Continuous Pipes Research Articles

Eigenvalue branches and modes for flutter of cantilevered pipes conveying fluid

This paper describes the relationship between the eigenvalue branches and the corresponding unstable modes associated with flutter of cantilevered pipes conveying fluid. The order of branches in root locus diagrams is clearly defined. The flutter configuration of the pipes at the critical flow velocities are drawn graphically at every 12th period to define the order of quasi-mode of flutter configuration. The transferences of flutter-type instability from one eigenvalue branch to another are thoroughly investigated and discussed in case of continuous pipes conveying fluid. The critical mass ratios, at which the transference of the eigenvalue branches related to flutter take place, are definitely determined.

A DISCRETE APPROACH FOR ANALYSIS OF SOUND TRANSMISSION IN PIPES COUPLED WITH COMPACT COMMUNICATING DEVICES

A new discrete method is presented for acoustic modelling of pipes that are coupled by compact devices. This is based on an approximate source analogy that allows the communicating devices to be modelled as continuous two-port elements. One of the areas in which this method finds application is the acoustic analysis of mufflers with multiple perforated pipes. For this case, the present formulation assumes fundamental mode propagation for simplicity. Also presented in the paper are applications in which perforate holes are modelled as continuous visco-thermal pipes, the results of which are compared with the lumped parameter modelling of perforate impedance. In general, the present method is computationally simpler and more versatile than the more commonly known distributed parameter method.

Dynamic behaviour of continuous buried pipes subject to earthquakes

Although seismic events only rarely cause structural damage to buried pipelines, they can nevertheless sometimes result in a significant loss of functionality, which will hamper recovery in the affected areas immediately following the earthquake. While the dynamic response of a pipe is obviously dependent on the characteristics of the seismic event and the type of pipe in question, a careful assessment of the stresses induced by the earthquake cannot neglect the interaction between the pipe and the surrounding soil. In the present paper a numerical model is developed for evaluating the dynamic stresses acting on buried pipes under the hypothesis that the soil is a Winkler elastic medium and the pipe can be held to be continuous thanks to the welded joint employed. The particular feature of this approach lies in the fact that, unlike similar soil-pipe interaction models, the pipe is not considered to be of infinite length but introduces pipe length and the type of constraint into the assessment of earthquake effects. In particular, the numerical analysis so far conducted shows that once the characteristics of the seismic wave, the soil, and the pipe have been assigned, the pipe's maximum axial displacement values may even be greater than those of the soil; this displacement is also affected by pipe length and the type of constraint.

Effectiveness of Anti-Liquefaction Techniques for Buried Pipelines

Abstract In this paper, effectiveness of several existing anti-liquefaction methods for preventing large deformations of pipelines for lateral flow of liquefied grounds during earthquakes are investigated and compared, as well as a proposed method which fixes pipelines with expansion joints parallel to auxiliary continuous pipes using iron tie-plates. Stiffness of liquefied soils around pipes is represented as a static coefficient of subgrade reaction, based on the experiments on the interaction between liquefied sand deposits and pipes. Pipeline-spring systems which are characterized by those coefficients are analyzed based on the theory of “a beam on an elastic foundation” and transfer matrix method. Computations are performed with respect to the key parameters of pipes, coefficient of subgrade reaction, and several fixing conditions between pipes and underground structures. The sliding displacements of pipelines, rotational angles of joints, and stresses of pipelines are compared for such anti-liquefaction methods as soil-improving methods (sand-compaction pile or ballast-replaced soil methods) and structural-stiffening methods (parallel pipe or pile-supporting methods).

A study of the microstructure and properties of continuous casting rare earth ductile iron pipes

Abstract Continuous casting procedures are simpler than centrifugal casting. Continuous casting rare earth ductile iron can be obtained by adding REMgSiFe. This paper researches the effect of elements on structures and properties of rare earth ductile iron pipes. Methods for improving the properties of rare earth ductile iron pipes are discussed. The strength and elongation of the pipe are 515-485 MPa and 2.5–2.7% without heat treatment or 440-425MPa and 7–16% with heat treatment. The microstructure of the matrix of continuous casting rare earth ductile iron pipes are ferrite or pearlite or ferrite plus pearlite. In China, continuous casting rare earth ductile iron pipes have been produced successfully and used in different fields.

Applications of research on ductility of structures

A limit states criterion of ductility is described for nonlinear behaviour of structural members in flexure. Experimental results and theoretical models are reported for the behaviour of steel and composite continuous beams, portal frames, and continuous steel pipes. The ductility criterion is used to identify the basis for analyzing the load effects and resistances of these elements. Key words: limit states, ductility, analysis, design, beams, pipes, steel, composite, resistance.

Strength of pipes continuous over a series of saddle supports

Abstract An experimental investigation is described of the ultimate strength of pipe specimens representing the support region of continuous pipes on saddle supports. Variables that are considered include diameter-to-thickness ratios in the range from 28 to 100, span-to-diameter ratios from 16 to 98, and two different saddle arrangements. Ultimate-moment capacities are compared with code recommendations, and the influence of the saddle support is described.

Dynamic Behavior of Continuous Cantilevered Pipes Conveying Fluid Near Critical Velocities

The plane motion of a cantilevered pipe conveying fluid is examined when the flow velocity is in the neighborhood of that generating flutter. In contrast to previous studies, the flow velocity is not prescribed as a constant, but is determined from the laws of motion. We are thus led to a system of two nonlinear partial differential equations which are coupled through the nonlinear terms. The solution is found by the use of the Krylov-Bogoliubov averaging method and the results are discussed indicating the effect of nonlinearities.