Decoupled Hydrodynamic Models and Their Outdoor Identification for an Unmanned Inland Cargo Vessel with Embedded Fully Rotatable Thrusters

Expanding the automation level of the freshly introduced fleet of self-propelled Watertruck+ barges, which house fully-rotatable embedded thrusters, might increase their ability to compete with their less sustainable but dominating road-based alternatives. Hydrodynamic motion models, which reveal the manoeuvring capabilities of these barges, can serve as inputs for many pieces of this automation puzzle. No identified motion models or hydrodynamic data seem to be publicly available for the hull design and the novel actuation system configuration of these barges. Therefore, this study offers: (i) decoupled motion model structures for these barges for surge, sway, and yaw, with a focus on the thruster and damping models; (ii) two identification procedures to determine these motion models; (iii) all the experimental data, generated outdoors with a scale model barge to identify (i) based on (ii). In addition, the identified surge models were compared with both computational and empirical data. These comparisons offer more physical insights into the identified model structures and can aid in the model selection for which the desired complexity and accuracy evidently depend on their envisaged application. Finally, this methodology need not be limited to the vessel and actuation types utilised by us.

Augmenting Maneuverability of UUVs with Cycloidal Propellers

This paper investigates the novel concept of augmenting the maneuverability of underwater vehicles with cycloidal propellers. Cycloidal propellers have the potential of providing agile manoeuvring capabilities to an underwater vehicle such as enabling pure heave motion and spot turns. They will also enable the vehicle to surge in forward and backward directions with equal ease. Such manoeuvres are not possible with the more conventional screw propeller and control fin combinations. Moreover, cycloidal propellers can enable precise dynamic positioning in low speed applications like station-keeping, underwater surveying and maintenance, minesweeping and teaming activities. In this paper, manoeuvring capabilities of an underwater vehicle with conventional screw propeller and control fins only are compared with one augmented with cycloidal propellers. The cases considered include a turning circle manoeuvre, a low speed 180o turn and a low speed heave manoeuvre. A six degrees-of-freedom non-linear hydrodynamic motion prediction model was developed and validated. Simulation results demonstrated that compared to conventional propulsion systems, cycloidal propeller augmented underwater vehicles can be more swift and compact in low speed manoeuvres, making a case for further investigation into this concept.

INVESTIGATION OF HEAT DISTRIBUTION PROCESSES ON THE INNER SURFACE OF THE ENCLOSING STRUCTURE, TAKING INTO ACCOUNT THE MOVEMENT OF AIR IN THE BOUNDARY AREA BETWEEN THE DEVICE AND FENCING

A study was made of the nature of the movement of air mass in the space between the device that warms the room and the confining outer wall of the room. The hydrodynamic motion of the air mass was simulated on the basis of the two-dimensional in space Navier-Stokes equations and the convective heat conduction equation to find out a detailed picture of the physical processes that occur. Also for some particular cases, analytical solutions were obtained for the conjugate problem, where the movement of air is caused by its thermal expansion and the action of gravity in areas with different densities (Archimedes' forces). The simulation of more complex types of air movement with the formation of vortex flows using numerical methods and the corresponding program codes written in C++. It was found that the movement of air mass in the space between the device and the fence strongly depends not only on the temperature of the device, the wall, and the outside air. It was revealed that hydrodynamics and heat transfer are significantly influenced by two geometrical parameters: the distance between the device and the wall, and the distance from the flooring to the bottom of the device. In particular, a thin layer of the downward flow of cold air along the fence and above the floor is possible. The condition for the occurrence of such a downward flow has been found, it is determined by the ratio of the temperature of the wall, the device, and the average temperature in the room.

The Gravity of the Classical Klein-Gordon Field

The work shows that the evolution of the field of the free Klein–Gordon equation (KGE), in the hydrodynamic representation, can be represented by the motion of a mass density ∝ | ψ | 2 subject to the Bohm-type quantum potential, whose equation can be derived by a minimum action principle. Once the quantum hydrodynamic motion equations have been covariantly extended to the curved space-time, the gravity equation (GE), determining the geometry of the space-time, is obtained by minimizing the overall action comprehending the gravitational field. The derived Einstein-like gravity for the KGE field shows an energy-impulse tensor density (EITD) that is a function of the field with the spontaneous emergence of the “cosmological” pressure tensor density (CPTD) that in the classical limit leads to the cosmological constant (CC). The energy-impulse tensor of the theory shows analogies with the modified Brans–Dick gravity with an effective gravity constant G divided by the field squared. Even if the classical cosmological constant is set to zero, the model shows the emergence of a theory-derived quantum CPTD that, in principle, allows to have a stable quantum vacuum (out of the collapsed branched polymer phase) without postulating a non-zero classical CC. In the classical macroscopic limit, the gravity equation of the KGE field leads to the Einstein equation. Moreover, if the boson field of the photon is considered, the EITD correctly leads to its electromagnetic energy-impulse tensor density. The work shows that the cosmological constant can be considered as a second order correction to the Newtonian gravity. The outputs of the theory show that the expectation value of the CPTD is independent by the zero-point vacuum energy density and that it takes contribution only from the space where the mass is localized (and the space-time is curvilinear) while tending to zero as the space-time approaches to the flat vacuum, leading to an overall cosmological effect on the motion of the galaxies that may possibly be compatible with the astronomical observations.

Single pulse femtosecond laser ablation of silicon – a comparison between experimental and simulated two-dimensional ablation profiles

Ultrashort laser pulses are widely used for the precise structuring of semiconductors like silicon (Si). We present here, for the first time, a comparative study of experimentally obtained and numerically simulated two-dimensional ablation profiles based on parameters of commercially relevant and widely used near-infrared and diode pumped femtosecond lasers. Single pulse laser ablation was studied at a center wavelength of 1040 nm and pulse duration of 380 fs (FWHM) in an irradiating fluence regime from 1 J/cm2 to 10 J/cm2. Process thresholds for material transport and removal were determined. Three regimes, scaling with the fluence, could be identified: low and middle fluence regimes and a hydrodynamic motion regime. By comparing the simulated and experimental ablation profiles, two conclusions can be drawn: At 2 J/cm2, the isothermal profile of 3800 K is in excellent agreement with the observed two-dimensional ablation. Thus exceeding a temperature of 3800 K can be accepted as a simplified ablation condition at that fluence. Furthermore, we observed a distinct deviation of the experimental from the simulated ablation profiles for irradiated fluences above 4 J/cm2. This points to hydrodynamic motion as an important contributing mechanism for laser ablation at higher fluences.

Laser-supported hydrothermal wave in low-dense porous substance

The generalized theory of terawatt laser pulse interaction with a low-dense porous substance of light chemical elements including laser light absorption and energy transfer in a wide region of parameter variation is developed on the base of the model of laser-supported hydrothermal wave in a partially homogenized plasma. Laser light absorption, hydrodynamic motion, and electron thermal conductivity are implemented in the hydrodynamic code, according to the degree of laser-driven homogenization of the laser-produced plasma. The results of numerical simulations obtained by using the hydrodynamic code are presented. The features of laser-supported hydrothermal wave in both possible cases of a porous substance with a density smaller and larger than critical plasma density are discussed along with the comparison with the experiments. The results are addressed to the development of design of laser thermonuclear target as well as and powerful neutron and X-ray sources.

Numerical research on the ion-beam-driven hydrodynamic motion of fissile targets for nuclear safety studies

As a method to evaluate high-temperature equation of state (EOS) data of fissile materials precisely and safely, we numerically examined an experimental setup based on a sub-range fissile target and a high-intensity short-pulsed heavy-ion beam. As an example, we calculated one-dimensional hydrodynamic motion of a uranium target with ρ = 0.03ρsolid (ρsolid ≡ solid density = 19.05 g/cm3) induced by a pulsed 23Na+ beam with a duration of 2 ns and a peak power of 5 GW/mm2. The projectile stopping power was calculated using a density- and temperature-dependent dielectric response function. To heat the target uniformly, we optimized the experimental condition so that the energy deposition could occur almost at the top of the Bragg peak. The energy deposition inhomogeneity could be reduced to ±5% by adjusting the incident energy and the target thickness to be 2.02 MeV/u and 180 μm, respectively. The target could be heated homogeneously up to kT =7 eV well before the arrival of the rarefaction waves at the center of the target. In principle, the EOS data can be evaluated by iteratively adjusting the data embedded in the hydro code until the measured hydrodynamic motion is reproduced by the calculation. This method is consistent with the conditions of nuclear nonproliferation, because a very small amount of fissile material is enough to perform the experiment, and no shock compression occurs in the target.