Interactions of pipe instabilities under static loading

Hydroelastic systems can be characterized by a simultaneous manifestation of elastic and hydrodynamic instabilities and their interaction. Mutual effects of pipe bending, internal and external pressures, the action of compression force and fluid with a set density flowing along the pipe are under consideration. A thin elastic pipe is fixed on clamped sliding supports. In this case the supports do not hinder the flow of fluid travelling inside the pipe along its axis. Outside the pipe there is the fluid at rest. At the supports, the pipe bending and rotation angle are equal to zero. Assumptions are made regarding the incompressibility of the pipe midline and also the ideality and incompressibility of the fluids. The pipe is subjected to longitudinal compression. The smallness of inertial forces is conditioned by a relatively slow change of disturbances under slowly changing external effects (compressive forces in the pipe, hydrostatic forces, velocity of fluid motion in the pipe). External effects can be both independent and interconnected with each other. Here, the static mutual influence between those instabilities is called the instability interaction in the pipeline. We have obtained the linearized equation of the pipe bend and the critical value of the force that squeezes the pipe, which represents a generalization of the classical critical value for the static longitudinal compressive force acting on the pipe in the Euler problem due to the action of pressures inside and outside the pipe and the fluid motion inside the pipe. The investigation is focused on static instability interactions depending on the compression force in the pipe, internal and external pressures and fluid velocity. Given the large number of input parameters, it is possible to identify a great number of particular cases being important in their own right. Some of them are considered here. The domains of change for these parameters are determined by the occurrence of stabilization and destabilization of the rectilinear shape. Bending rigidity, tensile forces and external hydrostatic pressure stabilize the pipe. By contrast, compressive forces, internal hydrostatic pressure and fluid movement inside the pipe at any velocity have a destabilizing effect.