Outer Square Research Articles

Crashworthiness study of double square gradient hierarchical tubes

A new type of bi-double square gradient hierarchical tube (DSGHT) is proposed, and its crashworthiness under consistent wall thickness is analyzed. The results show that the energy absorption (EA), specific energy absorption (SEA), and crush force efficiency (CFE) of DSGHT3 are increased by 1305.14%, 430.14%, and 469.50%, respectively, compared to DSGHT0. The combination of double square tubes and gradient laminar design effectively enhances the crashworthiness of the structure. A parametric study indicates that increasing wall thickness significantly improves crashworthiness, with EA, SEA, and CFE improvements of 805.75%, 125.83%, and 126.83%, respectively, at a wall thickness of 0.8 mm compared to 0.2 mm. However, the effect of wall thickness gradient distribution on structural crashworthiness is minimal. Conversely, the ratio of the inner to outer square tube edge length (δ) significantly impacts crashworthiness; SEA and CFE increase by 37.77% and 37.35%, respectively, when δ is 6/12 compared to 8/12. Finally, DSGHT3 was compared to other hierarchical, tree-shaped fractal structures, and it demonstrated superior crashworthiness. Specifically, DSGHT3 has 35.32% and 34.29% higher SEA and CFE, respectively, compared with MSTL2-2.

Cubic coil system composed of three sets of cubic triple coils to produce wide area 0.66% uniform magnetic field in any direction.

A cubic coil system, which combines three sets of cubic triple square coils orthogonal to each other, is proposed, constructed, and tested. This coil system can generate a 0.66% (=±0.33%) uniform magnetic field in any direction over a large region of ∼2m, although there is some ripple. This system has the advantages of easy assembly, self-standing, and easy access to internal instruments. In one set of cubic triple square coils, the outer two square coils form a cube, and the middle square coil is located at the center of the cube. The number of turns in the center square coil is proposed to be 0.6 times that of the outer square coil.

Energy Absorption Characteristics and Parameter Optimization of Anti-Climb Energy-Absorbing Devices for Subway Vehicles under Impact Loads

To further enhance the crashworthiness of subway vehicle anti-climb energy-absorbing devices, this paper proposes a novel collapsible structure, which is embedded with honeycomb aluminum blocks and consists of an inner and outer double-layer square tube. An impact finite element model of the subway vehicle’s anti-climb energy-absorbing device was established using LS-DYNA (v.17.2). The effects of the connecting diaphragm thickness, the inner and outer tube thicknesses of the thin-walled tubes, and the yield strength of the honeycomb aluminum on the energy absorption and impact force of the anti-climb energy-absorbing device were investigated. The results indicate that changes in the inner and outer tube thicknesses of the thin-walled tubes significantly affect the energy absorption and impact force of the anti-climb energy-absorbing device. However, changes in the connecting diaphragm thickness only increase the maximum energy absorption by up to 7.5% but have a significant impact on the maximum peak force. It was also found that the difference in energy absorption due to changes in the yield strength of the honeycomb aluminum is only 3.6%, suggesting that the yield strength of the honeycomb aluminum and the connecting diaphragm thickness have a limited influence on the crashworthiness design of the anti-climb energy-absorbing device. Furthermore, a multi-objective surrogate model characterizing the specific energy absorption and maximum peak force was established for the aforementioned four influential parameters using the response surface method. The model was then optimized using a genetic algorithm, resulting in optimal parameters that increased the energy absorption and specific energy absorption by 27.3% and 13.8%, respectively, compared to the original values, leading to a significant improvement in crashworthiness. The findings provide valuable references for and insights into the crashworthiness design and optimization of subway vehicles’ anti-climb energy-absorbing devices.

Axial performance of square steel tube and sandwiched concrete jacketed circular CFST columns

Although extensive experimental and numerical studies have been conducted on the axial performance of steel tube and sandwiched concrete jacketed CFST columns, contableurations with outer square tubes and inner circular CFST components are rarely found. This paper investigates the axial performance of square steel tube and sandwiched concrete jacketed circular CFST columns, examining the effects of outer steel ratio and sandwiched concrete strength on failure patterns, relative load-strain curves, and load-bearing capacity. The analysis of ultimate compressive capacity confirmed the effective confinement provided by the outer square steel tube. Based on the experimental results, a finite element model was established to further study the working mechanism of retrofitted columns. The load on components, distribution of longitudinal stress and transverse constraint stress on concrete revealed that the inner concrete experiences dual confinement effects from both inner and outer steel tubes, with the constraint of the outer square steel tube becoming significant only during the load dropping phase. Furthermore, a simple equation was proposed for predicting the axial compressive load-bearing capacity of retrofitted columns using superposition methods and design codes. Comparison results demonstrated good agreement between experimental and calculated values.

Natural convection and heat transmission of two-phase Bingham Fe3O4-CoFe2O4-water hybrid nanofluid flow in an enclosure with a corrugated heated cylinder

The Galerkin weighted residual finite element method (GFEM) has been used to numerically investigate the natural convection flow of two-phase Bingham hybrid nanofluid in a square cavity with a corrugated cylinder at the center. The base fluid here is water. The hybrid nanofluid is made of Fe3O4-CoFe2O4 nanoparticles. The flow inside the enclosure is considered laminar, non-Newtonian, and incompressible. The corrugated cylinder is taken heated. The top and bottom walls of the outer square are considered adiabatic, and the left and right walls are considered cold. Several non-dimensional parameters, including the Rayleigh number (Ra = 104, 105, 106), the Bingham number (Bn = 0, 0.5, 1), the volume fraction (ϕ = 0.00, 0.04), the Brownian parameter (Nb = 0.1, 0.2, 0.3), thermophoresis parameter (Nt = 0.1, 0.2, 0.3), buoyancy ratio (Nr = 0.1, 0.2, 0.3), corrugation (N = 5, 6, 7), the Prandtl number (Pr = 6.2), and the Lewis number (Le = 1000) have been numerically simulated. The main focus of this work is to witness streamlines, isotherm, and nanoparticles’ volume fraction distribution and understand heat transmission with the help of average Nusselt number and local Nusselt number for several parameters for a two-phase Bingham hybrid nanofluid. The results show that an upsurge in Ra increases the extent of the upper two vortices and decreases the extent of the lower two vortices. All four vortices are seen to increase in dimension for an increase in Bn. The same observation is found for an increase in ϕ. The lower vortices are growing, and the top ones are nearly eliminated for base fluid, while those are visible for nanofluid when corrugation is increased. A further expansion completely destroyed the higher ones and increased the size of the bottom ones. The average Nusselt number ( Nu¯ ) increases when Ra is incremented. Nu¯ rises with a rise in ϕ. An increment in ϕ to 0.04 results in a 4.43% gain in Nu¯ . An increase in Bn is causing Nu¯ to drop by 18.02%. For Ra = 105 and Bn = 2, ϕ = 0.02 has the maximum heat transfer enhancement between 0.00 ≤ ϕ ≤ 0.04. In the future, we plan to use mixed convection in a three-dimensional domain along with the impact of magnetohydrodynamics (MHD).

Investigation on axial compression performance of self-compacting fly ash concrete filled square steel tube column: Tests and numerical simulation

Self-compacting concrete has the advantages of high fluidity, high uniform density, and low porosity. To promote the engineering application of self-compacting concrete, this article studies the axial compression test of ten square steel tube self-compacting concrete columns. The effects of design parameters such as different grades of concrete strength and internal structures of circular steel tubes, square steel tubes, and H-shaped steel on the mechanical properties of self-compacting fly ash concrete filled square steel tube columns are studied. The failure mode, characteristic load and characteristic displacement, ductility, and energy dissipation capacity of each specimen are analyzed. On the basis of the test, the finite element analysis model of steel tube self-compacting concrete column is established, and the test results and simulation results are compared and analyzed. The results show that: the failure mode of the square steel tube specimen is the multilayer middle and upper ring buckling failure. Internal structural measures of square steel tube and H-shaped steel can improve the bearing capacity, ductility, and energy dissipation capacity of the specimen. It is not recommended to use the specimen with an outer square and an inner circle design. The results of the finite element simulation have a high degree of matching with the test results, which intuitively reflects the changes in force of each component.

Research on Multi-Physical Field Characteristics of Deep Coal Seam Mining Based on the Rock-Coal-Rock Model

In order to disclose the multi-physical field characteristics of the deep coal seam mining process and their dynamic evolution legislation, based on the “rock-coal-rock” model, during the mining process, the stress field, displacement field, energy field, and plastic zone evolution process are all simulated using FLAC3D6.0. The findings show that stress in the original rock is redistributed as a result of coal seam mining, creating a pressure relief zone in the middle of the goaf and advanced support pressure in the front part of the working face. The roof falls following the termination of coal seam mining. The collapsed blocks fill the middle of the goaf, playing a supporting role. The floor bulges as a new supporting pressure zone forms and builds up high elasticity. The stress reduction zone shifts from a rectangular to an inner circular distribution and an outer square as the working face’s mining distance increases and the range of the fracture field expands accordingly. In addition, a complete model was constructed to verify the correctness of the “rock-coal-rock” model. The stress, displacement, and energy curves of the overlying strata at a distance of 12 m from the bottom of the coal seam in the middle of the goaf obtained by the two methods were basically consistent. Ultimately, the findings of the numerical simulation were compared with the advanced support pressure data that were acquired on-site and they were good. This work can provide a reference for the safe mining of deep coal seams.

Symmetrically structured epsilon negative metamaterial for antenna gain enhancement

An epsilon negative metamaterial (MTM) is presented in this article that bears a symmetrical structure and shows a transmission coefficient (S21) resonance at 2.78 GHz. The proposed MTM unit cell comprises an outer square ring with horizontally oriented splits, connected along the vertical axis to a circular inner ring featuring vertically oriented splits, forming an interconnected structure. The electrical dimension of the MTM cell is 0.08λ × 0.084λ, and here wavelength, λ is determined at 2.4 GHz. The MTM shows negative permittivity, near zero permeability as well as refractive index. The electric field, Magnetic field, and current distribution have been analyzed to realize resonance behavior. The compactness of the MTM is identified through an effective medium ratio (EMR) of 12.2. Moreover, an equivalent circuit is modeled and Advanced Design Systems (ADS) is utilized to confirm its performance. The prototype of the metamaterial is developed and a measured result is taken that exhibits a well-matching with the simulation result. Application of this metamaterial is checked through designing and developing an antenna and MTM is used as a superstrate over the antenna. Both the simulation and measured results reveal that as a superstrate, MTM helps to increase the antenna gain by more than 100% with less effect on the bandwidth. Thus, this new metamaterial can be a good candidate as an antenna element for increasing performance. Moreover, the proposed antenna-MTM system can be utilized for wireless power transmission as it provides an adequate gain in a compact 3D structure.

Numerical investigation and design of concrete-filled double square steel tube columns under axial compression

This paper introduces a novel cross-sectional design for concrete-filled steel tubular (CFST) columns termed “concrete-filled double square steel tube” (CFDSST). The CFDSST columns incorporate an inner square steel tube positioned diagonally at 45° relative to the outer square steel tube, which serves as a stiffener for the outer tube. A three-dimensional finite element simulation model is presented to accurately predict the behavior of axially loaded CFDSST short columns. This model considers the influence of concrete confinement by the steel tubes. Experimental data are employed to validate the accuracy of the finite element model. The validated model is then utilized to assess the performance of the proposed columns, considering various geometric and material properties. The results highlight the substantial enhancement in structural performance achieved by the innovative CFDSST column configuration compared to conventional square CFST columns. The integration of the inner CFST components enhances both buckling resistance and the confinement mechanism of the column. This contributes to the increased load-bearing capacity, ductility, and residual strength of the columns. Notably, the steel tube thickness, the yield strength, and the concrete compressive strength greatly affect the performance of the column. Lastly, a simplified design model is formulated to predict the compressive capacity of the CFDSST stub columns, providing accurate outcomes validated by numerical analysis.

An optically transparent dual-band frequency selective surface for polarization independent RF shielding

This article reports on a compact dual band, Frequency Selective Surface (FSS) based spatial filter for Wi-Fi and WLAN shielding applications on a transparent glass surface with optical transparency of 70%. The unit cell comprises an outer square loop resonator with a disconnected and concentric annular ring resonator. To introduce frequency tuning and compactness T shape stubs are strategically loaded on these resonators and it is ensured that the mutual coupling remains minimal. The outer square resonator suppresses the 2.4 GHz band, and the inner circular ring resonator stops the 5.4 GHz band. The unit element is four-fold symmetric thus it offers complete polarization independence. A detailed parametric and electromagnetic field analysis has been conducted to elucidate the significance of different sections of the unit element. An equivalent lumped circuit model is also derived for the proposed unit element to better explain the underlying working mechanism. A finite prototype of 15 × 11 elements is fabricated on a soda lime float glass by using ordinary adhesive copper foils with a standard chemical etching process. Polarization independence and angular stability up to 45° are measured and compared with the simulated responses. The FSS shield offers frequency suppression up to 45 dB and 43 dB for 2.4 GHz and 5.4 GHz bands respectively. With high optical transparency, the design allows maximum light through it and causes no extra burden on energy consumption for indoor applications. The compact dual band design and the possibility of direct application on host surfaces like glass windows and doors make this design an excellent candidate for data security and privacy applications in secure installations with an esthetically pleasing outlook.

Axial compression performance of square concrete filled double skin SHS steel tubular columns confined by CFRP

This paper focuses on the axial compression performance of 15 concrete-filled double skinned tubes CFDST columns with different CFRP reinforcement schemes. The design of this test used an outer square steel tube with a square steel tube inside, with concrete poured at the sandwich and the inner steel tube kept hollow. The structure is both cost effective and allows the hollow to be used for utility access. However, in recent years damage to CFDST has occurred due to fire, earthquakes, corrosion etc. Therefore, research into the reinforcement and repair of this structure is crucial. Compared to other reinforcement methods, FRP has the advantage of being lighter and more robust and does not significantly alter the original structure. In this study, the mechanical properties of the specimens were further analyzed from the data of load displacement, peak load and ultimate displacement by mainly observing and analyzing the damage mechanism of the specimens through the strengthening effect of different strengthening schemes for different hollow ratios. The results show that when the hollow ratio is not bigger than 0.33, the CFRP reinforcement effect is relatively obvious, especially the three-layer CFRP wrapped CFDST specimens have a substantial increase in bearing capacity and stiffness. Finally, an analytical study was carried out based on previous research and the experimental results agreed well with the calculated results.

Multi-objective optimization for a novel sandwich corrugated square tubes

The sandwich corrugated square tubes (SCSTs), which includes outer square tube (OST), inner square tube (IST) and middle corrugated square tube (CST), have been has been proved to have excellent energy absorption performances. In order to further increase its performance and obtain the optimal structural parameters, multi-objective optimization of SCSTs is carried out. The surrogate modals for the SCSTs were constructed, and the main effects and the interaction effects were analyzed in detail. Finally, multi-objective particle swarm (MOPSO) optimization was used for multi-objective optimization of the SCSTs. The optimization results show that Pareto frontier of the SCSTs can reach a larger range than the SCSTs with A = 0 mm. Due to the coupling effect, energy absorption (EA) and initial peak force (Fmax) of the optimal design solution of the SCSTs are increased by 13.76% and decreased by 8.76% respectively compared to the sum of IST, OST and CST crushing alone. Two key indicators, including Fmax and EA, have been improved at the same time.

Experimental and numerical study of flow field structure in U-shaped channels with different bend sections

Time-resolved particle image velocimetry is used to study the flow characteristics of rotating U-shaped channels with different types of bend sections: one with both inner and outer walls square, one with an inner circular wall and an outer square wall, and one with both inner and outer walls circular. The rotation number varies from 0 to 0.25, at a Reynolds number of 11 500. The present work aims at providing a detailed insight of the flow field occurring within a rotating U-shaped channel, typically resembling internal cooling channel embedded into first stages of turbine blades in aeroengines. A validated numerical simulation is carried out to determine the flow mechanism. A proper orthogonal decomposition and the Ω-criterion vortex identification method are used to study the vortical distribution and flow characteristics. The results show that a bend with both inner and outer square walls produces corner vortices on the outside of the bend section, and both the separation vortex and reattachment vortex are larger than those of the other two geometrical configurations. In the channels with a circular inner wall of the bend, separation is delayed, and both the separation vortex and reattachment vortex are smaller. When both walls of the bend are square, the peak Reynolds shear stress is twice than when they are both circular. With the increase in the rotation number, the size of vortical structures changes. The Coriolis force also changes the relative size of the secondary flow in the bend section, and the vortex near the leading surface becomes larger.

Axial-flexural behaviour of concrete filled double skinned steel tubular (CFDST) composite column: Experimental investigations

Concrete Filled Double Skinned Steel Tubular (CFDST) composite column comprising of outer and inner steel tubes is a class of CFST composite columns developed for improved structural performance and is evolving. An experimental investigation is carried out on total 10 nos. of CFDST composite column test specimens including one CFST column under axial-flexural loading. Parametric study is performed considering outer square steel tube with inner steel tubes of circular and diagonally oriented square shapes as well as without inner steel tubes of square and circular shapes, not commonly found in the literature. Influence of D/t ratio and confinement of concrete sandwiched between steel tubes are examined. An effective loading mechanism, utilizing the full length of the test specimen, is developed. Ultimate load carrying capacity, longitudinal and lateral strains as well as axial and lateral displacements are extracted for test specimens. It is shown that, CFDST column with outer and inner square tubes under axial load performs well in terms of ultimate load capacity, confinement effect, displacement behaviour and ductility vis-à-vis CFST column. Experimental load-moment (P-M) interaction curve is plotted for CFDST composite column. Shape and orientation of inner square steel tube w.r.t outer square steel tube does not have detrimental effect on axial strength of the CFDST columns. Axially loaded CFDST columns exhibit significant confinement of concrete at the level of loading ∼ 20–40% of the peak load.

Experimental investigation on eccentric compression behavior of FRP-confined concrete-encased cross-shaped steel columns

FRP-confined concrete-encased cross-shaped steel column (FCCSC), composed of an outer square glass-fiber-reinforced plastic (GFRP) tube, the internal cross-shaped steel, and the filled concrete, is a novel type of composite column. Eleven square FCCSCs were tested subject to eccentric axial compression load. The influence of eccentricity and slenderness ratio was evaluated and investigated. The test results showed that both the axial load-bearing capacity and lateral confinement efficiency of FRP tube reduced with the increase of eccentricity and slenderness ratio. The maximum reduction in axial load-bearing capacity was up to 50.7 % and 71.1 %, with the eccentricity varying from 0 mm to 50 mm and 100 mm, while the maximum reduction was about 18.1 % and 27.5 % when slenderness ratios increased from 10.44 to 20.87 and 34.79, respectively. The ductility of eccentric compressed FCCSCs can be evaluated by combined strain. It is indicated that short columns exhibited the best ductility, and the ductility increased with the increase of eccentricity. However, the ductility of slender columns reduced with the increase of eccentricity. Based on the test results, the experimental axial force (N)-moment (M) interaction curve of FCCSCs was obtained, and the balanced failure between compression and tension failure mode was recommended.

Pair-partitioned bulk localized states induced by topological band inversion

Photonic topological insulators have recently received widespread attention mainly due to their ability to provide directions in the development of photonic integration platforms. The proposal for a topological bulk cavity with a single-mode expands upon previous research works on topological cavities; thus, interest in topological edge states and corner states is beginning to shift into analysis on bulk properties and their applications. However, there remains a gap in research on a multi-mode cavity of the topological photonic crystals (PCs). In this Letter, a cavity of the topological PCs is proposed involving pair-partitioned bulk localized states (BLSs) from a two-dimensional inner and outer nested square lattice (2D IONSL), which can enable a multi-mode cavity for the topological PCs. First, the topological characteristics are described in terms of a Zak phase, and band inversions are achieved by changing the size of scatterers in the inner and outer circles that reside within the unit cell. Afterwards, analogous to the tight-binding model for electronic systems, the Hamiltonian and topological phase transition conditions of 2D IONSL PCs are derived. Furthermore, it is proposed that the demonstrated optical field reflection and confinement mechanism induced by topological band inversions due to the opposite parities of wavefunctions may lead to the phenomenon of pair-partitioned BLSs. This research increases the research works of bulk topological effects, creating a route for photonic integration platforms for near-infrared.

Experimental and numerical investigations on the behavior of a novel multilayer spirals reinforced square composite column under axial load

Existing studies have shown that under severe ground motion the column-end damage can be significant in rectangular (including square) RC columns due to the arch effect and the consequent insufficient lateral confinement by tie reinforcement. Improving the non-uniform confinement of tie reinforcement is necessary to enhance ductility and load bearing capacity of rectangular RC column. Against this background, the author proposed a novel multilayer spirals reinforced square composite column (MLSRSCC) consisting of one layer of outer square stirrup and two layers of spirals aligned with the centroid of the specimen section. Five MLSRSCC specimens and one conventional single spiral reinforced composite column (SSRSCC) for comparison were tested. The test results showed that the ultimate load and deformation capacity of MLSRSCC were greatly enhanced even with a slightly less amount of steel compared to reference SSRSCC. Moreover, a finite-element (FE) model is established to investigate the confinement mechanisms of MLSRSCC in relation to the distributions of axial stress, confining stress and principal stress ratio. An extensive parametric study containing 1,024 FE results is carried out to explore the effects of various key design parameters on the improvement of ultimate bearing load of MLSRSCC. Furthermore, a calculation method for the ultimate bearing capacity of MLSRSCC was subsequently developed, by which higher accuracy was obtained compared with those calculated from existing design specification.

The tunable single-/narrow-band terahertz metamaterial absorber through photoconductivity

In this work, a photo-excited terahertz metamaterial absorber (PETMA) switched between single-band and narrow-band absorption is reported. Such an absorber includes three layers, which are a metal plate on the bottom, a dielectric layer, and a top unit attached to the dielectric substrate. The upper unit of the proposed PETMA is composed of an innermost ring-shaped and a middle truncated ring-shaped high-impedance surfaces (HISs), a nested split ring-shaped resonator connected with an outer square ring-shaped metal resonator. It is noted that four corners of the square ring-shaped metallic resonator are embedded in photoconducting semiconductors (silicon), respectively. Furthermore, the quadrate air columns (ACs) are inserted in the dielectric substrate to promote the absorption effect of this absorber. The single-band (at 1.16 THz) and the narrow-band absorption (at 1.458–1.538 THz) conversion can be realized through the variation of the conductivity of silicon tuned by an optical pump beam. Besides, the absorption principle of the devised PETMA is analyzed by describing the surface currents, the electric field diagrams, the magnetic field distributions, and the power flow distributions. In addition, the simulations show that the proposed PETMA exhibits stable absorption performance at a wider incident angle.

Simulation of heat release from phase change material with insert of fins and addition of nano-powders

In present work, numerical simulation for freezing of paraffin (RT28) and CuO nanoparticles were applied through a geometry containing radial fins. Three models for fins with same surface area were applied and container was full of NEPCM. The outer square wall was adiabatic and inner circular wall has constant cold temperature and fins were connected to this wall. Homogeneous formulations for NEPCM were utilized and buoyancy effect was considered in momentum equation. The data of solid fraction has been verified according to previous published numerical article and nice agreement was reported. To selected optimized number of nodes, the grid study has been presented and structure configuration of mesh has been applied. The treatment of NEPCM in view of temperature, solid fraction and irreversibility has been analyzed in results. The poorest configuration in view of time of procedure is third model. For the first model with elevate of time from 5 to 50 min, SF rises around 384.33% while frictional and thermal irreversibility declines around 199.1% and 159.89%, respectively.

The effect of design parameters on mechanical performance of all-steel buckling restrained brace with double steel tubes

To explore the effect of design parameters on the mechanical performance of the proposed all-steel buckling-restrained brace (BRB), the finite element software ABAQUS is adopted. The brace consists of an inner round steel tube and an outer square steel tube to restrain its inner core, designed with both the cruciform-section core and the H-section steel core. Quasi-static tests are performed on the all-steel BRB to explore its energy dissipation capacity. The cyclic behavior of the specimen models is evaluated. The validity of the numerical model is verified by comparing the predicted results with the experimental results. Next, the effects of three parameters on the mechanical properties of the brace—the width-thickness ratio of the inner core, the clearance between the inner core and the inner round steel tube c1, and the constraint ratio—are investigated by the validated numerical model. The width-thickness ratio varies from 6 to 20, the gap value ranges from 1 to 7 mm, and the constraint ratio ranges from 0.43 to 1.03. Results show that the hysteresis curves of the two braces are full, with stable hysteretic performance and good energy dissipation capacity, which justifies the construction. Based on the parameters analysis results, the optimum values of the width-thickness ratio, gap, and constraint ratio have been recommended for steel BRBs.