Modelling study of transport time scales for a hyper-tidal estuary

This paper presents a study of two transport timescales (TTS), i.e., the residence time and exposure time, of a hyper-tidal estuary using a widely used numerical model. The numerical model was calibrated against field measured data for various tidal conditions. The model simulated current speeds and directions generally agreed well with the field data. The model was then further developed and applied to study the two transport timescales, namely the exposure time and residence time for the hyper-tidal Severn Estuary. The numerical model predictions showed that the inflow from the River Severn under high flow conditions reduced the residence and exposure times by 1.5 to 3.5% for different tidal ranges and tracer release times. For spring tide conditions, releasing a tracer at high water reduced the residence time and exposure time by 49.0% and 11.9%, respectively, compared to releasing the tracer at low water. For neap tide conditions, releasing at high water reduced the residence time and exposure time by 31.6% and 8.0%, respectively, compared to releasing the tracer at low water level. The return coefficient was found to be vary between 0.75 and 0.88 for the different tidal conditions, which indicates that the returning water effects for different tidal ranges and release times are all relatively high. For all flow and tide conditions, the exposure times were significantly greater than the residence times, which demonstrated that there was a high possibility for water and/or pollutants to re-enter the Severn Estuary after leaving it on an ebb tide. The fractions of water and/or pollutants re-entering the estuary for spring and neap tide conditions were found to be very high, giving 0.75–0.81 for neap tides, and 0.79–0.88 for spring tides. For both the spring and neap tides, the residence and exposure times were lower for high water level release. Spring tide conditions gave significantly lower residence and exposure times. The spatial distribution of exposure and residence times showed that the flow from the River Severn only had a local effect on the upstream part of the estuary, for both the residence and exposure time

Simulation of three-dimensional free-surface dam-break flows over a cuboid, cylinder, and sphere

A three-dimensional (3D) numerical study is undertaken to investigate dam-break flows over 3D structures. A two-phase flow model has been developed within the large-eddy simulation (LES) framework. The governing equations have been discretized using the finite-volume method, with the air-water interface being captured using a volume-of-fluid method while the Cartesian cut-cell method deals with complex geometries. The robustness and versatility of the proposed numerical approach are demonstrated first by applying it to a 3D dam-break flow over a cuboid. Good agreement is obtained between the simulation results and the corresponding experimental data and other numerical solutions. Then, a horizontal cylinder and a sphere are subjected to the same dam-break flow. Snapshots of water surface profiles are presented and discussed, and turbulent vortical structures are identified in the flow. In addition, the internal kinematics, hydrodynamic loading on the structure, and energy dissipation during dam-break flow impact are analyzed and discussed, providing more insight into such flows

Enhancing pedestrian evacuation routes during flood events

The increasing rate of anthropic activities in flood-prone areas and the effects of climate change are aggravating the dangers posed by floods to people. One of the main reasons for fatality during flood events is walking through floodwaters. Although authorities strongly advise against walking in flood waters, evacuations or the accessing of flooded areas by emergency services might be necessary. This research proposes a novel approach to increasing resilience by retrofitting existing infrastructures to enhance evacuation and access routes by reducing flood hazard rate based on flood and pedestrian characteristics. The methodology was applied to flash floods in two case studies in the UK, namely Boscastle and Borth, highlighting that retrofitting small regions of the existing roads and pathways to reduce flood hazard can enhance people’s safety during the evacuation, and hence provides a solution to improve the resilience of the existing environment

Boundary variation diminished conservative semi-Lagrangian method for both compressible and incompressible flows

Motivated by the enlightenment that diminishing the jump at the cell boundary can effectively reduce numerical dissipation near the critical region, and a novel constrained interpolation profile conservative semi-Lagrangian method is proposed based on a newly designed boundary variation diminishing algorithm. First, a constrained interpolation profile conservative semi-Lagrangian scheme with the piecewise tangent of hyperbola for interface capturing scheme is proposed as one candidate to represent jump-like discontinuities. Second, the constrained interpolation profile conservative semi-Lagrangian scheme with a fourth-order weighted essentially non-oscillatory limiter is used as another candidate to keep the high-order and non-oscillatory reconstruction for smooth solutions. The selection criterion of these two candidates is designed by minimizing the total variations of the first derivative at cell boundaries. A unified pressure-based projection formulation with a fractional step procedure is implemented with the proposed scheme to simulate both compressible and incompressible flows. A variety of numerical tests are studied, including linear and nonlinear scalar wave transport problems and compressible and incompressible flow problems. Results show that the proposed method can effectively eliminate numerical oscillation and diffusion, suggesting it has great potential to be applied to various types of engineering problems including both compressible and incompressible flows

Criterion of vehicle stability in floodwaters based on theoretical and experimental studies

Vehicles parking on streets or roads can cause various hazards to people and property when they are swept away by urban floods. It is therefore appropriate to investigate the criterion of vehicle stability for such flood conditions, especially for different scenarios and where the criterion of vehicle stability is usually represented by the incipient velocity for the vehicle. In the current study, different forces acting on a partially submerged vehicle are outlined, together with the corresponding expressions of these forces, and a mechanics-based formula of incipient velocity is given for partially submerged vehicles under different orientation angles. About 200 runs of flume experiments were conducted to obtain the conditions of water depth and corresponding velocity at the threshold of vehicle instability for three orientation angles, using two types of die-cast model vehicles at two model scales. Experimental data obtained from the large-scale model vehicles were then used to determine two parameters in the derived formula. Finally, incipient velocities for three vehicle orientation angles were estimated using two different approaches, including predictions using the scale ratios from the small-scale model vehicles and computations based on derived formula using the prototype vehicle parameters. These critical conditions for the prototype conditions, based on the scale ratios, compared well with the calculations obtained using the derived formula, which guaranteed the predicative accuracy of the formula. In addition, the effect of different ground slopes on the vehicle incipient motion was also investigated, using similar experiments and based on the theory of similarity, which indicated that the incipient velocity for a small passenger vehicle on a ground slope of 1:50 was about 25 % lower than the value on a flat ground for an incoming depth of 0.25 m

New criterion for the stability of a human body in floodwaters

Extreme flood events often lead to heavy casualties, with flood risk to humans varying with the flow conditions and the body attributes. Therefore, it is important to propose an appropriate criterion for the stability of a human body in floodwaters in the form of an incipient velocity. In this study, two formulae for the incipient velocity of a human body for sliding and toppling instability were derived, based on a mechanics-based analysis, and with both formulae accounting for the effect of body buoyancy and the influence of a non-uniform upstream velocity profile acting on the flooded human body. More than 50 tests were conducted in a flume to obtain the conditions of water depth and velocity at instability for a model human body, with the experimental data being used to calibrate two parameters in the derived formulae. Finally, the proposed formulae were validated in detail against existing experimental data for real human subjects, with different stability thresholds being obtained for children and adults in terms of assessing their stability related to floodwaters

Hazard and vulnerability in urban inundated underground space: Hydrodynamic analysis of human instability for stairway evacuation

Underground flooding events are being exacerbated due to the rapid expanding of underground space in urban and the extreme precipitation events by climate change. It is increasingly necessary to study hydrodynamics and instabilities of human on staircases in the flood-prone underground space for risk identification and disaster reduction. However, the turbulent complexity and complicated fluid-human interaction still challenge the study of flow structure and the calibration of human instability model. In this work, a hydrodynamic model coupled with the mechanics-based method was proposed to study fluid-human interactions and hazard risks on flooding stairways. Numerical validations show that the model can obtain reliable solutions of flow characteristics on staircases. It is found that there exists a jet flow downstream the rest platform and the critical region after the 3rd step downstream the platform is identified as a high risk area to cause sliding instability. The risk of sliding instability for a child is higher than that for an adult in jet flow region. In addition, results show that the downstream vortical flow structure and turbulent effect are obviously enhanced because of the interdict of jet flow by the human obstacle

Selection of optimal escape routes in a flood-prone area based on 2D hydrodynamic modelling

Optimizing escape routes during an extreme flood event is an effective way to mitigate casualties. In this study, a model for selecting optimal escape routes in a flood-prone area has been proposed, which includes a module for predicting the two-dimensional hydrodynamics and modules for assessing the hazard degree for evacuees, calculation of evacuation times and determination of different escape routes. In the module for determining escape routes, two evacuation schemes were used: Scheme A to find optimal escape routes based on established road networks, and Scheme B to design a new optimal evacuation route. Extreme overbank floods occurred in the Lower Yellow River (LYR) in July 1958 (‘58.7’) and August 1982 (‘82.8’) and the proposed model was applied to select the optimal escape routes on a typical floodplain area of the LYR for these two floods. Model predictions indicated that: (i) the optimal escape routes for these two floods were the same for all three starting locations, and the optimized routes provided 3 h more time for evacuees to escape; and (ii) the time of evacuation would need to be earlier for the ‘58.7’ flood because of its larger amount of water volume and higher peak discharge

Reliability and validity of the Mental Health Self-management Questionnaire among Chinese patients with mood and anxiety disorders

BackgroundSelf-management plays an important role in promoting and restoring mental health for individuals with mental health issues. However, there is no valid and reliable Chinese tool assessing the self-management behaviors of people with mood and anxiety disorders. This study aimed to develop a Chinese version of the Mental Health Self-management Questionnaire (MHSQ-C) and to verify its psychometric properties.MethodsA total of 440 potential participants were recruited by convenience sampling from June to August 2020. Item analysis and analyses of internal consistency, test-retest reliability, content validity, construct validity and criterion validity were performed.ResultsData from 326 participants were used. Three factors obtained via principal component analysis and varimax rotation explained 53.68% of the total variance. The average content validity index was 0.99. The Cronbach’s α coefficient (total: 0.874, clinical: 0.706, empowerment: 0.818, vitality: 0.830) and test-retest reliability (ICC: total: 0.783, 95% confidence interval (CI) [0.616, 0.882], clinical: 0.525, 95% CI [0.240, 0.725], empowerment: 0.786, 95% CI [0.622, 0.884], vitality: 0.748, 95% CI [0.564, 0.862]) were good. The MHSQ-C was well correlated with the Partners in Health scale and showed no floor or ceiling effect.DiscussionThe MHSQ-C is a reliable and valid tool to evaluate the self-management strategies of patients with mood and anxiety disorders

Genetic testing and prognosis of sarcomatoid hepatocellular carcinoma patients

BackgroundSarcomatoid hepatocellular carcinoma (SHC) is a rare epithelial malignancy with high invasiveness and poor prognosis. However, the molecular characteristics and main driver genes for SHC have not been determined. The aim of this study is to explore the potentially actionable mutations of driver genes, which may provide more therapeutic options for SHC.MethodsIn this study, DNA extraction and library preparation were performed using tumor tissues from 28 SHC patients. Then we used Miseq platform (Illumina) to sequence the target-enriched library, and we aligned and processed the sequencing data. The gene groups were tested for SNVs/Indels/CNVs. Tumor mutation burden (TMB) was assessed by the 425-cancer-relevant gene panel. Multivariate analysis of COX’s model was used for survival analysis (OS) of patients’ clinical characteristics.ResultThe median overall survival (OS) of the patients was only 4.4 months. TP53, TERT, and KRAS were the top three frequently mutated genes, with frequencies of 89.3%, 64.3%, and 21.4%, respectively. A considerable number of patients carried mutations in genes involved in the TP53 pathway (96%) and DNA Damage Repair (DDR) pathway (21%). Multiple potentially actionable mutations, such as NTRK1 fusions and BRCA1/2 mutations, were identified in SHCs.ConclusionsThis study shows a landscape of gene mutations in SHC. SHC has high mutation rates in TP53 pathway and DDR pathway. The potentially actionable mutations of driver genes may provide more therapeutic options for SHC. Survival analysis found that age, smoking, drinking, and tumor diameter may be independent prognostic predictors of SHC