WAVE FIELD GENERATED BY FINITE-SPAN HYDROFOILS OPERATING BENEATH A FREE SURFACE

The present paper focuses on the numerical investigation of the flow around the fully submerged 2D and 3D hydrofoils operating close to a free surface. Iterative boundary element method is implemented to predict the flow field. This study aims to investigate the aspect ratio effect on the free surface interactions and hydrodynamic performance of the hydrofoils under a free surface by using potential flow theory. Three different submergence depths and aspect ratios are studied in the wide range of Froude Numbers. In 3D cases, spanwise width of the numerical wave tank model is selected both equal and wider to the foil span, to observe the sidewall effects. Wave field seems to be two dimensional at low Froude numbers. On the other hand, signs of three dimensionalities are observed on the free surface structure for higher Fn, even the predicted wave elevations are very close to 2D calculations in the midsection. Increment in the Fn give a rise to the amplitude of the generated waves first, however a further increase in Fn has a lowering effect with the beginning of waves spill in the spanwise direction in the form of Kelvin waves. Free surface proximity and resultant wave field are also seeming to be linked with the lift force on the hydrofoil. As aspect ratio of the foil increase, 3D lift values are getting closer to those of 2D calculations. However, it is seen that, 3D BEM predictions of a hydrofoil under free surface effect cannot be considered two-dimensional even the aspect ratio is equal to 8

Numerical investigation of marine propeller underwater radiated noise using acoustic analogy part 2 : the influence of eddy viscosity turbulence models

The present study focuses on the impact of eddy viscosity turbulence models on the benchmark INSEAN E779A marine propeller hydroacoustic performance under non-cavitating and open water conditions. In the numerical calculations, Realisable k-epsilon (k-ε), k-ω Shear Stress Transport (k-ω SST) and Spalart-Allmaras turbulence models, which are widely used in hydrodynamic fields, are selected. Hydroacoustic performance of the model propeller is predicted with the porous FW-H formulation coupled with Reynolds-averaged Navier Stokes (RANS) solver. This study aims to show the effects of different turbulence models on marine propeller hydroacoustic performance at high and low blade loading conditions both in the near and far-fields. The numerical results show that the underwater radiated noise (URN) levels, which are predicted by using different eddy viscosity turbulence models together with the porous FW-H formulation, are found to be similar at low blade loading conditions. The reason behind this similarity is due to the analogous wake structure and hydrodynamic field. However, when the propeller loading is high, the propeller's wake loses its stability; hence, the coherent vortex structures break-up and evolve into the far-field of the propeller's slipstream. The instability process of the propeller's wake is predicted in a different manner by eddy viscosity turbulence models, and these differences cause dissimilar prediction of the URN in the far-field. Consequently, the underwater pressure field is considerably affected by the instability of the vortex structures (as a non-linear noise source) for far-field noise estimations. As a result, vortex instability in the propeller's slipstream might be the main noise source of the URN for far-field noise estimations under non-cavitating and high blade loading conditions

Numerical investigation of marine propeller underwater radiated noise using acoustic analogy part 1 : the influence of grid resolution

This study investigates the effects of grid resolution on hydroacoustic performance of the benchmark INSEAN E779A propeller operated in uniform flow, open water and non-cavitating conditions. In the numerical calculations, an incompressible hydrodynamic solver together with the porous FW-H (Ffowcs-Williams Hawkings) equation is used to predict the propeller URN (Underwater Radiated Noise). The first aim within this study is to explore the sensitivity of the grid resolution on the prediction of propeller hydroacoustic performance. Furthermore, amongst the contribution of nonlinear noise sources on overall acoustic pressure, the role of the tip vortex is believed to be dominant under non-cavitating conditions. The inadequate extension of the tip vortex is one of the drawbacks in the RANS (Reynolds-averaged Navier-Stokes) solver for accurate prediction of propeller URN, especially at the receivers located in the propeller's slipstream. Thus, the second aim within this study is to examine the contribution of tip vortex on overall acoustic pressure. In order to visualise the numerical noise and determine the realistic extension of the vortex distributions in the propeller's slipstream, the time derivative of the pressure technique is proposed in this study. The results indicate that insufficient grid resolution in the numerical simulations causes unphysical numerical noise which is attributed to the sliding interfaces, and it leads to contamination of the overall acoustic pressures. Moreover, an increase in grid resolution reduces numerical diffusion in the RANS solver, allowing for an extended tip vortex distribution. However, an increase in tip vortex extension and intensity alongside the downstream of the propeller is not adequate itself to make a reliable prediction of propeller URN by using RANS. Consequently, a more realistic prediction of propeller URN requires the use of advanced models (i.e. LES (Large Eddy Simulation) and DES (Detached Eddy Simulation)) together with the porous FW-H equation, particularly if the receivers located in the downstream are of great interest

A NUMERICAL APPLICATION TO PREDICT THE RESISTANCE AND WAVE PATTERN OF KRISO CONTAINER SHIP

In this study, the computational results for KRISO Container Ship (KCS) are presented. CFD analyses are performed to simulate free surface flow around KCS by using RANS approach with success. Also the complicated turbulent flow zone behind the ship is well simulated. The RANS equations and the non-linear free surface boundary conditions are discretized by means of a finite volume scheme. The numerical methodology is found to be appropriate for simulating the turbulent flow around a ship in order to estimate ship total resistance and free surface. By the numerical results, total resistance is calculated for the ship model and the result is satisfactory with regard to the experimental one. As a result of well captured free surface, the wave elevation on/around the hull is compared with the experimental results

Deciding Heavy Metal Levels in Soil Based on Various Ecological Information through Artificial Intelligence Modeling

The aim of this paper is to decide on heavy metal levels based on ecological parameters by effectively eliminating common disadvantages such as high cost and serious time-consuming laboratory procedures via an effective artificial intelligence approach. Therefore, this study is hinged on an artificial intelligence technique, ANN, because of its low cost and high accuracy in overcoming the mentioned limitations and obstacles in the determination process of the amounts of elements. The ANNs have thus been employed to determine essential heavy metals, such as Fe, Mn, and Zn depending on Ca, K, and Mg concentrations of soil samples obtained from different altitudes in Mount Ida. To the best knowledge of the authors, this is the first study in the literature in which altitude was considered as a parameter in the prediction of nutrient heavy metals. The computed relative errors are significantly low for each of the considered elements (Fe, Mn, and Zn); and are found to be between 1.0–4.1%, 1.0–4.2%, 1.5–7.1%, respectively, for the training, testing, and holdout data. The findings indicate that the relative errors could still be decreased further by assuming the altitude as a factor variable

Treatment delays and in-hospital outcomes in acute myocardial infarction during the COVID-19 pandemic: A nationwide study

© 2020 by Turkish Society of Cardiology.Objective: Delayed admission of myocardial infarction (MI) patients is an important prognostic factor. In the present nationwide registry (TURKMI-2), we evaluated the treatment delays and outcomes of patients with acute MI during the Covid-19 pandemic and compaired with a recent pre-pandemic registry (TURKMI-1). Methods: The pandemic and pre-pandemic studies were conducted prospectively as 15-day snapshot registries in the same 48 centers. The inclusion criteria for both registries were aged ≥18 years and a final diagnosis of acute MI (AMI) with positive troponin levels. The only difference between the 2 registries was that the pre-pandemic (TURKMI-1) registry (n=1872) included only patients presenting within the first 48 hours after symptom-onset. TURKMI-2 enrolled all consecutive patients (n=1113) presenting with AMI during the pandemic period. Results: A comparison of the patients with acute MI presenting within the 48-hour of symptom-onset in the pre-pandemic and pandemic registries revealed an overall 47.1% decrease in acute MI admissions during the pandemic. Median time from symptom-onset to hospital-arrival increased from 150 min to 185 min in patients with ST elevation MI (STEMI) and 295 min to 419 min in patients presenting with non-STEMI (NSTEMI) (p-values <0.001). Door-to-balloon time was similar in the two periods (37 vs. 40 min, p=0.448). In the pandemic period, percutaneous coronary intervention (PCI) decreased, especially in the NSTEMI group (60.3% vs. 47.4% in NSTEMI, p<0.001; 94.8% vs. 91.1% in STEMI, p=0.013) but the decrease was not significant in STEMI patients admitted within 12 hours of symptom-onset (94.9% vs. 92.1%; p=0.075). In-hospital major adverse cardiac events (MACE) were significantly increased during the pandemic period [4.8% vs. 8.9%; p<0.001; age- and sex-adjusted Odds ratio (95% CI) 1.96 (1.20-3.22) for NSTEMI, p=0.007; and 2.08 (1.38-3.13) for STEMI, p<0.001]. Conclusion: The present comparison of 2 nationwide registries showed a significant delay in treatment of patients presenting with acute MI during the COVID-19 pandemic. Although PCI was performed in a timely fashion, an increase in treatment delay might be responsible for the increased risk of MACE. Public education and establishing COVID-free hospitals are necessary to overcome patients' fear of using healthcare services and mitigate the potential complications of AMI during the pandemic