Experimental and finite element prediction of bursting pressure in compound cylinders

Aluminium cylinders with a constant ratio of outer to inner radii, k=2.2, with different diametral interferences and various shrinkage radii were subjected to bursting and autofrettage pressures. Numerical simulations of the compound cylinders were also performed using the finite element code, NISA. The results can predict the optimum shrinkage radius to a reasonable accuracy with the use of finite element analysis. This radius corresponds to the situation when the maximum von-Mises stress at the internal radii of both the inner and outer cylinders become equal. It was shown that the maximum von-Mises stress across the wall of the cylinder is at the minimum at this shrinkage radius. The optimum diametral interference was found to be that which sufficiently brought the contact surface of the inner and outer cylinders to the point of yielding. Should the shrinkage pressure exceed the elastic limit, the pressure capacity of the cylinder will not be improved. The numerical and experimental results show that autofrettage had no effect on the bursting pressure of the thick-walled compound cylinder for the material tested.     

Effect of chamfering on heat transfer and friction characteristics of solar air heater having absorber plate roughened with compound turbulators

Artificial roughness in the form of repeated transverse chamfered rib-groove roughness on one broad wall has been proposed as a convenient method for enhancement of thermal performance of solar air heater. An experimental investigation on heat and fluid flow characteristics of fully developed turbulent flow in a rectangular duct having repeated integral transverse chamfered rib-groove roughness on one broad wall has been carried out. The roughened wall is uniformly heated while the remaining three walls are insulated. These boundary conditions correspond closely to those found in solar air heaters. Six roughened plates have been tested placing a 60° V-groove at the centre line in between two consecutive chamfered ribs. The ribs' top have been chamfered having chamfer angles of 5°, 12°, 15°, 18°, 22° and 30°, while relative roughness pitch (P/e) and relative roughness height (e/D_h) of the ribs were kept constant having values of 10 and 0.03 respectively. The flow Reynolds number of the duct varied in the range of approximately 3000–21,000, most suitable for solar air heater. The effects of chamfer angle on Nusselt number and friction factor have been discussed and the results are compared with the square rib-grooved and smooth duct under similar flow conditions to investigate the enhancement in Nusselt number and friction factor. The conditions for the maximum enhancement of Nusselt number and friction factor have been determined. It has been found that the thermo-hydraulic performance of the solar air heater provided with such roughness is considerably enhanced.     

Periodic heat conduction in a solid homogeneous finite cylinder

Analytic solution of the steady periodic, non-necessarily harmonic, heat conduction in a homogeneous cylinder of finite length and radius is given in term of Fourier transform of the fluctuating temperature field. The solutions are found for quite general boundary conditions (first, second and third kind on each surface) with the sole restriction of uniformity on the lateral surface and radial symmetry on the bases. The thermal quadrupole formalism is used to obtain a compact form of the solution that can be, with some exception, straightforwardly extended to multi-slab composite cylinders. The limiting cases of infinite thickness and infinite radius are also considered and solved.     

Heat Transfer in a Horizontal Cylinder With Eccentric Surfaces

Heat transfer in horizontal cylinders exposed to free convection and radiation is of importance in many industries. Usually this problem is treated by adopting a concentric geometry, disregarding that the external surface temperature is not uniform. If an eccentric geometry is used, the external surface temperature should have a larger variation, changing the flow around the cylinder and the heat transfer coefficient, either improving or reducing the heat transfer. A numerical analysis is presented of the heat transfer in a horizontal cylinder with an internal isothermal surface eccentric to the external surface that is exposed to air free convection and radiation. The conduction problem was solved analytically and integrated numerically, while the free convection was solved by the PHOENICS software. The parameters analyzed were the ratio of radius, the ratio between the material and air thermal conductivities, the Rayleigh number, the emissivity of the outer surface, and the eccentricity between the external and inner surfaces. The parameters of a proposed equation to estimate the total heat of an eccentric arrangement in terms of the total heat of the corresponding concentric arrangement and the ratio between the convective and conductive thermal resistances were determined for given ratios of radius and eccentricities.     

Three-dimensional analyses of surface cracks in pressurised thick-walled cylinders

Stress intensity factors for semi-elliptical surface cracks in internally pressurised thick-walled cylinders of radius ratio 3 are presented for a wide range of crack sizes. These solutions were obtained using the boundary integral equation method for three-dimensional stress analysis. Only one crack shape is considered—a semi-ellipse with the length of its semi-minor axis equal to 0·6 times the length of its semi-major axis —but the ratio of crack depth to wall thickness ranged from 0·2 to 0·8. Hoop strain distributions at the outer circumference of the cylinder are also presented for the different crack sizes analysed; the results are useful for experimentally monitoring crack growth.     

Calculation of stress intensity factors for semielliptical cracks in a thick-wall cylinder

Weight functions for the surface and the deepest point of an internal semielliptical crack in a thick-wall cylinder were derived from a general weight function and two reference stress intensity factors. For several linear and nonlinear crack face stress fields, the weight functions were validated against finite element data. Stress intensity factors were also calculated for the Lamé through the thickness stress distribution induced by internal pressure. The weight functions appear to be particularly suitable for fatigue and fracture analysis of surface semielliptical cracks in complex stress fields. All stress intensity factor expressions given in the paper are valid for cylinders with an inner radius to wall thickness ratio, R_i/t = 4.     

Computing the SCF for a hollow cylinder with hoop groove under torsion by means of a spherical section assumption

In this paper, a new method for calculating the stress concentration factor (SCF) and the elastoplastic limit load of a hollow cylinder with hoop groove under torsion is proposed by means of spherical section assumption. The relations of SCF at notch root with the notch depth t, the radius of the notch root and the internal radius a₁ of the cylinder are discussed. The elastoplastic limit torsions are derived for a hollow cylinder for two cases. The results obtained show the effectiveness of this method.     

二冲程液压自由活塞发动机半直接喷射的仿真研究

利用CONVERGE软件建立了半直喷式液压自由活塞发动机的三维计算流体力学(computational fluid dynamics,CFD)仿真模型,研究了喷射角度、喷油定时、缸头倾角、进气压力对燃料捕集和混合气生成的影响.结果表明:随喷射时刻的推迟,燃料捕获率增加,蒸发时间变长;喷射角度越大,燃料捕获率越高,蒸发时...     

Elastic analysis of semi-elliptical axial cracks in cylinders under thermal shock using the BS 7910 framework

One of the most common and important situations involving flaws in pressure vessels is the internal thermal shock of a hollow circular cylinder with an axial semi-elliptical internal surface crack. The current approaches available to analyse this specific problem are excessively conservative or cumbersome. This paper considers the internal thermal shock problem and determines the stress-intensity factors for shallowest and deepest points for cylinders with the ratio of thickness to inner radius 0.1 and 0.25. The results of calculations are presented in a similar form to the draft standard BS 7910:1997 and thus permit numerous practical applications. These results are in many cases much less conservative than the draft standard and also reveal some important cases.     

A parametric study of two normally intersecting cylindrical shells subjected to out-of-plane moment

There are studies which suggest that design equations in the ASME Pressure Vessel Codes¹ may be unconservative for diameter ratios of branch and run shells less than, as well as larger than, 0·5. Since several investigations exist for cases in which this ratio is less than 0·5, this study mainly concentrates on ratios larger than 0·5. Five models with radius ratios ranging from 0·528 to 1·000 were considered for a study of the problem caused by out-of-plane moment loading. For each diameter ratio different combinations of thickness ratios and radius-to-thickness ratios of the run shell were considered, for a total of 52 cases. A numerical technique (finite element method) was used to find the magnitude and location of the maximum stress. Depending on the location of the maximum stress on the branch or run shell, the result from the numerical technique was divided into two sections. Each part was statistically analyzed to find the dependency of the stress index on diameter ratio, thickness ratio and radius-to-thickness ratio of the run shell.     

激光微珩磨缸套润滑耐磨性能理论分析

基于摩擦学理论和缸套／活塞环的润滑磨损特征，采用激光微造型技术，在缸套内表面进行规则微观几何形貌的造型。通过分析缸套／活塞环摩擦副的物理模型，建立了具有规则微观几何形貌特征的缸套内表面润滑理论模型，用变异的多重网格法进行了数值求解，并对微观几何形貌参数进行了初步的优化设计。研究结果表明，即使在两个平面摩擦副上进行简单的激光微凹腔造型，也能维持良好的动压润滑效果。同时得出，微凹腔的面积占有率为15％、深径比为0．5时，润滑油膜厚度增加了10％-15％，平均摩擦力减小了20％，润滑减磨效果较好。     

Quenching residual stresses in 7060 aluminium alloy gas cylinder necks

A destructive technique under development to determine residual stresses in thick-walled pressure vessels has been employed to determine quenching residual stresses in 7060 aluminium alloy gas cylinder necks. The gas cylinders were supplied with interference fit collars attached to the apex of the gas cylinder neck. The effect the elastic interference fit stresses have on the quenching residual stresses in the gas cylinder neck was also investigated. Maximum tensile circumferential quenching residual stresses were detected in the gas cylinder neck below the threaded region of the bore. The magnitude of the maximum tensile circumferential quenching residual stress was in the order of half the yield strength of the aluminium alloy. The interference fit stresses only altered the quenching residual stresses in the immediate vicinity of the threaded bore. It was concluded that the interference fit collar provided no significant effect on the magnitude of the maximum tensile circumferential quenching residual stress in the gas cylinder neck.     

A comparison of methods of calculating stress intensity factors for cracks in pipes and thin walled cylinders

This paper presents results of a study undertaken to compare stress intensity factor solutions for various crack geometries in pipes and thin walled cylinders against the equivalent flat plate K solutions. The exercise was restricted to cylinders and pipes with wall thickness to radius ratios (t/R) of 0·1.

The results of the exercise indicate that structural integrity assessments of pipes and thin walled cylinders which contain flaws should ideally incorporate representative stress intensity factor solutions. Nevertheless there are a number of crack geometries for which flat plate K solutions can provide reasonable estimates of the stress intensity factor.     

Experimental and numerical study of the natural convection from a heated horizontal cylinder wrapped with a layer of textile material

Natural convection heat transfer enhancement from a horizontal cylinder with a textile coating is studied experimentally and numerically. The coating layer may be used for two purposes. According to the thickness of the coating it may be used as an insulating material or for surface augmentation. In the experimental study, two cylinders having different diameters of 4.8 mm and 9.45 mm are used. The bare cylinders having a radius smaller than a certain critical size were wrapped with a textile material. Wrapped cylinder diameters were increased to 9 and 12.8 mm respectively after coating and constant heat flux was applied to all bare and wrapped cylinders. Experimental study was carried out at different ambient temperatures in a conditioned room which can be maintained at a stable required value and inside a sufficiently designed test cabin. The ambient and cylinder surface temperatures (T_∞ and T_w) varied between 10 °C – 40 °C and 20 °C – 60 °C respectively. Heat transfer rates from bare and wrapped horizontal cylinders were compared and heat transfer enhancement was observed. On the basis of the experimental data average Nusselt numbers were calculated and compared with the well known correlations on natural convection heat transfer from a horizontal cylinder in the specified range of Rayleigh number, and it is seen that the results are in good agreement. The problem is also investigated numerically. Experimental and the numerical results fall in ± 30% band.     

HEAT TRANSFERPREDICTIONS AROUND THREE HEATED CYLINDERS BETWEEN TWO PARALLEL PLATES

The objective of this article is to investigate the heat transfer of convective flow across three heated cylinders arranged in an isosceles right-angled triangle between two parallel plates. The variations in drag coefficient and time-averaged Nusselt number around the surface of the three cylinders as well as the surface-averaged values of the time-averaged Nusselt number for each cylinder are investigated. This investigation is considered under the conditions where the gap-to-diameter ratio is changed (0.5 to 1.25) with forced convection (Re = 100 to 300) and mixed convection (Gr = 80,000 and 200,000). The maximum value of surface- and time-averaged Nusselt number for both forced convection and mixed convection is obtained at a gap-to-diameter ratio equal to 0.75 among the gap-to-diameter ratios considered in this article.     

Stress intensity factors for internal and external cracks in pressurised thick-walled cylinders

Stress intensity factors for both internal and external semi-circular and semi-elliptical surface cracks in internally pressurised thick-walled cylinders of radius ratios between 2 and 3 are presented for a wide range of crack sizes. These solutions were obtained using the boundary integral equation (BIE) method for three-dimensional numerical stress analysis. Hoop strain distributions at the outer circumference of the cylinder are also presented for some external cracks, and shown to be useful for experimentally monitoring crack growth.     

Elastic fracture properties of all-steel gas cylinders with different axial crack types

All steel cylinders are being used for on-board storage of compressed natural gas in vehicles. Typical maximum fill pressure for these cylinder is 25.85 MPa (3750 psi). These cylinders are subjected to fluctuating pressures, due to the refueling operation. In order to establish a relevant test method to ensure leak before break failure performance in the event of a through-wall cracking, the finite element stress analysis of the design containing various defects has to be firstly carried out to get some theoretical basis for the establishment of the test method. External and internal axial semi-elliptical surface cracks are modeled. Crack front regions are modeled using singular elements, whereas the rest of the cylinder is modeled using twenty-node hexahedron elements. Not only the cylindrical body but also the neck and transition areas of the cylinder are considered in the modeling. Slender cracks with approximately 10 times the wall thickness of the cylinder, which often appear in the engineering application of all steel gas cylinders, are considered. The crack depths varied from 25% to 100% of the wall thickness. Analysis is also carried out for the cylinder with through-wall axial cracks, which have similar crack lengths with external and internal surface cracks. The cylinders are assumed to be in the elastic deformation state. Stress intensity factor, K_I, and crack mouth opening displacement, CMOD, as the functions of internal pressure, crack size, location (external verdus internal) and shape (elliptical versus straight-fronted), are established. Calculated results are compared with published results. Deep axial external cracks are found to be more severe than axial internal surface cracks having similar crack lengths. Crack driving force for a semi-elliptical through-wall crack is found to be significantly less than that of a straight-fronted through-wall cracks, which have the same crack length. So, the establishment of a relevant test method to ensure leak before break failure performance in the event of through-wall cracking is of high practical value for the engineering design and application of these cylinders.     

Numerical investigation of laminar natural convective heat transfer from a horizontal triangular cylinder to its concentric cylindrical enclosure

A numerical simulation was conducted to investigate the steady laminar natural convective heat transfer for air within the horizontal annulus between a heated triangular cylinder and its circular cylindrical enclosure. The Boussinesq approximation was applied to model the buoyancy-driven effect and the governing equations were solved using the finite volume method. Four different Rayleigh numbers and four different radius ratios were considered, and four different inclination angles for the inner triangular cylinder were investigated as well. The computed flow and temperature fields were demonstrated in the form of streamlines and isotherms. Variations of the maximum stream function and the local and average Nusselt numbers were displayed as functions of the above-mentioned parameters. Correlations of the average Nusselt number were proposed based on curve fitting. At constant radius ratio, inclination angles of the inner triangular cylinder are found to have negligible effects on the average Nusselt number.     

A numerical study of laminar natural convective heat transfer around a horizontal cylinder inside a concentric air-filled triangular enclosure

A numerical investigation of steady-state laminar natural convective heat transfer around a horizontal cylinder to its concentric triangular enclosure was carried out. The enclosure was filled with air and both the inner and outer cylinders were maintained at uniform temperatures. The buoyancy effect was modeled by applying the Boussinesq approximation of density to the momentum equation and the governing equations were iteratively solved using the control volume approach. The effects of the Rayleigh number and the aspect ratio were examined. Flow and thermal fields were exhibited by means of streamlines and isotherms, respectively. Variations of the maximum value of the dimensionless stream function and the local and average Nusselt numbers were also presented. The average Nusselt number was correlated to the Rayleigh number based on curve-fitting for each aspect ratio. At the highest Rayleigh number studied, the effects of different inclination angles of the enclosure and various cross-section geometries of the inner cylinder were investigated. The computed results indicated that at constant aspect ratio, both the inclination angle and cross-section geometry have insignificant effects on the overall heat transfer rates though the flow patterns are significantly modified.     

Laminar Momentum and Heat Transfer in a Channel with a Built‐In Tapered Trapezoidal Bluff Body

Effects of wall confinements on the laminar flow and heat transfer around a heated tapered trapezoidal bluff body are investigated numerically in the confined domain (Reynolds number, Re = 1 to 40; blockage ratio = 0.125 to 0.5; and Prandtl number, Pr = 0.71). The onset of flow separation is found between Re = 4 and 5 for the blockage ratio of 0.125 and between Re = 5 and 6 for the blockage ratios of 0.25 and 0.5. If compared with a long circular obstacle on the basis of equal projected area, the total drag coefficient of the trapezoidal cylinder is found to be larger than the circular one, but an opposite trend is observed for the heat transfer. The augmentation in heat transfer for trapezoidal and circular cylinders is found to be approximately 46, 72, 74, and 65 percent for Re = 1, 5, 10, and 40, respectively for the blockage ratio of 0.25. The maximum enhancement in heat transfer for a tapered trapezoidal bluff body with respect to a square bluff body is found to be approximately 104 percent and 101 percent for blockage ratios of 0.25 and 0.5, respectively. Finally, simple correlations of wake length, drag, and average cylinder Nusselt number are established.