Harish Mukundan

Surface to Surface Intersections

AbstractThis paper presents an overview of surface intersection problems and focuses on the rational polynomial parametric/rational polynomial parametric surface intersection case including transversal and tangential intersections. Emphasis is placed on marching methods with a discussion of the problems with conventional tracing algorithms. An approach using a validated interval ordinary differential equation system solver is outlined and illustrated with examples, which offers significant advantages in robustness over conventional marching schemes.

Applications of Accurate VIV Response Reconstruction Schemes

Quantifying vortex-induced vibration of long flexible slender structures exposed to ocean currents is critical to their design, analysis, installation and maintenance. These oscillations often driven at high frequencies for extended time may result in fatigue induced damage. Further, these primarily cross-flow oscillations results in an amplification of drag which may lead to possible riser interference issues especially when dealing with inline motions. Developments in instrumentation and installation of data acquisition systems on board marine risers have made accurate measurement of riser responses possible. On the other hand, recent developments in accurately reconstructing the VIV response of the riser using data from these acquisition systems have opened up entirely new array of methods to accurately interrogate, interpret and further improve VIV modeling of such structures. This paper presents with some depth the accurate reconstruction method developed by the authors and their use to identify new basic features of riser VIV. These include in-situ measurements of fatigue damage, identification of new phenomena and their quantification in empirical prediction codes by improving both the empirical models and empirical databases. Examples demonstrating each use of the reconstruction method are applied to data from a model-scale riser experiment.Copyright

VIV Hydrodynamic Data Extraction From Field Data

In this paper we extend a methodology to extract a VIV hydrodynamic database from field data to accommodate partially straked cylinders. There are two databases, each consisting of the lift and added mass coefficients as functions of reduced velocity and amplitude of response; the first for the bare part of the riser, and the second for the straked part. The field data can be either in the form of acceleration, strain, or a combination of acceleration and strain time traces, together with the shape of the current profile. First, the program VIVA together with a nominal force database obtained from laboratory hydrodynamic experiments is used in order to get an initial prediction of the riser response under a particular flow profile. The nominal databases are then parameterized and altered in a systematic way until the new VIVA predicted response best matches the measured field response, thus resulting in an optimal database. Examples from the Norwegian Deepwater Program VIV experiments demonstrate the effectiveness of the methodology.Copyright

Intersections With Validated Error Bounds for Building Interval Solid Models

Interval arithmetic has been considered as a step forward to counter numerical robustness problem in geometric and solid modeling. The interval arithmetic boundary representation (B-rep) scheme was developed to tackle this problem. In constructing an interval B-rep solid, robust and efficient computation of intersections between the bounding surfaces of the solid is a critical issue. To address this problem, a marching method based on a validated interval ordinary differential equation (ODE) solver was proposed, motivated by its potential for the interval B-rep model construction. In this paper, we concentrate on the issue of error control in model space using the validated ODE solver, and further explain that the validated ODE solver can be used in the construction of an interval B-rep solid model using such an error control.Copyright