Numerical Parametric Study Research Articles

Patch Loading Resistance of Slender Plate Girders with Multiple Longitudinal Stiffeners

AbstractThere is currently no reliable and simple design method available in international literature for the determination of the patch loading resistance of slender plate girders having multiple longitudinal stiffeners. Previous investigations focused mainly on girders having one longitudinal stiffener, which is not the common case for box‐girder bridges. Therefore, the current research – partly published in this paper – has a focus on the patch loading resistance of slender web girders having multiple longitudinal stiffeners. An advanced numerical model is developed and verified by own laboratory test results to determine the patch loading resistance. A numerical parametric study is executed to investigate the load‐carrying capacity of girders having typical bridge geometries. Analysing the numerical simulation results the structural behavior obtained is classified based on the stiffener stiffness. Effect of the different geometrical parameters on the patch loading resistance is evaluated with special focus on the stiffener stiffness and distance between the longitudinal stiffeners. The failure modes depending on the stiffener stiffness are investigated and the local buckling type failure is characterised by a minimum stiffness. For this specific failure mode an improved design method is developed for girders having multiple longitudinal stiffeners giving reliable resistance for the analysed cases within the analysed parameter range. The presented resistance model is consistent with the design philosophy of EN1993‐1‐5.

Buckling Check with Consideration of an Eccentric Load Introduction during Launching

AbstractIn general, two types of launching bearings are used for launching: sliding rockers and systems with hydraulic bearings. During incremental launching, the centre of the webs of the superstructure is not perfectly in line with the centre of the launching bearings due to unavoidable tolerances. These eccentricities are not considered in the current design against plate buckling according to EN 1993‐1‐5 [2]. Furthermore, there is a significant difference between the different types of launching bearings due to their boundary conditions. At the Technical University of Munich, large‐scale buckling tests of longitudinally stiffened plates under biaxial stresses with different types of launching bearings and eccentric load introduction were carried out. The results from the validated numerical model and parameter study of the influence due to different types of launching bearings on the buckling behaviour are shown. The results are compared with the buckling verification according to the reduced stress method proposed in EN 1993‐1‐5:2019 [2]. A proposal is given that makes it possible to consider an eccentric load in the buckling verification while keeping the economical aspects in mind.

Design Procedure for Stainless Steel Slender I Section Members in Bending

AbstractStainless steel welded I sections are used in structures not as often as cold‐rolled hollow sections or laser‐welded sections. But the design rules for both local buckling of very slender sections as well as lateral torsional buckling reduction factors are based on a very limited experimental and numerical research. For this reason, a new research covering these phenomena was carried out at the Czech Technical University in Prague. The contribution shows a numerical parametric study of welded slender stainless steel I‐section beams as a follow‐up of previous experimental program. The numerical study based on a validated FE model was carried out to develop a procedure for LTB of I section beams. The proposal follows the procedure of Taras, which is part of prEN 1993‐1‐1:2019, where modified constants are proposed. It was also found, that the local buckling reduction factor used in EN 1993‐1‐4:2006 may be unsafe for ordinary welded sections. The procedure in the Eurocode was developed mainly for SHS/RHS and laser‐welded sections. These fabrication methods result in significantly lower geometrical imperfections and slightly lower residual stresses than common welding methods (e.g. MIG). Therefore, a safe procedure proposal for Class 4 welded section resistance was also provided, despite not being the focus of the paper.

Buckling Resistance of Longitudinally Stiffened Panels with Closed Stiffeners under Direct Longitudinal Stresses

AbstractThe buckling behaviour of panels may be determined according to EN 1993‐1‐5 [1]. Most of the design rules relating to stiffened panels in EN 1993‐1‐5 were derived on the basis of open‐section stiffeners. Several recent investigations have shown that the application of the design rules according to EN 1993‐1‐5 [1] taking into account the torsional stiffness of the stiffeners may overestimate the resistance of the panels. Therefore, the recent Amendment A2 to EN 1993‐1‐5 states that the torsional stiffness of stiffeners should generally be neglected in determining critical plate buckling stresses. In addition, prEN 1993‐1‐5 [2] provides rules for considering the torsional stiffness of stiffeners. However, in this paper it will be shown that even the rules of prEN 1993‐1‐5 are not reliable as far as torsional stiffness is concerned. The paper focuses on the investigation of the buckling behaviour of stiffened panels with closed section stiffeners subjected to constant longitudinal compression stresses and shows improved rules to consider the torsional stiffness of the stiffeners. For this purpose, a new interpolation equation between column‐like and plate‐like behaviour is proposed, based on an extensive numerical parametric study. The proposal provides a safe and economic solution, as it considers the torsional stiffness of stiffeners when applying the rules of prEN1993‐1‐5.

Structural Stability Verification for Steel Beam‐columns in Fire ‐ a Consistent Approach with Ambient Temperature Rules

AbstractSteel structures are characterized by a slender design, which makes stability verifications particularly important. While the design methods for steel members at ambient temperatures have been continuously developed and revised for the second generation of Eurocode 3, the method for elevated temperatures in prEN 1993‐1‐2 is still based on the corresponding rules of ENV 1993‐1‐1 of 1992. This leads to a divergence of methodology for ambient and elevated temperatures and to unnecessarily complex design methods for the engineering practice. Therefore, a harmonization of design models for ambient temperature and fire design is desirable.This paper presents a theoretical and numerical study on the stability behaviour of steel members at elevated temperatures. The structural fire behaviour of steel beams, columns and beam‐columns, i.e. flexural buckling under pure compression, lateral torsional buckling under major axis bending and spatial buckling of members under combined bending and axial compression has been investigated. Based on results available in the literature as well as an extensive numerical parametric study, reduction factors and interaction factors were determined. The new reduction and interaction factors were used to develop a design model for the member stability verification in fire that follows the format of FprEN 1993‐1‐1. Thus, engineering practice is provided with a harmonized verification method for steel members in bending and compression for ambient temperature and fire design.

Exploiting spring-back differences for joining and pre-stressing sheet metal structures with tendons during forming – A mathematical-physical process model

Pre-stressing enables slender and high-strength structures in civil engineering. Previous studies have shown that it also offers a high potential for lightweight design of load-bearing sheet metal structures. Here, it is not only possible to join the sheet metal structures with the necessary tendons during a forming process, but also to pre-stress them at the same time. However, a targeted application of this technology requires a comprehensive understanding of the process mechanisms as well as calculation methods enabling an efficient structure and process design. To achieve this, the present article describes an analytical model of the underlying process mechanisms during the elastic-plastic forming process as well as the creation of the pre-stressing force acting between tendon and metal structure after spring-back. It is then transferred to two application-oriented processes. Numerical parameter studies serve the validation of these models and the further comprehension of additional process phenomena. It is shown that only a few geometrical, material and process related parameters are required to accurately calculate the pre-stressing force with a deviation of mostly less than 10 % from the numerical results.

Numerical study of racking resistance of timber-made double-skin facade elements

The use of a double-skin façade (DSF) is a quite new approach in the building renovation process, complementing conventional renovation strategies. A double-skin façade is an envelope wall construction that consists of two transparent surfaces separated by a cavity and can essentially improve the thermal and acoustic resistance of the building envelope. The main double-skin wall components are usually composed of a hardened external single glazing pane and a double or triple thermal insulating internal glass pane, which are connected to the frame structure. Recently, many studies have analysed the thermal and acoustic performance of DSF elements, but almost none in terms of structural behaviour, especially in terms of determining the racking resistance of such wall elements. Moreover, with a view to reduce the global warming potential, an eco-friendly timber frame instead of a commonly used steel, aluminium or plastic frame is studied in this analysis. However, structurally combining timber and glass to develop an appropriate load-bearing structural element is a very complex process involving a combination of two materials with different material properties, where the type of bonding can be selected as a crucial parameter affecting the racking resistance range. Since the costs of experiments performed on such full-scale DSF elements are very high and such experiments are time-consuming, it is crucial to develop special mathematical models for analysing the influence of the most important parameters. Therefore, the main goal of this paper is to develop the finite element mathematical model of the studied DSF structural elements with a highly ecological solution by using a timber frame. In the second step, the developed model is further implemented in the numerical analysis of racking stiffness and followed by a comprehensive parametric numerical study on different parameters influencing the horizontal load-bearing capacity of such DSF timber elements. The obtained results indicate that the new approach of the developed load-bearing prefabricated timber DSF elements can essentially improve racking resistance and stiffness compared with the widely studied timber-glass single-skin wall elements and can thus be fully recommended especially in the structural renovation process of old buildings.

Numerical study of microwave impact on gas hydrate plugs in a pipeline

Purpose. Development of a technique for the numerical study on the decomposition of gas hydrate plugs in deep-water pipelines under microwave radiation using a coaxial source. Theoretical efficiency evaluation of using such an impact to unblock the pipelines. Methodology. Mathematical modeling and computational experiment. Findings. An original mathematical model is proposed to describe heat transfer processes during the decomposition of gas hydrates in a pipeline under the action of heat sources distributed over the volume. The non-stationary problem of heat transfer was considered in a one-dimensional formulation. An algorithm for numerical computation is proposed. A mathematical expression is obtained for distributed heat sources generated by the microwave radiation from a coaxially located SHF antenna. Parametric numerical studies on temperature fields and decomposition dynamics of a gas hydrate plug are performed for specified parameters of pipe and microwave radiation power. The boundaries of the decomposition area and the dynamics of change in this area are determined. The decomposition time of a gas hydrate plug with a diameter of 0.3 m was determined using a 300 W microwave source. The complete decomposition took approximately 40 hours. Originality. The task of thermal decomposition of a cylindrical gas hydrate plug in a pipeline due to microwave heating using a coaxial microwave power source has been considered for the first time. The process is viewed as a sequence of several stages: heating, heating and decomposition, decomposition after complete heating of the gas hydrate layer. To model the volumetric dissociation of gas hydrate, it was proposed to use special functions that characterize the amount of decomposed gas hydrate. The introduction of such functions makes it possible to construct an efficient computational algorithm taking into account the action of volumetric sources in the decomposition area. The known models mainly consider only surface thermal effect or microwave impact on gas hydrate in porous mediums. The presented model allows describing the decomposition during volumetric heating of a solid hydrate adequately. Practical value. Blocking plugs may occur due to hydrate formation when transporting gas through deep-water pipelines or through pipelines in cold environments. The elimination of such complications is a complex technical task. In particular, a special source of microwave radiation, which was proposed by the authors in previous works, can be used to unblock the pipeline. The device that makes the microwave radiation is located along the pipe axis. The results of this work allow us to evaluate the effectiveness of the microwave method for eliminating the gas hydrate plug. The mathematical model and computational method can be used in the development of appropriate technologies using a coaxial microwave heating source.

Structural properties of a chain of dust particles in a field of external forces.

This paper presents a numerical study of the structural parameters of a one-dimensional chain of three dust particles levitating in the near-electrode layer of an rf discharge or in the stratum of a dc discharge. The model considers the motion of dust particles under the action of gravity, external electric field, the Coulomb repulsion, and the electrostatic force from the space charge surrounding the dust particles. Particular attention is paid to the effect of plasma polarization around dust particles and the wake formation under the action of the external electric field. Calculations showed that the charge of the first dust particle in the chain and the total charge of the entire chain, as well as the length of the chain, grow linearly with the external electric field strength. Obtained data are in qualitative agreement with the experimental and numerical data presented in the literature. It was shown that for a certain large value of the external electric field, the charge of the third dust particle is the smallest of all the particles in the chain. It was found that with an increase in the mean value of the external electric field, the chain of dust particles is displaced as a whole in the direction opposite to the action of the electrostatic force on them.

Experimental and Numerical Parametric Study of the Mechanical Properties in a Steel–Concrete Joint Section

Experimental and Numerical Parametric Study of the Mechanical Properties in a Steel–Concrete Joint Section

Wake topology and energy recovery in floating horizontal-axis wind turbines with harmonic surge motion

Floating horizontal-axis wind turbines (FHAWTs) enable us to harvest offshore wind energy in deep water area. Although the wake structure of an FHAWT causes secondary effects on its own aerodynamic performance, the wake characteristics are significant in both the performance of rear FHAWTs and the layout of floating wind farms, however, not sufficiently understood so far. To this end, a parametric numerical study is conducted to investigate the FHAWT's wake characteristics influenced by platform's surge motion. An improved delayed detached eddy simulation (IDDES) is applied on a 1/50 scale rotor of NREL 5 MW wind turbine, showing that surge motion evidently influences FHAWT's wake structure, as well as its' energy recovery. Specifically, the surge period is the predominant factor that influences FHAWT's wake topology. In addition, the unique vortex ring structures in the wake of the FHAWT under surge motion is reported for the first time. Moreover, the energy recovery of the FHAWT's wake depends on the surge period principally, and may be faster or slower than that of fixed-bottom wind turbines at different positions, indicating that the interval between two adjacent FHAWTs in floating wind farms should be considered carefully depending on prevailing or unprevailing wind directions.

Probabilistic Models for the Tensile Properties of Split Boards and Their Application for the Prediction of Bending Properties of Engineered Timber Products Made of Norway Spruce

The main strength and elastic properties of structural timber products, such as glued laminated timber (glulam; GLT) and cross-laminated timber (CLT), are usually described via load-bearing models, which use the tensile properties parallel to the grain of the base material boards and finger joints as input parameters. These load-bearing models assume that the strength-graded boards will retain their full dimensions in the final product. In some applications or use cases, however, the structural timber products are split lengthwise, e.g., split/resawn glulam, or comprise a random share of in width randomly lengthwise split lamellas. As a result of splitting, the material properties assigned to these boards during the grading process in their full cross-sections are no longer valid. Examples of such structural timber products are the novel flex_GLT-beams which are cut out from large dimensional multi-laminated timber panels. In the following paper, the bending properties and system effects of resawn glulam and flex_GLT-beams are described by means of a 3D stochastic-numerical beam model that uses probabilistic models to create the input values for unsplit and split boards as well as finger joints. The models are successfully validated by our own tests and tests from literature and applied in numerous parameter studies.

Numerical simulation of the human thermophysiological responses with a liquid circulating garment: Experimental validation and parametric study

Liquid circulating garments (LCG) can effectively alleviate the heat strain of people in hot environments. This work used a human thermoregulatory model integrated with a thermal and comfort model to comprehensively study the design factors of LCG. The model was firstly validated by human trials and showed good simulation performance in predicting both thermophysiological and subjective responses with LCG in a hot temperature. Then a numerical parametric study was performed to examine the effect of inlet water temperature, clothing insulation, pipe length, and cooling mode on cooling performance under different hot environments. The results indicate that the comfortable inlet water temperatures are 22, 19, and 16 °C under 30, 34, and 38 °C environments, respectively for a standing person wearing an LCG with thermal insulation of 1.0 clo and water pipe length of 8 m. Higher clothing insulation is beneficial for reducing the core and skin temperatures in very hot environments (i.e., 38 °C). The pipe length has a significant impact on the cooling performance. Furthermore, compared to the continuous cooling mode, intermittent cooling in high frequency (i.e., time cycle period = 5 min) can mitigate the heat stress of wearers with less energy consumption. The study could provide a helpful guideline for designing LCG to offer better thermal comfort and energy-saving strategies for people in hot environments.

Performance of precast concrete beam-column joint with a hidden corbel under progressive collapse scenarios

Collapse incidents of structures caused by extreme loads have attracted the attention of academia and building regulatory bodies worldwide. Due to inherent structural discontinuity, precast concrete (PC) structures are more vulnerable to progressive collapse than cast-in-situ reinforced concrete (RC) buildings. Therefore, studies on resisting collapse performance of PC beam-column joints for PC buildings are needed. In this paper, four 1/2-scaled PC beam-column joints with an in-built L-shaped corbel at each beam end were tested for progressive collapse under column removal scenario. These four joint specimens with identical non-seismic PC details were extracted from adjacent bays of the removed column, and the main parameters were the variations in the boundary and loading conditions. The deformation capacity, load-carrying capacity, catenary action (CA) and failure mode were evaluated and discussed. Parametric studies were also conducted by a proposed component-based mechanical joint model, to investigate the effects of PC interface location, mid-height reinforcement ratio and span-to-height ratio on the collapse resistance of the 2-span substructures. The experimental results show that this type of PC joint could achieve excellent hogging moment resistance but relatively lower sagging resistance. However, both PC joints under downward and upward applied loads could achieve a subsequent increase in resistance due to catenary action at large deformation stage. Numerical parametric studies indicated that shifting the precast interface inwards towards 1/3 point of single beam span and increasing mid-height reinforcement ratio could remarkably improve load-carrying capacity at the compressive arch action (CAA) stage. These detailing features could offset the negative effect caused by the discontinuous bottom longitudinal reinforcement, which is typical for gravity-dominant design in non-seismic countries, such as Singapore.

Damage evaluation of axial-loaded H-section steel columns during and after impact loading

The H-section steel members are usually employed as the key load-bearing elements in industrial buildings, which are vulnerable to the vehicle or crane-load collision. This paper presents the performance of H-section steel columns exposed to impact loading, including the course of impact and post-impact stages. A total of 12H-section steel columns were fabricated and tested to obtain failure patterns, impact forces and mid-height deflections as well as post-impact residual load carrying capacities. Additionally, finite element (FE) models were established and were calibrated with testing data. The calibrated models were then employed to conduct further numerical simulation and parametric study to reveal damage mechanism. Results demonstrated that the axial loading reduced the impact resistance significantly. The global deflection and the local indentation in the impact zone were found to result in reduction of the load-bearing capacity. Moreover, based on the post-impact deformations, an empirical equation was proposed to estimate the residual load carrying capacity of H-section steel columns, which can be used for rapid evaluation of damage after impact.

Numerical simulation of a thermally driven hydrogen compressor as a performance optimization tool

For the first time, a thermal study and optimization of a thermally driven hydrogen compressor has been performed. Experiments on this compressor, which is a proof of concept we developed, are time-consuming, making it difficult to know the behavior of the compressor under a variety of possible thermal conditions. In order to understand its behavior, we developed a numerical model to study the evolution of hydrogen pressure, flow rate, and temperature when heat transfers are intensified by changing the heating power, the setpoint temperature, or the convective regime. Hydrogen compression and discharge were simulated by finite elements and the tank was modeled by an axisymmetric 2D geometry. The heat and mass conservation equations for hydrogen were solved and the predictions were validated by using three heating powers during desorption: 100 W, 200 W and 300 W. A parametric numerical study on the effect of heating power and final set temperature showed that the higher the power, the more hydrogen is discharged, and that the amount of hydrogen discharged varies quasi-linearly with the final set temperature, as long as it is below 500 K. Finally, we have shown that increasing the heat transfer by convection with the outside air reduces the time to reach the room temperature by approximately 75%.

Parametric Study on Thermo-Hydraulic Performance of NACA Airfoil Fin PCHEs Channels

In this work, a discontinuous airfoil fin printed circuit heat exchanger (PCHE) was used as a recuperator in a micro gas turbine system. The effects of the airfoil fin geometry parameters (arc height, maximum arc height position, and airfoil thickness) and the airfoil fin arrangements (horizontal and vertical spacings) on the PCHE channel’s thermo-hydraulic performance were extensively examined by a numerical parametric study. The flow features, local heat transfer coefficient, and wall shear stress were examined in detail to obtain an enhanced heat transfer mechanism for a better PCHE design. The results show that the heat transfer and flow resistance were mainly increased at the airfoil leading edge owing to a flow jet, whereas the airfoil trailing edge had little effect on the thermo-hydraulic performance. The airfoil thickness was the most significant while the arc height and the vertical spacing were moderately significant to the performance. Moreover, only the airfoil thickness had a significant effect on the PCHE compactness. Based on a comprehensive investigation, two solutions NACA-6230 and -3220 were selected owing to their better thermal performance and smaller pressure drop, respectively, with horizontal spacings of 2 mm and vertical spacings of 2 or 3 mm.

Numerical modeling and parametric study of a hollow fiber dialyzer using double porous media approach

Mathematical modeling is one of the efficient methods to improve the design of hemodialyzer and study affecting parameters on dialyzer performance.In this paper, mathematical modeling of hollow fiber dialyzer is done to investigate the effect of various parameters on the clearance of urea and creatinine. The computational domain is considered two-dimensional axisymmetry. The hollow fibers bundle is defined as a double porous media. The Darcy-Brinkman-Forchheimer equation is employed to determine flows in porous media. Modified Kedem–Katchalsky equations are used to calculate the transmembrane flow. Continuity, Navier–Stokes and concentration equations are solved by finite element method.The numerical results showed a change in the thickness of hollow fibers from 100 to 25 µm and a decrease in their inner diameter from 240 to 150 µm, could improve clearance of urea by 66.7 and 20.7 percent respectively. The increase in blood flow (40 to 120 mL.min−1), dialysate flow (80 to 200 mL.min−1), dialyzer diameter (28 to 38 mm) and length of hollow fibers (15 to 30 cm) increase the clearance of urea by 88.2, 20.4, 35 and 26.2 percent, respectively.The model has been validated and shows good agreement with experimental results. Such studies advance our understanding of the parameters affect the performance of the dialyzer.

Local buckling of cold-formed high-strength steel hollow section columns at elevated temperatures

A numerical investigation is conducted on the local buckling behavior of cold-formed square hollow section (SHS) and rectangular hollow section (RHS) columns made of normal and advanced high-strength steels at elevated temperatures. Shell finite element models validated against experimental results are used in a parametric numerical study to evaluate the local buckling strength at ambient and elevated temperatures of SHS and RHS columns fabricated with G450, dual-phase, and martensitic steels. The modeling uses recent experimental data on the elevated temperature behavior of advanced high-strength steels. The numerical results are compared with the design strengths calculated by the Direct Strength Method in AISI S100. Results show that the current method in AISI S100 consistently captures the trend but overestimates the ultimate capacity of G450 cold-formed columns both at ambient and elevated temperatures by about 10% for the SHS columns and 6% for the RHS columns. The current Direct Strength Method also yields higher estimates of capacity than the finite element models for advanced high-strength steel grades. Therefore, a modification to the method for local buckling capacity is proposed for these sections. The modified Direct Strength Method proposed herein can be used to evaluate the local buckling strength of cold-formed SHS and RHS columns made of normal and advanced high-strength steels at temperatures up to 700 °C.

Development of a Flexible Metamaterial Film with High EM Wave Absorptivity by Numerical and Experimental Methods.

The present study is intended to develop and test a cost-effective and efficient printing method for fabricating flexible metamaterial film with high electromagnetic wave absorptivity. The film can be easily applied to the surfaces with curved aspects. Firstly, numerical parametric study of the absorption characteristics of the film is performed for the range of frequency varying from 2.0 to 9.0 GHz based on commercial software package. Secondly, the flexible metamaterial films are fabricated, and experiments are conducted. The flexible metamaterial film consists of a flexible dielectric film made of polyimide (PI) and an array of split-ring resonators. The split-ring resonators of different geometric dimensions are fabricated on the PI film surface by using a silver nanoparticles ink jet printer. The performance of the flexible structure is then measured and dependence of operation frequency with higher absorptivity on the dimensions of the split-ring resonators is investigated. A comparison between the numerical and experimental data shows that the numerical predictions of the operation frequency with higher absorptivity closely agree with the experimental data.