Earticle

The Climate chamber system is an essential facility for aerodynamic performance development of commercial vehicles to investigate air flow field characteristics in different climatic conditions. In particular, the analysis of airflow fields within the chamber system is an essential consideration for optimal design. In this study, the pressure characteristics and velocity uniformity in the test section area were predicted with blower impeller rotational speed using CFD. The velocity uniformity is affected by the distance from the blower nozzle outlet, reaching up to 72.7% at 695 RPM. The pressure differential between 300 RPM and 740 RPM shows an approximate difference of 2651 Pa, with a high-pressure distribution observed along the right side wall of the blower. These results are expected to be used as design data applicable for improving the performance of environmental chamber systems.

모든 설계는 정보가 불완전하고 또 불확실성 하에서 이루어지고 있어 재난을 초래할 수도 있다. 구조물 설계시에도 현행 결정론적인 설계방법은 구조물의 안전정도나 신뢰도를 나타내지 못하고 있다. 설계시 모든 사항들은 신뢰도 해석에 근거해 결정하는 것이 바람직하다. 토질에 있어서는 다른 구조재의 성질보다 불확실성이 더 크기 때문에 더 큰 문제를 내포하고 있어 신뢰도 해석에 의거한 설계방법의 연구가 절실한 형편이다. 주동토압에 관계되는 구조물의 신뢰도 해석이나 설계의 과정을 단순화할 수 있도록 확률변수의 수를 줄여 토질의 기본정수로부터 계산되는 토압을 하나의 확률변수로 간주하고 토압의 변동계수 및 분포형태를 구할 필요가 있다. 모의실험을 사용하여 사질토의 Rankine 주동토압들을 계산, 통계처리하고 중선형회귀법을 통해 기본 토질정수와 토압의 변동계수의 관계를 구할 수 있는 회귀식들을 제시하였고 각 기본 토질정수들이 토압의 변동계수에 미치는 영향을 분석하였으며 Pearson system을 이용하여 토압의 분포를 분석한 결과, 기본 토질정수들이 정규분포일 때 토압은 베타분포로 간주해도 무난할 것으로 나타났다.

In the development of engineering designs, decisions are required irrespective of the state of completeness and quality of information, and are formulated under conditions of uncertainty. Furthermore, under conditions of uncertainty the design invokes risks. Thus, in the design of the structures, the currently used deterministic design method does not provide a realistic assessment of the actual safety or the reliability of the structures. It is desirable that decisions required in The process of the design invariably must be made based on the reliability analysis. Properties of soil material are subject to more uncertainty than those of other structural material. In the field of soil mechanics and foundation engineering, it needed to develop reliability-based design methods. In order to simplify the reliability analysis or the reliability-based design process of the structures associated with the active earth pressure, it is necessary to find the variation and the distribution type of the active earth pressure calculated from the basic properties of soils. Monte Carlo simulation is performed to obtain the relationship between the variation of the active earth pressure for cohessionless soils calculated by using Rankine formula and the basic soil properties and the distribution type of the earth pressure. A series of regression equations obtained by utilizing the multi-linear regression analysis is suggested in this paper and the sensitivity of the basic soil properties to the variation of The earth pressure is investigated. The type of distribution of the active earth pressure was found to be the beta distribution in most cases or to be very similar to the beta distribution, if the basic soil variables are normally distributed.

Air blower has been widely used in many industrial fields such as wind tunnel and large ventilation systems. Its performance is affected by operating conditions and system geometry of inpeller and duct, and these design parameter optimization is essential for the effective development. CFD analysis is carried out to investigate the air flow field characteristics with outlet total pressure in a blower system. Intake air into the impeller blade through the inlet is compressed, and then gradually discharged from the outlet with ascending total pressure, and predicted results are compared with test data. Especially this overall pressure difference in the blower system severely depends on the flow rate. These results are expected to be used as applicable design data for blower performance improvement.

The change in the performance of the range hood according to the pressure change was investigated through a comparative experiment, and the conclusion is as follows. KS C 9304: In 2020, static pressure was applied at 100 Pa according to the fan standard, and the test was conducted by varying the outlet diameter and power consumption. In the case of Motor power 55W, the air volume value was 184.6 when the outlet diameter was 125mm. As a result of the test, if the power consumption is 52.0W, the diameter of the outlet is 125mm, and the power consumption is 60.8W, and the diameter of the outlet is 100mm, it meets 160 or more and less than 200 (constant pressure 100Pa).

The change in pressure measurement according to the low pressure tap blockage rate of the Venturi flowmeter used in domestic nuclear power plants was approached numerically. Blockage rates were modeled dividing by 1/10dT to the downstream side of the low pressure tab to identify differential pressure changes. As a result, differential pressure increased in proportion to the blockage rate, and there was no change in differential pressure measurement at 10 to 40 percent with relatively small blockage rate, but the error rate of 50% to 0.3% or higher was shown.

Unmanned underwater vehicles (UUVs) are essential tools for marine exploration, research, and surveillance. Accurate state estimations are critical for effective navigation, but conventional methods, such as Doppler velocity logs (DVLs) and inertial navigation systems, are expensive and vulnerable to environmental conditions. Inspired by the biological lateral line system in fish, this study proposes an enhanced pressure variation model (PVM) that estimates the velocity and drift angles using the data from pressure sensors. The improved model introduces unified regression coefficients and accounts for nonlinear flow effects, reducing the reliance on motion-specific parameters and increasing the adaptability across various maneuvering conditions. The model was validated by conducting extensive computational fluid dynamics (CFD) simulations across multiple motion scenarios. The enhanced PVM achieved high estimation accuracy while maintaining robustness under different dynamic conditions. The contributions of this study include the following: (1) a refined estimation framework using a unified coefficient model, (2) a low-cost, environment-resilient alternative to traditional systems, and (3) verified reliability through CFD-based performance evaluations. Future work will focus on experimental validation, extending the performance to large-angle motions, and developing a real-time data processing module to enable in situ application. This approach supports more autonomous and reliable UUV navigation for marine robotics and underwater missions.

This paper propose a new method to investigate combustion phenomena using the variation of crankshaft speed. From the idea which the variation of crankshaft speed contains the information of combustion the energy method is applied as a single degree of freedom. Through the comparison of measured and calculated crankshaft speed the proposed energy model is proved to be moderate. When the crankshaft speed is used in the energy equation filtering of speed is required. The frequency components of cylinder pressure is analyzed and the coefficients of Fourier series above the twelfth frequency of engine speed is considered as u noise. As an example for application of this research some combustion analysis like as mean effective pressure and heat release rate, and misfire detection were carried out.

Pulse waves continuously change with respect to the characteristics and status of the cardiovascular system and in relation to the blood pressure (BP) and the pulse wave velocity (PWV). Monitoring the vascular condition by analyzing the variations in pulse waveforms has been used to diagnose vascular disorders and in drug treatment of arteriosclerosis and peripheral circulatory obstruction. In this paper, we investigated the vascular characteristic index with regard to the BP and classified by pulse wave signals. The pressure pulse wave and photoplethysmography (PPG) were measured simultaneously while subjects exercised, producing changes in the BP, to analyze the variation in the vascular characteristic index. We investigated the correlation between the BP and vascular characteristic index with regard to the classification methods of the pulse wave. The reflection index (RI) and vascular stiffness index were correlated with the diastolic BP, but no correlation was found between these parameters and the systolic BP. These results suggest the possibility of estimating BP through simple measurements of pulse waves.

Pulse waves continuously change with respect to the characteristics and status of the cardiovascular system and in relation to the blood pressure (BP) and the pulse wave velocity (PWV). Monitoring the vascular condition by analyzing the variations in pulse waveforms has been used to diagnose vascular disorders and in drug treatment of arteriosclerosis and peripheral circulatory obstruction. In this paper, we investigated the vascular characteristic index with regard to the BP and classified by pulse wave signals. The pressure pulse wave and photoplethysmography (PPG) were measured simultaneously while subjects exercised, producing changes in the BP, to analyze the variation in the vascular characteristic index. We investigated the correlation between the BP and vascular characteristic index with regard to the classification methods of the pulse wave. The reflection index (RI) and vascular stiffness index were correlated with the diastolic BP, but no correlation was found between these parameters and the systolic BP. These results suggest the possibility of estimating BP through simple measurements of pulse waves.

Experimental study has been conducted to clarify the internal and external pressure variation characteristics for KTX(Korea Train eXpress) passing through tunnel. Abrupt pressure variation gives rise to the ear-discomfort for passenger and fatigue for car body. In this study, the internal and external pressure variation are measured by using KTX real train experiment and on-board portable data acquisition system in Gyeongbu high speed commercial line. The tunnels from 200 m to 4000 m in length are chosen for the investigation of tunnel length effects. From the results of experiment, the internal pressure variation rate for all the test tunnels is lower than the standard criteria of 200 Pa/s. And, the critical tunnel lengths for pressure wave pattern are classified into 7 groups by using the theoretical L-t diagram analysis.

Many hydraulic structures are damaged by under flood flow and storm waves year after year. Many cases of dike and breakwater failure are caused by the suck out of sand from behind the revetment. This type of failure will be in close relation to the dynamic behavior of sand bed around the revetment. In this paper, from this point of view we investigated the basic characteristics of such sand movement by small model tests and tried to explanation the hydro- and soil mechanical mechanism of this phenomenon theoretically.

Compression ignition direct injection diesel engines employed a high pressure injection system have been developed as a measure to improve a fuel efficiency and reduce harmful emissions. In order to understand the effects of the pressure variation, many experimental works have been done, however there are many difficulties to get data in engine condition. This work gives numerical results for the high pressure effects on spray characteristics in wide or limited space with near walls. The gas phase is modelled by Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction. The liquid phase is modelled using the discrete droplet model approach in Lagrangian form and the drop behavior on a wall is calculated with a new droplet-wall interaction model based on the experiments observing individual drops. The droplet distributions, vapour fractions and gas flows are shown in various injection pressure cases. In free spray case which the injection spray has no wall impaction, the spray dispersion and vapour fraction increase and drop sizes decrease with increasing injection pressure. The same phenomena appears more clearly in wall impaction cases.

Background: Non-dippers were reported as showing different left atrial function, compared to dippers, but no study to date investigated the changes in the left atrial function according to the diurnal blood pressure pattern, using tissue Doppler and strain imaging. Methods: Forty never treated hypertensive patients between 30 and 80 years of age were enrolled in this study. Patients were classified as non-dippers when, during night time, they had a blood pressure decrease of less than 10%. Strain of the left atrium was measured during late systole, and peak strain rates of the left atrium were measured during systole, early and late diastolic periods. Results: The left atrial expansion index, left atrial active emptying volume and left atrial active emptying fraction were all significantly increased in non-dippers. They also had increased values of mean peak left atrial strain (dippers = 21.26 ± 4.23% vs. non-dippers = 24.91 ± 5.20%, p = 0.02), strain rate during reservoir (dippers = 1.29 ± 0.23 s-1 vs. non-dippers =1.52 ± 0.27 s-1,p = 0.01) and contractile period (dippers = -1.38 ± 0.24 s-1 vs. non-dippers = -1.68 ± 0.32 s-1, p < 0.01). Conclusion: Strain and strain rate acquired from color Doppler tissue imaging demonstrate exaggerated reservoir and booster pump function in never-treated, non-dipper hypertensive patients. These methods are simple and sensitive for the early detection of subtle changes in the left atrial function.

Hydrogen energy is becoming popular day by day due to its renewability and pollutaaant free natures. Hydrogen gas pressure which is after passing through reciprocating compressor part has high pulsation wave form. A unit, snubber is used as compressor components to reduce the harmful pulsation waveform and to remove the impurities in the hydrogen gas. An experiment has been conducted to investigate the pulsation reduction performance of different arrangement of snubber i.e. snubber array used in reciprocating compression system. Analyzing the snubber array experimental data, it is found that the pressure fluctuations are reduced from 90.1977% ~ 92.6336% with pressure loss 1.5013% ~ 4.9034% for compressor operation at different speed which ensure the good performance of snubber-array as pulsation damper in hydrogen compressing system.

The behavior of pore pressure and effective stress in a highly saturated sand bed under variations in the water pressure in its surface were investigated to determine the mechanism of the collapse of hydraulic structures during flooding or when attacked by storm waves. The vertical, one-dimensional model was used as a basic model to clarify the effect of water pressure variation on only to the vertical direction. The theoretical results show that a sand bed under variations of water pressure is weakened by an increase in excess pore pressure and that under certain conditions the sand bed will liquefy. Although many factors related to water pressure variation and property of the material determine this phenomenon, the mist important factor seems to be the small amount of air present in the sand bed. The theoretical results reported are verified by experiments.