Water Cylinder Research Articles

Non-reciprocal acoustics in a viscous environment.

It is demonstrated that acoustic transmission through a phononic crystal with anisotropic solid scatterers becomes non-reciprocal if the background fluid is viscous. In an ideal (inviscid) fluid, the transmission along the direction of broken P symmetry is asymmetric. This asymmetry is compatible with reciprocity since time-reversal symmetry (T symmetry) holds. Viscous losses break T symmetry, adding a non-reciprocal contribution to the transmission coefficient. The non-reciprocal transmission spectra for a phononic crystal of metallic circular cylinders in water are experimentally obtained and analysed. The surfaces of the cylinders were specially processed in order to weakly break P symmetry and increase viscous losses through manipulation of surface features. Subsequently, the non-reciprocal part of transmission is separated from its asymmetric reciprocal part in numerically simulated transmission spectra. The level of non-reciprocity is in agreement with the measure of broken P symmetry. The reported study contradicts commonly accepted opinion that linear dissipation cannot be a reason leading to non-reciprocity. It also opens a way for engineering passive acoustic diodes exploring the natural viscosity of any fluid as a factor leading to non-reciprocity.

Scattering proton CT

Proton computed tomography (CT) is an imaging modality investigated mainly in the context of proton therapy as a complement to x-ray CT. It uses protons with high enough energy to fully traverse the imaged object. Common prototype systems measure each proton’s position and direction upstream and downstream of the object as well as the energy loss which can be converted into the water equivalent thickness. A reconstruction algorithm then produces a map of the relative stopping power in the object. As an alternative to energy-loss proton CT, it has been proposed to reconstruct a map of the object’s scattering power based on the protons’ angular dispersion which can be estimated from the measured directions. As in energy-loss proton CT, reconstruction should best be performed considering the non-linear shape of proton trajectories due to multiple Coulomb scattering (MCS), but no algorithm to achieve this is so far available in the literature.In this work, we propose a filtered backprojection algorithm with distance-driven binning to account for the protons’ most likely path. Furthermore, we present a systematic study of scattering proton CT in terms of inherent noise and spatial resolution and study the artefacts which arise from the physics of MCS. Our analysis is partly based on analytical models and partly on Monte Carlo simulations.Our results show that the proposed algorithm performs well in reconstructing relative scattering power maps, i.e. scattering power relative to that of water. Spatial resolution is improved by almost a factor of three compared to straight line projection and is comparable to energy-loss proton CT. Image noise, on the other hand, is inherently much higher. For example, in a water cylinder of 20 cm diameter, representative of a human head, noise in the central image pixel is about 40 times higher in scattering proton CT than in energy-loss proton CT. Relative scattering power in dense regions such as bone inserts is systematically underestimated by a few percent, depending on beam energy and phantom geometry.

Characterization of acoustic streaming in water and aluminum melt during ultrasonic irradiation

It is well known that ultrasonic cavitation causes a steady flow termed acoustic streaming. In the present study, the velocity of acoustic streaming in water and molten aluminum is measured. The method is based on the measurement of oscillation frequency of Karman vortices around a cylinder immersed into liquid. For the case of acoustic streaming in molten metal, such measurements were performed for the first time. Four types of experiments were conducted in the present study: (1) Particle Image Velocimetry (PIV) measurement in a water bath to measure the acoustic streaming velocity visually, (2) frequency measurement of Karman vortices generated around a cylinder in water, and (3) in aluminum melt, and (4) cavitation intensity measurements in molten aluminum. Based on the measurement results (1) and (2), the Strouhal number for acoustic streaming was determined. Then, using the same Strouhal number and measuring oscillation frequency of Karman vortices in aluminum melt, the acoustic streaming velocity was measured. The velocity of acoustic streaming was found to be independent of amplitude of sonotrode tip oscillation both in water and aluminum melt. This can be explained by the effect of acoustic shielding and liquid density.

Dosimetry of a sonolucent material for an ultrasound-compatible gynecologic high-dose-rate brachytherapy cylinder using Monte Carlo simulation and radiochromic film

Purposehe purpose of this study was to study the dosimetric characterization of sonolucent material “TPX” to be used toward gynecologic high-dose-rate brachytherapy treatments using ultrasound-compatible cylinders in non–model-based dose calculation workflows. MethodsMonte Carlo simulations were performed using EGSnrc application egs_brachy in cylinders of polymethylpentene (TPX) plastic, water, and PMMA. Simulations were performed of five 192Ir sources placed longitudinally in ∼3.7 cm diameter, 5.0 cm length cylinders (matching physical cylinders used in film measurements). TPX and PMMA dose distributions and percentage depth dose curves were compared relative to water.Film measurements were performed to validate egs_brachy simulations. TPX and PMMA cylinders were placed in a water tank using 3D-printed supports to position film radially and touching the surface of the cylinders. The same five 192Ir dwell positions were delivered as simulated in egs_brachy. ResultsThe egs_brachy and film percentage depth doses agreed within film uncertainties. The egs_brachy relative dose difference between TPX and water was (0.74 ± 0.09)% and between PMMA and water was (-0.79 ± 0.09)% over the dose scoring phantom. Dose differences for TPX and PMMA relative to water were less than ± 1% within 5 cm of the cylinder surface. ConclusionsIn a solid sonolucent sheath of TPX, the dosimetric differences are comparable with PMMA and other applicator materials in clinical use. No additional uncertainty to dose calculation is introduced when treating through TPX cylinders compared with current applicator materials, and therefore, it is acceptable to perform gynecologic brachytherapy treatments with a sonolucent sheath inserted during radiation delivery.

Wave scattering by an array of metamaterial cylinders

Abstract

Tunable water-based metasurface for anomalous wave reflection

Metasurfaces (MSs) are artificial structures which enable the full control of electromagnetic waves and they continue to be of great scientific importance. In particular, they can tailor their reflection and transmission properties by using electrically small metallic/dielectric scatterers with imprinted spatial phase variation. In the present work, we design and characterize a water-based MS with a tunable reflection at 1 GHz. The MS comprises a collection of water cylinders and we demonstrate its ability to reflect a normally incident wave at an angle of 51.3° and with a total reflection efficiency of 33%. A prototype was fabricated and is shown to exhibit an excellent agreement with the simulation results. The proposed water-based MS may serve as a cheap and bio-friendly tunable alternative for a variety of microwave communication systems.

Dependence of added mass on cylinder cross-sectional geometry and orientation

This paper presents an experimental study on the added masses associated with the cylinders of different cross-sectional geometries (circular, square and rectangular of side ratio of 4) and angles of attack (θ = 0°- 90°) with respect to incident flow. Two fluid media are considered, i.e. water and paraffin oil. The added mass is investigated from three different perspectives. Firstly, the added mass is estimated from a shift in the oscillation frequency of the cylinder in water or paraffin oil from that in still air, referred to as the average added mass. Thus defined added mass is dependent on both cylinder cross-sectional geometry and orientation but is independent of the fluid medium. The average added mass decreases from 1.52 at θ = 0°to a minimum of 1.20 at θ = 45°for the square cylinder but grows monotonically from 0.55 at θ = 0°to 4.90 at θ = 90°for the rectangular cylinder. Secondly, the added mass is calculated from the equation of structural dynamics. This added mass decreases linearly with the decreasing oscillation amplitude, thus called the amplitude-dependent added mass. Thirdly, the amplitude-dependent added mass is reduced to the unique added mass in the absence of vibration. The unique added mass is in general smaller (< 11.3% depending on geometry and θ) than the average added mass but displays a similar dependence on the cylinder cross-sectional geometry and θ.

Runup on a vertical column in strong water wave events

Runup on a slender cylindrical column exposed to long, steep waves, at finite and great depth is quantified by high speed camera technique in wave channel. Ratio between water depth (h) and cylinder diameter (D) is h/D=10,4.16,2.5. Breaking and non-breaking wave events are made by focusing technique. The trough-to-trough period (TTT), crest height (η0.m), frequency (ω=2π/TTT) and reference speed (g/ω) of each wave event are defined (g denotes acceleration of gravity). Wavenumber (k) is obtained from the dispersion relation. Experimental runup maximum (Rum) is presented in terms of variable Z=[2ω2(Rum−η0,m)/g]1/2. Measurements at finite water depth collapse along a linear relationship kη0,m=a+bZ where coefficients are obtained from the experiments. Results from other studies including large scale measurements fit to this curve, for h/D<5, kh<2 and kD<0.52. Results at great water depth with h/D=10 show, beyond a threshold wave slope, a similar relationship. Growth factor (1/b) is then much stronger. Gradual transition between results at finite depth and great water depth occurs for 5<h/D<10 and kh>2.5. Measured runup velocity along the column is up to 1.8 times the reference speed at great depth (h/D=10) and up to 1.2 times the reference speed at finite depth. Wave slope kη0,m is up to 0.56.

Hydrodynamic Forces on a Submerged Horizontal Circular Cylinder in Uniform Finite Depth Ice Covered Water

Hydrodynamic forces on a submerged cylinder in uniform finite depth ice-covered water is formulated by using the method of multipoles, the ice-cover being modelled as an elastic plate of very small thickness. The forces (vertical and horizontal) are obtained analytically as well as numerically and depicted graphically for various values of flexural rigidity of the ice-cover to show the effect of its presence. When the flexural rigidity and surface density of the ice-cover are taken to be zero, then the curves for the forces almost coincide with the curves for the case of uniform finite depth water with free surface.

Photon fluence and dose estimation in computed tomography using a discrete ordinates Boltzmann solver

In this study, cone-beam single projection and axial CT scans are modeled with a software package—DOCTORS, which solves the linear Boltzmann equation using the discrete ordinates method. Phantoms include a uniform 35 cm diameter water cylinder and a non-uniform abdomen phantom. Series simulations were performed with different simulation parameters, including the number of quadrature angles, the order of Legendre polynomial expansions, and coarse and fine mesh grid. Monte Carlo simulations were also performed to benchmark DOCTORS simulations. A quantitative comparison was made between the simulation results obtained using DOCTORS and Monte Carlo methods. The deterministic simulation was in good agreement with the Monte Carlo simulation on dose estimation, with a root-mean-square-deviation difference of around 2.87%. It was found that the contribution of uncollided photon fluence directly from the source dominates the local absorbed dose in the diagnostic X-ray energy range. The uncollided photon fluence can be calculated accurately using a ‘ray-tracing’ algorithm. The accuracy of collided photon fluence estimation is largely affected by the pre-calculated multigroup cross-sections. The primary benefit of DOCTORS lies in its rapid computation speed. Using DOCTORS, parallel computing with GPU enables the cone-beam CT dose estimation nearly in real-time.

Experimental validation of an analytical microdosimetric model based on Geant4-DNA simulations by using a silicon-based microdosimeter

PurposeTo study the agreement between proton microdosimetric distributions measured with a silicon-based cylindrical microdosimeter and a previously published analytical microdosimetric model based on Geant4-DNA in-water Monte Carlo simulations for low energy proton beams. Methods and materialDistributions for lineal energy (y) are measured for four proton monoenergetic beams with nominal energies from 2.0 MeV to 4.5 MeV, with a tissue equivalent proportional counter (TEPC) and a silicon-based microdosimeter. The actual energy for protons traversing the silicon-based microdosimeter is simulated with SRIM. Monoenergetic beams with these energies are simulated with Geant4-DNA code by simulating a water cylinder site of dimensions equal to those of the microdosimeter. The microdosimeter response is calibrated by using the distribution peaks obtained from the TEPC. Analytical calculations for y‾F and y‾D using our methodology based on spherical sites are also performed choosing the equivalent sphere to be checked against experimental results. ResultsDistributions for y at silicon are converted into tissue equivalent and compared to the Geant4-DNA simulated, yielding maximum deviations of 1.03% for y‾F and 1.17% for y‾D. Our analytical method generates maximum deviations of 1.29% and 3.33%, respectively, with respect to experimental results. ConclusionSimulations in Geant4-DNA with ideal cylindrical sites in liquid water produce similar results to the measurements in an actual silicon-based cylindrical microdosimeter properly calibrated. The found agreement suggests the possibility to experimentally verify the calculated clinical y‾D with our analytical method.

RED WoLF: Combining a battery and thermal energy reservoirs as a hybrid storage system

Energy consumption of households is not evenly distributed. To satisfy peak demand, additional CO2 intensive generators are turned on when demand peaks. To avoid peak demand from dwellings, the RED WoLF (Rethink Electricity Distribution Without Load Following) hybrid storage system is proposed, consisting of batteries, storage heaters and a water cylinder. This aims at avoiding the use of these peak generators and integrating a higher share of renewables on the Power Grid. This system is planned to be tested in 100 houses distributed in 6 pilot sites in Great Britain, Ireland and France, which are currently undergoing construction or refurbishment. This study presents the theoretical model of the controlling algorithm, which enables the uptake of Grid electricity only when CO2 intensity is below a dynamically computed threshold. The algorithm is tested in computer simulations over the four seasons with varying size of batteries and photovoltaic arrays. Results show how RED WoLF algorithm satisfies households demands while, at the same time, successfully avoiding domestic peak demand, with a significant drop of CO2 emissions. This is achieved by both increasing photovoltaic self-consumption and uptake of low carbon Grid energy. For example, with a 7 kWh battery and a 4 kW photovoltaic array, CO2 emissions drop by 30% to almost 100%, depending on the season, relative to the same house without the RED WoLF system. The system has the potential to shift residential demand from peak power/peak times to low value electricity at a time of low demand.

Estimation of absorbed gamma dose rate from granite by Monte Carlo simulation approach

Apart from the continuous exposure of humans to background ionising radiation, an increased level of radiation may also originate from the use of building materials with an enhanced level of radioactivity. Thus, it is necessary to examine the content of radionuclides present in building materials, as well as the corresponding dose which may be received by residents from these materials. In this paper, particular attention was dedicated to finding the absorbed dose rate and annual effective dose caused by the presence of naturally occurring radioisotopes 226Ra, 232Th, and 40K in granite, a widely used building material, by means of Monte Carlo simulations. In addition, the obtained dose rate simulation results were compared with values estimated from commonly used simple equations, relating to the dose rate emitted by granite plates, covering the interior of a standard room. In the simulation, a room was constructed with standard dimensions (4 m × 5 m × 2.8 m), and with floor and walls covered with 3 cm thick granite. A water cylinder (approximate mass 65 kg) was positioned in the center of the room, representing a human body. The emission of the most intense gamma rays from 226Ra and 232Th progenies, as well as from 40K, emanating from the granite matrix, was simulated. The number of generated photons in each simulation (typically it was an order of magnitude of ~106) precisely represented actual activity concentrations of 226Ra, 232Th, and 40K in granite samples. All processes playing a role in the interactions of gamma photons with the granite matrix itself, the outer concrete shell, the air within the room, and the water cylinder, were taken into account by GEANT4 simulation software, after which the spectra of deposited energy inside of the water cylinder were obtained. Based on the deposited energy, the absorbed dose rate and annual effective dose were calculated for 6 analysed granite samples, each with different 226Ra, 232Th, and 40K contents. Furthermore, the effect of the position of the water cylinder in the simulated room on the absorbed dose rate was considered, as well as the distribution of the deposited energy within the water cylinder. The absorbed dose rates, and consequently annual effective dose, obtained in the simulations were found to be 30%–40% higher than the values obtained from using a standard formula.

MFC: An open-source high-order multi-component, multi-phase, and multi-scale compressible flow solver

MFC is an open-source tool for solving multi-component, multi-phase, and bubbly compressible flows. It is capable of efficiently solving a wide range of flows, including droplet atomization, shock–bubble interaction, and bubble dynamics. We present the 5- and 6-equation thermodynamically-consistent diffuse-interface models we use to handle such flows, which are coupled to high-order interface-capturing methods, HLL-type Riemann solvers, and TVD time-integration schemes that are capable of simulating unsteady flows with strong shocks. The numerical methods are implemented in a flexible, modular framework that is amenable to future development. The methods we employ are validated via comparisons to experimental results for shock–bubble, shock–droplet, and shock–water–cylinder interaction problems and verified to be free of spurious oscillations for material-interface advection and gas–liquid Riemann problems. For smooth solutions, such as the advection of an isentropic vortex, the methods are verified to be high-order accurate. Illustrative examples involving shock–bubble–vessel-wall and acoustic–bubble–net interactions are used to demonstrate the full capabilities of MFC. Program summaryProgram title: MFC (Multi-component Flow Code)CPC Library link to program files:http://dx.doi.org/10.17632/8y55zscjd3.1Developer’s repository link: https://mfc-caltech.github.ioLicensing provisions: GNU General Public License 3Programming language: Fortran 90 and PythonNature of problem: Computer simulation of multi-component flows requires careful physical model selection and sophisticated treatment of spatial and temporal derivatives to keep solutions both thermodynamically consistent and free of spurious oscillations. Further, such methods should be high-order accurate for smooth solutions to reduce computational cost and promote sharper interfaces for discontinuous ones. These problems are particularly challenging for flows with material interfaces, which are important in numerous applications.Solution method: The present software incorporates multiple physical models and numerical schemes for treatment of compressible multi-phase and multi-component flows. Additional physical effects and sub-grid models are included, such as an ensemble-averaged bubbly flow model. The architecture was designed to ensure that further development is straightforward.

Study on the Scattering Properties of Cylinders in Suspensions Containing Sediment Particles

A method is presented that combining the Mcclements suspension model with the cylindrical model to solve the complexity of calculating the scattered acoustic pressure around the cylinder, when suspended particles are contained in the water. The scattered acoustic pressure of an infinitely long cylinder in water is derived based on the boundary conditions. Then, the wave number of the particle-containing suspension is calculated by the Mcclements suspension model, which is combined with the scattered acoustic pressure of an infinitely long rigid cylinder in water. The scattered acoustic pressure of an infinitely long rigid cylinder in suspension is obtained. The results show that the content of sediment particles has a greater impact on the distribution of scattered acoustic pressure. The scattered acoustic pressure is more directional with the increase of the content of sand particles, laying a foundation for further research on other target objects in suspension.

Eight-channel acoustic demultiplexer based on solid-fluid phononic crystals with hollow cylinders

We design a novel eight-channel demultiplexer in a solid-fluid phononic crystal structure. The basic structure has been formed by square arrangement of holes filled by water in tungsten background. These holes are embedded in background with filling fraction of 46 %. Generally, the proposed structure consists of nine type line defects for input and output channels. These line defects consist of two types of hollow cylinders. One of them is used in input channel and the other creates output channels. Input waveguide contains an L-branch waveguide which has been made by a row of hollow cylinders of water which is internally filled with tungsten. Each of output channels contains a row of hollow cylinders of Methyl Nonafluorobutyl Ether filled with tungsten. Hollow cylinders have different inner radii in each output waveguides. Hence, each output channels can transmit diverse narrow frequency passbands. We use the finite element method to determine the eigenfrequencies of structure. This structure can separate eight acoustic waves in frequency range between 166.6 kHz and 168.1 kHz. Separation of frequencies is accomplished with high quality factor and the width of frequency spectra between outputs are about 200 Hz. Crosstalk values of the proposed structure show that the eight-channel demultiplexer has efficient performance so that, the worst case of crosstalk value is equal to -26.68 dB.

Simultaneous emission and attenuation reconstruction in time-of-flight PET using a reference object

BackgroundSimultaneous reconstruction of emission and attenuation images in time-of-flight (TOF) positron emission tomography (PET) does not provide a unique solution. In this study, we propose to solve this limitation by including additional information given by a reference object with known attenuation placed outside the patient. Different configurations of the reference object were studied including geometry, material composition, and activity, and an optimal configuration was defined. In addition, this configuration was tested for different timing resolutions and noise levels.ResultsThe proposed strategy was tested in 2D simulations obtained by forward projection of available PET/CT data and noise was included using Monte Carlo techniques. Obtained results suggest that the optimal configuration corresponds to a water cylinder inserted in the patient table and filled with activity. In that case, mean differences between reconstructed and true images were below 10%. However, better results can be obtained by increasing the activity of the reference object.ConclusionThis study shows promising results that might allow to obtain an accurate attenuation map from pure TOF-PET data without prior knowledge obtained from CT, MRI, or transmission scans.

Hydrodynamic interaction among multiple columns in front of a vertical wall

The berthing or mooring facilities in ports and/or harbors are usually in the form of a group of vertical columns. These structures are arranged in close proximity to the long vertical harbor wall. Accurate prediction of wave force on such structures is of importance, yet, challenging, as both interferences among cylinders as well as between cylinders and the wall must be correct. In this work, a novel analytical model has been developed to investigate the hydrodynamic characteristics of such structures within the framework of linear wave theory. The original problem is considered to be equivalent to that of two symmetrical arrays of cylinders in open water; both are exposed to the ambient incident waves. The original array of cylinders is labelled as real cylinders hereafter, and the second array as image cylinders. The assumption of full wave reflection on the wall is essential by using this treatment. Due to the symmetry, simple relationships between the diffracted waves from the real and image cylinders are found, which reduces the number of unknowns associated with the velocity potential by half. After solving the velocity potential, the wave forces as well as the surface elevation are evaluated. Two different solutions have been developed for the calculation of mean drift wave force. One is based on the direct pressure integration and the other is based on the application of momentum conservation theorem in a limited fluid volume surrounding a certain cylinder in the array. Then, the systematic analysis is performed for a line array of equally-spaced cylinders parallel to a vertical wall. Largely amplified wave forces are found at specific wave frequencies, which occur with the appearance of pronounced wave runup around the cylinders. Furthermore, the relative contribution of the first-order and the mean drift wave forces to the total wave force is examined.

Function-Reconfigurable Water Short Backfire Antenna

A novel short backfire antenna realized by replacing the metallic wall with water wall is described in this paper. Through controlling the water flow in different layers, the proposed short backfire antenna based on a cylindrical waveguide made of water can switch between two different functions. When the proposed antenna works in Function I, it is a short backfire antenna with pencil beam. When it operates in the other function, conical beam is achieved, and its beam angle can be changed by controlling the height of water cylinder and water wall. Measured results show that when working in Function I, the proposed water short backfire antenna has an impedance bandwidth (|S11| <; -10 dB) of 11.3% (3.6 GHz to 4.05 GHz). A maximum gain of 10.8 dBi is observed. While working in Function II, the beam angle of a conical radiation beam can be switched between 25° and 60°. The operating frequency of the antenna working in Function II covers a range of 5% (3.9 GHz to 4.1 GHz). Maximum gain of 6.8 dBi for 25° and 2.7 dBi for 60° is obtained. Due to its low cost, good radiation performances, transparent characteristic, and reconfigurability, this novel water antenna may be potentially useful in future communication applications.

Lateral Vibration of Offshore Piles Considering Pile-Water Interaction

The dynamic response of an offshore pile in saturated soil subjected to lateral harmonic loading is theoretically investigated by considering the dynamic pile-water interaction. The governing equation of water is solved based on the separation of variable method, and the analytical expression of the hydrodynamic force applied on the pile is then obtained. Based on the continuous conditions at the pile-soil interface and pile-water interface, the analytical solution of the dynamic impedance of the offshore pile is derived by using transfer matrix method. To verify this solution, the dynamic impedance obtained for a cylinder in water is compared with that of a partially embedded pile. Based on this solution, the effect of hydrodynamic pressure and other parameters on the dynamic response of offshore piles is investigated. The results show that the analytical model ignoring the hydrodynamic force applied on the pile misestimates the impedance of the pile in the high frequency range.