Simplified Finite Element Model Research Articles

Seismic damage assessment of a supertall tubed mega frame structure based on a simplified finite element model

SummaryA tubed mega frame structure is composed of tubes located at the perimeter of the structure as mega columns and mega beams. This paper explores the applicability of this structural system to supertall buildings in high seismic intensity areas. First, a refined finite element (FE) model of a 585‐m tall tubed mega frame structure was built in ABAQUS, as well as a mega‐braced frame‐core structure on which the tubed mega frame structure is based. In order to improve the efficiency of nonlinear analyses, beam‐based simplified FE models of the two structures were developed in OpenSees and validated against the refined FE models. Then, incremental dynamic analyses of the tubed mega frame structure were conducted based on its simplified model. The damage of the tubes was quantified by a modified Park–Ang damage model. The analyses indicate that the seismic damage of the tubes in the tubed mega frame structure develops rapidly after yielding, because tubes at the perimeter of the structure suffer severe axial load under high‐intensity earthquakes. It is suggested that the axial load ratio of the tubed mega columns should be controlled to avoid brittle failure in the seismic design of supertall tubed mega frame structures.

Application and Benchmarking of a Novel Coupled Methodology for Simulating the Thermomechanical Evolution of Sodium-cooled Fast Reactors Fuel Subassemblies

We employ a novel methodology to simulate the irradiation of Sodium cooled Fast Reactors (SFR) subassemblies. The proposed approach allows considering the coupling between key thermal–hydraulic and thermomechanical phenomena, which is usually neglected in traditional simulation methods. Comparisons between results obtained from coupled and uncoupled methodologies show that the latter can significantly over predict the stresses and the strains of highly irradiated fuel bundles. Additionally, we explore different options for the pin mechanical modeling. In particular, we show that a relatively simple beam-based finite element model for the fuel pins can be used to efficiently compute swelling and irradiation creep strains averaged over the cross section of the fuel claddings. However, if a prediction of the cladding swelling gradients is needed, the beam model must be replaced by a more computationally expensive 3D fuel pin model. An efficient method to estimate the fuel cladding temperature evolution based on a limited number of Computational Fluid Dynamics (CFD) simulations is also presented in this work, and its performance is evaluated. Finally, a numerical benchmark against the state-of-the-art coupled code system for the simulation of SFR subassemblies is presented. This benchmark shows that the proposed coupled methodology allows obtaining results that are in good agreement with the reference methodology. However, two clear advantages of the proposed methodology were identified. Firstly, the use of detailed CFD simulations in our methodology, compared to the lower resolution thermal-hydraulic model employed in the state-of-the-art approach. Secondly, considering the reduction of the coolant mass flow rate caused by the fuel bundle deformation, neglected in the pre-existing approach, which is shown in this work to have a potentially large impact on the coolant temperature distribution.

A crashworthiness optimisation procedure for the design of full-composite fuselage section

Crashworthiness of composites is a key-point in the design of new aeronautical structures. Special attention has been addressed in the last years to the energy absorption mechanisms of dedicated components in order to limit the structural damages and to preserve the occupants’ safety. Remarkable progress has been made in this field. Despite this, to further improve the design of crashworthy composite structures, components modification, sensitivity analysis, design of experiments and optimisation procedures are needed. In this work, crashworthiness improvements, related to a simplified finite element model of a full-composite fuselage section subjected to a vertical drop-test, have been introduced. The genesis of the model has been described together with its main features and details and a high-speed vertical fall has been simulated, paying attention to velocity and payload. In addition, sensitivity analyses of some components and a discussion on the main crashworthiness characteristics have been carried out. Finally, the parent fuselage section and its simplified model have been compared under both energy and deformation points of view, showing a good results agreement.

Essential work of fracture assessment of acrylonitrile butadiene styrene (ABS) processed via fused filament fabrication additive manufacturing

Experiments and finite element (FE) calculations were performed to study the raster angle–dependent fracture behaviour of acrylonitrile butadiene styrene (ABS) thermoplastic processed via fused filament fabrication (FFF) additive manufacturing (AM). The fracture properties of 3D-printed ABS were characterized based on the concept of essential work of fracture (EWF), utilizing double-edge-notched tension (DENT) specimens considering rectilinear infill patterns with different raster angles (0°, 90° and + 45/− 45°). The measurements showed that the resistance to fracture initiation of 3D-printed ABS specimens is substantially higher for the printing direction perpendicular to the crack plane (0° raster angle) as compared to that of the samples wherein the printing direction is parallel to the crack (90° raster angle), reporting EWF values of 7.24 kJ m−2 and 3.61 kJ m−2, respectively. A relatively high EWF value was also reported for the specimens with + 45/− 45° raster angle (7.40 kJ m−2). Strain field analysis performed via digital image correlation showed that connected plastic zones existed in the ligaments of the DENT specimens prior to the onset of fracture, and this was corroborated by SEM fractography which showed that fracture proceeded by a ductile mechanism involving void growth and coalescence followed by drawing and ductile tearing of fibrils. It was further shown that the raster angle–dependent strength and fracture properties of 3D-printed ABS can be predicted with an acceptable accuracy by a relatively simple FE model considering the anisotropic elasticity and failure properties of FFF specimens. The findings of this study offer guidelines for fracture-resistant design of AM-enabled thermoplastics.Graphical abstract

Simulation and Experimental Validation of Sound Field in a Rotating Tire Cavity Arising from Acoustic Cavity Resonance

As we all know, the tire acoustic cavity resonance noise (TACRN) can cause irritating noise in a vehicle, but it is evidently difficult to be weakened. To obtain accurately the characteristics of TACRN is a key step of attenuating TACRN. In this paper, a simulation method, in which a simplified finite element model of automobile tire with acoustic cavity introducing the rotation of automobile tire is established, is proposed to gain the sound field in the cavity of a rotating automobile tire. And the test of sound pressure in a rotating tire is also performed to validate the proposed simulation method. The comparisons between the simulation and experimental consequences show a satisfying conclusion. Furthermore, the influence factors of the rotating speed, the inflation pressure of the tire and the load on the sound field of automobile tire acoustic cavity are calculated and analyzed.

Improvement in the accuracy of the dynamic behaviour prediction of a bolted structure using a simplified finite element model and model updating

Bolted joints in assembled structures contribute to the dynamic behaviour of the structures but also increase uncertainties in modelling and prediction of the dynamic behaviour. This paper presents a modelling scheme able to reduce uncertainties and increase the accuracy of the prediction. A finite element (FE) model of a bolted joint structure was developed using CBUSH, CBEAM and 3D elements representing the bolts, contacting interfaces, and structural components, respectively. Normal modes analysis was performed on the FE model to calculate the natural frequencies and mode shapes. Sensitivity analysis was formulated and used in identifying the highly sensitive design parameters of the FE model. Model updating was adopted in correlating the FE model with experimental modal analysis (EMA) and producing an updated FE model. It was found that the updated FE model is capable of predicting the dynamic behaviour of the bolted joint structure with 95 per cent accuracy. This proposed scheme demonstrated potential for applicability to the dynamic behaviour analysis of complex bolted structures.

Impact of hydrogen solubility on depleted gas field's caprock: an application for underground hydrogen storage

Depleted gas fields are considered a low-risk location for underground hydrogen storage purposes to balance seasonal fluctuations in hydrogen supply and demand. The objective of this study was to identify any significant risk of hydrogen leakages stored in depleted gas fields. The capability of the storage area in terms of sealing efficiency varies with parameters such as rate of diffusion, solubility, thickness and capillary threshold pressure of the caprock. The most common caprock are shales, which contain organic material. The solubility of hydrogen into organic material could change the petrophysical properties of the rock, such as porosity and permeability. Any changes in these petrophysical characteristics can reduce the capillary threshold pressure thus reducing the caprock efficiency for the safe storage of hydrogen. There is about 20% of the remaining gas volume in the depleted gas field, which helps to prevent brine from entering the production streamlines and maintain reservoir pressure. The characteristic data of hydrogen at different high pressures and temperatures have been evaluated and imported into the simple finite element model using the Python programming language. Most of the parameters that influence reducing the strength of the caprock are identified. Crucial parameters are the rate of diffusion, the solubility of hydrogen in kerogen, geomechanical deformation, threshold capillary pressure, long period of injection and withdrawing of hydrogen. The model shows that the native gas production with hydrogen is low due to significant density variation and mobility ratio between methane and hydrogen. Finally, a wide range of parameters and reservoir conditions has been considered for minimising the potential risks of possible leakages.

Investigation of asymmetrical fiber metal hybrids used as load introduction element for thin-walled CFRP structures

Due to the industrial success of fiber reinforced plastic (FRP) light-weight components, the demand for joining methods suitable for FRP increases as well. Conventional joining elements like rivets and screws or simple clamping are designed for an application in conventional isotropic materials such as steel or aluminum. Therefore, by design these joining elements do not consider characteristic FRP properties such as the orthotropic (fiber) or the setting behavior of matrix materials that are subjected to a constant load. Thus, without any FRP specific adjustments, conventional joining elements will, in most cases, lead to poor results and an inferior joint. Hence, this investigation presents the concept of a layered local metal-hybrid area that can be used as a load introduction element, the “Multilayer-Insert”. The design aspects of the hybrid area are discussed for several stacking options. Furthermore, the sensitivity to geometrical design variables and asymmetrical stackings are investigated by a simplified two-dimensional finite element model. The deduced parameter relations are discussed in the context of an application in an automated fiber placement process in order to formulate recommendations for the geometrical parameters.

Seismic performance of steel columns corroded in general atmosphere

Steel structures exposed to general atmosphere for a long time are highly susceptible to corrosion damage, which would lead to the degradation of service performance of the components and even structures. This article focuses on the effect of corrosion on the seismic performance of steel column. The accelerated corrosion tests in general atmosphere were conducted on 7 H-shaped steel columns and 20 steel plates. Then the obtained plate specimens were subjected to monotonic tensile tests and cyclic loading tests, and the steel columns were subjected to pseudo-static tests, respectively, to study the effects of corrosion on their mechanical properties and seismic performance. Then, a simplified three-dimensional finite element model (FEM) capable of accurately simulating the hysteretic response of corroded steel columns under low-cycle loading was established. Experimental results indicated that the yield strength, tensile strength, elastic modulus and peak strain of corroded steel plate decreased linearly with the proposed corrosion damage parameter Dn, and the energy dissipations under low-cycle loading were significantly reduced. There is a correlation between the cyclic hardening parameters of corroded steel and the yield-tensile strength difference (SD), and then a simplified formula was proposed. Corrosion could result in the premature entrance of each loading stage of corroded columns and the deterioration of buckling deformation range, bearing capacity and energy dissipation, etc. In addition, a larger axial compression ratio (CR) would further accelerate the failure process of corroded columns. The parametric finite element analysis (FEA) indicated that greater damage was found for steel columns with non-uniform corrosion, and hysteretic performance degraded more significantly when corrosion distributed at flanges or foot zone.

Review of compatibility between SANS 10400 deemed-to-satisfy masonry wall provisions and loading code

South Africa has a housing shortage estimated in excess of 2 million units. This backlog is being addressed predominantly with the construction of 40 m2 low-income, single-storey, detached, state-subsidised houses built with conventional concrete masonry units, regulated by the Application of the National Building Regulations, SANS 10400. However, several developments warrant a reconsideration of SANS 10400 deemed-to-satisfy masonry wall provisions. Two critical configurations of single-storey, unreinforced, bonded masonry walls are generated, based on these deemed-to-satisfy provisions. Subsequently, a simplified micro-scale finite element model is used to analyse these configurations under serviceability and ultimate limit state loading conditions. Characterisation tests of the concrete masonry material, together with numerical fitting to test data and data taken from literature, generate the necessary parametric input. The numerical analyses reveal that in half of the load cases, the walls' resistances failed to achieve the design load as required by the South African loading code. A significant shortfall was found for the out-of-plane resistance against the wind load, as well as structural vulnerability under seismic loading due to the geometric layout permitted by the deemed-to-satisfy rules. This indicates that the SANS 10400 provisions for masonry wall panel geometries require reconsideration, especially given the recent revision of the South African loading code.

Biomechanical Analysis of Left Ventricle Considering Myocardial Infarction and Regenerative Therapy Using Dynamic Finite Element Method

It is well known that myocardial infarction (MI) greatly degrades the pulsation function of the heart. Such MI may gradually grow in size and harden as ischemic necrosis proceeds, resulting in further degradation of its pulsation behavior. However, regenerative therapy has successfully been used in the medical treatment of MI, specifically the use of cell sheet technology. In this procedure, thin sheets of biomechanical effects of regenerative therapy on the LV with MI. A simple 3D finite element model of a LV was developed and dynamic FEA with a cardiac mechanics theory was conducted to simulate the time-dependent cyclic deformation behavior. It was found that increasing size and stiffness of the MI dramatically reduced both the maximum displacement of beating mechanical behavior. It was also determined that the cardiac cell sheet regenerative therapy can effectively restore the pulsation function.

Reinforcing Effect of Strain Gauges on 3D Printed Polymers: An Experimental Investigation

Strain gauges are ordinary transducers for strain measuring; their operation relies on the electrical resistance, which varies as the underlying substrate is subjected to mechanical deformation. The mechanical strain can be obtained by converting the electrical signal through a gauge factor, provided by the manufacturer. It was demonstrated that its values are not unique; it may be influenced by the geometrical characteristics of both the specimen and the strain gauge and by their respective moduli of elasticity. This can be extremely dangerous when low modulus materials are studied. This study confirms that even with commercial strain gauges specifically designed for low modulus materials the effect might be present. An experimental method for its evaluation is discussed; tensile specimens are used as a test bench and their modulus is determined using both strain gauges and a non-contact method (Digital Image Correlation). The results show that a local reinforcing effect is present and a higher tensile modulus is obtained when contact transducers are bonded to polymeric specimens. The amplitude of this effect is predicted with established methods available in the literature and through a simple 2D Finite Element (FE) model. All these models require the elastic modulus of the strain gauge to be considered; a digital procedure to estimate it for any wired transducer is therefore proposed. The predicted results were found to be consistent with those experimentally measured; this validated the method, thus advising on how to evaluate the phenomenon also when this information is not available.

Active Vibration Control of Helicopter Maneuvering Flight Using Feedforward‐Robust Hybrid Control Based on Reference Signal Reconstruction

Current control laws for active control of helicopter structural vibration are designed for steady‐state flight conditions, while the vibration response of maneuvering flight has not been taken into consideration yet. In order to obtain full‐time vibration suppression capability, the authors propose a filtered least mean square‐mixed sensitivity robust control method based on reference signal reconstruction (LMS‐MSRC), driving piezoelectric stack actuators to suppress helicopter structural vibration response in maneuvering flight. When feedback controller designed by H∞ theory is implemented, active damping is added on the secondary path to weaken the adverse effects of its sudden changes in maneuvering flight state. Furthermore, a reference signal reconstruction scheme is given concerning equivalent secondary path. In addition, the reconstruction accuracy, the convergence speed, stability, and global validity of the hybrid controller are analysed. Compared with multichannel Fx‐LMS, numerical simulations of LMS‐MSRC for vibration suppression are undertaken with a helicopter simplified finite element model under several typical flight conditions. Further experiments of real‐time free‐free beam vibration control are performed, driven by a stacked piezoelectric actuator. The instantaneous overshoot of measured response is 42% less than the peak value and its attenuation reaches 85% within 2.5 s. Numerical and experimental results reveal that the proposed algorithm is practical for suppressing transient disturbance and multifrequency helicopter vibration response during maneuvering flight with faster convergence speed and better robustness.

Modelling Adhesive Using Non-Linear Truss Elements in Mode I Delamination Problems

A fast and simple finite element model is presented in this paper to simulate the crack propagation in notched beam structures with two layers and one interface medium in Mode I delamination. The truss elements from FEAP element library are endowed with a user material law describing the bilinear cohesive zone model (CZM) with the material unloading path defined by embedding a history variable in the response. The layer is modelled with linear elastic Timoshenko beam elements. The method is used for damage growth and damage propagation simulations in interfaces with both ductile and brittle materials. The method is robust for ductile interfaces, but for brittle interfaces more specific numerical techniques are required. The results are evaluated using available analytical and numerical solutions and a good agreement is achieved.

Self-interference channel modeling for in-band full-duplex underwater acoustic modem

In-band full-duplex (IBFD) underwater acoustic (UWA) communication can significantly improve the throughput of UWA communication networks. In this paper, we focus on the self-interference (SI) channel modeling which is essential for SI cancellation in an IBFD modem. The SI consists of direct self-loop interference (SLI) and self multi-path interference (SMI) due to reflections from water surface and bottom. Therefore, we first propose a simplified finite element model for SLI in an IBFD UWA modem. Then we model the underwater vertical channel to obtain the SMI path loss and propagation delays. Simulation results show that the SLI signal is composed of diffraction and scattering components, and it is greatly affected by the modem housing material and shape. The SLI channel has a long (several tens of ms) impulse response. To verify the proposed model, based on the IBFD UWA communication modem developed by our team, we conducted a lake experiment in December 2019 at Qiandao Lake in Hangzhou, China. The simulated results match well with the experimental results in time/frequency features and transmission loss. This study reveals the complexity of SI channel in IBFD UWA communication.

Practical Model Proposed for the Structural Analysis of Segmental Tunnels

The construction of tunnels has become increasingly common in city infrastructure; tunnels are used to connect different places in a region (for transportation and/or drainage). In this study, the structural response of a typical segmental tunnel built in soft soil was studied using a simplified model which considers the coupling between segmental rings. From an engineering point of view, there is a need to use simple and reliable finite element models. Therefore, a 1D model based on the Finite Element Method (FEM) composed of beam elements to model the segments and elastic-linear springs and non-linear springs to model the mechanical behavior of the joints was performed. To validate the modeling strategy, the numerical results were compared to (lab-based) experimental results, under an Ultimate Limit State, obtained from the literature, and a comparison between numerical results considering a 3D numerical complex model which included the nonlinearity of concrete, reinforcing steel and the joints was performed. With this simplified model, we obtained a prediction of approximately 95% of the ultimate loading capacity compared to the results developed in the experimental and 3D models. This proposed model will help engineers in practice to create “rational” structural designs of segmental tunnel linings when a “low” interaction between rings is expected.

Research on the impact effect of AP1000 shield building subjected to large commercial aircraft

This study addresses the numerical simulation of the shield building of an AP1000 nuclear power plant (NPP) subjected to a large commercial aircraft impact. First, a simplified finite element model (F.E. model) of the large commercial Boeing 737 MAX 8 aircraft is established. The F.E. model of the AP1000 shield building is constructed, which is a reasonably simplified reinforced concrete structure. The effectiveness of both F.E. models is verified by the classical Riera method and the impact test of a 1/7.5 scaled GE-J79 engine model. Then, based on the verified F.E. models, the entire impact process of the aircraft on the shield building is simulated by the missile-target interaction method (coupled method) and by the ANSYS/LS-DYNA software, which is at different initial impact velocities and impact heights. Finally, the laws and characteristics of the aircraft impact force, residual velocity, kinetic energy, concrete damage, axial reinforcement stress, and perforated size are analyzed in detail. The results show that all of them increase with the addition to the initial impact velocity. The first four are not very sensitive to the impact height. The engine impact mainly contributes to the peak impact force, and the peak impact force is six times higher than that in the first stage. With increasing initial impact velocity, the maximum aircraft impact force rises linearly. The range of the tension and pressure of the reinforcement axial stress changes with the impact height. The perforated size increases with increasing impact height. The radial perforation area is almost insensitive to the initial impact velocity and impact height. The research of this study can provide help for engineers in designing AP1000 shield buildings.

Plastic-yielding analysis in the pipe-bending process of AZ31 and AA7050 using the normalized Cockcroft and Latham criterion

Compared with other sheet-metal-forming processes, the deformation conditions of pipe bending are affected by the material, equipment, die, and multiple other factors. Therefore, it is urgent to explore methods that avoid forming defects and improve the bend-forming quality. Wall-thinning induced ductile fracture is one of the dominant defects in the pipe-bending process, especially for materials with lower ductility. In this study, the normalized Cockcroft and Latham criterion is embedded into the user subroutine USDFLD within the Abaqus finite element (FE) software to predict the fracture tendency of a bent pipe. Through a comparison of theoretical calculations and simulation results, a simplified FE model of rotary draw bending was established, and the damage evolution and distribution of bent pipes composed of AZ31 and AA7050 materials were investigated. The results show that the two materials have similar regularity, and damage mainly generates and accumulates in the outer surface of the deformation zone due to wall thinning. The damage value remains at a certain level after the bending deformation enters the stable stage. This study provides a concept and strategy for more efficiently predicting the fracture tendency of a bent pipe.

3-Dimensional finite element modelling of asphalt mixtures for thermal conductivity determination

ABSTRACT Laboratory determination of the thermal conductivity k of asphalt materials is time consuming. Numerical determination of k is more viable practically for the purpose of mix design and paving temperature control. Researchers have applied microstructure finite element models for k determination. The method requires modelling skills and is computational resources demanding. This study shows that a simple row-column finite-element model of cubical cells can be employed to predict k with the same level of accuracy as microstructure models. Based on theoretical considerations of heat conduction mechanism and the construction and paving process of asphalt mixtures, this study reveals that exact mixture microstructure representation is unnecessary and impractical for the k determination problem. The simple proposed model, having straight-forward finite-element mesh representation and high computational efficiency, offers a practical tool for k determination to enable timely thermal evaluation of mix design, temperature analysis for paving control, and structural behaviour study under thermal loading.

Experimental and numerical investigation of underwater composite repair with fibre reinforced polymers in corroded tubular offshore structural members under concentric and eccentric axial loads

Repair of offshore steel structural members become essential due to the corrosive marine environment in which they exist. Structural repair using composite material has significant advantages in these cases than the conventional repair by welding or bolting steel sleeves. However, the composite repair technology with fibre reinforced polymers (FRP) is not very well established for their usage on load bearing offshore steel structural members either in underwater or above water conditions. The study had attempted to do a pilot experimental study on steel tubular members under the combination of axial compression and bending loads to address this gap in knowledge. The specimens were grouped into four categories: intact, corroded, repaired in air and repaired underwater. The repair scheme remained the same for in air and underwater repairs with one layer of glass and two layers of carbon fibre reinforced polymers, but with resin and repair methodology being different for both. The repaired specimens showed notable improvement in the ultimate strength from the corroded members to match the intact strength. Underwater repairs proved to be adequate to replicate the ultimate strength achieved by the conventional in air repairs. Investigations into parameters like load displacement behaviour, energy absorption, ductility and strain values also revealed that the underwater repair performed very similar to the conventional in air repair. A simplified Finite Element model simulating the repaired specimens was also presented in the paper which had predicted the experimental behaviour with great accuracy. In conclusion, the underwater and above water repair of structural steel tubular members using FRP composite materials seem a very viable solution for the corroded load bearing members in the offshore industry, however more detailed study on long term performance and cyclic behaviour of the composite repaired members is yet to be carried out.