Time zero corresponds with the beginning of launch. The values for the right vertical axis of the specrogram are computed using Equation 1. As can be seen in Fig. In addition, the radar has a strong signal return for several milliseconds of free flight.

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However, several notable features exist in the signal spectrogram. First, the radar introduces noise into the signal in the form of replications of the stronger frequencies. These replications are visible as banding or ripples around the velocity profile and are not physical in nature. Third, WIPT loses the projectile for 60 us in the region of muzzle exit. This dropout is believed to be due to compressed gas ahead of the projectile expanding into the ambient atmosphere as it nears the muzzle. The expansion effectively occludes the radar return for a brief time, after which the signal quickly recovers.

This event is also visible in data from the pulse forming network which drives the railgun, though its origin is unknown. The remainder of this paper will focus on analysis of the measured velocity profile. As indicated in the previous section, spectral analysis is required to extract the projectile velocity from the recorded data. The velocity time-history of the data presented in Fig.

## Numerical modeling of electromagnetic railgun rail temperature field

The measured velocity agrees with the majority of the velocity derived from the B-dot sensors. No reliable B-dot information is available in the first 1. The projectile is moving at a relatively low velocity, but high acceleration in this region.

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As a result, the error associated with calculating the numerical gradient of the B-dot position data is relatively high at the first data point. Additional B-dot data in the first millisecond of launch would be insightful. The WIPT velocity can be integrated to obtain a continuous measure of projectile position during launch.

This integrated WIPT position agrees well with the discrete position vs. Launch occurs between 0 and 5 ms. The radar return is strong for an additional 5ms of projectile free flight. In-bore frictional effects during launch can be determined from knowledge of the acceleration vs. The theoretical launch force on the projectile is given by the following equation. Assuming constant values for L' and launch mass m , the drag force acting on the projectile is the difference between the applied launch force and the measured accelerating force on the launch package.

Combining Equations 2 and 3 , the frictional drag on the projectile is:. Care must be taken in computing the time derivative in Equation 4 as small errors in the velocity profile will be exacerbated by numerical differentiation.

A comparison of the forces acting on the projectile is shown in Fig. Note that the calculated drag force includes some negative values early in launch. This is due to assumptions made in interpolating values for the velocity profile very near the noise floor of the measurement and can be addressed with a more careful analysis. If one assumes that the losses shown in the figure above are strictly due to friction, the friction coefficient can be calculated using the following equation:.

Solving for p yields the results shown in Fig. Again, errors in the velocity profile produce unreliable results early in the launch. Values beyond 1 ms are not corrupted by the low velocity interpolation above, however, the coefficient of friction between this location and about 1. A preliminary comparison with the calculations by UMN indicated that, in all cases considered, ABRES overpredicted the total stagnation-point recession, compared to the results of Gosse [26]. The resolution of these remaining differences will be one of the objectives of future studies.

The mass budget. In parallel, experiments with the UT approach to designs can then be validated and further refined with the codes achieving hypervelocities appears promising, with velocities of currently under development by UMN. In the studies undertaken 5.

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As a first step, the UNO effort focused success. The authors would like to thank all the members of the UMN.

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Second, ASCC typically takes less than 5 min to run on a MURI team, and the coinvestigators and team members for their desktop or laptop computer; therefore, parameter studies can be contributions, particularly including Dr. Stefani, Dr. Wetz, and D. Motes IAT , then the preliminary designs refined with the more sophisticated Prof. Mankowski, R. Karhi TTU , Prof. Candler and Dr. Gosse UMN , and Prof.

## Potential Chinese Railgun Testing Illustrates the US Navy’s Biggest Long-Term Challenge | RUSI

Guillot UNO , without whom The preliminary studies adopted a sphere cone geometry of this paper would not have been possible. For all the computa- [1] D. Brast and D. Rashleigh and R.

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The initial temperature of the projectile was —, Apr. As an example, the final ablated profile [4] I. This can be compared [5] I. The lateral recession on Trans. Stefani, I. McNab, J. Parker, M. Alonzo, and T. Clearly, that additional velocity decrement for Trans. Meeting Plasma Sci. PST, no. McNab, F. Stefani, and D. Karhi, J. Mankowski, M.

Kristiansen, D. Hemmert, and S.