Process of pore pressure diffusion in saturated clay soil and impact of adsorbed water

LianSheng Tang,HaoKun Chen,Jing Song 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.5

Water molecules are adsorbed onto the surface and interlayer of clay minerals and form a film, which causes that pore pressure diffusion in clayey soils differs from that in granular material. In this paper, adsorbed water is classified into strongly adsorbed water and loosely adsorbed water, which provide a better understanding of the physical mechanisms of the adsorbed water. To investigate the impact of adsorbed water on pore pressure diffusion, a series laboratory tests were conducted, including the uplift pressure test, pore pressure diffusion test and adsorbed water content test. The experimental results implies that strongly adsorbed water can neither flow nor participate in pressure diffusion, but loosely adsorbed water shears at pressure gradients and participates in laminar flow. Therefore, as long as the dense clayey soil contains loosely adsorbed water, the pore pressure change at a local site can diffuse throughout the material. A concept called “loosely adsorbed water index (Ilo) is defined to characterize both the content and physical properties of loosely adsorbed water: (1) when Ilo ≥ 1, the peripheral water molecules of loosely adsorbed water layer essentially behave the same as free water; (2) as Ilo → 0, the physical properties of adsorbed water may evolve from a gel-like state to a solid-like state (strongly adsorbed water). According to the density of clay and the content of adsorbed water, the process of pore pressure diffusion can be divided into three modes: flow channels of free fluid, deformations of the adsorbed water layer and shear motions of the peripheral-adsorbed water molecules. Pore pressure response to additional water pressure strongly depends on the permeability, seepage path and boundary conditions. The time-lag effect of pore pressure diffusion should be considered in applications of effective stress in engineering.

Investigation of the effect of operating pressure on the performance of proton exchange membrane fuel cell: In the aspect of water distribution

Ko, Donggun,Doh, Seungwoo,Park, Hyun Sun,Kim, Moo Hwan Elsevier 2018 RENEWABLE ENERGY Vol.115 No.-

<P><B>Abstract</B></P> <P>The effect of operating pressure on the water distribution and its effect on performance of proton exchange membrane fuel cell (PEMFC) was investigated. The experiment was conducted by changing the relative humidity (25%, 100%) and the back pressure value (0.2, 0.4 bar). The PEMFC was either not pressurization, or pressurization on both sides, or on the anode side or on the cathode side. In these conditions, the PEMFC showed higher performance when the cathode side was pressurization than when the anode side was pressurization. The performance difference was analyzed based on the water distribution utilizing X-ray visualization technique. Increase of water saturation in membrane was measured when the cathode side was pressurization at water deficient condition. And the saturation was getting increased as the value of pressure increased. This change caused significant increase in proton conductivity, and performance eventually. At water abundant condition, this phenomenon became weaken and performance difference became narrow. However, increase in pressure on the cathode side increased the air penetration through water and reduced the concentration over-potential. Precedent researches concentrated on the reaction kinetics to analyze the effect of pressure, but the change of water distribution should be considered simultaneously to understand the effect of pressure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> To comprehend the effect of operating pressure on the PEMFC, the change of water distribution should be considered. </LI> <LI> Pressurizing cathode side show higher performance than pressurizing anode side at low pressure value. </LI> <LI> Pressurizing cathode side disturbs the water removal and enhances the water concentration in PEMFC. </LI> <LI> Proper value of operating pressure exists that can manage liquid water effectively. </LI> </UL> </P>

시뮬레이션과 1일 급수량 분석을 이용한 갈수기 감압에 의한 제한급수 방법

남영욱,김경수,현인환,김두일 대한상하수도학회 2020 상하수도학회지 Vol.34 No.5

Due to global climate change, mega-droughts have occurred frequently. Since long-term droughts make it difficult to secure the water resources, water supply needs to be restricted in a reasonable manner. In the event of limited water supply, the waterworks need to develop a restricted water supply strategy. This study showed that analyzing daily water supply could be used to respond to the first stage of a drought. According to an analysis of Korea's major water authorities, there was about 7~21% of room for daily minimum water supply in case of a drought. Restricting the water supply by lowering pressure is a good strategy for local water authorities with high water leakage rate since leakage is inversely dependent with pressure. For this method, it is necessary to quantify water deficiency and pressure at each node using a simulation. Since DDA-based software is not possible to predict changes in demand at nodes with pressure reduction, WaterGEMS, a PDA software, was used to quantitatively predict water shortages and pressures at each node. Locations where water is deficient need to install booster pumps or to be dispatched with water tank truck and bottled water. Without these support, lowering pressure could not be an option for water works. This paper suggests a method for waterworks to plan a drought by lowering pressure to restrict water supply using daily water supply analysis and PDA based simulation.

WaterGEMS모형을 이용한 상수관망 블록시스템의 비상급수계획 평가

백천우,전환돈,김중훈,유도근,이광춘 한국방재학회 2008 한국방재학회논문집 Vol.08 No.06

Hydraulic analysis of water distribution system can be divided into demand-driven analysis and pressure-driven analysis. Demand-driven analysis can give unrealistic results to simulate hydraulic conditions under abnormal operating conditions such as sudden demand increase and pipe failure. In Korea, demand-driven analysis has been used to establish emergency water supply plan in many water projects, but it is necessary to use pressure-driven analysis for establishment of emergency water supply plan. In this study, WaterGEMS model that was developed for pressure-driven analysis is used to evaluation of emergency water supply plan of J city. As the results, it was able to draw up more efficient plan for water supply in small block, and established emergency water supply plan of J city was determined to be appropriate. 상수관망의 수리해석 방법은 demand-driven analysis와 pressure-driven analysis로 구분할 수 있으며, 급작스런 용수수요증가, 관거파괴 등과 같이 비정상운영상태인 용수공급시스템의 수리모의에 demand-driven analysis를 사용할 경우 비현실적인 결과를 줄 수 있다. 특히 현재 국내에서는 비상상황에 대한 비상급수계획 수립 시에 demand-driven analysis를 사용하고 있으나, pressure-driven analysis의 적용을 통한 비상급수계획의 적정성 평가가 수행되어야 할 것이다. 본 연구에서는 pressure-driven analysis를 위해 최근 개발된 WaterGEMS모형을 이용하여 2007년 수도정비 사업을 계획한 J시의 비상급수계획의 적정성을 평가하였다. 적용 결과 소블럭의 용수공급 안정성 향상을 위한 방안 제시가 가능하였으며, 수립된 비상급수계획이 적합한 것으로 판단되었다.

Porous Cellulose Acetate by Specific Solvents with Water Pressure Treatment for Applications to Separator and Membranes

Lee, Woong Gi,Kim, Do Young,Kang, Sang Wook The Polymer Society of Korea 2018 Macromolecular Research Vol.26 No.7

In this study, straight nanoporous cellulose acetate (CA) membranes were fabricated by utilizing N-methyl pyrrolidinone (NMP) and acetone with water pressure, without the use of inorganic additives. The nanoporous CA polymer was fabricated as a result of the difference in vapor pressure between NMP and acetone. As the vapor pressure of NMP is lower than that of acetone, NMP could be contained in the CA membrane by regulating the drying process. Furthermore, the incorporation of NMP incorporated into the CA membrane led to an increase in the plasticization effect via an increase in the free volume of the CA chains. Thus, the CA chains weakened by NMP were exposed by high water pressure, producing a porous region. The pore size and porosity could be easily controlled by both the NMP content and the water pressure in the CA polymer. It was confirmed that the pore size and porosity were controlled by water pressure because the water flux of the porous CA polymer gradually increased with an increase in water pressure. Moreover, the water flux increased with increasing NMP content in the CA polymer. The water flux of the CA polymer containing 1 wt% NMP was found to be <TEX>$58.38L/m^2h$</TEX> at 8 bar. In contrast, the CA polymer with 2 wt% NMP exhibited an improved water flux of <TEX>$155.50L/m^2h$</TEX> at 8 bar.

Control Performance of Simple Adaptive Control on Simulated Water Hydraulic Servo Motor System with Changed Supply Pressure

Pha N. Pham,Kazuhisa Ito 유공압건설기계학회 2015 유공압건설기계학회 학술대회논문집 Vol.2015 No.10

Recently, the application of water hydraulics has been paid attention because of its inherent merits such as environmental friendliness, clean, high safety against fire hazard and easy availability. However, water hydraulic devices themselves have lower energy efficiency than in oil systems and this prevents from widening its application. The original method for reducing energy consumption and therefore raising the energy efficiency is to make the supply pressure to change depending on the demand. On the other hand, the variable supply pressure affects the control performance besides larger friction force and considerable leakage flow. Thus, the requirement for reducing the effect of the variable parameters in water hydraulic systems becomes very important for highly precise application. In this paper, the simple adaptive control (SAC) algorithm applied to a water hydraulic servo motor system is introduced for compensating the effects of the fast changing of supply pressure that affects strongly to control response. SAC and conventional PID control performances are compared together in case of using constant supply pressure and variable supply pressure. The simulation results show that for constant supply pressure; the responses in SAC and PID are almost same for steady state error and only better for SAC in transient response. However, for the case of changed supply pressure, SAC response is improved with much smaller error and shorter time for recovering into specified error band in advance than PID response. These results prove that SAC deals with the variable supply pressure well even the changing is very fast. Hence, the robustness of SAC should be applied in the systems with fast changing of supply pressure.

Effects of pressure on structure and extinction limits of counterflow nonpremixed water-laden methane/air flames

Lee, Seungro,Ha, Heonrok,Dunn-Rankin, Derek,Kwon, Oh Chae Pergamon Press 2017 Energy Vol.134 No.-

<P><B>Abstract</B></P> <P>Structure and extinction limits of counterflow nonpremixed water (H<SUB>2</SUB>O)-laden methane (CH<SUB>4</SUB>)/air flames at various pressures are computationally investigated to better understand combustion processes of fuel having naturally high H<SUB>2</SUB>O (vapor) content under elevated pressures. Using a detailed kinetic mechanism and a statistical narrow-band radiation model, the flame structure and extinction limits are predicted for elevated pressures and a wide range of flame strain rates and compared with those at atmospheric pressure. Results show that with increasing pressure the maximum flame temperature increases and the extinction limits are generally extended due to the reduced amount of dissociation and the enhanced radiation reabsorption of H<SUB>2</SUB>O, indicating that flames can sustain more H<SUB>2</SUB>O vapor at elevated pressure. The concentration of active radicals and the flame thickness decrease with increasing pressure. The observed flammable range of the H<SUB>2</SUB>O to CH<SUB>4</SUB> molar ratio at elevated pressures is comparable to that found in self-sustained combustion of CH<SUB>4</SUB> hydrates at atmospheric pressure, and the chemical effects of H<SUB>2</SUB>O addition on flame structure are insignificant. Elevated pressure enhances the formation of soot precursors such as acetylene (C<SUB>2</SUB>H<SUB>2</SUB>), implying an opposite tendency from the water addition effects.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Maximum flame temperature increases with increasing pressure. </LI> <LI> Extinction limits are extended with elevated pressure. </LI> <LI> Enhanced recombination and radiation reabsorption of H<SUB>2</SUB>O cause these tendencies. </LI> <LI> Elevated pressure enhances formation of soot precursor C<SUB>2</SUB>H<SUB>2</SUB>. </LI> <LI> Thermal effect of H<SUB>2</SUB>O addition on flame structure at elevated pressure is dominant. </LI> </UL> </P>

분산형 상수관망 구축을 위한 인라인 급수탱크 위치 최적화

박용균,정성균,유도근,전환돈 한국방재학회 2015 한국방재학회논문집 Vol.15 No.6

Providing customers with the desirable amount of water with sufficient pressure is the most critical issue in operating a water supply network. It is possible to secure the necessary amount of water for stable operation by taking water from a reservoir or a dam, whereas supplying water with sufficient pressure stably is determined by how they properly design and operate a water supply network. In cases of mountainous areas such as Korea or where customers are widely distributed, too much pressure head loss in conveying water makes it difficult to maintain the design pressure head at demand locations. Usually, the utility resolves this problem by introducing a booster pump to the system. Besides booster pumps, another alternative will be an elevated tank for the system. It is, however, important to determine the number and locations of elevated tanks for obtaining the maximum advantages by installing an elevated tank. In this study, we suggest a methodology for determining the number and locations of elevated tanks by the quantification of being pressure-stable. The advantage obtained by elevated tank combinations is quantified in terms of “the number of pressure-improved nodes” and “Index of pressure improvement”and the methodology is applied to a sample network to prove its applicability. 상수관망의 운영에서 가장 중요한 것은 수용가에 필요한 수량과 수압으로 용수를 공급하는 것이다. 수량 확보는 취수원의 확보 등을 통해서 안정적으로 운영하는 것이 가능하지만 적정한 수압을 안정적으로 공급하는 것은 상수관망의 시설물 설계와 운영방법 등에 의해서 결정된다. 우리나라와 같이 산지가 많은 지형이거나 수용가가 널리 분산되어 존재하는 경우에는 송수과정에서 발생하는 과다한 손실수두에 의해서 안정적인 수압으로 공급하는 것이 어렵다. 이와 같은 경우에는 일반적으로 가압장을 설치하여 부족한 수압을 확보하게 된다. 가압장 이외의 대안으로 블록 내 설치하는 고가탱크가 하나의 대안이 될 수 있다. 그러나 고가탱크 설치에 의한 이점을 최대화하기 위해서는 필요한 위치와 개수의 결정이 중요하다. 이를 위해서 본 연구에서는 고가탱크의 위치와 개수조합에 따른 압력의 안정화를 정량화하여 최적탱크 조합과 위치를 결정할 수 있는 방법론을 제시하였다. 고가탱크 개수조합 별 이점은 압력개선 절점 수와 압력개선 지수로 정량화 하였다. 제안된 방법을 샘플관망에 적용하여 적용성을 평가하였다.

Pressure analysis in grouting and water pressure test to achieving optimal pressure

Amnieh, Hassan Bakhshandeh,Masoudi, Majid,Kolahchi, Reza Techno-Press 2017 Geomechanics & engineering Vol.13 No.4

In order to determine the rate of penetrability, water pressure test is used before the grouting. One of the parameters which have the highest effect is pressure. Mathematical modeling is used for the first time in this study to determine the optimum pressure. Thus, the joints that exist in the rock mass are simulated using cylindrical shell model. The joint surroundings are also modeled through Pasternak environment. In order to validate the modeling, pressure values obtained by the model were used in the sites of Seymareh and Aghbolagh dams and the relative error rates were measured considering the differences between calculated and actual pressures recorded in these operations. In water pressure test, in Seymareh dam, the error values were equal to 4.75, 3.93, 4.8 percent and in the Aghbolagh dam, were 22.43, 5.22, 2.6 percent and in grouting operation in Seymareh dam were equal to 9.09, 32.50, 21.98, 5.57, 29.61 percent and in the Aghbolagh dam were 2.96, 5.40, 4.32 percent. Due to differences in rheological properties of water and grout and based on the overall results, modeling in water pressure test is more accurate than grouting and this error in water pressure test is 7.28 percent and in grouting is 13.92 percent.

최초의 평가시험 방법을 고려한 수격흡수기의 장치에 관한 연구

염문천,한용택 한국화재소방학회 2015 한국화재소방학회논문지 Vol.29 No.1

배관시스템의 불안정한 유동에 의해 생성되는 수격현상은 관내 압력의 과도한 변화, 진동 및 소음을 일으킬 수 있다. 이러한 수격현상은 관로, 펌프 및 밸브등의 시설물에 기계적인 사고를 유발시키는 원인이 되기도 한다. 한편, 국내에서는수격현상으로 인한 피해를 최소화하기 위하여 수격흡수기를 제조 및 사용하여 왔으며, 그동안 별도의 기준이 없어 저가위주로 생산 및 설치되어 왔다. 따라서, 본 연구에서는 수격흡수기 성능에 대한 최소 가이드라인을 제시하기 위하여, 하나의 배관으로 검증 가능한 시험방법, 수계소화설비에서 수격발생을 가정한 시험방법, 개방충격압과 차단충격압으로 구분한 흡수시험 방법, 배관을 분기한 시험시설 구성 방법 등의 다양한 방법들을 통하여 수격흡수기의 성능을 기준화 할수 있는 방법등에 대하여 고안하였다. 그리고, 최종적으로는 U자형 배관과 시험용 추를 이용한 간단한 기계적 방식으로수격흡수기의 수격압 흡수성능을 검증할 수 있는 실험 장치를 최초로 고안하여, 소방용 수격흡수기의 인정기준이 제정되었다. Water hammering created by an unsteady flow in pipeline systems can cause excessive change in pressure, vibration,and noise. So, water hammer analysis is very important for limiting the damage caused to pipeline, pump and valve systemsby operation conditions. On the other hand, water hammer arrester has been manufactured and used in order to minimizethe damage caused by water hammering phenomenon in domestic, and it has been produced and installed as the lowcost-oriented because of being no separate standard in the meanwhile. Therefore, our research team investigated about thestandardization of water hammer arrester performance through the various methods, such as test methods for verificationof one pipe, assuming the occurrence of water hammer in a water-based fire extinguishing system, separated for openingimpact pressure and shut off impact pressure and for a branch pipe in order to make guideline for water hammer arresterperformance. And finally, verified the performance of the water hammer pressure as the simple mechanical way using theU-shaped pipe and a test weight, so KFI standards for the water hammer arrester could be established.