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Particle image velocimetry (PIV) processing of free surface flow images often requires the use of digital masks to overcome the problems caused by the interface. In cases where a large number of particle images are collected it is essential that the time-varying boundary between the two phases can be tracked automatically to produce the binary masks. The Radon transform-based technique presented in this paper allows the automatic detection of the air-water interface in a stream of particle images acquired from a single camera. It is applied to time-resolved PIV measurements in the liquid phase of a stratified multiphase flow in a circular pipe. Accuracy estimations are provided using synthetic and real wave profiles. An extension to the more complex case of an overturning wave is also discussed.

In many future subsea projects, there will be a requirement to cool various fluid streams, either multi-phase or single phase. To meet this need, FMC Kongsberg Subsea AS (FMC) has undertaken a project to develop a practical and robust subsea cooler. The cooler is passive in that heat is transferred to the surrounding sea water by natural convection only. Because of the subsea application, the cooler must have a special geometry to meet requirements for modularization and easy installation/removal. The passive nature of the cooler means that the flow rate of the seawater coolant is not an independent variable, but is directly linked to the cooler geometry. Developing a design method for such coolers requires detailed knowledge of the important heat transfer parameters, to an accuracy far in excess of that normally required for industrial cooler design. This problem has been approached on several levels, including an extensive literature search, theoretical studies, and model testing. One of the first observations was that little research had been done previously on this type of cooler. Much information is available for various pieces of the problem, but it became clear that designing the cooler would require significant development work. Based on the knowledge gained during the initial theoretical studies, a theory for calculating cooler performance presuming one dimensional external coolant flow has been developed. While it is clear that the actual external flow is three-dimensional, the simplified theory gives important insights into how the various design parameters affect cooler performance. To fill in the gaps in theoretical knowledge, a series of model tests designed to quantify internal and external heat transfer coefficients for the special geometry is being proposed. The testing program covers several technical areas and has required the utilization of a number of advanced measurement techniques. For the next phase of the testing program, a complete new test facility has been constructed capable of testing coolers with cross-flows typical of ocean bottom currents. The cooler development program has provided new technology which will be used to construct robust and compact subsea coolers. Because of the emphasis on basic research, fundamental knowledge and insight of the heat transfer mechanisms governing the performance of this type of cooler are acquired. This knowledge gives FMC the capability to design and manufacture subsea coolers which are custom-made to match the exact requirements of a given application.

VIV experiments in two degrees of freedom are performed with a new apparatus designed to achieve a very low mass ratio and structural damping (ζ = 0.01). We investigated the influence of the ratio between the natural frequencies in the horizontal (fx) and vertical (fy) directions on the system response. Experiments were conducted at fx/fy = 0.42, 0.87, 1.16, 1.36 and 1.44 with mx* = 2.87 and my* = 1.65. For fx/fy < 1, the amplitude and frequency response were found to be similar to the classical case where fx/fy = 1, except in the transition zone between the upper and lower branches. For fx/fy > 1 however, radical changes were observed in the system response in amplitude, frequency and phase θ between the horizontal and vertical displacements. The most obvious is the appearance of a local maximum of Ay* in the middle of the upper branch. Secondly, the nature of the transition between the upper and lower branches changes from intermittent switching to a hysteretic one. The shape of the figure-of-eights describing the cylinder trajectory is also affected so that the cylinder is moving upstream at the top of its trajectory instead of downstream, indicating a profound modification of the interaction between the two degrees of freedom. Lastly, the range of reduced velocities over which stable, two-degrees-of-freedom oscillations were recorded is greatly increased up to 3.8 < U* < 8.4.