• Journal of the Society of Naval Architects of Korea
• /
• v.29 no.2
• /
• pp.115-122
• /
• 1992

A sandwich element is a special Hybrid structural form of the composite construction, which is consisted of three main parts : thin, stiff and relatively high density faces separated by a thick, light, and weaker core material. In a sandwich construction, the shear deformation of the faces. Therefore, in the calculation of the bending stiffness, the shear effect should be included. In this paper, the minimum weight is selected as an object function, as the weight critical structures are usually composed of these kind of construction. To obtain the minimum weight of sandwich panel, the principle of minimum potential energy is used and as for the design constraints, the allowable bending stress of face material, the allowable shear stress of core material, the allowable value of panel deflection and the wrinkling stress of faces are adopted, as well as the different boundary conditions. For the engineering purpose of sandwich panel design, the results are tabulated, which are calculated by using the nonlinear optimization technique SUMT.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.23 no.4
• /
• pp.1-9
• /
• 2019

Recently, in the space market, there has been a rapid reduction of the launch price. The major reason is that a few commercial companies, especially SpaceX, began to enter into the space market about ten years ago, which has changed the space market from monopolization to competition, and accelerated the adoption of commercial efficiency in the technology and management. Also, the successful landing and recovery of a first stage in 2016 by SpaceX proved to be a prelude to opening a new era of reusable launch vehicles, and SpaceX declared the groundbreaking launch price through using the reusable launch vehicle. This study calculates the total launch cost required to put a certain satellite into the LEO, compares the launch cost in three cases with different payload weights, and reviews the impacts of the payload on the cost effectiveness of a reusable vehicle. The total launch cost is divided into 6 subsections cost, namely development cost, production cost, refurbishment cost, operation cost, fixed-cost of factory and launch site, and insurance cost. The cost estimation relationships used in the calculation are taken from the commonly proven cost models such as TRANSCOST.

• Journal of Aerospace System Engineering
• /
• v.17 no.6
• /
• pp.27-34
• /
• 2023

This paper presents the application of a magnetic gear to the electric propulsion system for an aircraft. Since high torque is required in aircraft electric propulsion systems, combining a speed reducer can amplify the torque. However, mechanical gears have issues, such as friction, vibration, and heat generation, which lead to maintenance challenges. In the case of a direct-drive motor that does not use mechanical gears, the size and weight of the motor increase to achieve high torque. This paper proposes the application of a magnetic gear to solve the maintenance issues of mechanical gears and the weight increase problem of direct-drive motors in aircraft electric propulsion systems. In this paper, a magnetic gear suitable for aircraft electric propulsion systems is designed, and it is compared with a direct-drive motor in terms of performance and the feasibility of applying the magnetic gear is verified.

• Korean Journal of Agricultural Science
• /
• v.20 no.2
• /
• pp.167-180
• /
• 1993

Most of small size diesel engines are widely used with the same size and weight flywheel in the levels of 6.0kW and 7.5kW. This study was conducted to obtain basic data which affect the engine performance of the power tiller. The flywheel weight was considered as a major factor in this research. Basically, fuel consumption ratio, motoring loss, torque, vibration and mechanical efficiency of the engine were measured and analyzed on four levels of flywheel weight, 32.2, 29.4, 26.2 and $24.2kg_f$, respectively. Results were obtained as follows: 1. The weights of flywheel were $23.7kg_f$ from design program of JSME and $24.5kg_f$ from ASME and SAE design criteria. Therefore, the flywheel weight of $32.2kg_f$ might be reduced about $8kg_f$ in 7.5kW engine. 2. The rated outputs of 6.0kW and 7.5kW engine were actually 7.43kW and 7.85kW, respectively. When flywheel weight was reduced from $32.2kg_f$ to $24.2kg_f$, outputs were increased from 7.43kW to 7.70kW in 6.0kW engine and from 7.85kW to 8.25kW in 7.5kW engine. 3. When the flywheel weight was reduced from $32.2kg_f$ to $24.2kg_f$, fuel consumption ratio was decreased from 300.8 to 296.8g/kW-hr in 6.0kW engine and also from 313.6 to 312.8g/kW-hr in 7.5 kW engine, respectively. 4. When the flywheel weight was reduced from $32.2kg_f$ to $24.2kg_f$, mechanical efficiency of engine was increased from 76.1% to 76.8% in 6.0kW engine and also from 76.7% to 77.0% in 7.5kW engine, respectively. 5. When the flywheel weight was reduced from $32.2kg_f$ to $24.2kg_f$, vibration was decreased at X-axis and Z-axis in 6.0kW engine, however, slightly increased at Y-axis in 6.0kW engine and at all axes in 7.5kW engine. 6. When the flywheel weight was reduced from $32.2kg_f$ to $24.4kg_f$ motoring loss was decreased from 2.33kW to 1.75kW in 6.0kW engine and also from 2.46kW to 1.84kW in 7.5kW engine.

• Journal of the Society of Naval Architects of Korea
• /
• v.31 no.4
• /
• pp.109-118
• /
• 1994

In this study, an optimization method to design the hull structure of the surface effect ships with twin hulls is proposed for the purpose of minimization of weight based on the regulations of DnV class, and computer programs following the method are developed. The method uses simple formulas as to bending and buckling strength of beams and plates to design local structures, and considers the effect of interaction between longitudinal girders and transverse web frames by grillage analysis and calculates torsional strength of the cross structure by the simplified method. Global optimization of the midship section is attained by integration of optimized substructures. According to optimized results by applying the method to the designed ship, reduction of 20 percent of hull weight can be shown, and optimum transverse frame space can be obtained.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2004.11a
• /
• pp.317-322
• /
• 2004

In this study the structural design of conveyor frame was carried out for the high efficiency gantry crane which can improve the productivity of the container transportation job by reducing cycle time. When the gantry crane was operated, the conveyor frame was deflected largely by its deadload and the total weight of containers placed on it. Therefore thicknesses of conveyor frame to minimize its deadload were designed by the size optimization using ANSYS program as the bending stress and the deflection of frame due to this simulation satisfied their required values.

• Journal of Navigation and Port Research
• /
• v.28 no.10 s.96
• /
• pp.941-946
• /
• 2004

In this study the structural design of conveyor frame was carried out for the high efficiency gantry crane which can improve the productivity of the container transportation work by reducing cycle time. When the gantry crane was operated, the conveyor frame was deflected largely by its deadload and the total weight of containers placed on it. Therefore thicknesses of conveyor frame to minimize its deadload were designed by the size optimization using ANSYS program as the bending stress and the deflection cf frame due to this simulation satisfied their required values.

• Journal of Aerospace System Engineering
• /
• v.12 no.4
• /
• pp.26-34
• /
• 2018

Structural static test and the performance test were conducted to determine whether the propeller developed for a multi-copter with the take-off weight of 25 kg satisfies the design requirement. The result of the structural test revealed that the propeller had a safety margin of 3 or more as the ultimate load and requirement load did not cause the specimen breakage. In the performance test, the propeller generated the hover thrust and maximum thrust of design requirement, and hover efficiency in the operating thrust range was greater than 0.73. Maximum hover efficiency increased by more than 3% compared to the reference propeller and electric power consumption decreased by more than 4% in the operating range. The propeller was found to be successfully developed based on the satisfaction rate of the structural strength requirement and the performance requirement.

• Korean Journal of Food Science and Technology
• /
• v.16 no.3
• /
• pp.329-335
• /
• 1984

The effect of peeling methods, spherecity and weight of potatoes and carrots on the peeling efficiency were investigated. The changes in the surface texture by peeling were estimated by Rheometer and were related to the changes in the microstructure. The optimum mechanical peeling conditions using abrasion type rotary peeler were 90 sec. at 300 rpm for potatoes, 70 sec. at 300 rpm for sweet potatoes and 60 sec. at 300 rpm for carrots. The peeling loss was influenced by the sphericity and weight of the sample. The optimum conditions for alkali peeling were 90 sec. immersion in boiling 10% NaOH solution for potatoes, 300 sec. in boiling 10% NaOH solution for sweet potatoes and 60 sec. in boiling 6% NaOH solution for carrots. Severe damage of surface structure was noticed by alkali peeling, demonstrated by denaturation of starch granules in the cell. The structural damage observed by microscope was related to the reduction of cutting force after peeling.

• Aerospace Engineering and Technology
• /
• v.7 no.1
• /
• pp.24-29
• /
• 2008

Aircraft fuel efficiency is one of main concerns to aircraft manufacturers and to aviation companies because jet fuel price has tripled in last ten years. One of simple and effective methods to increase fuel efficiency is to reduce aircraft induced drag by using of wingtip devices. Induced drag is closely related to the circulation distribution, which produces strong wingtip vortex behind the tip of a finite wing. Wingtip devices including winglets can be successfully applied to reduce induced drag by wingtip vortex mitigation. Winglet design, however, is very complicated process and has to consider many parameters including installation position, height, taper ratio, sweepback, airfoil, toe-out angle and cant angle of winglets. In current research, different shapes of winglets are compared in the view of vortex mitigation. Appropriately designed winglets are proved to mitigate wingtip vortex and to increase lift to drag ratio. Also, the results show that winglets are more efficient than wingtip extension. That is the reason B-747-400 and B-737-800 chose winglets instead of a span increase to increase payload and range. Drag polar comparison chart is presented to show that minimum drag is increased by viscous drag of winglet, but at high lift, total drag is reduced by induced drag decrease. So, winglets are more efficient for aircraft that cruises at a high lift condition, which generates very strong wingtip vortex.