[en] The dynamic fluid-structure interaction (FSI) during hydraulic transient is known to be of special importance for flexible or movable pipeline system. Some kinds of FSI effects can be observed however even for relatively rigidly supported pipeline. Such effects, not anticipated by the classic waterhammer theory, were identified during experiments on waterhammer phenomenon conducted at a laboratory rig in the Szewalski Institute of Fluid-Flow Machinery of the Polish Academy of Sciences in Gdansk (IMP PAN). Additional pressure oscillations of higher frequencies observed during experiments were supposed to be the result of dynamic fluid-structure interaction. The problem of hydraulic transient with FSI effect taken into account has been of IMP PAN interest for some time and the four equation model of the phenomenon was applied and implemented at a computer program. A method of characteristics with time marching procedure and a 'wave method' for solving the resulted finite difference equations were used at the algorithm. Selected measured and computed pressure records during the transient are presented in the paper. The analyses of the results allows to conclude that the additional effects observed at experiments were really produced by FSI effect (Poisson coupling). Some discrepancies between experimental and numerical results exist however and the analysis and attempt to explain the causes of them are proposed as well.

[en] Highlights: • Different spatial-temporal resolution for fluid and solid structure. • Position-based Verlet time integration scheme. • Time-averaged velocity and acceleration to enhance structure-fluid force matching. In this paper, we present a multi-resolution smoothed particle hydrodynamics (SPH) method for modeling fluid-structure interaction (FSI) problems. By introducing different smoothing lengths and time steps, the spatial-temporal discretization is applied with different resolutions for fluid and structure. To ensure momentum conservation at the fluid-structure coupling, a position-based Verlet time integration scheme is introduced. Furthermore, the time-averaged velocity and acceleration of solid particles are introduced to enhance force matching in the fluid and solid equations. A set of numerical examples including several bio-mechanical problems are considered to demonstrate the efficiency, accuracy and robustness of the present method. An open-source code for all the examples is also provided.

[en] This paper analyses the origin of accuracy loss near the axis of revolution in explicit methods and proposes remedies. Two important and popular practical elements are investigated: a thin conical shell element and the nine-node isoparametric continuum element (Lagrange). The mass lumping procedure which is of prime importance to ensure good performance in an explicit method is identified to be the principal cause of the observed troubles. While in the shell element the incompatibility lies mainly in the definition of external forces to be compatible with the lumped masses, the continuum element apparently fails due to the appearance of zero mass terms on the axis. These short-comings are discussed and a suitable conical shell element for thin structures coupled to a fluid is presented. It is furthermore shown that the presence of zero mass terms in the nine-node elements are profitable rather than disturbing, in particular as far as representation of the symmetry conditions is concerned. (orig./HP)

No abstract available

[en] This study numerically investigates the effects of fluid-structure interaction (FSI) on the trailing-edge noise, particularly for the cases of wake instability and Karman vortex shedding. The trailing edge is modeled as a flat plate with an elastic cantilever end and its flow-induced vibration is solved by an eigenmode analysis with the Galerkin method. The flow and sound coupled in the FSI analysis are computed on the moving grid by a direct numerical simulation (DNS) procedure. The computed result of wake instability shows that when the first-eigenmode natural frequency ωn of the cantilever is close to be resonant with the wake characteristic frequency ωc, the sound pressure level (SPL) is significantly reduced by 20 dB at ωn/ωc=0.95, or increased by 15 dB at ωn/ωc=1.05, for all angles. For the Karman vortex shedding, a similar frequency modulation occurs via FSI, if ωn is close to ωc. The flow and acoustic details are somewhat different for this case but a considerable noise reduction was also possible for angles from -120 .deg. to +120 .deg.

[en] The dynamic behavior of a submerged structure is of interest to various engineering applications such as the nuclear industry. Typically, the dynamic effect of fluid on a submerged structure is modeled as added-mass terms in the structure mass matrix. This approach is quite effective for a simple structure, where the added mass term is known analytically and the well-developed analysis techniques for the dry structure can be applied. However, the dynamic behavior of a submerged structure can be significantly affected by neighboring structures, and this is not an uncommon case for a general structural system. In this work, using concentric pipes, it will be shown that the added-mass approach is invalid and the FSI (fluid-structure interaction) analysis is practically the only viable option for such a structural system

[en] INSCSP-R7 Standard Problem based on ENTEK BM Test Facility is investigated by RELAP5 code for prediction of averaged cross-section void fraction in vertical boiling channel of 7 m height. This standard problem also gives a challenge in application of CFD code such as ANSYS CFX to predict void fraction along the channel mentioned above due to: (a) only ten measured averaged cross-section void fraction given along the channel of 7 meters and (b) CFD simulation of boiling flow is mainly appropriate with sub cooled boiling. This study presents prediction of averaged cross-section void fraction along the channel of INSCSP-R7 Standard Problem using ANSYS CFX with calibration of parameter in boiling model based on experiment measured results.(author)

[en] This device includes a lower annular lagging ring, marking an inside peripheral edge, clear of the main vessel and secured to the lower end of an inside lagging baffle the upper end of which is secured to the main vessel, and an outside peripheral edge clear of the safety vessel and secured to the lower end of an outside lagging baffle of which the upper end is secured to the safety vessel, each one of the lagging baffles being flexible so as to offset any differential expansion or deformation of the vessels

[en] Investigations of bistable flow structure past a pair of cylinders positioned side-by-side in shallow water is conducted experimentally applying dye observation and the particle image velocimetry (PIV) method. For the gap ratio of G/D = 1.25, the jet-like flow between cylinders deflects asymmetrical flow structures forming a large-scale wake as well as a small-scale wake downstream of cylinders. The small vortices around the right cylinder get closer to each other forming a larger vortex in the large-scale wake region, which leads the jet-like flow to changeover side to side. The small frequency (f = 0.352 Hz) associated with frequency of vortex shedding of cylinder with wider wake and the higher frequency (f = 0.793 Hz) which depicts the smaller wakes frequency. (author)

[en] A 'channel' model was developed for the purpose of simulating the interactive fluid-structural response of curved pipes to pressure pulses. Simulation is shown to have been achieved analytically in both the axisymmetric ('breathing') and transverse ('bending') modes of interactive behavior. An experimental program which was aimed at the validation of the model is also described. Tests were run in both straight and curved pipe configurations. Comparisons between measurements and model calculations demonstrate the validity of the model within the range of parameters under consideration. The model was implemented into the DISCO code for nonlinear fluid-shell interaction. (orig.)