Front Foil Research Articles

The propulsion performance of the semi-active tandem flapping foils for wave gliders: A study on vortex interactions and hydrodynamic performance

An investigation is conducted on the propulsion performance of semi-active flapping foils in tandem configuration of the wave glider, considering different vortex effects and tandem distances. The Finite Volume Method is utilized with commercial CFD software Fluent to solve the URANS equations around the flapping foil. A mesh comprising a 2D NACA0012 foil with Reynolds number Re = 42,000 is used in all simulations. The study investigates the propulsion performance of tandem flapping foil systems, focusing on the differing impacts of wave interaction on the front and rear foils. It explores how varying tandem distances and reduced frequencies influence thrust enhancement and degradation. The research reveals that while the front foil consistently benefits from thrust enhancement, the rear foil's performance is more complex, being subject to thrust enhancement or reduction due to wake vortex interactions. Detailed analyses of instantaneous thrust coefficients, pitching trajectories, and pressure contours provide insights into the hydrodynamic performance of these systems. The findings emphasize the importance of synchronization in motion between the foils for optimal propulsion and highlight the rear foil's susceptibility to changes in the wake flow, affecting its thrust generation capability. Thus, the optimal tandem distance can fully capitalize on the thrust enhancement effect of the wake interaction to improve the performance of the tandem flapping foil propulsion system.

Investigation of front hydrofoil position influence on the hydrofoil-assisted craft

The hydrofoil is utilized to generate lift force and craft center of gravity (CoG) rise-up, resulting in reduced total resistance and improved performance of hydrofoil-assisted craft. This study focuses on the performance of a hydrofoil-assisted craft equipped with a double front foil and a single rear foil. The position of the front hydrofoil is adjusted by shifting it back and ahead by one chord length in the longitudinal direction to investigate the craft's performance. Various parameters including hydrodynamic resistance, trim angle, CoG rise-up, and hydrofoil pressure coefficient are examined at different volume Froude numbers (Fn∇). The results indicate that the total resistance coefficient exhibits similar behavior across all three states within the Fn∇ range of 0.73–2.2. However, when the Fn∇ is increased to 2.93 and the front hydrofoil is shifted one chord length ahead, a significant increase of 27% in CoG rise-up and 18% in trim angle is observed compared to the base case study. Likewise, a back shift of the front hydrofoil leads to a 54% increase in CoG rise-up and a 30% increase in trim angle.

Pulse width dependence of magnetic field generation using laser-powered capacitor coils

Megagauss magnetic fields were generated by a current flowing through a U-shaped coil connecting two parallel copper foils. Two kJ-class lasers at various pulse widths from 2 ns to 9.9 ns passed through holes in the front foil and were focused on the back foil with an intensity of ∼1.7×1016 W/cm2. The coil current and resulting magnetic fields were characterized using ultrafast proton radiography, timed at the end of the laser pulses. The measurements show that magnetic field strength decays with increasing laser pulse width. A lumped-circuit model was developed and showed consistency with the experimental measurements, demonstrating an ion shorting effect: as the ion current neutralizes the electron current contribution to interplate voltage, the coil current peaks on a timescale close to the ion transit time ti=d/vion. FLASH simulations of the coil current are performed, and the calculated resistance values are used to constrain ion speed as a function of hot electron temperature.

Deflected wake interaction of tandem flapping foils

Abstract

Effects of stern-foil submerged elevation on the lift and drag of a hydrofoil craft

Effects of the stern-foil submerged elevation on the lift and drag of a hydrofoil craft are studied by using computational fluid dynamics (CFD) and by considering three alternative stern-foil submerged elevations. The submerged elevation of the front foil is kept constant in all the alternatives. From among the alternatives, the deepest stern-foil placement results in the highest stern-foil lift with the highest foil’s lift-to-drag ratio. However, considering the lift-to-drag ratio of the whole foil-strut-hull system, the shallowest stern-foil placement results in the highest lift-to-drag ratio. The struts and the foil’s submerged elevation significantly affects the drag of the whole foil-strut-hull system.

Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ∼1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ∼3 × 1016 W/cm2. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ∼40–50 T magnetic fields at the center of the coil ∼3–4 ns after laser irradiation. The experiments provide significant insight for future target designs that aim to develop a powerful source of external magnetic fields for various applications in high-energy-density science.

Flat Plate Collector for Process Heat with Full Surface Aluminium Absorber, Vacuum Super Insulation and Front Foil

A new flat plate collector is under development for economic process heat of temperatures between 80° and 150°C. A vacuum super insulation (VSI) with micro-porous powders (perlite or fumed silica) in an evacuated (0.1 mbar) stainless steel envelope has been developed for the rear side of the collector which replaces the mineral wool insulation of standard collectors. CFD simulations of the equivalent thermal conductivity of the VSI including losses via the powder and edge losses have been performed depending on geometry. Applying a 100μm thin VA foil as VSI cover, the collector losses can be reduced by about 0.6W/m2K. Between glass cover and absorber the collector will be equipped with a transparent ETFE foil reducing the loss coefficient further by about 1.2W/m2K. Additionally, a full surface aluminium absorber with a very high collector efficiency factor F’ of 0.97 is used, reaching maximum collector efficiencies of about 0.9. Up to a temperature difference of 110K, the new collector is estimated to have higher efficiencies than standard flat plate and vacuum tube collectors. In the temperature range of 80° and 150°C the efficiency is expected to lie between 65% and 35%. Four different and successively improved prototypes are under test and construction, respectively. The first prototype showed the principal feasibility of the concept and was the first VSI collector operated under outdoor conditions at temperatures up to 120K over ambient.

The Upgrade of the Neutron Induced Positron Source NEPOMUC

In summer 2012, the new NEutron induced POsitron Source MUniCh (NEPOMUC) was installed and put into operation at the research reactor FRM II. At NEPOMUC upgrade 80% 113Cd enriched Cd is used as neutron-gamma converter in order to ensure an operation time of 25 years. A structure of Pt foils inside the beam tube generates positrons by pair production. Moderated positrons leaving the Pt front foil are electrically extracted and magnetically guided to the outside of the reactor pool. The whole design, including Pt-foils, the electric lenses and the magnetic fields, has been improved in order to enhance both the intensity and the brightness of the positron beam. After adjusting the potentials and the magnetic guide and compensation fields an intensity of about 3·109 moderated positrons per second is expected. During the first start-up, the measured temperatures of about 90°C ensure a reliable operation of the positron source. Within this contribution the features and the status of NEPOMUC upgrade are elucidated. In addition, an overview of recent positron beam experiments and current developments at the spectrometers is given.

The anomalous currents in the front foils of the JET lost alpha diagnostic KA-2

We have examined the observed currents in the front foils of the JET Faraday cup lost alpha particle diagnostic KA-2. In particular, we have sought to understand the currents during Ohmic plasmas for which the ion flux at the detectors was initially assumed to be negligible. We have considered two sources of this current: plasma ions (both deuterium and impurity) in the vicinity of the detector (including charge exchange neutrals) and photoemission from scattered UV radiation. Based upon modeling and empirical observation, the latter source appears most likely and, moreover, seems to be applicable to the currents in the front foil during ELMy H-mode plasmas. A very thin gold or nickel foil attached to the present detector aperture is proposed as a solution to this problem, and realistic calculations of expected fluxes of lost energetic neutral beam ions during TF ripple experiments are presented as justification of this proposed solution.

The experimental studies on hydrofoil resistance

This paper presents the hydrofoil resistance model tests which were performed at Ship Design and Research Centre (CTO S.A.). The measurements were carried out in the large towing tank of Ship Hydromechanics Division. A four meters long wooden hydrofoil model was tested. The model was equipped with two lifting foils and a stabilizing front foil. The measurements were conducted for a combination of three values of static trim and two foil angles of attack. A new methodology of shaft angle optimisation with vertical force simulation is presented. The simulation system is an integral extension of the standard dynamometric system for resistance measurements. This paper presents some aspects of the test methodology. The results are briefly presented in the form of standard non-dimensional coefficients in the function of volume Froude number.

Interference of diffraction and transition radiation and its application as a beam divergence diagnostic

We have observed the interference of optical diffraction radiation (ODR) and optical transition radiation (OTR) produced by the interaction of a relativistic electron beam with a micromesh foil and a mirror. The production of forward directed ODR from electrons passing through the holes and wires of the mesh and their separate interactions with backward OTR from the mirror are analyzed with the help of a simulation code. By careful choice of the micromesh properties, mesh-mirror spacing, observation wavelength, and filter band pass, the interference of the ODR produced from the unperturbed electrons passing through the open spaces of the mesh and OTR from the mirror are observable above a broad incoherent background from interaction of the heavily scattered electrons passing through the mesh wires. These interferences (ODTRI) are sensitive to the beam divergence and can be used to directly diagnose this parameter. We compare experimental divergence values obtained using ODTRI, conventional OTRI, for the case when front foil scattering is negligible, and computed values obtained from transport code calculations and multiple screen beam size measurements. We obtain good agreement in all cases.

Measurement of the residual radioactivity induced in the front foil of a target assembly in a modern medical cyclotron

The levels of residual radioactivity induced in Havar ® foils at the entrance of a high-pressure 18O-enriched water target used for the production of 18F − in a medical cyclotron with 16 MeV protons have been determined using high-resolution γ-ray spectrometry. Whole body and skin dose rates arising from exposure to these foils during their periodic replacement have been estimated. The results indicate that irradiated foils do not represent a significant radiological hazard for the cyclotron operating staff and that no waste disposal difficulties should be encountered after an appropriate ‘cooling’ period of 2 years.

Optical diffraction–transition radiation interferometry and its application to the measurement of beam divergence

Optical transition radiation (OTR) interferometry has been shown to be a very useful technique to measure the divergence of electron beams with energies in the range of 15–100 MeV. However, application of this method to low energy or very high quality beams is limited by scattering in the front foil of the interferometer. To overcome this limitation we propose to use a perforated front foil. For the beam energy and hole sizes we are considering, the unscattered beam electrons passing through the holes will produce diffraction radiation (ODR). The total radiation produced from the first and second foils then will be a spatially coherent sum of ODR and OTR from unscattered and scattered electrons. By controlling the number and size of the perforations, the inter-foil spacing, the thickness of the first foil and the wavelength and band pass of the observed radiation, the coherent interferences due to the unscattered portion of the beam can be isolated and observed. The visibility of these interferences can then be used to determine the rms beam divergence. We have developed a general computer code which can be used to calculate diffraction radiation from any type of perforation and another code to compute the ODR–OTR interference pattern for a given set of beam and optical parameters. These codes are employed in the design of an interferometer to measure the divergence of the ATF accelerator operating at 30 MeV. This beam will be used in an initial proof-of-principle experiment for the ODR–OTR interferometer. We present the results of our code calculations which show that the expected divergence, 200 μrad, can be readily measured.

Specific activity of [11C]CO2 generated in a N2 gas target: effect of irradiation dose, irradiation history, oxygen content and beam energy

Pure and O2-mixed nitrogen gases were irradiated by 18 MeV protons (14.2 MeV on target) and analyzed directly by a specially designed radio-GC system with a FID coupled to a methanyzer. Non-radioactive carbon, especially CO2 was observed to be generated in the target chamber by irradiation and to decrease gradually with repeated irradiation. The amount of carbon was increased by the use of new materials for the front foil, transport line, and so on. Higher irradiation dose also increased the carrier carbon, where beam current affected carbon generation more strongly than irradiation time. The addition of oxygen gas to nitrogen gas also increased the amount of carrier carbon, nearly all of which was observed to be generated in the chemical form of CO2. The ratio of [11C]CO2 to total C-11 was always low in a pure N2 gas target and increased with higher irradiation dose, addition of oxygen gas and by changing some part of the irradiation system. The ratios of [11C]CO2 were 22.4±1.5%, 77.8±7.1% and 94.0±4.0% in a pure N2 gas, 9.8 ppm O2-mixed N2 gas and 2000 ppm O2-mixed N2 gas, respectively. The specific activity of [11C]CO2 increased by the addition of O2 gas, but the effect of irradiation dose was not clear. Maximal specific activity of 610±150 GBq/μmol was obtained at the irradiation condition of 15 μA and 20 minutes in a 2000 ppm O2-mixed N2 gas. The effect of proton energy on the CO2 generation was also examined by degrading the proton energy with different thick energy absorbers. The amount of CO2 generated in the target depended on the proton energy, i.e., larger amount of CO2 generated with higher proton energy. Surprisingly, some amount of CO2 (1.5±0.3 nmol) was still observed in the target, even in the condition that all the protons stopped in the front foil and did not irradiate the target gas.

The Medium-Energy Particle Analyzer (MEPA) on the AMPTE CCE Spacecraft

The medium-energy particle analyzer (MEPA) was designed to measure the spectra and composition of magnetospheric particle populations from 10 keV per nucleon (for oxygen) to more than 6 MeV The instrument provides for high background rejection and a geometry tactor large enougn (10-2 cm2 * sr) to be sensitive to rare natural species and tracer ions beyond geosynchronous orbit, while having the ability to operate without saturation in the very high flux regions of the inner magnetosphere. The MEPA telescope measures time of flight and thus velocity of energetic ions from a thin front foil to a rear solid-state total-energy detector, determining the incident ion mass. The telescope is capable of isotopic resolution of hydrogen and helium, of elemental resolution up through oxygen, and can resolve major species and groups to beyond iron with 32-sector angular resolution and temporal resolution of 0.2-24 s. MEPA represents a new and extremely promising technology for space-particle instrumentation in that it has the capability of measuring low-energy heavy ions with high efficiency while discriminating against high natural fluxes of protons.

Two-stage acoustic penetration and impact detector for micrometeoroid and space debris application

An active impact detector is described which has recently been developed and tested in the Munich Plasma Accelerator Facility. Piezo microphones are used for detection of penetration and impact events in a set-up which consists of a thin front foil and an impact plate. The elastic-wave propagation times between the impact location and the microphones will be measured in both the foil and the target and, by correlation of these time sequences and the signal amplitudes, the impact event time, the impact location, the projectile velocity, the flight path direction and the mass of the impacting particle can be evaluated. This measurement principle can be applied to a wide range of projectile size and velocity. Results of impact simulation experiments are presented and discussed with respect to a flight experiment application.

A High Resolution, High Efficiency Proportional Counter X-Ray Camera

A high-resolution, high-efficiency, gas-filled, position-sensitive x-ray camera for diagnostic Nuclear Medicine will be described. The simple integral parallel hole collimator allows a spatial resolution of less than 1 mm. and holds down the front foil allowing the counter to be pressurized to greater than 10 atmospheres for high efficiency.