Curvature Correction Research Articles

On the role of f (G, T) terms in structure scalars

This work is devoted to explore the effects of $f(G,T)$ terms on the study of structure scalars and their influences in the formulations of the Raychaudhuri, shear and Weyl scalar equations. For this purpose, we have assumed non-static spherically symmetric geometry coupled with shearing viscous locally anisotropic dissipative matter content. We have developed relations among the Misner-Sharp mass, Weyl scalar, matter and structure variables. We have also formulated set of $f(G,T)$ structure scalars after orthogonally breaking down of the Riemann curvature tensor. The influences of these scalar functions in the modeling of relativistic radiating spheres are also studied. The factor involved in the emergence of inhomogeneities is also explored for the constant and varying modified curvature corrections. We inferred that $f(G,T)$ structure scalars could lead provide an effective tool to study Penrose-Hawking singularity theorems and Newman-Penrose formalism.

Numerical simulation and experiments on turbulent air flow around the semi-circular profile at zero angle of attack and moderate Reynolds number

Two-dimensional flow around a semi-circular profile at the zero angle of attack and at Re = 50000 on the self-oscillatory period is extensively studied by the URANS method involving the standard semi-empirical SST turbulence models, the SST turbulence model with the correction for streamline curvature modified within the Rodi-Leschziner-Isaev and Smirnov-Menter approaches, as well as involving Hanjalic's four-parameter eddy viscosity elliptic relaxation model and its analog - eddy viscosity elliptic blending model proposed in the present work. This has been done with the use of different-structure grids (multiblock with structured overlapping and unstructured composite). Different numerical approximation methods realized in six codes (VP2/3, SigmaFlow, Fluent, CFX, OpenFOAM, and StarCCM+) are used. An underestimation (up to 30%) of time-averaged integral aerodynamic loads is revealed by means of the standard near-wall SST model. This is explained by the high vortex viscosity production in the profile wake. Wind tunnel tests show that the location of cutoff washers on the semi-circular profile provides a quasi-two-dimensional flow around it and allows applying measurement data to verify two-dimensional turbulent flow. The best agreement of experimental results and numerical predictions when comparing the Strouhal number and time-averaged surface pressure coefficient distributions is achieved using both the modified SST model with the correction for streamline curvature and the modified eddy viscosity elliptic blending model. When the SST model with the correction for streamline curvature, modified within the Rodi-Leschziner-Isaev, Smirnov-Menter and Durbin approaches, is used, all the above codes yield close predictions of a vertical aerodynamic load on the oscillation period.

PO-01-106 Penile curvature correction with autologous foreskin graft

PO-01-106 Penile curvature correction with autologous foreskin graft

Simultaneous curvature correction at the time of the penile fracture repair: surgical and functional outcomes.

Purpose: After a penile fracture (PF), an early surgical exploration and defect closure of the lesions are recommended to prevent long-term complications. However, postoperative unsatisfactory penile curvatures are frequent in the literature. In this study, we wished to present surgical outcomes of PF after surgical repair approach with an early intraoperative curvature correction and update our series with postoperative follow-up.Patients and methods: An institutional retrospective review study of 36 patients undergoing surgical treatment for PF was performed. Mean age of patients was 53.2 years. All surgical explorations were performed within 12 hours after the traumatic event. The surgical repair with a contemporary penile plication was then made to straighten the tunica angulations in patients with curvature greater than 30°, using 2– 3 pairs of 2–0 absorbable suture of polydioxanone.Results: The length of the tear ranged from 8 to 20 mm. 77.7% of the patients required a correction of the cavernous body deviation. No early complications occurred in any case. The median patient stays in the hospital was 3.4 days. At a mean follow-up of 20.6 months, all patients were able to insert the penis in the partner’s vagina, and were satisfied overall with sexual intercourse; three patients (10.7%) reported residual pain and discomfort for the knots of the sutures.Conclusions: An early intraoperative curvature correction may be used for a variety of angulation deformities and severe degrees of deviations secondary to a repair after penile trauma, and may be helpful in preventing postoperative morbidity.

Design and test of 704 MHz and 2.1 GHz normal conducting cavities for low energy RHIC electron cooler

The Low Energy RHIC electron Cooler (LEReC) is currently under commissioning at BNL to improve RHIC luminosity for heavy ion beam energies below 10 GeV/nucleon. The linac of LEReC consists of a DC photoemission gun, one 704 MHz superconducting radio frequency (SRF) booster cavity, and three normal conducting cavities. It is designed to deliver a 1.6 MeV to 2.6 MeV electron beam, with peak-to-peak momentum spread dp/p of less than 7e4. Two of the three normal conducting cavities will be used in LEReC for energy spread correction. A single-cell 704 MHz cavity for energy de-chirping and a three-cell 2.1 GHz third harmonic cavity for RF curvature correction. In this paper, we present the designs and RF test results of these two cavities.

A study of thermo-fluid characteristics of Czochralski melt using rotation and curvature corrected Partially-Averaged Navier-Stokes (PANS) turbulence models

A Czochralski melt flow encounters the effects of anisotropic body forces owing to the system rotation as well as significant streamline curvature due to inherent vortical structures and flow past curved surfaces. Two-equation eddy-viscosity models lack the ability to capture the flow anisotropy and curvature effects. Here we present the first study on the thermo-fluid characteristics of Czochralski melt using rotation and streamline curvature corrected Partially-Averaged Navier-Stokes (PANS) adaptations of the low-Re k-ε and SST k-ω models. The paper presents physical insights to the new PANS turbulence modelling approach highlighting improvements in the predicting capability of PANS models with the incorporation of rotation and curvature corrections. The PANS models showed good agreement with the results available in the literature (both experimental and computational). In addition for the PANS low-Re k-ε model it was observed that the prediction of the typical Czochralski melt flow structure in terms of shape, relative size and orientation of the characteristic cells improved with rotation and curvature corrections. Further thermal fluctuations and vortex cores also reduced in the melt in the case of the PANS low-Re k-ε model showing stabilization of flow. The corresponding rotation and curvature modification to the PANS SST k-ω model corrected the flow dynamics from a buoyancy dominated to rotationally driven along with an increase in the thermal fluctuations and vortex cores in the Czochralski melt resulting in a destabilization of the melt flow.

Numerical Investigation of Flow Near a Round Exhaust Channel Screened by an Annular Swirled Jet

Based on the Reynolds equations closed with the aid of the model of shear stresses transfer and of the model with a correction for curvature and rotation, numerical simulation of air flow near a round exhaust hole screened by an annular swirled jet was carried out. The influence of the swirling intensity on the air flow velocity field in the range of action of an exhaust device and its range of action at different flow rate ratios of the sucked and inflowing air and also at different distances of the circular hole from the axis has been determined. The results obtained will be of use in designing effective systems of exhaust ventilation of lowered energy capacity.

Calculation of cavitation evolution and associated turbulent kinetic energy transport around a NACA66 hydrofoil

The physical mechanism of flow unsteadiness is one of the key problems in cavitating flow. Significant efforts have been exerted to explain the cavitation-vortex interaction mechanism. As well, the process of kinetic energy transport during the evolution of unsteady cavitating flow must be elucidated. In this work, 2D calculations of cavitating flow around a NACA66 hydrofoil were performed based on the open source software OpenFOAM. The modified shear stress transport k-ω turbulence model, which considers curvature and turbulent eddy viscosity corrections, was employed to close the governing equations. The Schnerr-Sauer cavitation model was adopted to capture the cavitation phase change process. Numerical results showed reasonable consistency with the results of the experiments conducted by Leroux et al. (2004). The results showed that cavitation promotes turbulence intensity and flow unsteadiness around the hydrofoil. During the attached sheet cavity growth stage, high-value regions of turbulent kinetic energy are located substantially at the interface of the cavity, particularly at the rear portion of the cavity region. During the cloud cavity shed-off stage, the cavity begins to break off and the maximum value of turbulent kinetic energy is observed inside the shed cavity. Finally, the influence of cavitation on the turbulence intensity is illustrated using the turbulent kinetic energy transport equation, which shows that the pressure diffusion and turbulent transport terms dominate as cavitation occurs. In addition, cavitation promotes turbulence production and increases dissipation with fluid viscosity and flow unsteadiness. The viscous transport term only acts in the cavitation shedding stage under large-scale vortex shedding. Overall, these findings are of considerable interest in engineering applications.

Numerical study on cavitating flow-induced vibration of liquid rocket engine inducer

The cavitating flow-induced vibrations have become one of the major issues for the operation safety and stability of the liquid rocket engine. The objective of this paper is to numerically investigate the cavitating flow around a four-blade inducer, with focus on the cavitating flow-induced vibration characteristics. In the numerical simulation, the curvature correction turbulence model and the Zwart cavitation model is used for the simulation of the flow field. The loose coupled method is adopted for the prediction of the fluid structure interaction, including the calculation of the fluid forces based on the multiphase fluid dynamics, computation of the structural deformation via the governing equation of the structural motion, and then the update the fluid and structure mesh. The results showed that good agreement has been obtained between the experimental and numerical results. The reverse flow vortex cavitation develops and rotates with the blade, but with a much lower rotational speed than that of the blade. The vibration of the hydrocone is mainly affected by the blade rotation of the inducer, and the blade vibration is mainly affected by the reverse flow vortex cavitation

THE INFLUENCE OF FEATURES OF VORTEX FLOW ON AERODYNAMIC CHARACTERISTICS OF THE SUPERSONIC MANEUVERABLE AIRCRAFT MODEL

The paper presents the influence of the vortex flow features, in particular, the phenomenon of vortex burst on the longitudinal and lateral aerodynamic characteristics of the maneuverable aircraft model with a sharp-edged fore-body. Numerical simulation of vortex flow has been conducted at low subsonic speeds (M = 0.15) in a wide range of angles of attack α = 0 ÷ 35° at zero sideslip β = 0°, as well as at fixed values of angles of attack a = 10,25,30,35° in a wide range of slip angles β = 0 ÷ 20° using k - ω SST turbulence model with curvature correction due to the insensitivity of the standard model to such effects. A satisfactory agreement of the numerical results with the experimental data on both longitudinal and lateral aerodynamic characteristics in a wide range of angles of attack and sideslip is obtained. According to the results of the numerical simulations, all the main nonlinearities in the integral characteristics associated with the vortex breakdown phenomenon and the interference of vortex structures were explained. The physical features of the vortex flow around the maneuverable aircraft model with a sharp-edged nose and their influence on the longitudinal and lateral aerodynamic characteristics are revealed. The phenomenon of vortex breakdown significantly affects the aerodynamic characteristics of the model. And with the increase of the angle of attack the point of vortex breakdown moves up the stream. At non zero sideslip vortices are destroyed asymmetrically, which leads to a loss of transverse stability of the model. The interaction of the nose and wing vortices, as well as the relative position of the points of vortex breakdown in the range of angles of attack 18° < α < 28° at zero slip angle lead to nonlinearities in the dependence of the lift coefficients and the longitudinal moment of the angle of attack. At large angles of attack, the main vortices forming from the sharp-edged nose make a major contribution to the change in the aerodynamic coefficients, in contrast to the round nose, where the yawing stability is often determined by secondary vortices. The phenomenon of vortex breakdown significantly affects the contribution of the sharp-edged nose to the yawing stability. Moreover, its effect can be radically different at different angles of attack (a = 25-30° and 35°). The local change in the contours of the fore-body in the plan view also significantly affects the directional stability due to the delaying of the vortex burst.

Surgical Technique for Complex Cases of Peyronie’s Disease With Implantation of Penile Prosthesis, Multiple Corporeal Incisions, and Grafting With Collagen Fleece

IntroductionPatients with Peyronie’s disease (PD) and erectile dysfunction (ED) concomitant with shortening or other malformations benefit from prosthesis implantation and penile lengthening procedures. AimTo evaluate the safety and efficacy of a multi-incisional technique with penile prosthesis implantation with multiple corporeal incisions and collagen grafting for the surgical management of complex cases of PD with ED and severe penile shortening. MethodsFrom February 2015–May 2018, 43 consecutive patients with complex PD were treated using this technique. Implantation of a penile prosthesis (malleable or inflatable [IPP]) together with multiple relaxing tunica albuginea incisions and grafting with a self-adhesive collagen-fibrin fleece (TachoSil, Baxter Healthcare) was performed in all patients by a single surgeon (J.I.M.S.). Main Outcome MeasurePenile length and curvature correction, operative time, and incidence of postoperative complications were recorded as outcome measures. Functional outcomes were measured with questionnaires (International Index of Erectile Function-5, Erection Hardness Score, modified Erectile Dysfunction Inventory of Treatment Satisfaction questionnaire, PD Questionnaire) before and 3 and 6 months after surgery. ResultsWith a median follow-up of 21 months (range 10–31), mean postsurgical penile lengthening was 2.5 (range 1–5) cm, with an improvement in the Bother domain of the PD Questionnaire of 4.4 (range 2–5) points. The average operative time was 86.7 and 71.6 minutes for the IPP and malleable penile prosthesis procedure, respectively. No glans ischemia was recorded; however, 1 IPP infection and 1 delayed distal corporeal erosion were recorded. Hematoma or bruising was observed in 23.2% of patients. The modified Erectile Dysfunction Inventory of Treatment Satisfaction questionnaire was completed by 39 (90.7%) patients. Overall, 89.7% would recommend this surgery. Patient satisfaction with straightness and length was 94.9% and 82.1%, respectively. Clinical ImplicationsThe described technique helps restoration of penile length and erectile function in patients with complex PD. Strengths & LimitationsThe strength of the study is that it offers a simple, easy-to-apply technique for surgeons to correct shortening and other malformations in patients with ED and complex PD. The study is limited by the small number of patients, the short follow-up period and the performance of the technique by a single high-volume implanter. ConclusionThe implantation of a penile prosthesis (malleable or inflatable) together with multiple incisions of the plaque/tunica albuginea and grafting with a collagen fleece is a safe and efficient treatment for patients with complex PD in addition to ED and significant shortening.Fernández-Pascual E, Gonzalez-García FJ, Rodríguez-Monsalve M, et al. Surgical Technique for Complex Cases of Peyronie’s Disease With Implantation of Penile Prosthesis, Multiple Corporeal Incisions, and Grafting With Collagen Fleece. J Sex Med 2019;16:323–332.

Curvature correction to the field emission current

The curvature of field emitter tips leads to an altered tunneling potential that assumes significance when the radius of curvature is small. The authors provide here an analytical curvature corrected formula for the field emission current from axially symmetric emitters aligned in the direction of the asymptotic electric field. Its domain of applicability is tested across a range of apex radius, Ra, and local electric field, Ea. It is found to give excellent results for Ra>5nm and Ea>5V/nm with errors generally less than 10%. Surprisingly, for the uncorrected potential, the authors find the errors to be high even at Ra=100nm (>35% at Ea=3V/nm) and conclude that curvature correction is essential for apex radius less than a micron.

Penile Stretching as a Treatment for Peyronie's Disease: A Review.

Peyronie's disease (PD) is a debilitating condition that affects a sizable number of men worldwide. Current treatment options consist of oral therapy, intralesional injections, and surgery. Penile stretching has been used as a treatment for PD, including penile traction therapy (PTT) and vacuum erection devices (VEDs), with numerous trials completed or underway. To present and summarize the current literature on penile stretching for the treatment of PD. Using PubMed, we performed a literature review of studies from January 1990 through July 2018 that focused on penile stretching for PD management. PTT and VED were included in the search criteria. Penile curvature correction was effective, and stretched penile length was improved. PD therapies that use penile stretching as a mechanical intervention to alter tissue characteristics were studied. PTT has been successful in primary penile lengthening and curvature correction in the acute phase of PD. PTT also improved length retention in men undergoing plication and incision/grafting procedures. Combination of PTT and intralesional injection therapy for PD treatment requires further investigation. There are fewer studies investigating VEDs and their role in PD management, but initial small trials suggest a role in curvature correction and penile lengthening. Penile stretching is an effective therapy for PD. Data from limited trials suggest a role for PTT and VEDs in the management of PD, although further research is needed. Cowper MG, Burkett CB, Le TV etal. Penile Stretching as a Treatment for Peyronie's Disease: A Review. Sex Med Rev 2019;7:508-515.

An All-Digital Time-Domain Smart Temperature Sensor With a Cost-Efficient Curvature Correction

This paper presents an all-digital time-domain smart temperature sensor (TDSTS) with a cost-efficient curvature correction, which can effectively improve the accuracy and cost. Inverter-based TDSTSs are low cost and low complexity but they exhibit a significant curvature, which severely impairs their accuracy. Linearity enhancement through linear interpolation reduces the curvature and results in a twofold improvement in the accuracy. In this paper, the proposed curvature correction not only simplified the scheme to reduce the hardware cost but also successfully eliminated the curvature to achieve the most suitable accuracy. In addition, the correction procedure was also simplified. The TDSTS was implemented in eight Xilinx field-programmable gate arrays for performance verification and occupied 74 slices per sensor. The logic utilization for the proposed curvature-corrected circuit was 17 slices, and its cost was only 23% of the hardware cost. The experimental results indicated that the maximum inaccuracy decreased from 5 °C to 1.8 °C over the temperature range of −20 °C–100 °C, resulting in an approximate threefold improvement in the accuracy. Compared with a previous study, the improvements of 30% and 43% in the accuracy and cost, respectively, successfully validate the proposed technique.

EFFECT OF THE HORIZONTAL CANARD OF THE SHARP-EDGED FOREBODY OF THE MANEUVERABLE AIRCRAFT MODEL ON THE VORTEX FLOW STRUCTURE

This paper presents the results of numerical studies of the effect of horizontal canard installation in a maneuverable aircraft model with a sharp-edged forebody, which smoothly turns into the leading edge extension, on the longitudinal aerodynamic characteristics at low subsonic speeds (M = 0.15) within the range of angles of attack α = 0°–35° using the two-parameter k-ω shear stress transport turbulence model with empirical correction for the streamline curvature. The results of the numerical calculations are in satisfactory agreement with the experimental data obtained in the T-102 wind tunnel at TsAGI within the entire range of the angles of attack. Based on the numerical and experimental studies, it is shown that installation of a horizontal canard has a positive effect on the aerodynamic characteristics of the maneuverable aircraft model at rather high angles of attack (α > 19°). The positive effect of the horizontal canard installation is mainly due to the influence of the vortex structures generated from the sharp-edged forebody on the trajectory, which yields favorable interference of the forebody and wing vortices.

Study on the Accuracy of RANS Modelling of the Turbulent Flow Developed in a Kaplan Turbine Operated at BEP. Part 2 - Pressure Fluctuations

The aim of the paper is to investigate the limitations of unsteady Reynolds-averaged Navier-Stokes (RANS) simulations of the flow in an axial turbine. The study is focused on modelling the pressure pulsations monitored on the runner blades. The scanned blade geometry renders the meshing process more difficult. As the pressure monitor points are defined on the blade surface the simulation relies on the wall functions to capture the flow and the pressure oscillations. In addition to the classical turbulence models, a curvature correction model is evaluated aiming to better capture the rotating flow near curved, concave wall boundaries. Given the limitations of Reynolds-averaged Navier-Stokes models to predict pressure fluctuations, the Scale Adaptive Simulation-Shear Stress Transport (SAS-SST) turbulence model is employed as well. The considered test case is the Porjus U9, a Kaplan turbine model, for which pressure measurements are available in the rotating and stationary frames of reference. The simulations are validated against time-dependent experimental data. Despite the frequencies of the pressure fluctuations recorded on the runner blades being accurately captured, the amplitudes are considerably underestimated. All turbulence models estimate the correct mean wall pressure recovery coefficient in the upper part of the draft tube.

An Efficient SAR Ground Moving Target Refocusing Method Based on PPFFT and Coherently Integrated CPF

The problem of ground moving target imaging and detection is difficult due to the large range cell migration (RCM) and time-varying Doppler frequency migration (DFM) in synthetic aperture radar (SAR) system. To finely refocus a moving target, motion parameters need be accurately estimated for compensating the RCM and DFM. In this work, an efficient ground moving target refocusing method based on pseudopolar fast Fourier transform (PPFFT) and coherently integrated cubic phase function (CICPF) is proposed without a priori knowledge of the motion parameters. First, based on the known radar platform motion parameters, the range curvature correction is completed, and then the range walk is corrected using the efficient PPFFT via estimating the slope of the range walk. In doing so, the energy of the moving target has been focused into the same range cell. Second, time-varying DFM parameters are obtained utilizing the proposed CICPF, and thus the well-focused result of the moving target is obtained. Compared with the existing methods, the proposed method has the advantages in computational complexity due to avoiding the searching and interpolation operation, and anti-noise performances thanks to fully exploiting the two-dimensional (2-D) coherently accumulation characteristics and the energy of all the scatterers in moving target for estimating motion parameters. Finally, both the simulated and real SAR data processing results are presented to validate the proposed method.

A Resistorless High-Precision Compensated CMOS Bandgap Voltage Reference

A resistorless high-precision compensated CMOS bandgap voltage reference (BGR), which is compatible with a standard CMOS process, is presented in this paper. A higher-order curvature correction method called base-emitter voltage linearization is adapted to directly compensate the thermal nonlinearity of base–emitter voltage. With proper mathematical operations of high-order temperature currents, most of the nonlinear temperature terms in $V_{\mathrm {BE}}$ can be greatly eliminated. The proposed BGR, which is implemented in 0.35- $\mu \text{m}$ CMOS technology, is capable of working down to 2 V supply voltages with 1.14055 V mean output voltage. A minimum temperature coefficient of 1.01 ppm/°C with a temperature range from −40 °C to 125 °C is realized, and a power-supply noise attenuation of 61 dB is achieved without any filter capacitors. The line regulation is better than 2 mV/V from 2 V to 5 V supply voltage while dissipating a maximum supply current of $33~\mu \text{A}$ . The active area of the presented BGR is 180 $\mu \text {m}\times 220\,\,\mu \text{m}$ .

Evaluation of curvature correction methods for tip vortex prediction in SST [formula omitted] turbulence model framework

This paper presents and studies effects of curvature correction (CC) methods to improve two equation RANS simulations of tip vortex flows, exemplified using the SST k−ω turbulence model. Performance of the CC models is first evaluated in the classical Rankine vortex flow field, and then extended into the study of tip vortex flows over an elliptical foil. The results have been compared with experimental measurements in terms of the vortex strength and velocity field, and the importance of the turbulence closure in tip vortex simulations is highlighted.Contribution of the CC models in different terms of the turbulent kinetic energy and specific dissipation transport equations are described, and it is discussed why a CC model may have mesh resolution dependent results. By considering the distribution of the CC function, it is shown that although some of the models can predict the location of the tip vortex core accurately, they still do not significantly improve the vortex prediction as the impact on the turbulent viscosity is wrong or not enough. It is further noted that as some of these models have been calibrated on specific vortex flows, they may not be completely applicable for other cases without recalibration. It is shown that some CC models provide accurate tip vortex predictions, primarily the ones based on the sensitization of the turbulent viscosity. Further, it is noteworthy that the successful models are active not only around the vortex, but also change the boundary layer characteristics on the foil, and the boundary layer separation lines, which consequently can provide the required momentum for the vortex core accelerated axial velocity.

Black Holes in an Effective Field Theory Extension of General Relativity.

Effective field theory methods suggest that some rather general extensions of general relativity include, or are mimicked by, certain higher-order curvature corrections, with coupling constants expected to be small but otherwise arbitrary. Thus, the tantalizing prospect to test the fundamental nature of gravity with gravitational-wave observations, in a systematic way, emerges naturally. Here, we build black hole solutions in such a framework and study their main properties. Once rotation is included, we find the first purely gravitational example of geometries without Z_{2} symmetry. Despite the higher-order operators of the theory, we show that linearized fluctuations of such geometries obey second-order differential equations. We find nonzero tidal Love numbers. We study and compute the quasinormal modes of such geometries. These results are of interest to gravitational-wave science but also potentially relevant for electromagnetic observations of the galactic center or x-ray binaries.