• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.1
• /
• pp.168-174
• /
• 2022

In a wave power generation system, the overtopping system is known as an overtopping wave energy converter (OWEC). The performance of an OWEC is affected by wave characteristics such as height and period because its power generation system is sensitive to those characteristics; these, as well as wave direction, depend on the sea. As these characteristics vary, it is hard for the OWEC to produce power in a stable manner. Therefore, it is necessary to find an appropriate shape for an OWEC, according to the characteristics of the sea it is in. This research verified the effect of the design of the OWEC ramp on the hydraulic efficiency using the smoothed particle hydrodynamics (SPH) particle method. A total of 10 models were designed and used in simulations performed by selecting the design parameters of the ramp and changing the attack angle based on those parameters. The hydraulic efficiency was calculated based on the rate of discharged water obtained from the analysis result. The effect of each variable on the overtopping performance according to the shape of the ramp was then confirmed. In this study, we present suggestions for determining the direction for an appropriately shaped OWEC ramp, based on a specific sea area.

• 한국도로학회:학술대회논문집
• /
• 2008.03a
• /
• pp.103-111
• /
• 2008

• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 2001.02a
• /
• pp.103-108
• /
• 2001

• Journal of Institute of Control, Robotics and Systems
• /
• v.16 no.11
• /
• pp.1068-1073
• /
• 2010

When a robot navigates in an outdoor environment, a curb or a sidewalk separated from the road can be used as a robust feature. However, most algorithms could detect the curb only in the straight road, and could not detect highly curved corners, ramps, and so on. This paper proposes an algorithm which enables the robot to detect and follow the curbs in various types of roads. In the proposed method, the robot tilts a laser scanner and computes the error between the predicted and the measured distances to the road in front of the robot. Based on this error, the curbs at corners and curves can be classified. It is also difficult to detect a curb near a ramp because of its low height. In this case, the robot also tilts a laser scanner to detect the curb beyond the ramp. Once the robot classifies the road into the curve, corner, ramp, the robot selects the proper navigation strategies depending on the classified road types and is able to continue to detect and follow the curb. The results of a series of experiments show that the robot can stably detect and follows the curb in curves, corners and ramps as well as the straight road.

• Journal of Korean Society of Transportation
• /
• v.20 no.7
• /
• pp.107-116
• /
• 2002

Crash Cushion is a kind of safety facilities on roadside which acts the role of absorbing impact energy when vehicles are driven out of normal route such as Gore area of freeway off ramp. Criteria for severity index considering accident occurrence possibility are needed to have strong effect on installing the facilities. However, present criteria for establishing crash cushion design do not include such processes. Therefore, the paper presents two kinds of study to develop criteria for severity index. First of all, development of accident forecasting model on freeway off ramp is presented. The module is a relationship between accidents and road environment by negative binomial distribution (NB) which is called to reflect very well quality of accidents at Gore of crash cushion installed freeway Secondly, freeway exiting behavior model is developed because the human factor is the most important one. However, many literatures have shown between road environment and accidents which are more quantitative than human factor. The study supposed advanced process steps on actual freeway and analysed correlation between variables and accidents. The criteria for severity index is presented to determine whether to install or not by benefit cost analysis for each module. The standard for severity index will help to determine whether to install the crash cushion or not and to estimate severity for freeway and off ramp.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.20 no.5
• /
• pp.35-44
• /
• 2021

In recent times, several studies have been conducted focusing on crashes occurring on the main segment of the highway. However, there is a dearth of research dealing with traffic safety relating to other highway facilities, especially ramp areas. According to the Korea Expressway Corporation's Expressway Information Service, 6,717 crashes have occurred on ramps in the five years from 2015~2019, which accounts for about 15% of all highway accidents. In this study, the simple and full safety performance functions (SPFs) were evaluated and explored using different statistical distributions (i.e., Poisson Gamma (PG) and Poisson Inverse Gaussian (PIG)) and techniques (i.e., fixed effects (FE) and random effects (RE)) to provide more accurate crash prediction models for highway ramp sections. Data on the geometric characteristics of traffic and roadways were collected from various systems and with extensive efforts using a street-view application. The results showed that the PIG models present more accurate crash predictions in general. The results also indicated that the RE models performed better than FE models for simple and full SPFs. The findings from this study offer transportation practitioners using the Korea Expressway Corporation's Expressway a dependable reference to enhance and understand traffic safety in ramp areas based on accurate crash prediction models and empirical evidence.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.42 no.3
• /
• pp.409-415
• /
• 2022

The length of the acceleration lane in the area of entrance terminals is calculated based on 13 PS/ton horsepower of a cargo truck in Korea, so it is generally overestimated compared with the capacity of most vehicles traveling on an entrance ramp. Most drivers have, therefore, an indiscreet tendency to enter the main lane in all sections of an acceleration lane, which affects the traffic flow of the main lane. Because of this tendency, measures are required to minimize the impact on traffic flow of the main lane. The operating speed, rate of entrance, and traffic volume for each vehicle were investigated at the entrance terminals of the interchanges (ICs) of Yangji IC, Suseok IC, Yongin IC, and Osan IC, and the level of improvement in traffic flow was analyzed via VISSIM simulation. From the VISSIM simulation analysis, 74.0 % of the total vehicles traveled over the specified speed from the nose point where drivers would be able to recognize the traffic condition of the main carriageway, or the point at which there is a simplification of the curve section. In addition, 88.6 % of the vehicles entered the main carriageway up to 0.8 points compared with the entire length of the acceleration lane. It was subsequently found that an improvement of average speed in the main carriageway and at the entrance ramp can be achieved from 60.1 km/h to 68.5 km/h by intentionally limiting the entrance point onto the main carriageway up to 0.265 points of the entrance ramp.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.04a
• /
• pp.64-69
• /
• 2004

The work presented here deals with controller design using error model constructed with proportional control ramp response. The design aims at the improvement of transient response, steady-state error reduction with stability preservation, generation of the consistent contour error through the proportional gain regulation of a mismatched system. The first step is to generate tracking-error curve with proportional control only and decide the added error signal shape on the error curve. The next is to construct a table for the steady-state loop gain with step input. The table is used for selecting the proportional gain. The effectiveness of the proposed controller is confirmed through the simulation and experiment.

• Journal of Korean Society for Quality Management
• /
• v.27 no.3
• /
• pp.79-93
• /
• 1999

The common accelerated life test(ALT) consists of test methods applying a constant stress, higher than the use condition stress, to items. There we, however, situations for which a progressive stress ALT, in which the stress on a test item is continuously increased with time, Is more convenient to perform testing and simpler in analyzing data than a constant stress ALT. When a product under constant stress s follows a Weibull distribution with parameters $\theta$(5) and $\beta$, maximum likelihood(ML) estimators of parameters involved in the model are obtained and their asymptotic distributions are derived under stress bounded ramp tests in which the stress is increased linearly from use condition stress to the stress upper bound. The optimum test plans are also found which minimize the asymptotic variance of the ML estimator of the log mean life at design constant stress. For selected values of the design parameters, tables useful for finding optimal test plans are given. The effect of the pre-estimates of design parameters is studied.

• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.3
• /
• pp.57-65
• /
• 1997

In this study, a cutting force in the Ball-end milling process is calculated using Z-map. Z-map can describe any type of cutting area resulting from the previous cutting geometry and cutting condition. Cutting edge of a ball-end mill is divided into infinitesimal cutting edge elements and the position of the ele- ment is projected to the cutter plane normal to the Z axis. Also the cutting area in the cutter plane is obtained by using the Z-map. Comparing this projected position with cutting area, it can be determined whether it engages in the cutting. The cutting force can be calculated by numerical integration of cutting force acting on the engaged cutting edge elements. A series of experiments such as contouring and upward/downward ramp cutting was performed to verify the calculated cutting force.