Natural gas is one of the most important global energy sources, and is commonly transported in pipelines (in gaseous state) or specially-designed LNG vessels (in liquid state). As LNG is stored inside the ship cargo containment system at atmospheric pressure and low temperatures, just below the boiling point of circa -162 ◦C (depending on the composition), small perturbations in pressure or temperature may result in phase changes between the liquid and vapor phase. During transportation overseas, the motion of the ship induces movements of the LNG inside the containment system. Sloshing may result into wave impacts that potentially cause damage to the containment system. During these wave impacts, phase changes inside the LNG fluid domain are likely to occur, which alter the fluid properties locally. Insights into these phase changes during sloshing impacts are of key importance for the accurate, efficient and safe designs of cargo containment systems inside LNG vessels. The main objectives of this dissertation are twofold : (1) the development and validation of non-intrusive measurement techniques to characterize the propagation of shock waves through multiphase fluids, and (2) quantifying the energy partitioning and emission of shock waves by collapsing vapor bubble clouds. To this aim, two novel measurements techniques are developed and validated for accurately quantifying the two-phase liquid properties and the shock wave propagation, non-intrusively. Also, the emission of shock waves by collapsing vapor bubbles is assessed non-intrusively with state-of-the-art high-speed X-ray densitometry....@en

Abstract: A novel experimental imaging-based method is presented for the non-intrusive determination of shock wave characteristics (i.e. shock wave speed and magnitude, and shock-induced liquid velocity) in a bubbly flow solely from gas bubble velocities. Shock wave speeds are estimated by the relative motion between gas bubbles at two locations by splitting the camera field-of-view using a mirror construction, increasing the dynamic spatial range of the measurement system. Although gas bubbles have in general poor tracing properties of the local fluid velocity, capturing the relative dynamics provides accurate estimates for the shock wave properties. This proposed imaging-based method does not require pressure transducers, the addition of tracer particles, or volumetric reconstruction of the gas bubbles. The shock wave magnitude and shock-induced liquid velocity are computed with a hydrodynamic model, which only requires non-intrusively measured variables as input. Two reference measurements, based on pressure transducers and the liquid velocity field by particle image velocimetry, show that the proposed method provides reliable estimates for the shock wave front speed and the shock-induced liquid velocity within the experimental range of 70 < U_s< 400 m/s. Graphical abstract: [Figure not available: see fulltext.].

@en

The dynamic response of pressure sensors for model tests of sloshing impacts is paramount to recording these highly dynamic events. In this study, we investigated the dynamic behavior of the new pressure sensors presented at ISOPE 2018 (Schreier and Poelma, 2018), which increased the spatial resolution of sloshing pressure measurements by a factor of 5 compared to common sloshing pressure sensor arrangements. Wet drop tests were conducted and the resulting pressure signals were compared to theoretical results of the Wagner solution. For peak pressures over the full measurement range of the sensors, the rise time was found to be less than 0.25 ms, which was close to the theoretical minimum rise time of the generated pressures. Furthermore, the pressure sensors were found to have low sensitivity to accelerations. The results of this study indicated that these new pressure sensors were applicable for sloshing investigations.@en

The challenge presented in this research is to determine the local volumetric bubble concentration (or void fraction) in the center of a microbubble cloud with limited optical access and without disturbing the flow. By applying defocused volumetric shadowgraphy to an aerated water column we were able to measure the characteristics of single microbubbles in the control volume for a void fraction of 0.078 percent. The time-averaged local bubble concentration in the center of the water column was measured over four periods (800 seconds each) to investigate the repeatability. Two reference methods, based on differential pressure (ΦV = 0.081 percent ± 0.011) and direct observation of the bubble's in-depth z-position, both validate the results independently.@en