ABSTRACT. In this paper the motion of a small sport boat running on a lake is simulated using alaska tools. External forces and torques from water during movement have been taken into account. Using results from measurements the simulation has been validated. Keywords. multibody system equations, fluid forces and torques to running boat, validations by measurement.
While drop oscillation dynamics has been widely studied for many decades, the influence of a moving contact line on the oscillation modes of drops remains underexplored. Herein, we report the oscillation dynamics of drops on thin liquid films with different viscosities where lower viscosities provide a slipping surface and higher viscosities immobilize the contact line. A gently deposited drop onto an oil film undergoes shape oscillations due to capillarity, where the frequency, amplitude, and apparent contact angle are tracked via a high-speed camera. This study demonstrates that restraining the mobility of the drop contact line by increasing the viscosity of a thin oil film underneath the drop increases the extent of the drop oscillation time as well as affecting the natural frequency of the drop oscillation. The drop oscillation time was defined by the time at which the changes in the drop height dropped to values less than 1% of the equilibrium height. The experimental results for the first longitudinal mode oscillation frequencies as a function of the equilibrium contact angles for the pinning and slipping contact lines were in good agreement with previously reported numerical simulations and model predictions.
presented for the various drop impact regimes for the thin (i.e., O(1 μm))and thick (i.e., O(100 μm)) liquid film thickness limits. The incidence of the contact bouncing phenomenon was also characterized and found to be intimately tied to the late-stage gas film failure where a small volume of liquid is deposited onto the liquid film prior to bouncing. This study sheds new light on the bouncing-merging transitions for drops on ultrathin liquid films and gas entrainment dynamics relevant to applications such as precise drop deposition techniques.
Recent studies have revealed the air-cushioning effect of droplet impact upon various surfaces and although pure water droplets have been studied extensively, the air entrainment dynamics for aqueous polymeric droplets is the focus of this study. Herein, we show that for low to moderate Weber numbers, We ~ O(1 - 10), the air film thickness gradient is strongly influenced by the viscoelastic properties of the aqueous polymeric droplets in the dilute to the semidilute unentangled regimes. Droplets of aqueous polyethylene oxide (PEO) impacting a smooth thin oil film surface formed a submicron air layer moments prior to impact, which was tracked by a high-speed total internal reflection microscopy (TIRM) technique. The radial changes in the air film thickness were related to the polymer concentration, thus providing an alternative tool for comparing the rheometer-derived overlap concentrations with a contactless optical technique.
This study proposes and investigates the impact of a modification, accounting for the influence of vortices and flow properties on the liquid rupture, to improve the modeling of mass transfer rate in cavitation. The threshold phase-change pressure is calculated by the fluid-saturated pressure at rest and the added vortex pressure term. The explicit simulation of the fully turbulent, homogeneous compressible, cavitating flow around the NACA0015 hydrofoil and the hemispherical body is performed. Saito cavitation model and Wilcox k-ω turbulence model are implemented for the evaluation of the proposed modification. The pressure coefficient distribution -Cp and cavitation behavior, including the vapor formation-collapse processes and the flow mechanism, are investigated. The analysis shows that the present modification, coupled the local flow viscosity with the vorticity magnitude, making the cavitation model better sensitive to the flow condition. The modification has a weak impact on the steady sheet cavitation around a hemispherical body but is the key factor underlying the improvement in the predicted complex flow around the NACA0015 hydrofoil. In that, the predicted -Cp and cavity structure around the hydrofoil is improved in comparison with the existing numerical data by other research groups and that by the Singhal turbulent pressure fluctuation model.
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