| 44171. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Numerical Friction Lines for CFD Based Form Factor Determination Method
- 2019
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Ingår i: 8th International Conference on Computational Methods in Marine Engineering, MARINE 2019. - : International Center for Numerical Methods in Engineering. - 9788494919435 ; , s. 694-705
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Konferensbidrag (refereegranskat)abstract
- In this study, frictional resistance coefficients of an infinitely thin 2D plate have been computed at 14 Reynolds numbers (between log(10)(Rn) = 6.25 to 9.5) in sets of five geometrically similar structured grids in order to perform reliable grid dependence studies. Additional grid dependency studies have been performed by using 5 sets of grids which have the same number of cells in all directions but varying first cell sizes normal to the flat plate at log(10)(Rn) = 6.25. Average y(+) values for each grid set for the finest grid varies between 0.0075 and 0.5 (from set 1 to 5 respectively) while none of the simulations exceeded average y+ value of 1. All simulations were performed with the direct application of the no-slip condition at walls. Therefore, no wall functions were used. Two turbulence models have been used for the investigations: k - omega SST and EASM. Extensive grid dependence studies have been performed with two different CFD codes SHIPFLOW and FINE (TM)/MARINE, using the same grids. Special attention was paid to the transition from laminar to turbulent flow at the lowest Reynolds number since laminar part can cover a significant part of the plate. At log(10)(Rn) = 6.25 for both CFD codes, laminar flow and transition to turbulent flow was distinctive even though no transition models were applied. Significant dependency on y+ has been observed with FINE (TM)/MARINE on friction resistance coefficient. On the other hand, SHIPFLOW exhibited less sensitivity to the first cell size variation, hence, revealed smaller numerical uncertainties in general. To ensure a numerical uncertainty of frictional resistance component below 1%, average y(+) < 0.016 have been used for generating the data points of friction line with SHIPFLOW for each turbulence model. Data points of 14 Reynolds number have been transformed into numerical friction lines by applying curve fits. Obtained friction lines are compared with ITTC57 line, Schoenherr, Hughes, Toki, Katsui, Grigson lines and two numerical friction lines.
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| 44172. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Scaling of wetted-transom resistance for improved full-scale ship performance predictions
- 2022
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 266
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Tidskriftsartikel (refereegranskat)abstract
- Determining a ship's propulsive power is a critical stage in the design phase in which the evaluation of the stern plays a crucial role. Different flow regimes can be observed depending on the position and shape of the transom. This paper investigates the wetted-transom flow characteristics and their implications on the 1978 ITTC Performance Prediction Method. In the case of flow separation, such as the wetted-transom flow, the current ITTC-78 procedure does not provide an alternative method. Therefore, two alternative methods were proposed based on the investigations of CFD computations on seven hull forms. The firstly proposed method is a combined EFD&CFD method called the two form factor method. It requires CFD computations in model and full-scale, and it can handle any case of flow separation, including the wetted-transom flow. The second proposed method is an empirical correction formula for the hulls with a wetted-transom flow. Finally, the full-scale speed-power relations between the speed trials and the full-scale predictions from the two alternative methods and the standard ITTC-78 method were presented. It is observed that the two suggested methods considerably improve the correlation between the predictions and the speed trials.
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| 44173. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Verification and Validation of CFD Based Form Factors as a Combined CFD/EFD Method
- 2021
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 9:1, s. 1-30
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Tidskriftsartikel (refereegranskat)abstract
- Predicting the propulsive power of ships with high accuracy still remains a challenge. Well established practices in the 1978 ITTC Power Prediction method have been questioned such as the form factor approach and its determination method. This paper investigates the possibility to improve the power predictions by the introduction of a combined CFD/EFD Method where the experimental determination of form factor is replaced by double body RANS computations. Following the Quality Assurance Procedure proposed by ITTC, a best practice guideline has been derived for the CFD based form factor determination method by applying systematic variations to the CFD set-ups. Following the verification and validation of the CFD based form factor method in model scale, the full scale speed-power-rpm relations between large number of speed trials and full scale predictions using the CFD based form factors in combination with ITTC-57 line and numerical friction lines are investigated. It is observed that the usage of CFD based form factors improves the predictions in general and no deterioration is noted within the limits of this study. Therefore, the combination of EFD and CFD is expected to provide immediate improvements to the 1978 ITTC Performance Prediction Method.
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| 44174. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Virtual captive tests as a new tool for early maneuvering performance assessment
- 2018
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Ingår i: SNAME Maritime Convention, SMC 2018.
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Konferensbidrag (refereegranskat)abstract
- Maneuverability is an important aspect of ship performance, and often evaluated in late stages of ship design process. In order to include maneuvering assessment in the early design stage, virtual captive test (VCT) method have been developed as a new tool for early maneuvering performance assessment. In this study, a destroyer hull form with complex appendages and a MR tanker have been analyzed with VCT. Hydrodynamic coefficients were compared to the captive model tests for both hulls and maneuvering simulations of the destroyer hull form is presented in comparison to model tests.
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| 44175. |
- Korkusuz, Duygu, et al.
(författare)
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Process Capability Analysis for Non-normal Distribution with Lower Specification Limit
- 2011
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Ingår i: IEEE International Conference on Industrial Engineering and Engineering Management. - 2157-3611 .- 2157-362X. - 9781457707391 ; , s. 1466-1470
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Konferensbidrag (refereegranskat)abstract
- Process capability analysis is an important element of any quality improvement initiative. However, estimating process capability is often problematic when it comes to non-normal distributions since the conventional methods sometimes give misleading results. In this paper, a new method for estimating process capability of non-normal distribution with only lower specification limit is proposed. The proposed method only considers the left tail of thedistribution rather than taking all of the data points. Forestimating the process capability, it employs least squarestechnique and normal approximation to the selectedobservations from the left tail. Here, the proposed method is only tested on lognormal distribution. Simulations and real-world data analysis are used for verification and validation purpose, respectively. An easy and practical guideline is also developed.
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| 44176. |
- Korneliusson, Marie, 1993, et al.
(författare)
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Generative Modelling of Semantic Segmentation Data in the Fashion Domain
- 2019
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Ingår i: 2019 IEEE/CVF International Conference on Computer Vision Workshop (ICCVW). ; , s. 3169-3172
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Konferensbidrag (refereegranskat)abstract
- In this work, we propose a method to generatively model the joint distribution of images and corresponding semantic segmentation masks using generative adversarial networks. We extend the Style-GAN architecture by iteratively growing the network during training, to add new output channels that model the semantic segmentation masks. We train the proposed method on a large dataset of fashion images and our experimental evaluation shows that the model produces samples that are coherent and plausible with semantic segmentation masks that closely match the semantics in the image.
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| 44177. |
- Korner, Anna, et al.
(författare)
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Influence of Different Polymer Types on the Overall Release Mechanism in Hydrophilic Matrix Tablets
- 2009
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Ingår i: Molecules. - : MDPI AG. - 1420-3049. ; 14:8, s. 2699-2716
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Tidskriftsartikel (refereegranskat)abstract
- The effect of three different types of polymer chain structures on the polymer release from hydrophilic matrix tablets was investigated by comparing a synthetic semi-crystalline linear polymer (PEO), a branched amorphous polysaccharide (dextran) and an amorphous substituted cellulose derivative (HPMC). The polymer release rates for tablets containing mixtures of high and low molecular weight grades in different ratios were determined by using a modified USP II method and a SEC-RI chromatography system. The results showed that independent of polymer type: (i) plots of the release versus time had similar shapes, (ii) the release of long and short polymer chains was equal and no fractionation occurred during the release and (iii) the release rate could be related to the average intrinsic viscosity of the polymer mixtures. This confirms the hypothesis that the release rate can be related to a constant viscosity on the surface of the hydrophilic matrix tablet and that it is valid for all the investigated polymers.
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| 44178. |
- Kornev, V. K., et al.
(författare)
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Dynamics of underdamped Josephson junctions with non-sinusoidal current-phase relation
- 2006
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 435:1-2, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- Results on analytical and computational investigations of high-frequency dynamics of Josephson junctions, characterized by non-zero capacitance and the second harmonic in the current-phase relation are presented. These attributes each have influence on the behaviour of integer Shapiro steps and lead to the formation of non-integer Shapiro steps. Analytic theory of the integer and non-integer Shapiro steps has been developed for the so-called high-frequency limit. The analytical and numerical results are compared with experimental data for hybrid heterostructures YBCO/Au/Nb. Detector response for the case of high fluctuation level has been considered as well.
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| 44179. |
- Korniyenko, Yevgeniy, 1989, et al.
(författare)
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Nonlinear response of a ballistic graphene transistor with an ac-driven gate: High harmonic generation and terahertz detection
- 2016
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 94:12
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Tidskriftsartikel (refereegranskat)abstract
- We present results for time-dependent electron transport in a ballistic graphene field-effect transistor with an ac-driven gate. Nonlinear response to the ac drive is derived utilizing Floquet theory for scattering states in combination with Landauer-Buttiker theory for transport. We identify two regimes that can be useful for applications: (i) low and (ii) high doping of graphene under source and drain contacts, relative to the doping level in the graphene channel, which in an experiment can be varied by a back gate. In both regimes, inelastic scattering induced by the ac drive can excite quasibound states in the channel that leads to resonance promotion of higher-order sidebands. Already for weak to intermediate ac drive strength, this leads to a substantial change in the direct current between source and drain. For strong ac drive with frequency Omega, we compute the higher harmonics of frequencies n Omega (n integer) in the source-drain conductance. In regime (ii), we show that particular harmonics (for instance, n = 6) can be selectively enhanced by tuning the doping level in the channel or by tuning the drive strength. We propose that the device operated in the weak-drive regime can be used to detect THz radiation, while in the strong-drive regime, it can be used as a frequency multiplier.
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| 44180. |
- Korniyenko, Yevgeniy, 1989
(författare)
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Quantum theory of time-dependent transport in graphene
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-quality ballistic electronic devices made from graphene are becoming an experimental reality. Carbon-based electronics is heralded if not to succeed or surpass then to complement the existing semiconducting technology. This thesis investigates graphene-based devices from a theoretical point of view with the focus on high-frequency applications, where the material is expected to have a large impact. We develop a quantum-mechanical description of time-dependent transport in mesoscopic graphene samples based on a scattering matrix approach similar to Landauer-Büttiker treatment of non-relativistic charge carriers. We investigate scattering processes involved in transport through a GFET and identify resonant mechanisms that lead to enhancement of the source-drain current under an oscillating gate signal. We propose a tunable selective frequency multiplication scheme and a radiation detector with operation relying on such mechanisms. The performance of the proposed devices is investigated in terms of their shot noise and Fano factor, which we show to be suppressed due to Klein tunnelling even for strong driving of the system. Finally, we apply the formalism to a quantum pump based on an asymmetric potential profile with respect to the gate electrode doping and compute the current through it, revealing that the temperature and the back gate bias can be used to switch the direction of the current.
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