt 1.0mg/cm , On room temperature and inlet hydrogen gauge pressure 0.15atm air-breathing, total output power of the cylinder (II) can reach 1.85W, and the power density of unit area can reach about 137mW/cm^2.

In the present study, circular cylinders in the cross-flow or the motions of circular cylinders in a fluid at rest are especially of interest in fields, such as offshore and civil engineering or heat exchanger. For last two decades, the researches of the force caused by the fluid on the cylinder surface are mainly studied by the ways of experiment and numerical methods. A time-independent finite different method is developed to solve the two-dimensional fixed or transversely oscillating cylinder passing by a cross flow. The present study focuses on the cylinder under a cross flow with only two kinds of conditions, which are Re = 100, KC = 5 and Re=200, KC=4. The benchmark tests of the present numerical results are made and validated by the reported numerical simulation and experimental results, for instant, the flow visualization of the vorticity contours and the in-line force for a flow across a moving circular cylinder. The developed numerical method can easily apply on the analyses of interactions between viscous flow and motion cylinder. Besides, we also consider the oscillatory flow passes a circular cylinder connecting with a spring. The spring -linking cylinder is released in the beginning on the position of zero deflection of the spring and stares moving due to the influence of the in-line force acting on the cylinder. We can find that the spring-linking cylinder under a oscillating flow produces restoring force and drag force due to considering the influence of the spring and damping effect, the developed numerical method can easily apply on the analyses of interactions between viscous flow and oscillating cylinder.

The problem of the forced film condensation heat transfer of pure steam and steam-air mixture flowing downward a tier of horizontal cylinders is investigated numerically and experimentally. Liquid and vapor-air mixture boundary layers were solved by an implicit finite difference scheme. The effects of the free stream non-condensable gas (air) concentration, free stream velocity (Reynolds number), cylinder diameter, temperature difference and angle of inclination on the condensation heat transfer are analyzed. Inline and staggered tubes arrangements are considered. The mathematical model takes into account the effect of staggering of the cylinders and how condensation is affected at the lower cylinders when condensate does not fall on to the center line of the cylinders. An experimental setup was also manufactured and mounted at METU workshop. A set of experiments were conducted to observe the condensation heat transfer phenomenon and to verify the theoretical results. Condensation heat transfer results are available in ranges from (U&amp / #61605 / = 1 - 30 m/s) for free stream velocity, (m1,&amp / #61605 / = 0.01 -0.8) for free stream air mass fraction, (d = 12.7 -50.8 mm) for cylinder diameter and (T&amp / #61605 / -Tw =10-40 K) for temperature difference. Results show that / a remarked reduction in the vapor side heat transfer coefficient is noticed when very small amounts of air mass fractions present in the vapor. In addition, it decreases by increasing in the cylinder diameter and the temperature difference. On the other hand, it increases by increasing the free stream velocity (Reynolds number). Average heat transfer coefficient at the middle and the bottom cylinders increases by increasing the angle of inclination, whereas, no significant change is observed for that of the upper cylinder. Although some discrepancies are noticed, the present study results are inline and in a reasonable agreement with the theory and experiment in the literature. Down the bank, a rapid decrease in the vapor side heat transfer coefficient is noticed. It may be resulted from the combined effects of inundation, decrease in the vapor velocity and increase in the non-condensable gas (air) at the bottom cylinders in the bank. Differences between the present study results and the theoretical and the experimental data may be resulted from the errors in the numerical schemes used. These errors include truncation and round off errors, approximations in the numerical differentiation for interfacial fluxes at the vapor-liquid interface, constant properties assumption and approximations in the initial profiles. Mixing and re-circulation in the steam-air mixture at the lower tubes may be the other reasons for these deviations.

An axisymmetric finite cylinder with rigid ends and a circumferential edge crack is considered in this study. The finite cylinder is under the action of uniformly distributed loads at two rigid ends. Material of the finite cylinder is assumed to be linearly elastic and isotropic. This finite cylinder problem is solved by considering an infinite cylinder containing an internal ring-shaped crack located at z=0 plane and two penny-shaped rigid inclusions located at z=&plusmn / L planes. General expressions of the infinite cylinder problem are obtained by solving Navier equations with Fourier and Hankel transforms. This infinite cylinder problem is then converted to the target problem by letting the radius of the rigid inclusions approach the radius of the cylinder and letting the outer edge of the crack approach the surface of the cylinder. Consequently, these rigid inclusions form the rigid ends and internal crack form the circumferential edge crack resulting in the problem of a finite cylinder with rigid ends having an edge crack. The problem is reduced to a set of three singular integral equations. These singular integral equations are converted to a system of linear algebraic equations with the aid of Gauss-Lobatto and Gauss-Jacobi integration formulas and are solved numerically.

none

This experiment is to investigate the effects of fluid with and without mass injection through a slit on the vortex shedding from a single cylinder. We research Reynolds Numbers on ranges from 800 to 4000. We used four kinds of ways which contain no mass injection, steady blowing, steady suction and oscillatory jet to study of the wake behind a circular cylinder under excitation in this experiment. No mass injection is measured for the sake of its reliability and comparability of experiment. Steady blowing and suction are applied to influence the wake flow. An oscillatory jet is used to influence the wake flow with varying frequencies and amplitudes. The experiment looks forward to use the results of this experiment so as to research into the effects on the wake flow, including the velocity values of fluctuation and turbulence intensity of the vortices structure, the dominant frequency in the flow pattern on a single cylinder. The main parameters in the study are the frequency, momentum and the location of the blowing and suction jet, which are a steady jet or unsteady oscillatory jet. Flow visualization has been carried out to investigate the interaction of steady or unsteady fluid perturbation and the vortex shedding of a cylinder.

For the method of fundamental solutions(MFS), many reports deal with 2D problems. Since the MFS is more advantageous for 3D problems, this thesis is devoted to Laplace's equation in 3D problems. Since the fundamental solutions(FS) £X(x,y)=1/(4£k||x-y||), x,y∈R^3 are known, the location of source points is important in real computation. In this thesis, we choose a cylinder as the solution domain, and the source points on larger cylinders and spheres. Numerical results are reported, to draw some useful conclusions. The theoretical analysis will be explored in the future.

<p>Detta examensarbetet har utförts i samarbete med företaget BXB Industrial Fittings och med handledning från Jönköpings Tekniska Högskola.</p><p>Uppdraget ändrades under projektets gång, därför beskrivs genomgörandet i rapporten i två delar då vissa moment gjordes två gånger. Från början bestod uppdraget i att utveckla ett lås för maskinskyddsgaller, men ändrades till att istället utveckla adaptrar för oval- och PZ-cylindrar så att de enkelt kan monteras i det tidigare nämnda låshuset.</p><p>Ovalcylindern är den låscylinder som är vanligast i Skandinavien, medan PZ-cylindern är den cylinder som är vanligast i övriga Europa. Problemet med dessa två låscylindrar är att de har olika dimensioner vilket gör att de inte kan monteras i samma låshus. Eftersom BXB:s lås säljs över hela Europa och kunder efterfrågar lås med samma funktion, men med olika låscylindrar anses en adapter som en bra lösning på detta problem.</p><p>Då författarna inte tidigare hade någon erfarenhet av konstruktion av lås gjordes en grundlig patent- och marknadsundersökning för att skapa en bra grund för fortsatt arbete. Efter undersökningen startade författarna idégenereringsprocessen som resulterade i ett stort antal skisser på olika lösningsförslag. Efter idégenereringen gjordes en sållning för att få fram det slutliga förslaget, detta förslag måttsattes och justerades sedan i CAD.</p><p>Arbetet resulterade i två adaptrar med samma utvändigt mått som utvinner en identisk rörelse och kraft. Adaptrarna underlättar vid konstruktionen av lås eftersom de medgör att både PZ-cylindern och ovalcylindern kan monteras i samma låshus. Adaptrarna har konstruerats på ett användarvänligt sätt genom att hänsyn har tagits till de personer som kommer i kontakt med dem. Antalet komponenter har minimerats och enkla mekanismer har använts, vilket gör adaptrarna enklare att montera under tillverkningen. Detta leder i sin tur till att tillverkningskostnaderna minimeras och att adaptrarna både genom sitt pris och sin användarvänlighet anses vara konkurrenskraftiga på dagens marknad. Adaptrarnas konstruktion och inre mekanik beskrivs i rapporen utifrån CAD-bilder.</p>