Inlet Side Research Articles

Analysis of the Tunnel Face Failure during the Excavation and Evaluation of Excavation Method and Sequential on Ciuyah Tunnel, Lebak Regency, Banten Province

The difference in geological and geotechnical conditions during design and implementation are frequent due to the lack of data collection and diverse rock variations. An important step in designing the excavation method, stages, and support system are determining the rock mass’s actual condition. Inaccuracy in evaluating rock mass quality can cause a collapse during tunnel excavation. This study used an example of a collapse case on the inlet side of the Ciuyah tunnel. The classification system used in the design was the JSCE 1975, but collapses occurred at several locations during excavations. An additional assessment of the tunnel stability was carried out by doing surface surveys and evaluations in STA 0+123 using the RMR89, GSI, and JSCE 2016 classification systems. The rock mass in this location consists of tuffaceous claystone and tuffaceous sandstone with very poor quality. The empirical evaluation showed that Daraei’s multigraph could be used to determine the collapse pattern for very poor rock. For the excavation method, stages, and support systems, it is preferable to apply the RMR classification system with consideration for the maximum stand-up time. This research aims to provide information that may be used for other projects with similar geological circumstances.

Experimental study of a hydraulic model of the side inlet and outlet of a pumped storage power station

Inlets/outlets have bi-directional characteristics and complex structures, which have important implications for practical operational safety and efficiency. In this paper, the hydraulic characteristics of the lateral inlet/outlet of a pumped storage power station are studied by means of model tests. The flow velocity distribution at the leading edge of the inlet/outlet orifice and the barrage section is more uniform, and the flow velocity distribution at the left, middle, and right of each orifice is the same. The formation of swirl is related to the relative submergence depth s/d and the Froude number Fr, with the inlet/outlet Fr< 0.23, relative submergence depth s/d> 0.5 and it has no harmful eddies.

Simulation of Air Ingestion in a Mechanical Seal With Inward Pumping Spiral Grooves

Abstract Inward pumping spiral groove seals are used in many applications, such as transmission gearboxes or electric vehicles, as they can provide zero leakage and very low operating friction. The spiral grooves are connected to the low pressure side (typically atmosphere) and pump the fluid inward that is to say toward the high pressure side (inlet). If the rotational speed is high enough, the low pressure fluid (air) completely occupies the sealing area and is used as a low friction lubricant. However, for lower operating speeds or higher fluid pressures, the seal can be lubricated by both fluids simultaneously. This occurs particularly during start-up and shutdown. In this work, a numerical simulation of the two phases in the sealing gap of an upstream pumping spiral groove seal during start-up is performed. The establishment of the film is analyzed and the effect of the rotational speed and operating pressure on the fluid composition (air and liquid) in the sealing interface is studied. For the analyzed seal, it is shown that the amount of air pumped in the sealing area is controlled by the duty parameter.

Thermal performance of a low-profile cross-ventilated freestall dairy barn with evaporative cooling pads in a hot and humid climate.

A commercial low-profile cross-ventilated system (LPCV) free-stall barn with evaporative cooling pads on the air intake side was used to assess the potential of cross-ventilation with evaporative cooling to alleviate heat stress in lactating dairy cows. A total of 5712 records (238 days × 24 h) of air temperature (AT) and relative humidity (RH) values were collected. In order to state the effectiveness of the ventilation system and potential heat stress, the temperature humidity index (THI) and enthalpy (h) were calculated outside and inside the LPCV barn. The cooling capacity of the LPCV system is greater in conditions of low humidity, and the difference between the values of the internal and external temperature reached -12 °C. The LPCV reduced exposure to heat stress, increasing the time cows spent in thermoneutral conditions. This system could reduce the occurrence of temperature above 25 °C from 33 to 5% and 11% in sections A (represents the inlet side of the barn) and D (represents the outlet side of the barn), respectively. On the other hand, the LPCV kept a high and constant rate of RH throughout the day. The average inside and outside AT were significantly different, but differences in temperature were observed across the width of the barn. Analyzing the barn by the indexes, the THI showed that the barn promoted cows more time confined under non-stressful thermal conditions (between 83.8 and 90% vs 68.7%) and stress period much lower compared to the external environment (between 10 and 16.2% vs. 31.3%). The enthalpy index showed that there was not much difference between the internal and external environments. The LPCV system is another installation alternative for raising dairy cow in a hot and humid climate.

Study on Coal Spontaneous Combustion Dangerous Zone Under Different Air Leakage in the Shallow Buried Coal Seam Fissure

ABSTRACT In the western region of China, the coal seam is shallowly buried. Overburden fissures readily develop upwards through the surface, and provide channels for wind to flow into the gob. Here, a model for the coal spontaneous combustion in gob caused by air leakage from fissures in shallow coal seams was established. The accuracy of the model is verified by comparing the oxygen concentration on the inlet and outlet sides of the field monitoring data with the results of numerical simulation. In addition, the distribution of oxygen concentration and wind speed in gob and their influence on spontaneous combustion dangerous zone were studied by numerical simulation when the air leakage volume varied from low to high (36–600 m3/min). The results showed no significant change in the distribution ranges of oxygen concentration and wind speed along the Z-direction when there is no air leakage from the gas conducting fissure in the gob. With the increase of air leakage, the oxidation zone defined by oxygen concentration moves to the depth of the gob, and the oxygen concentration near the fissure increases. In addition, the oxidation zone defined by the wind speed moves significantly deeper into the mining area, and the wind speed is higher at the location corresponding to the fissure close to the working face, and the overall symmetrical distribution of the flow field in the mining area. According to the oxygen concentration and wind speed, the size of dangerous zone initially increased, before decreasing and finally plateauing.

A numerical study on microfluidic devices to maintain the concentration and purity of dielectrophoresis-induced separated fractions of analyte.

Determining the physical and chemical properties of biologically important particles such as cells, organelles, viruses, exosomes, complexes, nucleotides, and proteins is needed to understand their function. These properties are determined with common analytical tools (mass spectrometry, cryo-EM, NMR, various spectroscopies, nucleotide sequencing, etc.) whose function can be improved when samples are pure and concentrated. Separations science plays acentral role in conditioning samples, ranging from low-resolution benchtop operations like precipitations or extractions to higher-resolution chromatography and electrophoresis. In the last two decades, gradient insulator-based dielectrophoresis (g-iDEP) has emerged as a high-resolution separation technique capable of highly selective enrichment of cells, viruses, exosomes, and proteins. Specific evidence has been shown that pure homogeneous and concentrated fractions of cells and exosomes can be generated from complex mixtures. However, recovering those fractions for analysis has not been developed, limiting the technique to an analytical rather than a preparative one. Here, a finite element analysis was undertaken to identify geometries and operational parameters to efficiently remove the enriched fraction while retaining maximum concentration and providing total mass transfer. Geometric factors (e.g., side channel width and distance from the gradient-inducing gap) were studied, along with the addition of a second inlet side channel. Two flow-generating mechanisms-electroosmosis and hydrostatic pressure-were evaluated for semi-optimized device designs, including a comparison of the one- and two-inlet designs. Simulations indicate effectively one hundred percent mass transfer and a concentration increase by an order of magnitude for several device configurations and operational parameters.

Performance investigation of a novel composite channel considering tapered-3D wavy structure

In this study, a novel composite flow channel was proposed to address issues of gas transport obstruction, poor water removal performance, high pressure drop, and low current density within the cathode flow channel of proton exchange membrane fuel cells (PEMFCs). The flow channel could optimize performance by combining a tapered design with a 3D wave structure. Based on a controlled variable method and three-dimensional (3D) multiphase computational fluid dynamics (CFD) simulations, the effects of the flow channel inlet and outlet side length ratio LD/d, amplitude A, and wavelength λ on PEMFC performance were investigated. As shown by results, appropriate decrease of LD/d, increase of A, and reduction of λ could increase convective mass transfer in the flow channel, improve the uniformity of the reaction gas distribution, and enhance the Water removal performance. Moreover, the optimal performance was achieved when LD/d=1/3, A = 0.3 mm and λ=4 mm for PEMFC. Finally, when the cell output voltage was 0.4 V, the current density of the novel composite flow channel was up to 6.26% higher than that of the traditional 3D wave-shaped flow channel.

Examining heat transfer of a buried pipe heat exchanger in arch tunnel lining with protection engineering

Cooling towers and internal reservoirs are two conventional heat transfer methods used in protection engineering. However, they have the drawbacks of easy exposure and limited capacity. Although the traditional ground source heat pump system can become a new heat transfer method, its high installation cost and space requirements are obstacles to the development of this technology. To address this problem, the heat exchange pipe of the ground source heat pump system being directly laid in the tunnel lining was proposed in this study. A heat transfer performance test platform for a lined buried pipe heat exchanger based on an arch tunnel was built, and the water velocity, wind velocity, and temperature of each measuring point were recorded under appropriate working conditions. The effects of the inlet water temperature, inlet water velocity, ventilation velocity, and initial soil temperature on the heat transfer performance were analyzed. The results have shown that the heat transfer performance of the tunnel reached its maximum when system operation commenced and then decreased gradually with time, and the rate of decrease gradually slowed. Along the radial direction of the tunnel, the shorter the distance to the buried heat exchanger, the greater the increase in soil temperature, and the shorter the time for the temperature to reach the peak value. As the distance increased, the temperature gradient gradually decreased. Along the circumferential direction of the tunnel, the lining temperature on the inlet side of the buried heat exchanger was higher than that on the outlet side. The temperature distribution on both sides of the symmetrical surface of the tunnel was not uniform, resulting in additional temperature stress in the horizontal direction. The time required for the heat transfer capacity of the tunnel to return to its initial value was approximately eight times that of the system. Compared with the ventilation and water velocities, the inlet water temperature and initial soil temperature had a greater impact on heat transfer. The heat-transfer law of an arch tunnel differs from that of a circular tunnel. There were some deviations when comparing the experimental data of the circular tunnel with those of the actual arch tunnel.

Sources of organic matter and carbon stocks in two mangrove sediment cores and surface sediment samples from Qinglan Bay, China

The carbon stocks (Corg stocks) in mangrove sediments and the distribution and source changes of sedimented organic matter in Qinglan Bay are not understood as the mangrove forests decrease. In this paper, we collected two sediment cores in the interior mangrove and 37 surface sediment samples from mangrove-fringe, tidal flat and subtidal habitats and then analysed the total organic carbon (TOC), total nitrogen (TN), and the stable organic carbon isotope (δ13C) and nitrogen isotope (δ15N) in the sediment samples to obtain the organic matter sources and carbon stocks in two different mangrove sediment cores from Qinglan Bay. The δ13C and TOC/TN values showed that mangrove plants and algae were the main sources of organic matter. Relatively high contributions of mangrove plants (>50 %) were distributed in the mangrove areas in Wenchang estuary, the northern region of Bamen Bay and the eastern side of the Qinglan tidal inlet. The enriched δ15N values might be related to anthropogenic nutrient inputs, including increased aquaculture wastewater, human sewage and ship wastewater. The Corg stocks in cores Z02 and Z03 were 357.79 Mg C ha−1 and 265.78 Mg C ha−1, respectively. This Corg stock difference might have been related to the salinity and the benthos activities. The high Corg stock values measured in Qinglan Bay were caused by the mangrove maturity and stand age. The total Corg storage of the mangrove ecosystem in Qinglan Bay was estimated to be approximately 263.93 Gg C. This study contributes to organic carbon stocks and sources of sedimented organic matter in global mangroves.

Calculation and analysis of fluid-solid coupling of rocket sled supersonic water bucket braking process

In order to solve the problem of structural damage during the braking process of a rocket sled supersonic water bucket, which affects the braking effect, it is proposed to use the FEM fluid-solid coupling calculation technology to analyze the process of the water bucket entering the water brake. The fluid-solid coupling calculation results show that the limit braking state After the water bucket enters the water brake for 0.06ms, the stress at the entrance position exceeds the yield limit of the material, and the structure is severely deformed and damaged; under normal braking conditions, the water bucket enters the water brake for 0.4ms, the plate at the entrance of the bucket bends, and the structure is seriously deformed at 2ms, The structure is destroyed at 3ms. Using the penalty function fluid-structure coupling method, the numerical analysis of the model water bucket was carried out under two working conditions. Due to the unreasonable design of the bucket, the bucket entrance deformed and destroyed during braking. It is recommended to increase the structural strength of the water inlet side plate.

Multi-Inlet Spheroid Generator for High-Throughput Combinatorial Drug Screening Based on the Tumor Microenvironment.

Tumor spheroids are powerful tools for drug screening and understanding tumor physiology. Among spheroid formation methods, the hanging drop method is considered most suitable for high-throughput screening (HTS) of anticancer drugs because it does not require surface treatment. However, it still needs to increase the liquid-holding capacity because hanging drops often fall due to the increased pressure caused by the addition of drugs, cells, etc. Here, we report a multi-inlet spheroid generator (MSG) enabling the stable addition of liquid-containing drugs or cells into a spheroid through its side inlet. The MSG was able to load additional solutions through the side inlet without increasing the force applied to the hanging drop. The volume of the additional liquid was easily controlled by varying the diameter of the side inlet. Furthermore, the sequences of the solution injections were manipulated using multiple side inlets. The feasibility of the MSG in clinical application was demonstrated by testing the efficacy of drugs in patient-derived cancer (PDC) cells and controlling the stromal cell ratio in the tumor microenvironment (TME) containing spheroids. Our results suggest that the MSG is a versatile platform for HTS of anticancer drugs and recapitulating the TME.

Comparative experimental analysis of potato slice drying using a multiple phase change material cascaded modified indirect solar dryer and conventional indirect solar dryer

In the present research, multiple phase change materials (M-PCMs) have been utilized to enhance the performance of conventional indirect solar dryer (ISD). The bheem paraffin and paraffin wax having phase change temperatures of 50–55 °C and 60–62 °C were cascaded in rectangular chambers at beneath of absorber plate at the inlet and outlet side up to nearly half the length of the absorber plate of the solar air heater (SAH), known as a modified ISD. The experiments were carried out on conventional and modified ISD simultaneously under the climate of Valsad (20.61° N, 72.91° E), Gujarat, India. An atmospheric air with a velocity of 15 m/s was flown through conventional and modified ISD. In the first batch, 0.5 kg of pre-processed potato slices were placed in the bottom and top trays of conventional and modified ISD whereas in the second batch, 0.3 kg was placed on each tray. A 2 h and 1 h faster drying of potato slices was achieved in the bottom and top trays for the first batch in modified ISD than in conventional ISD. In the second batch, nearly 92.11% and 54.35% drying of potato slices in the bottom and top trays was achieved in modified ISD, which was 269.92% and 227.41% higher than conventional ISD. During 12 h of the drying operation, a total of 1.13 kg of water evaporated from the potato slices in modified ISD compared to 0.87 kg in conventional ISD. Compared to conventional ISD, an enhancement of 22.29% and 7.92% in SAH efficiency without and with considering blower power, an enhancement of 29.69% in overall drying efficiency, and a reduction of 22.87% in specific energy consumption were achieved for modified ISD. The use of M-PCMs in conventional ISD significantly enhances the drying of potato slices during the sunshine as well as off-shine hours and enhances the performance of conventional ISD.

Analysis on flow structure in a vortex pump under all flow rates

Abstract Vortex pumps are usually designed based on its inner flow model. Currently, the flow models of vortex pump just consider flow rate at the design condition, which results in low efficiency under off-design flow rates in practical engineering. Therefore, the main objective of this article is to build a flow model that takes into account the impact of flow rates. To reveal the flow mechanism of vortex pump, we provide refined flow field simulations for a vortex pump. Performance experiments were conducted to validate the numerical simulation method. The study found that the vortex structure in the non-blade cavity can be regarded as a Rankine-like vortex. The inflow range is limited to the hub diameter (45 mm), smaller than the volute inlet diameter (85 mm). The action radius of the forced vortex gradually decreases from the impeller side to the inlet side. The maximum radius of the forced vortex on the impeller side is determined by the impeller diameter. As the flow rate increases, the action radius of the forced vortex on the inlet side gradually increases, while the axial length of the vortex in the inlet pipe gradually decreases. Based on the study of internal flow, a new flow model is proposed.

Dynamic modeling, optimization and exergy analysis of novel membrane reactor for enhanced olefin and pure hydrogen production via heavy paraffin dehydrogenation

Heavy paraffin dehydrogenation (HPD) is an equilibrium limited process for olefin production; therefore, selective H2 removal enhances olefin production and simultaneously produces pure H2. A hydrogen-selective membrane reactor may be utilized for this process. Sensitivity analysis reveals that reaction side inlet temperature/pressure and feed molar flow rate greatly affect the membrane reactor performance. H2 removal lowers reacting gas temperature/pressure and total molar flow rate and increases heavy paraffin (HP) consumption as well as olefins, H2, aromatics, light paraffins, and dienes production. Equilibrium shift increases rate, H2 permeation through membrane, and pure H2 production. Results of this study reveal that the average olefin production rate and selectivity in optimized membrane reactor are 14.45 and 6.24% higher than those of radial flow traditional reactor. Membrane reactor increases olefin production by 381.0 ton and produces 602.85 ton of pure H2 in a cycle. Membrane integration into the reactor does not negatively affect its exergy efficiency.

Enhanced mixing quality of ring-type electroosmotic micromixer using baffles

In this study, an attempt has been taken to enhance the mixing efficiency in a micromixer of two different concentration fluids using electrokinetic effects such as electroosmotic flow. Four microelectrodes are located at specific locations on the outer surface of the one ring-shaped micromixer chamber. In addition, rigid baffles at the inlet side of the microchannel have been considered to enhance the mixing quality. The computation is performed using the finite element-based solver. The influences of different parameters such as average inlet fluid velocity (U0), frequency of the alternating current (f), the voltage amplitude of the alternating current (V), angle of inclination of the baffles (α), and the orientation fashion of the baffles at the inlet side have been investigated to achieve best mixing quality. This technique produces rapid mixing in the microchamber. Higher mixing quality can be achieved by considering the baffles in a specific orientation. The best mixing quality (99.67%) is obtained at the low inlet velocity of 0.05 mm/s. On the contrary, the lowest mixing quality (15.78%) is concerned with the higher inlet velocity with a high frequency of AC electric field.

Study on Multifield Migration and Evolution Law of the Oxidation Heating Process of Coal Spontaneous Combustion in Dynamic Goaf.

To study the dynamic evolution law of the oxidation heating process of coal spontaneous combustion in the goaf during the advancing process of the working face, a dynamic model of oxidation heating of coal spontaneous combustion in the goaf was established on the basis of deformed geometry. Through numerical simulation research, the evolution and migration laws of seepage field, oxygen concentration field, temperature field, and high-temperature area of coal spontaneous combustion in the goaf during the advancement of the working face was obtained. The results indicate that the distribution of the bulking coefficient, porosity, and permeability of the falling coal and rock mass in the goaf is nonuniform. They are relatively large in the area near the working face and the inlet and return airway and remain relatively unchanged with the advancement of the working face, but they are constantly decreasing in the location of the gob in the middle and deep. The oxygen concentration in the goaf presents an asymmetrical distribution. The oxygen concentration distribution area on the inlet side is wider than that on the return air side. At the same depth of the goaf, the oxygen concentration gradually decreases from the inlet side to the return air side; after the advancement distance exceeds 200 m, the air leakage in the goaf basically disappears, and the oxygen concentration decreases to zero. The high-temperature area of coal spontaneous combustion oxidation in the goaf was mainly concentrated on the air inlet side and extended toward the return air side. The advancing speed has a significant effect on the oxidation heating process of coal spontaneous combustion in the dynamic goaf. Under the same propulsion distance, when the advancing speed is 6 m/day, the highest temperature in the goaf is about 40 °C, and when the advancing speed is 2 m/day, the highest temperature in the goaf is as high as 120 °C. The smaller the advancing speed, the higher the heating rate of the goaf and the closer the high-temperature area to the working surface. The higher the advancing speed, the lower the temperature of the high-temperature point of the goaf and the greater the depth of the high-temperature point of the high temperature area; when the advancing speed is 2 m/day, the highest temperature point in the goaf is 70 m away from the working face, whereas when the advancing speed is 6 m/day, it reaches 174.6 m.

Computational fluid dynamics modeling of floating treatment wetland retrofitted stormwater pond: Investigation on design configurations

Floating Treatment Wetland (FTW) is a cost-effective and easy-to-retrofit device for stormwater treatment. Its treatment efficiency largely depends on the fraction of inflow entering FTW and the residence time within it. Thus hydrodynamics play a crucial role, which is affected by the design configurations of FTW and stormwater pond. Despite a spike in research on FTWs, very little is known about how various design configurations affect treatment efficiency by an FTW. Our study hypothesizes that relative positions of FTW geometry, FTW position and pond inlet–outlet have impact on the hydrodynamics and as a consequence, treatment efficiency. To explore these design features, we employed computational fluid dynamics (CFD) modeling conducted in ANSYS Fluent, validated by experimental data to examine the impact of the aforementioned design features. The results revealed that circular FTW geometry positioned near inlet coupled with center inlet–side outlet configuration achieved the highest removal (94.8%) for a non-dimensional removal rate of krtHRT = 20 (kr is the first order removal rate in per day, tHRT is the nominal hydraulic residence time of the pond in days). Far side inlet–side outlet configuration performed the worst due to profound promotion of short-circuiting. FTW positioned near inlet performed better (61.8% mass removal on an average) than center (42.7%) and near outlet positions (54.1%) for krtHRT = 20. Sensitivity analysis revealed that the treatment efficiency is most sensitive to inlet–outlet configurations. The design implications of this study will help practitioners achieving better water quality and ecological improvement goals.

Numerical simulation study on the influence of air leakage on oxygen concentration in goafs of fully mechanized caving mining with shallow buried and large mining height

In order to reveal the influence of air leakage on oxygen concentration in goafs of fully mechanized caving mining with a shallow buried and high mining height, the air leakage of No.122108 working face in Caojiatan coal mine in different seasons was tested by the SF6 tracer gas test method. Based on the result of the air leakage test, the “three zones” of spontaneous combustion in the goaf were simulated using Ansys Fluent fluid dynamics software, and the simulated result was compared with that of the field test. The result shows that the vertical air leakage of the working face is serious, the wind speed is high, and the air leakage rate is up to 86.96%. The air leakage rate is higher in winter and lower in summer. The air leakage intensity decreases from the air inlet side to the air return side through the middle of the goaf. The range of the oxidation heating zone of the goaf is 98–245 m on the air inlet side and 33–96 m on the air return side. The numerical simulation result is well consistent with the field test data. The research conclusion can guide fire prevention and the extinguishing of No.122108 working face and lay a foundation for the prevention and control of spontaneous fire in goafs of fully mechanized caving mining with a shallow buried and high mining height.

Prediction on the axial water thrust characteristics of pump turbine runner under partial load

For the high head pump turbine, the unit instability during its operation mainly dues to the hydraulic vibration inside the machinery, which will cause the mechanical fatigue failure under certain circumstances. In this paper, the flow pattern and the runner axial water thrust in turbine model under partial load were analyzed by numerical simulation. The internal flow field instability and vortex load characteristics of the runner were analyzed to obtain the reasons for the different axial water thrust characteristics of the runner under two different loads. The results showed that due to the reduction of the guide vane opening, the flow rate is smaller at 50% load, and the free flow vortex structure on the high-pressure side of the runner blade inlet strengthens the impact of the water flow on the runner. Moreover, when the pressure difference between the runner blades decreases and the axial water thrust of the blades decreases, the total axial water thrust of the runner decreases and fluctuates frequently with time.

Characteristics of Porosity Distribution and Gas Migration in Different Layers of Comprehensive Working Face Goaf

The fracture field and permeability distribution model of comprehensive working face goaf was integrated upon the theoretical examination to investigate the fracture field distribution law of goaf and gas migration and accumulation characteristics, and this model has been applied to the mathematical model of gas migration and accumulation in goaf. The ANSYS FLUENT numerical simulation software was used to obtain the characteristics of gas migration and accumulation in goaf and its influencing factors and analyze the applicability of solving the features of gas migration and proliferation using the porosity model of layer division in goaf. The results were as follows: the porosity around the caving zone was a little big, whereas the porosity in the middle was a little small. The porosity was almost equal along the inclination and strike in a symmetrical distribution. The porosity occurred at the fracture zone with an “O” shape. As the gob layer height increased, the porosity tended to be small. The maximum value of the porosity of the goaf would shrink to the middle of the goaf with the increase of gob layer height. The gas mass fraction along the goaf inclination showed the growth characteristics of “exponential function”, the gas mass fraction along the goaf strike on the air inlet side showed the growth characteristics of “Boltzmann function”, and the gas mass fraction along the goaf strike on the air outlet roadway side manifested the growth characteristics of “linear function”. The main influencing factors were air leakage speed, negative pressure, and porosity distribution. The distribution model of porosity and permeability of different layers of gob can more accurately simulate the characteristics of gas migration and storage.