• 한국지반신소재학회논문집
• /
• 제7권1호
• /
• pp.13-21
• /
• 2008

본 연구에서는 제주도 현무암에 대한 공학적 특성을 조사하기 위하여 서귀포시 성산읍 일대의 표선리 현무암, 조면암질 현무암 및 스코리아 시료를 채취하였으며, 채취된 시료를 대상으로 흡수율시험, 비중시험, 암반투수시험, 슈미트해머시험, 탄성파시험 및 일축압축시험을 시험을 실시하였다. 이들 시험결과를 토대로 표선리 현무암, 조면암질 현무암 및 스코리아의 흡수율, 비중, 투수계수, 탄성파속도, 일축압축강도를 조사 및 분석하였다. 특히, 슈미트해머 반발치와 일축압축시험으로 구한 일축압축강도의 관계를 회귀분석을 통하여 슈미트해머 반발치를 이용한 일축압축강도 산정식을 제안하였으며, 이를 통하여 간편하게 일축압축강도를 산정할 수 있는 방법을 마련하였다.

• Geomechanics and Engineering
• /
• 제9권3호
• /
• pp.345-360
• /
• 2015

Wave equation analysis programs (WEAP) such as GRLWEAP and TNOWave were primarily developed for pre-driving analysis. They can also be used for post-driving measurement applications with some refinements. In the case of pre-driving analysis, the programs are used for the purpose of selecting the right equipment for a given ground condition and controlling stresses during pile driving processes. Recently, the program is increasingly used for the post-driving measurement application, where an assessment based on a variety of input parameters such as hammer, driving system and dynamic behaviour of soil is carried out. The process of this type of analysis is quite simple and it is performed by matching accurately known parameters, such as from CAPWAP analysis, to the parameters used in GRLWEAP analysis. The parameters that are refined in the typical analysis are pile stresses, hammer energy, capacity, damping and quakes. Matching of these known quantities by adjusting hammer, cushion and soil parameters in the wave equation program results in blow counts or sets and stresses for other hammer energies and capacities and cushion configuration. The result of this analysis is output on a Bearing Graph that establishes a relationship between ultimate capacity and net set per blow. A further application of this refinement method can be applied to the assessment of dynamic formulae, which are extensively used in pile capacity calculation during pile driving process. In this paper, WEAP analysis is carried out to establish the relationship between the ultimate capacities and sets using the various parameters and using this relationship to recalibrate the dynamic formula. The results of this analysis presented show that some of the shortcoming of the dynamic formula can be overcome and the results can be improved by the introduction of a correction factor.

• 한국안전학회지
• /
• 제26권1호
• /
• pp.1-7
• /
• 2011

When the pumps stopped in the operation by the power failure, the hydraulic transients take place in the sudden change of a velocity of pipe line. Each and every water hammer problem shows the critical stage to be greatly affected the facts of safety and reliability in case of power failure. The field tests of the water hammer executed at Cheong-Yang booster pump station having an air chamber. The effects were studied by both the practical experiments and the CFD(Computational Fluid Dynamics : Surge 2008). The result states that the system with water hammering protection equipment was much safer when power failure happens. The following data by a computational fluid dynamic analysis are to be shown below, securing the system stability and integrity. (1) With water hammering protection equipment. (1) Change of pressure : Up to $15.5\;kg/cm^2$ in contrary to estimating $16.88\;kg/cm^2$. (2) Change rate of water level : 52~33% in contrary to estimating 55~27%. (3) Note that the operational pressure of pump runs approx. 145 m, lowering 155 m of the regularity head of pump. (4) Note that the cycle of water hammering delays from 80 second to 100 second, together with easing the function of air value at the pneumatic lines. (2) Change of pressure without water hammering protection equipment : Approximate $22.86\;kg/cm^2$. The comprehensive result says that the computational fluid dynamics analysis would match well with the practical field-test. It was able to predict Max. or Min. water hammering time in a piping system. This study aims effectively to alleviate water hammering in a pipe line to be installed with air chamber at the pumping station and results in making the stability of pump system in the end.

• 대한통합의학회지
• /
• 제10권4호
• /
• pp.137-143
• /
• 2022

Purpose : The purpose of this study was to evaluate the reliability analysis of the deep tendon reflex by using electromyography (EMG). Methods : The study was tested on 30 volunteers who are women in their 20s. Using an electronic reflective hammer of EMG, deep tendon reflex was measured on all subjects with the participation of three trained physical therapists as raters. First, the subjects were comfortably seated on a table with their knees bent at 90 °. The three raters tapped the electric hammer at intervals of 10 seconds to avoid habituation until a total of 10 compound muscle action potential records were collected. Intraclass correlation coefficients (ICCs) were calculated to assess the inter-rater reliability of the deep tendon reflex with the use of EMG. The items of analysis included amplitude (mV), latency (ms), duration (ms), and area (mV × ms) of the compound evoked potentials. Results : Based on the average records of 10 compound muscle action potential, excellent reliability (ICC: .912) was achieved in terms of area, and there was good reliability in terms of latency (ICC: .795) and duration (ICC: .800). In the shortest latency of the compound muscle action potential, good reliability was achieved in terms of amplitude (ICC: .865), duration (ICC: .781), and area (ICC: .832). In the amplitude of peak-to-peak of compound muscle action potential, excellent reliability was recorded in terms of amplitude (ICC: .924), and good reliability was recorded in terms of duration (ICC: .801) and area (ICC: .874). Conclusion : The findings in this study indicate that electromyography via an electric hammer is a reliable method of assessing and measuring deep tendon reflexes. Especially, it may be an excellent gauge in the area of average values of the compound muscle action potentials and the amplitude of peak-to-peak of compound muscle action potentials.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2001년도 추계학술대회 논문집
• /
• pp.228-232
• /
• 2001

Fatigue strength, electrical conductivity and stress-corrosion-cracking resistance are considered as important factors at aircraft Al alloys, therefore Al7050 alloy has been developed to improve such properties. However, hammer-forged Al7050 parts showed the undesirable structures such as severe local grain coarsening and inhomogeneous material flow, resulted in the degraded mechanical properties. In this paper, process conditions are investigated for elimination of the grain coarsening and improved material flow during forging process by both of experiments and FEM analysis. Particular interest has been given to understand role of preform shape on the grain coarsening behavior and magnitude of the hammer forging load The use of preform has been beneficial for reduction of the forging load and elimination of the grain coarsening. However, in the cases of as received bar and the round bar, which was machined to 2.5mm thickness in surface layer, some degree of local grain coarsening behavior has been observed. The optimized preform shape could be properly designed by applying the FEM simulation.

• 대한기계학회논문집A
• /
• 제28권6호
• /
• pp.763-773
• /
• 2004

This paper suggests the 2 D.O.F mathematical model of the High Frequency Vibro-Hammer (HFVH), introduces an experimental method for measuring of the attenuation of piling vibration and proves what experiments are coincident with the equation of wave propagation. As vibratory installation of piles and casings has many economic merits in the construction field, most of all contractors prefer to vibratory pile driving method than the other. Compared to impact pile driving, vibratory installation has the advantage of reducing vibration or noise pollution and can drive piles under high frequency. Experiments serve estimations of capabilities and limitations of the HFVH's excitation force and finding of sensitivity for important soil resistance parameters. Also, we discuss the HFVH that can drive with three kinds of input waves (triangular, sine and square wave) and propose the design of parameters to improve actuating performance in it.

• 지질공학
• /
• 제13권3호
• /
• pp.359-368
• /
• 2003

현재 건설중에 있는 부산 신항만의 매립을 위해 채석장이 가동중에 있으나, 실제 공사 중 채석된 암석이 당초 설계와는 다른 암질을 포함하고 있다. 따라서, 당초 설계와는 달리 많은 폐석이 발생되어 정상적인 공사추진에 애로사항이 있으므로, 현장조사 및 실내작업을 통하여 지정된 채석장에 대한 전체적인 암질을 구분하는 것이 본 연구의 목적이다. 이를 위해 측량, Schimidt Rock Hammer 시험, 절리간격조사를 시행하였고 실내에서 DIPS 및 Rockworks 프로그램을 이용하여 절리의 방향성 및 발파 후 암괴의 크기를 분석하였다. 그 결과 본 지역에는 절리밀도가 높아 토석 채취시 ${\Phi}100mm$ 이하의 필터사석이 많이 발생하는 것으로 분석되었다.

• 한국안전학회지
• /
• 제29권5호
• /
• pp.1-6
• /
• 2014

When the fluid energy convert into kinetic energy due to water hammer, the propagation velocity of pressure wave appear. The propagation velocity of pressure wave(1050 m/s) of very fast could be damage to the pipeline system. If the occurrence of water hammer is due to down-pressure, the faster the air exhaust or supply device is needed. it is high Speed Air Valve. In this paper, Each 3.12, 3.13, 3.72, $3.74kg/cm^2$ pipeline pressure were setting, and then executed pressure rapid drop for obtaining a high Speed Air Valve Operating time and pressure change data. the result was that pipe line pressure stabilization time were each 0.98, 1, 1.22, 1.25 sec. In other words, that pressure drop experimental results pipe line pressure was equal to atmospheric pressure without negative pressure After about one second. The study result would be useful to pipe line system stability design because this data could be foresee pressure stabilization time.

• Geomechanics and Engineering
• /
• 제10권1호
• /
• pp.109-124
• /
• 2016

In this paper, process of dynamic powder compaction is investigated experimentally using impact of drop hammer and die tube. A series of test is performed using aluminum powder with different grain size. The energy of compaction of powder is determined by measuring height of hammer and the results presented in term of compact density and rupture stress. This paper also presents a mathematical modeling using experimental data and neural network. The purpose of this modeling is to display how the variations of the significant parameters changes with the compact density and rupture stress. The closed-form obtained model shows very good agreement with experimental results and it provides a way of studying and understanding the mechanics of dynamic powder compaction process. In the considered energy level (from 733 to 3580 J), the relative density is varied from 63.89% to 87.41%, 63.93% to 91.52%, 64.15% to 95.11% for powder A, B and C respectively. Also, the maximum rupture stress are obtained for different types of powder and the results shown that the rupture stress increases with increasing energy level and grain size.

• 상하수도학회지
• /
• 제27권4호
• /
• pp.479-487
• /
• 2013

This study was to investigate characteristics for the pressure wave propagation and the maximum pressure near a rapid closure valve which was installed the end of multi piping network. The multi piping network consists of one inlet and three outlet with straight pipes. The diameter of the pipes including the valve was 100 mm, 80 mm, 80 mm respectively. The valve was rapidly closed with the instantaneous time which was 0.023s in the level for the water hammer. For the simulation, the influence of the pipe thickness and deformation due to pressure-wave-propagation was not considered. CFD was conducted under the following condition : the initial pressure was 1bar in the inlet and the mass flow rate was 7.83 kg/s in the outlet(the velocity in the pipe with 100 mm diameter was 1 m/s). As the valve have conditions that were status with and without fluid flow in the pipe after valve closing, the maximum pressure change and the frequency analysis were examined. As the results, the case that was status with fluid flow appeared the higher maximum pressure than another's, the maximum frequency band was about 10 ~ 11 Hz.