• Journal of Ocean Engineering and Technology
• /
• v.35 no.1
• /
• pp.13-23
• /
• 2021

Since the introduction of the mandatory energy efficiency design index (EEDI), several studies have been conducted on the maneuverability of waves owing to the decrease in engine power. However, most studies have used the mean wave force during a single cycle to evaluate maneuverability and investigated the turning performance. In this study, we calculated the external force in accordance with the angle of incidence of the wave width and wavelengths encountered by KVLCC2 (KRISO very large crude-oil carrier) operating at low speeds in regular waves using computational fluid dynamics (CFD). We compare the model test results with those published in other papers. Based on the external force calculated using CFD, an external force that varies according to the phase of the wave that meets the hull was derived, and based on the derived external force and MMG control simulation, a maneuvering simulation model was constructed. Using this method, a weather vaning simulation was performed in regular waves to evaluate the course-keeping ability of KVLCC2 in waves. The results confirmed that there was a difference in the operating trajectory according to the wavelength and phase of the waves encountered.

• International Journal of Contents
• /
• v.17 no.2
• /
• pp.1-8
• /
• 2021

Online streaming wars are intensifying. Netflix is known as the market leader in the streaming business. However, since 2019, Netflix has been losing subscribers in the United States and is at a turning point where it needs to reassess its current position in the market. While Netflix is losing dominance, rivals Amazon Prime and Hulu continue to gain market shares. Studies from Deloitte and PricewaterhouseCoopers indicated a new shift in the streaming landscape caused by the abundance of streaming options and rising subscription costs. Recent surveys showed that consumers are excited about new streaming services, such as Disney +. Nearly two-thirds of consumers intend to terminate or downgrade one or more of their current subscriptions to make room for a new service. Moreover, it seems that consumers want ad-supported options. In Deloitte's latest Digital Media Trends survey, 65% responded that they would watch ads to eliminate or reduce subscription costs. Seventy percent of Hulu's subscribers choose its lower-priced ad-supported plan. NBC recently launched its own streaming service, Peacock, with a free ad-supported option. This opposes Netflix's brand identity of "no ads" and premium differentiation. With increasing pressure from competition and the growing risk of subscriber loss, Netflix needs to diversify its price plans. The company could try implementing the lower-priced mobile-only plan they are currently testing or plan to test in other regions. Netflix should also consider features or benefits for loyal subscribers to maintain a stronger consumer base.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.843-855
• /
• 2020

X-plane submarines show better maneuverability as they have much longer span of control plane than that of cross plane submarines. In this study, captive model tests were conducted to evaluate the maneuverability of an X-plane submarine using Computational Fluid Dynamics (CFD) and a mathematical maneuvering model. For CFD analysis, SNUFOAM, CFD software specialized in naval hydrodynamics based on the open-source toolkit, OpenFOAM, was applied. A generic submarine Joubert BB2 was selected as a test model, which was modified by Maritime Research Institute Netherlands (MARIN). Captive model tests including propeller open water, resistance, self-propulsion, static drift, horizontal planar motion mechanism and vertical planar motion mechanism tests were carried out to obtain maneuvering coefficients of the submarine. Maneuvering simulations for turning circle tests were performed using the maneuvering coefficients obtained from the captive model tests. The simulated trajectory showed good agreement with that of free running model tests. From the results, it was proved that CFD simulations can be applicable to obtain reliable maneuvering coefficients for X-plane submarines.

• Journal of Surface Science and Engineering
• /
• v.55 no.5
• /
• pp.284-291
• /
• 2022

Herein, we studied ultrathin Cu-layer-based transparent heaters embedded between a ZnO underlayer and an Al₂O₃ overlayer. The anti-reflecting functions for the ZnO and Al₂O₃ layers by independently varying the layer thicknesses, with the Cu layer thickness fixed at 8.5 nm. The smallest visible light transmittance of 11.1% was achieved when the overlayer and underlayer thicknesses were 90 and 30 nm, respectively. We conducted electrically driven Joule heating test for the Cu layers having thicknesses of 8.5 nm (R_s: 14.7 Ohm/sq.) and 19 nm (R_s: 3.4 Ohm/sq.). External voltages were increased with an interval of 2 V until irreversible failures occurred at temperatures of ~390 ℃ and 550 ℃, respectively. At each voltage increase before heater failures, the heater exhibited superior thermal response with the heater temperatures reaching over 90% of the final temperatures. The heaters also showed excellent reproducibility when turning on and off the heater repeatedly.

• International Journal of Computer Science & Network Security
• /
• v.22 no.12
• /
• pp.217-228
• /
• 2022

The study aimed to build an electronic strategy in innovative learning situations for the role of education in combating intellectual currents. A total of 525 Saudi university faculty members and general education teachers were surveyed using two electronic questionnaires. Arithmetic averages and standard deviations, One-way ANOVA, Scheffé's test, Pearson's correlation coefficient, and Cronbach's alpha stability coefficient were used as statistical methods. The study statistically identifies the differences between the study sample at the level of significance (0.05). and the design of a digital application for individual learning to combat deviant intellectual currents to activate them in light of Saudi Vision 2030 by combining the theoretical academic material and turning it into a learning e-game called (crosswords). The game is equipped with hyper media that supports education with entertainment to direct ideas towards the promotion of identity, the development of values towards moderation and the consolidation of intellectual security. Additionally, the learning e-game represents awareness messages in three short films to activate the role of curricula and intellectual awareness centers to apply realistically, innovatively, and effectively.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.17 no.5
• /
• pp.257-263
• /
• 2022

Active stabilizers use signals such as steering angle, yaw rate, and lateral acceleration to vary the roll stiffness of the front and rear suspension depending on the vehicle's driving conditions, and are attracting attention as RSC (Roll Stability Control) system that suppresses roll when turning and improves ride comfort when going straight. Various studies have been conducted in relation to active stabilizer bars and RSC systems. However, accurate modeling of passive stabilizer model and active stabilizer model and vehicle dynamics analysis result verification are insufficient, and performance result analysis related to vehicle roll angle estimation and electric motor control is insufficient. Therefore, in this study, an accurate vehicle dynamics model was constructed by measuring the passive/active stabilizer bar model and component parameters. Based on this, the analysis result with high reliability was derived by comparing the roll angle estimation algorithm based on the lateral acceleration and suspension of the vehicle with the actual vehicle driving test result. In addition, it was intended to accurately analyze the motor torque characteristics and roll reduction effects of the electric motor-driven RSC system.

• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.67.2-67.2
• /
• 2020

Not only the magnitude of the mirror surface error, the pattern matters as it produces certain aberrations. In particular, the surface error of the freeform mirrors, which are optimized to eliminate specific aberrations, might show much higher sensitivity in optical performance. Therefore, we analyze the mirror surface error with Zernike polynomials with the goal of generating a realistic error surface. We investigate the surface error of the freeform mirror fabricated by diamond turning machine to analyze the realistic tendency of the error. The surface error with 0.22 ㎛ root-mean-square value is fitted to the Zernike terms using the incremental fitting method, which increases the number of the fitting coefficients through steps. Furthermore, optical performance via surface error pattern based on Zernike terms is studied to see the influences of each term. With this study, realistic error surface generation may allow higher accuracy not only for the feasibility test but also for all tests and predictions using optical simulations.

• Journal of Ocean Engineering and Technology
• /
• v.37 no.5
• /
• pp.198-204
• /
• 2023

In response to the complexity and time demands of conventional methods for estimating the hydrodynamic coefficients, this study aims to revolutionize ship maneuvering analysis by utilizing automatic identification system (AIS) data and the Support Vector Regression (SVR) algorithm. The AIS data were collected and processed to remove outliers and impute missing values. The rate of turn (ROT), speed over ground (SOG), course over ground (COG) and heading (HDG) in AIS data were used to calculate the rudder angle and ship velocity components, which were then used as training data for a regression model. The accuracy and efficiency of the algorithm were validated by comparing SVR-based estimated hydrodynamic coefficients and the original hydrodynamic coefficients of the Mariner class vessel. The validated SVR algorithm was then applied to estimate the hydrodynamic coefficients for real ships using AIS data. The turning circle test wassimulated from calculated hydrodynamic coefficients and compared with the AIS data. The research results demonstrate the effectiveness of the SVR model in accurately estimating the hydrodynamic coefficients from the AIS data. In conclusion, this study proposes the viability of employing SVR model and AIS data for accurately estimating the hydrodynamic coefficients. It offers a practical approach to ship maneuvering prediction and control in the maritime industry.

• Journal of Ocean Engineering and Technology
• /
• v.38 no.1
• /
• pp.10-17
• /
• 2024

This study assessed the potential for crabbing motion in waterjet ships by exclusively employing stern thrusters. The theoretical considerations were validated through practical sea trials on the naval vessel PKG (Patrol Killer Guided missile) equipped with three stern thrusters. The control forces were calculated using the force equilibrium equation. The results showed that the hull exhibited rotations and lateral movements under wind influence. The port tail exhibited a leftward turning tendency due to the wind. This phenomenon arises from the dominance of the rotational force generated by the stern thruster over the lateral force exerted by the hull, making it challenging to maintain force equilibrium. In the sea trial, the hull rotated by 10° and moved 10.8 m laterally, with a longitudinal movement of 0.26 m. Remarkably, the lateral movement surpassed the longitudinal displacement, indicating the success of the trial. The substantial lateral travel distance provided tangible evidence that the crabbing motion of the ship is achievable using only stern thrusters. This study contributes valuable insights into enhancing the maneuverability of waterjet ships, offering practical applications for naval operations and maritime activities.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.1
• /
• pp.91-96
• /
• 2010

The hydraulic hose can be divided with the low pressure, the medium pressure, and the high pressure hose according to the applied pressure. The power steering system in a passenger car can be divided with the high pressure and the low pressure hose. This study deals with the life prediction for high pressure hose to be given impulse pressure which was generated in turning the car. To adjust with external and internal condition, impulse pressure and oil temperature need to be controlled with impulse test system. The result, which is only controlled with the pressure and oil temperature, adapted Calibrated Accelerated Life Test(CALT) method to predict the life of the high pressure hose and analyzed the swagging part by finite element method during the impulse test.