A ship in waves may experience a water impact event known as a slam. In this paper, slam-induced bending of wave-piercing catamarans in head seas is predicted by way of fluid-structure interaction simulations. The slamming flow field during slamming of a wave-piercing catamaran is highly non-linear and cannot be accurately captured using potential flow methods as a result of the interactions between the flow fields produced by water entry of the separate demihulls and centre bow. Thus, the Reynolds-Averaged Navier-Stokes (RANS) equations are solved for rigid body motion of a vessel at model-scale. Verification and validation is conducted using model-scale data from a Hydroelastic Segmented Model (HSM). One-way and two-way interactions are computed considering vibration of the hull girder. In the case of one-way interactions, the computed fluid loads affect the structure, but the structural response does not affect the fluid domain solution whereas for the two-way interactions the structural response affects the fluid solution. A new method for capturing the non-linear time variation in added mass is developed and deemed necessary when computing one-way interactions, primarily as a result of the large changes in forward wetted area present for a wave-piercing catamaran. It is shown that two-way interaction simulation is not needed for predicting the slam induced hull girder loads. One-way interaction simulation can therefore be used allowing reduced computational effort.
When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure which has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort.
A customized vertical wind tunnel has been built by the University of Canterbury Rocketry group (UC Rocketry). This wind tunnel has been critical for the success of UC Rocketry as it allows the optimization of avionics and control systems before flight. This paper outlines the construction of the wind tunnel and includes an analysis of flow quality including swirl. A minimal modelling methodology for roll dynamics is developed that can extrapolate wind tunnel behavior at low wind speeds to much higher velocities encountered during flight. The models were shown to capture the roll flight dynamics in two rocket launches with mean roll angle errors varying from 0.26˝to 1.5˝across the flight data. The identified model parameters showed consistent and predictable variations over both wind tunnel tests and flight, including canard-fin interaction behavior. These results demonstrate that the vertical wind tunnel is an important tool for the modelling and control of sounding rockets.
When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short-duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure that has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort. The effect of the slam load temporal distribution on the whipping response and vertical bending moment are investigated here by using a continuous beam model with application to a 112 m INCAT wave-piercing catamaran and correlation to full-scale and model-scale experimental data. Experimental studies have indicated that the vertical bending moment is dominated by the fundamental longitudinal bending mode of the structure. However, it is shown here that although the fundamental mode is dominant in the global structural response, the higher order modes play a significant role in the early stages of the response and may not be readily identifiable if measurements are not taken sufficiently close to the slam location. A relationship between the slam duration and the relative modal response magnitudes is found, which is useful in determining the appropriate truncation of a modal solution.
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