Calibration Of Numerical Model Research Articles

Experimental Study on Rock-Support Interaction in Deep Tunnel Under Complex Geological Conditions

Rock-support interaction is one of the most core issues in underground engineering, which is of major interest to supporting structure design, construction safety and cost, as well as environmental protection. In order to study the rock-support interaction in deep tunnel under complex geological conditions, taking Xianglushan Tunnel of Yunnan Water Diversion Project in China as the engineering background, two true three-dimensional physical model tests were conducted. The model test results show: (1) the surrounding rock and support are a pair of opposite and united contradictions, which are both antagonistic and cooperative; (2) the rock-lining interaction and rock-bolt interaction are distinctly different. The lining is a type of outside supporting structure to bear the load from surrounding rock and the bolt is a kind of inside supporting structure to reinforce and protect surrounding rock; (3) the impacts of weak fault on mechanical behavior of surrounding rock and supporting structure are significant. The load bearing effects of surrounding rock and support system exhibit different characteristic depending on the corresponding geological conditions. The results can contribute to the development of construction scheme and optimization of support design, and also provide an ideal data set for the calibration and validation of numerical models to simulate the rock-support interaction.

Field measurements on a large natural sand boil along the river Po, Italy

Sand boils are the surface manifestation of an erosion process, known as backward erosion piping, which may take place beneath river embankments during high-water events. The risk of embankment failure greatly increases in locations affected by sand boils. Numerous studies have been carried out, mainly at the laboratory scale, providing significant advancements in this field. Nonetheless, there is still a gap between research and practice that needs to be filled. This study presents a set of field measurements carried out on a large sand boil reactivated near the toe of an embankment along the river Po, Italy. Hydraulic heads, velocity and discharge, concentration and pipe geometry were measured as a function of the water level in the river during the November 2018 flood. The collected data are compared with predictions of a theoretical model that provides the head loss in the vertical pipe. Furthermore, the local exit gradients, as deduced from measurements, are discussed, together with the operational critical gradients adopted in current design practice. The collected data provide important input parameters for the calibration of analytical and numerical models, typically implemented to investigate the sand boil evolution and then to assess the backward erosion piping risk at real scale.

Calibration of the Heston stochastic local volatility model: A finite volume scheme

The two most popular equity and FX derivatives pricing models in banking practice are the local volatility model and the Heston model. While the former has the appealing property that it can be calibrated exactly to any given set of arbitrage free European vanilla option prices, the latter delivers more realistic smile dynamics. In this paper, we combine both modeling approaches to the Heston stochastic local volatility model. We build upon a theoretical framework that has been already developed and focus on the numerical model calibration which requires special care in the treatment of mixed derivatives and in cases where the Feller condition is not met in the Heston model leading to a singular transition density at zero volatility. We propose a finite volume scheme to calibrate the model after a suitable transformation of the model equation and demonstrate its accuracy in numerical test cases using real market data.

Influence of track foundation on the performance of ballast and concrete slab tracks under cyclic loading: Physical modelling and numerical model calibration

Ballast and slab railway track structures are constructed from different materials, thus requiring different maintenance strategies. Therefore, this paper compares the settlement performance of both structures using laboratory experiments, and calibrates numerical models based upon the results. Firstly, a comparison of the short and long-term behaviour of ballasted and slab tracks under cyclic loading is performed at full-scale. Both tracks have the same track foundation but a different track superstructure, and are subject to 3 million cycles of loading. The results are used to develop and calibrate the short-term response of a 3D finite element model of both track structures. They are also used to calibrate an empirical permanent deformation model for the track foundation, where the number of load cycles and stresses are the main inputs. A strong agreement is found between the numerical and experimental results. This justifies the track modelling approach in predicting the long-term behaviour of track structures where the subgrade is influential.

CHALLENGES OF BOUNDARY CONDITIONS IN OPEN OCEAN MODELS

The development and calibration of coastal numerical models to support engineering design and environmental impact studies is a challenging process and one that requires professional judgement and continual assessment of all aspects of the model makeup. Fundamental to the integrity of the model are appropriate boundary conditions and quality observational data for calibration. Open ocean boundary conditions are typically the most complex and important aspect of a model build. They represent the influence of dynamics occurring beyond the model extent, bridging large-scale dynamics to the small-scale processes in the model. This study discusses the challenges of open ocean boundaries and how we utilised data to achieve an effective model.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/evL7f_17wZg

Assessing support alternatives for longwall gateroads subject to changing stress

Longwall gateroad entries are subject to changing horizontal and vertical stress induced by redistribution of loads around the extracted panel. The stress changes can result in significant deformation of the entries that may include roof sag, rib dilation, and floor heave. Mine operators install different types of supports to control the ground response and maintain safe access and ventilation of the longwall face. This paper describes recent research aimed at quantifying the effect of longwall-induced stress changes on ground stability and using the information to assess support alternatives. The research included monitoring of ground and support interaction at several operating longwall mines in the U.S., analysis and calibration of numerical models that adequately represent the bedded rock mass, and observation of the support systems and their response to changes in stress. The models were then used to investigate the impact of geology and stress conditions on ground deformation and support response for various depths of cover and geologic scenarios. The research results were summarized in two regression equations that can be used to estimate the likely roof deformation and height of roof yield due to longwall-induced stress changes. This information is then used to assess the ability of support systems to maintain the stability of the roof. The application of the method is demonstrated with a retrospective analysis of the support performance at an operating longwall mine that experienced a headgate roof fall. The method is shown to produce realistic estimates of gateroad entry stability and support performance, allowing alternative support systems to be assessed during the design and planning stage of longwall operations.

Numerical simulation of the effect of missile impact on the concrete layers

A two-dimensional particle flow cod (PFC) is used to study the effect of missile impact on the concrete target. For this purpose firstly calibration of numerical model was performed so that tensile strength of numerical models and experimental sample were the same. Secondly, a concrete model was built. The number of concrete layers and the angle of concrete layers related to horizontal axis were changed. Their numbers were 1, 2, 3 and 4. The angles were 0o, 15o, 30o, 45o, 60o, 75o and 90o. A semi-circle missile was simulated at top of the concrete layers. Its velocity in opposite side of Y direction was 100 m/s. three measuring circles were situated at the below the missile in the model to receive the applied force. The load in the missile and measuring circles together with failure pattern were registered at the beginning of the impaction. The results show that concrete layers number and concrete layers angle have important effect on the failure load while the failure pattern was nearly constant in all of the models.

Numerical and in-situ evaluation of explosive compaction effectiveness in railway subgrade improvement

Owing to its huge area coverage, explosive Compaction (EC) is as an attractive improvement technique in railway projects. Despite many EC case studies in the literature, few experimental tests are conducted to be used for calibration of numerical models. Thus in this study, a field test is conducted on a railway subgrade and simulated with an advanced numerical model followed by a parametric study on detonation delay. Beside showing promising advantages of the numerical model, it can also distinguish the effects of detonation delay such as change in wave arrivals or instant compaction in EC.

Numerical analysis of special concentric braced frames using experimentally-validated fatigue and fracture model under short and long duration earthquakes

Over the past decade, several long duration subduction earthquakes took place in different locations around the world such as Indonesia in 2004, China in 2008, Chile in 2010, and Japan in 2011. Long-duration and large-magnitude earthquakes are also possible to occur in the Cascadia subduction zone along the Pacific Northwest Coast of the United States. In this paper, numerical investigation was conducted to investigate the influence of earthquake duration on the structural response of steel special concentric braced frames (SCBFs). Calibration and validation of numerical models were achieved using results from recently completed shake table tests at the University of Nevada, Reno of three identical 1/2-scale one-story one-bay SCBFs under unidirectional short and long duration earthquakes. The objective of this paper is two-fold: (1) to use the experimental results to assess the suitability of current low-cycle fatigue models when incorporated into numerical models; (2) to utilize the calibrated numerical model in large number of simulations to extend and generalize the experimental results to quantify the effect of earthquake duration on SCBFs. For the latter, two suites of short and long duration ground motions were utilized to conduct incremental dynamic analysis (IDA) for the calibrated numerical models of the tested frames. The IDA, and resulting fragility curves, concluded that longer duration earthquakes result in 45% lower median displacement capacity, which could be regarded as premature low-cycle fatigue induced-failure of braces.

Robust calibration of numerical models based on relative regret

Classical methods of calibration usually imply the minimisation of an objective function with respect to some control parameters. This function measures the error between some observations and the results obtained by a numerical model. In the presence of uncontrollable additional parameters that we model as random inputs, the objective function becomes a random variable, and notions of robustness have to be introduced for such an optimisation problem.In this paper, we are going to present how to take into account those uncertainties by defining the relative-regret. This quantity allow us to compare the value of the objective function to its best performance achievable given a realisation of the random additional parameters. By controlling this relative-regret using a probabilistic constraint, we can then define a new family of estimators, whose robustness with respect to the random inputs can be adjusted.

Influence of the interval length of hydraulic packer systems on thermally-induced pore pressure measurements in rock

During the past several decades, hydraulic packer systems have generally been used to measure the thermally-induced pore pressures in many in-situ experiments in nuclear waste management programs. The measured value using hydraulic packer system is a combined value of the pore pressures in the rock along the packer interval, and not the pore pressure at the middle point. The suitability of using the packer system measured value to represent the thermally-induced pore pressure at the middle point of the packer interval needs to be assessed. The accuracy of using hydraulic packer systems is examined in this paper using a coupled thermal-hydraulic-mechanical (THM) model for fully saturated conditions developed using the finite element program COMSOL. The results indicate that there could be large errors in the measured values, with the size of the error dependent on the size of the packer interval, the variation of pore pressure gradient along that interval and the orientation of the packer measurement borehole. To improve the accuracy of the measurement using packer systems, the variation in pore pressure gradient along the packer interval should be small; or if a substantial gradient variation is expected, the length of the packer interval should be made as small as possible. A packer interval with a length less than 0.5 m is suggested. If a packer system has been installed with a large interval length in a location where a large pore gradient variation may exist, calibration of any associated numerical model using this measurement should incorporate the packer measurement system. The numerical results of this coupled THM model are in good agreement with the integration of a point heat source theoretical solution throughout the heater line.

A Simplified Representation of Pressure Flow from Surface Slopes in Urban Sewer Systems

A Constant Pipe Drainage (CPD) capacity for sewer systems is commonly applied when undertaking flood risk assessment, however data that are needed for calibration and validation of numerical models are scarce or unavailable. The CPD model neglects the effect of pressure flow and leads to significant deviation in flood volume estimate. This study proposes a new index Velocity Ratio (VR) to approximate pressure flow. A case study in Guangzhou, China is used to investigate the capability of reproducing a reasonable flood volume for two models, the CPD and the VR-based. Compared to the flood volume simulated by the Storm Water Management Model (SWMM), the CPD model shows a significant overestimation, Mean Relative Deviation (MRD) 192%. The VR-based model has a much better performance, MRD 18%. Therefore, the VR-based model is a simple and effective representation of pressure flow in urban sewer systems and can be easily applied in areas lacking detailed pipe data, especially for planning new pipe networks or updating the old pipes.

Frequency and magnitude variability of Yalu River flooding: numerical analyses for the last 1000 years

Abstract. Accurate determination of past flooding characteristics is necessary to effectively predict the future flood disaster risk and dominant controls. However, understanding the effects of environmental forcing on past flooding frequency and magnitude is difficult owing to the deficiency of observations (data available for less than 10 % of the world's rivers) and extremely short measurement time series (<100 years). In this study, a numerical model, HYDROTREND, which generates synthetic time series of daily water discharge at a river outlet, was applied to the Yalu River to (1) reconstruct annual peak discharges over the past 1000 years and estimate flood annual exceedance probabilities and (2) identify and quantify the impacts of climate change and human activity (runoff yield induced by deforestation and dam retention) on the flooding frequency and magnitude. Climate data obtained from meteorological stations and ECHO-G climate model output, morphological characteristics (hypsometry, drainage area, river length, slope, and lapse rate), and hydrological properties (groundwater properties, canopy interception effects, cascade reservoir retention effect, and saturated hydraulic conductivity) form significant reliable model inputs. Monitored for decades, some proxies on ancient floods allow for accurate calibration and validation of numerical modeling. Simulations match well the present-day monitored data (1958–2012) and the literature records of historical flood events (1000–1958). They indicate that flood frequencies of the Yalu River increased during 1000–1940, followed by a decrease until the present day. Frequency trends were strongly modulated by climate variability, particularly by the intensity and frequency of rainfall events. The magnitudes of larger floods, events with a return period of 50 to 100 years, increased by 19.1 % and 13.9 %, respectively, due to climate variability over the last millennium. Anthropogenic processes were found to either enhance or reduce flooding, depending on the type of human activities. Deforestation increased the magnitude of larger floods (100- and 50-year floods) by 19.2 %–20.3 %, but the construction of cascade reservoirs in 1940 significantly reduced their magnitude by 36.7 % to 41.7 %. We conclude that under intensified climate change and human activities in the future, effective river engineering should be considered, particularly for small- and medium-sized mountainous river systems, which are at a higher risk of flood disasters owing to their relatively poor hydrological regulation capacity.

Randomized reduced forward models for efficient Metropolis–Hastings MCMC, with application to subsurface fluid flow and capacitance tomography

Bayesian modelling and computational inference by Markov chain Monte Carlo (MCMC) is a principled framework for large-scale uncertainty quantification, though is limited in practice by computational cost when implemented in the simplest form that requires simulating an accurate computer model at each iteration of the MCMC. The delayed acceptance Metropolis–Hastings MCMC leverages a reduced model for the forward map to lower the compute cost per iteration, though necessarily reduces statistical efficiency that can, without care, lead to no reduction in the computational cost of computing estimates to a desired accuracy. Randomizing the reduced model for the forward map can dramatically improve computational efficiency, by maintaining the low cost per iteration but also avoiding appreciable loss of statistical efficiency. Randomized maps are constructed by a posteriori adaptive tuning of a randomized and locally-corrected deterministic reduced model. Equivalently, the approximated posterior distribution may be viewed as induced by a modified likelihood function for use with the reduced map, with parameters tuned to optimize the quality of the approximation to the correct posterior distribution. Conditions for adaptive MCMC algorithms allow practical approximations and algorithms that have guaranteed ergodicity for the target distribution. Good statistical and computational efficiencies are demonstrated in examples of calibration of large-scale numerical models of geothermal reservoirs and electrical capacitance tomography.

Structural System Identification of Elevated Steel Water Tank Using Ambient Vibration Test and Calibration of Numerical Model

This research aims to investigate the feasibility of using ambient vibration testing for system identification of an elevated water tank. To identify the natural dynamic properties, the experimental study is carried out on an elevated steel water tank located in Tehran. The tank is instrumented with a sensitive velocimeter sensor (microtremor), and the ambient velocity of the tank is recorded for 30[Formula: see text]min in three orthogonal axes. Employing the peak-picking method in the frequency domain, the fundamental frequency of the tank is determined as about 1.9[Formula: see text]Hz. Then, the numerical model of the tank is generated and calibrated based on the obtained data. In the primary modeling, the values of natural frequencies of the tank are in good agreement with the results of the ambient vibration data. This finding is judged to be reasonable considering no clear sign of corrosion in the steel material.

Modal analysis of a wind turbine tower by digital image correlation

Operational Modal Analysis is a method widely used in the wind industry to characterize structures and perform structural health monitoring or numerical model calibration. To reach this goal, optical techniques are becoming appealing because of their non-intrusiveness and their full-field feature in contrast to sensor-based methods. An innovative method is proposed herein for modal measurement with a single camera via Digital Image Correlation. The first resonance frequency of the tower is well captured from images of a shut down turbine.

Numerical modelling of FC bacteria using a dynamic and variable mortality rate

Abstract Faecal coliform (FC) microorganisms are one of the most important indicators in water quality management, since their presence reveals the possibility of existence of other dangerous microorganisms, leading to higher health risks. An accurate estimate of the concentration of this indicator helps better evaluation of the water pollution in riverine basins; thus, it is essential for future developments. The FC mortality rate depends on the physical, chemical, and biological processes in rivers. These processes are generally affected by environmental conditions. In this study, the decay coefficient (K) or mortality rate are related to the environmental parameters such as temperature, turbidity, pH, and salinity by an empirical equation. The results showed that turbidity and temperature are the most effective parameters. Moreover, an empirical equation was developed utilizing numerical model calibration, which describes the relationship of the mortality rate (K) with water temperature and turbidity. This equation was then added to the water quality module of the FASTER numerical model. Comparison of the measured FC concentrations with the predicted values obtained from the numerical model showed that the model accuracy significantly improved for the dynamic and variable decay coefficient.

Experimental dataset and numerical simulation of floating bodies transport in open-channel flow

Abstract Numerical models trying to faithfully represent the movement of floating bodies transport in open-channel flow require experimental data for validation. In order to provide an adequate dataset, flume experiments were carried out to analyse the transport of singular and grouped rigid bodies floating on the water surface. Both cylindrical and spherical samples were employed: they were released in a rectangular channel under steady conditions in one-dimensional (plain channel) and two-dimensional (2D) configurations using one rectangular side obstacle, one smooth side obstacle or two rectangular alternate obstacles. The outcomes of the experiments are the planar displacement and the rotation of the samples, which are related to the flow field in the different configurations. The detailed experimental analysis of the floating body motion provides information for the calibration of numerical models simulating floating bodies transport. This dataset is thus employed for the validation of the Eulerian–Lagrangian model ORSA2D_WT, highlighting its strengths and improvable aspects. Similar applications could be carried out with any 2D model which performs the simulation of discrete elements moving on the water surface.

Modeling of Screw-Dental Structure Interaction: First Step Toward Finite Element Analysis

This research is focused on the screw-structure interaction under dynamic impulses aimed to the contact analysis of gap propagation at dental implant-abutment interface under dynamic loading. The purpose is to investigate the fracture mechanism that occurs during the screw penetration in a support and during the support vibration. Numerical Finite Element (FEM) analyses are calibrated through experimental laboratory measurements on support materials and screws typologies. Uncertainty due to the laboratory error propagation is investigated using Polynomial Chaos Expansion (PCE) of experimental measurements. The research is planned through the following steps: FEM calibration trough laboratory experiments on materials; laboratory experiments and material mechanics identification; uncertainty error propagation analysis through PCE expansion; fragility curves for numerical model calibration; FEM models calibration trough laboratory measurements on cycling loads. Therefore, the main purpose of the research activity, of which this article constitutes a preliminary and an explorative step, is to study a methodology that minimizes the local damage of the dental material due to the generation of micro-cracks following the implantation actions. Accordingly, in this paper, preliminary results are reported.

Effects of size and position of openings on in-plane capacity of unreinforced masonry walls

In recent earthquakes, unreinforced masonry (URM) structures built of masonry walls containing openings such as doors and windows have been shown to have poor seismic capacity. However, although different sizes and positions of openings are known to reduce the stiffness and strength of URM walls, the relationships between the size and position of openings and seismic capacity of the walls are not clear. Therefore, a series of numerical analyses has, for the first time, explored many possible opening sizes and opening positions under simulated seismic loading to identify their impact on the in-plane behaviour of URM walls. The numerical models were built using the code “3DEC” which is based on the discrete element method (DEM). The key feature of the DEM is that it allows the development of large displacements between elements with contacts being recognized automatically during the analysis. Thus, this numerical method can capture the whole degradation progress from the initial cracking of the masonry walls right through to collapse, with the bricks being modelled as rigid blocks and the mortar as Coulomb-slip joints with zero thickness. Both load-based and displacement-based quasi-static pushover analysis procedures have been studied and the modelling methodology and the calibration of numerical models is described. The results from the analyses, the crack patterns and collapse mechanisms of the masonry walls are identified and discussed, and a key output from this work is the characterization of the relationships between the sizes and positions of openings and the in-plane performance of URM walls.