• Tribology and Lubricants
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• v.38 no.2
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• pp.33-40
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• 2022

In this study, we present rotor dynamic analysis and operation test of a turbo expander for a hydrogen liquefaction plant. The turbo expander consists of a turbine and compressor wheel connected to a shaft supported by two hydrostatic radial and thrust bearings. In rotor dynamic analysis, the shaft is modeled as a rigid body, and the equations of motion for the shaft are solved using the unsteady Reynolds equation. Additionally, the operating test of the turbo expander has been performed in the test rig. Pressurized helium is supplied to the bearings at 8.5 bar. Furthermore, we monitor the shaft vibration and flow rate of the helium supplied to the bearings. The rotor dynamic analysis result shows that there are two critical speeds related with the rigid body mode under 40,000 rpm. At the first critical speed of 36,000 rpm, the vibration at the compressor side is maximum, whereas that of the turbine is maximum at the second critical speed of 40,000 rpm. The predicted maximum shaft vibration is 3 ㎛, whereas sub-synchronous vibration is not presented. The operation test results show that there are two critical speeds under the rated speed, and the measured vibration value agrees well with predicted value. The measured flow rate of the helium supplied to the bearing is 2.0 g/s, which also agrees well with the predicted data.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.174-183
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• 2014

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (II).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.160-173
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• 2014

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (I).

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1090-1094
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• 2009

Many problems in geotechnical engineering such as slop failure, debris flow, ground heaving due to embankment, and lateral flow caused by liquefaction are related to large deformation rather than small deformation. Traditional numerical methods such as finite element and finite difference methods have a difficulty to solve such large deformations because they use grids. A particle method was developed for fluid dynamics. The particle method can solve large deformation problems because it uses particles to discretize differential equations. It can also include soil constitutive model and thus solve soil behavior on various boundary conditions. In this study, a particle method, which is based on particles rather than grids, is introduced and used to simulate large deformation including soil failure. The developed method can be applied for various large deformation problems in geotechnical engineering because it incorporates soil constitutive models.

• Journal of the Korean Institute of Gas
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• v.20 no.3
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• pp.46-51
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• 2016

Natural gas liquefaction process which spends a huge amount energy is operated under cryogenic conditions. Thus, many researchers have studied on minimizing energy consumption of LNG plant. However, a few studied for cost optimization have performed. This study focused on the cost analysis for the single mixed refrigerant (SMR) process, one of the simplest natural gas liquefaction process, which has different capacity. The process capacity is increased from 1 million ton per annum (MTPA) to 2.5 MTPA by 0.5 MTPA steps. According to the increase of plant size, only flow rate of natural gas and mixed refrigerant are increased and other operating conditions are fixed. Aspen Economic Evaluator(v.8.7) is used for the cost analysis and six tenths factor rule is applied to obtain multi stream heat exchanger cost data which is not supplied by Aspen Economic Evaluator. Moreover, the optimal plant sizes for different sizes of gas wells are found as the result of applying plant cost to small scale gas wells, 20 million ton (MT), 40 MT, and 80 MT. Through this cost analysis, the foundation is built to optimize LNG plant in terms of the cost.

• Journal of the Korean Geotechnical Society
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• v.28 no.10
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• pp.5-16
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• 2012

Geotechnical buried structures with relatively light weight have been suffering from uplift damage due to liquefaction in the past earthquakes. The factor of safety approach by Koseki et al. (1997a), which is widely used in seismic design, predicts the triggering of uplift. However, a method for "quantitative" estimates of the uplift displacement has yet to be established. Estimation of the uplift displacement may be an important factor to be considered for designing underground structures under the framework of performance-based design (ISO23469, 2005). Therefore, evaluation of the uplift displacement of buried structure in liquefied ground during earthquakes is needed for a performance-based design as a practical application. In order to predict the uplift displacement quantitatively, a simplified method is derived based on the equilibrium of vertical forces acting on buried structures in backfill during earthquakes (Tobita et al., 2012). The method is verified through comparisons with results of centrifuge model tests and damaged sewerage systems after the 2004 Niigata-ken Chuetsu, Japan, earthquake. The proposed flow diagram for performance-based design includes estimation of the uplift displacement as well as liquefaction limit of backfill.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.1013-1019
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• 2011

In this paper, simulation works for a multi-stage cascade refrigeration cycle using propane, ethylene and methane as refrigerants have been performed for the liquefaction of natural gas using Peng-Robinson equation of state built-in PRO/II with PROVISION release 8.3. The natural gas feed compositions were supplied from Korea Gas Corporation and the flow rate was assumed to be 5.0 million tons per annual. Supply temperature for propane refrigerant was fixed as $-40^{\circ}C$, that for ethylene refrigerant as $-95^{\circ}C$, and that for methane refrigerant as $-155^{\circ}C$. For the multi-stage refrigeration cycle, three-stage refrigeration was assumed for propane refrigeration cycle, two-stage refrigeration for ethylene refrigeration cycle and three-stage refrigeration for methane refrigeration cycle. Natural gas was finally cooled and liquefied to $-162^{\circ}C$ by Joule-Thomson expansion. Conclusively, 91.71% by mole of the natural gas liquefaction ratio was obtained through a cascade refrigeration cycle and Joule-Thomson expansion and 0.433 kW of compression power was consumed for the liquefaction of 1.0 kg/hr of natural gas.

• Transactions of the Korean hydrogen and new energy society
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• v.9 no.3
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• pp.93-100
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• 1998

The ortho-para $H_2$ catalytic conversion equipment has been developed to reduce the evaporation loss from stored liquid hydrogen. The ortho-para $H_2$ conversion heat is evaluated at liquid nitrogen temperature. This problem is of particular interest in the design of the ortho-para $H_2$ converter in a hydrogen liquefaction system. The ortho-para $H_2$ conversion equipment consists of a catalytic converter, a precooler, and a liquid nitrogen bath. 30-90 cc of $Fe(OH)_3$ are employed as a catalyst in the present converter. The conversion heat and conversion effectiveness are evaluated when mass flow rate of hydrogen is in the range of 0.05-l.6 g/min. It is found that the ortho-para conversion heat is increased while conversion effectiveness is decreased as the mass flow rate of hydrogen is increased. Both the ortho-para conversion heat and conversion effectiveness are increased with an increase in the amount of the catalyst.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.5
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• pp.347-355
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• 2021

This paper is a study on the thermal design of printed circuit heat exchanger (PCHE) to supply cryogenic high pressure liquid hydrogen stored from hydrogen liquefaction process by using computational fluid dynamics (CFD). This PCHE should be thermally designed to raise the temperature of cryogenic liquid hydrogen to a desired temperature and also to be anti-icing to avoid any local freezing in hot channel. This research presents the effect of inlet velocity and inlet temperature of hydrogen, and the effect of flow configurations of co/counter-flow on thermal design of PCHE heat exchanger based on various CFD simulation analysis.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.173-181
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• 2006

A Two Mobilized-Plane Model is proposed for monotonic and cyclic soil response including liquefaction. This model is based on two mobilized planes: a plane of maximum shear stress, which rotates, and a horizontal plane which is spatially fixed. By controlling two mobilized planes, the model can simulate the principal stress rotation effect associated with simple shear from different $K_0$ states. The proposed model gives a similar skeleton behaviour for soils having the same mean stress, regardless of $K_0$ conditions as observed in laboratory tests. The soil skeleton behaviour observed in cyclic drained simple shear tests, including compaction during unloading and dilation at large strain is captured in the model. Undrained monotonic and cyclic response is predicted by imposing the volumetric constraint of the water on the drained or skeleton behaviour. This constitutive model is incorporated into the dynamic coupled stress-flow finite difference program of FLAC (Fast Lagrangian Analysis of Continua). The model was first calibrated with drained simple shear tests on Fraser River sand, and verified by comparing predicted and measured undrained behaviour of Fraser River sand using the same input parameters.