RESUMO
This article develops a numerical model suitable for analysing elastic wave scattering in buried pipelines. The model is based on a previous so-called hybrid approach, where a nominally infinite length of pipe is split up into uniform and non-uniform regions. The key challenge for buried structures is in enforcing the appropriate boundary conditions in both the axial and radial directions, which must encompass the entire length of the structure, as well as the surrounding material. Accordingly, the focus of this article is on developing a model suitable for accurately applying these boundary conditions, and so the analysis is restricted here to the study of axisymmetric defects and to an incident sound field that consists of the fundamental torsional mode only. It is shown that this problem may be addressed in a numerically efficient way provided one carefully choses a perfectly matched layer for the surrounding material, and then integrates over this layer using a complex co-ordinate stretching function. This enables the use of mode matching to deliver a convergent system of equations that enforce the appropriate axial and radial boundary conditions.
RESUMO
Viscoelastic coatings are often used to protect pipelines in the oil and gas industry. However, over time defects and areas of corrosion often form in these pipelines and so it is desirable to monitor the structural integrity of these coated pipes using techniques similar to those used on uncoated pipelines. A common approach is to use ultrasonic guided waves that work on the pulse-echo principle; however, the energy in the guided waves can be heavily attenuated by the coating and so significantly reduce the effective range of these techniques. Accordingly, it is desirable to develop a better understanding of how these waves propagate in coated pipes with a view to optimising test methodologies, and so this article uses a hybrid SAFE-finite element approach to model scattering from non-axisymmetric defects in coated pipes. Predictions are generated in the time and frequency domain and it is shown that the longitudinal family of modes is likely to have a longer range in coated pipes when compared to torsional modes. Moreover, it is observed that the energy velocity of modes in a coated pipe is very similar to the group velocity of equivalent modes in uncoated pipes. It is also observed that the coating does not induce any additional mode conversion over and above that seen for an uncoated pipe when an incident wave is scattered by a defect. Accordingly, it is shown that when studying coated pipes one need account only for the attenuation imparted by the coating so that one may normally neglect the effect of coating on modal dispersion and scattering.
RESUMO
BACKGROUND: Guidelines advise chronic obstructive pulmonary disease (COPD) should be diagnosed and managed by using spirometry to demonstrate irreversible airflow limitation and monitor change in smokers and ex-smokers aged over 35 years. METHODS: A cross-sectional study of patients and their general practitioners investigating use of spirometry in COPD in two practices by lung function assessment, review of practice records, interviews and focus groups. RESULTS: Sixteen GPs, and 38 patients with a diagnosis of COPD participated. At diagnosis, although 72% had spirometry, this occurred in only 41% of 17 patients diagnosed by a GP; but in all 19 cases when a specialist was involved. Diagnosis often occurred late, despite all patients having previously recorded symptoms typical of COPD. General practitioners expressed a preference to diagnose COPD on clinical grounds. Although 58% of patients had recent spirometry for current management, only 32% were performed by their GP. There were organisational and technical barriers to spirometry and poor recognition of the essential role of spirometry in the diagnosis of COPD. DISCUSSION: There are a number of potentially reversible factors that hinder practice recommendations regarding the use of spirometry in general practice to diagnose and manage COPD.