Steady streaming of viscous surface layer in waves

An investigation of the drift velocity induced by water waves of a contminated surface layer is carried out. The theoretical analysis is based on a thin boundary layer on the free surface. The results of the analysis reveal that the drift velocity of a viscous layer on the water surface is 7/4 times the Stokes prediction ofc(ak) ² wherec is the wave celerity andak the wave slope. The present experimental investigation confirms the validity of the theoretical prediction for the drift velocity for a lightly contaminated surface layer; however, for a heavily contaminated surface layer, the experimental results exceed the theoretical prediction. An investigation for a heavily contaminated layer is carried out assuming an inextensible surface layer. Thus, in the experiment, vinyl sheets are used to substitute the contaminated layers. By balancing the wave-induced mean thrust force with the mean drag force, the drift velocity is obtained and compared with the experimental results. Based on the theoretical and experimental analyses, formulae for predicting the drift velocities for laminar and turbulent flow conditions are proposed.     

Quantitative assessment of hydrocarbon explosion and fire risks in offshore installations

A risk-based design framework should involve both risk assessment and risk management. This article introduces and describes a number of procedures for the quantitative assessment and management of fire and gas explosion risks in offshore installations. These procedures were developed in a joint industry project on the explosion and fire engineering of floating, production, storage and off-loading units (the EFEF JIP), which was led by the authors. The present article reports partial results, focussing on defining the frequency of fires and explosions in offshore installations. Examples of the aforementioned procedures’ application to a hypothetical floating, production, storage, and off-loading unit (FPSO) are presented. A framework for the quantitative risk assessment of fires and explosions requires the definition of both the frequency and consequences of such events. These procedures can be efficiently applied in offshore development projects, and the application includes the assessment of design explosion and fire loads as well as the quantification of effects of risk control options (RCO) such as platform layout, location and number of gas detectors, isolation of ignition sources etc.     

Interactive geovisualization of activity-travel patterns using three-dimensional geographical information systems: a methodological exploration with a large data set

A major difficulty in the analysis of disaggregate activity-travel behavior in the past arises from the many interacting dimensions involved (e.g. location, timing, duration and sequencing of trips and activities). Often, the researcher is forced to decompose activity-travel patterns into their component dimensions and focus only on one or two dimensions at a time, or to treat them as a multidimensional whole using multivariate methods to derive generalized activity-travel patterns. This paper describes several GIS-based three-dimensional (3D) geovisualization methods for dealing with the spatial and temporal dimensions of human activity-travel patterns at the same time while avoiding the interpretative complexity of multivariate pattern generalization or recognition methods. These methods are operationalized using interactive 3D GIS techniques and a travel diary data set collected in the Portland (Oregon) metropolitan region. The study demonstrates several advantages in using these methods. First, significance of the temporal dimension and its interaction with the spatial dimension in structuring the daily space-time trajectories of individuals can be clearly revealed. Second, they are effective tools for the exploratory analysis of activity diary data that can lead to more focused analysis in later stages of a study. They can also help the formulation of more realistic computational or behavioral travel models.     

Investigation of the effectiveness of tandem oil fences under currents

The behavior of the flow passing a tandem oil fence, and the performance of the fence, were investigated by experimental and numerical methods. The flow characteristics between tandem fences were measured by the particle image velocimetry (PIV) method for the rigid and open free surface between the two fences in order to gather reference data for numerical investigations. A method of assessing a tandem fence by tracing the movement of an oil droplet around the fence is introduced. The effect of the current speed, the separation distance between the two fences, the relative draft of the two fences, and the water depth on the oil containment between the fences was investigated.