The Effect of Diameter on Dynamic Seabed Penetration

Abstract

An accurate estimate of the undrained shear strength of seabed sediments is critical to the design of foundations and anchors of offshore structures. Naval mine warfare and undersea salvage also depend on the prediction of seafloor embedment depth, which is primarily a function of sediment strength. Direct measurement of in-situ sediment strengths in the offshore environment is often difficult using conventional methods, especially where depths prohibit the use of divers. Although there are current algorithms for predicting dynamic penetration of the seafloor in the Handbook, recent experiments have indicated these algorithms tend to under predict the penetration of objects which are larger than three inches in diameter. To improve the current algorithms, a numerical and experimental study of the seabed penetration event was conducted. A computational analysis of the seabed penetration problem was conducted using the LS-DYNA finite element analysis (FEA) code. LS-DYNA was used to model the experiments, and then the model predictions were compared with experimental results. The penetration depths predicted by the model showed good agreement with experimental results for cohesionless soils. Using the USNA Oceanography Research Vessel (YP-686), three and nine inch penetrometers were repeatedly dropped off the stern and allowed to free fall to the seabed. An accelerometer attached to each penetrometer measured acceleration output beginning before release and continually throughout the drop. By integrating the acceleration data twice, the penetration depth could be calculated. Using this experimental data and equations available in the Handbook for Marine Geotechnical Engineering, new values were calculated for the strain rate factors of objects larger than three inches in diameter.

Open PDF

Document Details

Document Type
Technical Report
Publication Date
May 02, 2008
Accession Number
ADA486586

Entities

People

  • Catherine M. Ortman

Organizations

  • United States Naval Academy

Tags

Communities of Interest

  • Air Platforms
  • Energy and Power Technologies
  • Ground and Sea Platforms
  • Sensors
  • Space

DTIC Thesaurus Topics

  • Bearing Strength
  • Civil Engineering
  • Cohesionless Soils
  • Engineering
  • Equations
  • Experimental Data
  • Finite Element Analysis
  • Geometry
  • Geotechnical Engineering
  • Measurement
  • Mechanics
  • Modulus Of Elasticity
  • Numerical Analysis
  • Seabed
  • Shear Modulus
  • Strain Rate
  • United States Naval Academy

Readers

  • Computational Modeling and Simulation
  • Geotechnical Engineering.
  • Marine Hydrodynamics