scholarly journals Systematic comparison of different numerical approaches for tsunami simulations at the Chilean coast as part of the RIESGOS project

2020 ◽  
Author(s):  
Sven Harig ◽  
Natalia Zamora ◽  
Alejandra Gubler ◽  
Natalja Rakowsky
Keyword(s):  
Numerical Models ◽  
Tide Gauge ◽  
Tsunami Propagation ◽  
Chilean Coast ◽  
The Andes ◽  
Source Determination ◽  
Probabilistic Study ◽  
Nested Grids ◽  
Element Approach ◽  
Numerical Approaches

<p>There is a growing number of numerical models for tsunami propagation and inundation available, based on different spatial discretizations and numerical approaches. Since simulations carried out with such models are used to generate warning products in an early warning context, it is crucial to investigate differences emerging from the chosen algorithms for simulation and warning product determination. Uncertainties regarding the source determination within the first minutes after a tsunami generation might be of major concern for an appropriate warning at the coast, still, the sensitivity of warning products with respect to pre-computed simulation database contents or on-the-fly calculations are of crucial importance as well.</p><p>In this study, we investigate the performance of three models (TsunAWI, HySEA, COMCOT) in the oceanic region offshore central and northern Chile with inundation studies in Valparaíso and Viña del Mar. The investigation forms part of the tsunami component in the RIESGOS project dealing more general with multi hazard assessments in the Andes region. The numerical implementation of the models include both a finite element approach with triangular meshes of variable resolution as well as finite difference implementations with nested grids for the coastal area. The tsunami sources are identical in all models and chosen from an ensemble of events used in an earlier probabilistic study of the region. Additionally, two historic events are considered as well to validate the models against the corresponding measurements.</p><p>We compare results in virtual gauges as well as actual tide gauge locations at the Chilean coast. Inundation areas are determined with high resolution and employing the model specific wetting and drying implementations. We compare the model results and sensitivities with respect to spatial resolution and parameters like bottom friction and bathymetry  representation in the varying mesh geometries.</p>

Mistuning Modeling and its Validation for Small Turbine Wheels

2013 ◽  
Author(s):  
David Hemberger ◽  
Dietmar Filsinger ◽  
Hans-Jörg Bauer
Keyword(s):  
Amplification Factor ◽  
Numerical Models ◽  
Lower Sensitivity ◽  
Fe Model ◽  
Mode Localization ◽  
Geometric Deviations ◽  
Probabilistic Study ◽  
Calculated Amplitude ◽  
Amplitude Amplification ◽  
The Ideal

The production of bladed structures, e.g. turbine and compressor wheels, is a subject of statistical scatter. The blades are designed to be identical but differ due to small manufacturing tolerances. This so called mistuning can lead to increased vibration amplitudes compared to the ideal tuned case. The object of this study is to create and validate numerical models to evaluate such mistuning effects of turbine wheels for automotive turbocharger applications. As a basis for the numerical analysis vibration measurements under stand-still conditions were carried out by using a laser surface velocimeter (LSV). The scope of this investigation was to identify the mistuning properties of the turbine wheels namely the frequency deviation from the ideal, cyclic symmetrical tuned system. Experimental modal analyses as well as blade by blade measurements were performed. Moreover 3D scanning techniques were employed to determine geometric deviations. Numerical FE models and a simplified multi degree of freedom model (EBM) were created to reproduce the measured mistuning effects. The prediction of mode localization and the calculated amplitude amplification were evaluated. The best results were obtained with a FE model that employs individual sectorial stiffnesses. The results also indicate that the major contribution to mistuning is made by material inhomogeneities and not by geometric deviations from ideal dimensions. With the adjusted FE model a probabilistic study has been performed to investigate the influence of the mistuning on the amplitude amplification factor. It has been found that at a certain level of mistuning the amplification factor remains constant or slightly decreases. By introducing intentional mistuning a lower sensitivity as well as a decrease of the amplitude amplification could be achieved.

scholarly journals Numerical models for assessing the risk of leaflet thrombosis post-transcatheter aortic valve-in-valve implantation

2020 ◽  
Vol 7 (12) ◽  
pp. 201838
Author(s):  
Romina Plitman Mayo ◽  
Halit Yaakobovich ◽  
Ariel Finkelstein ◽  
Shawn C. Shadden ◽  
Gil Marom
Keyword(s):  
High Risk ◽  
Aortic Valve ◽  
Numerical Models ◽  
Aortic Valves ◽  
Transcatheter Aortic Valve ◽  
Edwards Sapien ◽  
Valve In Valve ◽  
Sapien 3 ◽  
Valve Implantation ◽  
Numerical Approaches

Leaflet thrombosis has been suggested as the reason for the reduced leaflet motion in cases of hypoattenuated leaflet thickening of bioprosthetic aortic valves. This work aimed to estimate the risk of leaflet thrombosis in two post-valve-in-valve (ViV) configurations, using five different numerical approaches. Realistic ViV configurations were calculated by modelling the deployments of the latest version of transcatheter aortic valve devices (Medtronic Evolut PRO, Edwards SAPIEN 3) in the surgical Sorin Mitroflow. Computational fluid dynamics simulations of blood flow followed the dry models. Lagrangian and Eulerian measures of near-wall stagnation were implemented by particle and concentration tracking, respectively, to estimate the thrombogenicity and to predict the risk locations. Most of the numerical approaches indicate a higher leaflet thrombosis risk in the Edwards SAPIEN 3 device because of its intra-annular implantation. The Eulerian approaches estimated high-risk locations in agreement with the wall sheer stress (WSS) separation points. On the other hand, the Lagrangian approaches predicted high-risk locations at the proximal regions of the leaflets matching the low WSS magnitude regions of both transcatheter aortic valve implantation models and reported clinical and experimental data. The proposed methods can help optimizing future designs of transcatheter aortic valves with minimal thrombotic risks.

scholarly journals Optimizing Simulation and Analysis of Automated Top-Coal Drawing Technique in Extra-Thick Coal Seams

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 232 ◽  
Author(s):  
Qunlei Zhang ◽  
Ruifu Yuan ◽  
Shen Wang ◽  
Dongyin Li ◽  
Huamin Li ◽  
...  
Keyword(s):  
Numerical Models ◽  
Time Estimation ◽  
Engineering Practice ◽  
Coal Seams ◽  
Control Approach ◽  
Working Face ◽  
Geological Conditions ◽  
Round Number ◽  
Element Approach ◽  
Drawing Technique

A particle element approach based on continuum-discontinuum element method (CDEM) is applied to optimize the automated top-coal drawing techniques in extra-thick coal seams. Numerical models with 100 drawing openings are created according to the field engineering geological conditions of Tongxin coal mine in China. An automated coal drawing control approach in numerical modelling based on time criterion is proposed. The rock mixed rate, top-coal recovery rate and the variance of the drawn top coal amount are counted and set as the statistical indicators to evaluate the top-coal drawing techniques. The traditional top-coal drawing criterion, “rocks appear, close the opening”, leads to low recovery of top coal and waste of coal resources in extra-thick coal seams, significantly weakening the transport stability and efficiency of the scraper conveyer. A three-round unequal time top-coal drawing technique is proposed for automated top-coal drawing. Three drawing openings, corresponding to the three top-coal drawing rounds respectively, are working at the same time; in each round, the top-coal drawing sequence is from the first drawing opening at one end of the working face to last drawing opening at another end; the drawing time of each round is not equal and increases with the round number. The numerical inversion approach of iteration steps can be used for real top-coal drawing time estimation and automated drawing process design to achieve a better top coal drawing effect, while the exact time for each drawing round still needs to be corrected by engineering practice.

scholarly journals Numerical Investigations of Micro-Scale Diffusion Combustion: A Brief Review

2019 ◽  
Vol 9 (16) ◽  
pp. 3356 ◽  
Author(s):  
P. R. Resende ◽  
Mohsen Ayoobi ◽  
Alexandre M. Afonso
Keyword(s):  
Alternative Fuels ◽  
Numerical Models ◽  
Scientific Progress ◽  
Combustion Characteristics ◽  
Operating Conditions ◽  
Critical Parameters ◽  
Diffusion Combustion ◽  
Great Opportunity ◽  
Numerical Investigations ◽  
Numerical Approaches

With the increasing global concerns about the impacts of byproducts from the combustion of fossil fuels, researchers have made significant progress in seeking alternative fuels that have cleaner combustion characteristics. Such fuels are most suitable for addressing the increasing demands on combustion-based micro power generation systems due to their prominently higher energy density as compared to other energy resources such as batteries. This cultivates a great opportunity to develop portable power devices, which can be utilized in unmanned aerial vehicles (UAVs), micro satellite thrusters or micro chemical reactors and sensors. However, combustion at small scales—whether premixed or non-premixed (diffusion)—has its own challenges as the interplay of various physical phenomena needs to be understood comprehensively. This paper reviews the scientific progress that researchers have made over the past couple of decades for the numerical investigations of diffusion flames at micro scales. Specifically, the objective of this review is to provide insights on different numerical approaches in analyzing diffusion combustion at micro scales, where the importance of operating conditions, critical parameters and the conjugate heat transfer/heat re-circulation have been extensively analyzed. Comparing simulation results with experimental data, numerical approaches have been shown to perform differently in different conditions and careful consideration should be given to the selection of the numerical models depending on the specifics of the cases that are being modeled. Varying different parameters such as fuel type and mixture, inlet velocity, wall conductivity, and so forth, researchers have shown that at micro scales, diffusion combustion characteristics and flame dynamics are critically sensitive to the operating conditions, that is, it is possible to alter the flammability limits, control the flame stability/instability or change other flame characteristics such as flame shape and height, flame temperature, and so forth.

Study of the tsunami source in the Palu Bay following the Mw7.5 2018 Sulawesi earthquake

2020 ◽  
Author(s):  
Fabrizio Romano ◽  
Haider Hasan ◽  
Stefano Lorito ◽  
Finn Løvholt ◽  
Beatriz Brizuela ◽  
...  
Keyword(s):  
Tide Gauge ◽  
Joint Inversion ◽  
Seismic Source ◽  
Strike Slip ◽  
Tsunami Source ◽  
Fault System ◽  
Tsunami Propagation ◽  
Slip Mechanism ◽  
Short Period ◽  
Nonlinear Joint

<p>On 28 September 2018 a Mw 7.5 strike-slip earthquake occurred on the Palu-Koro fault system in the Sulawesi Island. Immediately after the earthquake a powerful tsunami hit the Palu Bay causing large damages and numerous fatalities.</p><p>Several works, inverting seismic or geodetic data, clearly estimated the slip distribution of this event, but the causative source of the tsunami is still not completely understood; indeed, the strike-slip mechanism of the seismic source alone might not be sufficient to explain the large runups observed (> 6 m) along the coast of the Palu Bay, and thus one or more additional non-seismic sources like a landslide could have contributed to generate the big tsunami. An insight of that can be found in an extraordinary collection of amateur videos, and on the only available tide gauge in the Bay, at Pantoloan, that showed evidence for a short period wave of at least 2-3 minutes, compatible with a landslide.</p><p>In this study, we attempt to discriminate the contribution in the tsunami generation of both the seismic source and  some supposed landslides distributed along the coast of the Bay.</p><p>In particular, we attempt to estimate the causative source of the tsunami by means of a nonlinear joint inversion of geodetic (InSAR) and runup data. We use a fault geometry consistent with the Sentinel-2 optical analysis results and analytically compute the geodetic Green’s functions. The same fault model is used to compute the initial condition for the seismic tsunami Green’s functions, including the contribution of the horizontal deformation due to the gradient of the bathymetry (10 m spatial resolution); the landslide tsunami Green’s functions are computed the software BingClaw by placing several hypothetical sources in the Bay. In both the cases the tsunami propagation is modelled by numerically solving the nonlinear shallow water equations.</p><p>In this work we also attempt to address the validity of Green’s functions approach (linearity) for earthquake and landslide sources as well as the wave amplitude offshore as predictor of nearby runup.</p>

Evaporation from homogeneous and heterogeneous soil systems: Modeling approaches and experimental data

2020 ◽  
Author(s):  
Shmuel Assouline ◽  
Tamir Kamai
Keyword(s):  
Experimental Data ◽  
Soil Profile ◽  
Numerical Models ◽  
Water Losses ◽  
Ongoing Research ◽  
Fundamental Limitations ◽  
Soil Systems ◽  
Heterogeneous Soil ◽  
The Impact ◽  
Numerical Approaches

<p>Accurate estimates of water losses from the soil by evaporation are important for hydrological, agricultural, and climatic purposes. Different analytical and numerical approaches were developed to provide the capability to simulate and predict the dynamics of the evaporation process in terms of fluxes, and water and thermal distributions in the soil profile. Experimental investigation of the process under different boundary conditions is also possible by means of columns and weighing lysimeters. As part, these experimental setups allow addressing the impact of heterogeneity in the drying soil profile. Experimental data resulting from evaporation experiments under natural and laboratory conditions with homogeneous and heterogeneous soil profiles are presented and analyzed. These data are also compared to results from available analytical and numerical models. This comparison points out fundamental limitations of the approaches that assume hydraulic connectivity up to the surface, as well as those that suppose monotonic drying when unsteady conditions prevail. Differences between experimental data and model prediction emphasize challenging knowledge gaps that are part of ongoing research.</p>

Investigations of Flutter and Aerodynamic Damping of a Turbine Blade: Experimental Characterization

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Charles E. Seeley ◽  
Christian Wakelam ◽  
Xuefeng Zhang ◽  
Douglas Hofer ◽  
Wei-Min Ren
Keyword(s):  
Mechanical Response ◽  
Numerical Models ◽  
Structural Vibration ◽  
Aerodynamic Damping ◽  
Actuation System ◽  
Electromagnetic Actuation System ◽  
Wide Range ◽  
Large Motion ◽  
Damping Effects ◽  
Numerical Approaches

Flutter is a self-excited and self-sustained aero-elastic instability, caused by the positive feedback between structural vibration and aerodynamic forces. A two-passage linear turbine cascade was designed, built, and tested to better understand the phenomena and collect data to validate numerical models. The cascade featured a center airfoil that had its pitch axis as a degree-of-freedom to enable coupling between the air flow and mechanical response in a controlled manner. The airfoil was designed to be excited about its pitch axis using an electromagnetic actuation system over a range of frequencies and amplitudes. The excitation force was measured with load cells, and the airfoil motion was measured with accelerometers. Extraordinary effort was taken to minimize the mechanical damping so that the damping effects of the airflow over the airfoil, that were of primary interest, would be observable. Assembling the cascade required specialized alignment procedures due to the tight clearances and large motion. The aerodynamic damping effects were determined by observing changes in the mechanical frequency response of the system. Detailed aerodynamic and mechanical measurements were conducted within a wide range of Mach numbers (Ma) from Ma = 0.10 to 1.20. Experimental results indicated that the aerodynamic damping increased from Ma = 0.10 to 0.65, dropped suddenly, and was then constant from Ma = 0.80 to 1.20. A flutter condition was identified in the interval between Ma = 0.65 and Ma = 0.80. The aerodynamic damping was also found to be independent of displacement amplitude within the tested range, giving credence to linear numerical approaches.

scholarly journals Simulated Changes in Northwest U.S. Climate in Response to Amazon Deforestation*

2013 ◽  
Vol 26 (22) ◽  
pp. 9115-9136 ◽  
Author(s):  
David Medvigy ◽  
Robert L. Walko ◽  
Martin J. Otte ◽  
Roni Avissar
Keyword(s):  
United States ◽  
Sierra Nevada ◽  
Numerical Models ◽  
Regional Climate ◽  
Regional Climate Change ◽  
The United States ◽  
Far Field ◽  
Adequate Model ◽  
Thermal Anomalies ◽  
The Andes

Abstract Numerical models have long predicted that the deforestation of the Amazon would lead to large regional changes in precipitation and temperature, but the extratropical effects of deforestation have been a matter of controversy. This paper investigates the simulated impacts of deforestation on the northwest United States December–February climate. Integrations are carried out using the Ocean–Land–Atmosphere Model (OLAM), here run as a variable-resolution atmospheric GCM, configured with three alternative horizontal grid meshes: 1) 25-km characteristic length scale (CLS) over the United States, 50-km CLS over the Andes and Amazon, and 200-km CLS in the far-field; 2) 50-km CLS over the United States, 50-km CLS over the Andes and Amazon, and 200-km CLS in the far-field; and 3) 200-km CLS globally. In the high-resolution simulations, deforestation causes a redistribution of precipitation within the Amazon, accompanied by vorticity and thermal anomalies. These anomalies set up Rossby waves that propagate into the extratropics and impact western North America. Ultimately, Amazon deforestation results in 10%–20% precipitation reductions for the coastal northwest United States and the Sierra Nevada. Snowpack in the Sierra Nevada experiences declines of up to 50%. However, in the coarse-resolution simulations, this mechanism is not resolved and precipitation is not reduced in the northwest United States. These results highlight the need for adequate model resolution in modeling the impacts of Amazon deforestation. It is concluded that the deforestation of the Amazon can act as a driver of regional climate change in the extratropics, including areas of the western United States that are agriculturally important.

scholarly journals Tsunami propagation kernel and its applications

2021 ◽  
Author(s):  
Takenori Shimozono
Keyword(s):  
Kernel Method ◽  
Numerical Models ◽  
Computational Cost ◽  
Specific Area ◽  
Tsunami Propagation ◽  
Kernel Convolution ◽  
Damping Parameter ◽  
Tsunami Risk ◽  
Convolution Kernels ◽  
Low Computational Cost

Abstract. Tsunamis rarely occur in a specific area, and their occurrence is highly uncertain. Generated from their sources in deep water, they occasionally undergo tremendous amplification over decreasing water depth to devastate low-lying coastal areas. Despite the advancement of computational power and simulation algorithms, there is a need for novel and rigorous approaches to efficiently predict coastal amplification of tsunamis during different disaster management phases, such as tsunami risk assessment and real-time forecast. This study presents convolution kernels that can instantly predict onshore waveforms of water surface elevation and flow velocity from observed/simulated wavedata apart from the shore. Kernel convolution involves isolating an incident-wave component from the offshore wavedata and transforming it into the onshore waveform. Moreover, unlike previous derived ones, the present kernels are based on shallow-water equations with a damping term and can account for tsunami attenuation on its path to the shore with a damping parameter. Kernel convolution can be implemented at a low computational cost compared to conventional numerical models that discretise the spatial domain. The prediction capability of the kernel method was demonstrated through application to real-world tsunami cases.

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