Hydraulic Response Research Articles

Analysis of primary side bleed and feed actions for severe accident management following total loss of feed water in a Swedish PWR

Severe accident management guidelines (SAMGs) have been developed and applied in nuclear power plants (NPPs) to provide the fourth level of defense worldwide since the TMI-2 accident which occurred in 1979. The primary objective of the SAMGs is to protect remaining safety boundaries and to limit release of fission products into the environment by specific severe accident management (SAM) actions with available safety equipment. This paper is concerned with the assessment of the primary side bleed and feed (PBF) actions in the SAMGs of a Swedish pressurized water reactor (PWR). The PBF actions are realized by operations of emergency injection pumps and power-operated relief valves (PORVs), following a severe accident induced by an event of total loss of feed water (TLOFW) and temporary station blackout. In the present study, MELCOR simulations are performed to investigate the effects of the SAM actions on severe accident progression and consequences. Different sets of available equipment and actuation time due to recovery of AC power are simulated. The interest of the MELCOR analysis is focused on how these uncertain parameters of SAM actions affect thermal–hydraulic response, hydrogen generation, core relocation, reactor pressure vessel failure and release of fission products. The results demonstrate the effectiveness of the PBF strategy to prevent RPV failure in the TLOFW accident and the effects of injection timing on accident consequences. The obtained insights are instrumental for validation and improvement of the strategies and actions in the plant specific SAMGs.

Effects of grass type on hydraulic response of the three-layer landfill cover system.

Soil column tests were conducted to investigate the effects of grass type on water infiltration in a three-layer landfill cover under drying and wetting conditions. Five soil columns were prepared, including one bare, two Bermuda grass-planted and the other two vetiver-planted. During the drying period, the suction of vetiver-planted soil column was the largest, while that of bare case was the lowest. During the wetting period, the infiltration rate shows a bimodal form due to the contrasting hydraulic properties of different soil layers. The infiltration rate of vetiver-planted soil column was the lowest, followed by Bermuda grass-planted and bare cases. Correspondingly, the vetiver-planted soil column retained the maximum suction and the deepest ponding depth during rainfall. This was likely due to the larger leaf area and deeper roots of vetiver than those of Bermuda grass, thus inducing the maximum initial suction by root water uptake before rainfall and reducing the water permeability by root occupations of soil pores. These results show that vetiver is more effective than Bermuda grass to reduce water percolation through the three-layer landfill cover.

Discovering the forest in plain sight: a pop-up Symposium focusing on seasonally dry tropical forests.

Discovering the forest in plain sight: a pop-up Symposium focusing on seasonally dry tropical forests.

Numerical study on stability of lignosulphonate-based stabilized surficial layer of unsaturated expansive soil slope considering hydro-mechanical effect

Numerous laboratory-based solutions have been proposed in the recent literature for the stabilization of unsaturated expansive soil by recycling lignosulphonate (LS). However, the practical assessments of these proposals for the treatment of the rainfall-induced surficial failure in unsaturated expansive soil slopes are required, considering the frequency of this failure and associated economic loss. Moreover, in conventional geotechnical practice, the slope stability is generally evaluated only with consideration of the hydraulic response of the soil, ignoring the hydro-mechanical coupling effect associated with the swelling behavior of soil. Since LS-based stabilizers mainly impart the reduction of the swelling potential of expansive soils, the assessment of the stability of the LS-treated surficial layer of unsaturated expansive soil slopes requires consideration of the hydro-mechanical effect. For this purpose, the uncoupled and hydro-mechanical coupled analyses were conducted for dealing with the hydraulic and hydro-mechanical responses of the surficial layer of soil slopes, respectively. Specialized experimentations and pertinent literature review were performed to acquire the required input data for these analyses. It is observed that the LS-based surficial layer treatment affects the pore water pressure (PWP) profiles as well as wetting front depth (WFD), which are the critical aspects for influencing the stability of unsaturated expansive soil slopes. Among all LS-based stabilizers, only the stabilizer named composite cementing admixture (CCA) reasonably ameliorated the PWP profiles and WFD of the slope considering disastrous environmental impacts (i.e., wetting–drying cycles). Moreover, the heave problem of expansive soil slopes was observed to be mitigated by LS-based treatment among which the CCA performed the most efficiently. Furthermore, the critical factor of safety (FS) required for slope stability was also affected by the LS-based treatment, whereas the CCA was observed to provide the safest critical FS for slope stability.

Drainage-induced ground response in a twin-tunnel system through analytical prediction over the seepage field

Leakage-induced hydraulic and ground responses in a twin-tunnel system are analyzed via the proposed analytical solution on the seepage field. The seepage continuity conditions are rigorously satisfied at the interface between the ground and the tunnel lining, in terms of both water pressure and seepage velocity. The analytical solution is verified by comparing the results of numerical simulations. A detailed parametric analysis is carried out to explore the effect of tunnels’ spatial layouts and degraded waterproof facilities on leakage-induced hydraulic and ground response, including head decline, water inflow and ground surface settlement. Our results show that the often used single tunnel model tends to overestimate the pore pressure on the lining along with water inflow into the tunnel, and underestimate the leakage-induced ground settlement.

Time-domain impedance method for transient analysis and leakage detection in reservoir pipeline valve systems

An alternative approach to modeling the hydraulic transient response and leakage detection is proposed for reservoir pipeline valve systems. Exponential-function-based impedance formulations are derived in the frequency domain, which are useful for identifying the pressure response of different pipeline elements and abnormalities. The time-domain impedance function (TIF) is introduced to address the transient response for a specific pipeline system. The TIF comprehensively simulates various valve maneuvers or flowrates in either the laminar or turbulent flow regimes. The delineated TIF from the measured pressure head in the pipeline system with leakage exhibits potential for leak location prediction. The integration of the particle swarm optimization scheme into the inverse TIF algorithm provides a robust evaluation capability under a wide range of surge amplitudes. The developed leakage-identified impedance function substantially improves the leakage detection ability through transient impact isolation. Both the numerical and experimental verifications demonstrate the potential of the proposed method for leak detection as well as water hammer simulation for pipeline systems.

Failure Mechanism of Weak Rock Slopes considering Hydrological Conditions

Landslides frequently occur on cutting slopes with weak rock during the rainy season. An understanding of the failure mechanism is essential for designers to adopt effective measures to mitigate potential impacts caused by landslides. Based on an enormous number of highway slope practices in Guangdong Province, China, this paper presents a whole train of numerical investigations on the hydraulic response and stability of weak rock slopes subject to a subtropical climate where the average annual rainfall is approximately 1,800 – 2,000 mm. This study explored a different failure mechanism of three different types of weak rock slopes in a modeling approach. A physics-based slope model coupled with a hydrological model is used to simulate the factor of safety and porewater pressure development of unsaturated slopes with various rock masses under diverse rainfall scenarios. The input parameters were determined from the rainfall intensity–duration–frequency (IDF) curves of regional hydrological conditions to comprehensively consider the impact of rainfall. The general suction range of rock masses was acquired using three hydraulic characteristic curves associated with sandstone, siltstone, and mudstone. Furthermore, the failure models of weak rock slopes under different rainfall conditions were assessed. Based on the theory of regional hydrology, a unified rainfall and intensity-duration threshold for different weak rock slopes was established. The results indicate that both siltstone and mudstone slopes are more sensitive to long-term rainfall than short-term rainstorms. However, the sandstone slope appears to be unstable under regional rainfall conditions of 40-year return periods. This also proves that the instability mode of the siltstone slope exhibits a retrogressive type in which the sliding surface of the slope increases with an increase in rainfall duration. Translational shallow landslides occurred in the transient saturation zone of the sandstone slope, and the depth of the failure plane was independent of rainfall patterns and duration. This study revealed the instability mechanism and provided a robust early warning measure for weak rock slopes by fusing engineering geology and regional hydraulics, providing insightful information for mitigating potential landslide disasters. The proposed model can also be used to predict the possible infiltration depth of rainfall and the spatial location of the sliding surface, prior to construction to assess whether slope stabilization and reinforcement measures are needed.

A Novel Double Redundant Brake-by-Wire System for High Automation Driving Safety: Design, Optimization and Experimental Validation

The high redundant brake-by-wire system reveals vehicular safety handling ability and rarely emerges in the automotive area at the present time. This paper presents a novel brake-by-wire system, DREHB (Double Redundant Electro-Hydraulic Brake), with extensible fail-safe operations for high-automation autonomous driving vehicles. The DREHB is designed as a decoupled-architecture system containing three-layer cascaded modules, including a hydraulic power provider, a hydraulic flow switcher, and a hydraulic pressure modulator, and each of the modules can share dual redundancy. The operating principles of the DREHB in normal and degraded initiative braking modes are introduced, especially for the consideration of fail-safe and fail-operational functions. The matching and optimization of selected key parameters of the electric boost master cylinder and the linear solenoid valve were conducted using computer-aided batched simulations with a DREHB system modeled in MATLAB/Simulink and AMESim. The prototype of the DREHB was tested in hardware-in-the-loop experiments. The test results of typical braking scenarios verify the feasibility and effectiveness of the DREHB system, and the hydraulic pressure response as 28.0 MPa/s and tracking error within 0.15 MPa and the desirable fail-safe braking ability fully meets the requirements of higher braking safety and efficiency.

Structural and hydraulic responses of humid tropical soils to lime and organic residue amendments

In humid tropical environments, where soils are characteristically acidic and low in organic matter, lime and organic residues have been used to improve soil quality. A systematic consideration of their interaction is, therefore, crucial for land-based ecosystem management. A 28-day incubation pot study was carried out to investigate the main and interactive effects of lime and organic residue type (corn stover and vermicompost) on aggregate stability under rapid wetting (WSAr), saturated hydraulic conductivity (Ksat), and soil water repellency (SWR) on three acidic soils with contrasting clay content from Trinidad: Cunupia (Aquic Hapludalfs), Sangre Grande (Fluvaquentic Endoaquepts), and Talparo (Aquertic Eutrudepts). Organic residue had a significant (P ≤ 0.001) increasing effect on WSAr and Ksat for all three soils, this being highest for corn stover and lowest for no residue. Lime and organic residue interactive effects were only significant (P ≤ 0.05) for WSAr in the Cunupia soil, where lime significantly reduced WSAr in the vermicompost and no residue, but not in the corn stover treatment. Soil water repellency increased with clay content and was highest in the lime–corn stover treatment of the Talparo soil. Overall, our results suggest that applying crop residue with lime may help minimise the short-term deleterious effects of lime on the structural and hydraulic properties of humid tropical soils. Nonetheless, future experiments with a wider range of soils and organic residues need to be carried out for a longer term to validate our results.

Thermohydraulic Responses of Unsaturated Sand around a Model Energy Pile

This paper examines the effects of monotonic and cyclic temperature changes of a model energy pile (diameter=25 mm, length=264 mm) on the variations in temperature and volumetric water content of surrounding unsaturated sand. Water flowed away from the pile during heating to 36°C and toward the pile during cooling to 5°C, causing soil drying and wetting near the pile, respectively. The change in volumetric water content was time-dependent, nonlinear, and slower than the change in soil temperature and continued to evolve after the soil temperature changes stabilized. Cyclic heating/cooling induced lower thermohydraulic changes in the soil than monotonic heating and cooling. The most significant changes in soil temperatures and volumetric water content were closest to the pile at a radial distance of 20 mm from the edge of the pile and reduced with increasing radial distance for all cases. The largest change in the degree of saturation was near the pile and was up to 6% for monotonic heating. Cyclic heating/cooling induced irreversible cyclic hydraulic responses near the pile with consecutive thermal cycles and caused a permanent reduction in the soil volumetric water content. However, these irreversible cyclic effects were dominant at a radius of 20 mm and reduced with increasing radial distance from the energy pile. The change in volumetric water content was time-dependent, indicating that the ratio of heating to cooling times during cyclic heating/cooling will have a significant effect on the reversibility of hydraulic responses under temperature cycles.

Computational fluid dynamics based numerical study to determine the performance of triangular solar air heater duct having perforated baffles in V-down pattern mounted underneath absorber plate

In the current analysis, the effect of perforated baffles in V-down pattern as artificial roughness on the thermal and hydraulic response of a solar air heater having equilateral triangular passage has been examined. A thorough numerical investigation has been done using ANSYS FLUENT-19.0. Effect of change in roughness parameters, viz., baffle height (e) and open area ratio (β) on thermo-hydraulic performance has been explored. Flow Reynolds number is systematically varied. Study reveals that upon varying the baffle height from 5 mm to 11 mm and open area ratio from 20% to 29%, maximum heat transfer rate is attained at e = 9 mm and β = 20%, respectively. Axial Velocity and Turbulence Kinetic Energy have been plotted for clear view of change in variables. Also, the correlations have been developed for Nusselt number and Friction factor. The thermo-hydraulic performance factor of proposed perforated baffle geometry has been observed to be 2.54 at e = 9 mm and β = 20%. Performance of the SAH with suggested roughness is found to be advantageous than other type of roughness elements studied in recent times.

ARPEC: A novel staggered perforated permeable caisson breakwater for wave absorption and harbour flushing

Perforated multichamber caisson breakwaters are widely used for deep water harbour protection from waves, causing a partial dissipation of wave energy, hence reducing wave reflection. The innovative patented geometry presented in this paper, the ARPEC, is an Anti Reflection PErmeable Caisson breakwater that allows a significant wave energy dissipation and a hydraulic connection between the sea side and the port side by means of a labyrinthine pattern of offset openings in all external and internal walls. The hydraulic response of this innovative structure is evaluated by means of both 2D physical and numerical models. It is shown that, when compared with traditional impermeable perforated caissons, the marginal increase of wave transmission (CT=HT/HI in the approximate range of 0.1–0.2, varying with wave period) is compensated by a slight reduction of wave reflection (CR=HR/HI in the approximate range of 0.3–0.6, varying with wave period) and by an enhanced water circulation in the sheltered basin, which is beneficial for flushing of microtidal harbours.

Investigations into the opening of fractures during hydraulic testing using a hybrid-dimensional flow formulation

We applied a hybrid-dimensional flow model to pressure transients recorded during pumping experiments conducted at the Reiche Zeche underground research laboratory to study the opening behavior of fractures due to fluid injection. Two distinct types of pressure responses to flow-rate steps were identified that represent radial-symmetric and plane-axisymmetric flow regimes from a conventional pressure-diffusion perspective. We numerically modeled both using a radial-symmetric flow formulation for a fracture that comprises a non-linear constitutive relation for the contact mechanics governing reversible fracture surface interaction. The two types of pressure response can be modeled equally well. A sensitivity study revealed a positive correlation between fracture length and normal fracture stiffness that yield a match between field observations and numerical results. Decomposition of the acting normal stresses into stresses associated with the deformation state of the global fracture geometry and with the local contacts indicates that geometrically induced stresses contribute the more the lower the total effective normal stress and the shorter the fracture. Separating the contributions of the local contact mechanics and the overall fracture geometry to fracture normal stiffness indicates that the geometrical stiffness constitutes a lower bound for total stiffness; its relevance increases with decreasing fracture length. Our study demonstrates that non-linear hydro-mechanical coupling can lead to vastly different hydraulic responses and thus provides an alternative to conventional pressure-diffusion analysis that requires changes in flow regime to cover the full range of observations.

Molecular mechanisms of stomatal closure in response to rising vapour pressure deficit.

Vapour pressure deficit (VPD), the difference between the saturation and actual air vapour pressures, indicates the level of atmospheric drought and evaporative pressure on plants. VPD increases during climate change due to changes in air temperature and relative humidity. Rising VPD induces stomatal closure to counteract the VPD-mediated evaporative water loss from plants. There are important gaps in our understanding of the molecular VPD-sensing and signalling mechanisms in stomatal guard cells. Here, we discuss recent advances, research directions and open questions with respect to the three components that participate in VPD-induced stomatal closure in Arabidopsis, including: (1) abscisic acid (ABA)-dependent and (2) ABA-independent regulation of the protein kinase OPEN STOMATA 1 (OST1), and (3) the passive hydraulic stomatal response. In the ABA-dependent component, two models are proposed: ABA may be rapidly synthesised or its basal levels may be involved in the stomatal VPD response. Further studies on stomatal VPD signalling should clarify: (1) whether OST1 activation above basal activity is needed for VPD responses, (2) which components are involved in ABA-independent regulation of OST1, (3) the role of other potential OST1 targets in VPD signalling, and (4) to which extent OST1 contributes to stomatal VPD sensitivity in other plant species.

Using artificial intelligence to identify the success window of FLEX strategy under an extended station blackout

The vulnerability of operational nuclear power plants (NPPs) to an extended station blackout (SBO) was revealed after the Fukushima Dai-ichi accident, which led to the development and implementation of new strategies such as the diverse and flexible (FLEX) strategy. The FLEX strategy has been adopted by several utilities around the world in support of existing emergency operating procedures (EOPs) to maintain the core coolability and hence ensure the plant safety under an extended SBO. In this paper an AI algorithm is developed to assess the success window of implementing the FLEX strategy, given the uncertainties related to the operator actions (specifically opening the ADVs and aligning FLEX pumps) as well as the underlying phenomena. The AI algorithm is constructed via an artificial neural network (ANN) which is trained using a database of the plant thermal hydraulic response generated by means of the best estimate plus uncertainty (BEPU) methodology. Once trained, the AI meta-model is used to identify the success window of the FLEX strategy under various conditions. The developed meta-model could predict the successful implementation with reasonable accuracy. However, it was not as successful in predicting the failed cases. Nonetheless, AI offers a cost effective computational tool for uncertainty quantification and verification of emergency procedures compared to traditional approaches.

Influence of blade leaning on hydraulic excitation and structural response of a reversible pump turbine

Blade leaning is commonly seen in the runner design of reversible pump turbines which operate under varying conditions. However, there is no certain law in determine the leaning mode and level. Considering performance, hydraulic excitation and structural response, five runners with strong rotational (RL+), rotational (RL), strong counter-rotational (CL+), counter-rotational (CL) and without (NL) blade leaning are compared under high-efficiency condition in pump mode and turbine mode. The head, efficiency, internal flow pressure pulsation and runner stress are comparatively studied. Among the five runners, CL+ runner is found has the highest efficiency as pump when RL+ runner has the highest efficiency as turbine. Pressure pulsation results show that the rotor-stator interaction region is the strongest pulsation source especially for runner and blade frequencies. In pump mode, pressure pulsation intensity decreases when blade leaning mode gradually changes from rotational to counter-rotational. In turbine mode, the NL runner has the strongest pressure pulsation intensity in runner and guide vane. Both rotational and counter-rotational leaning will reduce pressure pulsation. Velocity contours indicate that blade leaning will affect the velocity uniformity especially along rotational direction and cause stronger or weaker local hydraulic excitation. Under hydraulic excitation, RL+ runner suffers the highest equivalent stress as pump while CL runner suffers the highest equivalent stress as turbine. From rotational to counter-rotational blade leaning, the maximum stress moves on the crown from low pressure side to high pressure side. Considering hydraulic excitation and structural response, the strong counter-rotational leaning blade is found better in reversible runner design.

Simulation and optimal control for a long‐distance water diversion project under different rainfall types: A case study in the Middle Route of China's South‐to‐North Water Diversion Project*

AbstractRainfall and rainstorms pose potential risks and significant threats to open‐channel water diversion projects. In long‐distance water diversion projects, it is difficult to observe the hydraulic response through measured data directly and comprehensively. Without accurate hydraulic responses and advanced control strategies for the different rainfall types, operators or decision‐makers are unable to respond effectively to hydraulic changes in the case of sudden occurrences of rainfall or rainstorms. In this study, a simulation and optimal control model focusing on solving the Saint Venant equation based on the computational finite difference method and the combined particle swarm optimization algorithm, was established and applied to a long‐distance water diversion project, namely the Middle Route of the South‐to‐North Water Diversion Project, China, to analyse the hydraulic response and control the disturbance of various rainfall types. The simulation model was validated based on the calculation results, indicating that the simulation model yielded a relatively high precision with an error margin of 2.5%. The optimal control model can effectively reduce the maximum increase in water level caused by the different rainfall types in the range of 0.10–0.20 m.

Fault nucleation of tight sandstone by investigation of mechanical, acoustic, and hydraulic responses

To investigate the effect of water on the fracture mechanism and associated acoustic emission (AE) characteristics, triaxial compression experiments were performed on dry and water-saturated tight sandstone specimens sampled from the Sichuan Basin, China. The saturated specimen was precisely controlled by different drainage conditions at the two ends. The detailed spatiotemporal distribution of AE activities and the P-wave velocities were used to examine the initiation and propagation of microcracks, as well as fault nucleation process. There are significant differences in mechanical behavior, P-wave velocity, AE activities, and fault nucleation between the dry and saturated specimens. The mechanical behavior of the saturated specimen is characterized by water weakening, with 10% and 26% reductions in peak strength and elastic modulus, respectively, in comparison with those for the dry specimen. Water enhances inelastic axial deformation and strain softening. The evolution of P-wave velocity is associated with microcracking-induced dilatancy. The decrease in P-wave velocity is suppressed in the saturated specimen, especially at the drained end. Significant attenuation of AE energy is observed in the saturated specimen, resulting into a lower event rate compared with that for the dry specimen. It is shown that the saturated specimen has an extended fault nucleation duration and lower rupture velocity. The precursory phase of dynamic failure can be clearly mapped based on strain softening, accelerating AE event rate, and decreasing b-value, as well as decreasing pore pressure (in undrained condition) or increasing injection rate (in drained condition).

Earthquakes and very deep groundwater perturbation mutually induced

We report unique observations from drilling and hydraulic stimulation at a depth of approximately 4.3 km in two Enhanced Geothermal System (EGS) wells at the Pohang EGS site, South Korea. We surveyed drilling logs and hydraulic stimulation data, simulated pore pressure diffusion around the fault delineated by seismic and drilling log analyses, conducted acoustic image logging through the EGS wells, observed significant water level drops (740 m) in one of the two EGS wells, and obtained hydrochemical and isotopic variation data in conjunction with the microbial community characteristics of the two EGS wells. We discuss the hydraulic and hydrochemical responses of formation pore water to a few key seismic events near the hypocenter. We focused on how the geochemistry of water that flowed back from the geothermal wells changed in association with key seismic events. These were (1) a swarm of small earthquakes that occurred when a significant circulation mud loss occurred during well drilling, (2) the MW 3.2 earthquake during hydraulic stimulation, and (3) the MW 5.5 main shock two months after the end of hydraulic stimulation. This study highlights the value of real-time monitoring and water chemistry analysis, in addition to seismic monitoring during EGS operation.

Effects of loss of heat sink transient on flow characteristics in a closed natural circulation system

Flow characteristics during loss of coolant to the heat exchanger (HX) via the secondary loop cold leg of a natural circulation (NC) test facility referred here as loss of heat sink transient (LOHS) in a closed rectangular NC system having a single heated channel at two different heating powers and system pressures has been investigated experimentally. Two LOHS experiments (LOHS-1 and LOHS-2) were conducted in a well dimensioned closed loop NC test facility designed to represent the primary system of a nuclear reactor. Operating conditions were set and maintained at 6.0 kW and 9.0 kW with system pressures of 0.2 MPa and 0.5 MPa respectively for both single-phase and single-to-two-phase flow transition to determine their thermal hydraulic responses at these predetermined parameters. The transients were initiated by closing the cold leg of the secondary loop supplying coolant to the tube-in-shell heat exchanger while NC flow phenomena were monitored at each vital section along the flow map based on the pre-determined inlet operating conditions. LOHS experiment stops when critical heat flux (CHF) occurs or heat exchanger outlet (HXoutlet) temperature rises too high to approximately equal its inlet temperature. Results were acquired using a system-design platform and development environment LabVIEW, programmed in a dedicated computer that was interfaced with the coupled sensors in the measuring devices. Common computational tools which include MATLAB, Ms Excel and Origin software were used for the analysis of the acquired data. Results at the inlet and outlet of heated sections as well as the inlet and outlet of condensers of both tests were analyzed and discussed in details at various flow regimes with the associated phenomena. It is concluded that while stable flow was maintained before transient with slug flow occurring in the heating channel, the system experienced transient stability resulting in steady temperature increase and subsequently drops into an instability region when the transient scenario was activated. In addition, the NC system transited into stable two-phase flow and further loses stability when HXoutlet temperature surges to its inlet value with CHF occurrence. These results are presented to contribute to a more extensive utilization of NC systems and understanding of flow behavior during LOHS in advanced reactors.