Reduction of the auto seismic component of error of a ballistic laser gravimeter by excitation of an induction-dynamic catapult from an AC voltage source

The purpose of the study is to analyse the influence of the excitation of an induction-dynamic catapult of a ballistic laser gravimeter from an AC voltage source at different frequencies on electromechanical indicators that provide a reduced value of the auto seismic component of error in measuring the gravitational acceleration g due to a decrease in the recoil force. A mathematical model of the gravimeter catapult when excited from an AC voltage source is proposed, taking into account the interrelated electrical, magnetic and mechanical processes. The nature of the electromechanical processes in the catapult of the gravimeter with such excitation has been established. It is shown that a phase shift occurs between the currents in active elements, as a result of which positive (repulsive) pulses of the electrodynamic force alternate with negative (attractive) pulses of force. A criterion for the efficiency of the gravimeter catapult has been introduced, taking into account the maximum value of push of the test body at the smallest values of the electrodynamic force and current of the inductor winding. It was found that the highest efficiency of the gravimeter catapult is provided at a frequency of 250 Hz, at which the catapult efficiency is 3.5 times higher than at a frequency of 50 Hz. It is shown that the transition from the method of excitation of an induction-dynamic catapult with one short pulse to excitation from an AC voltage source makes it possible to reduce the uncertainty in measuring the gravitational acceleration.

ANALYSIS THE REACTION OF LIGHTARMOR MACHINES ON THE ACTION OF POLYPULSES FORCES

In modern conditions, lightarmored vehicles with powerful weapon modules are widely used in the armies of different countries. These modules are equipped with small-caliber automatic cannons, which have a rate of fire of several hundred rounds per minute and a high level of recoil forces. Moreover, there are tendencies towards an increase in the rate of fire and the caliber of weapons (and, accordingly, recoil forces). Considering that weapon modules rely on the lightarmored vehicles skeleton, which has higher responsiveness characteristics than heavy combat vehicles in terms of weight, the problem of determining the reaction of the «weapon module - armored hull - suspension» system to the action of recoil forces in order to ensure on the one hand, the strength of armored hulls, and on the other hand, reducing the load on the guidance and stabilization system of weapons during firing.To study the response of elements of lightly armored vehicles to the action of recoil forces when firing a burst of combat modules, numerous models have been built with a small number of degrees of freedom. Using these models, the reaction of a dynamic system to the action of a number of impulses was investigated.These impulses caused by the action of recoil forces when firing shots from combat modules. Keywords: lightlyarmored vehicle; weapon module; small-bore automatic cannon; recoil force targeting and weapon stabilization system; dynamic system; numerical modeling; method of finite elements; natural vibration frequency

Frequency domain measurements of melt pool recoil force using modal analysis

Recoil pressure is a critical factor affecting the melt pool dynamics during Laser Powder Bed Fusion (LPBF) processes. Recoil pressure depresses the melt pool. When the recoil pressure is low, thermal conduction and capillary forces may be inadequate to provide proper fusion between layers. However, excessive recoil pressure can produce a keyhole inside the melt pool, which is associated with gas porosity. Direct recoil pressure measurements are challenging because it is localized over an area proportionate to the laser spot size producing a force in the mN range. This paper reports a vibration-based approach to quantify the recoil force exerted on a part in a commercial LPBF machine. The measured recoil force is consistent with estimates from high speed synchrotron imaging of entrained particles, and the results show that the recoil force scales with applied laser power and is inversely related to the laser scan speed. These results facilitate further studies of melt pool dynamics and have the potential to aid process development for new materials.

Towards a high-precision analytical radiation force model for the GPS IIF spacecraft

<p>We present the status of our work on producing a new high-precision, physics-based radiation force model for the GPS IIF spacecraft. The details of the spacecraft model, i.e. geometry and surface material properties, are given. The methods used to build the spacecraft model from various information sources are described. Overall, the radiation force model accounts for the direct solar force, the recoil force due to reflected (diffuse and specular) radiation, and also thermal forces (re-radiation and solar panel thermal gradient). The bus component of the radiation force model is computed using ray-tracing techniques. The performance of the new model is compared against one that uses a box-wing spacecraft model. The assumptions and limitations of the modelling are discussed.</p>

Controlled levitation of nanostructured thin films for sun-powered near-space flight

We report light-driven levitation of macroscopic polymer films with nanostructured surface as candidates for long-duration near-space flight. We levitated centimeter-scale disks made of commercial 0.5-micron-thick mylar film coated with carbon nanotubes on one side. When illuminated with light intensity comparable to natural sunlight, the polymer disk heats up and interacts with incident gas molecules differently on the top and bottom sides, producing a net recoil force. We observed the levitation of 6-mm-diameter disks in a vacuum chamber at pressures between 10 and 30 Pa. Moreover, we controlled the flight of the disks using a shaped light field that optically trapped the levitating disks. Our experimentally validated theoretical model predicts that the lift forces can be many times the weight of the films, allowing payloads of up to 10 milligrams for sunlight-powered low-cost microflyers at altitudes of 50 to 100 km.

Frequency Domain Measurements of Melt Pool Recoil Force Using Modal Analysis

Recoil pressure is a critical factor affecting the melt pool dynamics during Laser Powder Bed Fusion (LPBF) processes. Recoil pressure depresses the melt pool, providing layer-to-layer fusion without introducing porosity. If the recoil pressure is too low, the process operates in a conduction mode where layers will not properly fuse, while excessive recoil pressure leads to a keyhole mode, which results in gas porosity. Direct recoil pressure measurements are challenging because it is localized over an area proportionate to the laser spot size producing a force in the mN range. This paper reports a vibration-based approach to quantify the recoil force exerted on a part in a commercial LPBF machine. The measured recoil force is consistent with estimates from high speed synchrotron imaging of entrained particles, and the results show that the recoil force scales with applied laser power and is inversely related to the laser scan speed. These results facilitate further studies of melt pool dynamics and have the potential to aid process development for new materials.