scholarly journals Accounting for Uncertainties in the Safety Assessment of Concrete Gravity Dams: A Probabilistic Approach with Sample Optimization

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 855
Author(s):  
Rocio L. Segura ◽  
Benjamin Miquel ◽  
Patrick Paultre ◽  
Jamie E. Padgett
Keyword(s):  
Probabilistic Approach ◽  
Sampling Strategy ◽  
Design Guidelines ◽  
Probabilistic Methods ◽  
Computationally Efficient ◽  
Promising Alternative ◽  
Concrete Gravity Dams ◽  
Dam Stability ◽  
The Stability ◽  
Parameter Ranges

Important advances have been made in the methodologies for assessing the safety of dams, resulting in the review and modification of design guidelines. Many existing dams fail to meet these revised criteria, and structural rehabilitation to achieve the updated standards may be costly and difficult. To this end, probabilistic methods have emerged as a promising alternative and constitute the basis of more adequate procedures of design and assessment. However, such methods, in addition to being computationally expensive, can produce very different solutions, depending on the input parameters, which can greatly influence the final results. Addressing the existing challenges of these procedures to analyze the stability of concrete dams, this study proposes a probabilistic-based methodology for assessing the safety of dams under usual, unusual, and extreme loading conditions. The proposed procedure allows the analysis to be updated while avoiding unnecessary simulation runs by classifying the load cases according to the annual probability of exceedance and by using an efficient progressive sampling strategy. In addition, a variance-based global sensitivity analysis is performed to identify the parameters most affecting the dam stability, and the parameter ranges that meet the safety guidelines are formulated. It is observed that the proposed methodology is more robust, more computationally efficient, and more easily interpretable than conventional methods.

Uncertainties in probabilistic seismic hazard assessment as a function of probability level: A case history for Vancouver, British Columbia

1983 ◽  
Vol 73 (4) ◽  
pp. 1225-1241
Author(s):  
Gail M. Atkinson ◽  
Robin G. Charlwood
Keyword(s):  
British Columbia ◽  
Case History ◽  
Probabilistic Approach ◽  
Seismic Hazard Assessment ◽  
Probabilistic Methods ◽  
Probabilistic Seismic Hazard Assessment ◽  
Probability Level ◽  
Low Probability ◽  
The Stability ◽  
Strong Ground

abstract The stability of probabilistic methods of evaluating expected strong ground motion levels is examined as a function of probability level. A case history for Vancouver, British Columbia, is used to show that when input parameters are screened on the basis of compatibility with low probability calculations, robust (±25 per cent) results are obtained for probabilities in the range of 10−2 to 10−4 per annum. There is no inherent loss of stability with decreasing probability. Probabilistic approaches are not in conflict with deterministic approaches, since deterministic data can be incorporated into the analysis. The usefulness of the probabilistic approach lies in providing a framework for evaluating uncertainties.

scholarly journals Experimental and computational study on roles of WOx promoting strong metal support promoter interaction in Pt catalysts during glycerol hydrogenolysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tinnakorn Saelee ◽  
Poonnapa Limsoonthakul ◽  
Phakaorn Aphichoksiri ◽  
Meena Rittiruam ◽  
Mongkol Lerdpongsiripaisarn ◽  
...  
Keyword(s):  
Density Of States ◽  
Design Guidelines ◽  
Total Density ◽  
High Electron ◽  
Metal Support Interaction ◽  
Metal Support ◽  
Glycerol Hydrogenolysis ◽  
The Stability ◽  
Total Density Of States ◽  
Promoter Interaction

AbstractBiodiesel is of high interest due to increased demand for energy with the concern regarding more sustainable production processes. However, an inevitable by-product is glycerol. Hence, the conversion of this by-product to higher-value chemicals, especially 1,3-propanediol (1,3-PDO) via glycerol hydrogenolysis reaction, is one of the most effective pathways towards a profitable process. In general, this process is catalyzed by a highly active Pt-based catalyst supported on γ-Al2O3. However, its low 1,3-PDO selectivity and stability due to surface deactivation of such catalysts remained. This led to the surface modification by WOx to improve both the selectivity by means of the increased Brønsted acidity and the stability in terms of Pt leaching-resistance. Hence, we applied experimental and density functional theory (DFT)-based techniques to study the fundamentals of how WOx modified the catalytic performance in the Pt/γ-Al2O3 catalyst and provided design guidelines. The effects of WOx promoter on improved activity were due to the shifting of the total density of states towards the antibonding region evident by the total density of states (TDOS) profile. On the improved 1,3-PDO selectivity, the main reason was the increasing number of Brønsted acid sites due to the added WOx promoter. Interestingly, the stability improvement was due to the strong metal-support interaction (SMSI) that occurred in the catalyst, like typical high leaching-resistant catalysts. Also, the observed strong metal-support-promoter interaction (SMSPI) is an additional effect preventing leaching. The SMSPI stemmed from additional bonding between the WOx species and the Pt active site, which significantly strengthened Pt adsorption to support and a high electron transfer from both Pt and Al2O3 to WOx promoter. This suggested that the promising promoter for our reaction performed in the liquid phase would improve the stability if SMSI occurred, where the special case of the WOx promoter would even highly improve the stability through SMSPI. Nevertheless, various promoters that can promote SMSPI need investigations.

scholarly journals The performance of ultra-lightweight foamed concrete incorporating nanosilica

2021 ◽  
Vol 21 (2) ◽  
Author(s):  
Mohamed Abd Elrahman ◽  
Pawel Sikora ◽  
Sang-Yeop Chung ◽  
Dietmar Stephan
Keyword(s):  
Wall Thickness ◽  
Probabilistic Approach ◽  
Drying Shrinkage ◽  
Dry Density ◽  
Optimal Dosage ◽  
X Ray ◽  
Mechanical And Physical Properties ◽  
Fresh State ◽  
Foamed Concrete ◽  
The Stability

AbstractThis paper aims to investigate the feasibility of the incorporation of nanosilica (NS) in ultra-lightweight foamed concrete (ULFC), with an oven-dry density of 350 kg/m3, in regard to its fresh and hardened characteristics. The performance of various dosages of NS, up to 10 wt.-%, were examined. In addition, fly ash and silica fume were used as cement replacing materials, to compare their influence on the properties of foamed concrete. Mechanical and physical properties, drying shrinkage and the sorption of concrete were measured. Scanning electron microscopy (SEM) and X-ray microcomputed tomography (µ-CT) and a probabilistic approach were implemented to evaluate the microstructural changes associated with the incorporation of different additives, such as wall thickness and pore anisotropy of produced ULFCs. The experimental results confirmed that the use of NS in optimal dosage is an effective way to improve the stability of foam bubbles in the fresh state. Incorporation of NS decrease the pore anisotropy and allows to produce a foamed concrete with increased wall thickness. As a result more robust and homogenous microstructure is produced which translate to improved mechanical and transport related properties. It was found that replacement of cement with 5 wt.-% and 10 wt.-% NS increase the compressive strength of ULFC by 20% and 25%, respectively, when compared to control concrete. The drying shrinkage of the NS-incorporated mixes was higher than in the control mix at early ages, while decreasing at 28 d. In overall, it was found that NS is more effective than other conventional fine materials in improving the stability of fresh mixture as well as enhancing the strength of foamed concrete and reducing its porosity and sorption.

A computationally efficient adaptive robust control scheme for a quad-rotor transporting cable-suspended payloads

2021 ◽  
pp. 095441002110136
Author(s):  
Nasim Ullah ◽  
Irfan Sami ◽  
Wang Shaoping ◽  
Hamid Mukhtar ◽  
Xingjian Wang ◽  
...  
Keyword(s):  
Robust Control ◽  
Fractional Order ◽  
Sliding Mode ◽  
Adaptive Robust Control ◽  
Computationally Efficient ◽  
Control Scheme ◽  
Control Schemes ◽  
Adaptive Laws ◽  
Unknown Disturbances ◽  
The Stability

This article proposes a computationally efficient adaptive robust control scheme for a quad-rotor with cable-suspended payloads. Motion of payload introduces unknown disturbances that affect the performance of the quad-rotor controlled with conventional schemes, thus novel adaptive robust controllers with both integer- and fractional-order dynamics are proposed for the trajectory tracking of quad-rotor with cable-suspended payload. The disturbances acting on quad-rotor due to the payload motion are estimated by utilizing adaptive laws derived from integer- and fractional-order Lyapunov functions. The stability of the proposed control systems is guaranteed using integer- and fractional-order Lyapunov theorems. Overall, three variants of the control schemes, namely adaptive fractional-order sliding mode (AFSMC), adaptive sliding mode (ASMC), and classical Sliding mode controllers (SMC)s) are tested using processor in the loop experiments, and based on the two performance indicators, namely robustness and computational resource utilization, the best control scheme is evaluated. From the results presented, it is verified that ASMC scheme exhibits comparable robustness as of SMC and AFSMC, while it utilizes less sources as compared to AFSMC.

scholarly journals Application of a computationally efficient method to approximate gap model results with a probabilistic approach

2014 ◽  
Vol 7 (1) ◽  
pp. 1535-1600
Author(s):  
M. Scherstjanoi ◽  
J. O. Kaplan ◽  
H. Lischke
Keyword(s):  
Climate Change ◽  
Efficient Method ◽  
Tree Species ◽  
Forest Dynamics ◽  
Probabilistic Approach ◽  
Age Distribution ◽  
Change Scenario ◽  
Model Parameters ◽  
Computationally Efficient ◽  
Tree Species Composition

Abstract. To be able to simulate climate change effects on forest dynamics over the whole of Switzerland, we adapted the second generation DGVM LPJ-GUESS to the Alpine environment. We modified model functions, tuned model parameters, and implemented new tree species to represent the potential natural vegetation of Alpine landscapes. Furthermore, we increased the computational efficiency of the model to enable area-covering simulations in a fine resolution (1 km) sufficient for the complex topography of the Alps, which resulted in more than 32 000 simulation grid cells. To this aim, we applied the recently developed method GAPPARD (Scherstjanoi et al., 2013) to LPJ-GUESS. GAPPARD derives mean output values from a combination of simulation runs without disturbances and a patch age distribution defined by the disturbance frequency. With this computationally efficient method, that increased the model's speed by approximately the factor 8, we were able to faster detect shortcomings of LPJ-GUESS functions and parameters. We used the adapted LPJ-GUESS together with GAPPARD to assess the influence of one climate change scenario on dynamics of tree species composition and biomass throughout the 21st century in Switzerland. To allow for comparison with the original model, we additionally simulated forest dynamics along a north-south-transect through Switzerland. The results from this transect confirmed the high value of the GAPPARD method despite some limitations towards extreme climatic events. It allowed for the first time to obtain area-wide, detailed high resolution LPJ-GUESS simulation results for a large part of the Alpine region.

scholarly journals A mass-conserving and multi-tracer efficient transport scheme in the online integrated Enviro-HIRLAM model

2013 ◽  
Vol 6 (4) ◽  
pp. 1029-1042 ◽  
Author(s):  
B. Sørensen ◽  
E. Kaas ◽  
U. S. Korsholm
Keyword(s):  
Prediction Model ◽  
Weather Prediction ◽  
Three Dimensional ◽  
Chemical Species ◽  
Numerical Weather Prediction Model ◽  
Computationally Efficient ◽  
Long Time ◽  
Dimensional Version ◽  
The Stability ◽  
Lagrangian Scheme

Abstract. In this paper a new advection scheme for the online coupled chemical–weather prediction model Enviro-HIRLAM is presented. The new scheme is based on the locally mass-conserving semi-Lagrangian method (LMCSL), where the original two-dimensional scheme has been extended to a fully three-dimensional version. This means that the three-dimensional semi-implicit semi-Lagrangian scheme which is currently used in Enviro-HIRLAM is largely unchanged. The HIRLAM model is a computationally efficient hydrostatic operational short-term numerical weather prediction model, which is used as the base for the online integrated Enviro-HIRLAM. The new scheme is shown to be efficient, mass conserving, and shape preserving, while only requiring minor alterations to the original code. It still retains the stability at long time steps, which the semi-Lagrangian schemes are known for, while handling the emissions of chemical species accurately. Several mass-conserving filters have been tested to assess the optimal balance of accuracy vs. efficiency.

Effects of Airfoil’s Polar Data in the Stall Region on the Estimation of Darrieus Wind Turbine Performance

2016 ◽  
Author(s):  
David Marten ◽  
Alessandro Bianchini ◽  
Georgios Pechlivanoglou ◽  
Francesco Balduzzi ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Unsteady Aerodynamics ◽  
Vertical Axis ◽  
Design Guidelines ◽  
Operating Conditions ◽  
Performance Estimation ◽  
Simulation Methods ◽  
Computationally Efficient ◽  
Urban Context ◽  
Lift And Drag ◽  
Thrust And Torque

Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 90’s, in favour of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT concept, especially in the Darrieus configuration, may outweigh their disadvantages in specific applications, like the urban context or floating platforms. To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guidelines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the Blade Element Momentum Theory for HAWTs’ applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the Double Multiple Streamtubes (DMS) Theory, based on momentum balances, and the Lifting Line Theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces. Since the incidence angles range experienced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition towards the “thin plate like” behaviour has a large effect on simulation results. This paper will demonstrate the importance of stall and post-stall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of post-stall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna-Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and torque are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both simulation methods is highlighted and discussed.

On Canadian methodologies of probabilistic seismic risk estimation

1979 ◽  
Vol 69 (5) ◽  
pp. 1549-1566
Author(s):  
D. H. Weichert ◽  
W. G. Milne
Keyword(s):  
Ground Motion ◽  
Seismic Risk ◽  
Risk Estimation ◽  
Historical Earthquakes ◽  
Extreme Value ◽  
Probabilistic Methods ◽  
Average Value ◽  
Risk Estimates ◽  
The Stability ◽  
Comparison Of The Results

abstract Three probabilistic methods for the estimation of seismic risk have been used in Canada. A reevaluation of the extreme value method shows no advantages over the average value method of Milne and Davenport. Conceptual improvements in the underlying assumptions of the latter method are a constrained release of historical earthquakes from their presumed epicenters and the averaging of earthquake rates over variable periods. Risk estimation can then proceed as suggested by Cornell. Comparison of the results of this modification of the average number method shows similar results as the Milne and Davenport average value method. The stability of risk estimates against new earthquakes is improved, but sensitivities at typical sites toward unavoidable deterministic elements in the model are similar to the older method. For certain site-source-seismicity combinations probabilistic estimates of ground motion could become almost quasi-deterministic.

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