Finite element analysis of a fluid-structure interaction in flexible pipe line

This paper describes the basic theory and computing method for transient flow of liquid in flexible pipe such as rubber tubing and arterial system. A mathematical model taking into account tube wall axial and radial motion (in which the dynamic fluid pressure causes circumferential and axial motion of the tube wall) is presented. The tube wall is assumed to be elastic material and the compressibility of the liquid is neglected. Circumferential and axial strain-stress relationships for the tube are considered. The obtained mathematical system is constituted of four non-linear hyperbolic partial differential equations describing the wave  propagation in both pipe wall and liquid flow. The fluid-structure interaction is found to be governed by Poisson’s ratio. In this steady finite element method based on Galerkin formulation is applied. Numerical results show a good similarity with those of the literature obtained by the characteristics method.Key words : Fluid-structure interaction, flexible pipe, rubber, finite element method

Transient analysis for leak detection in pipe with fluid-structure interaction

The use of fluid transients has the potential to provide insight into effect of leaks in pipeline systems and hence provide leak detection method. This paper presents a technique for detection and location of leaks in a single pipe by means of transient analysis. The method uses transient pressure waves initiated by the sudden closure of an upstream valve. The presence of a leak in a pipe partially reflects these pressure waves and allows for the location and magnitude of leaks. The two constitutive equations of continuity and momentum yield a set of two partial differential equations of hyperbolic type. The computed results obtained by the method of characteristics describe the influence of the leak on head and discharge time-histories. To put in evidence the fluid-structure, interaction the influence of friction and Young modulus of the pipe wall on the leak detection and sizing is also discussed

Water pipeline failure due to water hammer effects

A numerical model has been established in order to simulate the propagation of pressure waves in water networks. The present model formulation is based on a system of partial hyperbolic differential equations. This system has been solved via the characteristics method. The current model provides the necessary data and the necessary damping of water hammer waves, taking into account the structure of the pipe network and the pressure loss. The numerical algorithm estimates the maximum pressure values resulting from the water hammer when closing valves in the network and consequently, the maximum stresses in the pipes have been calculated. In the case of simultaneous closing of several valves, the over pressure can exceed the admissible pressure. In this case, the severity of a defect such as a corrosion crater (pit) has been estimated by computing a safety factor for the stress distribution at the defect tip. This allows the applied notch stress intensity factor to be obtained. To investigate the defect geometry effects, semi-spherical and semi-elliptical defects are deemed to exist in up to one-half of the thickness of the pipe wall. The outcomes have been introduced into the structural integrity assessment procedure (SINTAP) failure diagram assessment (FAD) in order to obtain the safety factor value. Conventionally, it is considered that a failure hazard exists if this safety factor is less than two

Visualizing Readable Instance Graphs of Ontology with Memo Graph

International audienceIn the context of the Captain Memo memory prosthesis for Alzheimer’s patients, we want to generate the family/entourage tree of the user from data structured based on the PersonLink ontology. This graph ought to be accessible and readable to this particular user. In our previous work, we proposed an ontology visualization tool called Memo Graph. It aims to offer an accessible visualization to Alzheimer’s patients. In this paper, we extend it to address the readability requirement based on the IKIEV approach. It extracts the most important instances (key-instances) from ontology and generates a “summary instance graph” (middle-out browsing method). The extraction and visualization processes are undertaken incrementally. First, an “initial summary instance graph” is generated, then permitting iteratively the visualization of supplementary key-instances as required. Key-instances’ extraction is based on measures that take into account the semantic similarity between the ontological elements and the user’s navigation history

Management of albinism: French guidelines for diagnosis and care

Albinism is a worldwide genetic disorder caused by mutations in at least 20 genes, identified to date, that affect melanin production or transport in the skin, hair and eyes. Patients present with variable degrees of diffuse muco-cutaneous and adnexal hypopigmentation, as well as ocular features including nystagmus, misrouting of optic nerves and foveal hypoplasia. Less often, albinism is associated with blood, immunological, pulmonary, digestive and/or neurological anomalies. Clinical and molecular characterizations are essential in preventing potential complications. Disease-causing mutations remain unknown for about 25% of patients with albinism. These guidelines have been developed for the diagnosis and management of syndromic and non-syndromic forms of albinism, based on a systematic review of the scientific literature. These guidelines comprise clinical and molecular characterization, diagnosis, therapeutic approach and management