• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.27 no.1
• /
• pp.13-22
• /
• 2017

Objectives: The objective of this study was to evaluate the exposure levels of door-to-door deliverers to fine particulate matter (PM2.5). Another objective was to confirm the general working patterns of door-to-door deliverers via survey. Methods: In the city of Daegu, ten door-to-door deliverers who wished to join the study were recruited. The general working characteristics of door-to-door deliverers were surveyed using self-reported questionnaires. In the cabin of each car driven by a deliverer, a real-time PM2.5 sampler (Sidepak, Model AM510, TSI Inc., MN, USA) and a GPS device (GPS 741, Ascen, Korea) were installed. Each deliverer was monitored for four days per week so that each day could be monitored at least four times. Results: A total of 40 measurements of PM2.5 concentrations were taken during delivery of parcels. The average exposure levels of door-to-door deliverers to PM2.5 was $44.62{\mu}g/m^3$ ($7-9443{\mu}g/m^3$. Exposure levels to PM2.5 according to the day of the week and coverage areas were not significantly different (p>0.05). Door-to-door deliverers using trucks with older diesel engines manufactured before 2006 had significantly higher exposure levels to PM2.5 than in the case of trucks with diesel engines manufactured after 2006 (p<0.05). Many of the door-to-door deliverers reported the status of having windows open during the delivery task. During delivery services, the working hours spent in residential areas were higher than on roadsides, but exposure levels to PM2.5 in residential areas and on roadsides were $46.17{\mu}g/m^3$ and $49.90{\mu}g/m^3$, respectively. Real-time PM2.5 exposure levels were significantly different between roadways and residential areas (p<0.001). Conclusions: PM2.5 exposure levels of door-to-door deliverers were found to be affected by higher vehicle emissions from the roadsides near their vehicle during deliveries and while driving to other locations compared to by PM2.5 from the diesel engines of their own trucks. Particle concentrations from roadsides and emissions from nearby vehicles through open windows were the main source of PM2.5.

• Wind and Structures
• /
• v.28 no.2
• /
• pp.71-87
• /
• 2019

The yaw and interference effects of blades affect aerodynamic performance of large wind turbine system significantly, thus influencing wind-induced response and stability performance of the tower-blade system. In this study, the 5MW wind turbine which was developed by Nanjing University of Aeronautics and Astronautics (NUAA) was chosen as the research object. Large eddy simulation on flow field and aerodynamics of its wind turbine system with different yaw angles($0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$ and $45^{\circ}$) under the most unfavorable blade position was carried out. Results were compared with codes and measurement results at home and abroad, which verified validity of large eddy simulation. On this basis, effects of yaw angle on average wind pressure, fluctuating wind pressure, lift coefficient, resistance coefficient,streaming and wake characteristics on different interference zone of tower of wind turbine were analyzed. Next, the blade-cabin-tower-foundation integrated coupling model of the large wind turbine was constructed based on finite element method. Dynamic characteristics, wind-induced response and stability performance of the wind turbine structural system under different yaw angle were analyzed systematically. Research results demonstrate that with the increase of yaw angle, the maximum negative pressure and extreme negative pressure of the significant interference zone of the tower present a V-shaped variation trend, whereas the layer resistance coefficient increases gradually. By contrast, the maximum negative pressure, extreme negative pressure and layer resistance coefficient of the non-interference zone remain basically same. Effects of streaming and wake weaken gradually. When the yaw angle increases to $45^{\circ}$, aerodynamic force of the tower is close with that when there's no blade yaw and interference. As the height of significant interference zone increases, layer resistance coefficient decreases firstly and then increases under different yaw angles. Maximum means and mean square error (MSE) of radial displacement under different yaw angles all occur at circumferential $0^{\circ}$ and $180^{\circ}$ of the tower. The maximum bending moment at tower bottom is at circumferential $20^{\circ}$. When the yaw angle is $0^{\circ}$, the maximum downwind displacement responses of different blades are higher than 2.7 m. With the increase of yaw angle, MSEs of radial displacement at tower top, downwind displacement of blades, internal force at blade roots all decrease gradually, while the critical wind speed decreases firstly and then increases and finally decreases. The comprehensive analysis shows that the worst aerodynamic performance and wind-induced response of the wind turbine system are achieved when the yaw angle is $0^{\circ}$, whereas the worst stability performance and ultimate bearing capacity are achieved when the yaw angle is $45^{\circ}$.

• The Korean Journal of Air & Space Law and Policy
• /
• v.34 no.1
• /
• pp.39-77
• /
• 2019

Crew members engaged in international air transportation provide work in many countries due to the nature of their work. According to the Private International Act, the place where the employee habitually carries out his/her work plays an important role in the determination of the governing law of the international labor contract (Article 28, Paragraph 2) and in the decision of international jurisdiction (Article 28, Paragraphs 3 and 4). The concept of the place where the employee habitually carries out his/her work was proposed by the EU to determine international jurisdiction and governing law. In international aviation law, the legislative purpose of the place where the employee habitually carries out his/her work is different from that of home base, which is a concept introduced for fatigue management of the crew in order to secure the aviation safety; thus the place where the employee habitually carries out his/her work and home base are not the same concept. In order to determine the place where the employee habitually carries out his/her work, following matters should be considered comprehensively; (i) where the crew starts and ends work, (ii) where the aircraft the crew is performing work on is primarily parked, (iii) where the crew is informed of the instructions and organizes his/her work activities, (iv) where the crew is obliged to reside according to the labor contract, (v) where there is an office provided by the employer and available to the crew, (vi) where the crew is obliged to be when he/she is ineligible for the work or subject to discipline. However, since all of the above items are the same as the location of the home base, it is reasonable to consider the home base as the most important factor when deciding on the place where the employee habitually carries out his/her work. In contrast, the state where the aircraft is registered (Article 17 of the Chicago Convention), should not be regarded as a place of where the employee habitually carries out his/her work. In this case, CJEU provided the first judging standard for the concept of the place where the employee engaged in international air transportation habitually carries out his/her work. It is the interpretation of the Brussels regulations which became a model -for the Korean Private International Act,- so it would be helpful to understand the concept of the place where the employee habitually carries out his/her work.