Online Integrated Violence Model

IVM - Integrated Violence Model

The Integrated Violence Model (IVM) is a resource for predicting the outcome from HD 1.3 reactions. It can be used to obtain venting recommendations and safe distances for HD 1.3 hazardous substances and articles. It has been validated for use with a variety of substances and configurations. It was developed by SMS and has been used for the last 10 years in public and private industry to estimate the effects from rapid burning of propellants, pyrotechnics, flammable gases or combustible dusts.

Try it!

Use the IVM code to estimate internal pressure of an example building with burning 1.3.

Examples

Brief details of the way IVM has been used.

Validation

Check out the ways IVM has been validated.

Description

Details and limitations of IVM.

Try it!

Use the IVM code to estimate the internal pressure and violence outcome (output at right or below) for any of three different scenarios with burning propellant.

Choose a simulation type:

The key parameters for the example ECM simulated are as follows:

M1 propellant (50 kg per barrel) with a density of 500 kg/m3;
A burn rate of 4 kg/s per barrel with 39 moles of gas per kg propellant burned;
A combustion temperature of 2400 K and an ignition time of 0.2 sec per barrel (e.g. 1.6 sec for all to ignite if there are 8 barrels);
Combustion gas fractions of 0.3, 0.37, 0, and 0.33 for inert, reactive, oxidative, and water, respectively;
One roll-up door (labeled vent 1 in the output) of size 25 ft x 14 ft with a mass of 350 kg and a burst pressure of 20 psig;
Gases can escape around the edges of the vent (labeled vent 0 in the output) with an area of 2% of the door's area;
The volume of the ECM is 750 cubic meters and afterburning is included.

Specify Number of Barrels of M1 Propellant (up to 360)

*This is an example implementation of IVM. For additional options and configurations, obtain a subscription. Disclaimer: liability for use of this resource is wholly assumed by the user.

IVM Simulation Output

Simulation output including graphs and conclusions output here. To start a simulation, choose a simulation type and input desired parameters and click Run at left or above.

Example Applications of IVM to Explosive Processes

In addition to the above described configurations, IVM has been applied to many other burning propellant scenarios including:

Buildings containing burning energetic substances and articles with and without vent panels;
Smokeless powder hoppers;
Class 1 Division 1 chamber (where the burning substance is an explosive dust);
Chemical processing oven (where the burning substance is a flammable gas);
Blast chambers with deflagrating substances;
Smokeless powder processing equipment including ribbon blenders, tumblers, dryers and baghouses;
Multi-hearth furnace;
Propellant critical height estimates;
Gas generators for the airbag industry; and
Gun projectile energies.

The purpose for applying IVM to these industry processes is to predict the reaction violence of the existing configuration and then to recommend additional venting (if necessary) to prevent an explosion resulting in hazardous fragments and overpressure. The majority of the above examples contain proprietary information and so details of such are not shared here. A redacted plot of IVM applied to determine the projectile velocity as a function of barrel length is given below.

Figure 1: Plot of an IVM application example for projectile speed versus barrel length.

Validation of IVM Physics and Approach for Burning Reactions

The Integrated Violence Model (IVM) was developed as a Fast Running Model (FRM) in 2011 for prediction of the reaction violence (internal pressures and fragment/debris velocities) for fast cook-off of rocket motors. As such the code was validated against subscale testing with pressure instrumentation of a small metal tube (Koenen tube) containing various rocket propellants. The tube was scored to facilitate high-speed video of the resulting debris speed. IVM does not predict the burst pressure of the containment structure. The burst pressure is an input parameter. The below image shows one of the burst Koenen tubes that were instrumented to measure the internal pressure and the speed of the burst tube.

Figure 2: Picture of one of the burst Koenen tubes

The figure below shows the pressurization rate for multiple trials. The model result matches well the experimental data. IVM predicted speeds of the ejected half of the tube pieces also matched well (not shown). These and other results indicate that the model fundamentals including the physics and thermodynamic principles applied (conservation of energy and mass in a varying sized volume) can successfully be applied in similar scenarios to accurately reflect actual results.

Figure 3: Plot showing the fidelity of the model relative to the experimental result of the modified Koenen testing.

Following the tuning of the model and associated verification, the model was extended to larger and larger confinement geometries similar to a rocket motor. Below is a plot showing the model's fidelity relative to validated empirical relationships published in Loss Prevention in Process Industries, 2nd Ed, Vol. 2, 1996, pg. 17/213.

Figure 4: Plot of the KE (debris kinetic energy) vs PV (pressure times volume) model and experimental results as well as the validated lines from burst pressure relationships. Cross hairs are Koenen experimental results, symbols from IVM simulations, and lines from “Disruptive Failure of Pressure Vessels,” M.R. Baum, 1987, quoted in Loss Prevention in Process Industries, 2nd Ed, Vol. 2, 1996, pg. 17/213.

IVM has successfully been extended to similar configurations (like a rocket motor firing inside a chamber) to predictively obtain internal pressures as a function of time. Use of the model always includes first tuning of the model with experimental results or a small scale test specific to the propellant and configuration. Afterwards, the model can be used to make predictions. Below is the IVM predicted internal pressure plot as well as the experimental result of the internal pressure when an MLRS motor is fired into a large containment unit. Model and experimental results match well. Model parameters were found by matching the internal motor-case pressures during a typical MLRS motor firing (not shown).

Figure 5: Plot of the model relative to the experimental result for a rocket motor fired into a containment vessel.

In the Try It! section above, a Kasun structure is modeled with a user specified amount of barrels of M1 propellant and a user specified vent area. China Lake NAWCWD completed testing where 39cm and 79cm vents were installed in a 2 m x 2 m x 2 m concrete structure with varying amount of propellant (A.Farmer et al. "Combustion of Hazard Division 1.3 M1 Gun Propellant in a Reinforced Concrete Structure," Aug 2015, NAWCWD TM 8742). IVM parameters (burn rate parameters, combustion gas temperature, etc.) were obtained from literature for the two different M1 propellant types and not from the test results. The blindly predicted results using IVM agreed with the violence measures obtained experimentally: Trials 1 and 3 did not result in explosion whereas Trials 2 and 4 did result in explosion. Below is a plot of the IVM predicted fragment distribution as well as the experimental result.

Figure 6: Plot showing the predicted IVM debris field (left) and the experimental result (right) for one of the Kasun structure tests. The colors relate to the debris from each unique wall or ceiling.

Model Fundamentals

IVM uses mass and energy balances to determine the internal temperature, pressure, and number of moles inside a volume according to the below standard thermodynamic equations. Shock pressures and shock physics are not included thus IVM is for burning reactions.

t is time, n is moles, U the internal energy, H enthalpy, and q_gen heat. The dot above the n represents a rate. q accounts for the afterburning of the generated carbon monoxide with oxygen present in the volume initially according to the following:

k_a is the afterburn constant and P the partial pressure of carbon monoxide or oxygen. H_comb is the combustion heat of the reacting gases.

The concentration of 4 gases are tracked as a function of time through the simulation: inert gases (modeled as CO2), reactive gases (modeled as CO), oxidizing gases (modeled as O2), and water vapor. The heat capacity and enthalpy of each gas are functions of temperature. Gases are treated as ideal.

The moles of gas generated (with a corresponding concentration of reactive, inert, and water) is:

where m is mass, and g is the moles of gases generated per mass of burned substance. The burn rate, or rate of mass change, is a function of pressure according to:

where k is the atmospheric burn rate, alpha is the burn rate pressure exponent, and ref indicates the reference pressure.

Vents can have an associated burst pressure and mass such that when the burst pressure is exceeded, the vent moves away exposing more and more area for the gases to escape according to standard equations of motion based on the force (pressure x area) and the vent mass. The flow of gases through a vent is found from the equations based on the internal pressure, downstream pressure, heat capacity ratio, and vent area according to the relations given in R. H. Perry and D. W. Green, Perry’s Chemical Engineer’s Handbook, Seventh Edition, McGraw-Hill 1997, page 6-22 and 6-23. A discharge coefficient of 0.9 is used for the above scenarios.

Time dependent equations were explicitly solved using the Velocity Verlet algorithm and fourth-order Runge-Kutta with an adaptive time-step size.

IVM - Integrated Violence Model

Try it!

IVM Simulation Output

Example Applications of IVM to Explosive Processes

Validation of IVM Physics and Approach for Burning Reactions

Model Fundamentals

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