Numerical Modelling Strategy Research Articles

Use of fiber-section beam elements for modelling the monotonic flexural response of RC jacketed columns

The use of reinforced concrete (RC) jacketing is a common technique for retrofitting existing RC columns with poor structural performances. Literature studies highlighted that the relative slip occurring at the interface between the new and the old concrete can affect substantially the flexibility and the strength of the retrofitted member. For this reason, several interface treatments are usually applied, aiming to induce a monolithic behaviour to the column. However, despite the commonness of RC jacketing, a limited number of studies investigated numerical modelling strategies for including these phenomena, especially with reference to the development of numerical models for design-oriented applications.This paper presents the results of a finite element modelling (FEM) approach for evaluating the flexural behaviour of members reinforced with RC jackets. The proposed method takes advantage of fiber-section beam elements connected through a non-linear interface. Monotonic static non-linear analyses are performed and results highlights the differences with the usual assumption of monolithic behaviour. The comparisons with experimental results confirm the reliability of the approach, which allows to obtain accurate results with a substantial reduction of the computational cost with respect to brick-based FEM.

Numerical study and experimental validation of blastworthy structure using aluminum foam sandwich subjected to fragmented 8 kg TNT blast loading

A blastworthy structure is defined as a structure that has the ability to deform with a controlled force and preserve sufficient residual space around the occupants to limit bodily injury during a blast impact incident. In this research, a blastworthy aluminum foam sandwich (AFS) structure that consisted of an occupant side plate (OSP), a struck side plate (SSP), and an aluminum foam (Al-foam) core were numerically and experimentally subjected to blast-fragmented loading. The explosion with high-pressure shock waves was produced by steel-covered TNT, creating a synergistic blast and fragment loading. The interaction between the blast-fragment loading and the AFS created a unique perforation pattern due to Monroe's effect. The measured blastworthiness characteristics included structural integrity, acceleration, and reaction force. A numerical modeling strategy to analyze the blastworthiness performance of the AFS structure was developed to capture the dynamic responses and the damage mechanism. Two types of blast loading, namely load blast enhanced (LBE) and smooth particle hydrodynamic (SPH) blast loading, were utilized along with the Cockcroft-Latham damage modeling on the AFS. A blast experimental setup with a fix-clamped method was used to evaluate the blastworthy characteristics of the panel to acquire the central acceleration and reaction force histories. A two-step process of experimental validation was carried out. First, a pre-test system validation with a very low explosive blast using 60 gram of TNT was conducted on the sandwich specimen to ensure the data acquisition system's functionality and to obtain comparable data for system validation. Second, a blast impact test using 8 kg of steel-covered TNT was carried out to validate the numerical modeling results. The results of the numerical analysis showed that the LBE model had good agreement with the test data for the small deformation blast impact loading with 60 gram TNT. For the large deformation blast impact loading with 8 kg TNT, the SPH models provided excellent agreement with the damage mode and dynamic responses, where the acceleration and the reaction force performances were both within 6.1% and 6.4% of the experimental validation, respectively. As for the structural performance of the AFS construction, it was observed that the sandwich panel met the structural integrity requirements. There were no cracks or fractures in the OSP. The SSP and Al-foam absorbed more than 98.3% of the blast impact energy, providing extra protection for the OSP. This research contributes to the dynamic structural-response and damage investigation of AFS subjected to fragmented 8 kg TNT blast loading.

Urban climate research and planning applications in China: a scientometric and long-term review (1963-2018) based on CiteSpace

Urban climate research is essential for sustainable development. Few review papers have focused on long-term research and planning applications in China. We conducted a bibliometric review by using CiteSpace to elaborate changes in hot spots, frontiers, development processes, and applications of urban climate research from 1963 to 2018. The identified research could be categorized into 4 major research hot spots: (1) the urban climate effect brought on by urbanization; (2) analysis of meteorological factors and conditions; (3) numerical simulation of urban climate; and (4) urban planning and design in the context of climate change. Moreover, 15 of the most frequently cited key words indicating research frontiers with specific time patterns were detected, and 4 key aspects were identified in terms of research topic: urban climate effects and mechanisms, progress and reform of meteorological service systems, multi-scale numerical modeling, and mitigation and adaptation strategies for addressing climate change. Climate applications in China have undergone changes from the early wind rose map, to the use of multiple meteorological elements as a guide to city planning, and recently, to the adoption of emerging applications. Challenges and prospects, including the probable effects of the government and policies, specific long-standing research gaps, the paradigm shift in urban planning, and the requirement for readily available urban data were also highlighted. This study provides a holistic perspective on the development process of long-term urban climate research in China. The findings may be pivotal in understanding the inner logic behind policies and their implementations and are expected to pave the way for exploring new paths in urban sustainable development and planning transformation.

The Roof Bracing as Minimum Intervention for the Reduction of the Seismic Vulnerability of Historical Industrial Buildings: Analytical and Numerical Simplified Strategies for the Assessment of the Performances

ABSTRACT The paper deals with the reduction of the seismic vulnerability of historical masonry buildings characterized by a wide room, of significant height, provided by a multi-sloping timber roof lying on perimeter walls and, internally, on columns or pillars (e.g. industrial buildings). Typically, these structures are extremely vulnerable to earthquakes but a minimum intervention, consisting in the bracing of the timber roof through wooden-based sheathing panels, can improve the seismic performances providing an adequate restraint against the walls overturning and fostering the box-behaviour of the entire structure. The case study of an ancient industrial building is analyzed. A smart analytical design strategy for the dimensioning of the bracings and the evaluation of the resisting ground acceleration is developed. A simplified numerical modelling strategy for pushover analysis, based on the equivalent frame method for the masonry walls and on equivalent diagonal springs for the roof bracings, is also presented.

An approach for the accurate investigation of full-scale ship boundary layers and wakes

Existing recommended practices in the literature do not provide clear and concise guidance for the selection of the most suitable numerical modelling strategy for investigating the boundary layer around a ship at full scale. For example, the International Towing Tank Conference procedure for calculating the nominal wake fields of full-scale ships does not clearly specify which turbulence modelling approach should be used to accurately represent the near-wall flow in the ship's aft region.This paper presents a numerical approach that can accurately represent the boundary layer of full-scale ships. Three turbulence modelling strategies, suitable for the simulation of ship flows, have been assessed: k-ε, k-ω SST RANS and an IDDES formulation. Results from each method have been compared against the full-scale ship propeller torque data of the MV Regal, a 138m long general cargo vessel. Additionally, the capability of each turbulence strategy to resolve time-dependent features of the flow, such as the bilge vortex and its effect on the boundary layer velocity fields, has been evaluated.The results from this investigation show that the IDDES based numerical model replicated the sea trials measurements with the highest degree of accuracy. Furthermore, this study confirmed that the choice of turbulence strategy has a major impact on the full-scale velocity fields in the aft region of a ship.

Numerical analysis and prediction of ground surface movement induced by coal mining and subsequent groundwater flooding

Ground surface movement shows different features during mining and post-mining period. If the mine goaf is dry, surface subsidence is observed in both periods. If the mine goaf is flooded by groundwater, however, ground surface uplift can be observed although much smaller in amplitude compared to the preceding subsidence. A numerical modeling strategy is proposed to predict uplift during the flooding process of an excavated coal mining area under complex geological conditions. The modeling approach considers three phases: virgin state before mining, stage immediately after mine closure, flooding phase. The model considers elasto-plastic material behavior including faults represented by interfaces. In-situ measurements are used for calibration of the model. The Oelsnitz abandoned coal mine is used for model validation and prediction. The measured subsidences up to 17 m were reproduced as well as the uplift within the last 10 years with values between 0.5–2.0 mm/year. Spatial distribution of uplift areas is well reproduced. Predictions up to the year 2051 show an increase in uplift velocity between 0.5–3.0 mm/year and additional total uplift of up to 300 mm.

Finite Element Simulation of Tensile Preload Effects on High Velocity Impact Behavior of Fiber Metal Laminates

As primary structures and protective structures, fiber metal laminates (FMLs) in practical application are always in preload states before possible impact damage threats. In this work, a nonlinear finite element (FE) model is developed to study the impact damage scenario where tensile preloaded FMLs are impacted by a hemispherical nose projectile at high velocities. In the modeling, the intra-layer damage in aluminum sheets and composite laminates and the delamination between adjacent plies are entirely included. The FE model is verified with available experimental results in non-preload condition and then applied to predict the high velocity impact behavior in uniaxial and biaxial tensile preload cases. The ballistic performance and damage response of representative FMLs with different preloads and impact velocities are discussed and analyzed in detail. The numerical results and modeling strategy here provides applicable reference for preloaded impact issues in other FMLs.

Numerical investigation of the behaviour of hydraulically dredged fine-grained soils during and after filling of the containment facility of the port of Gaeta

Fine-grained dredged sediments can be efficiently and sustainably handled by hydraulically filling containment facilities, which can then be reclaimed. This study presents two numerical modelling strategies, characterized by markedly different levels of complexity, that simulate the gradual filling and subsequent consolidation process. Both numerical models employ hydro-mechanical constitutive relations apt to cover wide state ranges, starting from very low effective stresses. Class A predictions of a well-documented case study, where an articulated construction sequence was implemented, are reported and the effectiveness of the two proposed strategies is compared. After updating the numerical predictions according to the recorded construction timeline, the numerical results are validated against field data, specifically versus the monitored height of dredged mud. Finally, the monitoring data are back-analysed, emphasizing the influence of the hydro-mechanical behaviour at high void ratios. The results show that both modelling strategies are sufficiently accurate and can provide substantial benefits to the design of the filling works and to the evaluation of the actual storage capacity of the impoundments, especially if the available volume is limited or if complex construction procedures are implemented.

A two-phase modeling strategy for analyzing the failure process of masonry arches

The anisotropy and meso-structure of masonry materials bring great difficulty for the numerical modeling of masonry arch bridges. To overcome this problem, a two-phase numerical modeling strategy based on cohesive elements is proposed and used to analyze the failure process of masonry arches in this study. According to the proposed strategy, masonry is assumed to be a two-phase material, which consists of two important components: stone blocks and mortar joints. Stone blocks are represented by solid elements where the compression failure is considered by introducing a nonlinear constitutive model. Mortar joints are described by zero-thickness cohesive elements, which are inserted into the interfaces of adjacent stone blocks automatically by a user-defined program. A Mohr-Coulomb type constitutive model supported by experimental results is proposed to describe the mechanical behavior of mortar joints, and two failure modes (tension and shear failure) are considered. The effectiveness of the proposed strategy is firstly identified by comparing with the experimental results, and then a sensitivity analysis is conducted to investigate the influence of the friction coefficients and load positions on failure behavior of the masonry arch.

A numerical-homogenization based phase-field fracture modeling of linear elastic heterogeneous porous media

Most porous media, such as geomaterials and biomaterials are highly heterogeneous in nature, and they contain large variations of microscopic pore structures, such as pore sizes, pore distribution, and pore shapes. The oscillation of microscopic structures is a substantial challenge in theoretical characterization and is usually ignored in continuous modeling. However, mechanical behavior of porous media such as deformation and failure, are essentially impacted by the microscopic heterogeneity which needs to be considered in modeling a porous media. This research proposes a numerical modeling framework with a capability to investigate the effect of microscopic heterogeneity on the macroscopic fracture behavior in porous media by using a numerical homogenization technique, combined with the phase-field fracture modeling method. This numerical modeling strategy computes a homogenized elasticity tensor based on microscopic heterogeneous pore structures heterogenous porous domain by solving boundary value problems at microscopic domain. The strain energy and subsequent propagation of macroscopic fractures will be updated using homogenized stiffness information. Using this numerical scheme, the microscopic pore structure’s impact on the fracture behavior through the homogenized elastic tensor will be taken into account. This multiscale technique is benchmarked against classical problems. The results highlight the importance of the underlying pore structure and reveal that both fracture strength and propagation path can be influenced by the microscopic heterogeneity.

A numerical modeling strategy for passive electro-acoustic transducers

In this paper an alternative numerical/analytical method for determining the directivity-dependent receiving sensitivity of general electro-acoustic transducer is presented. Unfortunately, the computational effort of calculating the directivity-dependent receiving sensitivity is more expensive by orders of magnitude than determining the transmitting sensitivity. Using the underlying integral representation of the problem and the existence of resolvent kernels, a postprocessing approach is derived which enables simulations of the receiving sensitivity with the effort of calculating the transmitting sensitivities.

Hydro-mechanical behaviour of a pellets based bentonite seal: Numerical modelling of lab scale experiments

In most of the concept designs for nuclear waste disposals, bentonite-based materials are used to seal underground galleries and shafts. In order to assess the safety of such engineered barriers and to provide a good prediction for the material behaviour, a number of experimental campaigns and constitutive models have been developed mainly focusing on bentonite compacted blocks. On the other hand, in recent years, the use of high density bentonite pellets combined with powdered bentonite has also been considered as an interesting alternative. The bentonite pellets mixtures present a prominent initial heterogeneity level as a result of the inter-pellets porosity, which evolves strongly during hydration. This paper aims to present the numerical modelling strategy adopted for a swelling pressure test on pellets mixture carried by CEA (France). Taking advantage of the finite element code LAGAMINE, the Barcelona Basic model is considered for the bentonite mechanical behaviour and the double porosity model proposed by [1] is used for the water retention behaviour and permeability evolution. Given the already-known complexity of the multiphysical and multiscale coupled processes taking place during bentonite-hydration, the obtained numerical results are in good agreement with experimental measurements. Especially, the non-monotonic evolution of the swelling pressure during the hydration phase is well captured by this model, which is always a challenge for this type of problem.

FEM-Based Numerical Strategy for Analysis of Composite Modular Floor Prototype for Emergency Housing Applications

AbstractThis paper presents a numerical modeling strategy based on the finite-element method (FEM) for the analysis of a temporary residential floor prototype composed of three jointed composite fl...

An image-based computational modeling approach for prediction of temperature distribution during photothermal therapy

Nanoparticle-assisted photothermal therapy (NPTT) has recently renewed the interest of using hyperthermia in cancer therapy due to selective heating of tumor by utilizing light-responsive nanoparticles such as gold nanoparticles (AuNPs). Pre-treatment planning of NPTT can help to predict temperature distribution within the body in order to optimize the treatment parameters before the actual heating operation. The use of actual tumor geometry and nanoparticle distribution are key requirements for accurate prediction of temperature distribution during numerical calculations of the heat transfer process. This study attempts to develop a numerical modeling strategy for NPTT based on computed tomography (CT) imaging. To this end, CT26 colon tumor-bearing mice were injected with alginate-coated AuNPs (Au@Alg) and then underwent CT imaging. The tumor geometry and nanoparticle distribution map were obtained directly from CT image of the tumor and exported into a finite element simulation software for subsequent heat transfer modeling. The predicted temperature of the tumor from numerical modeling was found to be in reasonable agreement with the measured data from in vivo thermometry. This model has the potential to be used as a pre-treatment planning tool to design an individualized heating protocol for various tumor geometry before the actual heating treatment.

MRI-based numerical modeling strategy for simulation and treatment planning of nanoparticle-assisted photothermal therapy

Nanoparticle-assisted photothermal therapy (NPTT) has recently emerged as a promising alternative to traditional thermal therapy methods. Computational modeling for simulation and treatment planning of NPTT seems to be essential for clinical translation of this modality. Non-invasive identification of nanoparticle distribution within the tissue is a key perquisite for accurate prediction of NPTT in real conditions. In the present study, we have developed a magnetic resonance imaging (MRI)-based numerical modeling strategy for simulation and treatment planning of NPTT. To this end, we have utilized the core-shell γ-Fe2O3@Au nanoparticle comprising a gold layer with plasmonic properties and a magnetic core that enables to track the location of this structure via MRI. The map of nanoparticle distribution in the tumor derived from T2-weighted MR image was imported into a finite element simulation software, and Pennes bioheat equation and Arrhenius damage model were applied to simulate the temperature and damage distributions, respectively. The validation of the model developed herein was assessed by monitoring the superficial and the central temperature variations of the tumor in experiment. Both the numerical modeling and experimental study proved that a localized heating and then a focused damage could be achieved due to nanoparticle inclusion. There is quite satisfactory agreement between the numerical and experimental results. The model developed in this study has a good capability to be used as a promising planning method for NPTT of cancer.

Strategies for structural modelling of CLT panels under cyclic loading conditions

Cross Laminated Timber (CLT) is an extensively used technology to build medium- and high-rise buildings, especially thanks to the rapidity of execution, environmental sustainability, and good mechanical performances. Since this material is presently employed also in seismic-prone areas, the assessment of numerical modelling strategies to reproduce the cyclic behavior of CLT-wall systems has become a relevant research topic within the structural engineering field. Two different modelling approaches can be adopted to model the seismic behavior of such systems: the phenomenological approach and the component-level one. After a comparative presentation of the two approaches, the paper focuses on the different strategies used to create reliable component-level models able to reproduce the CLT panel-connection system behavior both at the global and local level (i.e., in terms of force-displacement curve and cumulative energy, as well as uplift and slip displacements). The experimental tests carried out at CNR-IVALSA during the SOFIE project – after a preliminary phase of interpretation of the experimental dataset, necessary to identify the peculiarities of the test procedures – are used as a comparative basis to assess the quality of the numerical results. The obtained outcomes demonstrate that the component-level approach could be a feasible and reliable method to reproduce the CLT panel connection systems cyclic behavior, also at a local level, provided that the behavior of each individual component is properly calibrated.

Modelling of debonded reinforcement in ABC connections designed for seismic zones

There are multiple design and detailing approaches for accelerated bridge construction (ABC) in seismically active zones. One of the most common methods is the use of precast components. When using precast components, a technique that can improve seismic behavior is debonding of the longitudinal reinforcement and/or prestressing strands; this can achieve the following objectives: (1) reducing concrete stress concentration, (2) promote rocking behavior, and (3) controlling/delaying the fracture of longitudinal bars. One example of debonding column reinforcement for ABC systems was a pretensioned rocking system that was tested using the shake table facility at the University of Nevada, Reno in 2014. A new numerical modelling strategy was developed to model the debonded reinforcement using external elements explicitly modelled and connected to the column element using rigid links at their proper arms. A numerical model was developed using Opensees for the selected bridge specimen by implementing the suggested strategy to capture the measured response in global and local domains. By incorporating a fatigue material with the reinforcement steel model, this strategy showed excellent agreement with the measured response. Then, the calibrated numerical model was used to explore methods to improve the performance of the system by delaying reinforcing steel fracture. The parametric studies show that increasing the bar sizes and the locally debonded length of the reinforcement were both effective strategies to reduce and delay bar fracture.

Experimental and numerical assessment of the seismic response of steel structures with clutched inerters

Supplemental rotational inertia devices provide an efficient means of suppressing ground-induced vibrations over a large range of structural periods. The beneficial effects of the inerter can be further enhanced by coupling it with a clutch system that prevents it from driving the structural response and ensures that its supplemental rotational inertia is only employed to resist the motion. In this paper, we examine the behaviour of single-degree-of-freedom and multi-degree-of-freedom structures equipped with twin inerter-clutch devices subjected to strong ground-motion. The influence of the clutch stiffness, gears play, viscous damping and dry friction, on the non-linear dynamics of the system are explored first, by analysing the stable periodic solutions of a structure with inerters under harmonic-sweeps. We demonstrate that, for the range of parameters typically expected in earthquake engineering practice, the influence of dry-friction and clutch damping are limited, although the clutch stiffness and gear play may need to be accounted for when large inertances or defective clutches are considered. Based on these findings, we propose a simplified numerical modelling strategy suitable for implementation in conventional Finite Element simulations. Small scale experiments on bare elastic structures as well as structures equipped with 3D-printed inerter and inerter-clutch twins are presented and employed for concept demonstration and for the validation of the numerical model proposed. Finally, a series of studies on detailed numerical models of multi-storey steel frames under idealized and real pulse-like ground-motions are used to demonstrate the vibration absorbing capabilities brought about by the twin inerter-clutch system and to highlight practical aspects related to their structural implementation.

Numerical Modelling of Energy Dissipative Steel Cushions

Energy dissipative steel cushions (EDSCs) are simple units that can be used to join structural members. They can absorb a substantial amount of seismic energy due to their geometric shapes and the ductile behavior of mild steel. Large deformation capability and stable hysteretic behavior were obtained in monotonic and cyclic tests of EDSCs in the framework of the SAFECLADDING project. Discrete numerical modeling strategies were applied to reproduce the experimental results. The first and second models comprise two-dimensional shell elements and one-dimensional flexural frame elements, respectively. The uncertain points in the preparation of the models included the mesh density, representation of the material properties, and interaction between contacting surfaces. A zero-length nonlinear link element was used in the third attempt in the numerical modeling. Parameters are recommended for the Ramberg–Osgood and bilinear models. The obtained results indicate that all of the numerical models can reproduce the response, and the stiffness, strength, and unloading and reloading curves were fitted accurately.

Numerical predictions of distortional-global buckling interaction of perforated rack uprights in compression

This paper describes a numerical investigation into distortional-global buckling interaction of cold-formed steel perforated rack uprights when subject to axial compression. The numerical modelling strategy is carefully validated against existing experimental data. The strengths and failure modes of perforated uprights obtained from finite element analysis are compared with design strengths predicted using the direct strength method (DSM). The comparisons indicate that the ultimate strengths predicted by the current DSM are unsafe for perforated rack uprights. Hence, modifications on the DSM formulae were proposed and are presented by considering the interaction of distortional and global buckling modes for perforated rack uprights.