• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.4
• /
• pp.41-47
• /
• 2011

Turbopump, which is a part of 75 ton open cycle liquid rocket engine has a super sonic impulse turbine. This paper investigated the leading edge thickness effect on the turbine performance experimently. Two rotors were tested with the different leading edge thickness. The ratios (rotor thickness to Pitch) are 1.9 and 1.4 times to 30 ton turbine rotor. As a result, a rotor with 1.4 times ratio had a 1.5% higher efficiency gain than a rotor with 1.9 times ratio. The pressure ratio with the maximum efficiency on the same rotational speed was increased to the full expansion ratio of nozzle.

• Journal of the Korean Chemical Society
• /
• v.30 no.1
• /
• pp.105-108
• /
• 1986

Ultrasound(50KHz) accelerated the reduction reaction of aromatic nitro group to aromatic amino group in high yield with mild condition using iron, hydrazine hydrate and activated carbon under room temperature and atmospheric pressure. The activated carbon has been used as a mixing material to highly active metals. However, aromatic nitro group does not reduce at all only with iron-hydrazine witliout adding activated carbon even under ultrasonic irradiation. We also discovered that the conversion yield from nitro group to amino group is directly proportional to the amount of activated carbon.

• Korean Journal of Materials Research
• /
• v.19 no.3
• /
• pp.169-173
• /
• 2009

In chemistry, the study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems. In the area of chemical kinetics, it has been observed that ultrasound can greatly enhance chemical reactivity in a number of systems by as much as a million-fold. Nano-technology is a super microscopic technology in which structures of 100 nanometers or smaller can be investigated. This technology has been used to develop $TiO_2$ materials and $TiO_2$ devices of that size. Thus far, electrochemistry methods and photochemistry methods have generally been used to create $TiO_2$ nano-size particles. However, these methods are complicated and create pollutants as a by-product. In the present study, nano-scale silver particles (5 nm) were prepared in a sonochemistry method. Sonochemistry deals with mechanical energy that is provided by the collapse of cavitation bubbles that form in solutions during exposure to ultrasound. $TiO_2$ powders 25 nm in size doped with Ag were formed using an ultrasonic sound technique. The experimental results showed the high possibility of removing pollution through the action of a photocatalyst. This powder synthesis technique can be considered as an environmentally friendly powder-forming processing owing to its energy saving characteristics.

• Journal of Institute of Control, Robotics and Systems
• /
• v.14 no.3
• /
• pp.242-247
• /
• 2008

As an absolute positioning system, iGS is designed based on ultrasonic signals whose speed can be formulated clearly in terms of time and room temperature, which is utilized for a mobile robot localization. The iGS is composed of an RFID receiver and an ultra-sonic transmitter, where an RFID is designated to synchronize the transmitter and receiver of the ultrasonic signal. The traveling time of the ultrasonic signal has been used to calculate the distance between the iGS system and a beacon which is located at a pre-determined location. This paper suggests an effective operation method of iGS to estimate position of the mobile robot working in unstructured environment. To expand recognition range and to improve accuracy of the system, two strategies are proposed: utilization of beacons belonging to neighboring blocks and removal of the environment-reflected ultrasonic signals. As the results, the ubiquitous localization system based on iGS as a pseudo-satellite system has been developed successfully with a low cost, a high update rate, and relatively high precision.

• Magazine of korean Tunnelling and Underground Space Association
• /
• v.1 no.1
• /
• pp.81-87
• /
• 1999

Effects of blasting vibrations on curing concrete have not been well studied. As a result, unrealistic and costly blasting vibration constraints have been placed on blasting when it occurs in the vicinity of curing concrete. To study the effects of blasting, concrete blocks of $30\times20\times20cm$ were molded and placed on the quarry Different sets of concrete blocks were subjected to peak vibrations of 0.25, 0.5, 1.0, 5.0, and 10cm/sec. The impulses of blasting vibrations were applied at thirty minutes intervals . Along with unvibrated concrete blocks, the vibrated concrete samples with 60.3mm in diameters were measured for elastic moduli, sonic velocity and uniaxial compressive strength. Test results can be summarized as follows : 1) The blasting vibrations between 6 and 8 hours after pour generally have exerted bad influences on the uniaxial compressive strength of the concrete 2) Under low vibration of 0.25cm/sec variations of the uniaxial compressive strength were not shown. As the magnitudes of blasting vibration increased, compressive strength of concrete decreased. But under the vibrations between 5 and 10cm/sec decreases in strength were almost same. 3) Physical properties of the p-wave velocity, Young's modulus, and Poisson's ratio appeared to decrease for the concrete blocks subjected to vibration for 6 to 8 hours.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.5 no.4
• /
• pp.94-101
• /
• 2001

The shock structure of dual coaxial jet is experimentally investigated. Eight different kinds of coaxial, dual nozzles are employed to observe the major features of the near field shock structure on the supersonic, coaxial, dual jets. Four convergent-divergent supersonic nozzles having the Mach number 2.0 and 3.0 are used to compare the coaxial jet flows discharging from two sonic nozzles. The primary pressure ratio is changed in the range between 1.0 and 10.0, and the assistant jet ratio from 1.0 to 4.0. The results show that the impinging angle, nozzle geometry and pressure ratio significantly affect the near field shock structure, Mach disk location and Mach disk diameter.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.2 no.3
• /
• pp.10-19
• /
• 1998

When an under-expanded supersonic jet impinges on an inclined flat surface, a complex flow structure is established due to the intersection between the flat surface and the shock system of the free jet. This study reports on an experimental results of flows due to under-expanded axisymmetric sonic jets impinging on flat plate. Plate inclination from $60^{\cire}$~$90^{\cire}$ were investigated by means of detailed measurements of the surface pressure and schlieren photograph and surface flow visualization. The schlieren photograph are consistent with the pressure distribution and the surface flow visualization pictures are clearly related to the pressure distributions. The maximum wall pressure is found to be large on the inclined plate than on the perpendicular plate.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.6 no.1
• /
• pp.63-70
• /
• 2002

Computational modeling and simulation can provide an effective predictive capability for the major features of the supersonic microjets. In the present study, computations using the axisymmetic, compressible, Navier-Stokes equations are applied to understand the supersonic microjet flow physics. The pressure ratio of the microjets is changed between 0.2 and 1.25 to obtain both the under- and over-expanded flows at the exit of the micronozzle. and Reynolds number Re is changed between 600 to 40000. For both laminar and turbulent microjet flows, sonic and supersonic microjets are simulated and compared with some experimental results available. Based on computational results, two microjets are discussed in terms of total pressure, jet decay and supersonic core length.

• Journal of the Ergonomics Society of Korea
• /
• v.16 no.1
• /
• pp.29-45
• /
• 1997

This study aims at designing sleeves which are suitable for arm shapes and arm movements. With the samples of of ordinary 24 women aged from 20 to 22, the arm shapes and movements were measured 3-dimensionally using a motion analyzer and a sonic digitizer, and then clasified into three characteristic types (A, B, and C). Our analysis leads to the following conclusion. The factors classifying arm shapes are the length from acromion to posterior armpit point, arm hole length, the cap height, difference in height between anterior and posterior armpit points, armhole circumference, upper arm circumferemce, armhole depth, and underarm circumference. The characteristics of arm type A is that the armhole depth and the length from acromion to posterior armpit point are the largest, while the circumference inbe- tween upper arm and elbow is the smallest among the three arm types. Thus, the large circumference difference between upper and lower arms is the most notable in arm type A. The factors classifying arm shapes for arm type B are the smallest except for the circumference inbetween upper arm and elbow which is larger than that for arm type A. The circumference difference betweemn upper and lower arms is small for arm type B. Arm type C has the smallest armhole depth, while other factors are similar to those for arm type B. In type C, the size of upper arm is comparatively small on the frontal plane, while it is the largest on the sagital plane.

• The Journal of the Convergence on Culture Technology
• /
• v.6 no.1
• /
• pp.395-401
• /
• 2020

Sound Art retains heterogeneous and borderless inborn-characteristics on it. Despite it is a non-mainstream art which could not foster fertile soil to bring up many established artists yet, the domestic area is keep growing and expanding. And now it will soon be that time of overcoming the debates between the art world and the music world to widely embrace de-facto artworks and practices, and bringing more quality critiques. This article talks about a concise history of sound art by addressing some singularities and chronicle traces of it which may be helpful information to lead into more opened future discussion forums in the domestic sound art field.