Statistics for Spatial Data.

Numerous of maintenance policies were developed due to the change in the manufacturing environment and the growing of technologies in the past few decades. Due to fluctuation (oscillation, instability) phenomena of the manufacturing industry, it is difficult to identify an optimal maintenance policy that actually suit for a manufacturing system. Thus, a lot of efforts have been done in order to assist manufacturing industry in finding an optimal maintenance policy. This paper attempts to review past and current research on optimal maintenance policy selection issues associated with methods used as well as the applications. Published literatures were systematically classified based on certainty theory in operation management classification model in term of certainty, uncertainty, and risk. Furthermore, a sub family had been classified based on the approaches used in determining the optimal maintenance policy. The possible gap occurred between academic research and industrial application in maintenance policy optimization is also discussed in detail, and several possible ideas are put forward to reduce the gap. More importantly, the paper is intended to provide a different view on classifying these models and give useful references for personnel working in industrial as well as researchers.

Maintenance policy optimization—literature review and directions

The flow characteristics over a NACA4412 airfoil are studied in a low turbulence wind tunnel with moving ground simulation at a Reynolds number of 3.0 x 105 by varying the angle of attack from 0 to 10 deg and ground clearance of the trailing edge from 5% of chord to 100%. The pressure distribution on the airfoil surface was obtained, velocity survey over the surface was performed, wake region was explored, and lift and drag forces were measured. To ensure that the flow is 2-D, particle image velocimetry measurements were performed. A strong suction effect on the lower surface at an angle of attack of 0 deg at the smallest ground clearance caused laminar separation well ahead of the trailing edge. Interestingly, for this airfoil, a loss of upper surface suction was recorded as the airfoil approached the ground for all angles of attack. For angles up to 4 deg, the lift decreased with reducing ground clearance, whereas for higher angles, it increased due to a higher pressure on the lower surface. The drag was higher close to the ground for all angles investigated mainly due to the modification of the lower surface pressure distribution.

Aerodynamics of a NACA4412 airfoil in ground effect

Nonlinear dynamic response structural optimization using equivalent static loads

Design optimization and analysis of selected thermal devices using self-adaptive Jaya algorithm

The application of the CFD and Kriging method to an optimization of heat sink

A numerical analysis is performed to investigate the aerodynamic characteristics and static height stability of the endplate on aspect-ratio-one wing in ground effect. The investigation is carried out on angles of attack from 0° to 10° and ground clearances at a trailing edge from 5% of chord to 50%. The analysis shows that the ground effect increases the lift by high pressure on the lower surface, reduces the induced drag, increases the suction on the upper surface, and consequently considerably enhances the lift-drag ratio. The endplate, which prevents the high-pressure air escaping from the air cushion and reduces the influence of wing-tip vortex, augments lift and lift-drag ratio further. Interestingly, the drag with the endplate does not increase as much as the lift does when the airfoil is brought close to the ground. From the analysis and visualization of computation results with the endplate, it is found that two wing-tip vortices are generated from each wing surface, their strengths are stronger, diminished rapidly and the influence of the wing-tip vortices are decreased. The outward drift of wing-tip vortex, which is generated from the lower wing surface, is observed. Irodov’s criteria are also numerically evaluated to investigate the static height stability of wings with and without the endplate. The comparison of Irodov’s criteria shows that the endplate is not favorable for static height stability but reduces the deviation of the static height stability with respect to pitch angles and heights.

http://www.j-mst.org/On_line/admin/files/30-04178_2578-2589_.pdf

Influence of endplate on aerodynamic characteristics of low-aspect-ratio wing in ground effect †

Optimal design of heat exchangers using the progressive quadratic response surface model

Optimal design of two-dimensional wings in ground effect using multi-objective genetic algorithm

During the fast-filling of a high-pressure hydrogen tank, the temperature of hydrogen would rise significantly and may lead to failure of the tank. In addition, the temperature rise also reduces hydrogen density in the tank, which causes mass decrement into the tank. Therefore, it is of practical significance to study the temperature rise and the amount of charging of hydrogen for hydrogen safety. In this paper, the change of hydrogen temperature in the tank according to the pressure rise during the process of charging the high-pressure tank in the process of a 82-MPa hydrogen filling system, the final temperature, the amount of filling of hydrogen gas, and the change of pressure of hydrogen through the pressure reducing valve, and the performance of heat exchanger for cooling high-temperature hydrogen were analyzed by theoretical and numerical methods. When high-pressure filling began in the initial vacuum state, the condition was called the “First cycle”. When the high-pressure charging process began in the remaining condition, the process was called the “Second cycle”. As a result of the theoretical analysis, the final temperatures of hydrogen gas were calculated to be 436.09 K for the first cycle of the high-pressure tank, and 403.55 for the second cycle analysis. The internal temperature of the buffer tank increased by 345.69 K and 32.54 K in the first cycle and second cycles after high-pressure filling. In addition, the final masses were calculated to be 11.58 kg and 12.26 kg for the first cycle and second cycle of the high-pressure tank, respectively. The works of the paper can provide suggestions for the temperature rise of 82 MPa compressed hydrogen storage system and offer necessary theory and numerical methods for guiding safe operation and construction of a hydrogen filling system.

Kyoungwoo Park

Papers

The application of the CFD and Kriging method to an optimization of heat sink

Influence of endplate on aerodynamic characteristics of low-aspect-ratio wing in ground effect †

Optimal design of heat exchangers using the progressive quadratic response surface model

Optimal design of two-dimensional wings in ground effect using multi-objective genetic algorithm

An Analysis on the Compressed Hydrogen Storage System for the Fast-Filling Process of Hydrogen Gas at the Pressure of 82 MPa