Plain Cylinder Research Articles

The use of MRI to observe fractures in concrete

This study extends previous work and demonstrates that magnetic resonance imaging (MRI) of water allows the internal crack pattern of hardened concrete to be observed along with the internal aggregate structure. The ability to reconstruct three-dimensional images is demonstrated and the importance of image registration is discussed. By using aramid fibre-reinforced plastics (AFRP), it is possible to make reinforced concrete specimens that can be measured by MRI. Plain concrete cylinders and others externally confined by AFRP spirals have been tested in compression and scanned after various amounts of load have been applied to show the progress of fracture development. Samples have also been made with straight AFRP rods cast into the concrete which, when pulled out, give bond failures and internal cracking. It is possible not only to observe the fractures, but also to relate them to the internal concrete structure determined by previous scans of the freshly prepared concrete samples.

The use of MRI to observe fractures in concrete

This study extends previous work and demonstrates that magnetic resonance imaging (MRI) of water allows the internal crack pattern of hardened concrete to be observed along with the internal aggregate structure. The ability to reconstruct three-dimensional images is demonstrated and the importance of image registration is discussed. By using aramid fibre-reinforced plastics (AFRP), it is possible to make reinforced concrete specimens that can be measured by MRI. Plain concrete cylinders and others externally confined by AFRP spirals have been tested in compression and scanned after various amounts of load have been applied to show the progress of fracture development. Samples have also been made with straight AFRP rods cast into the concrete which, when pulled out, give bond failures and internal cracking. It is possible not only to observe the fractures, but also to relate them to the internal concrete structure determined by previous scans of the freshly prepared concrete samples.

The Effect of Monocularly and Binocularly Induced Astigmatic Blur on Depth Discrimination Is Orientation Dependent

Naturally occurring astigmatism varies according to the age of the person. Although uncorrected astigmatism may be associated with meridional amblyopia, there is little information of its effect on stereopsis. The purpose of this study was to determine the effect of astigmatism on depth discrimination and whether this was dependent on the axis of the astigmatism. Astigmatic blur was induced in four healthy subjects (mean age, 31.5 years; range, 22 to 42 years) using plain cylinders (-8.75 D to +11.5 D) for orientation control and Jackson cross-cylinders (0 to 12 D) for spherical neutrality. Horizontal, vertical, and oblique astigmatism was induced with five monocular and three binocular axis steps. Depth discrimination was recorded at near using Frisby, TNO, and Titmus stereoacuity tests and at distance (4 m) using the variable distance stereoacuity test. Visual acuity was recorded at 0.4 m and 4 m. Visual acuity and depth discrimination degraded with increasing astigmatic blur. The effect of monocular astigmatic blur on depth discrimination and visual acuity was not dependent on the axis of orientation. For binocular astigmatic blur, the reduction in depth discrimination was dependent on the axis of the induced astigmatism (p < 0.01). The maximum effect occurred with orthogonal-oblique orientations (x45 left; x135 right), followed by against-the-rule (ATR) astigmatism; with-the-rule (WTR) astigmatism had the least effect (p < 0.001). The lesser effect of WTR compared with ATR astigmatic blur on depth discrimination may reflect the contribution of horizontal compared with nonhorizontal disparity processing in stereopsis. The pronounced effect of oblique astigmatic blur may be because of the effects on horizontal and nonhorizontal disparity and interocular differential image blur.

The plastic work required to induce the limit pressure of a plain cylinder

There has recently been a revival of interest in the definition of the limit and plastic loads of a structure, particularly piping components. Recent proposals have suggested definitions based upon plastic work. In order to normalise such quantities, the plastic work associated with the limit pressure of a plain cylinder may be required. Whilst no unique value for this quantity can be obtained through analysis, this article demonstrates that classical methods allow solutions to be obtained through an empirical route and through an analysis using several approximations. This latter analysis is shown to be adequate for the applications envisaged here.

Overstraining of flush plain cross-bored cylinders

A three-dimensional finite element method computer program was developed to establish the elastic-plastic, residual and service stress distributions in thick-walled cylinders with flush and non-protruding plain cross bores under internal pressure. The displacement formulation and eight-noded brick isoparametric elements were used. The incremental theory of plasticity with a 5 per cent yield condition (an element is assumed to have yielded when the effective stress is within 5 per cent of the material yield stress) and von Mises yield criterion were assumed. The frontal solution technique was used. The incipient yield pressure and the pressure resulting in a 0.3 per cent overstrain ratio were established for various cylinder thickness ratios and cross bore-main bore radius ratios. For a thickness ratio of 2.25 and a cross bore-main bore radius ratio of 0.1, the stresses were determined for varying overstrain and an optimum overstrain ratio of 37 per cent was established. To find the accuracy of the results, the more stringent yield condition of 0.5 per cent was also considered. The benefits of autofrettage were presented and alternative autofrettage and yield condition procedures proposed.

同心円筒状の金網によって囲まれた円柱を過ぎる流れ(S22-3 物体周り流れの制御-1,S22 流れ制御の技術)

Characteristics of the flow past a circular cylinder surrounded by concentric screen gauze with a diameter of 5 times the cylinder are investigated by means of LDV. The mesh and open area ratio of the screen gauze, used are 18, 0.74 and 30, 0.50, respectively. It is found that the static pressure distribution shows a similar one to the plain cylinder but the drag coefficient decreases substantially. The recirculation region of the cylinder is elongated to the flow direction and the wake shows significantly different features from those for the plain cylinder. The wake behavior differs considerably even for the screen gauze with the mesh 18 and 30.

Experimental studies of passive control of vortex-induced vibration

Measurements of vortex-induced vibration of a plain circular cylinder and cylinders fitted with strakes and bumps are presented. Experiments were carried out in water with mass ratios in a range from about 1.5 to 5.5 and combined mass and damping values between about 2×10 −3 and 7×10 −3. Reynolds numbers were within the range 10 3 to 10 4. Although the wakes of fixed cylinders with strakes or bumps show little or no evidence of regular vortex shedding it was found to establish itself across a range of reduced velocity when the mass and damping parameters are sufficiently small. However, the amplitudes of vibration were less than those for a plain cylinder. It is observed that the modes of shedding found for an oscillating plain cylinder are also present for a responding cylinder fitted with vortex suppression devices.

Drag reduction of a circular cylinder at subcritical flow regime using base shield plates

Experimental studies on drag reduction of a circular cylinder of diameter D were conducted in the subcritical flow regime at Reynolds numbers in the range <TEX>$4{\times}10^4{\leq}Re{\leq}10^5$</TEX>. To shield the cylinder rear surface from the pressure deficit of the unsteady vortex generation in the near wake, two shield plates were attached downstream of the separation points to form a cavity at the base region. The chord of the shield plates, L, ranged from 0.22 to 1.52 D and the cavity width, G, was in the range from 0 to 0.96 D. It is concluded that significant drag reductions from that of a plain cylinder may be achieved by proper sizing of the shield plates and the base cavity. The study shows that using a pair of shield plates at G/D of 0.86 and angular position <TEX>${\theta}$</TEX> of <TEX>${\pm}121^{\circ}$</TEX> results in a configuration with percentage drag reduction of 40% for L/D of 0.5, and 55% for L/D of 1.0.

Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods

The effects of tripping rods on flow characteristics and fluid forces acting on a single cylinder and on two cylinders in side-by-side and tandem arrangements were investigated in a smooth cross stream at a Reynolds number of 5.5×10 4. At first, tripping rods of 4, 5 and 6 mm in diameter were used on a single cylinder of diameter 49 mm. The angular position of the tripping rods was varied from 20° to 60°. The optimum angular position of tripping rods for reducing fluid forces was found to be 30°. Two tripping rods, each of 5 mm in diameter, positioned symmetrically at this angle reduced steady drag, fluctuating drag and fluctuating lift forces acting on the cylinder by 67%, 61% and 87%, respectively. A bistable nature of the flow on the single cylinder appears when the tripping rods were positioned at 41°–44°. Next, fluid forces acting on two circular cylinders in a side-by-side or tandem arrangement were reduced by using tripping rods on both cylinders. A significant reduction in both steady and fluctuating fluid forces acting on the side-by-side cylinders was observed when the gap spacing between the cylinders was greater than the diameter of a cylinder. In the case of tandem cylinders with tripping rods, fluid forces acting on the upstream cylinder were almost independent on the downstream cylinder at any spacing of the cylinders. The critical spacing at which a bistable flow appears was found at spacing ratios of 3.0 and 2.6 for the plain cylinders and the cylinders with tripping rods, respectively. At the critical spacing, however, there was no considerable jump in fluid forces acting on the upstream cylinder when tripping rods were used on the cylinder. Wavelet analysis was used to study the bistable flow for the single cylinder with tripping rods and for the tandem cylinders.

Effectiveness of sealers in counteracting alkali-silica reaction in highway median barriers exposed to wetting and drying, freezing and thawing, and deicing salt

This study follows another experimental study where different types of sealers were applied on plain and air-entrained large concrete cylinders made with high-alkali contents and highly alkali–silica reactive limestone aggregates. The main objective was to determine the effectiveness of these sealers in counteracting concrete expansion and surface deterioration due to alkali–silica reaction under various exposure conditions. This study indicated that all three sealers tested, the silane-, oligosiloxane-, and polysiloxane-based sealers, could stop concrete expansion due to ASR and even produced contraction, even for concrete cylinders subjected to wetting and drying, freezing and thawing, and sodium chloride solutions. In 1991, the same silane, oligosiloxane, and polysiloxane were applied on sections of median barriers showing various degrees of deterioration due to ASR. These sections were subjected to wetting and drying, freezing and thawing, and, during winter, to deicing salt. The silane was also applied on other sections of the same barriers in 1994. Observations and measurements over 10 years indicate that the aesthetic appearance of these median barriers, particularly those sealed with the silane, was greatly improved, while internal humidity was significantly reduced, and concrete expansion as well, when not arrested. The period of time during which the above three sealers were capable to stop ASR expansion varies with the sealer used and the degree of concrete deterioration at the time of sealing. For instance, the silane, which was the best among all products tested, caused concrete contraction for at least 6 years in median barriers that were severely affected by ASR, and likely for more than 10 years in moderately affected barriers. The overall results confirm the conclusions obtained previously in the laboratory: a good sealer such as the silane tested may greatly improve the aesthetic appearance and stop the expansion of non-massive ASR-affected concrete members, at least up to about 300 mm in thickness, and subjected to wetting and drying, freezing and thawing, and salt water. However, the poor result obtained in the field with another silane-based sealer indicates that a sealer cannot be selected based on its composition only.Key words: alkali–silica reaction, concrete; cracking, expansion, internal humidity, median barrier, sealer, silane, siloxane.

Effectiveness of sealers in counteracting alkali-silica reaction in plain and air-entrained laboratory concretes exposed to wetting and drying, freezing and thawing, and salt water

Low- and high-alkali, plain and air-entrained large concrete cylinders, 255 mm in diameter by 310 mm in length, were made with a highly alkali–silica reactive limestone. After curing, a number of cylinders were sealed with silane, oligosiloxane, polysiloxane, linseed oil, or epoxy, with others subjected to 179 freezing and thawing cycles in humid air (one cycle per day). All cylinders were then subjected to 14-day exposure cycles, including in the most severe case periods of humid storage in air, drying, wetting in salt water, and freezing and thawing cycles. All low-alkali specimens did not either expand or develop surface cracking, even those with a deficient air void system and exposed to freezing and thawing cycles. All unsealed high-alkali cylinders subjected early to a series of freezing and thawing cycles did not significantly expand during these cycles, but presented high expansion afterwards. Wetting and drying significantly reduced alkali–silica reaction (ASR) expansion compared with constant humid storage; however, it promoted map-cracking. Regardless of the air content, freezing and thawing increased greatly the concrete expansion in the presence of ASR, even after ASR was almost complete; freezing and thawing also greatly promoted surface cracking. On the other hand, all cylinders early sealed with silane, oligosilixane, or polysiloxane did not either significantly expand or show map-cracking, whatever the exposure conditions and the air content; these cylinders progressively lost mass with time. On the other hand, the epoxy resin was not effective. The linseed oil prevented map-cracking while significantly reducing expansion, however not sufficiently. After one or 1.5 years, some expanding cylinders were sealed with silane, oligosiloxane, or polysiloxane; they started to loose mass and contracted immediately after being sealed, whatever the exposure conditions. The results obtained thus indicate that a good sealer may greatly improve the aesthetic appearance (e.g., map-cracking) and stop expansion of ASR-affected concrete elements of 255 mm or less in thickness, made with a water-to-cement ratio in the range of 0.50, and exposed to wetting and drying, freezing and thawing, and salt water.Key words: air entrained, alkali–silica reaction, concrete, cracking, expansion, freezing and thawing, sealer, silane, siloxane, wetting and drying.

Biologically-Inspired Bodies Under Surface Waves—Part 1: Load Measurements

Measurements have been carried out in a tow tank on cylindrical bodies submerged in proximity of traveling surface waves. Two bodies are considered: a reference plain cylinder and another cylinder containing a pair of wings (or hydrofoils) below the cylinder, not above. The latter body owes its origin to certain species of fish which has small wings for maneuverability. The wavelength of the surface waves (λ) is of the order of the cylinder length (L) or higher (1 &lt; λ/L &lt; 10). Temporal measurements of axial and vertical forces and pitching moments, phase matched to the surface elevation of traveling waves, have been carried out. The time periods of the waves and depth of water pertain to deep water and intermediate depth waves. The forces and moments exhibit characteristic phase relationship with water elevation. Towing affects only vertical forces in the speed range of 0 to 1 m/s. The effect of towing and surface waves on vertical forces is roughly additive. Within the low speed range of towing evaluated, the effects of surface waves dominate those of towing. The presence of the hydrofoil and intermediate depth waves bring in some additional effects which are not well understood. In intermediate depth waves, a small plain cylinder may encounter a resonance with traveling waves which can be averted by attaching a pair of small wings to dampen pitching moment and make it speed invariant, although at a cost of increased vertical forces.

Benchmarking of a destructive technique to determine residual stresses in thick-walled axisymmetric components

A proposed destructive technique to determine residual stresses in thick-walled axisymmetric pressure vessels employs incremental strain gauge data in a finite element algorithm to construct the initial residual stress distribution. The data acquisition component of the proposed technique has similarities with Sachs' bore out method, enabling independently obtained data to be employed by the finite element algorithm. A comparison between the two methods based on the same strain data enables the accuracy of the finite element algorithm to be assessed. Results to date suggest that the new algorithm determines residual stress distributions to an accuracy comparable with Sachs' bore out method. An advantage that the proposed technique has over Sachs' bore out method is that it can be applied to axisymmetric thick-walled pressure vessels of geometries more complex than plain cylinders.

Experimental Study on the Near Wake Behind a Circular Cylinder with Helical Surface Protrusions

Surface protrusions have been attached on a cylinder surface to reduce the flow-induced structural vibration by controlling the wake flow. Wind tunnel tests on the near wake of a circular cylinder with surface protrusions were carried out to investigate the flow characteristics of the controlled wake. Three experimental models were used in this experiment; one plain cylinder of diameter D and two cylinders wrapped helically by three small wires of diameter d=0.075D with pitches of 5D and 10D, respectively. Free stream velocity was ranged to have Reynolds number from 5000 to 50,000. Streamwise and vertical velocity components of the wake were measured by a hot-wire anemometry. The spanwise velocity component measured by a one-component fiber optic LDV revealed that time-averaged wake field has a nearly two-dimensional structure. It was found that the surface protrusions elongate the vortex formation region, which decrease the vortex shedding frequency. The suppression of vortices caused by the surface protrusions increases the velocity deficit in the center of wake region.

Composite cylinder models of DNA: application to the electrostatics of the B-Z transition

We develop and test a Poisson-Boltzmann model of the electrostatics of the B-Z transition of DNA. Starting from the detailed geometries of the two forms, we compute at each radius the fractions of DNA matter, of volume forbidden (for nonpoint-like ions), and of volume accessible to the center of ions. These radial distributions are incorporated in a composite cylinder model; availability to ions (porosity) and the dielectric constant at each radial distance are then obtained. The phosphate charge is distributed with cylindrical symmetry on two layers at the appropriate radial distances. The porous sheath, between the axis and the charge distribution, provides much more room for ions in B-DNA than in Z-DNA. By using previously developed methods, the Poisson-Boltzmann problem of such cylinders is easily solved. The computational load is small, so that results can be obtained for a large set of salt concentrations and for a number of ionic radii. The variation of the electrostatic free energy difference with salt concentration compares favorably with the experimental value (it is half as large). There is also qualitative agreement with experiments on supercoiled DNA, including a maximum of the free energy difference at submolar salt concentrations. The results for this cylinder with porous sheath are in line with those of the earlier simple planar model and of a plain cylinder with sheath, which is also presented here. They are thus insensitive to details of the model. They support the proposition that the main electrostatic feature of the B-Z transition is the better immersion of the B-DNA phosphates into the solution. They also give confidence in the validity of the Poisson-Boltzmann approach, despite the large salt concentrations involved. Prior studies using an approach based on the potential of mean force are discussed.

Fatigue Strength of Thick-Walled Cylinders Containing Cross Bores with Blending Features

This paper reports on an investigation into the fatigue strength of thick-walled cylinders that contain a small transverse hole or cross bore in the cylinder wall having either a chamfer or a blending radius at its intersection with the main cylinder bore. Fatigue tests surprisingly show that plain cross-bore cylinders having thickness ratios K = 1.4 and 2.0 have a fatigue life that is marginally greater than comparable cylinders with blending features. A finite element investigation shows that local high stresses are produced on the surface of blending features and these stresses are considerably greater in magnitude than those found in plain cross-bore cylinders. These stress findings are used to explain the experimental fatigue life results obtained.

Fatigue cracking in damaged cylinders subjected to cyclic compressive loading

This paper presents the results of analytical and experimental investigations of the occurrence of cracking in thin-walled structures which are damaged and subjected to axial compressive loading with cyclically varying magnitude. The experimental investigation comprised nine test specimens, namely three plain cylinders, three plain ring stiffened and three T-ring stiffened cylinders. The paper describes the method whereby damage was inflicted on the cylinders and describes test results, including strain gauge data. The analysis was performed using a commercial finite element program which incorporated non-linearities in the strain-displacement and stress-strain relationships. The results of the analysis were found to be in good agreement with the test results, and the occurrence of cracking was noted to be dependent on the combined levels of tensile residual stresses due to the damage and to the levels of compressive stresses due to the imposed loading.

Forming of thin V-section rings by ring rolling

An account is given of the development of a ring rolling process for the manufacture of V-sectioned rings from thin-walled plain cylinders. The rings were required in different diameters and sectional dimensions for a specific application, and in the absence of any design information an analysis of the forming process was made to provide guidance on the design of the forming rolls. The analysis is shown to predict satisfactorily the conditions needed for smooth development of the profile and the blank size required to produce a given ring size.

Equilibrium element analysis of plain concrete and steel-concrete composite cylinders subjected to external pressure

Synopsis An equilibrium element method is derived for the axisymmetric analysis of the mid-length region of thick- walled cylinders of non-linear material construction. The method is used to examine the behaviour of plain concrete and steel-concrete composite cylinders subjected to externalfluid loading. The incremental form of a nonlinear elasticity model is adopted for the concrete and the steel is described be elasto-plasticity.

Limit pressure of a cylindrical shell with a two-dimensional array of nozzles with associated axial cracks

The limit pressure of a cylindrical shell with a two-dimensional array of penetrating nozzles and associated defects covering the whole shell has been calculated and compared with the limit pressure of the plain cylindrical shell. A lower-bound method was used. The conventional ligament efficiency method of calculating the limit pressure is too conservative. It is necessary to claim some strength from the nozzles. Hence a more elaborate method has been used here. If there are axial cracks in the main vessel tangential to some nozzles, the limit pressure is reduced to a value which is between the ligament efficiency and the value for a single crack in a plain cylinder. The actual reduction has been calculated for a range of crack lengths for a typical geometry.