Cavity Profile Research Articles

Numerical and theoretical investigation of the high-speed compressible supercavitating flows

The objective of this paper is to investigate the high-speed compressible supercavitating flows with numerical and theoretical methods. In the numerical simulation, calculations are performed by solving the Unsteady Reynolds-averaged Navier-Stokes (URANS) Equations using a cell-centered finite-volume method, and the k-ω SST turbulence model is applied as the closure model. Compressibility effects in liquid phase are modified by the equation of state (EOS), and vapor phase is treated as ideal gas. Firstly, the numerical results are validated with experiments conducted by Hrubes (2001). Results are shown for high-subsonic and transonic projectiles, there is a general agreement between the predicted cavity profiles and the experimental data. Secondly, the influence of the Mach number on the flow structure and cavitation dynamics from subsonic to supersonic flows is investigated. The results show that with the increase of Mach number, the radial dimension of the front cavity is reduced, which is caused by the dramatic increase of pressure around the projectile. An expression is proposed to analyze the flow parameters before and behind the shock wave based on the isentropic and potential assumption at the Mach number on the interval 1 ≤ Ma≤2.2. The relationship between pressure and density across the shock wave is also investigated. Overall, these findings are great interest in engineering applications.

Experiment and analytical model of laser milling process in soluble oil

The liquid-assisted laser machining process is a promising method to cut materials with minimum thermal damage caused by laser, and water is typically used in the process due to its high thermal conductivity, nontoxicity, and relatively low price. However, water can intrinsically oxidize ferrous metals and in turn deteriorate the workpiece through corrosion during laser ablation in water. This study has for the first time proposed laser ablation in soluble oil to effectively cut the ferrous metals by using laser in a high cooling rate and low potentiality of corrosion to the metals. A nanosecond pulse laser was used to scan over the AISI H13 steel sheet to create a square cavity, while the workpiece surface was covered by a thin and flowing soluble oil film throughout the laser milling process. The effects of laser scan overlap, traverse speed, and liquid flow rate on cavity dimensions and milled surface morphology were experimentally examined. The results revealed that a clean and uniform cavity with a smooth machined surface can be attained by using 70% scan overlap, 6 mm/s traverse speed, and 3.9 cm3/s soluble oil flow rate. Furthermore, analytical models based on heat transfer equations were formulated to predict the cavity profile and cooling of molten droplets in flowing liquid. The predicted profile was found to correspond well to the experiment, and the calculated temperature of cut particles can endorse the experimental findings on debris deposition and recast formation. The implications of this study could bring a new technological approach for damage-free fabrication and fine-scale manufacturing.

Microbiological profile of the nasal cavity of professionals from the emergency sector and mobile urgency care service localized in a southwest municipality of Goiás

Microbiological profile of the nasal cavity of professionals from the emergency sector and mobile urgency care service localized in a southwest municipality of Goiás

Wideband Fabry-Perot Cavity Antenna With a Shaped Ground Plane

This paper proposes a novel approach to broaden the 3-dB gain bandwidth of Fabry–Perot cavity (FPC) antennas by utilizing a shaped ground plane. The shaped ground plane is flat in the middle to accommodate the source antenna, and then angled up in the shape of trapezoids. Compared with an FPC antenna with a traditional flat ground plane, the 3-dB gain bandwidth of the one with a shaped ground plane is improved from 11% to 20.2% with the maximum realized gain and the 10-dB impedance bandwidth almost unchanged. To validate the feasibility of the proposed approach, an FPC antenna prototype has been designed, fabricated, and measured. It consists of a U-slot rectangular microstrip patch antenna as the source, a Rogers RT6006 superstrate as the partially reflective surface, and the proposed shaped ground plane. Measured results on input reflection coefficients and radiation patterns agree well with simulated ones. Therefore, this new approach can be an effective way to enhance the gain bandwidth without increasing the cavity profile or using multi-layer superstrate structures.

Effect of oxygen flow rate and temperature on supersonic jet characteristics and fluid flow in an EAF molten bath

ABSTRACTA new operation method for the oxygen lance of an electric arc furnace (EAF) was proposed, meeting the simultaneous demand for low oxygen flow rate and high stirring power in a particular smelting stage. When the oxygen flow rate needs to be reduced, the stirring power of the jet can be improved by increasing oxygen temperature properly. Free supersonic jet characteristics at different flow rates and stagnation temperatures were studied by numerical simulation and validated by a jet measurement experiment. The results showed that the designed Mach number can be maintained by coupling adjustment of flow rate and stagnation temperature. Meanwhile, a three-phase, full-scaled numerical model for a commercial 75t EAF with three oxygen lances on the side-wall was established to study the fluid flow in the molten bath. The velocity distribution, cavity profile and total kinetic energy of the EAF bath induced by the impingement of supersonic jets onto the liquid bath were discussed and compared. It was found that the fluid flow characteristics of the EAF molten bath can be improved even if the oxygen flow rate was reduced as long as the oxygen temperature could be increased reasonably.

A new cavity profile for a diaphragm compressor used in hydrogen fueling stations

The short operating life of metallic diaphragm caused by fracture is one of the main disadvantages for diaphragm compressors used in hydrogen fueling stations. A new generatrix for cavity profile is proposed through optimization using the complex method to decrease the maximal radial stresses on both oil and gas sides of the diaphragm clinging to the cavity surface. In the optimization, the convex part of the cavity generatrix is subjected to a constraint that the generatrix has a lower slope than the deformed diaphragm under a uniform pressure load. This constraint aims to avoid cavity dead volume at the end of the gas discharge process. Thus, an analytical solution for the deflection of an edge-clamped metallic diaphragm under a uniform pressure load is firstly developed. The solution employs the principle of minimum energy and the Rayleigh-Ritz method, which based on the theory of thin plates with large deflections. Experimental measurements, as well as the finite elements method (FEM), are employed to validate the solution. The analytical results are found to be in good agreement with the results of measurements and FEM simulations. Secondly, the stress of the diaphragm with a specific deflection is calculated, and the radial stress concerning both gas side and oil side of the diaphragm is taken as the objective function. Finally, a new generatrix is obtained through the optimization. The radial stress of the diaphragm clinging to the new cavity profile is validated via the FEM simulation, and results match well with each other. It also approves that the cavity dead volume is eliminated by the new generatrix at the end of the gas discharge process. Moreover, the maximal and the centric radial stress of the working diaphragm were compared between the new generatrix and the traditional generatrix under the same design parameters, the maximal and the centric radial stress of the diaphragm decreased by 8.2% and 13.9%, respectively. Based on the proposed design method, effects of the cavity volume, cavity radius, diaphragm thickness and diaphragm material properties on the maximal radial stress of the working diaphragm are further discussed.

Quantitative Analysis of the Efficiency of OLEDs.

We present a comprehensive model for the quantitative analysis of factors influencing the efficiency of organic light-emitting diodes (OLEDs) as a function of the current density. The model takes into account the contribution made by the charge carrier imbalance, quenching processes, and optical design loss of the device arising from various optical effects including the cavity structure, location and profile of the excitons, effective radiative quantum efficiency, and out-coupling efficiency. Quantitative analysis of the efficiency can be performed with an optical simulation using material parameters and experimental measurements of the exciton profile in the emission layer and the lifetime of the exciton as a function of the current density. This method was applied to three phosphorescent OLEDs based on a single host, mixed host, and exciplex-forming cohost. The three factors (charge carrier imbalance, quenching processes, and optical design loss) were influential in different ways, depending on the device. The proposed model can potentially be used to optimize OLED configurations on the basis of an analysis of the underlying physical processes.

PREPARATION OF PERSONALIZED BRAIN CAVITY SCAFFOLD WITH THREE-DIMENSIONAL PRINTING TECHNOLOGY BASED ON MAGNETIC RESONANCE IMAGING

To explore a method of three-dimensional (3D) printing technology for preparation of personalized rat brain tissue cavity scaffolds so as to lay the foundation for the repair of traumatic brain injury (TBI) with tissue engineered customized cavity scaffolds. Five male Sprague Dawley rats[weighing (300±10) g] were induced to TBI models by electric controlled cortical impactor. Mimics software was used to reconstruct the surface profile of the damaged cavity based on the MRI data, computer aided design to construct the internal structure. Then collagen-chitosan composite was prepared for 3D bioprinter of bionic brain cavity scaffold. MRI scans showed the changes of brain tissue injury in the injured side, and the position of the cavity was limited to the right side of the rat brain cortex. The 3D model of personalized cavity containing the internal structure was successfully constructed, and cavity scaffolds were prepared by 3D printing technology. The external contour of cavity scaffolds was similar to that of the injured zone in the rat TBI; the inner positive crossing structure arranged in order, and the pore connectivity was good. Combined with 3D reconstruction based on MRI data, the appearance of cavity scaffolds by 3D printing technology is similar to that of injured cavity of rat brain tissue, and internal positive cross structure can simulate the topological structure of the extracellular matrix, and printing materials are collagen-chitosan complexes having good biocompatibility, so it will provide a new method for customized cavity scaffolds to repair brain tissue cavity after TBI.

An approach for the numerical prediction of the compressible supercavitating flows over ultrahigh-speed underwater object

Purpose Ultrahigh-speed projectile running in water with the velocity close to the speed of sound usually causes large supercavity. The computation of such transonic cavitating flows is usually difficult, thus high-speed model reflecting the compressibility of both the liquid and the vapor phases should be introduced to model such flow. The purpose of this paper is to achieve a model within an in-house developed solver to simulate the ultrahigh-speed subsonic supercavitating flows. Design/methodology/approach An improved TAIT equation adjusted by local temperature is adopted as the equation of state (EOS) for the liquid phase, and the Peng-Robinson EOS is used for the vapor phase. An all-speed variable coupling algorithm is used to unify the computations and regulate the convergence at arbitrary Mach number. The ultrahigh-speed (Ma=0.7) supercavitating flows around circular disk are investigated in contrast with the case of low subsonic (Ma=0.007) flow. Findings The characteristic physical variables are reasonably predicted, and the cavity profiles are compared to be close to the experimental empirical formula. An important conclusion in the compressible cavitating flow theory is verified by the numerical result that, at any specific cavitation number the cavity’s size and the drag coefficient both increase along with the rise of Mach number. On the contrary, it is found as well that the cavity’s slenderness ratio decreases when Mach number goes up. It indicates that the compressibility has different influences on the length and the radius of the supercavity. Originality/value A high-speed model reflecting the compressibility of both the liquid and the vapor phases was suggested to model the ultrahigh-speed supercavitating flows around underwater projectiles.

Controlling mode competition by tailoring the spatial pump distribution in a laser: a resonance-based approach.

We introduce a simplified version of the steady-state ab initio laser theory for calculating the effects of mode competition in continuous wave lasers using the passive cavity resonances. This new theory harnesses widely available numerical methods that can efficiently calculate the passive cavity resonances, with negligible additional computational overhead. Using this theory, we demonstrate that the pump profile of the laser cavity can be optimized both for highly multi-mode and single-mode emission. An open source implementation of this method has been made available.

A four phase model for the macrosegregation and shrinkage cavity during solidification of steel ingot

A four-phase mixed columnar–equiaxed solidification model is introduced to calculate the formation of macrosegregation and shrinkage cavity during solidification of steel ingot. The four phases are the liquid melt, the solidifying solid with columnar morphology, the solidifying solid with equiaxed morphology, and the gas phase (or covering liquid slag). Multiphase/multiphysics transport phenomena (mass, momentum, species and enthalpy) are solved with a volume-average approach. Solidification induced mass and species transfers among metal phases are considered according to the thermodynamics and diffusion-governed crystal growth kinetics. The gas phase (or covering liquid slag) is only required to feed the shrinkage cavity and no mass/species exchange with other metal phases occurs. The following modeling results are obtained: the progress of columnar tip front and growth of columnar tree trunks, the nucleation and growth of equiaxed grains, the melt flow and equiaxed crystal sedimentation, the solute partitioning at the solid/liquid interface, the transport of the solute species and induced macrosegregation, the shrinkage cavity, the interaction or competition between growing columnar and equiaxed phases and the occurrence of columnar to equiaxed transition (CET). Those modeling capacities were verified by the calculation of a 10.5tons steel ingot. The experimentally determined profile of the shrinkage cavity, Sulfur print and chemical analysis of macrosegregation of the ingot in a vertical section were also available. Satisfactory agreement was obtained between the simulation and experimental result. Finally, a new hypothesis for the initialization of A-segregates is proposed: the motion of equiaxed phase and its interaction with the melt flow in the vicinity of growing columnar tip front lead to formation of an A-shape segregation band starting from the ingot corner just above the columnar-to-equiaxed transition area. This A-segregation band might provide a favored location for the initialization of A-segregates. Further dedicated experiment should be carried out to verify it.

Research on the flowrate and diaphragm movement in a diaphragm compressor for a hydrogen refueling station

The diaphragm compressor flowrate and diaphragm radial stress are the two evaluation criteria of diaphragm compressors when applied in hydrogen refueling stations. The diaphragm radial stress had been investigated in former researches and two new generatrice of the diaphragm cavity profile had been developed to decrease the diaphragm radial stress. This paper focused on the influence of the generatrice on the cavity clearance volume and compressor flowrate. Experimental and numerical method were applied to compare the diaphragm movements in the cavity defined by different generatrices during the working processing. The flowrates and clearance volume of the diaphragm compressor also were discussed by using experimental method. Furthermore, the effects of the generatrix parameters on the relative clearance volume were analyzed to obtain the optimal parameters value range. The results showed that the diaphragm cavity defined by new generatices had an additional clearance volume between the diaphragm and cavity surface, which was 1.11% and 3.44% of the cavity volume, respectively. And the minimum flowrate decrease rate of the compressor with the cavities defined by new generatrices even reached over 4.11%.

Cavity formation and surface modeling of laser milling process under a thin-flowing water layer

Laser milling process normally involves a number of laser scans over a workpiece to selectively remove the material and then to form cavities with shape and dimensions required. However, this process adversely causes a heat accumulation in work material, which can in turn damage the laser-milled area and vicinity in terms of recast deposition and change of material properties. Laser milling process performing in a thin-flowing water layer is a promising method that can overcome such damage. With the use of this technique, water can flush away the cut debris and at the same time cool the workpiece during the ablation. To understand the potential of this technique for milling application, the effects of process parameters on cavity dimensions and surface roughness were experimentally examined in this study. Titanium sheet was used as a workpiece to be milled by a nanosecond pulse laser under different water flow velocities. A smooth and uniform cut feature can be obtained when the metal was ablated under the high laser pulse frequency and high water flow velocity. Furthermore, a surface model based on the energy balance was developed in this study to predict the cavity profile and surface roughness. By comparing to the experiments, the predicted profiles had a good agreement with the measured ones.

Predictive Value of 1 Month Postoperative MRSI and FDG-PET Evaluations of Glioblastomas

Aim: The purpose of this study was to investigate prospectively the predictive value of positron emission tomography with proton magnetic resonance spectroscopic imaging (MRSI) and 18F-fluorodeoxyglucose (FDG-PET) performed the 1st month after surgery and before radio- chemotherapy in 43 patients with glioblastoma (GBM). Patients and methods: Metabolite concentrations were quantified using LCModel. Overall survival (OS) and progression free survival (PFS) were calculated including all 43 patients using Kaplan-Meier curves, and the Cox proportional hazard model was used to calculate the predictor of survival. Results: At the end of the follow-up period, all patients died within a period of 1–70.2 months. In 32 patients (74.4%), increased FDG-uptake was seen around the resection cavity and abnormal metabolic profiles on MRSI, indicative of residual disease, were present in all patients. There was no significant difference between the median OS in patients with hypometabolic FDG lesions compared to patients with hypermetabolic FDG lesions. On univariate analysis, normalized choline-containing compounds/creatine (nCho/Cr) and normalized lactate/creatine (nLac/Cr) were significantly predictive of OS and nLac/Cr and normalized N-Acetylaspartylglutamate and NAcetylaspartate/ creatine (NAA/Cr) were significantly predictive of PFS. Conclusions: nCho/Cr and nLac/Cr ratio after surgery and before radio-chemotherapy were independent metabolic predictive factors of OS times in newly diagnosed patients with GBM.

Water jet indentation for local elasticity measurements of soft materials.

We present a novel elastography method for soft materials (100Pa-100kPa) based on indentation by a μm-sized water jet. We show that the jet creates a localized deformation ("cavity") of the material that can be easily visualized. We study experimentally how cavity width and depth depend on jet speed, height, incidence angle and sample elasticity. We describe how to calibrate the indenter using gels of known stiffness. We then demonstrate that the indenter yields quantitative elasticity values within 10% of those measured by shear rheometry. We corroborate our experimental findings with fluid-solid finite-element simulations that quantitatively predict the cavity profile and fluid flow lines. The water jet indenter permits in situ local stiffness measurements of 2D or 3D gels used for cell culture in physiological buffer, is able to assess stiffness heterogeneities with a lateral resolution in the range 50-500μm (at the tissue scale) and can be assembled at low cost with standard material from a biology laboratory. We therefore believe it will become a valuable method to measure the stiffness of a wide range of soft, synthetic or biological materials.

Determination of Cavity Dimensions Induced by Impingement of Gas Jets onto a Liquid Bath

This paper presents an experimental and theoretical study on the cavity profile induced by the impingement of top-blown multiple gas jets onto a water or oil/water bath. The depth and diameter of the cavity were measured with respect to the lance height, gas flow rate, jets inclination angle, and oil volume. The experimental results show that the cavity depth increases with the increase of gas flow rate or oil thickness but the decrease of lance height or jets inclination angle. The cavity diameter is much less affected by gas flow rate compared to other variables. Then, the importance of the surface tension in the modeling of the cavity was theoretically identified. It was found that in the cratering process, the effect of the liquid surface tension on the cavity depth could be remarkably significant for a basic oxygen furnace (BOF) cold model but negligible for a real BOF steelmaking system. An improved theoretical model was hence proposed and validated using the experimental data obtained from both the single- or two-layer liquid baths. The new model includes not only the explicit consideration of the liquid surface tension but also that of the energy utilization efficiency of the jets impinging kinetic energy contributed to the cratering process.

The motion of entrapped air cavities in inclined ducts

ABSTRACTThe paper reports a study of the water surface profile of an entrapped air cavity while emptying water in an initially filled inclined duct. A one-dimensional (1D) model, which consists of the continuity and momentum equations applicable for open channel flow, pipe flow and air–water interface flow, is developed based on the finite volume method. A pressure drop model is proposed to reproduce a better profile around the cavity front, with a particular focus on air pressure changes inside the confined cavity to simulate a kind of transient flow with an entrapped air cavity. In contrast to the previous studies, the application of the model shows that when the pressure drop is not considered and the air pressure is not changed, the confined cavity soon vanishes. A comparison between the simulated and experimental results shows that the model is able to accurately reproduce the water surface profile of an entrapped air cavity while emptying inclined ducts.

Chromospheric seismology above sunspot umbrae

The acoustic resonator is an important model for explaining the three-minute oscillations in the chromosphere above sunspot umbrae. The steep temperature gradients at the photosphere and transition region provide the cavity for the acoustic resonator, which allows waves to be both partially transmitted and partially reflected. In this paper, a new method of estimating the size and temperature profile of the chromospheric cavity above a sunspot umbra is developed. The magnetic field above umbrae is modelled numerically in 1.5D with slow magnetoacoustic wave trains travelling along magnetic fieldlines. Resonances are driven by applying the random noise of three different colours---white, pink and brown---as small velocity perturbations to the upper convection zone. Energy escapes the resonating cavity and generates wave trains moving into the corona. Line of sight (LOS) integration is also performed to determine the observable spectra through SDO/AIA. The numerical results show that the gradient of the coronal spectra is directly correlated with the chromosperic temperature configuration. As the chromospheric cavity size increases, the spectral gradient becomes shallower. When LOS integrations is performed, the resulting spectra demonstrate a broadband of excited frequencies that is correlated with the chromospheric cavity size. The broadband of excited frequencies becomes narrower as the chromospheric cavity size increases. These two results provide a potentially useful diagnostic for the chromospheric temperature profile by considering coronal velocity oscillations.

Design and validation of new cavity profiles for diaphragm stress reduction in a diaphragm compressor

The application of diaphragm compressors is severely limited by the low reliability and short life of diaphragms. The cavity profile has considerable influence on a diaphragm's stress level and therefore on its fatigue life. This experimental and theoretical analysis of the traditional cavity profile (as defined by a single-parameter generatrix) indicated that the short life of diaphragms may be caused by the superposition of peak radial stress and additional stress due to the discharge holes in the central region that occur when the diaphragm clings to the cavity surface. Therefore, two new kinds of cavity profiles are proposed to decrease the diaphragm's radial and total stress. The new cavity profiles based on different generatrices were designed in an attempt to reduce the peak radial stress in the central region. These cavities were manufactured to experimentally validate the designs. Experiments were carried out under various design conditions to investigate the radial stress distribution in the diaphragms. The reductions of radial stress on the diaphragms in the new cavities were compared with stress levels found in the traditional design. Although their cavity volumes and radii were all the same, the radial stress levels on diaphragms in the cavities designed by the new generatrices were less than those found in the traditionally designed cavity. The greatest decline in radial stress on the diaphragms in the cavities based on new generatrices was 13.8%. With the additional stress taken into account, the decline in radial stress in the diaphragm's central region reached as high as 19.6%.

Integrated dynamics modeling for supercavitating vehicle systems

We have performed integrated dynamics modeling for a supercavitating vehicle. A 6-DOF equation of motion was constructed by defining the forces and moments acting on the supercavitating body surface that contacted water. The wetted area was obtained by calculating the cavity size and axis. Cavity dynamics were determined to obtain the cavity profile for calculating the wetted area. Subsequently, the forces and moments acting on each wetted part-the cavitator, fins, and vehicle body-were obtained by physical modeling. The planing force-the interaction force between the vehicle transom and cavity wall-was calculated using the apparent mass of the immersed vehicle transom. We in-tegrated each model and constructed an equation of motion for the supercavitating system. We performed numerical simulations using the integrated dynamics model to analyze the characteristics of the supercavitating system and vali-date the modeling completeness. Our research enables the design of high-quality controllers and optimal supercavita-ting systems.