scholarly journals An Innovative Approach to Minimizing Uncertainty in Sediment Load Boundary Conditions for Modelling Sedimentation in Reservoirs

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1411 ◽  
Author(s):  
Sardar Ateeq-Ur-Rehman ◽  
Minh Bui ◽  
Shabeh Hasson ◽  
Peter Rutschmann
Keyword(s):  
Boundary Conditions ◽  
Sediment Load ◽  
Sediment Supply ◽  
Coefficient Of Determination ◽  
Computational Time ◽  
Indus River ◽  
Sediment Deposits ◽  
Subsequent Decrease ◽  
Delta Formation ◽  
Near Future

A number of significant investigations have advanced our understanding of the parameters influencing reservoir sedimentation. However, a reliable modelling of sediment deposits and delta formation in reservoirs is still a challenging problem due to many uncertainties in the modelling process. Modelling performance can be improved by adjusting the uncertainty caused by sediment load boundary conditions. In our study, we diminished the uncertainty factor by setting more precise sediment load boundary conditions reconstructed using wavelet artificial neural networks for a morphodynamic model. The model was calibrated for hydrodynamics using a backward error propagation method. The proposed approach was applied to the Tarbela Reservoir located on the Indus River, in northern Pakistan. The results showed that the hydrodynamic calibration with coefficient of determination (R2) = 0.969 and Nash–Sutcliffe Efficiency (NSE) = 0.966 also facilitated good calibration in morphodynamic calculations with R2 = 0.97 and NSE = 0.96. The model was validated for the sediment deposits in the reservoir with R2 = 0.96 and NSE = 0.95. Due to desynchronization between the glacier melts and monsoon rain caused by warmer climate and subsequent decrease of 17% in sediment supply to the Tarbela dam, our modelling results showed a slight decrease in the sediment delta for the near future (until 2030). Based on the results, we conclude that our overall state-of-the-art modelling offers a significant improvement in computational time and accuracy, and could be used to estimate hydrodynamic and morphodynamic parameters more precisely for different events and poorly gauged rivers elsewhere in the world. The modelling concept could also be used for predicting sedimentation in the reservoirs under sediment load variability scenarios.

scholarly journals Effect of Sediment Load Boundary Conditions in Predicting Sediment Delta of Tarbela Reservoir in Pakistan

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1716 ◽  
Author(s):  
Zeeshan Riaz Tarar ◽  
Sajid Rashid Ahmad ◽  
Iftikhar Ahmad ◽  
Shabeh ul Hasson ◽  
Zahid Mahmood Khan ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Boundary Conditions ◽  
Sediment Load ◽  
Indus River ◽  
Robust Modeling ◽  
Modeling Concept ◽  
Reconstruction Performance ◽  
Rating Curves ◽  
The Stability ◽  
Tarbela Reservoir

Setting precise sediment load boundary conditions plays a central role in robust modeling of sedimentation in reservoirs. In the presented study, we modeled sediment transport in Tarbela Reservoir using sediment rating curves (SRC) and wavelet artificial neural networks (WA-ANNs) for setting sediment load boundary conditions in the HEC-RAS 1D numerical model. The reconstruction performance of SRC for finding the missing sediment sampling data was at R2 = 0.655 and NSE = 0.635. The same performance using WA-ANNs was at R2 = 0.771 and NSE = 0.771. As the WA-ANNs have better ability to model non-linear sediment transport behavior in the Upper Indus River, the reconstructed missing suspended sediment load data were more accurate. Therefore, using more accurately-reconstructed sediment load boundary conditions in HEC-RAS, the model was better morphodynamically calibrated with R2 = 0.980 and NSE = 0.979. Using SRC-based sediment load boundary conditions, the HEC-RAS model was calibrated with R2 = 0.959 and NSE = 0.943. Both models validated the delta movement in the Tarbela Reservoir with R2 = 0.968, NSE = 0.959 and R2 = 0.950, NSE = 0.893 using WA-ANN and SRC estimates, respectively. Unlike SRC, WA-ANN-based boundary conditions provided stable simulations in HEC-RAS. In addition, WA-ANN-predicted sediment load also suggested a decrease in supply of sediment significantly to the Tarbela Reservoir in the future due to intra-annual shifting of flows from summer to pre- and post-winter. Therefore, our future predictions also suggested the stability of the sediment delta. As the WA-ANN-based sediment load boundary conditions precisely represented the physics of sediment transport, the modeling concept could very likely be used to study bed level changes in reservoirs/rivers elsewhere in the world.

scholarly journals Stiffness Estimation and Equivalence of Boundary Conditions in FEM Models

2021 ◽  
Vol 11 (4) ◽  
pp. 1482
Author(s):  
Róbert Huňady ◽  
Pavol Lengvarský ◽  
Peter Pavelka ◽  
Adam Kaľavský ◽  
Jakub Mlotek
Keyword(s):  
Boundary Condition ◽  
Finite Element ◽  
Boundary Conditions ◽  
Model Updating ◽  
Element Model ◽  
Computational Time ◽  
Stiffness Coefficients ◽  
First Case ◽  
Numerical Approaches

The paper deals with methods of equivalence of boundary conditions in finite element models that are based on finite element model updating technique. The proposed methods are based on the determination of the stiffness parameters in the section plate or region, where the boundary condition or the removed part of the model is replaced by the bushing connector. Two methods for determining its elastic properties are described. In the first case, the stiffness coefficients are determined by a series of static finite element analyses that are used to obtain the response of the removed part to the six basic types of loads. The second method is a combination of experimental and numerical approaches. The natural frequencies obtained by the measurement are used in finite element (FE) optimization, in which the response of the model is tuned by changing the stiffness coefficients of the bushing. Both methods provide a good estimate of the stiffness at the region where the model is replaced by an equivalent boundary condition. This increases the accuracy of the numerical model and also saves computational time and capacity due to element reduction.

scholarly journals Watershed Suspended Sediment Supply and Potential Impacts of Dam Removals for an Estuary

2021 ◽  
Author(s):  
David K. Ralston ◽  
Brian Yellen ◽  
Jonathan D. Woodruff
Keyword(s):  
Suspended Sediment ◽  
River Estuary ◽  
Dam Removal ◽  
Hudson River ◽  
Sediment Traps ◽  
Sediment Supply ◽  
Watershed Area ◽  
Natural Lakes ◽  
Sediment Deposits ◽  
Dam Removals

AbstractObservations and modeling are used to assess potential impacts of sediment releases due to dam removals on the Hudson River estuary. Watershed sediment loads are calculated based on sediment-discharge rating curves for gauges covering 80% of the watershed area. The annual average sediment load to the estuary is 1.2 Mt, of which about 0.6 Mt comes from side tributaries. Sediment yield varies inversely with watershed area, with regional trends that are consistent with substrate erodibility. Geophysical and sedimentological surveys in seven subwatersheds of the Lower Hudson were conducted to estimate the mass and composition of sediment trapped behind dams. Impoundments were classified as (1) active sediment traps, (2) run-of-river sites not actively trapping sediment, and (3) dammed natural lakes and spring-fed ponds. Based on this categorization and impoundment attributes from a dam inventory database, the total mass of impounded sediment in the Lower Hudson watershed is estimated as 4.9 ± 1.9 Mt. This represents about 4 years of annual watershed supply, which is small compared with some individual dam removals and is not practically available given current dam removal rates. More than half of dams impound drainage areas less than 1 km2, and play little role in downstream sediment supply. In modeling of a simulated dam removal, suspended sediment in the estuary increases modestly near the source during discharge events, but otherwise effects on suspended sediment are minimal. Fine-grained sediment deposits broadly along the estuary and coarser sediment deposits near the source, with transport distance inversely related to settling velocity.

Fast CT-FFR Analysis Method for the Coronary Artery Based on 4D-CT Image Analysis and Structural and Fluid Analysis

2015 ◽  
Author(s):  
Mitsuaki Kato ◽  
Kenji Hirohata ◽  
Akira Kano ◽  
Shinya Higashi ◽  
Akihiro Goryu ◽  
...  
Keyword(s):  
Blood Flow ◽  
Coronary Artery ◽  
Boundary Conditions ◽  
Coronary Arteries ◽  
Computational Time ◽  
Ct Image ◽  
Analysis Method ◽  
Fractional Flow ◽  
4D Ct ◽  
Fluid Analysis

Non invasive fractional flow reserve derived from CT coronary angiography (CT-FFR) has to date been typically performed using the principles of computational fluid analysis in which a lumped parameter coronary vascular bed model is assigned to represent the impedance of the downstream coronary vascular networks absent in the computational domain for each coronary outlet. This approach may have a number of limitations. It may not account for the impact of the myocardial contraction and relaxation during the cardiac cycle, patient-specific boundary conditions for coronary artery outlets and vessel stiffness. We have developed a novel approach based on 4D-CT image tracking (registration) and structural and fluid analysis based on one dimensional mechanical model, to address these issues. In our approach, we analyzed the deformation variation of vessels and the volume variation of vessels to better define boundary conditions and stiffness of vessels. We focused on the blood flow and vessel deformation of coronary arteries and aorta near coronary arteries in the diastolic cardiac phase from 70% to 100 %. The blood flow variation of coronary arteries relates to the deformation of vessels, such as expansion and contraction of the cross-sectional area, during this period where resistance is stable, pressure loss is approximately proportional to flow. We used a statistical estimation method based on a hierarchical Bayes model to integrate 4D-CT measurements and structural and fluid analysis data. Under these analysis conditions, we performed structural and fluid analysis to determine pressure, flow rate and CT-FFR. Furthermore, the reduced-order model based on fluid analysis was studied in order to shorten the computational time for 4D-CT-FFR analysis. The consistency of this method has been verified by a comparison of 4D-CT-FFR analysis results derived from five clinical 4D-CT datasets with invasive measurements of FFR. Additionally, phantom experiments of flexible tubes with and without stenosis using pulsating pumps, flow sensors and pressure sensors were performed. Our results show that the proposed 4D-CT-FFR analysis method has the potential to accurately estimate the effect of coronary artery stenosis on blood flow.

scholarly journals Multimineral Fingerprinting of Transhimalayan and Himalayan Sources of Indus-Derived Thal Desert Sand (Central Pakistan)

Minerals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 457 ◽  
Author(s):  
Wendong Liang ◽  
Eduardo Garzanti ◽  
Sergio Andò ◽  
Paolo Gentile ◽  
Alberto Resentini
Keyword(s):  
Relative Proportion ◽  
Foreland Basin ◽  
Sediment Supply ◽  
Heavy Mineral ◽  
Mineral Species ◽  
Provenance Analysis ◽  
Indus River ◽  
Mineral Concentration ◽  
River Sand ◽  
Desert Sand

As a Quaternary repository of wind-reworked Indus River sand at the entry point in the Himalayan foreland basin, the Thal Desert in northern Pakistan stores mineralogical information useful to trace erosion patterns across the western Himalayan syntaxis and the adjacent orogenic segments that fed detritus into the Indus delta and huge deep-sea fan throughout the Neogene. Provenance analysis of Thal Desert sand was carried out by applying optical and semi-automated Raman spectroscopy on heavy-mineral suites of four eolian and 11 fluvial sand samples collected in selected tributaries draining one specific tectonic domain each in the upper Indus catchment. In each sample, the different types of amphibole, garnet, epidote and pyroxene grains—the four dominant heavy-mineral species in orogenic sediment worldwide—were characterized by SEM-EDS spectroscopy. The chemical composition of 4249 grains was thus determined. Heavy-mineral concentration, the relative proportion of heavy-mineral species, and their minerochemical fingerprints indicate that the Kohistan arc has played the principal role as a source, especially of pyroxene and epidote. Within the western Himalayan syntaxis undergoing rapid exhumation, the Southern Karakorum belt drained by the Hispar River and the Nanga Parbat massif were revealed as important sources of garnet, amphibole, and possibly epidote. Sediment supply from the Greater Himalaya, Lesser Himalaya, and Subhimalaya is dominant only for Punjab tributaries that join the Indus River downstream and do not contribute sand to the Thal Desert. The detailed compositional fingerprint of Thal Desert sand, if contrasted with that of lower course tributaries exclusively draining the Himalaya, provides a semi-actualistic key to be used, in conjunction with complementary provenance datasets and geological information, to reconstruct changes in paleodrainage and unravel the relationship between climatic and tectonic forces that controlled the erosional evolution of the western Himalayan-Karakorum orogen in space and time.

Data-Driven Probabilistic Thermal Stress Analysis of a Gas Turbine Casing

2018 ◽  
Author(s):  
Zixi Han ◽  
Mian Li ◽  
Zixian Jiang ◽  
Zuoxing Min ◽  
Sophie Bourmich
Keyword(s):  
Monte Carlo ◽  
Thermal Stress ◽  
Boundary Conditions ◽  
Gas Turbine ◽  
Probabilistic Approach ◽  
Computational Time ◽  
Strength Assessment ◽  
Fixed Design ◽  
Design Values ◽  
Turbine Casing

Strength requirement is one of the most important criteria in the design of gas turbine casing. Traditionally, deterministic analyses are used in strength assessment, with boundary conditions and loads set as fixed design values. However, real boundary conditions and loads in the operation can often differ from the fixed design values, such that the mechanical integrity of the turbine casing can vary from the strength and fatigue calculations. In this work, the effect of the variability of the boundary conditions and loads is investigated on the static thermal stress problem of gas turbine casings using a probabilistic approach. The probability distribution is estimated using a Monte Carlo simulation based on the distribution of boundary conditions and loads obtained from field measurements. The finite element analysis is used to calculate the stress corresponding to different boundary conditions and a surrogate model is built to reduce the computational time of Monte Carlo simulations. This methodology is applied to a real engineering case which better quantifies the strength assessment result.

Long-term history of sediment inputs to the eastern Arabian Sea and its implications for the evolution of the Indian summer monsoon since 3.7 Ma

2018 ◽  
Vol 157 (6) ◽  
pp. 908-919 ◽  
Author(s):  
Mingjiang Cai ◽  
Zhaokai Xu ◽  
Peter D. Clift ◽  
Boo-Keun Khim ◽  
Dhongil Lim ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Sediment Supply ◽  
Deccan Traps ◽  
Indus River ◽  
Eastern Arabian Sea ◽  
Monsoon Intensity ◽  
History Of

AbstractWe present a new set of clay mineral and grain-size data for the siliciclastic sediment fraction from International Ocean Discovery Program (IODP) Site U1456 located in the eastern Arabian Sea to reconstruct the variabilities in the continental erosion and weathering intensity in the western Himalaya, elucidate the sediment source-to-sink processes and discuss the potential controls underlying these changes since 3.7 Ma. The clay minerals mainly consist of smectite (0–90%, average 44%) and illite (3–90%, average 44%), with chlorite (1–26%, average 7%) and kaolinite (0–19%, average 5%) as minor components. The compositional variations in the clay minerals at IODP Site U1456 suggest four phases of sediment provenance: the Indus River (phase 1, 3.7–3.2 Ma), the Indus River and Deccan Traps (phase 2, 3.2–2.6 Ma), the Indus River (phase 3, 2.6–1.2 Ma) and the Indus River and Deccan Traps (phase 4, 1.2–0 Ma). These provenance changes since 3.7 Ma can be correlated with variations in the Indian summer monsoon intensity. The siliciclastic sediments in the eastern Arabian Sea were mainly derived from the Indus River when the Indian summer monsoon was generally weak. In contrast, when the Indian summer monsoon intensified, the siliciclastic sediment supply from the Deccan Traps increased. In particular, this study shows that the smectite/(illite+chlorite) ratio is a sensitive tool for reconstructing the history of the variation in the Indian summer monsoon intensity over the continents surrounding the Arabian Sea since 3.7 Ma.

scholarly journals Interactions between channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

2019 ◽  
Author(s):  
Sara Savi ◽  
Stefanie Tofelde ◽  
Andrew D. Wickert ◽  
Aaron Bufe ◽  
Taylor F. Schildgen ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Signal Propagation ◽  
Main Channel ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Alluvial Fans ◽  
Fluvial System ◽  
Channel Network ◽  
Fluvial Deposits ◽  
The Impact

Abstract. Climate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel-network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may promote or prevent sediment to be moved within the fluvial system, creating different coupling conditions. A prograding alluvial fan, for example, has the potential to disrupt the sedimentary signal propagating downstream through the confluence zone. By analyzing different environmental scenarios, our results indicate the contribution of the two sub-systems to fluvial deposits, both upstream and downstream of the tributary junction, which may be diagnostic of a perturbation affecting the tributary or the main channel only. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which is essential for a correct reconstruction of the climatic or tectonic history of a basin.

scholarly journals A Comparative Study on Acoustic Optimization and Analysis of CLD/Plate in a Cavity Using ESO and GA

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Dongdong Zhang ◽  
Shuwen Wang ◽  
Ling Zheng
Keyword(s):  
Boundary Conditions ◽  
Radiation Power ◽  
Sound Radiation ◽  
Computational Time ◽  
Sound Power ◽  
Normal Velocity ◽  
Flexible Plate ◽  
Rejection Ratio ◽  
Sound Radiation Power ◽  
Element Method

An acoustic radiation model of a cavity with a flexible plate treated with constrained layer damping (CLD) is developed by a combination of finite element method (FEM) and boundary element method (BEM). An acoustic topology optimization model is established with the objective of minimizing sound radiation power at specific modal frequency and design variables defined as locations of CLD treatments. The evolutionary structural optimization (ESO) method and genetic algorithm (GA) are employed to search optimal CLD configurations. Sound power sensitivity for CLD/plate is derived to determine search direction in ESO optimization procedure. The optimal CLD layouts for the flexible plate with two different boundary conditions are obtained and analyzed. Computational time, optimal layouts, and minimum sound power obtained using ESO and GA are compared. The results demonstrate effectiveness of the two methods, and ESO is more efficient to obtain deterministic and more practical optimal CLD material layouts for minimizing sound radiation power. The influences of CLD materials thickness and exciting force locations on optimal results obtained using ESO are discussed in detail. It is shown that the optimal rejection ratio varies with thicknesses of CLD materials and distribution of normal velocity of the flexible plate. Variation trend of the optimal rejection ratio is opposite for the two boundary conditions.

Dynamics of sediment delivery to mangrove forests of the Ganges-Brahmaputra-Meghna Delta

2020 ◽  
Author(s):  
Richard Hale ◽  
Alexandra Garnand ◽  
Carol Wilson
Keyword(s):  
Sediment Load ◽  
Monsoon Season ◽  
Sediment Concentration ◽  
Water Velocity ◽  
Sediment Supply ◽  
Tidal Range ◽  
Mangrove Forests ◽  
Southern Coast ◽  
Sediment Delivery ◽  
The Ganges

<p>The Ganges-Brahmaputra-Meghna Delta (GBMD) is among the largest in the world, nourished by the ~1 Gt/yr sediment load of its titular rivers. Approximately 75% of this sediment load is debouched to the Bay of Bengal, with ~180 Mt subsequently reworked by tidal processes across the southwestern portion of the delta. This region includes this Sundarbans National Reserve Forest (SNRF), which is the words’ largest continuous mangrove stand. In addition to global sea level rise and the enhanced subsidence intrinsic to deltas, ongoing and proposed alterations to the upstream fluvial sediment supply threaten the future viability of this important ecological and cultural resource.</p><p> </p><p>In this study, we use data collected in situ by acoustic and optical instrumentation to examine the physical processes controlling sedimentation in the mangrove forest along the southern coast during both the monsoon (October 2019) and dry seasons (March 2020).  These data are then compared with sedimentation rates measured using sediment elevation tables and marker horizons, as well as observations made 100 km further inland near the northern extent of the SNRF. At this inland site, sediment supply, inundation depth, and salinity have been identified as important factors controlling sediment deposition to the mangrove platform, which ranges from ~1 cm during the dry season (November – June), to > 2 cm during the monsoon (July-October). Data from the second location along the coast are vital for understanding the regional nature of the various threats to delta viability.</p><p> </p><p>Preliminary analysis of the 2019 monsoon season data from the southern coast reveals the relative importance of water depth, water velocity, and mangrove pneumatophore density on modulating both water velocity and suspended sediment concentration. Previous studies have identified that while the inland location features a larger tidal range (~5 m vs. ~3 m), frequent cyclone activity likely impacts sedimentation at the coastal site. Data collected in March 2020 will address how these variables impact controls on sedimentation both seasonally and regionally. Results from this study demonstrate the importance of providing regional context to sedimentation studies, as delta communities adapt to dynamic forcing conditions.   </p>

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