A BASIC PROGRAM TO CALCULATE GRAVITATIONAL AND CENTRIFUGAL SETTLING PARAMETERS

Gravitational settling methods, such as by pipette or hydrometer, are still commonly used to analyze fine-grained sediments because the required equipment is relatively inexpensive and because it is generally accepted that hydrodynamic characteristics of particles are often more useful than geometrically defined measures of size. Also, difficulties associated with decanting the finest sediment fractions and with separating minerals in heavy liquids make centrifugal settling methods attractive. Therefore, to facilitate settling analyses, we have written a computer program (CENTRISET) to calculate settling velocities based on Stokes Law for gravitational procedures, and to derive angular velocities or total settling times for specific particles from a given medium by centrifuge. Our program is written in BASIC, runs under Windows 98/2000/XP operating systems, provides a window to facilitate execution, and allows users to select options and parameter input boxes using mouse-click events. Detailed documentation, schematics, and tables for water density and viscosity at various temperatures, as well as tables for densities of common materials, are available within the program through a virtual information button. To calculate a settling velocity for gravitational analyses, the user must enter the following five variables: fluid viscosity, fluid density, particle density, particle radius, and gravitational acceleration. For settling by centrifuge, the user must enter: fluid viscosity, fluid density, particle density, particle radius, time of acceleration, time of deceleration, initial distance from axis of rotation, final distance from axis of rotation, and either angular velocity or total time. Running the program generates the calculated variable in standard units for the selected process and displays it in the results window. This software, with the necessary support files, installation instructions, external documentation and readme files, is available free of charge, along with our other non-laboratory specific sediment-processing software (e.g., SEDCLASS, GSSTAT, SEDPLOT) online from the USGS Woods Hole Science Center at: http://woodshole.er.usgs.gov/software/sediment-software.html