• Korean Journal of Soil Science and Fertilizer
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• v.44 no.5
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• pp.944-958
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• 2011

Soil hydraulic properties such as hydraulic conductivity or water retention which are costly to measure can be indirectly generated by soil pedotransfer function (PTF) using easily obtainable soil data. The field soil structure description which is routinely recorded could also be used in PTF as an input to reduce the uncertainty. The purposes of this study were to use qualitative morphological soil structure descriptions and soil structural index into PTF and to evaluate their contribution in the prediction of soil hydraulic properties. We transformed categorical morphological descriptions of soil structure into quantitative values using categorical principal component analysis (CATPCA). This approach was tested with a large data set from the US National Pedon Characterization database with the aid of a categorical regression tree analysis. Six different PTFs were used to predict the saturated hydraulic conductivity and those results were averaged to quantify the uncertainty. Quantified morphological description was successively used in multiple linear regression approach to predict the averaged ensemble saturated conductivity. The selected stepwise regression model with only the transformed morphological variables and structural index as predictors predicted the $K_{sat}$ with $r^2$ = 0.48 (p = 0.018), indicating the feasibility of CATPCA approach. In a regression tree analysis, soil structure index and soil texture turned out to be important factors in the prediction of the hydraulic properties. Among structural descriptions size class turned out to be an important grouping parameter in the regression tree. Bulk density, clay content, W33 and structural index explained clusters selected by a two step clustering technique, implying the morphologically described soil structural features are closely related to soil physical as well as hydraulic properties. Although this study provided relatively new method which related soil structure description to soil structure index, the same approach should be tested using a datasets containing the actual measurement of hydraulic properties. More insight on the predictive power of soil structure index to estimate hydraulic properties would be achieved by considering measured the saturated hydraulic conductivity and the soil water retention.

• Journal of the Korean Institute of Landscape Architecture
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• v.34 no.4 s.117
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• pp.96-104
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• 2006

Impervious pavement is primary contributor to the malfunctioning of the urban water circulation system. The aim of this research is to provide basic information and data for new pavement materials and paving technology which could enhance the urban water circulation system. For the study purposes, physical properties of soils sampled from 16 stations were analyzed. The sampling spots were paved with grass block porous pavement material. The findings from the analysis are as follows. The hardness of soils under the pavement was $17{\sim}22mm$ for thoroughfare and $6{\sim}32mm$ for parking areas. The bulk density was $1.42{\sim}1.81g/cm^{3}$ for thoroughfare and $1.38{\sim}1.75g/cm^{3}$ for parking area. The solid phase ration was $46.9{\sim}62.5m^{3}/m^{3}$ for thoroughfare and $45.6{\sim}61.3m^{3}/m^{3}$ for parking area. The porosity was $37.5{\sim}53.1m^{3}/m^{3}$ for thoroughfare and $38.7{\sim}54.4m^{3}/m^{3}$ for parking area. The saturated hydraulic conductivity was $8{\sim}164mm/hr$ for thoroughfare and $14{\sim}201mm/hr$ for parking area. The saturated hydraulic conductivity of the H sample area (the area was completed three months ago) and that of the other area were compared. There was up to 80% decreases of the saturated hydraulic conductivity within one year after the completion of pavement. After the first year, decrease in the saturated hydraulic conductivity was modest. Also there are changes in both surface and under soil physical properties of the grass block porous pavement depending on compaction. The extent of change depends on the degree of compaction. All these factors are combined to influence the permeability of the soil under the pavements. The results of this suggest that it is required to develop a new pavement technology which ensures both the durability and porosity of the pavement to improve the water circulation system by applying Ecological Area Rate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.101-111
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• 1993

Many processes such as machining, injection-moulding and metal-forming are usually operated by hydraulic servo-systems. The dynamic characteristics of these systems are complex and highly non-linear and are often subjected to the uncertain external disturbances associated with the processes. Consequently, the conventional approach to the controller design for these systems may not guarantee accurate tracking control performance. An effective neuro-fuzzy controller is proposed to realize an accurate hydraulic servo-system regardless of the uncertainties and the external disturbances. For this purpose, first, we develop a simplified fuzzy logic controller which have multidimensional and unsymmetric membership functions. Secondly, we develop a neural network which consists of the parameters of the fuzzy logic controller. It is show that the neural network has both learning capability and linguistic representation capability. The proposed controller was implemented on a hydraulic servo-system. Feedback error learning architecture is adopted which uses the feedback error directly without passing through the dynamics or inverse transfer function of the hydraulic servo-system to train the neuro-fuzzy controller. A series of simulations was performed for the position-tracking control of the system subjected to external disturbances. The results of simulations show that regardless of inherent non-linearities and disturbances, an accuracy tracking-control performance is obtained using the proposed neuro-fuzzy controller.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.6
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• pp.460-472
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• 2023

This study was conducted based on the case of an accident (excessive deformation) that occurred during the hydraulic test of a shipboard tank manufactured in accordance with the design regulations. Over-pressure phenomenon was noted as the main cause of accidents in the process of testing tanks without physical damage, which can be found in external factors such as cross-sectional difference between inlet pipe and air pipe and higher water filling rate than the recommended one. The main goal of this paper is to establish a safe water filling rate according to the range of sectional area ratio(SAR) reduced below the regulations for each test situation. The simulation was conducted in accordance with the hydraulic test procedure specified in the Ship Safety Act, and the main situation was divided into two types: filling the tank with water and increasing the water head to the test pressure. The structural safety evaluation of the pressure generated inside the tank and the effect on the structure during the test was reviewed according to the SAR range. Based on the results, guidelines for the optimal filling rate applicable according to SAR during the hydraulic test were presented for the shipboard tanks used in this study.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.386-391
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• 2006

This study presents experimental results of sloshing phenomenon done on rectangular box. A simple harmonic excitation was done on the box. Two kinds of filling ratio, 20% and 30% of height, were tested. A total of 15 pressure sensors were installed to monitor the impact pressure. Each test was repeated for 20 times to ensure the repeatability. The high speed camera captured the flaw filed and the corresponding pressure were synchronize with video signal so that the video image can help the interpretation of the impact pressure. The two filling ratio made difference in the flaw characteristic and impact pressure. The use of high speed camera made it possible to understand the bubble generation mechanism. The pressure time histories were presented.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.578-595
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• 2020

Submarine pressure hulls must withstand high hydraulic pressure and be free of defects. To improve the precision of defect detection, we herein examined different probes for optimal defect assessment by applying the Phased Array Ultrasonic Testing (PAUT) method. Two sets of probe design parameters were selected by considering pressure hull characteristics and analyzed through modeling. PAUT probes were applied, and defect assessment results were compared based on ultrasonic signals of various simulated defects in specimens designed to be the same as actual pressure hulls. The final selected design parameters for the submarine probe, which were designed to minimize the grating lobe of wave interference effect and improve the ultrasonic resolution of pressure hull welds, were identified through the experiment. The improvement in the probe's ability to detect defects in a pressure hull was verified. Furthermore, the accuracy of defect length measurement was improved, enhancing the applicability of the technique.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.1
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• pp.87-92
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• 2012

Alignment of the main plates during the tack welding is essential to block assembly since most of the curved blocks and outfitting parts are assembled on the jigs and fixtures. Tact welding of main plates is the initial process of the curved hull block assembly. Due to the heavy weight of the main plates it is difficult to locate the plate on the accurate position of the jig and fixtures before welding. The conventional masonry process requires much time and manual work in order to achieve the accurate alignment. This labour-intensive process results in relatively high errors and correction works. Due to their larger dimensions and heavier weights, these hull blocks are not ergonomically desirable and, therefore, various mechanical devices such as hydraulic balancers or hydraulic jigs are used for the plate alignment. In this study, the position-sensing scheme implemented by sensors is presented in order to align the main plates on the accurate position during the hull block assembly. Integrating the Infrared photo sensors and micro processor unit, a small scaled prototype of the position-sensing module is developed to determine the alignment of main plates.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.2
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• pp.59-66
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• 2003

A novel application of nano-technology in the field of engineering, called colloidal damper, is investigated. This device is complementary to the hydraulic damper, having a cylinder-piston construction. Particularly for colloidal damper, the hydraulic oil is replacedby a colloidal suspension, which is consisted from a nano-porous matrix with controlled architecture and a lyophobic fluid. In this experimental work, the porous matrix is composed from silica gel, with labyrinth architecture, coated by organo-silicones substances in order to achieve a hydrophobic surface. Water is considered as associated lyophobic fluid. The colloidal damper test rig and the measuring technique of the hysteresis are described. the influence of the hydrophobicity level upon the colloidal damper hysteresis is investigated, for silica gels with similar pores distribution. A certain desired shape of the hysteresis can be achieved by employing mixture of silica gels with different level of hydrophobicity and/or architecture. With these results, it is believed that the proposed damper can be designed and be applied to the desired structure.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.5
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• pp.475-486
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• 2016

Four-rotor dish-shaped unmanned underwater vehicles (FRDS UUVs) are new type underwater vehicles. The main goal of this paper is to develop a quick method to optimize the design of hydraulic support landing platform for the new UUV. In this paper, the geometry configuration and instability type of the platform are defined. Computational investigations are carried out to study the hydrodynamic performance of the landing platform using the Computational Fluid Dynamics (CFD) method. Then, the response surface model of the optimization objective is established. The intelligent particle swarm optimization (PSO) is applied to finding the optimal solution. The result demonstrates that the stability of landing platform is significantly improved with the global objective index increasing from 1.045 to 1.158 (10.86% higher) after the optimization process.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.289-298
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• 2011

This paper provides procedures to effectively determine arrangement of hydraulic type top-bracings, which are popular for the main engine of the mid and large sized commercial vessels. Analyzing the operation mechanism of hydraulic top-bracing, ideal unified nonlinear stiffness curve is presented for linear frequency response analysis and nonlinear transient response analysis. Nonlinear stiffnesses of the curve are determined based on the regression analysis of test results. It is noted from linear frequency response analysis, initial setting pressure is most important among the setting values of the other stiffness intervals. From transient response analyses for two top-bracing arrangement scenarios, it is recognized that, as far as initial setting pressure is well controlled for the concerning vessels, only two top-bracings are enough to suppress H-mode excitation forces from main engine.