Advanced Numerical Analysis Research Articles

Improving the indoor climate of the traditional Ottoman houses in the Medina of Algiers

The implementation of energy efficiency in historic buildings is limited and different parameters inhibit the improvement of microclimate conditions or energy performance. The aim of our research is to study the residential buildings of the old city of Algiers and to highlight the colonial and post-colonial transformations. The hygrothermal comfort is studied in order to identify a typical model of house having undergone transformations. This work requires a scientific and multidisciplinary approach integrating historical understanding, modern non-destructive inspection techniques and advanced experimental and numerical analysis methods (modelling and thermal dynamic simulation). The results show that in some cases of traditional houses, the transformations have been positive. The modification had a good functioning to modulate the variations of temperature and an indoor air quality allowing the occupants to profit from various zones of comfort. In other cases the undergone transformations generated enormous disorder resulting from discomfort situations. This work will provide adequate solutions to improve energy efficiency and sustainability for this residential heritage.

Advanced numerical analysis for vibration characteristics and ride comfort of ultra-high-speed maglev train

Magnetic levitation (maglev) trains are environmentally-friendly, require little maintenance, and allow for mass transportation. For these reasons, the demand for ultra-high-speed maglev trains has been increasing. Maglev trains can be classified with two suspension types, electro dynamic suspension (EDS) and electromagnetic suspension (EMS). EDS-type trains are suitable for ultra-high-speed because levitation suspension gap is over 100 mm compared with levitation suspension gap of 10 mm for EMS. When speed goes faster, it is hard to control the small suspension gap rapidly in EMS type. To analyze the EDS-type maglev train, electromagnetic forces were calculated with the superconducting coils and magnets using 2D analytical model. Based on the calculated forces, the lookup tables for the levitation and guidance force were employed in the total couple-fielded analysis. Ultra-high-speed maglev train was simulated by using the ADAMS multi-body dynamic program. The simulation was carried out with two car body models, rigid and flexible car body. In order to construct flexible car bodies with the modal information, the finite element method was used and they were constructed with the equivalent elements using ANSYS™. The final framework was constructed in MATLAB Simulink, and we co-simulated the dynamics and the electromagnetics with the constructed simulation frame work. To consider disturbances caused by irregularities, random and power spectral density (PSD) were used to analyze the vibrational interaction. As results, the ride comforts for PSD were a little bit worse than the results for random irregularity because the characteristics of PSD irregularity have more low excitation frequencies. The use of PSD inputs and flexible car body models need to be considered to improve the simulation accuracy.

Bearing capacity assessment for a timber girder when subject to a localised fire

Timber girders are often used as roofs in large-area buildings. One of the most important issues concerning the design of timber structures are fire safety requirements. Safe design requires adequate knowledge and modelling of the physical and chemical reactions inside the timber members exposed to fire. Wood is a combustible material. At 300°C the pyrolysis takes place which cause loss in mass and decrease the strength and mechanical properties. European standards introduce simplified methods for assessing load-bearing capacity in fire conditions. The second approach is advanced numerical modelling. This paper presents results from numerical studies on fire resistance of timber girder when subject to a localised fire. The numerical simulations have been performed with application of the SAFIR computer program. The numerical model of a timber girder was made. European standards recommend estimating the fire resistance of a structure based on the ISO fire curve. The advantage of such an approach is simplicity. It can lead to overestimating load-bearing capacity. Therefore, the cost of construction and fire protection will be higher. Another approach is implementation of appropriate fire models. Then, determining the temperature-time relationship for the analysed structure members. In this paper localised and IS0 fire were assumed. The heat was applied for three sides of the beam. An uneven cross-section along the length was also assumed. The obtained results indicate that advanced numerical analysis allows for a more accurate estimation of the load-bearing capacity of timber elements exposed to fire.

Stochastic Single Footfall Trace Model for Pedestrian Walking Load

Developing a model for the dynamic force generated by a pedestrian’s foot on a supporting structure (single footfall trace model) is crucial to advanced numerical analysis and vibration serviceability assessment of the structure. A reliable model needs to reflect the inter-subject and intra-subject randomness of human walking. This paper introduces a stochastic single footfall trace model in the form of a Fourier series in which body weight, walking frequency, and the first eight harmonics are treated as random variables. An experiment used 73 test subjects, walking at a range of pacing frequencies, to record force time histories and the corresponding gait parameters. Two variability descriptors were used to indicate inter-subject and intra-subject randomness. Further statistical analysis identified the relationships between key parameters as well as the probability distribution functions of random variables. In the final step, an application of the proposed single footfall trace model was developed and tested. The proposed model represented the experimental data well in both time and frequency domains.

Collapse performance of composite steel frames under fire

Collapse of steel structures under extreme hazards has been placed at the forefront of research in recent decades. While significant number of studies has been conducted in the past on steel members and subassemblies under fire, the response of steel buildings exposed to fire loadings has not received a similar level of attention. In addition, only handful of previous studies, mainly 2D with only one study pertaining to 3D frames, encompassed the full response of the system up to and including collapse. In this study, a 3D numerical finite element model is developed for a six-story steel-frame building with moment frames, gravity frames, and center concentrically braced frame to evaluate the collapse behavior of the structure under fire loading. A standard and a parametric fire curve are selected to simulate the fire loadings and are applied independently to the building model under two different contained fire scenarios. The two scenarios include first floor corner compartment fire and whole first floor fire. This allowed for the assessment of different global system response where collapse is triggered by twist of the entire structure accompanied by lateral deformation in the case of a corner compartment fire and progressive vertical displacement of the entire system in the case of the whole first floor fire. The simulation results show that structural response of steel buildings including collapse mechanism and behavior of structural members and connections during fire events can be predicted with reasonable accuracy using advanced numerical finite element analysis.

Damage Assessment by Numerical Modeling of Sant'Agostino's Sanctuary in Offida During the Central Italy 2016–2017 Seismic Sequence

The subject of this work is the Sant’Agostino Sanctuary in Offida (Italy); we investigated both the dynamic behavior and the seismic vulnerability of the complex, used nowadays in its parts as school building, oratory, and church. Offida is in central Italy; the village has been severely damaged by the last seismic events of 2016. The sanctuary was heavily damaged by the earthquake of 24 August 2016. We recurred to finite elements to estimate the vulnerability of the sanctuary and its dynamic response, considering masonry’s nonlinear behavior by means of proper constitutive assumptions. To estimate how the monastery bears the lateral loads related to the expected demands resulting from seismic actions (N2 method) using nonlinear static analysis (Pushover), we recurred to a homogenized material and smeared cracking and crushing constitutive law. As may be remarked by observing buildings that share the same features of the sanctuary and, moreover, by comparing seismic demand vs. capacity, the structure is prone to massive damage leading to collapse. The paper underlines how advanced numerical analysis grants fundamental data on how historical masonry buildings behave under seismic action, providing a method that may easily be implemented at historic monasteries in Europe.

Advances in numerical analysis of creep effect in time-dependent deflection of light-weight concrete slabs

Using a wide range of creep models, the experimental results of long-term deflection of lightweight concrete slabs subjected to two levels of early-age loading are investigated. Different creep models give considerably different estimation of the experimental deflection of slabs. The included factors in each creep model to simulate the experimental creep behavior of the concrete, and loading level on the slabs are the main causes of different results. Among the investigated models, the BP1 and FIBMC-2010 models including the aggregate type and concrete density is shown to be in good agreement with the experimental data in both loading levels.

Out-of-plane bending stiffness and hotspot stress based on advanced numerical analysis techniques

ABSTRACTThis paper aims to presents an integrated procedure to reach the out-of-plane bending (OPB) moment-induced hotspot stress distribution for the mooring chains of an 8MW class floating offshore wind turbine platform (FOWT). Three-link models of the mooring chains were used to obtain the OPB stiffness, mid-span stress distribution, hotspot stress, and stress concentration factor based on the prescribed rotation approach (PRA), direct tension approach (DTA), and empirical formula. Multi-link analyses were also conducted to build a tension angle-interlink angle relationship between two successive links at a given tension level. A combination of three-link and multi-link analyses produced the relation of the hotspot stress-tension angle. After a stress interpolation procedure for the hotspot stress history, the hotspot stress range distributions were presented using rainflow counting technique. The tension-induced stress range distribution well followed the Rayleigh distribution, while the OPB moment elevated the hotspot stress which will seriously affect the fatigue accumulation.

A smooth contact-state transition in a dynamic model of rolling-element bearings

We present a new formulation to calculate the response of a system containing rolling-element bearings operating under a radial clearance and a dominant radial load. The nonlinear bearing force- and stiffness-displacement characteristics in combination with the bearing clearance necessitate an advanced numerical analysis. The response of a shaft-bearing-housing assembly can be unstable in the transient regions, e.g., at the start of a system run-up or when passing the critical speed of a system. This can lead to long computational times or even to non-converged solutions. In this paper, a new analytical bearing-stiffness model is presented that is capable of overcoming these problems by smoothing the nonlinear bearing force- and stiffness-displacement characteristics in the discontinuous regions. The smoothing is implemented on the deformation scale. The proposed model is modular, allowing us to define a specific value of the smoothing to each rolling element that comes into contact. A simple case study that involves two bearings of different types (ball and cylindrical roller) is presented. They support an unbalanced rotor, subjected to a constant angular acceleration. We show that a small smoothing value can significantly enhance the numerical calculation of the chosen system in terms of speed and stability.

Advanced numerical analysis of landslide debris mobility and barrier interaction

Mitigation of natural terrain hazards through the use of flexible and rigid barriers has become a common type of geotechnical work in Hong Kong. The current design approach for these structural cou...

Analysis of ideal sorption compressor cycles operating with gas mixtures

Sorption-based compressors are thermally driven and because of the absence of moving parts they are vibration free, and have the potential for long life. Sorption-based compressors have been reported to operate Joule–Thomson (JT) cryogenic coolers with pure working fluids. However, using mixed refrigerants instead of pure refrigerants is attractive since that would dramatically improve the system coefficient of performance. Our on-going research aims to develop an efficient JT sorption cryocooler, operating with mixed refrigerants, and is focused on studying the characteristics of the sorption compressor cycle. This paper presents the results of an advanced numerical analysis, which is based on a previous model, and its experimental verification. The analysis relates to the ideal cycle of a sorption compressor operating with a gas mixture. Obviously, dynamics and kinetics play a major rule in a real sorption compressor cycle. However, since there are no reported gas-mixture sorption compressors and the existing experience in this field is poor, a preliminary ideal cycle analysis is considered. Satisfying agreement between the numerical and experimental results is obtained and the processes in the sorption cycle are discussed. The outcomes of the current study are the basis for the next phase in which a sorption compressor prototype will be built operating with gas mixtures.

Geotechnical characterization of the Miocene formations at the location of Ivens shaft, Lisbon

The design of complex underground structures in an urban environment requires in the first instance an appropriate characterization and interpretation of the ground conditions and of the mechanical behaviour of soil formations in the ground profile. With such information it is then possible to select and calibrate appropriate soil constitutive models for application in advanced numerical analysis, with the objective of predicting the induced ground movements and the potential damage to existing structures and services. This paper provides an interpretation of the site investigation data collected for the numerical analysis and design of the Ivens shaft excavation in Lisbon, Portugal. For the first time a comprehensive set of interpreted data is obtained for two of the main formations in the Lisbon area, Argilas e Calcários dos Prazeres (AP) and Areolas da Estefânia (AE), improving the understanding of their mechanical behaviour and making the data available for application in most soil constitutive frameworks. It is evident from the results that even with careful testing procedures the data may appear to be inconsistent, requiring further assumptions when deriving soil parameters. Such assumptions are discussed and emphasis is placed on the need to combine data from laboratory and field investigations.

Mode discrimination criterion for effective differential amplification in Yb-doped fiber design for high power operation

The mode discrimination criterion for single mode operation, usually considered in fiber amplifiers designed for high power operation, has been investigated and tested on three different fiber designs, a large pitch fiber and two symmetry free photonic crystal fibers. To have a significant collection of results, parameters like pump configuration, pump power, and amplifier length have been varied. The analysis has been carried out through the use of a custom numerical tool provided with efficient thermal and spatial amplification models. From the obtained results, it is possible to observe that the mode discrimination criterion is helpful but not strictly necessary to pledge an effective single mode operation through differential amplification. This fact extends the possibility for the study, as well as for the optimization, of different fiber designs. The use of advanced numerical analysis, which takes into consideration amplification along with thermally influenced modes guidance, becomes extremely useful for an effective fiber design.

Optimization-Based Inverse Identification of the Parameters of a Concrete Cap Material Model

Issues concerning the advanced numerical analysis of concrete building structures in sophisticated computing systems currently require the involvement of nonlinear mechanics tools. The efforts to design safer, more durable and mainly more economically efficient concrete structures are supported via the use of advanced nonlinear concrete material models and the geometrically nonlinear approach. The application of nonlinear mechanics tools undoubtedly presents another step towards the approximation of the real behaviour of concrete building structures within the framework of computer numerical simulations. However, the success rate of this application depends on having a perfect understanding of the behaviour of the concrete material models used and having a perfect understanding of the used material model parameters meaning. The effective application of nonlinear concrete material models within computer simulations often becomes very problematic because these material models very often contain parameters (material constants) whose values are difficult to obtain. However, getting of the correct values of material parameters is very important to ensure proper function of a concrete material model used. Today, one possibility, which permits successful solution of the mentioned problem, is the use of optimization algorithms for the purpose of the optimization-based inverse material parameter identification. Parameter identification goes hand in hand with experimental investigation while it trying to find parameter values of the used material model so that the resulting data obtained from the computer simulation will best approximate the experimental data. This paper is focused on the optimization-based inverse identification of the parameters of a concrete cap material model which is known under the name the Continuous Surface Cap Model. Within this paper, material parameters of the model are identified on the basis of interaction between nonlinear computer simulations, gradient based and nature inspired optimization algorithms and experimental data, the latter of which take the form of a load-extension curve obtained from the evaluation of uniaxial tensile test results. The aim of this research was to obtain material model parameters corresponding to the quasi-static tensile loading which may be further used for the research involving dynamic and high-speed tensile loading. Based on the obtained results it can be concluded that the set goal has been reached.

Common computational model for coupling panel method with finite element method

PurposeConceptual and preliminary aircraft concepts are getting mature earlier in the design process, than ever before. To achieve that advanced level of maturity, multiple multidisciplinary analyses have to be done, often with usage of numerical optimization algorithms. This calls for right tools that can handle such a demanding task. Often the toughest part of a modern design is handling an aircraft’s computational models used for different analysis. Transferring geometry and loads from one program to another, or modifying internal structure, takes time and is not productive. Authors defined the concept of a common computational model (CCM), which couples programs from different aerospace scientific disciplines. Data exchange between the software components is compatible, and multidisciplinary analysis can be automated to high degree, including numerical optimization.Design/methodology/approachThe panel method was applied to aerodynamic analysis and was coupled with open-source FEM code within one computational process.FindingsThe numerical results proved the effectiveness of developed methodology.Practical implicationsDeveloped software can be used within the design process of a new aircraft.Originality/valueThis paper presents an original approach for advanced numerical analysis, as well as for multidisciplinary optimization of an aircraft. The presented results show possible applications.

10.36: Advanced numerical analysis of steel, concrete and composite structures under fire conditions

ABSTRACTHigh temperature in common fire causes changes in physical characteristics and mechanical strength of the materials used in the structures. In both steel and concrete, such characteristics deteriorate during the exposure to fire, and the structure load capacity and stiffness are reduced significantly with the increasing temperature. This work is on advanced analysis context of structures under fire, and it aims to develop a computational system for analysis of steel, concrete and composite structures in fire situation, based on the finite element method. The use of advanced analysis as a methodology of analysis/design of structures has various advantages. Among these advantages, there is the capture of strength limit and stability of a structural system and its members directly, without the need for separate verification of each member capacity. This provides a more realistic analysis and determine adequately the performance of a structure in a real fire. To achieve the objective, the CS‐ASA (Computational System for Advanced Structural Analysis) is used and expanded to advanced analysis of structures in fire situation, taking advantage of existing features and adding new ones. Two new modules were created: CS‐ASA/FA (Fire Analysis) and CS‐ASA/FSA (Fire Structural Analysis). The first aims to determine the temperature field in the cross section of the structural elements by FE thermal analysis in permanent and transient regimes. The second was created to perform the inelastic second‐order analysis of structures under fire considering the refined plastic hinge method coupled to strain compatibility method. The adopted numerical methodology is described and, for a more comprehensive validation of the implemented modules, various structural systems under fire are analyzed.

Seismic Reliability Assessment of a Concrete Water Tank Based on the Bayesian Updating of the Finite Element Model

Abstract Failure or malfunction of complex engineered networks involves relevant social and economic aspects, so that their maintenance is of primary importance. In assessing the reliability of such networks, it should be duly considered that they are a whole made of different parts, and that some of these individual parts or structures are often crucial to assure the proper operation of the entire network. Moreover, each of these structures can be considered a complex system by itself: structural reliability theory should be thus combined with advanced numerical analysis tools in order to obtain realistic estimates of the probability of failure. Accurate estimations are especially required in seismic zones, aiming to efficiently plan future interventions. This paper presents a method for the reliability assessment of a critical element of engineered networks. The method is discussed with special reference to a relevant case study: a concrete water tank, which is a key component of a water supply system. Special attention is devoted to the reliability assessment of the tank under seismic loads, based on a structural identification approach. The calibration of the finite element model (FEM) of the structure is carried out on probabilistic basis, applying the Bayes theorem and response surface methods. The proposed approach allows to significantly speed up the structural identification process, leading to sounder estimate of the input parameters. Finally, the seismic fragility curves of the structure are developed according to the relevant limit states, demonstrating that information regarding the global structural behavior and local checks can be effectively combined in structural reliability assessments.

Identification of the Parameters of a Concrete Damage Material Model

Today, the advanced numerical analysis of concrete structures requires the use of nonlinear material models of concrete in order to take into account the nonlinear behavior of concrete within finite element simulations. However, the effective application of nonlinear concrete material models within numerical simulations often becomes problematic because material models often contain parameters whose values are difficult to obtain. Modern computers are advanced enough to solve this problem through the inverse identification of the used material model's parameters. This inverse identification is based on the combination of optimization methods or procedures with the experimental approach. The aim of this paper is to perform the identification of some parameters of the Karagozian & Case Concrete model - Release III, which is implemented in LS-Dyna software, on the basis of an experimentally-measured loading curve. For this purpose, numerical and experimental approaches were combined with optimization procedures. The loading curve was obtained from a triaxial compression test performed on a concrete cylinder.

Experimental Prediction and Numerical Modeling of Ductile Damage and Failure Modeling of Aluminium Sheet Metal Specimen

Aluminium sheet metal is nowadays used to fabricate lighter, crashworthy, fuel efficient and environment friendly vehicles. Ductile damage of sheet metals affects significantly the crashworthiness, as it naturally exhibits anisotropic behavior due to the grain orientation. Johnson-Cook (J-C) damage model is widely used in numerical simulation for assessing the failure modeling of crash component in particular at high strain rate. The Johnson-Cook material model available in literature is meant for isotropic material behavior which cannot be used directly for anisotropic behavior of materials. To characterize the plastic anisotropy of the rolled sheet, the modified Johnson-Cook material model should be developed. In this research the combination of experimental work and numerical analysis with clear and simpler calibration strategy for damage model is demonstrated. It aims to reduce laboratory tests using advanced numerical analysis to predict failure in order to save overall cost and development time.

Progress in the engineering design and assessment of the European DEMO first wall and divertor plasma facing components

The European DEMO power reactor is currently under conceptual design within the EUROfusion Consortium. One of the most critical activities is the engineering of the plasma-facing components (PFCs) covering the plasma chamber wall, which must operate reliably in an extreme environment of neutron irradiation and surface heat and particle flux, while also allowing sufficient neutron transmission to the tritium breeding blankets. A systems approach using advanced numerical analysis is vital to realising viable solutions for these first wall and divertor PFCs. Here, we present the system requirements and describe bespoke thermo-mechanical and thermo-hydraulic assessment procedures which have been used as tools for design. The current first wall and divertor designs are overviewed along with supporting analyses. The PFC solutions employed will necessarily vary around the wall, depending on local conditions, and must be designed in an integrated manner by analysis and physical testing.