The FNGUN Internal Ballistics Software Suite provides a powerful, Windows based simulation and design tool for predicting practically all aspects of the performance of propellant burning gun systems.
FNGUN is particularly valuable in cases where realistic gun and charge layouts are to be simulated and where the propagation of pressure waves and barrel heating is important.
FNGUN has been developed over a period of 10 years. This means that the code has undergone a considerable range of verification and validation tests. The extent of the validation means that considerable confidence can be gained from the results obtained from FNGUN.
The FNGUN Internal Ballistics Software Suite comprises three integrated packages as follows:
- The "core" FNGUN Internal Ballistics software for designing charges and predicting muzzle velocity and gun pressure
- The FNGUN Thermal Module for predicting barrel heating
- The FNGUN Recoil Module for assessing barrel motion and buffer forces
An overview of the technical approach used in each of these packages can be found here.
Clicking one of the above links will scroll the page to the relevant section.
This product is available for purchase as a complete technology transfer package or it can be used by Frazer-Nash staff on a consultancy basis to provide solutions to specific customer requirements. More detailed product literature is available, together with past conference papers that describe how this software tool has been applied to resolve specific problems.
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The FNGUN Internal Ballistics Software Suite is fully compatible with Windows 95 and NT4.0 and is operated via a sophisticated user interface which enables the user to build and save models, calculate results, and view the results within a single application. A comprehensive on-line help guide is also provided.
A link to customer’s databases of propellant data is also available as an option.
The FNGUN Internal Ballistics Solver was originally developed by Frazer-Nash for the UK Defence Evaluation and Research Agency (DERA). Therefore, part of the code is currently provided under licence from the DERA.
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Technical Overview
Internal Ballistics
The FNGUN Internal Ballistics Software provides a full two-phase simulation of the internal ballistic process and is based on a one dimensional finite difference approach. This means that the barrel and chamber are sub-divided axially into a number of calculation cells.
The properties, such as temperature and pressure, within each of these cells are assumed to be uniform. However, the distribution of properties from cell to cell, and hence over the length of the gun, is not constrained by any intrinsic assumption, eg: a Lagrangian pressure distribution, as would be the case with a lumped parameter code. By avoiding any pressure distribution constraints, FNGUN is well suited to the simulation of pressure waves within the barrel.
The rate of energy generation, from the combustion of the propellant, is governed by three propellant factors, namely:
- The burn law
- The surface area of the propellant grain at any instant in time
- The thermochemical properties of the propellant.
The first of these factors, the burn law, relates the distance burnt in a given time to the local pressure and temperature, etc. The instantaneous surface area of the grain and the thermochemical properties are then used to calculate the energy released.
A summary of the more important capabilities possessed by the software is as follows:
- Simulation of multipart charges, each built up of different propellant types and geometries.
- A library containing a wide variety of standard grain geometries, eg: slotted sticks, 7 and 19 hole multiperforated, etc.
- A library of different "burn laws" ranging from the common bPa law through to tabulated functions.
- Simulation of the propellant motion arising from gas flow.
- A variety of different ignition models including an explicit simulation resulting from heat transfer to the propellant.
Thermal Module
Gun erosion is a complex function of parameters such as the composition of the propellant, including any wear reducing additives that it may contain, the rate of fire and the barrel geometry. However, the high surface temperatures to which the bore of the gun is exposed play a significant role in determining the wear. By using the FNGUN Thermal Module, it is possible to obtain a comprehensive prediction of bore and gun temperatures under a wide range of operational scenarios and thus assess barrel durability and wear.
The FNGUN Thermal Module utilises the spatial and time varying temperature of the propellant gases, determined from its internal ballistic simulation, to make an accurate prediction of the bore and temperature distribution within the gun tube. In particular, the following effects are fully simulated:
- Peak transient bore temperatures
- Steady state temperature rise
- Axial and radial temperature gradient.
Recoil Module
The FNGUN Recoil Module predicts the motion history of the gun tube assembly and transient forces within the recoil system.
Consequently, the module provides valuable information for the design and modification of gun recoil systems. It can also be used to assess the effects of changes to the propelling charge on the gun recoil characteristics.
The transient loads transmitted to the gun tube and recoil system are determined from both the pressure within the gun tube and gas flow through the muzzle brake (if present), the performance of the muzzle brake being defined by a simple efficiency factor. The Recoil Module automatically uses the appropriate gas dynamics data obtained from the internal ballistics simulation.
The characteristics of the recoil system are defined by the user in a "look-up table" as a function of recoil distance. Consequently, it is possible to simulate typical, non-linear stiffness and damping characteristics. Both the velocity and displacement of the gun tube, together with the transient forces in recoil stiffness and damper, are predicted.
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