A. Khayyer, A. Yeganeh Bakhtiari, A. Ghaheri, T. Asano,
Volume 2, Issue 4 (December 2004)
Abstract
A two-dimensional numerical model has been developed to study wave breaking on a
sloping beach. The basic elements of numerical model are Reynolds Averaged Navier-Stokes
(RANS) equations that describe the mean flow motion of a turbulent flow a k turbulence
closure model that describes the turbulent transport and dissipation process an efficient
technique (VOF- Volume Of Fluid method) for tracking the free surface motion and a new scheme
developed by Lin and Liu (1999) for wave generation. Shoaling, breaking and overturning of
solitary wave on a slope of 1/16 have been studied with the main emphasis on turbulence
characteristics. Turbulence characteristics i.e., turbulence kinetic energy, k turbulence
dissipation rate, turbulence production, pr turbulence eddy viscosity, vt and their spatial
distribution during the breaking process have been discussed in great details. Spatial distribution
of turbulence characteristics and the order of magnitude have been found to be in agreement with
existing experimental and numerical studies. The main characteristic of plunging breaking waves,
the shoreward advective transport of turbulence, has also been investigated and numerically
proved.
A. Yeganeh Bakhtiary, A. Ghaheri, R. Valipour,
Volume 5, Issue 1 (March 2007)
Abstract
Determination of allowable free span length plays a crucial role in design of offshore
pipelines. The seabed intervention cost and safety of an offshore pipelines project are largely
influenced by pipelines free spanning during the project life time. Different criteria are proposed by
both the current designing guidelines and researchers there is however lack of comprehensive
assessment of independent parameters affects the design length of free span. In this note, it is
intended to investigate the effects of seabed formation along with axial force on Natural Frequency
of offshore pipelines. Based on this assessment a new simple formula is proposed. Finally, to
evaluate the result of this study, the allowable free span length of Qeshem Island pipelines is
calculated as a case study and compared with those of the DNV (1998) and ABS (2001) guidelines
and the modal analysis.
