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This work deals with fracture mechanisms in quasi-brittle materials, focusing on the characterization of the Fracture Process Zone (FPZ) of specimens under tensile load. Particularly, paper was used as model material. Experiments were conducted on notched and unnotched specimens. Based on an image analysis of these observations, a stochastic finite element model was developed, using both a nonlocal stress-based approach and a discretized random field modeling of the Young's modulus. The proposed methodology allowed characterizing the damage zone and the size of the FPZ, analyzing the influence of the mesostructure, composed of flocs (fiber aggregates where the basis weight is larger than the average one) and antiflocs (complement of flocs). The area of the active FPZ and the normalized stress drop were linked using a surface energy dissipated in the active FPZ. The stress drop, until limiting value, increased with the width of the active FPZ. Finally, a relationship between the surface energy and the nonlocal internal length was established. [ABSTRACT FROM AUTHOR]

Thin-walled tubular deployable composite boom (DCB) has gained significant attention due to its lightweight, simple structure and high packaging efficiency. The experimental and numerical simulation methods were employed in this paper to investigate the folding behavior of the DCB. Using T700/epoxy unidirectional reinforced prepreg as raw material, DCB specimens were prepared by the vacuum bag method. To complete the folding experiments of DCB specimens, a folding mechanism was designed and manufactured. Folding experiments of DCB specimens were conducted and folding moment versus rotational displacement curves were measured. In addition, a Finite Element Model (FEM) was established to predict the folding behavior of the DCB. Different failure criteria were considered in the numerical analysis, including the Tsai‐Hill criterion and maximum stress criterion. Prediction results using the FEM were compared with experimental results, and both sets of results were in good agreement. It is shown that the DCB can achieve the folding function without failure. The research results in this paper are of great significance to the practical engineering application of the DCB. [Display omitted] • Six tubular deployable composite boom specimens and a precise folding mechanism were designed and prepared. • Folding experiments were conducted to measure the folding moment and rotational displacement curves. • A finite element model for predicting the folding behavior of the tubular deployable composite boom was established. [ABSTRACT FROM AUTHOR]

Ultrasonic plastic welding is widely used in the bonding process of medical device accessories. In this paper, a thermo-force indirect coupling finite element analysis model was established in the ultrasonic plastic welding process between the blood cap and the shell of polypropylene (PP) dialyzer. The temperature field distribution between the blood cap and the shell was simulated and analyzed by using finite element analysis software, and the influence of welding process parameters on the temperature field was studied. The results show that: by changing the ultrasonic amplitude parameters, welding time parameters, initial pressure, etc., the longer the ultrasonic welding time, the temperature of the welding area will increase. In order to ensure the quality of the dialyzer, it should be controlled within 0.8-1 seconds. The increase of ultrasonic amplitude will make the welding temperature continue to rise, and in order to avoid poor welding, the amplitude should not exceed 120 μm. The initial pressure has little effect on the temperature field. [ABSTRACT FROM AUTHOR]

In order to analyze the impact angle of pick cutter, the angle of alloy head and the cutting line spacing on rock breaking effect, the three-dimensional model of rock cutting by pick cutter was established by solidworks, and the three-dimensional finite element model of rock breaking by pick cutter based on penetration failure and compression damage was established by using dynamic simulation software ANSYS/LS-DYNA. For the drum with a diameter of 1200 mm, a length of 900 mm and a rotational speed of 30 rot/min, when the impact angles of the picks are 30°, 37°, 45° and 52°, the angles of the alloy heads are 70°, 80°, 90° and 100°, and the intercept distances are 250 mm, 275 mm, 300 mm and 325 mm, the rock breaking simulation based on the finite element analysis software is carried out, and the load and specific energy consumption of the drum are obtained. Finally, through the analysis and comparison, the existing parameters are optimized, and a better parameter model is obtained. [ABSTRACT FROM AUTHOR]

This paper presents a numerical parametric study to examine the structural response of drilled shaft footings (pile caps) presenting different design characteristics, which have not been studied in depth in previous experimental studies. The numerical analyses were conducted with nonlinear finite element models representing typical designs and details of actual footings. The modeling scheme was validated using experimental data from large-scale drilled shaft footings. Key parameters of the numerical study included footing geometric properties, concrete strength, and reinforcement ratios. The results of the parametric studies were examined to identify key behavioral and design aspects to be considered when using 3D strut-and-tie models for the design of drilled shaft footings. The analysis results show that influences associated with footing and column aspect ratios were essentially negligible. However, it was estimated that an increase of the angle of inclination between the compression strut and the vertical axis led to significant reductions in footing stiffness and load capacity. The effect of shaft diameter was also examined in light of lateral concrete confining effects, and it was found that larger shaft diameters provide increased footing capacities. Analyses performed to estimate the influence of concrete compressive strength showed that splitting of the strut controlled the concrete-governed failure mechanism of footings. Finally, the models developed with different amounts of reinforcement revealed that increasing bottom mat reinforcement leads to increased ultimate loads; however, the rate of strength increase decreases with increasing reinforcement ratio. Providing a minimal amount of top mat and side face reinforcement was estimated to impact the structural responses of the footings positively; however, increasing the ratios of the top mat and side face reinforcing bars beyond this minimum did not significantly impact footing strength. [ABSTRACT FROM AUTHOR]

The paper presents selected results of numerical analysis and experimental verification. The subject is the analysis of cold forging of a thin-walled hollow ball. The process of making a ball out of aluminum alloy and steel was considered. A distinctive feature of this process is the use of a special deformable insert assembly. It consists of two shaped expanding tubes, a distance ring and a centering tube. Each of these elements has a specific function, which was characterized in this article. Finite element analysis (FEA) simulation allowed proving the functionality of the insert assembly and comparing the cold forging of a steel and aluminum part, using the same inserts. Attention was also focused on the impact of the accuracy of the positioning of the insert assembly. Experimental verification confirmed the correctness of the modeling and complemented the results from FEA analysis. [ABSTRACT FROM AUTHOR]

Induction heating is a clear, cheap, and highly effective technology used for many industrial and commercial applications. Generally, a time-varying magnetic field produces the required heat in the workpiece with a specially designed coil. The efficiency of the heating process depends highly on the coil design and the geometrical arrangement. A detailed and accurate finite element analysis of the induction heating process usually needs to resolve a coupled thermoelastic–magnetic problem, whose parameters values depend on the solution of another field. The paper deals with a shrink-fitting process design problem: a gear should be assembled with an axe. The interesting part of this case study is given the prescribed low limits for critical stress, the temperature of the gear material, and the heat-treated wearing surfaces. A coupled finite-element-based model and a genetic algorithm-based parameter determination methodology were presented. A thermal imaging-based measurement validated the presented numerical model and parameter determination task. The results show that the proposed methodology can be used to calibrate and validate the numerical model and optimize an induction heating process. [ABSTRACT FROM AUTHOR]

This paper aims to discuss aspects of modeling prestressed concrete sleepers based on experimental results. Midspan Positive Moment tests were performed on four prestressed sleepers. Using the ATENA 3D software, based on the Finite Element Method, numerical models were simulated through nonlinear analysis to adequately represent the behavior of the sleepers. To evaluate the influence of the crack model, the Young's modulus, and the fracture energy, a parametric numerical analysis was performed, varying these parameters in stages to achieve a more realistic model. The crack model was evaluated by modifying the "fixed crack model" to a "rotated crack model" while the Young's modulus and fracture energy were penalized by 0.00%, 5.00%, 10.00%, and 15.00% in relation to the value calculated according to the CEB FIP Model Code (2010). The numerical model with the "rotated crack model" and penalties of 0.00% and 5.00% for the Young's modulus and fracture energy, respectively, presented a better approximation to the results presented in the experimental tests. Finally, from this calibrated model, an experimental versus numerical comparative analysis was performed, comparing the load versus displacement curves, failure loads, maximum displacements, and crack pattern behavior. In the future, constitutive models of bond slip and expansive reactions will be applied to the calibrated model. [ABSTRACT FROM AUTHOR]

Cracking failure of cement-treated base (CTB) has always been the concern of highway constructors. Mesoscale cracking analysis is an important means to study the damage degradation mechanism, which is difficult to be characterized by experimental techniques alone. The objective of this paper is to develop a random aggregate modelling method to simulate the mesoscopic cracking of CTB material. A minimum rectangle area method was proposed to calculate the polygon aggregate size, which is closer to the sieving analysis than the average radius method. A buffer zone method was proposed to determine the distance between randomly generated polygon aggregates. Based on the proposed random algorithm, finite element method (FEM) was adopted to build the mesoscopic model of CTB including aggregate, mortar, interfacial transition zone (ITZ) and air voids. Laboratory tests were conducted to validate the numerical model. Then the sensitivity analyses were conducted to study the influencing factors on cracking behavior. The simulation results indicate that the higher aggregate content and the finer gradation lead to the increase of ITZ, thus reducing the cracking resistance of the CTB material. Low porosity content is able to significantly reduce the stress concentration and thus improves the cracking resistance. The research results of this paper could be used to guide the crack resistant design of CTB material. [ABSTRACT FROM AUTHOR]

Numerical reconstruction is the process of modeling, analyzing, and evaluating the performance of structures or a sequence of events using the finite element method and other numerical engineering methods. Although numerical analysis is used extensively in contemporary engineering problems, it can be equally useful in the study of ancient structures and events of the past. The materials and design of structures are different, e.g., when comparing a modern containership with an old galleon, but the main problem to be solved is essentially the same—will the ship sail efficiently and safely for many years? This paper aims to provide an overview of recent achievements in numerical reconstruction in maritime archaeology. Since it is clearly an interdisciplinary activity, research is often carried out within a specific project by project team members or interested groups of researchers. While the paper aims to provide a comprehensive overview of such efforts, special attention is paid to activities related to the AdriaS (Archaeology of Adriatic Shipbuilding and Seafaring) and NEREAS (Numerical Reconstruction in the Archaeology of Seafaring) projects supported by the Croatian Science Foundation, to which the authors actively contribute. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of a single and a group of laterally loaded barrettes using a series of numerical models in a three-dimensional finite element software. The simulation of laterally loaded barrettes in both directions is verified by comparing numerical predictions to field measurements previously published in the literature. This paper defines the soil wedge around the barrette sheared at a strain equivalent to the minimum shear strain value at the barrette side or higher as the effective strain wedge. The results from a suite of numerical experiments show that the size of the effective shear strain wedge remains constant at different lateral loads, soil density, barrette shape (aspect ratio), and barrette stiffness. This paper also delineates the effect of spacing in a group of barrettes on the mobilized strain wedges and the associated lateral deformations. The paper then suggests equivalent dimensions for laterally loaded barrettes to be used as input parameters in analyses using p-y curves based on the shape of the effective strain wedge. The predictions from p-y analyses are improved in all the studied cases when equivalent dimensions are used compared to the finite element computations. The paper studies the appropriate design multipliers recommended in literature to be used in the p-y curves method for laterally loaded barrette groups in single and multiple rows. Comparisons with finite element results show the validity of employing the equivalent shape dimensions in determining suitable p-multipliers. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to investigate the influence of fabrication process uncertainty on terahertz metasurface quality. The focus was on the effect of metasurface fabrication inaccuracy on resonances. To the best of our knowledge, this is the first paper to study the effect of the metasurface fabrication process on its resonant frequency. The terahertz split ring resonator-based metasurface is under consideration. Using a numerical model, the influence of the uncertainty of various geometrical parameters obtained during the fabrication process (mainly layer deposition, photolithography, and etching processes) is analyzed according to the resonance of the designed metasurface. The influence of the following parameters causes a shift of resonant frequencies of the considered metasurface: etching deviation e, metallization thickness tAl and SiO2 layer thickness tSiO2. The quality of the metasurface affected by the variations of obtained geometrical parameters was determined by the deviation of resonant frequency Δfr. The developed numerical model was verified by THz-TDS (terahertz time-domain spectroscopy) measurements of the fabricated structure. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for analyzing steel frames with semi-rigid connections and displacement constraints, using a condensed finite element formulation. The paper outlines a systematic approach for constructing the condensed stiffness matrix and the condensed force vector. The proposed analysis can predict accurately the nonlinear effects of connections on the behavior and strength of semi-rigid steel frames. Kishi-Chen power model is applied to describe the nonlinear behavior of semi-rigid connections. The proposed method's effectiveness is demonstrated through analytical and numerical analysis of a semi-rigid steel frame structure, highlighting the procedure's simplicity and robustness. To verify the validity and applicability of the proposed method, several examples of realistic structures and benchmark cases are provided. The strengths predicted by the proposed method demonstrate good agreement with the available experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we present an electric field analysis for the optimal structural design of lightning rods for high performance with a charge transfer system (CTS). In the case of a conventional rod that is produced with an empirical design and structure without quantitative data because the design is structurally very simple, only the materials and radius of curvature of the lightning rod to concentrate the electric field at the tip part of the rod are considered. Recently, the development of new types of lightning rods, such as early streamer emission (ESE) and charge transfer system (CTS), has been introduced through simulation analysis and experiments, but detailed specifications and information about the optimal design and structure have not been fully reported. In this paper, we performed an electric field analysis of the structures and materials for the optimal structural design of lightning rods with a function of CTS through computer software analysis with consideration for the radius of curvature, the size of corona ring, and optimal position (X-axis and Y-axis) of the floating electrode. For optimal structural design of lightning rods based on electric field analysis, we used a source of lightning voltage with 1.2/50 µs based on a double exponential equation. The results revealed that the electric field on the relaxation part decreases as the radius of curvature and corona ring increases. For the radius of curvature, the electric field first decreases and then increases with increasing radius of curvature and reaches a minimum at 7 mm and a maximum above 8 mm. For the case of the corona ring, the electric field decreases with increasing corona ring, and the optimal size of the corona ring was selected as 4 mm; the size of the 4 mm corona ring uniformly formed the electric field both at the tip part of the ground current collector and the corona ring. For the electric field concentration part, we found that the optimal X-axis position of the floating electrode and the Y-axis position between the ionizer conductor and floating electrode are 7 mm and 0.1 mm, respectively. These simulation results in this paper are expected to provide useful information for the design of optimized CTS-type lightning rods. [ABSTRACT FROM AUTHOR]

The segment misalignment is a common defect in the segment installation of a shield tunnel construction, due to the complexity and uncertainty of its construction conditions. This raises a concerning about the safety of the segment lining for the shield tunnel. In this paper, the integrated numerical models with surrounding rock, peastone grouting and segment lining were built using three-dimensional finite element method, by introducing two kinds of misaligned defects of segments. One was the misalignment that elongated the horizontal axis of the transversal ring section of segment lining, another was the misalignment between adjacent rings of segments. To eliminate the impact of boundary on numerical results, seven rings of segments are built for the three-dimensional finite element models, and the middle ring is dealt with for the results analysis under V-class surrounding rock, including the circumferential stress of outer and inner layers of the segment, the contact stress on joint surface between segments, and the stress of locating pins between adjacent rings. Results indicate that the two kinds of misaligned defects create pronounced impact on tensile stress of segment at the bottom and the crown segments, respectively, which produces a greater tensile stress to increase cracking risk even abrupt fracture of segment. However, the misaligned defects have a slight impact on the contact stress and the locating pins stress. Therefore, attention should be paid to the cracking of bottom or crown segments in the segment lining of shield tunnel. [ABSTRACT FROM AUTHOR]

In this paper, a thermoelastic problem involving a viscous strain gradient beam is considered from the analytical and numerical points of view. The so-called type II thermal law is used to model the heat conduction and two possible dissipation mechanisms are introduced in the mechanical part, which is considered for the first time within strain gradient theory. An existence and uniqueness result is proved by using semigroup arguments, and the exponential energy decay is obtained. The lack of differentiability for the semigroup of contractions is also shown. Then, fully discrete approximations are introduced by using the finite element method and the backward time scheme, for which a discrete stability property and a priori error estimates are proved. The linear convergence is derived under suitable additional regularity conditions. Finally, some numerical simulations are presented to demonstrate the accuracy of the approximations and the behavior of the discrete energy decay. [ABSTRACT FROM AUTHOR]

The misalignment of segments in installation is a common issue in the construction of TBM tunnels. This raises a question of whether misalignment affects the operation safety of a hydraulic TBM tunnel. Using a water transfer engineering project as an example, this paper built a three-dimensional finite element model composited with segment, grout layer and surrounding rock for the numerical analysis of the behavior of single-directionally misaligned segments. The crown or invert segment was separately misaligned towards to the center of segment ring in a value of 5 mm, 10 mm, 20 mm, 30 mm or 40 mm. The strength grade of the segment concrete was C50. A weaker surrounding rock composed of V-class rock was considered for the tunnel. The results indicate that the misalignment of the crown or invert segment, respectively, creates the tensile stress in the inner surface of the corresponding segment, the tensile stress will be over the limit of C50 concrete when the misalignment is over 30 mm, indicating a risk of concrete cracking. The contact surfaces of the segment ring basically remain in compression, and the locating pins between the segment rings exhibit an evident increase in tensile stress at misaligned positions. The key points that can be obtained from this study are that a special supervision is needed to ensure the accuracy of segment installation, and strengthening measures are needed for existing misaligned segments. [ABSTRACT FROM AUTHOR]

Shaped charge perforation is an important technology for sandstone gas reservoirs. In the process of shaped charge perforating, the initial permeability and porosity of the formation are greatly reduced, directly affecting oil and gas production. This paper uses smooth particle hydrodynamics (SPH) and finite element methods (FEMs) to study the formation damage caused by the shaped charge perforation. In this perforation simulation, the impact characteristics of the metal jet formed by the liner are coupled with the damage characteristics of the sandstone. A new mathematical model is proposed to describe the damage of permeability and porosity based on the Morris and Xue models. The simulated results show that a large-scale abdominal section appears at the perforation site, and the axis of the hole tilts with the increase in the perforation depth. The porosity damage at the perforation site is the greatest, up to 60%, while the permeability recovers to 90% of its initial state after pressure relief. The degree of porosity damage decreases with the increase in negative pressure, and when the negative pressure is 30 MPa, it may cause a large amount of sand production. [ABSTRACT FROM AUTHOR]

In this paper, Computing the eigenvalues of the Conformable Sturm-Liouville Problem (CSLP) of order 2α, 1/2 < α; ≤ 1, and dirichlet boundary conditions is considered. For this aim, CSLP is discretized to obtain a matrix eigenvalue problem (MEP) using finite element method with fractional shape functions. Then by a method based on the asymptotic form of the eigenvalues, we correct the eigenvalues of MEP to obtain efficient approximations for the eigenvalues of CSLP. Finally, some numerical examples to show the efficiency of the proposed method are given. Numerical results show that for the nth eigenvalue, the correction technique reduces the error order from O(n4h²) to O(n²h²). [ABSTRACT FROM AUTHOR]

The paper presents a static analysis of the buckling and post-buckling state of thin-walled cold-formed steel (TWCFS) lipped channel section beam-columns subjected to eccentric compression. Eccentricity is taken into consideration relative to both major and minor principal axes. An analytical–numerical solution to the buckling and post-buckling problems is described. The solution is based on the theory of thin plates. Equations of equilibrium of section walls are derived from the principle of stationary energy. Then, to solve the problem, the finite difference (FDM) and Newton–Raphson methods are applied. Linear (buckling) and nonlinear (post-buckling) analyses are performed. As a result, pre- and post-buckling equilibrium paths are determined. Comparisons of the obtained numerical results, FE simulation results, and experimental test results are carried out and presented in comparative load-shortening diagrams. Additionally, a comparison of the buckling forces and buckling modes obtained from theoretical analysis and experiments is presented. [ABSTRACT FROM AUTHOR]

This study develops a rapid algorithm coupled with the finite element method to predict the fatigue crack propagation process and select the enhancement factor for the equivalent random load spectrum of accelerated fatigue tests. The proposed algorithm is validated by several fatigue tests of an aluminum alloy under the accelerated random load spectra. In the validation process, two kinds of panels with different geometries and sizes are used to calculate the stress intensity factor, critical crack length, and crack propagation life. The simulated and experimental findings indicate that when the aluminum alloy is in a low plasticity state, the crack propagation life exhibits a linear relationship with the acceleration factor. When the aluminum alloy is in a high plasticity state, this study proposes an empirical formula to calculate the equivalent stress intensity factor and crack propagation life. The normalized empirical formula is independent of the geometry and size of different samples, although the fracture processes are different in the two kinds of panels used in our study. Overall, the numerical method proposed in this paper can be applied to predict the fatigue crack propagation life for the random spectrum of large samples based on the results of the simulated accelerated crack propagation process and the accelerated fatigue tests of small samples to reduce the cost and time of the testing. [ABSTRACT FROM AUTHOR]

The increasing demand for deep excavations in construction projects emphasizes the necessity of robust support structures to ensure safety and stability. Support structures are critical in stabilizing excavation pits, with a primary focus on enhancing their bearing capacity. This paper employs finite element modeling techniques to conduct a numerical analysis of nails and helical anchors' bearing capacity. To reinforce the stability of pit walls, selecting an appropriate method for guard structure construction is imperative. The chosen method should efficiently redistribute forces induced by soil mass weight, displacements, and potential loads in the pit vicinity to the ground. Various techniques, including trusses, piles, cross-bracing systems, nailing, and anchorage systems, are utilized for this purpose. The study evaluates numerical models for two guard structure configurations: nailing systems and helical anchorage. It examines the impact of parameters such as displacement, helical helix count, helix diameter variations, and the integration of nailing systems with helices. Comparative analyses are conducted, including displacement comparisons between different nailing systems and helical anchor systems, along with laboratory-sampled data. The research yields significant insights, with a notable finding highlighting the superior performance of helical bracings compared to nailing systems. The conclusions drawn from this study provide specific outcomes that contribute valuable knowledge to the field of deep excavation support structures, guiding future design and implementation practices. [ABSTRACT FROM AUTHOR]

In this study, geomechanical behavior of fractures and faults in rocks as a saturated deformable discrete fracture-porous medium has been evaluated using coupled fluid flow-geomechanics numerical modeling. The purpose of this paper is to observe and evaluate the effects of fractures and faults on the pore pressures during fluid flow through reservoirs. This issue involves solving the equations that have been derived from the Biot consolidation theory such as fluid mass balance equation, Darcy law and momentum balance equations. Govern coupled equations were solved using the standard Galerkin finite element method for continuous porous medium. Elements called "zero-thickness elements" were also used to discretize the fault as a discontinuous part of the porous medium. In compared with the previous and similar methods, the method introduced in this paper, made modifications in either the choice of the element and the method of solving the governing equations. The main advantage of this paper is providing clear precise formulations of the double node zero-thickness element in hydro-mechanical modeling of fractures and faults. Verification of the proposed process and models presented in this paper were done by providing three index problems which their analytical and numerical solutions are available. The results of our model provide a good agreement to these reference solutions which indicates the accuracy of the method presented in this paper. [ABSTRACT FROM AUTHOR]

Damping through friction tends to be one of the most efficient methods to suppress damage to structures from earthquakes. Realizing robust structures is therefore highly dependent on designing for the dynamic forces of friction-damped structures and exploring their reliability against natural disasters. This paper presents a simplified matrix analysis algorithm for multi-story friction-damped buildings. The behavior of friction-damped systems has analyzed more accurately by modeling the master-slave degree of freedom of the joints. First, the formulation of the problem is discussed, and a condensed general equation is derived. Then, an end-to-end solution is proposed to find the responses of structures. The displacement response of each story has been carried out in both condensed and non-condensed general equations, and the results clearly show the accuracy of the proposed method. The numerical analysis and the results of the simulation of various friction-damped structures depicts the proposed approach consists with the commercial finite element method and is applicable for the analysis various types of structures. It is noted that the acceleration and displacement responses of the structures investigated under the proposed method and the traditional finite element method are so consistent that only a 1.5% difference is observed. Moreover, as a result of the proper allocation of degrees of freedom during the analysis, this method yields a reduction in computational costs especially in large buildings. [ABSTRACT FROM AUTHOR]

This paper is concerned with the calibration and validation of a numerical procedure for the analysis of pile performance in soft clays during seismic soil–pile–superstructure interaction (SSPSI) scenarios. Currently, there are no widely accepted methods or guidelines. Centrifuge and shaking table model tests are often used to supplement the available field case histories with the data obtained under controlled conditions. This paper presents a new calibration method for establishing a reliable and accurate relationship between full-scale numerical analysis and scaled laboratory tests in a 1g environment. A sophisticated approach to scaling and validating full-scale seismic soil–structure interaction problems is proposed that considers the scaling concept of implied prototypes as well as "modelling of models" techniques that can ensure an excellent level of accuracy. In this study, a new methodology was developed that can provide an accurate, practical, and scientific calibration for the relationship between full-scale numerical analysis and scaled laboratory tests in the 1g environment. The framework can be followed by researchers who intend to validate their seismic soil–structure interaction findings. [ABSTRACT FROM AUTHOR]

In this paper, we deal with the issue of asphalt concrete microstructure recognition for further numerical analysis. An efficient reconstruction of the underlying microstructure makes the composite analysis more reliable. We propose for this purpose a methodology based on the image processing and focus on a two-dimensional case (it can be easily used as a part of the 3D geometry reconstruction, however). Initially obtained geometry of the inclusions is further simplified to reduce the cost of the finite element mesh generation. Three straightforward geometry simplification algorithms are used to perform this process in a controlled way. Subsequently, we present the solutions of two problems, i.e., heat flow and elasticity (plane strain), in order to illustrate the effectiveness of the whole elaborated methodology. The numerical results were obtained using the finite element method. Consequently, an error analysis is demonstrated in order to refer the overkill mesh solutions to the ones presented in this study. The main finding of this paper is the efficient methodology dedicated to a digital reconstruction of the asphalt concrete microstructure by the image processing. It can be also extended to other materials exhibiting similar microstructure. [ABSTRACT FROM AUTHOR]

The failure mechanism of MSE (mechanically stabilized earth) walls was studied via numerical analysis with the finite element strength reduction method, which was verified as an effective technique by simulating the experimental results reported in previous papers. The finite element program was applied to explore the effects of reinforcement, geometry, and seismic parameters on failure mechanism control at the design stage of MSE walls to avoid the unavoidable errors experienced in common numerical analysis caused by the assumptions of the failure mode and complex input parameters. The research parameters included the wall height, length, and spacing of the geogrid-reinforced retaining wall and seismic load. The results indicated that the wall height and reinforcement length play a major role in failure mode change. When the reinforcement length is less than 2 m, overturning failure could occur, which was unrelated to the other parameters in all cases studied in this paper. In this paper, the parametric study results were presented by evaluating the critical reinforcement length, generating the failure surface pattern, and summarizing design recommendation. [ABSTRACT FROM AUTHOR]

This paper presents the results of a numerical study of a planar antenna with a complex form factor. The antenna is based on a combination of two resonators, a disc resonator and a ring resonator. The feeding of the ring resonator is performed using a coplanar structure: pointwise by galvanic contact between the central conductor of the coplanar line and the ring resonator and by distributed electromagnetic coupling of the ring resonator and the aperture of the outer conductor of the coplanar line. The antenna was placed over a metal plane whose geometric dimensions were significantly larger than those of the antenna to exclude the influence of edge diffraction effects. In numerical simulation a complex approach including the method of semi-open resonator and the finite element method (FEM) implemented within the commercial package HFFS was used. The dependences of spectral, energy and polarization characteristics on material constants and frequency parameter have been investigated. It was found that within the framework of single-parameter optimization it is impossible to simultaneously achieve a high level of all important parameters. The values of frequencies of spectral lines in the spectral characteristics of the antenna are found with a relative error not worse than 1200 Hz. Frequency ranges within which there is no degeneration of oscillation types are established. The distributions of surface currents on the metal elements of the antenna, allowing to determine the position of phase centers of excitation, are presented. It is shown that the proposed antenna can provide an acceptable level of matching both at fixed frequencies and in sufficiently wide local frequency bands, reaching 11% with respect to the center frequency of the sub-band. The boundary values of gain coefficients in frequency bands are established. The simulation results allow to predict effective radiation with formation of practically single-lobe radiation pattern and presence of elliptical polarization. [ABSTRACT FROM AUTHOR]

In this paper, we are interested in fnding an optimal control support design for controlling vibrations due to pedestrian-bridge interactions. Therefore, we derive the topological derivatives of the proposed functionals using the averaged adjoint approach. A numerical algorithm initialized by these sensitivities is used as a solution strategy. The algorithm is tested numerically for two different cases of initial conditions. [ABSTRACT FROM AUTHOR]

In reinforced concrete flat slab buildings, the transference of unbalanced moments in the slab–column connections usually results from the asymmetry of spans, vertical loads, and horizontal forces from the wind. The punching strength of the slab–column connections can limit the load-carrying capacity of the structure in these cases, leading to structural collapse. The design code provisions are still based on empirical or semi-empirical equations; as the punching shear failure mechanisms are complex, and the ultimate strength is affected by several parameters. In this context, this paper presents the results of the computational investigation of the mechanical behaviour of flat slabs subjected to balanced and unbalanced moments using numerical Finite Element models. The numerical models were calibrated and accurately reproduced the behaviour and the punching resistance for concentric and eccentric loading. Furthermore, a parametric study was conducted to evaluate the mechanical behaviour of flat slabs under different load eccentricities, confirming that the increase in the unbalanced moment negatively impacts the load-carrying capacity of the slab–column connection. Furthermore, it was observed that all computational results obtained from models with unbalanced bending moments were higher than those estimated by the design codes. [ABSTRACT FROM AUTHOR]

API Recommended Practice (RP) 1183 considers three levels of assessment. Its Level 1 and Level 2 processes were considered viable for single peak dents with smooth profiles. The RP deals with more complex dents by way of a Level 3 approach that was reliant on finite element (FE) analysis. Part II of this four-part series of papers has identified the assumptions central to the practices of the RP, and evaluated them in regard to fully symmetric dents whose geometry is broadly aligned with those assumptions. Thereafter, it has examined the effects of asymmetry and skew angle benchmarked relative to the symmetric dents. It becomes apparent that even for symmetric dents significant errors emerge in the RP's practices based on its reliance on dent profiles characterized along their axial and transverse axes cut through the apex, and the effects of the plastic deformation history developed in forming the dent. As for Part I, it was found that the practices of RP 1183 can (1) incorrectly categorize dents, and (2) grossly underestimate dent severity due to asymmetry and skew angles considered acceptable for Level 2 assessment. Error analyses and trending indicated conservative as well as nonconservative errors, with some more than 300%. As noted in Part I, Part III will consider cyclic loading of dents, and the viability of the dent stress and fatigue analyses that underlie the API RP 1183 Level 1 and Level 2 assessment practices, whereas Part IV considers the viability of the numerical formulations and modeling that underlie its practices. [ABSTRACT FROM AUTHOR]

This paper thoroughly examines the application of the Finite Element Method (FEM) to the numerical modal analysis of Herøysund Bridge, focusing on the theoretical backdrop, the construction process, and FEM techniques. This work examines the specific applied FEM approaches and their advantages and disadvantages. This Herøysund Bridge analysis employs a two-pronged strategy consisting of a 3D–solid model and a shell model. To forecast the physical behavior of a structure, assumptions, modeling methodologies, and the incorporation of specific components such as pillars are applied to both approaches. This research also emphasizes the importance of boundary conditions, examining the structural effects of standard Earth gravity, a post-tensioned load, and a railing and asphalt load. The Results section thoroughly explores the mode shapes and frequencies of the 3D–solid and shell models. The conclusion of this work includes findings obtained from the study, implications for Herøysund Bridge, and a comparison of both modeling strategies. It also incorporates ideas for future research and guides employing FEM 3D–solid and shell methods to design and construct more efficient, resilient, and durable bridge structures. [ABSTRACT FROM AUTHOR]

Concrete slabs are widely used in modern railways to increase the inherent resilient quality of the tracks, provide safe and smooth rides, and reduce the maintenance frequency. In this paper, the elastic performance of a novel slab trackform for high-speed railways is investigated using three-dimensional finite element modelling in Abaqus. It is then compared to the performance of a ballasted track. First, slab and ballasted track models are developed to replicate the full-scale testing of track sections. Once the models are calibrated with the experimental results, the novel slab model is developed and compared against the calibrated slab track results. The slab and ballasted track models are then extended to create linear dynamic models, considering the track geodynamics, and simulating train passages at various speeds, for which the Ledsgård documented case was used to validate the models. Trains travelling at low and high speeds are analysed to investigate the track deflections and the wave propagation in the soil, considering the issues associated with critical speeds. Various train loading methods are discussed, and the most practical approach is retained and described. Moreover, correlations are made between the geotechnical parameters of modern high-speed rail and conventional standards. It is found that considering the same ground condition, the slab track deflections are considerably smaller than those of the ballasted track at high speeds, while they show similar behaviour at low speeds. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of an open hole on the stability of a compressed laminated composite plate. The study was carried out in two ways: using experimental tests and numerical analysis. As a result of the experiment, the buckling form and path of the plate were recorded. The form of buckling was determined using the ARAMIS non-contact measurement system. The critical load value was determined from the working path using the approximation method. The experimental results were verified by numerical analysis based on the finite element method. FEM investigations were carried out in terms of a linear eigenproblem analysis. This allowed the bifurcation load and the corresponding buckling form of the numerical model of the plate to be determined. Investigating the effect of the hole in the compressed plate at a critical state showed high agreement between the proposed test methods. No clear effect of the hole size on the buckling of the plate was observed. In contrast, a clear effect of the hole on the critical load value was determined. The maximum decrease in the critical load value was 14%. The same decrease was observed for the stiffness of the post-critical characteristics. It was shown that the [45|−45|90|0]s composite plate had more than three times lower strength compared to [0|−45|45|90]s and [0|90|0|90]s. The novelty of this article is the development of a research methodology based on new interdisciplinary research methods for describing the influence of the central hole on the stability of compressed composite plates. The ABAQUS system was used for the numerical analysis. [ABSTRACT FROM AUTHOR]

This manuscript concerns the investigation of the influence of the open hole on stability of the compression plate made of carbon-epoxy composite. Experimental tests carried out on the real plate resulted in a postcritical path from which the critical load value was determined using appropriate approximation method. In parallel, an independent study was carried out based on a numerical analysis using the finite element method (FEM). Investigations were conducted in terms of a linear eigenproblem analysis, from which the value of the bifurcation load was determined for the FEM model of the plate. Its values resulting from the numerical analyses were validated against the experimental results, thus confirming the adequacy of the designed FEM model of the plate. The paper shows that the incremental increase of the hole in the plate monotonically influences the decrease in the critical load of the plate. The largest decrease was observed for the specimen with the largest hole analysed and was 13.5% compared to a plate without a hole. The newness of the paper is the application of interdisciplinary investigation methods to describe the influence of the open hole compression (OHC) on the stability of composite plates. ABAQUS® was used as the tool with which the numerical analyses were realised. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical analysis of the response of a scaled double-bottom structure with high and penetrated girders and floors impacted vertically by a rock-shaped indenter. The specimen, scaled from the bottom structure of the power-battery cabin of a new energy ship, is struck by a spherical indenter. The special double-bottom structure is designed to protect the power batteries and to facilitate heat dissipation. The experimental overall impact response, vibration acceleration, and stress of the inner bottom plate are measured in order to evaluate the impact environment in the target cabin. The investigation provides valuable information to evaluate the safety of power-battery cabins in a ship grounding scenario. The experimental results show good agreement with the finite element analyses using the explicit LS-DYNA software. The numerical analysis outlines the influence of the structural openings on the impact response and also the effect of battery mass and striking velocity on the impact environment in the target cabin. [ABSTRACT FROM AUTHOR]

The powder mixed electrical discharge machining (PMEDM) process was simulated via finite element analysis in the current study to assess heat behavior and material removal rate. The goal of this paper is to conduct a thorough experimental and thermal examination of electrical discharge machining (EDM) in order to forecast its cutting characteristics and subsequently optimize the output variables using a response surface methodology for simulations and choosing the most suitable set of process variables related to the PMEDM process. This study's objective is to design a 2D axisymmetrical transient thermal model that might also describe the physics of material removal in a single spark PMEDM operation on a Titanium Zirconium Molybdenum (TZM) superalloy. ANSYS (version 9.1) software is used to perform transient heat transfer simulations to determine the temperature profile with the amount of material removal at different current, pulse on and off times, gap voltages, and fraction of heat that enters the specimen. The PMEDM process produced craters with a lower diameter and depth, which increased the material removal rate and enhanced the surfacing quality. Compared to the conventional EDM process, the inclusion of powder raised the heat flux given to the work material by 10%–12%. It has been determined that with the single spark modeling technique, the temperature significantly dropped in both the radial and depth directions. The computational results are compared with experimental observations for similar machining conditions, and both results agree satisfactorily. [ABSTRACT FROM AUTHOR]

This paper focuses on the finite element analysis simulation of the impact properties of composite sandwich structures made of carbon fiber-reinforced polymer lamina. In the existing studies, the composite sandwich structures with A-shaped cores have superior mechanical properties under quasi-static plane compression loads compared to W-shaped, Y-shaped, and X-shaped cores. However, there is limited research on the impact resistance of this structure. This paper studied the resistance of a composite A-shaped core structure to ballistic impact. Using ABAQUS/explicit finite element analysis software, ballistic impact tests for the composite A-shaped core structure were simulated based on the Hashin and Yeh failure criteria with a progressive damage model introduced in the user-defined subroutine VUMAT. First, the composite Y-shaped core sandwich structure was verified via experiments and simulations to determine the accuracy of the method, and then the composite A-shaped sandwich structure was subjected to a series of ballistic impact simulations. With varied impact velocity, the damage to the front and rear face sheet and cores via ballistic loads was simulated to illustrate the overall dynamic response process of the sandwich structure. Subsequently, a curve was fitted using a ballistic limit velocity equation, which was used as the criterion to evaluate the impact resistance of the composite A-shaped core structure. The results showed that, under the same relative density and the same number of component layers, the ballistic limit velocity of the composite A-shaped core sandwich structure was bigger than the composite Y-shaped core sandwich structure. The composite A-shaped core structure had 12.23% higher ballistic limit velocity than the composite Y-shaped core, indicating the impact resistance capabilities of the A-shaped core structure. In addition, the impact location's effect on the impact response was investigated. [ABSTRACT FROM AUTHOR]

Crack size and undermatching effects on fracture behavior of undermatched welded joints are presented and analyzed. Experimental and numerical analysis of the fracture behavior of high-strength low-alloyed (HSLA) steel welded joints with so-called small and large crack in undermatched weld metal and the base metal was performed, as a part of more extensive research previously conducted. J integral was determined by direct measurement using special instrumentation including strain gauges and a CMOD measuring device. Numerical analysis was performed by 3D finite element method (FEM) with different tensile properties in BM and WM. Results of J-CMOD curves evaluation for SUMITEN SM 80P HSLA steel and its weld metal (WM) are presented and analyzed for small and large cracks in tensile panels. This paper is focused on some new numerical results and observations on crack tip fields and constraint effects of undermatching and crack size keeping in mind previously performed experiments on the full-scale prototype. In this way, a unique combined approach of experimental investigation on the full-scale proto-type and tensile panels, as well as numerical investigation on mismatching and crack size effects, is achieved. [ABSTRACT FROM AUTHOR]

Laboratory research of wood–CFRP (carbon fiber reinforced polymer) structural elements, especially beams, is a scientific issue undertaken by many scientists. Research is often complemented with numerical analysis with the use of complex finite element method (FEM) models. Modern FEM software offers models that can reproduce such properties and phenomena as orthotropy and plasticity of wood and CFRP, delamination and mechanical behavior of adhesive layers, and damage of a strengthened element. The author of the paper reproduces numerical laboratory research of a four-point bending test of a glulam beam strengthened with CFRP tape. The main goal of the numerical research is an analysis of how the complexity of the FEM model influences the results of calculations, especially stress, deflection, and bearing capacity of the glulam beam. In some cases, a simpler model can be satisfactory, especially for a structural engineer, who takes into account serviceability limit states (permissible deflection of a structural member) and assumes that stress should not exceed the yield stress of timber. [ABSTRACT FROM AUTHOR]

It is difficult to separate Luer lock adapters during the external ventricular drainage (EVD) since they are often connected by a threaded connection, and the infusion needle put into the patient's body gets pulled out when extubation occurs unexpectedly. The paper described a new magnetic connection assembly made up of ring magnetic permanents and a Hall sensor that could be used to replace Luer lock adapters for quicker disconnection and reconnection of the drainage catheter. For the design and analysis of the device, the finite element method magnetics (FEMM) was used to estimate the size of magnetic permanents and the best detection site of the Hall sensor for detecting whether the magnetic permanents were closely attracted and/or pulled apart. Then an experiment was conducted to confirm our findings. Both simulation and experiment revealed that a pair of hollow cylindrical magnetic permanents, each with height 10 mm, outer diameter 8 mm, and inner diameter 4 mm, could achieve the same force as the Luer lock adapters held, and that the best Hall sensor detection position was in the middle of the permanent magnets, with a radial distance of about 2 mm. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to program the weak coupling between magnetic and structural vector fields in an electromagnetic device modeled in two dimensions. The magneto-mechanical coupling phenomenon is present in electromagnetic devices where magnetic forces cause displacements in metallic materials. This work proposes a numerical solution to this problem by applying the 2D finite element method to the governing equations of this coupled multiphysics phenomenon. The well-known formulation yields accurate results; however, it is often not properly integrated into a computer program. This manuscript proposes a flexible and intuitive methodology for the implementation of the complex mathematics involved in this phenomenon into a computer program. The computer code receives the input parameters, discretizes the geometry by generating a 2D finite mesh, solves the resulting equations using the finite element method, and finally exports the results of the magnetic ang mechanical fields. The modeling is performed using an open-source platform for programming the finite element method in the programming language Python, and afterwards, the results are compared against a commercial software as validation of the proposed numerical approach. The novel magneto-mechanical coupling methodology is used to solve an engineering application, namely an electromagnetic actuator. [ABSTRACT FROM AUTHOR]

Introduction/purpose: In recent times, with the tendency to develop new types of armor-piercing ammunition, constant investments in the development of new types of armored obstacles is necessary. Obstacles made of high-alloy steel plates are still the best form of protection against larger caliber ammunition. There are a number of factors to consider when selecting an alloy, including the weight, dimensions, intended use, desired ballistic performance, and costs. According to that, a numerical analysis of penetration of a 30mm armor-piercing fin-stabilized discarding sabot projectile into the steel alloy Weldox 460 plates of different thicknesses at a distance of 1000m with a velocity of 1300m/s is presented in this paper. Methods: The stresses and deformations of the penetration effect were calculated through numerical analysis and finite element modeling. To specify material characteristics, the Johnson-Cook material model and the fracture of materials model have been utilized. In order to define models and carry out numerical calculations, the software packages FEMAP and LS Dyna have been used in this paper. Results: For a numerical analysis of the penetration process of this projectile type against armor obstacle, four different armor plate thicknesses are calculated: 10mm, 50mm, 100mm, and 110mm. For each of them, the results are shown in a form of stress and displacement, so that the interaction phenomena between the sub-projectile and the armor plate can be described. Conclusion: Modeling the impact on armor-piercing obstacles is extremely difficult, time-consuming, and complex, and the resulting models very successfully (or with some deviation) approximate the real problem of projectile penetration. One of the most effective methods for solving problems of this kind and others of a similar nature in recent times is the finite element method analysis. The material and the target dimensions, as well as the ballistic parameters and the material of the projectile have the biggest influence on projectile penetration. The target's resistance to penetration increases when all input parameters are maintained at the same level and its thickness is increased, and vice versa. [ABSTRACT FROM AUTHOR]

The arched cellular beam has the advantages of both the solid-web arch and the straight beam with web opening, and has become increasingly admired by architects in recent years. In this paper, four arched cellular beam specimens are designed using an orthogonal test method (OTM) with a three-factor and two-level approach. Firstly, the static loading test is carried out to analyze the mechanical response of the arched cellular beam under concentrated load. Then, a numerical analysis based on ABAQUS finite element (FE) software is carried out. The results show that the simulation results agree well with the test results, which indicates the accuracy of the simulation analysis method. Finally, the buckling load of the arched cellular beam under three different loads is calculated using the variable parameter FE analysis. Combined with the range analysis in the OTM, the influence of the target factor on the buckling load of the arched cellular beam is determined. The results show that the order of the factors affecting the out-of-plane elastic buckling is rise–span ratio > web height–thickness ratio > diameter–depth ratio. [ABSTRACT FROM AUTHOR]

In structural construction practice, the use of reinforced concrete slabs is extremely common due to their structural and economic advantages. An important issue is the study of structural behavior given to horizontal effects. The significance of this is centered not only on the scales caused by wind and construction loads, which are considered to be "normal" i.e., the quasi-static, which is essentially one-way monotonically increasing but also the most researched seismic, i.e., cyclically varying, direction and magnitude effects. The most widespread methods for sizing flat plate slabs to unidirectional, quasi-static horizontal loads are the so-called Equivalent Frame Method and the Effective Beam Width Method. In addition to analytical and basically linear numerical theoretical methods, several laboratory experiments have been performed and published. In this paper, we investigate the behavior of columnsupported flat plate slabs against unidirectional, monotonically increasing horizontal loads using an advanced nonlinear numerical modeling method. Numerical models constructed with different geometric dimensions were created with ATENA 3D three-dimensional nonlinear finite element software. In the numerical studies, in addition to the vertical loads in the global sense, the horizontal loads were also taken into account. In our studies, we analyzed the global behavior of the structure, crack propagation, and internal stresses. The results were illustrated on force - displacement diagrams and compared with the results of the laboratory experiments used, thus showing the accuracy and limitations of the numerical modeling procedure. The numerical results were also compared with the results determined on the basis of the equivalent framework models. [ABSTRACT FROM AUTHOR]

In this paper, a methodical approach is presented to approximate the multi-term fractional advection-diffusion model (MT-FAD). The Lagrange squared interpolation is used to discretize temporal fractional derivatives, and Legendre polynomials are shifted as an operator to discretize the spatial fractional derivatives. The advantage of these numerical techniques lies in the orthogonality of Legendre polynomials and its matrix operations. A quadratic implicit design as well as its stability and convergence analysis are evaluated. It should be noted that the theoretical proof obtained from this study represents the first results for these numerical schemes. Finally, we provide three numerical examples to verify the validity of the proposed methods and demonstrate their accuracy and effectiveness in comparison with previous studies shown in [W. P. Bu, X. T. Liu, Y. F. Tang, J. Y. Yang, Finite element multigrid method for multi-term time fractional advection diffusion equations, Int. J. Model. Simul. Sci. Comput., 6 (2015), 1540001]. [ABSTRACT FROM AUTHOR]

The water leakage through segmental joint gaskets has become a major concern that adversely affects the normal serviceability of underwater shield tunnels throughout the construction and operational periods. Therefore, it is of great significance to investigate the sealing performances of the joint gaskets, which directly helps evaluate the waterproof capacity of underwater shield tunnels. To date, the numerical modeling plays an irreplaceable role in the analysis on the waterproof capacity of the joint gaskets. Nevertheless, conventional methods tend to ignore the self-sealing effect induced by the water seepage pressurization, thus failing to reveal the progressive evolution of the water infiltration process through the joint gasket. To remedy this defect, this paper proposed a novel numerical model to simulate the penetration process of the sealing gasket based on the Python language-enabled secondary programming in the ABAQUS software, which could fully consider the superimposed seepage squeezing effect. Based on the proposed model, the waterproof failure process and the dynamic contact stress of the gasket's water seepage path subject to excessive hydraulic pressure were thoroughly investigated. Moreover, indoor tests on the waterproof capacity of the gasket were also performed to validate the proposed model. It is found that the numerical results from the developed model are consistent with the experimental results. This research will contribute to better understanding of the gaskets' hydraulic penetration process and more accurate prediction of the maximum waterproof capacity in underwater shield tunnels. [ABSTRACT FROM AUTHOR]

Based on elasticity theory, this paper discusses the static analysis of a cracked double-beam system in the presence of a Winkler-type medium. It is further assumed that the double-beam system is constrained at both ends by elastically flexible springs with transverse and rotational stiffness. Using a variational formulation, the governing static equations are derived and solved using analytical and numerical approaches. In the first approach, closed-form solutions for the displacement functions are obtained based on the Euler–Bernoulli beam theory. In the second approach, the Cell Discretisation Method (CDM) is performed, whereby the two beams are reduced to a set of rigid bars connected by elastic constraints, in which the flexural stiffness of the bars is concentrated. The resulting stiffness matrix is easily deduced, and the governing equations of the static problem can be immediately solved. A comparative analysis is performed to verify the accuracy and validity of the proposed method. The study focuses on the effect of various parameters, including crack depth and position, boundary conditions, elastic medium and slenderness. The validity of the proposed analysis is confirmed by comparing the current results with those obtained from other approaches. In particular, the results obtained by closed-form solution and CDM are compared with the Finite Element Method (FEM). The accuracy of the results was assessed by making comparisons with results found in the literature and reported in the bibliography. It was shown that the proposed algorithm provides a simple and powerful tool for dealing with the static analysis of a double-beam system. Finally, some concluding remarks are made. [ABSTRACT FROM AUTHOR]

The development of small-sized parabolic trough collectors (PTCs) for processing heat production at medium temperatures (100–250 °C) represents an interesting approach to increase the utilization of solar thermal technologies in industrial applications. Thus, the development of simplified models to analyze and predict their performance under different operative and climatic conditions is crucial for evaluating the application potential of this low-cost technology. In this paper, we present a numerical method that by combining three-dimensional finite element simulations (implemented with COMSOL Multiphysics software version 6.1) with a one-dimensional analysis (based on a MATLAB script) allows for the theoretical determination of the power output of a small-PTC with a nonevacuated tubular receiver operating at a medium temperature. The finite element model considers both the nonuniformity of the concentrated solar flux on the receiver tube (evaluated using Monte Carlo ray-tracing analysis) and the establishment of natural convection in the air gap between the glass envelope and absorber tube. The model calculates, for several values of direct normal irradiance (DNI) and inlet temperatures, the thermal power transferred to the heat transfer fluid (HTF) per unit length. The data are fitted using the multiple linear regression method, obtaining a function that is then used in a one-dimensional multi-nodal model to estimate the temperatures and the heat gains along the receiver tube. The outputs of the model are the outlet temperature and the total thermal power transferred to the HTF. In order to validate the developed methodology for the assessment of the heat transfer characteristics in the small-PTC with a nonevacuated receiver, an experiment at the ENEA Trisaia—Solar Thermal Collector Testing Laboratory was carried out. This work compares the theoretical data with those acquired through experimentation, obtaining a good agreement, with maximum differences of 0.2% and 3.6% for the outlet temperatures and the power outputs, respectively. [ABSTRACT FROM AUTHOR]