Detailed Numerical Models Research Articles

Hybrid simulation framework with mixed displacement and force control for fully compatible displacements

AbstractA novel framework for hybrid simulation of the seismic response of structures is presented that employs a mixed displacement and force control strategy. A key feature of this framework is a controller‐based displacement‐to‐force transformation that enables compatible displacements between the numerical and experimental model for force‐controlled degrees of freedom. The framework can be applied within conventional displacement‐based time‐integration algorithms allowing for implementation across a variety of software and hardware architectures; it is demonstrated here using OpenSees software with detailed nonlinear numerical models. This study includes numerical verification of the proposed force control strategy and actual implementation in a hybrid simulation of special moment frames with full‐scale beam‐column subassemblies. In the hybrid tests, the experimental column axial load is applied in force control due to the large stiffness and when combined with lateral seismic loads, results in column local buckling with significant axial shortening. The hybrid simulation results verify that the proposed mixed displacement and force control strategy effectively enforces displacement compatibility and force equilibrium between the numerical and experimental structures at the boundary degrees of freedom.

Comparative study of three hybrid air-conditioning systems based on multiple evaporative coolers and run-around reheating coils

Existing evaporative-cooling hybrid air conditioning systems cannot fully utilize the synergistic energy-saving potential of multiple evaporative-cooling technologies. Moreover, they cannot meet simultaneously the energy-saving requirements of standard mechanical vapor compression (MVC) systems in the terms of fresh air pre-treatment, condenser pre-cooling and supply air reheating. Therefore, in this paper, integrating MVC system with the indirect evaporative cooler, outdoor-air evaporative-cooling unit, and run-around reheating coils, three alternative hybrid systems were proposed to meet the aforementioned three requirements. The three hybrid systems have different outdoor-air unit configurations (single condenser with direct evaporative cooler, dual condenser with direct evaporative cooler, and dual condenser with two-stage evaporative-cooling configuration) and reheat sources (exhaust, outdoor, and mixed air of fresh and return air). Then, the parameter effects and application potentials of the three hybrid systems were analyzed comparatively based on detailed numerical models. The results showed that the third proposed hybrid system (HAC-R3) exhibits the best energy-saving advantages in almost the range of ambient temperature, relative humidity and fresh airflow rate studied. The first proposed hybrid system (HAC-R1) has the simplest outdoor-air side configuration, which is also a good choice in medium–low humidity conditions. In hot-humid summer in southern China, HAC-R3 has the highest average energy-saving rate and seasonal COP of 16.0 % and 7.0 respectively. In addition, HAC-R1 has the lowest static equipment payback period of 3.3 years, slightly lower than that of HAC-R3 (3.4 years).

Theoretical analysis and model manufacturing of innovative mortise and tenon hollow spherical joint

One of the main challenges for free-form surface reticulated shell structure recently is the development of a new joint that is able to implement complex-shaped curvature and fulfill the required loading capacity, whilst also meeting various important requirements such as convenient on-site assembly and suitability for connecting members with various cross-sectional forms. This article draws inspiration from the construction idea of Chinese traditional mortise and tenon structure and proposes a new type of mortise and tenon hollow spherical joint. To investigate the joint’s mechanical performance, the detailed numerical models of 29 mortise and tenon hollow spherical joints with different size parameters are established by SolidWorks and Ansys, and the effects of the hollow spherical wall thickness, tooth width, tooth spacing, tooth height and tenon face width on the joint bearing performance are analyzed. The joint failure modes under bending limit states are discussed, and the calculation formulas for the initial and elastic-plastic stage rotational stiffness are derived. The results show that the joint initial rotational stiffness is increased by 34.45%, 4.69%, 4.29%, and 3.25%, respectively, after the parameter optimization analysis of the hollow spherical wall thickness, tooth width, tooth spacing and tenon face width. The mortise and tenon hollow spherical joint has good mechanical performance, and possesses the advantages of simple and beautiful appearance, fast construction speed and high positioning accuracy. Finally, a reduced-scale model of the mortise and tenon hollow spherical joint is manufactured using 3D printing technology to visually showcase its external feature and validate its assembly characteristic.

Nonlinear data-driven zero-thickness joint element for concrete dam shear keys

Shear keys have been designed into the contraction joints of many concrete gravity dams to provide interlocking and shear transfer between adjacent monoliths. Their shear transferring capacity is usually estimated as the friction and cohesion that can be mobilized across a 2D plane located at the base of the keys. Once the shear stress in the contraction joint exceeds its estimated shear capacity, the shear keys are typically considered failed, and the joint may subsequently only transfer shear through concrete-concrete friction. This behaviour is often simulated in practice by placing tiebreak contact formulations along contraction joints. However, the nonlinear response and potential residual strength of the keys are usually ignored. In this paper, a novel nonlinear zero-thickness joint element named Macro Shear Key Joint Element (MSKJE) is proposed to simulate the response of a detailed shear key while capturing its nonlinear behaviour. A detailed geometrical numerical model of shear keys using a concrete Continuous Surface Cap Model (CSCM) is first validated against experimental data. Then, a parametric analysis of the number of keys in the joint, confinement pressure, initial opening and lateral boundary condition is performed using the validated detailed shear key numerical models. The stress-displacement responses obtained from the parametric analysis are used to calibrate the proposed MSKJE. At the local shear key scale, the MSKJE models present a very similar stress-displacement response compared to the detailed geometrical key models in terms of stiffness, maximum shear capacity, residual strength and nonlinear softening. At the global dam scale, the MSKJE presents a somewhat similar behaviour to the conventional tiebreak formulations. However, the advantages of the MSKJE over the tiebreak contact include its capability to simulate the nonlinear softening of shear keys, and residual sliding displacement, and, once calibrated, it is not necessary to estimate the shear keys capacity a priori.

Numerical investigation of lateral behaviour of steel‐timber hybrid frames

AbstractThis paper examines the response of steel‐timber hybrid (STH) lateral stability systems for medium‐rise buildings. A ten‐storey baseline STH structure was designed to codified procedures and compared with a steel‐concrete composite structure. Detailed numerical models were constructed in which specific constitutive representations were assigned to steel‐timber and timber‐timber connections. Parametric investigations on the STH structure were carried out in which the cross laminated timber panel layups, timber shear wall length, and connection characteristics were modified. The study indicated that the STH structure had larger lateral deformations compared to the steel‐concrete structure, both within code limits. For the same design loads, the reduction in self‐weight from the steel‐concrete structure to the STH structure was 73.1%, whilst the floor depth was reduced by 17.2%, respectively. Parametric studies showed that the lateral response of STHs is generally improved with the effective thickness of the timber infill panel and is influenced by the panel layup. Increasing the shear wall length generally enhances the lateral stiffness, yet the overall performance is reduced with the increase of panel connections. The reduction in self‐weight, member sizes and replacement of the concrete with timber led to a reduction in embodied carbon of more than 32.7% whilst achieving similar structural performance.

A Numerical Modeling Approach for Better Differentiation of Boulders Transported by a Tsunami, Storm, and Storm‐Induced Energetic Infragravity Waves

AbstractCoastal boulders are often indicators of past extreme wave events. In fact, the coastal boulder distribution induced by infragravity‐dominated storm waves (energetic IG waves) may be similar to that induced by tsunamis; however, this assumption is yet to be investigated. We show that the factors responsible for generating energetic IG waves under storm scenarios are not identical to those affecting the boulders' transport distances. Our results indicate that the storm waves typically only transport boulders over short distances as compared to boulders deposited by tsunamis, even when energetic IG waves are being generated. When the dimensionless transport distance of a boulder (=transport distance of a boulder/offshore wave height) is less than 4.0 × 10 over planar topography and 3.0 × 10 over reef topography, both waves can potentially be responsible for the transport distance. In this case, whether a reasonably‐sized storm or tsunami can explain a boulder location in a study area should be investigated through detailed numerical modeling. We found a clear relationship between the dimensionless transport distance of tsunami boulders and the Iribarren number, and it is plausible to directly estimate offshore wave height or wavelength from the tsunami boulder distribution and beach slope without numerical simulation.

Numerical Modeling Unlocks Remarkable Ion Selectivity of Capacitive Deionization

Ion-selective water treatment is an important frontier in water research, as for many applications removing all ions indiscriminately leads to significant extra energy and downstream re-ionization costs. Capacitive deionization (CDI) is under intensive investigations for ion-selective treatment of polluted feedwaters [1]. CDI has the remarkable feature of being not only highly selective, but additionally dynamically tuneable to adjust, real-time, to varying feedwater composition and produced water targets [1]. However, we will show that to further develop CDI technologies to achieve desired separations, in feedwaters of several competing anions and cations, requires detailed numerical models. Such models couple ion transport theory to nanopore electrosorption, and often include pH dynamics. We here describe our recent work exploring the limits of ion-ion selectivity by capacitive deionization with inexpensive nanoporous carbon electrodes. We show how theory enabled us to achieve in the lab remarkable selectivity and a diverse set of separations, such as “perfect” divalent cation selectivity[2], monovalent ion selectivity[3], and removal of amphoteric pollutant species such as boric acid and nutrient species[4]. We show using strong-acid functionalized electrodes that the same two-electrode system can be used for either excellent divalent selectivity, or long-lasting monovalent ion selectivity, depending on cell operational parameters [2,3]. Our work furthers the argument that membraneless CDI, based on inexpensive and easily-scalable porous carbon electrodes, can address a wide variety of important applications in water treatment.

Разработка численных геомеханических моделей с различной степенью детализации на примере шахты «Ангидрит» рудника «Кайерканский»

As mining conditions are getting more complex, numerical modelling is becoming one of the most promising areas to obtain data for developing efficient technological solutions. However, creation of high-quality numerical models is an extremely labour-intensive and knowledge consumptive task. Optimization of the numerical modelling process is currently highly demanded. The use of global numerical models with a high level of detail not only makes it possible to evaluate the stress-and-strain state of the rock mass over a large area, but also to qualitatively assess some local effects. Such models help to select more correctly the most hazardous areas for designing local calculation models. Thanks to the high level of detail of the simulated underground structure, the global numerical model can act as a "donor" of the initial geometry for local calculation models, and the exported stress tensor can be used as the boundary conditions, which will increase the accuracy of the local numerical simulation. This approach to numerical modelling can significantly improve the quality of numerical simulations. Although the detailed global numerical models can represent some local phenomena of the rock mass response, they should not be taken as a cure-all solution. The results obtained in a global numerical model are rather aggregated and in case of local tasks only indicate the presence of this or that phenomenon in a particular zone, but cannot describe it quantitatively. Therefore, the transition from global to local numerical models is a necessary part of the work. This paper provides an example of a complete cycle of creating a set of detailed global and local numerical models. The cycle includes all stages of development from optimization of the initial geometry to the step-by-step calculation and analysis of the obtained results. Thanks to the approach used, both qualitative and quantitative convergence was achieved with the results of in-situ observations.

Development and Improvement of Numerical Models of Welded Joints with Multiple Defects

This paper presents the development of numerical models which were used to simulate the behaviour of welded joints containing different combinations of multiple defects under tensile loads. Four representative combinations of defects were selected (including undercuts, incomplete root penetration, misalignments...), based on practical experience. In order to create accurate and functional models, this research involve a number of stages. This paper will focus on the various improvements made to the models, which started in relatively simple form. For this purpose, initial experimental and numerical analyses were carried out on specimens made of low-alloyed low-carbon steel S235, and after their accuracy was verified, the same methodology was applied to specimens made of higher quality material, steel S275. Improvements made to the models involved geometry, different combinations of boundary conditions and loads, and some were based on stress-strain states obtained by a combination of tensile testing and digital image correlation. The final result was a set of detailed numerical models which accurately simulated the behaviour of welded joints with multiple defects in them.

Effects of constitutive soil models on the seismic response of an offshore jacket platform in clay by considering pile-soil-structure interaction

Offshore jacket platforms are widely used for wind energy generation and gas and oil field development. The South Pars gas field, located in the Persian Gulf, stands as one of the largest gas fields in the world. This gas field is situated in a seismically active region predominantly characterized by clay soil. Considering the significant impact of clay soil on the seismic response of offshore structures and their vulnerability to damage, it is essential to conduct comprehensive studies on the seismic behavior of offshore structures in this particular area while considering the nonlinear behavior of soil and pile-soil-structure interaction (PSSI). However, due to the laboratory limitations, it is difficult to experimentally investigate the seismic behavior of these structures on a real scale by considering the actual soil environment. This paper aims to adopt a nonlinear kinematic hardening model for clay in Abaqus software and calibrate this model parameters for the South Pars gas field region to carefully investigate the effects of nonlinear behavior of soil and PSSI on the seismic response of an offshore jacket platform. In addition, the perfectly elasto-plastic Mohr-Coulomb model is employed as a simple and common constitutive soil model to compare the results. To achieve the study goals, firstly, the numerical modeling techniques are validated. Subsequently, the main parameters of the nonlinear kinematic hardening model are calibrated for the South Pars gas field region, which has not been done for this region in previous works. Detailed numerical models, including the fixed-base model and the pile-soil-structure (PSS) model, are then developed and analyzed using different selected ground motion records. The results indicate that considering the effect of PSSI has a significant effect on the seismic responses of the structure. Moreover, PSSI effect has a great dependence on the constitutive soil model. The results of this study are expected to provide useful insights into the seismic design of offshore structures in similar geological conditions.

SEISMIC RETROFIT OF SUBSTANDARD RC BRIDGES USING CONTEMPORARY MITIGATION MEASURES

As essential infrastructure components, existing substandard bridges may cause significant economic losses at the urban scale as they are prone to different damage modes under seismic excitations. Due to the large number of existing RC bridges in earthquake-prone regions and the continuous updates in seismic design criteria, there is increasing interest in developing effective seismic retrofit techniques for enhancing the performance of these structures. This study thus investigates the effectiveness of contemporary retrofit measures for upgrading the seismic performance of RC bridges, namely ultra-high-performance concrete (UHPC) jackets and self-centering energy dissipating (SCED) braces. Detailed fiber-based numerical models are developed for scaled RC bridge substructures retrofitted with the adopted mitigation measures. The hysteretic behavior of the bridge substructures from quasi-static cyclic loading experiments conducted in previous studies is utilized to verify the developed fiber-based models. The validated modeling approaches of retrofit strategies are then applied to an old benchmark bridge located in a medium seismicity zone. The inelastic response of the benchmark bridge substructure before and after the retrofit with different mitigation measures is assessed using the verified fiber-based numerical models. The results demonstrate that the retrofit measures increased the lateral strength of the bridge bent by 37.5%. Also, 10% improved ductility was observed in the UHPC retrofitted bent. This performance assessment study enabled the selection of effective measures to mitigate the vulnerability of substandard bridge members to ensure their post-earthquake functionality.

Experimental and numerical study of 3D printed steel plates stiffened by sinusoidal waves for enhanced stability

This paper reports the first experimental tests on additively manufactured steel plates stiffened by sinusoidal waves, followed by a detailed numerical modelling programme to account for the imperfection sensitivity of these shapes. This innovative study focuses on stiffened plates (plates simply supported along both longitudinal edges), which were experimentally tested employing square hollow section (SHS) stub columns. The experimental study comprised of 5 tensile coupon tests, 15 stub column tests and measurements on geometric accuracy and residual stresses on 316L stainless steel samples made by selective laser melting (SLM). Validating against the experimental results, numerical models accounting for realistic manufactured dimensions and geometric imperfections have been developed. The validated numerical models were used to perform a parametric study considering a wider range of geometries and plate slendernesses. Based on the results of the parametric study, the efficiency of this stiffening method across a range of plate slendernesses has been assessed and optimum wave patterns identified, which were shown to be able to enhance buckling strength up to 50% compared to the flat counterparts. Provisional design equations have also been proposed for SLM 316L stainless steel plates stiffened by the optimum stiffening patterns selected.

Evolution of an elastic blister in the presence of sloping topography

The propagation of a finite blister of fluid beneath an elastic sheet is controlled by the local dynamics at the peeling periphery of the current. Previous works have described constant volume elastic blisters by considering the peeling due to curvature at these edges. Here, we show that an along-slope component of gravity fundamentally changes the dynamics by removing the role of curvature at the trailing, upslope edge. The local dynamics of this trailing edge is instead controlled by shear stress in the sheet, as in the elastic Landau–Levich problem, and thereby allows for a receding edge, in contrast to propagation by peeling for which only an advancing contact line is possible. Using an asymptotic analysis, we show that this receding edge condition allows for a new, nearly translating regime in which the body of the blister moves at an approximately constant speed, leaving behind a thin layer of fluid. This prediction is verified by detailed numerical modelling of the two-dimensional downslope spreading. We conclude by discussing the applicability of these results in the rapid spreading of subglacial meltwater.

Numerical analysis of the thermomechanical behavior of rubber concrete at high temperatures

AbstractInsufficient research has been done on the mechanical and thermal properties of rubber concrete in the presence of fire. In this paper, we do detailed numerical modeling of the rubber concrete's thermomechanical behavior under dynamic conditions at high temperatures (800°C) using different percentages of rubber aggregate (0%, 10%, 20%, and 30%). The novelty of this work lies in its analysis of the temperature profiles over time in rubber concrete. This analysis is carried out using finite difference models developed with the MATLAB tool to predict thermomechanical parameters such as elastic modulus, thermal strain, tensile strength, and compressive strength. In addition, the dynamic behavior of the rubber concrete under impact loading was predicted, including stress and velocity change as a function of time at elevated temperatures. By the equations of motion and transient conduction, the mathematical model developed is based on density, thermal conductivity, heat capacity, and thermal expansion. The comparison between numerical and experimental results, and the analysis of the influence of the percentage of rubber aggregates on thermomechanical parameters, as well as the influence of temperature on the evolution of stress and velocity as a function of time, have shown the effectiveness of the mathematical and numerical model developed.

Re-purposing of shallow wind turbine foundations for power capacity increase

Re-purposing the foundations of older wind turbines to install new and larger wind turbines can reduce the investment costs and carbon emissions of wind energy development projects. In this paper, detailed numerical modeling is used to assess the behavior of a shallow foundation designed for a 5 MW wind turbine under the aerodynamic loads and seismic motions of larger replacement wind turbines. The finite element modeling scheme used for the soil under rocking foundations is validated based on experimental data. Results of this study indicate that maximum gapping and maximum tilting have similar trends of increase with increasing turbine power. Relaxing the no-uplift rule for normal operation conditions allows for installing an 8 MW wind turbine on the foundation designed for 5 MW, without compromising the foundation safety or serviceability requirements. However, the foundation does not perform satisfactorily with the 10 MW wind turbine. The no-uplift rule of design regulations for operational conditions is overly conservative. The limits of capacity increase for individual projects can be determined using the procedure presented in this paper.

Ballistic Impact Analysis of Thin Shell and Curved Surface against Different Projectile Nose Shape

Abstract: Numerical simulations are increasingly becomingan important tool to obtain efficient designs of protectivestructures, and the existing literature shows that manyphenomena can be accurately described by standard methodsand models. This thesis, specifically, focuses on novelmethods of modeling and simulating ballistic impact.Experiments are needed to validate such simulations, so numerous tests were studied to investigate how projectile nose-shape, plate layering, target strength, ductility, and workhardening affect the penetration and perforation behavior of various structural configurations. These tests provide new information about the behavior of materials subjected to ballistic impact, and are valuable input for the evaluation ofthe numerical simulations. As more complex materialssystems are introduced in engineering practice, the design engineer faces the of utilizing homogenization techniques or detailed numerical models. The latter offers a number of advantages, such as the ability to introduce separateconstitutive laws and failure criteria for each phase, at theexpense of computation cost. The aim of this study is to givegeneral information about the most commonly used materialsand ballistic test methods. In addition, to summarize the topicsrelated to simulation methods such as FEM and numericalmethods which are use most in ballistics.A generalizednumerical and experimental formulation is presented for theprediction of ballistic impact behavior on various surfacesagainst different projectile nose shape. The ballistic resistance,failure mechanism and the energy absorption of the structurewas investigated thoroughly through experimentation andnumerical simulations. influence of projectile shape, incidencevelocity of the projectile.

Seismic performance evaluation of high‐post‐yield stiffness concentrically braced steel frames under mainshock‐consistent‐aftershock sequences

AbstractStructures may be subjected to earthquake sequences after major mainshock (MS) events in seismically active sites within a short time. As a result, they may be susceptible to damage accumulation, which may hinder their performance under consecutive seismic loading. This study evaluates the effects of earthquake sequences on the seismic performance of seismic‐resistant concentrically braced steel frames designed to Eurocode‐8. The frames under investigation have concentric chevron‐type braces with replaceable hourglass‐shaped pins made of duplex stainless steel. The seismic energy is dissipated through inelastic deformations concentrated in the pins while keeping the other members elastic. The stainless‐steel pins provide the frame with high‐post‐yield stiffness to reduce the residual drifts after a seismic event. The seismic behaviour of the frame is assessed using site hazard‐specific mainshock‐consistent‐aftershock (MS‐AS) sequences selected for a site in Terni, Central Italy. Nonlinear back‐to‐back dynamic analyses are performed at multiple intensity levels while adopting detailed numerical nonlinear models created in OpenSees. We show that the implemented behaviour factor satisfies the life safety assurance objective while keeping the maximum residual inter‐storey drifts below 1/300 to permit an easy substitution of the damaged pins after the design‐level earthquake without being curtailed by the potential following events. We then develop prediction models for the damage accumulation in the pins, considering different energy‐based intensity measures and we show that the cumulative absolute velocity‐based model is the most efficient predictor in this particular case. Finally, the damage accumulation in the pins is evaluated, confirming their superior low‐cycle fatigue capacity under earthquake sequences.

Trends in the 40 + -year development of advanced structural acoustic and vibration computational modeling

Over the course of the past 40-45 years of computational modeling in the fields of structures, structural acoustics, and vibrations, there have been extreme advancements made in numerous areas that have greatly increased and improved the size, accuracy, efficiency, and complexity of numerical solutions possible. Most of this progress has been made through a combination of improvements in the distinct areas of computer processing approaches/speed and available memory, primarily evolutionary enhancements in detailed numerical material and continuum mechanics models, development of entirely new physics-based numerical vibroacoustic modeling approaches, etc. This paper presents a historical review of the detailed progress made in computational structural acoustics and vibration from the “early days” in the 1980s through current state-of-the-art advanced numerical approaches, much of which would not have been dreamed possible back four decades ago! While most of the examples utilized in this talk are pulled from the speaker’s specific technical area of undersea vehicle/ system structural acoustics, the overall trends presented are certainly represented across the broad spectrum of vibro-acoustics modeling applications.

Simulation of RC Beams during Fire Events Using a Nonlinear Numerical Fully Coupled Thermal-Stress Analysis

The collapse and deterioration of infrastructures due to fire events are documented annually. These fire incidents result in multiple deaths and property loss. In this paper, a reliable and practical numerical methodology was introduced to facilitate the whole process of fire simulations and increase the practicality of performing comprehensive parametric studies in the future. These parametric studies are crucial for understanding the factors that affect thermal–structural responses and avoiding the high cost of destructive tests. The proposed algorithm comprises a fully nonlinear coupled thermal-stress analysis involving thermal and structural material nonlinearity and the thermal–structural response during a fire. A detailed numerical modeling analysis was performed with ABAQUS to achieve the proposed algorithm. The results of the proposed numerical methodology were validated against published experimental work. The experimental work includes a full-scale RC beam loaded with working loads and standard heating conditions to simulate real-life scenarios. The tested beam failed during the fire, and its fire resistance was recorded. The results demonstrated a good correlation with the experimental results in thermal and structural responses. Moreover, this paper presents the direct coupling technique (DCT) and the advantages of using DCT over the traditional sequential coupling technique (SCT).

Mesh‐size independent rigid‐body spring network for simulation of the dynamic fracture behavior of concrete

AbstractIn this study, a numerical approach is developed for simulating the rate‐dependent behaviors of concrete without mesh sensitivity. The rheological units (e.g., dashpot) are integrated with the six directional springs in the rigid‐body spring network (RBSN) elements to reflect the rate‐dependent behavior of concrete. Previously, the viscoplastic damage model was associated with the elemental degrees of freedom. However, in the present approach, a viscoelastic constitutive law is newly defined for the normal direction as a function of the strain rate, from which the internal forces can be updated from the regularized elemental stresses. Such improvements are validated through the numerical simulations of the direct tensile test and spalling test using the modified split‐Hopkinson pressure bar (SHPB). The simulated results show consistent structural responses without mesh dependence on the strain rate. In addition, the influences of the softening curve shapes on the crack localizations are examined. It is shown that the rheological parameters can be optimized and determined for consistent applications through virtual experiments. The proposed numerical approach enables the mesh construction procedure without concerning the mesh‐size sensitivity due to the strain rate, and various applications are expected for the simulations of detailed numerical models of concrete materials and structures under high loading rates.