In order to create the force vs time profile for dynamic analysis of Slug flow, I want to know how to get the rise time for the slug load.

The <em>rise time</em> is the time it takes the leading edge of the slug to round the elbow, from weld-line to weld-line. The same applies to the <em>decay time</em>.

Rich, I was mid-reply when yours went up.
I'll post anyway; a bit more detail...

Presuming that the slug will be traveling at the vapor flowing velocity, the 0,0 point of the force-time data would correspond to the leading edge of the slug arriving at the near-weld line of a bend. The rise time would correspond to the amount of time required for the slug to fully envelope the bend, that is, to travel from the near- to the far-weld line of the bend.
Time = Distance/Velocity
Distance = 1/4 of the arc-length of the circle corresponding to the bend radius.
If the pipe is 12" diameter, a long-radius bend radius = 18 inches, diameter of the corresponding circle = 36 inches.
In this case, rise time = 1/4*pi*36/Velocity.
Full load will be applied for as long as the slug is in the bend = slug length/velocity (which is added to the t=0 mark, not the rise time point).
As Rich says, the decay time will be the same as the rise time (same velocity, same distance, so same duration).

Dear Richard, Jim and Anindya

Mr. Tony Paulin, PRG, http://www.paulin.com/ SPLASH Bos Fluids Documentation (Draft) (10/15/02) BOS Fluids 2d CFD Calculation.doc

Richard Ay Moderator Member # 3
jrwilcox Member Member # 33
Anindya Member Member # 553

BOS Fluids SPLASH 2d CFD Calculation Version 2.2

Overview:
SPLASH is a 2d CFD Free Surface computer program based on the SOLA-VOF algorithm. (Ref. 1) (SOLution Algorithm-Volume Of Fluid, Hirt and Nichols, 1981; and Nichols, Hirt, and Hotchkiss, 1980). It is designed to allow the user to simulate arbitrary geometries, and has preset models for vertical and horizontal vessels, tanks, and pipes with elbows. Several such models are shown below:

Baffles in a Horizontal Vessel Insufficient Freeboard in 10 m. Tank

Tank Fill and Spillover Sequences Slug Impact on Elbow

Available Simulations Include:

1) Sloshing Frequency for Fluids in Tanks and Trays
2) Wave Motion Periodic Loading on Tanks or Vessels
3) Slug Loads on Elbows
4) Slug Loads on Pipe U-Bends
5) Seismic/Periodic Time History Loading
6) Falling Fluids
7) Tank Fill Simulations
8) Baffle Design
9) Slug Breaker Design
10) Loads on Flow Obstructions
11) Deceleration of Tank Cars or Containers

Features:

1) Interactive Data plotting
2) RTF Report Generation with User Selected Embedded Graphics
3) Stored movies for easy replay
4) User Solution Control
5) Preset Models
6) Frequency, Shear and Overturning Moment Calculations

SPLASH is written for the piping and pressure vessel engineer that needs to study free surface, sloshing or fluid impact problems in tanks, pressure vessels, pipes and related components. Default settings for tolerances and maximum pressure smoothing algorithms are designed to provide quick, reasonable solutions with a minimum of user interaction. Examples are given that show the user how to adjust tolerances and be sure that a reasonable and conservative solution is obtained.

The Internation Building Code 2000 Paragraph 1621.3.11 states in part that, “Seismic effects that shall be considered in the design of a boiler or pressure vessel include …dynamic effects …and the sloshing of liquid contents” SPLASH is designed to produce the seismic shear and overturning base moments needed by most standard design programs to satisfy these and other Code requirements. El Centro time history spectra may be applied easily to any model along with ship-board pitch and roll loads, global accelerations, or velocities indicative of slugs or impinging liquid loads on vortex breakers or diverter plates.

SPLASH may also be used to simulate the decelerating fluid in a rapidly stopping tank car or truck and can be used to design baffles to reduce system sloshing periods and minimize loads.

SPLASH is surprisingly easy to use, but the user is encouraged to read through the examples in this manual to get a better understanding of the program and the options and methods available that can be used to document, verify and present the results.