Hydrophobic surfaces, enabling flow slip past a solid boundary, can be effective for suppressing flow unsteadiness, as well as for heat transfer enhancement; both are important for heat exchanger applications. In the present work, a computational investigation of forced convection heat transfer in cross-flow past a hydrophobic circular cylinder is performed at a Reynolds number value of 300, for which flow past a non-hydrophobic cylinder is three-dimensional. Here, the cylinder surface is maintained at a constant temperature, whereas a Prandtl number of unity is considered. Surface hydrophobicity is modelled based on the Navier model. In a first step, slip conditions are implemented on the entire cylinder surface (full slip), for a nondimensional slip length b* = b/D = 0.20, b being the slip length and D the cylinder diameter. This results in a suppression of flow unsteadiness, as well as in a simultaneous heat transfer enhancement; the latter is quantified by the increase of the mean Nusselt number. Next, in order to reduce the extent of the hydrophobic region, and thus the associated cost, a partial slip setup is considered. This setup consists of alternating hydrophobic and non-hydrophobic strips along the spanwise direction, the width of which is selected considering the spanwise wavelength, λ z , of three-dimensional flow. Further, following recent studies of the authors on two-dimensional flow, a non-hydrophobic region is considered around the average rear stagnation point (in the circumferential direction), for all hydrophobic strips. It is shown that the present setup can result in values of mean Nusselt number comparable to those attained with full slip. Overall, the present results illustrate that a proper implementation of partial hydrophobicity on the cylinder surface, along the circumferential and the spanwise direction, results in a suppression of wake unsteadiness and fluctuating forces, as well as in a simultaneous enhancement of heat transfer rates.

This paper describes the results of weld model analysis and deep hole-drilling measurements undertaken to evaluate residual stress distributions in austenitic and ferritic steel thick section electron beam welds. The work was undertaken in support of a Rolls-Royce and TWI development programme in the UK, for a Reduced Pressure Electron Beam (RPEB, 0.1 to 1mbar) welding process using a mobile local vacuum seal for the manufacture of thick section pressure vessel and pipe welds for nuclear power plant applications. Measurements were undertaken on representative mock-ups including a 160mm thick SA508-3 forging circumferential seam weld, in both the as-welded and furnace post weld heat treated condition. A 316L stainless steel plate butt weld and a 304L pipe girth weld of 80mm and 36mm thickness respectively were also analysed. There is now considered to be sufficient understanding of the residual stress fields generated by thick Electron Beam (EB) welds, to propose through thickness ‘upper bound’ R6 Level 2 stress profiles for use in defect tolerance assessments. The intention is to incorporate residual stress profiles of this type into the R6 structural integrity assessment procedure, following peer review. This would represent a significant step forward in demonstrating technology readiness for plant applications. It is also anticipated that an ASME Code Case will be drafted and proposed for the RPEB welding process. EB welding is a relatively low heat input process, compared with a multi-pass arc weld, such that the fusion zone and heat affected zone are narrow. The centre of an EB weld is the last region to solidify and cool-down, so typically there is a high degree of restraint to weld metal contraction, thereby generating a highly tri-axial yield magnitude tensile stress state at the mid-thickness location. The stress components acting in the longitudinal welding direction and through-thickness orientation tend to be large in the centre of EB welds of high aspect ratio (depth / width). By contrast, lower stress levels are produced on the surfaces acting transverse to the weld plane compared to conventional multi-pass metal arc welds. The transverse stress component is most likely to be required for the assessment of any postulated EB welding defects. The residual stress field decays rapidly with distance from the EB joint into the adjacent parent metal. Symmetrical stress distributions are typically generated in a 1-pass EB plate weld and stress fields are characteristically sinusoidal of wavelength between 1 and 4 times the section thickness.

This paper analyzes the adequacy of shell models for predicting stresses and strains in thick-walled tubes subjected to detonation loads. Of particular interest are the large axial strains which are produced at the inner and outer surfaces of the tube due to bending along the tube axis. First, comparisons between simple shell theory and a static finite element model are used to show that the axial strain varies proportionally with wall thickness and inversely with the square of the axial wavelength. For small wavelengths, this comparison demonstrates nonlinear behavior and a breakdown of the shell model. Second, a dynamic finite element model is used to evaluate the performance of transient shell equations. This comparison is used to quantify the error of the shell model with increasing wall thickness and show that shell models can be inaccurate near the load front where the axial curvature is high. Finally, the results of these analyses are used to show that the large axial strains which are sometimes observed in experiments cannot be attributed to through-wall bending and appear to be caused instead by non-ideal conditions present in the experiments.

Striation’s width is useful to estimate stress intensity factor range. To estimate maximum and minimum stress intensity factor, the relationship between stress ratio and aspect ratio of striation obtained by Furukawa, is used. However, accuracy of that method depends on the observer’s skill. In this paper, the parameter ( P.S. sum ), which relates to the striation height, is proposed and method for estimation of stress ratio, which is independent of observer’s skill, is also proposed. In order to calculate P.S. sum , the frequency analysis is applied to the three-dimensional geometry of striation obtained by laser microscope. The wavelength and the power spectrum are considered to indicate the striation width and height respectively. To consider the variation of striation, P.S. sum is calculated by the integration of power spectrum. The method is applied to the fatigue fracture surface of aluminum (A2024), steel (0.25% carbon) and high-tension steels. The condition of fatigue test was Δ K constant to keep the crack growth rate constant, in other words, to make the striations of which width were same. Applying the method, almost linear relationship between stress ratio and P.S. sum was obtained. Therefore, stress ratio can be quantitatively estimated by P.S. sum .

The offshore oil and gas industry uses pipes which are made flexible by means of a corrugated construction. Those pipes that run from a platform to the seabed are known as risers while those that connect two pipes on the seabed are known as jumpers. Gas flowing within the pipe interacts with the corrugations and generates noise. This noise is of concern because it is of sufficient amplitude to cause pipework vibration with the threat of fatigue and pipe breakages. This paper examines the conditions that give rise to the large noise levels. The conditions for the onset of noise are investigated using an eigenvalue approach which involves the effect of damping due to losses from the pipe boundaries and pipe friction. The investigation which is conducted in terms of reflection conditions shows why only few of the very many possible natural frequencies are selected. The conditions for maximum noise response are also investigated using a non-linear model of vortex shedding. Here an approach is developed in which the net power generated along a single wavelength is calculated.

The methods used in predicting the thermal profile of a high-pressure mercury arc lamp housed in an electronics enclosure are discussed. These types of enclosures are typically operated in harsh environments. High temperature and low pressure air is typically used to cool the electronics inside. A lamp, which dissipates roughly one half of the total power within the box, must be cooled sufficiently so as to not affect the performance of the circuit cards. Since the majority of the heat being transferred from the lamp’s center arc tube to its surrounding atmosphere (to the lamp housing and then to the circuit cards inside the electronics box) is via radiation, a Computational Fluid Dynamics (CFD) code with a radiation solver was essential to drive the design. Fluent Icepak was chosen as a capable code for electronic box type problems. However, lcepak does not account for radiative transfer through non-opaque surfaces. Since the lamp housing is very transmissive in the infrared at certain wavelengths, the energy equations could not be solved using only analytical techniques. Therefore, tests were conducted that first characterized the thermal performance of the lamp and then predicted the energy that was conducted and absorbed by the glass housing (made up of a reflector and front cover). The remaining power was then assumed to be transmissive in nature. In the computational model, powers were iteratively applied to various locations on the lamp housing until the model matched the empirical results. Once the lamp model was characterized, it could be used to drive the design of any type of enclosure in any type of environment.

The main objective of this work was to develop techniques of non-destructive testing and give them a strong theoretical underpinning to render them as quantitative as possible. Thus in ultrasonic testing the objective was to combine the traditional manual search for flaws with computer automated search and elastic scattering theory to provide quantitative data on location, size, shape, and orientation. This approach led to several schemes to solve the Inverse Scattering Problem or the reconstruction of a flaw from just a few reflected ultrasonic echoes. Early efforts led to successes with idealized man-made flaws consisting of single and compound flaws embedded in Titanium-alloy. Later this work produced results with naturally occurring flaws in aerospace components.

The nondestructive testing of concrete structures has been attempted using ultrasonic methods such as impact echo methods, though no automated remote testing method has been realized yet. The laser ultrasonic method is a non-contact nondestructive evaluation method that uses short laser pulses to generate and Continuous Wave (CW) laser radiation to detect ultrasonic waves. In the applications of ultrasonic to nondestructive testing, it is necessary to choice the characteristics of the ultrasonic field radiated by the ultrasonic transmitter. The characteristics of that exited by laser pulses determine the usefulness in detecting flaws. In this paper, we present experimental results of investigation of relation between the waveforms of the ultrasonic exited by Q-switched pulse laser and the wavelengths of the pulse laser in concrete. The experiment was carried out using the Q-switched pulse laser of several wavelengths. We clarify that it is possible to control the amplitude and the pulse width of P-wave by a choice of the pulse energy and the wavelength of the laser source respectively.

Side branches are small diameter pipes attached to a main pipeline. If a high noise level is present in the pipeline then the side branch may suffer from damaging vibration or fatigue. The mechanics of the vibration involve an acoustic resonance of the fluid within the side branch which is coupled to a structural resonance. The particular conditions investigated in this paper are where the acoustic and structural natural frequencies coincide. It is shown that the resonant vibration amplitude is controlled by the following factors: (i) the degree of correlation of the acoustic wavelength with the distances between bends in the side branch, (ii) the structural and acoustic damping and (iii) the ratio of the structural mass to the mass of the internal fluid. Simple equations are presented for conditions that will result in coupling and for the maximum amplitude of the coupled vibration.

This paper investigates the aeroacoustic response of an annular duct with co-axial side branches, and examines the effect of several passive countermeasures. The investigated geometry is inspired by the design of the Roll Posts in the Rolls-Royce LiftSystem® engine, which is currently being developed for the Lockheed Martin Joint Strike Fighter aircraft. The effects of design parameters, such as diameter ratio, branch length ratio and thickness of the annular flow on the frequency and resonance intensity of the first acoustic mode are studied experimentally. Numerical simulations of the acoustic mode shapes and frequencies are also performed. The annular flow has been found to excite several acoustic modes, the strongest in all cases being the first acoustic mode, which consists of an antisymmetric quarter wavelength along the length of each branch. The ratios of the branch length and diameter, with respect to the main duct diameter, have been found to have strong effects on the frequency of the acoustic modes. The effects of passive measures to weaken the acoustic coupling between the co-axial branches have been also investigated. These include detuning the co-axial branches, by decreasing the length of one branch, and installing a pair of splitter plates in the annular flow duct.