Element Level Research Articles

Linear Concrete Tension Stiffening Model for Reinforced Concrete Elements

Linear expressions for tension stiffening of concrete are nowadays widely used in software packages of structural analysis. Nevertheless, more elaborated expressions of tension stiffening available in the literature have been used successfully in the past. The use of linear approximations is justified since the influence of the tension stiffening effect in the deformation of the structure is small but not negligible. In this sense, linear approximations are simpler and can be accurate enough. However, this linear approximation, in its present form, does not provide good results in terms of deformations at the element level. This paper proposes a linear expression of the tension stiffening supported by the experimental formulation used to predict the flexural behavior of concrete beams. A detailed example is presented.

Experimental behaviour of aeronautical notched carbon fibre reinforced thermoplastic panels under combined tension-shear-pressure loadings

The demonstration of compliance of aeronautical structures with certification requirements is generally based on the building block approach, considering tests from the coupon level up to full-scale level. Coupon-scale tests are numerous and generally focused on uniaxial loading to target elementary failure modes, whereas structures are submitted to complex and combined loadings, leading to costly test campaigns on thousands of coupons. This paper considers intermediate-scale tests to study structural issues at element level. Thin flat samples (558 × 536 mm2) made of carbon fibre reinforced thermoplastic with a large, sharp central notch of 100 mm are considered. The VERTEX test rig is used to apply complex and combined loadings in tension, shear and internal pressure. Metrics are defined and computed to describe the multiaxial loading state and the failure scenario of the samples. Pressure addition clearly precipitates the first failure for shear tests but not for tension tests. With or without pressure, shear tests tend to show failure for lower equivalent fluxes than tension tests.

FRAMEWORK FOR SUCCESSFUL PROBLEM-SOLVING IN LEAN: A FOCUS GROUP RESEARCH IN MALAYSIAN AUTOMOTIVE

From household issues to complex organizational cases, problem-solving is a common but critical matter in our life. Organizations have tried to harness maximum benefit from lean, but evidence of implementing problem-solving principles is rare. This study intends to emphasize on importance and expose the highly influencing success factors to establish continuous problem-solving and learning in any organization with the example of an automotive industry case in Malaysia. A list of elements of problem-solving principles of lean and another for success factors to implement lean has been compiled through a comprehensive review of contemporary literature. Then a focus group of sixteen professional experts selected meticulously from a reputed Malaysian Automotive industry thoroughly discussed the subject matter in group meetings to get their judgments based on experience and shared knowledge. The approach of grading success factors at the element level of principles of lean is an added methodology to the existing knowledge, and the results of highly influencing success factors for the implementation of elements of principles of problem-solving in lean is a new and helpful insight for organizational leaders and researchers. The author assumes this research may take lean implementation to the next level of success. Modern organizations must build lean problem-solving culture by motivating and empowering management employees who have process-level understanding and are accountable with different metrics. The key to success also depends highly on operators’ inclusiveness and managing their reactions to change. Both management and process workers must drive lean as a team.

Unconditional stability and convergence analysis of fully discrete stabilized finite volume method for the time-dependent incompressible MHD flow

In this paper, we consider the stability and convergence of fully discrete stabilized finite volume method for the unsteady incompressible magnetohydrodynamics (MHD) equations on the quasi-uniform and regular triangulations. The spatial discretization is based on the lowest equal-order mixed finite element pair for the velocity, pressure and the magnetic fields, while the time discretization is based on the backward Euler semi-implicit scheme. In order to overcome the restriction of the discrete inf-sup condition, the local pressure projection stabilized method on the element is employed. This stabilized method has the advantages of parameter-free, no need to calculate the high-order derivatives or the edge-based data structures and it can be implemented at the element level. The unconditional stability of numerical scheme is established by using the Gronwall lemma, mathematical induction and choosing different test functions. Optimal error estimates of numerical approximations in various norms are also presented by constructing the corresponding dual problem. Finally, some numerical results are proposed to verify the established theoretical findings and show the performances of the considered numerical method.

Scan-Loss Compensation for Full-Azimuth Multi-Facet Phased Array Antennas

An approach to compensate scan losses displayed by full-azimuth multifacet phased arrays is proposed in this article. This approach is based on a constructive superposition of scanned beams from adjacent array panels resulting in enhanced composed coverage. Said constructive superposition is achieved by coordinating the insertion phase shifts applied at the array element level. Special attention is given to panel arrays arranged in equilateral triangle and square prisms. The benefits of the proposed beamforming approach are validated by full-wave simulations, as well as passive antenna measurements taken on physical prototypes. The achieved improvement in equivalent isotropically radiated power (EIRP) excessively compensates for the experienced scan loss and reaches 6 dB at the maximal scan angles. An additional advantage of the developed methodology consists in the mitigation of the composed beam squint at wide scan angles.

Two-field formulation of the inertial forces of a geometrically-exact beam element

An independent velocity field is introduced via Legendre transformation of the kinetic energy of a geometrically-exact beam, leading to a first-order system of twice as many governing equations as a one-field formulation. Nevertheless, the new field does not have to be assembled across elements and can be eliminated at the element level, so that the assembled system has the same size as a one-field formulation. Furthermore, because the new field does not have to satisfy the compatibility equations that the original velocity field is subjected to, its finite-element discretization is simpler and leads to simplified inertial forces.

Modelling of fracture intensity increase due to interacting blast waves in three-dimensional granitic rocks

The complexity of the physics of rock blasting is a longstanding modelling challenge. This work presents in detail a three-dimensional, material non-linear finite element based model for wave propagation, combined with a postprocessing procedure to determine the fracture intensity caused by blasting. The rock is described with the Johnson–Holmquist-2 constitutive model, an elastoplastic-damage model designed for brittle materials undergoing high strain rates and high pressures and fracturing; it is also combined with an instantaneous tensile failure model. Additionally, material heterogeneity is introduced into the model through variation of the material properties at the element level, ensuring jumps in strain. A detailed algorithm for the combined Johnson–Holmquist-2 and tensile failure model is presented and is demonstrated to be energy-conserving, and is complemented with an open-source MATLABTM implementation of the model. A range of sub-scale numerical experiments are performed to validate the modelling and postprocessing procedures, and a range of materials, explosive waves and geometries are considered to demonstrate the model’s predictive capability quantitatively and qualitatively for fracture intensity. Fracture intensities on 2D planes and 3D volumes are presented. The mesh dependence of the method is explored, demonstrating that mesh density changes maintain similar results and improve with increasing mesh quality. Damage patterns in simulations are self-organising, and form thin, planar, fracture-like structures that closely match the observed fractures in the experiments. The presented model is an advancement in realism for continuum modelling of blasts as it enables fully three-dimensional wave interaction, handles damage due to both compression and tension, and relies only on measurable material properties.

A new higher-order mixed four-node quadrilateral finite element for static bending analysis of functionally graded plates

In this paper, a new C0 four-node quadrilateral plate element (MiQ4) is proposed for the static bending analysis of functionally graded (FG) plates based on a C0 higher-order shear deformation theory. By introducing a quadratic shape function for higher-order terms and a constant shear result, which is eliminated at the element level, the transverse shear stresses are free on two surfaces of the plates. The present finite element model has high accurateness and a fast rate of convergence, especially for both thin and very thin plates. In addition, the proposed element is insensitive to distorted mesh, hence, it is compatible with the investigation of complex geometrical plates. Although the proposed element does not need any shear correction coefficients and selected or reduced integrations, the shear-locking phenomenon does not appear even for very thin plates. Therefore, the computation cost and time are reduced and the spurious deformation or hourglass modes are avoided. A large number of examples have been exhibited that help to validate the convergence rate, correctness, and reliability of the proposed element. Then the present element is applied for analysis of FG structures to demonstrate the potential applications of the present plate element. Significantly, the paper provides a good element that can be used in many areas of engineering for the design, testing, analysis, and optimization of complex structures to reduce the computation cost and time as well as increase the reliability of the numerical results.

Finite elements with embedded interphases for strain localization in quasi-brittle materials

The paper presents a continuous–discontinuous numerical strategy for simulating localized failure in structures made of quasi-brittle materials using finite elements. The strategy is based on observing acting stresses scenarios, when a diffuse degradation is followed by high deformation bands localizing in certain regions of the structure. The numerical strategy should encompass both situations in accordance with the material’s constitutive model. This objective is achieved by introducing a thin layer into a finite element at a certain level of the deformation process. In this study, the thin layer is modeled for the first time by an interphase mechanical device whose constitutive behavior is the same as the bulk material. This is possible since the interphase adds internal strains and stresses to the contact ones. As a consequence, no additional constitutive model and parameters are needed, unlike the zero-thickness interface or cohesive zone models commonly employed. The proposed numerical strategy is illustrated in detail both at the element level and at the structural level. A new crack tracking algorithm has been developed based on decomposition of the model into substructures to allow cracks to cross arbitrary meshes. Some benchmark examples are presented showing the mesh-size and mesh-bias independence of results, together with the convergence behavior of the model.

Finite element level validation of an anisotropic hysteresis model for non-oriented electrical steel sheets

This paper presents the finite element level validation of the anisotropic Jiles–Atherton hysteresis model. Numerical analysis of a round rotational single sheet tester is performed using the 2D finite element method. Anisotropic extension of the Jiles–Atherton hysteresis model is coupled with the 2D finite element method. The finite element simulations are performed for the cases when the magnetic field alternates and rotates in the lamination plane. The simulated results for alternating and rotational flux density excitations agree with the measured data. The measured data used in this paper corresponds to the M400-50A nonoriented silicon steel.

Efficient formulation of a two‐noded geometrically exact curved beam element

AbstractThe article extends the formulation of a 2D geometrically exact beam element proposed by Jirásek et al. (2021) to curved elastic beams. This formulation is based on equilibrium equations in their integrated form, combined with the kinematic relations and sectional equations that link the internal forces to sectional deformation variables. The resulting first‐order differential equations are approximated by the finite difference scheme and the boundary value problem is converted to an initial value problem using the shooting method. The article develops the theoretical framework based on the Navier–Bernoulli hypothesis, with a possible extension to shear‐flexible beams. Numerical procedures for the evaluation of equivalent nodal forces and of the element tangent stiffness are presented in detail. Unlike standard finite element formulations, the present approach can increase accuracy by refining the integration scheme on the element level while the number of global degrees of freedom is kept constant. The efficiency and accuracy of the developed scheme are documented by seven examples that cover circular and parabolic arches, a spiral‐shaped beam, and a spring‐like beam with a zig‐zag centerline. The proposed formulation does not exhibit any locking. No excessive stiffness is observed for coarse computational grids and the distribution of internal forces is not polluted by any oscillations. It is also shown that a cross effect in the relations between internal forces and deformation variables arises, that is, the bending moment affects axial stretching and the normal force affects the curvature. This coupling is theoretically explained in the Appendix.

Electromagnetic Functional Surfaces Related to Frequency Response Control Using Back-Loaded Radio Frequency Circuits

A novel scheme for designing electromagnetic functional surfaces (EMFSs) is proposed in this article. Different from traditional frequency selective surface (FSS), this scheme uses the antenna array and the back-loaded radio frequency circuit (BLRFC) to control the frequency response of EMFSs. The antenna array and the BLRFC can be designed independently resulting in great design flexibility and functional diversity. The sharp skirt out-of-band suppression and tunable frequency response can be achieved by using this scheme. Three design levels (element level, subarray level, and array level) are introduced to illustrate the design philosophy. Several EMFSs are designed, and one of them has been fabricated and measured. Actually, the prototype is a dual-polarized absorptive frequency selective reflector (AFSR). For both TE and TM polarizations with normal incidence, the AFSR exhibits one reflection band with 3 dB bandwidth from 10.6 to 16.3 GHz, two absorption bands with the absorptivity greater than 90% from 6 to 10 GHz, and from 16.8 to 19 GHz. The AFSR has a stable angular performance up to 50°. All the design examples and fabricated prototype verify the flexibility and the superiority of the novel scheme, and a multiplicity of EMFSs can be realized by using the BLRFC technique.

An improved Material Mask Overlay Strategy for the desired discreteness of pressure-loaded optimized topologies

This paper presents a Material Mask Overlay topology optimization approach with the improved material assignment at the element level for achieving the desired discreteness of the optimized designs for pressure-loaded problems. Hexagonal elements are employed to parametrize the design domain. Such elements provide nonsingular local connectivity; thus, checkerboard patterns and point connections inherently get subdued. Elliptical negative masks are used to find the optimized material layout. Each mask is represented via seven parameters that describe the location, shape, orientation, material dilation, and erosion variables of the mask. The latter two variables are systematically varied in conjunction with a grayscale measure constraint to achieve the solutions' sought 0-1 nature. Darcy's law with a drainage term is used to model the pressure load. The obtained pressure field is converted into the consistent nodal forces using Wachspress shape functions. Sensitivities of the objective and pressure load are evaluated using the adjoint-variable method. The efficacy and robustness of the approach are demonstrated by solving various pressure-loaded structures and pressure-driven compliant mechanisms. Compliance is minimized for loadbearing structures, whereas a multicriteria objective is minimized for mechanism designs. The boundary smoothing scheme is implemented within each optimization iteration to subdue the designs' undulated boundaries.

Inverse design of perimeter-controlled InAs-assisted metasurface for two-dimensional dynamic beam steering.

The current commercially viable light detection and ranging systems demand continuous, full-scene, and dynamic two-dimensional point scanning, while featuring large aperture size to ensure long distance operation. However, the biasing architecture of large-area arrays with numerous individually controlled tunable elements is substantially complicated. Herein, inverse design of a perimeter-controlled active metasurface for two-dimensional dynamic beam steering at mid-infrared regime is theoretically presented. The perimeter-control approach simplifies biasing architecture by allowing column-row addressing of the elements. The metasurface consists of a periodic array of plasmonic patch nanoantennas in a metal-insulator-metal configuration, wherein two active layers of indium arsenide are incorporated into its building block. The metasurface profile facilitates wide phase modulation of on the reflected light at the individual element level through applying independent voltages to its respective columns and rows. The multi-objective genetic algorithm (GA) for optimizing user-defined metrics toward shaping desired far-zone radiation pattern is implemented. It is demonstrated that multi-objective GA yields better results for directivity and spatial resolution of perimeter-controlled metasurface by identifying the design tradeoffs inherent to the system, compared to the single-objective optimizer. A high directivity and continuous beam scanning with full and wide field-of-view along the azimuth and elevation angles are respectively maintained.

Electrically Driven Reprogrammable Vanadium Dioxide Metasurface Using Binary Control for Broadband Beam Steering.

Resonant optical phased arrays are a promising way to reach fully reconfigurable metasurfaces in the optical and near-infrared (NIR) regimes with low energy consumption, low footprint, and high reliability. Continuously tunable resonant structures suffer from inherent drawbacks such as low phase range, amplitude-phase correlation, or extreme sensitivity that makes precise control at the individual element level very challenging. We computationally investigate 1-bit (binary) control as a mechanism to bypass these issues. We consider a metasurface for beam steering using a nanoresonator antenna and explore the theoretical capabilities of such phased arrays. A thermally realistic structure based on vanadium dioxide sandwiched in a metal–insulator–metal structure is proposed and optimized using inverse design to enhance its performance at 1550 nm. Continuous beam steering over 90° range is successfully achieved using binary control, with excellent agreement with predictions based on the theoretical first-principles description of phased arrays. Furthermore, a broadband response from 1500 to 1700 nm is achieved. The robustness to the design manufacturing imperfections is also demonstrated. This simplified approach can be implemented to optimize tunable nanophotonic phased array metasurfaces based on other materials or phased shifting mechanisms for various functionalities.

Serum immunoglobulins, C-reactive protein, and trace element level in preeclamptic Nigerian subjects.

The mechanism involved in the pathogenesis of preeclampsia (PE) remains uncertain, and the research into a better understanding, its possible prediction, and subsequent prevention continues. This study evaluated changes in serum immunoglobulins (IgG, IgA, and IgM), C-reactive protein, and trace elements (Zn, Cu, and Mn) in preeclamptic, normotensive pregnant, and non-pregnant females. The study was conducted among 150 subjects consisting of 50 preeclamptic subjects, 50 healthy normotensive pregnant women in their third trimester, and 50 non-pregnant women, all within the same age bracket. The serum concentration of the immunoglobulins and C-reactive protein were measured using standard immunoturbidimetric methods, whereas the trace elements were assayed using the atomic absorption spectrophotometric method. Serum IgG and IgM levels were observed to be significantly lower (P < 0.05) in preeclamptic subjects (101.22 ± 4.44 and 769.43 ± 1.43 mg/dl), respectively, when compared to the normotensive pregnant women (123.87 ± 1.81 and 881.71 ± 2.80 mg/dl), respectively. There was a non-significant difference in immunoglobulin A levels between the groups (P > 0.05). The C-reactive protein was significantly higher, whereas the trace elements were significantly lower (P < 0.05) in preeclamptic subjects compared to the normotensives. There was a positive correlation between the immunoglobulin G and Zn levels (r = 0.334; P = 0.046) and also between immunoglobulin G and C-reactive protein levels (r = 0.340; P = 0.043) and a negative correlation between systolic blood pressure and manganese levels in preeclamptic subjects (r = -0.375; P = 0.024). This study therefore reveals significantly lower levels of immunoglobulins and trace elements among the preeclamptic subjects. These micronutrient deficiencies and low levels of immunoglobulins could be risk factors for the development of high blood pressure and PE.

A response reconstruction method based on empirical mode decomposition and modal synthesis method

With the increasing the complexity of civil structures and diversity of the structural components, reconstructing the responses of complex civil engineering structures based on the conventional time-domain reconstruction method is very challenging. Apart from the massive computer storage needed in the calculation process, the enormous calculation times may also hinder the response reconstruction of the civil structures. This paper proposes a novel strategy of the time-domain reconstruction method by combining the modal synthesis method and empirical mode decomposition with intermittency criteria in the time domain. The response reconstruction method is conducted at two levels. The first level is performed on the reduced super-element from the interface DOFs to the internal DOFs of the critical substructure, and then at the element level to extrapolate dynamic responses at critical locations. In each level’s reconstruction, the number of calculation parameters decreases significantly. The response of the whole structure can be quickly obtained at one time, not only decreasing the computation time but also ensuring reconstruction accuracy. The numerical studies and experimental validation are both conducted on a simply supported beam and a complex cooling tower for verification, and the effects from some external parameters, including measurement noise, the order of substructural normal modes, the number of substructures and the number of sensors, are considered. The results illustrate that the proposed reconstruction method based on the modal synthesis method improves the calculation effectiveness considerably and ensures accuracy.

Optimal Configuration of Array Elements for Hybrid Distributed PA-MIMO Radar System Based on Target Detection

This paper establishes a hybrid distributed phased array multiple-input multiple-output (PA-MIMO) radar system model to improve the target detection performance by combining coherent processing gain and spatial diversity gain. First, the radar system signal model and array space configuration model for the PA-MIMO radar are established. Then, a novel likelihood ratio test (LRT) detector is derived based on the Neyman–Pearson (NP) criterion in a fixed noise background. It can jointly optimize the coherent processing gain and spatial diversity gain of the system by implementing subarray level and array element level optimal configuration at both receiver and transmitter ends in a uniform blocking manner. On this basis, three typical optimization problems are discussed from three aspects, i.e., the detection probability, the effective radar range, and the radar system equipment volume. The approximate closed-form solutions of them are constructed and solved by the proposed quantum particle swarm optimization-based stochastic rounding (SR-QPSO) algorithm. Through the simulations, it is verified that the proposed optimal configuration of the hybrid distributed PA-MIMO radar system offers substantial improvements compared to the other typical radar systems, detection probability of 0.98, and an effective range of 1166.3 km, which significantly improves the detection performance.

Sector‐specific scenarios for future stocks and flows of aluminum: An analysis based on shared socioeconomic pathways

Aluminum is an energy-intensive material that is typically used as an alloy. The environmental impacts caused by its production can potentially be spread out over multiple uses through repeated recycling loops. However, inter-alloy contamination can limit the circularity of aluminum, which highlights the importance of analyzing prospective stock dynamics of aluminum at an alloy and alloying element level to inform a more sustainable management of this resource. A dynamic material flow analysis (MFA) of aluminum alloys was developed in line with the shared socioeconomic pathways (SSP) framework to generate consistent scenarios of the evolution of aluminum stocks and flows from 2015 to 2100 covering 11 economic sectors in 5 world regions. A sector-specific and bottom-up modeling approach was developed. Results show no saturation of global stock per capita before 2100, reaching a range between 200 and 400 kg per capita according to different socioeconomic scenarios. For the business-as-usual scenario, the global annual inflow rises to 100 Mt in 2050 and peaks at 130 Mt in 2090, showing a saturation in total stock. Electricity-sector demand has the highest relative growth over the century, while building and construction demand saturates and decreases from 2090. No major mismatch between inflows and outflows of aluminum alloy is observed. This means that with appropriate dismantling and sorting, changes in alloy demand would not limit the implementation of a closed-loop aluminum industry. This study demonstrates the advantages of combining detailed MFAs and SSPs, both for greater consistency in circular economy modeling and for furthering scenario development efforts. This article met the requirements for a gold-gold JIE data openness badge described at http://jie.click/badges

Numerical and experimental study of diffusion law of foamed polymer grout in fracture considering viscosity variation of slurry

As a new type of chemical grouting material, polymers have been widely used in fractured rock masses, but the understanding of the diffusion characteristics of polymers still needs to be further improved. Due to the expansion of polymer slurry, the change of grouting pressure is not synchronized with the time change of diffusion radius, leading to the diffusion law of polymer slurry more complicated. Therefore, based on the rheological properties of the slurry and the theory of viscous hydrodynamics, a polymer fracture grouting diffusion model was established. Through the finite element level set method and adjusting the liquid level according to the fluid velocity, it can be obtained the diffusion interface of the fluid at the corresponding point in time and the change law of the pressure at the corresponding diffusion interface with time. Finally, the validity of the model is verified by the polymer slurry parallel plate grouting diffusion experiment. The research results indicated that: (1) The diffusion mode of the polymer fracture grouting diffusion model is basically consistent with the test results. (2) The grouting pressure gradually decreases along the direction of the diffusion radius, increases with the decrease of the crack width, and increases with the time, but the change of the grouting pressure lags behind the change of the diffusion radius. (3) The results are consistent with the pressure field curve measured by the experiment, indicating that the main factor causing the hysteresis effect of the pressure field change is the time-varying viscosity of the polymer slurry.