The energy absorption characteristic of steel tube material and concrete material is an important indicator to reflect the impact resistance of circular concrete-filled steel tubular (CFST) members. ...In order to efficiently simulate the material energy absorption of the steel tube and concrete under lateral impact, a nonlinear finite element model considering the material strain rate of the circular CFST member was established and validated based on the drop weight tests. Then, the energy absorption mechanism of circular CFST members subjected to lateral impact was investigated including the revelation of the energy absorption process and the determination of the energy absorption distribution for the steel tube material and concrete material, which are obtained respectively based on the comprehensive analysis of dynamic response and innovative establishment of the segmented numerical model. In addition, the influence of impact momentum on energy absorption process and the effect of impact location on energy absorption distribution are further carried out. The observations of this investigation can provide reference for the anti-impact design and damage reinforcement of circular CFST members subjected to lateral impact.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We have conducted hydraulic experiments in an open channel with cubic and rectangular shaped solid blocks on the slope for investigating the boulder transport process by tsunami. In our experiments, ...the block was mainly seen to be transported by a bore due to rolling or saltation rather than by sliding. Previous models for the boulder transport by tsunamis assumed sliding as a mode of transport for the boulder. Therefore, these models underestimated the distance of the boulder moved by the tsunami when it was transported due to rolling or saltation. In this study, we have developed a practical model for the transport of a boulder by tsunami, which takes into account the various transport modes. We introduce an empirical variable coefficient of friction by assuming that the coefficient decreases with decrease in ground contact time when the block was transported by rolling or saltation. With the aid of this parameter, the model can explain various modes of transport, i.e., sliding, rolling, and saltation, and reproduces the experimental results well. We further applied this improved model to a tsunami boulder at Inoda area in Ishigaki Island, Japan, which was transported by the 1771 Meiwa tsunami. The calculated distance of transport of the boulder was approximately 650 m, which is consistent with the description in the historical document. Based on our calculations, we estimated hydraulic values of the tsunamis. Estimation of such hydraulic values is important for understanding the behavior and power of the historical tsunamis, besides aiding future disaster mitigation efforts.
Groundwater resources are increasingly exposed to significant overexploitation in many parts of the world, markedly in Iran, one of the most arid areas. Social, economic and environmental aspects ...including water quality and quantity concerns are necessary for sustainable management of water resources. The aim of the current study was to investigate the changes in groundwater levels and quality in the Isfahan-Borkhar aquifer. Groundwater fluctuation contour lines maps provided in Geographic Information System (GIS) during 1971–2005 in this area indicate that excessive extraction of wells has led to major decline in water levels and a marked increase in concentration of Total Dissolved Solids (TDS). The Groundwater Modeling System, a three-dimensional MODFLOW model paired with MT3D, was utilized to survey the aquifer characterization in the area. In the first step, usage high amount of hydrological and geological data, the conceptual model was developed and calibrated in both steady and transient states. The results of the calibration showed that the error between calculated and observed levels was in optimal level. Subsequently, since rainfall is decreasing annually in the study area and the aquifer is in danger of drought, and uncontrolled exploitation of wells has led it to a crisis, two scenarios were considered to simulate quantity changes in the aquifer: Simulation in drought and rainfall reduction. The results indicate that during both the drought period and increasing exploiting from the pumping wells, the level of water has fallen 0.5–0.1 m/s annually, and it will destroy the aquifer. Finally, the calculated hydraulic heads and velocity of flow of groundwater in the aquifer are recovered in the mass transport modelling package MT3D to find the concentration of TDS in the groundwater. Simulation results indicate that concentration of TDS is with far more amount in the areas around the lake located in central parts due to evaporation of Borkhar-Isfahan Aquifer and geological structure of the region. Scenarios considered for prediction by transport model show that concentration of TDS would enhance if the current situation continues; however, this is mainly influenced by hydrology and geology of the area.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The effective thermal conductivity (ETC) of porous rocks is primarily controlled by the matrix thermal conductivity (MTC) and the thermal conductivity of the pore fluid as a function of porosity. ...Rock ETC has been investigated widely, however, information on MTC is rather sparse. This study proposes a new approach using a numerical model to determine the MTC of porous rocks by parameter fitting to the measured ETC. The model represents realistic rock textures as detailed information on grain and pore geometries was obtained from microscopic images of thin sections. MTC fitted from water saturated condition (water as pore fluid) showed plausible values between 4.9 and 7.6W/(m∙K), while MTC values from dry condition (air as pore fluid) were disproportionate, except for one model with consistent MTC for both conditions. This supports the idea that at constant temperature and pressure, MTC is an intrinsic property independent of fluid saturation. For this reason, MTC from water saturated condition was used to calculate dry ETC. The model showed lower dry ETC than the lab measurements, but within a reasonable range for dry sandstones. Investigation of ETC regarding saturation degree revealed that the samples may contain 12%–45% residual moisture, which explained the higher measured dry ETC. Additionally, the models allowed observation of textural influences, showing that grain size, distribution, and connectivity affected the heat conduction of porous rocks.
•Microscale numerical modeling of rock thermal properties with realistic geometries.•Rock thermal conductivity can vary within a few millimeters.•Matrix thermal conductivity can be determined by inverse parameter fitting.•Dry samples contained residual moisture of 12%–45%.•Matrix thermal conductivity of sandstone samples ranged between 4.9 and 7.6W/(m·K).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Two-phase numerical model of falling film evaporation with co-current gas-phase.•Full elliptic governing equations with fundamental interface conditions.•New excess moisture condensation model to ...eliminate supersaturation.•Thermal and solutal buoyancy effects demonstrated in recirculating flow.•Careful comparisons with previous work and new parametric study results for a water film.
A fully coupled elliptic numerical method is used to conduct a detailed numerical analysis of laminar water falling film evaporation with a co-current laminar gas vapour mixture flow inside a partially heated vertical parallel plate channel. In order to obtain a fully coupled implicit solution, a complete set of elliptic two-phase two-dimensional governing equations is solved. The liquid-gas interface is obtained over a non-orthogonal structured moving mesh (grid) during the solution process. An excess moisture condensation model is proposed as a novel numerical method to address supersaturation in the system. Comparisons with the previous studies are made to verify the accuracy and capability of the present numerical model. The effects of the liquid and mixture Reynolds numbers variation on the hydrodynamic and thermal characteristics of the evaporation process inside the partially heated channel are investigated. Thermal and solutal buoyancy effects are seen in the form of recirculating flow in the gas phase.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In-vessel retention (IVR) of molten corium is a key severe accident management strategy adopted in pressurized heavy water reactors (PHWRs) and is recognised as the only option to manage a complete ...core melt scenario. Since the PHWR calandria vessel is completely surrounded by a large pool of water, the vessel itself is expected to act as a ‘core catcher’. The success of IVR strategy depends up on whether the actual heat flux imparted by molten corium is less than the critical heat flux (CHF). In the present work, a hydrodynamics model is developed and applied to obtain the variation of CHF along outer surface of 220 and 700 MWe Indian PHWR calandria vessel and tube. The thermal margin available for success of IVR strategy is evaluated. The governing equations for external buoyancy driven boundary layer flow are derived and solved in non-dimensional form. The details of the mathematical model, benchmarking exercises, validation aspects and application of the model to PHWR calandria vessel and tube are discussed. Parametric studies are presented to bring out the influence of diameter, system pressure, subcooling of water, depth of submergence and slip ratio on the variation of CHF along the cylindrical vessel surface.
•A CHF model based on macro-layer dryout phenomena is developed for external buoyancy driven boundary layer flow over cylindrical surfaces.•It is validated with experimental data from several facilities reported in literature.•Parametric studies are carried out to bring out the influence of geometrical and thermal hydraulic variables on CHF.•CHF for Indian PHWR calandria vessel and tubes are estimated to assess thermal margin available for preventing failure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Detailed numerical model of free-piston engine generator is presented.•Sub models for both starting process and steady operation are derived.•Simulation results show good agreement with prototype ...test data.•Engine performance with different starting motor force and varied loads are simulated.•The efficiency of the prototype is estimated to be 31.5% at a power output of 4kW under full load.
This paper focuses on the numerical modelling of a spark ignited free-piston engine generator and the model validation with test results. Detailed sub-models for both starting process and steady operation were derived. The compression and expansion processes were not regarded as ideal gas isentropic processes; both heat transfer and air leakage were taken into consideration. The simulation results show good agreement with the prototype test data for both the starting process and steady operation. During the starting process, the difference of the in-cylinder gas pressure can be controlled within 1bar for every running cycle. For the steady operation process, the difference was less than 5% and the areas enclosed on the pressure–volume diagram were similar, indicating that the power produced by the engine and the engine efficiency could be predicted by this model. Based on this model, the starting process with different starting motor forces and the combustion process with various throttle openings were simulated. The engine performance during stable operation at 100% engine load was predicted, and the efficiency of the prototype was estimated to be 31.5% at power output of 4kW.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Depending on the repository concept, buffer materials around the canister may play an important role for the performance of deep geological repositories for high-level radioactive waste (HLW). ...Coupled thermo-hydro-mechanical (THM) processes are initiated in the buffer material, as heat produced by the HLW typically causes an initial drying of this sealing layer, which may be followed by re-saturation with fluid from the host rock. In this study, a fully coupled and process-oriented numerical model was applied to simulate laboratory experiments investigating two buffer materials, i.e. clay pellets as well as a sand-bentonite mixture. The developed models account for heat transport, multiphase flow and mechanical effects from swelling and thermal expansion. Model calibration was achieved by first determining the most sensitive parameters for heat and multiphase flow effects. A good fit between experimental data and model results was achieved for temperature, relative humidity, water intake and swelling pressure measurements. It is found that a unique set of thermal parameters for the insulation materials of the two experiments can be identified, which allows for a reliable estimate of the heat balance of the experiments. The most important parameters identified are the intrinsic and relative permeability, the water retention curve and the saturation dependent thermal conductivity of the buffer materials. It is further shown that the transient saturation state of the buffer material strongly influences its hydraulic and thermal behavior. The buffer material behavior thus identified contributes to the evaluation of larger scale in-situ experiments, and to better design deep geological repositories.
•The design of deep geological repositories requires buffer materials around the canister.•A fully coupled and process-oriented numerical model was applied to simulate column experiments.•A sensitivity analysis was performed to identify the most important parameters.•A unique set of thermal parameters for the insulation materials of the two experiments can be identified.•The most important parameters are: permeability, water retention curve and thermal conductivity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Anomalous physical and microbial properties were detected in the middle Adriatic.•Local and remote drivers contributed to record-breaking salinities.•Picoplankton biomass and production sharply ...declined in high salinity conditions.•The documented conditions could be more frequent in the future climate.
Oceanographic measurements carried out in the middle Adriatic during summer 2017 revealed anomalous conditions in both physical and microbial properties. High salinities were observed throughout the entire water column, with an ‘inverse’ salinity profile in August and a maximum in the surface layer, recorded for the first time in the middle Adriatic. Surface salinity of 39.02 recorded in August was 2.5 standard deviations above the long-term average (1961–2016). The observed salinity distributions are the result of both local and remote drivers, whereby the North Ionian cyclonic gyre controlled by the Adriatic-Ionian Bimodal Oscillating System has been responsible for the overall above-average salinities since 2011. Yet, local factors present in 2017, such as strong evaporation caused by extremely high air temperatures, lack of precipitation and low river discharges, combined with a decrease in horizontal transport estimated from the Regional Ocean Modeling System simulations, contributed substantially to the observed surface salinity anomaly. The decrease in horizontal advection was conjoined with high values of repelling barriers in the fields of the finite-time Lyapunov exponent. Documented physical conditions were synchronized with considerably lower bacterial production and abundance of the most studied picoplankton groups in comparison to values during the last decade. The exception was the euryhaline organism Synechococcus, whose abundance was 88% higher than the average in the study area. Nutrient content and chlorophyll-a concentrations followed regular seasonal cycles during 2017, with typical low values pointing to salinity as a possible driver of the observed changes in the microbial food web. Following ongoing climate change and future projections, these documented anomalous physical and microbiological conditions may become more frequent in the Adriatic Sea.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Understanding saltwater intrusion processes is crucial for both ecosystem health and water resource management in river estuaries. With the development of the global coastal economy, many estuaries ...worldwide have undergone shipping engineering constructions. Channel deepening in coastal areas adversely impacts the quality of freshwater required for ecological purposes, human consumption, and agricultural and industrial activities. Many studies have focused on saltwater intrusion processes in artificial canals capable of high and medium runoff characteristics; however, little is known about seawater intrusions in canals with low runoff and ship locks located far away from the estuary. This study focuses on the saltwater intrusion process in such a canal, using the Pinglu Canal of Qinjiang River Estuary in China as a prototype example. A three-dimensional (3D) numerical saltwater intrusion model using the standard k–ε turbulence closure was developed to simulate the saltwater intrusion process pre- and post-canal construction. The verification was conducted by comparing the simulated time series of the tidal level, velocity magnitude, and salinity with observations, and the impact of channel deepening on the saltwater intrusion in the Qinjiang River was analysed based on various numerical experiments. After channel deepening, mixing decreased following the decrease in flow velocity, the saltwater intrusion extent could reach the Youth Ship Lock after an increase of 5 km compared to the extent under natural conditions during high tide, and seawater remained in the channel during ebb tide, with freshwater discharge being Q < 20 m3/s. Furthermore, during the dry season, salinity in the approach channel downstream the Youth Ship Lock exhibited a trend of cumulative increase toward a stable value, and the correlation with the tide range cycle decreased from 0.62 under natural conditions to 0.09, whereas the correlation with the upstream inflow increased from 0.10 under natural conditions to 0.51. Results further indicated that the sensitivity of the saltwater intrusion to the flow rate was at a maximum, and its sensitivity to the tidal range was of minor significance after canal construction. Accordingly, a dimensionless function was constructed to quantify freshwater discharge from the Youth Hydro-hub to reduce the saltwater intrusion under variations in the tidal range and salinity during the low-water discharge period. This study can aid water resource management and suggest methods for mitigating saltwater intrusions in this type of artificial canal.
•Salt intrusion process is investigated in an artificial canal with low runoff.•Saltwater intrusion extent can reach the ship lock far away from the estuary.•The sensitivity to water discharge is the strongest downstream the ship lock.•The sensitivity to tidal range decreased as increasing of the distance from estuary.•An empirical function is developed to quantify salinity reduction freshwater.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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