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During operation mechanical structures can experience large vibration amplitudes. One of the challenges encountered in gas-turbine blade design is avoiding high-cycle fatigue failure usually caused by large resonance stresses driven by aeroelastic excitation. A common approach to control the amplitude levels relies on increasing friction damping by incorporating underplatform dampers (UPD). An accurate prediction of the dynamics of a blade-damper system is quite challenging, due to the highly nonlinear nature of the friction interfaces and detailed validation is required to ensure that a good modelling approach is selected. To support the validation process, a newly developed experimental damper rig will be presented, based on a set of newly introduced non-dimensional parameters that ensure a similar dynamic behaviour of the test rig to a real turbine blade-damper system. An ini- tial experimental investigation highlighted the sensitivity of the measured response with regards to settling and running in of the damper, and further measurements identified a strong dependence of the nonlinear behaviour to localised damper motion. Numerical simulations of the damper rig with a simple macroslip damper model were performed during the preliminary design, and a comparison to the measured data highlighted the ability of the basic implicit model to capture the resonance frequencies of the system accuratelyю

Correct interpretation of the urinary sodium concentration (NaU) and its relation to renal function in critically ill patients is lacking. Our aim was to evaluate the relationship between simultaneous NaU value and serum creatinine (sCr). The hypothesis is that a NaU value greater than 140 mmol/l (normal equivalent value in plasma) is only found in patients with normal sCr. We made a retrospective analysis of 1153 simultaneous samples of NaU and sCr, divided according to diuretic use in the previous 24 hours and grouped in five distinct NaU ranges (< 20, 20 to 39, 40 to 139, 140 to 169, ≥ 170 mmol/l). NaU values below 140 mmol/l were found simultaneously with both normal and increased sCr. NaU values above 140 mmol/l were almost always found in patients with normal sCr, even if diuretics were used. Median sCr values in the NaU ranges above 140 mmol/l were significantly lower than in the other NaU ranges. Estimated glomerular filtration rates were lower and intensive care unit and hospital mortalities were higher in patients with NaU values lower than 140 mmol/l compared to patients with a NaU higher than 140 mmol/l. We concluded that a high natriuretic capacity reflects significant residual renal function in the critically ill. NaU greater than normal plasma sodium is a possible biomarker of normal/improving renal function and also of better outcome. Sole NaU values below 140 mmol/l are difficult to interpret but it is possible that very low NaU values may signify some threat to normal kidney function and worse prognosis even in the presence of normal sCr. Our way to interpret NaU values in critically ill patients needs further careful evaluation.

This paper investigates the three dimensionality of the unsteady flow responsible for stall flutter instability. Nonlinear unsteady Reynolds-averaged Navier–Stokes (RANS) computations are used to predict the aeroelastic behavior of a fan blade at part speed. Flutter is experienced by the blades at low mass flow for the first flap mode at nodal diameter 2. The maximal energy exchange is located near the tip of the blade, at 90% span. The modeshape is radially decomposed to investigate the main source of instability. This decomposition method is validated for the first time in 3D using a time-marching nonlinear solver. The source of stall flutter is finally found at 65% span where the local vibration induces an unstable oscillation of the shock-wave of large amplitude. This demonstrates that the radial migration of the pressure fluctuations must be taken into account to predict stall flutter.

Snaking bifurcations in a chain of mechanical oscillators are studied. The individual oscillators are weakly nonlinear and subject to self-excitation and subcritical Hopf-bifurcations with some parameter ranges yielding bistability. When the oscillators are coupled to their neighbours, snaking bifurcations result, corresponding to localised vibration states. The snaking patterns do seem to be more complex than in previously studied continuous systems, comprising a plethora of isolated branches and also a large number of similar but not identical states, originating from the weak coupling of the phases of the individual oscillators. [ABSTRACT FROM AUTHOR]