Sophisticated Numerical Models Research Articles

In situ root identification through blade penetrometer testing – part 1: interpretative models and laboratory testing

Root architecture and reinforcement are important parameters to measure the safety of vegetated slopes and stream banks against slope instability and erosion or to assess the stability of plants against environmental loading (e.g. windthrow of trees). However, these are difficult to measure without time-consuming sampling or counting procedures. Previous studies proposed using a penetrometer with an adapted geometry, and showed that individual root breakages could be detected as sudden drops in penetrometer resistance. However, there are no existing models to derive root properties from the measured traces. Here, several interpretative models are developed and their performance at identifying and characterising buried acrylonitrile butadiene styrene root analogues of varying diameter and architecture in sand are assessed. It was found that models, assuming the analogues broke in bending rather than tension, provided good predictions for the force–displacement behaviour. The simple analytical bending model developed here was shown to perform almost as well as more sophisticated numerical models. For all models, the predictions of additional penetrometer force required to break the root analogue were more accurate than predictions for lateral root displacement required to reach failure. The root analogue diameter and to a lesser extent the soil resistance and root angle were shown to affect the penetrometer resistance strongly. Root branching, root length and the distance between the point of load application and a root boundary (root tip or parent root) had a much smaller effect. When the root failure mechanism, root strength, root stiffness and soil resistance are known, an accurate prediction of the root diameter can be made based on the root peak resistance value identified from a blade penetration test. Penetrometer testing, a test which is easy to perform in the field, coupled with an accurate interpretative model might therefore be an effective method to rapidly quantify the spatial distribution, depths and diameters of roots.

Coastal Processes Assessment Under Extreme Storm Events Using Numerical Modelling Approaches

Storm events lead to sudden and drastic impacts on coastal areas, causing serious damages, flooding and severe coastal erosion. These extreme weather conditions seriously affect the nearshore system by reshaping the shoreline and moving large amounts of sand cross-shore. For the assessment of the consequences of such extreme storm events, an interdisciplinary approach simulating atmospheric, wave, hydraulic and geological processes is required, necessitating the use of sophisticated numerical models. Within this study, MIKE 21 and XBeach numerical models are employed for the estimation of the prevailing wave, hydrodynamic and morphodynamic characteristics in a coastal area. The results of the two models are utilized in a comparative approach to assess coastal processes. Furthermore, an alternative solution is also proposed for effective protection of a nearshore area. The approach is demonstrated in the coastal zone of the city of Rethymno in Greece, an area significantly affected by extreme storm events in the recent past, and results are presented and discussed.

Deep Part Load Flow Analysis in a Francis Model turbine by means of two-phase unsteady flow simulations

Hydropower plants are indispensable to stabilize the grid by reacting quickly to changes of the energy demand. However, an extension of the operating range towards high and deep part load conditions without fatigue of the hydraulic components is desirable to increase their flexibility. In this paper a model sized Francis turbine at low discharge operating conditions (Q/QBEP = 0.27) is analyzed by means of computational fluid dynamics (CFD). Unsteady two-phase simulations for two Thoma-number conditions are conducted. Stochastic pressure oscillations, observed on the test rig at low discharge, require sophisticated numerical models together with small time steps, large grid sizes and long simulation times to cope with these fluctuations. In this paper the BSL-EARSM model (Explicit Algebraic Reynolds Stress) was applied as a compromise between scale resolving and two-equation turbulence models with respect to computational effort and accuracy. Simulation results are compared to pressure measurements showing reasonable agreement in resolving the frequency spectra and amplitude. Inner blade vortices were predicted successfully in shape and size. Surface streamlines in blade-to-blade view are presented, giving insights to the formation of the inner blade vortices. The acquired time dependent pressure fields can be used for quasi-static structural analysis (FEA) for fatigue calculations in the future.

Dynamic simulation and critical assessment of a composite bridge in high-speed railway

Evaluation of critical responses of a bridge including resonances in high-speed (HS) railway is a dominant issue in order to confirm the structural safety of bridge and the stability of ballast on bridge deck. In numerical way for critical assessment, it is important to make a sophisticated numerical model and considering the variation of actual properties of structural members. This study proposed a train-track-bridge interaction model focusing on Sesia viaduct, and calibrated the model properties as matching these modal characteristics and dynamic responses to measured ones. By the numerical and experimental comparison, calibrated model could reproduce accelerations up to 30 Hz both of on the time and frequency domains accurately. Especially, good agreements on sleeper accelerations can indicate the high reproducibility of interaction force, which is one of key factors of train-track-bridge interaction simulation. Numerical computation by calibrated model clarified that the deck acceleration up to 30Hz increases by seventh and eighth resonances between passing vehicle length and structural modes, not only global third bending or third torsional but also high order local deck modes. In addition, high performance computing technique based on super computer in RTRI was adopted for parametric analysis in order to investigate the requirements to realize highly accurate estimation for the maximum deck acceleration by the numerical way. As the results of parametric study focusing on design assumption, calculation modal order and train/bridge interaction, it was clarified that the design model causes overestimation by twice maximum acceleration on the deck, and the amplification of excitation forces caused by passage on deflected rails, which is considered in high-order modes and train/bridge interaction, is a key factor to achieve accurate deck acceleration evaluation.

Influence of pulsation in thermo-mechanical analysis on laser micro-welding of Ti6Al4V alloy

The pulse parameters of laser heat source have a definite effect on the weld joint structure. However, the complexity in parameter selection increases many folds with reduction in geometric dimensions of the specimen. Hence, an attempt has been made to investigate the laser microwelding of 500µm thick Ti6Al4V alloy in butt joint configuration using pulse Nd:YAG laser. The influence of laser scanning speed and pulse energy is analyzed to produce a defect-free joint. High peak power is actually dampen by pulsation of laser cratered to use in microwelding process. The feasible range of process parameters like laser scanning speed of 3–7mm/s and peak power of 1–5kW produces high quality weld joint using other favorable conditions that mainly diminishes the formation of oxides in welding of titanium alloy. A sophisticated numerical model is always beneficial to capture the thermo-mechanical behavior under differential influence of process parameters. A 3D finite element based sequentially coupled thermo-mechanical model is developed by considering the pulse mode of heat flux. There is considerably variation in temperature profile using actual pulse mode of heat flux as compared to average laser power. Typical hourglass heat source for over penetrated weld is developed for the simulation of microwelding process. Large-displacement theory is considered to predict the weld-induced distortion for laser microwelding process. The computed results are well agreed with experimentally measured values and show the robustness of the present numerical model used for micro scale welding process.

Calibration of parameters for cardiovascular models with application to arterial growth.

We present a computational framework for the calibration of parameters describing cardiovascular models with a focus on the application of growth of abdominal aortic aneurysms (AAA). The growth rate in this sort of pathology is considered a critical parameter in the risk management and is an essential indicator for the assessment of surveillance intervals. Parameters describing growth of AAAs are not measurable directly and need to be estimated from available data often given by medical imaging technologies. Registration procedures often applied in standard workflows of parameter identification to extract the image encoded information are a source of significant systematic error. The concept of surface currents provides means to effectively avoid this source of errors by establishing a mathematical framework to compare surface information, directly accessible from image data. By utilizing this concept it is possible to inversely estimate growth parameters using sophisticated numerical models of AAAs from measurements available as surface information. In this work we present a framework to obtain spatial distributions of parameters governing growth of arterial tissue, and we show how the use of surface currents can significantly improve the results. We further present the application to patient specific follow-up data resulting in a spatial map of volumetric growth rates enabling, for the first time, prediction of further AAA expansion.

Development of an Improved Pollution Source Identification Model Using Numerical and ANN Based Simulation-Optimization Model

The identification of unknown pollution sources is an important and challenging task for the engineers working on pollution management of a groundwater aquifer. The locations and transient magnitude of unknown contaminant sources can be identified using inverse optimization technique. In this approach, the absolute difference between the simulated and the observed contaminant concentration at the observation locations of the aquifer is minimized by using an optimization algorithm. The simulated concentrations is calculated using the aquifer simulation model. As such, there is a need to incorporate the aquifer simulation model with the optimization model. Thus the performance of the model is highly related to the aquifer simulation model. The incorporation of the sophisticated numerical simulation model will give better performance, but the model will be computationally expensive. On the other hand, the model will be computationally less expensive if an approximate simulation model is used in place of the numerical simulation model. However, in this case, the predictive performance of the model will decline. For achieving efficiency in both computational time as well as in predicting the performance, this study presents a new genetic algorithms based simulation-optimization method incorporating both the numerical and the approximate simulation models. The efficiency and field applicability of the model is demonstrated using illustrative study areas. The performance evaluation of the model shows that the proposed model has the potential for real-world field applications.

Permafrost Studies in Kullu District, Himachal Pradesh

Collaborative Indo-Swiss research on permafrost has thrown new light on this rarely studied component of the Indian Himalayan cryosphere. Under a pilot study, first maps of estimated permafrost distribution in Kullu district, Himachal Pradesh, India have been produced, using a combination of simple topographic and climatic principles, more sophisticated numerical modelling, and mapping of permafrost indicators. Overall, 9% (420 sq. km) of the land area in Kullu is classified as permafrost terrain, extending down to as low as ~4200 m amsl in isolated instances. Between ~4200 and 5000 m amsl, permafrost underlies a surface area comparable in size to that overlaid by glacier ice. Hence, permafrost is identified as a significant component of the local cryosphere. These results now provide a scientific basis for assessing the wideranging potential impacts, hazards and risk associated with warming and thawing of frozen ground, with relevance for climate change adaptation studies across the entire Himalaya.

Tides and angular momentum redistribution inside low-mass stars hosting planets: a first dynamical model

We introduce a general mathematical framework to model the internal transport of angular momentum in a star hosting a close-in planetary/stellar companion. By assuming that the tidal and rotational distortions are small and that the deposit/extraction of angular momentum induced by stellar winds and tidal torques are redistributed solely by an effective eddy-viscosity that depends on the radial coordinate, we can formulate the model in a completely analytic way. It allows us to compute simultaneously the evolution of the orbit of the companion and of the spin and the radial differential rotation of the star. An illustrative application to the case of an F-type main-sequence star hosting a hot Jupiter is presented. The general relevance of our model to test more sophisticated numerical dynamical models and to study the internal rotation profile of exoplanet hosts, submitted to the combined effects of tides and stellar winds, by means of asteroseismology are discussed.

A simple, low-cost approach to predicting the hydrogeological consequences of coalfield closure as a basis for best practice in long-term management

The closure of individual coal mines usually entails a cessation of mine dewatering, which can give rise to significant changes in the local and regional hydrogeological regime. Where the last colliery in an entire coalfield closes, these changes can be very large-scale and potentially damaging, with potential for pollution of major rivers and aquifers. While a number of modelling approaches have been developed in recent decades to predict these changes and facilitate their proactive (and prophylactic) management, when the last mine in a given coalfield is closing the mine owners typically have neither the time nor money to commission extended and sophisticated numerical modelling studies. In such circumstances, a simplified, lower-cost approach is required to provide regulators with predictions of rates of water level rise, future equilibrium water levels and the rates and quality of any future outflows of mine water to rivers and/or aquifers. These predictions can also be useful in guiding the decisions of future site owners over alternative uses of colliery infrastructure after the cessation of coal production. An approach to such predictions has been developed which is based on summary information on the extent of workings, dewatering pumping rates, locations and collar elevations of unfilled shafts and adits attached to the deep workings, as well as surface topography and the geometry of any overlying aquifers. Uncertainties over hydraulic gradient after the completion of water level recovery are handled by analogy to a range of post-recovery gradients from similar large coalfields. A brief example of the application of the approach to a real coalfield is presented. This approach could be used either on its own or as a prelude to more detailed modelling and monitoring during the years following mine closure. The insights into system behaviour gained from such exercises could well be valuable in future re-use of flooded voids as resources for heat recovery or disposal as part of low-carbon heating systems.

Prediction of lake surface temperature using the air2water model: guidelines, challenges, and future perspectives

<p>Water temperature plays a primary role in controlling a wide range of physical, geochemical and ecological processes in lakes, with considerable influences on lake water quality and ecosystem functioning. Being able to reliably predict water temperature is therefore a desired goal, which stimulated the development of models of different type and complexity, ranging from simple regression-based models to more sophisticated process-based numerical models. However, both types of models suffer of some limitations: the first are not able to address some fundamental physical processes as e.g., thermal stratification, while the latter generally require a large amount of data in input, which are not always available. In this work, lake surface temperature is simulated by means of <em>air2water</em>, a hybrid physically-based/statistical model, which is able to provide a robust, predictive understanding of LST dynamics knowing air temperature only. This model showed performances that are comparable with those obtained by using process based models (a root mean square error on the order of 1°C, at daily scale), while retaining the simplicity and parsimony of regression-based models, thus making it a good candidate for long-term applications.</p><p>The aim of the present work is to provide the reader with useful and practical guidelines for proper use of the <em>air2water</em> model and for critical analysis of results. Two case studies have been selected for the analysis: Lake Superior and Lake Erie. These are clear and emblematic examples of a deep and a shallow temperate lake characterized by markedly different thermal responses to external forcing, thus are ideal for making the results of the analysis the most general and comprehensive. Particular attention is paid to assessing the influence of missing data on model performance, and to evaluating when an observed time series is sufficiently informative for proper model calibration or, conversely, data are too scarce thus leading to the risk of overfitting. The final aim of the work is to facilitate the use of the model also by scientists that do not necessarily have a solid background on modelling or physics. However, this work should not be considered simply as a collection of best practices, but also as the attempt to foster the communication and interaction among colleagues of a branch of science, limnology, that suffer of significant fragmentation. This is summarized in the future perspectives and challenges concerning potential improvements of the <em>air2water</em>, with a particular emphasis on possible cross-sectoral applications.</p>

Tropical cyclone evolution in a minimal axisymmetric model revisited

An improved version of a minimal model for a tropical cyclone is described. The model is used to revisit some fundamental aspects of vortex behaviour in the prototype problem for tropical cyclone intensification. After rapidly intensifying to a mature phase in which the maximum tangential wind speed remains quasi‐steady for a few days, the vortex ultimately decays. In a 20‐day simulation, the vortex never becomes globally steady. In particular, the upper anticyclone continues to expand for the duration of the integration. These results are consistent with those of recent studies using more sophisticated numerical models. As in the latter models, an important feature of the dynamics of spin‐up is the development of supergradient winds in the boundary layer and the vertical advection of the associated high tangential‐momentum air from the boundary layer to spin up the eyewall region. This mechanism, while consistent with some recently reported results, is not part of the classical theory of spin‐up.

Practical Nonlinear Modeling of Reinforced Concrete Structural Walls

AbstractCurrent engineering practice typically relies on the use of fiber-based modeling approaches with uncoupled axial-bending (P-M) and shear (V) responses to simulate nonlinear behavior of reinforced concrete (RC) structural walls. However, more sophisticated numerical models are available that incorporate coupled P-M-V behavior. The effect of using uncoupled and coupled modeling approaches and the influence of various modeling assumptions, particularly modeling parameters related to wall shear behavior, on computed global and local building responses are reported. A five-story archetype RC wall-frame building designed according to current U.S. code provisions is used for the assessment. The results indicate that modeling parameters associated with wall shear behavior have a significant effect on computed responses for uncoupled models; use of commonly recommended effective shear stiffness of 0.2EcAw to account for effects of concrete cracking provides a reasonable estimate of roof displacement respon...

Numerical Model of the Static Loading of a Stitched Seam in the Composite Cover of Car Seat

Fundamental knowledge of the mechanical properties of used materials are the basic preconditions for a successful construction of a final product. For seam as well as the reliability of its strength in some cases we need to know certainty when there will be the malfunction. In this study a spun of polyester thread were sewn on a material used for car seat cover. A single or multiaxial loading either static or dynamic has been used in the field of automotive textiles as well as for conventional materials. There is no standard method of measurement for the determination of dynamic strength of sewn seams and therefore it was necessary to construct a device that may measure the strength of seams under dynamic stress. It was carried out an experimental determination of the tensile strength under a static and shock loading for the textile part itself, then for the thread and also for them all together. A lot of very sophisticated numerical models of the individual materials structures in the world generally exist but considerably less is in this field taken into account the behavior of the whole.The aim of this work is with using the commercial software ANSYS create a contact numerical model that will be able to predict behavior of stitched seams and can be used instead of the classical experiments.

Numerical model simulations for optimisation of tidal lagoon schemes

This study considers environmental impacts and the power production potential of a number of coastally attached tidal lagoons, proposed along the North Wales coast, UK. Initially, the impoundment shape, turbine and sluice gate locations were modified according to the regional bathymetric data. A refined 0-Dimensional approach was implemented to optimise the lagoon operation, based on given turbine and sluice gate specifications. In turn, a two-dimensional numerical model, based on an unstructured triangular mesh, has been refined to simulate the hydrodynamic processes, initially without and subsequently in the presence of the lagoons. The hydrodynamic model adopts a TVD finite volume method to solve the 2D shallow water equations, based on a second-order accurate spatial and temporal numerical scheme. An encouraging performance is apparent in reproducing the established conditions encountered in the region through comparisons against available data. The incorporation of tidal lagoons in the model appears to have a considerable effect on the flow structure in the region, by inducing high velocity accelerations near the sluices and turbines, depending on the stage of the tidal cycle. Considering a two-way generation regime, it is outlined that the loss of intertidal regions can be minimised, which is a major source of concern with regards to the environmental impact of such schemes through an ebb-generation operation. Particular focus is directed towards the comparisons between the 0-D and 2-D modelling results, an aspect which has not been reported previously. Predictions of the models diverge as the scale of the lagoon project increases, but it is highlighted that the 0-D methodology can be utilised for the optimisation of the processes in the initial stages of design before proceeding to more sophisticated numerical model simulations.

Interaction Evaluation with Subsoil and Global Stability Evaluation of High MSW Structure

Today's situation at designing of complicated reinforced soil structures requires creating of detailed numerical model of structure to analyse limit states. Especially second limit states procedure is demanded due to classics theory limitations. Calculated limit states by FEM software Plaxis on two examples of designed structures composed from micropiles, and reinforced soil structures by geogrids will be presented in this article. High reinforced walls known as MSE type of structure (mechanically stabilized earth) requires detailed evaluation of interaction with foundation soil. There has been no problem to design reinforced soil structure by geosynthetics, it means body of wall structure can be evaluated according to various standards and design procedures, which is supported by various analytical software offered by GSY (geosynthetics) selling companies. Based on long years’ experience, there is the most problematic part of design of complicated and high structures on new parts of motorways and high speed train lines proper evaluation of interaction of new structure with foundation soil and global stability evaluation. These analyses are generally complicated for estimation of parameters in interaction and requires to use more sophisticated numerical modelling.

Software sensor as distributed parameter system for the control of secondary cooling in the continuous casting of steel

Abstract: Sophisticated numerical models are created nowadays for the continuous casting of steel, partly thanks to the rapid development of information technology. These models are based on the numerical solutions of nonlinear partial differential equations describing the dynamics of modelled phenomena. Such distributed parameter numerical models used as “software sensors” offer the possibility to control the secondary cooling process. However, in current engineering practice the control synthesis is solved by lumped parameter systems approach. This paper shows how to solve the control synthesis problem based on distributed parameter system approach, using widely available software products for numerical modelling of continuous casting of steel combined with algorithms for control of lumped and distributed parameter systems.

Empirical Assessment of the Mean Block Volume of Rock Masses Intersected by Four Joint Sets

The estimation of a representative value for the rock block volume (Vb) is of huge interest in rock engineering in regards to rock mass characterization purposes. However, while mathematical relationships to precisely estimate this parameter from the spacing of joints can be found in literature for rock masses intersected by three dominant joint sets, corresponding relationships do not actually exist when more than three sets occur. In these cases, a consistent assessment of Vb can only be achieved by directly measuring the dimensions of several representative natural rock blocks in the field or by means of more sophisticated 3D numerical modeling approaches. However, Palmstrom’s empirical relationship based on the volumetric joint count Jv and on a block shape factor β is commonly used in the practice, although strictly valid only for rock masses intersected by three joint sets. Starting from these considerations, the present paper is primarily intended to investigate the reliability of a set of empirical relationships linking the block volume with the indexes most commonly used to characterize the degree of jointing in a rock mass (i.e. the Jv and the mean value of the joint set spacings) specifically applicable to rock masses intersected by four sets of persistent discontinuities. Based on the analysis of artificial 3D block assemblies generated using the software AutoCAD, the most accurate best-fit regression has been found between the mean block volume (\(V_{{{\text{b}}_{\text{m}} }}\)) of tested rock mass samples and the geometric mean value of the spacings of the joint sets delimiting blocks; thus, indicating this mean value as a promising parameter for the preliminary characterization of the block size. Tests on field outcrops have demonstrated that the proposed empirical methodology has the potential of predicting the mean block volume of multiple-set jointed rock masses with an acceptable accuracy for common uses in most practical rock engineering applications.

A simple approximation for wave refraction – Application to the assessment of the nearshore wave directionality

This work presents a simple and relatively quick methodology to obtain the nearshore wave angle. The method is especially valuable for curvilinear coasts where Snell’s law may provide excessively inaccurate results. We defined a correction factor, K, that depends on the geometry of the coast and on the wave climate. The values of this coefficient were obtained minimizing the differences with a sophisticated numerical model. The limitations and performance of the methodology are further discussed. The procedure was applied to a beach in Southern Spain to analyze the influence of shoreline geometry on nearshore wave directionality. Offshore and nearshore distributions of wave period and directions were analyzed, and the results showed that the geometry of the coast played a crucial role in the directionality of the nearshore waves, which also plays an important role in hydrodynamics. The methodology presented here is able to analyze and quantify the importance of this directionality without a noticeable computational cost, even when a long time series of wave data are considered. Hence, this methodology constitutes a useful and efficient tool for practical applications in Coastal and Ocean Engineering, such as sedimentary, wave energy, and wave climate studies.

A conceptual data model coupling with physically-based distributed hydrological models based on catchment discretization schemas

Summary In hydrology, the data types, spatio-temporal scales and formats for physically-based distributed hydrological models and the distributed data or parameters may be different before significant data pre-processing or may change during hydrological simulation run time. A data model is devoted to these problems for sophisticated numerical hydrological modeling procedures. In this paper, we propose a conceptual data model to interpret the comprehensive, universal and complex water environmental entities. We also present an innovative integration methodology to couple the data model with physically-based distributed hydrological models (DHMs) based on catchment discretization schemas. The data model provides a reasonable framework for researchers of organizing and pre-processing water environmental spatio-temporal datasets. It also facilitates seamless data flow fluid and dynamic by hydrological response units (HRUs) as the core between the object-oriented databases and physically-based distributed hydrological models.