Rectangular Unit Research Articles

Multiple high-Q resonances from mirror-coupled dielectric arrays

This paper reports how high-Q resonances can be created at multiple designated wavelengths in a low-index-contrast dielectric nanoparticle array coupled with a metal mirror. A rectangular array of TiO2 nanoparticles over a silver film (separated by a SiO2 spacer layer) can support collective resonances of magnetic and electric dipoles with their wavelengths determined mainly by the lattice spacings of the rectangular lattice. These resonances can be modulated by the spacer layer thickness to form accidental bound states in the continuum. Furthermore, resonances related to the periodicity along the diagonal of the rectangular unit cell can be produced by perturbing the lattice through modifying the dimensions of adjacent nanoparticles in the unit cell. Our result expands the potential of lattice resonances in low-index-contrast dielectric lattices, making them promising for applications in compact multi-wavelength and unidirectional light-emitting devices.

CONTEXTUAL REANALYSIS OF THE ARCHITECTURAL FORM AND SOCIO-ECONOMIC STATUS OF THE PANAGIA HOUSES AT MYCENAE

The Panagia Houses, one of the building complexes at Mycenae, located to the south-west of the Citadel, were interpreted by the excavators as a group of three independent units. They were constructed and occupied during the Late Helladic (LH) IIIB phase, with two main phases distinguishable in the archaeological record, followed by a reoccupation phase. Careful analysis of the archaeological data published by Mylonas-Shear, which focused on the arrangement of individual units, formality of layout, access and movement patterns, and visibility, suggests that the group should be interpreted rather as a single complex, developed during the period of the maximum expansion of the settlement. The building was gradually expanded to form an extended household, with primary living space surrounded by a number of additional rooms for storage, work and habitation. It was composed of a rectangular main unit, surrounded by an extension formed around a small inner courtyard. The movement between the two levels was organised through a system of connected rooftops, with trapdoors and staircases ensuring access to the various rooms of the complex. During the LH IIIB2 Early phase, Mycenae was hit by a devastating earthquake. Much of the town was left in ruin, but the Panagia Houses were rebuilt, although in a smaller form, with the main unit abandoned and the courtyard inside the extension transformed into the main room of the complex. The status of the complex probably changed, but it was still inhabited by a middle-class family, who possessed a number of valuables and took part in the palatial mobilisation system. The household probably suffered in a widespread fire which destroyed Mycenae at the end of LH IIIB. Its remains were then used as two small dwellings by the survivors of the catastrophe. The history of the complex reflects the changing vicissitudes of the Lower Town of Mycenae.

Partitions influence on rectangular latent heat thermal energy storage unit performance during melting and solidification

The growing use of renewable energy sources demands efficient storage solutions due to their variability. Thermal energy storage systems utilising phase change materials are emerging as viable options to address this challenge. This study evaluates the impact of various partition types on phase change duration in thermal energy storage systems. The well-known and validated enthalpy-porosity algorithm implemented in the Fluent 2021R2 software was used. The shortest melting time was observed in the case with four vertical tubes and three horizontal partitions, which was 82 % shorter than in the reference case. The highest change in specific enthalpy of phase change material (252.5 kJ/kg) during melting was also noted for this system. The shortest solidification time was observed for the case with four tubes and two diagonal partitions, which was 72 % shorter than in the reference case. The greatest increase in the specific enthalpy of phase change material (240.4 kJ/kg) during the solidification process was also observed in this system. In conclusion, due to the thermal conductivity of the partitions, the temperature distribution throughout the domain becomes more homogeonous, thus contributing to more uniform heat flux extraction and supply throughout the process.

Analytical prediction of the formation factor for anisotropic mono-sized unconsolidated porous media

The rectangular Representative Unit Cell (RUC) models for mono-sized isotropic unconsolidated porous media have been extended to anisotropic media. Volume averaging was applied to Ohm's law in order to propose analytical expressions for the formation factor for electrical conduction in terms of the pore-scale linear dimensions. The formation factor, crucial for understanding electrical conduction in porous media, has significant applications in subsurface geophysics, petroleum reservoir characterization, and the durability assessment of construction materials. These analytical models provide valuable insights for optimizing the electrical properties of porous structures in various engineering fields, for example in mapping groundwater resources, differentiating oil-bearing zones in reservoirs, and predicting ion migration in concrete. Aspect ratios of the cell and solid dimensions have been introduced, and the formation factor expressed in terms thereof for five different arrays, i.e. a regular, a non-overlapping streamwisely fully staggered, an overlapping streamwisely fully staggered, a non-overlapping transversally fully staggered, and an overlapping transversally fully staggered array. The Laplace equation has furthermore been solved numerically for two-dimensional versions of the different arrays and the formation factor computed for several values of the aspect ratios. The proposed analytical models have been validated against the generated numerical data and compared to experimental and numerical data obtained from the literature. The proposed models have also been adapted to include a percolation threshold porosity in order to improve the model predictions for very low porosity media.

Optimizing thermal energy storage in rectangular unit: Exploring the impact of moving fin with phase change material

This research presents an innovative moving fin design for a latent heat storage unit, with the objective of improving thermal performance. The methodology integrates numerical simulation, a machine learning approach, and a multi-objective genetic optimization algorithm (NSGA-II). The study optimizes fin parameters, such as fin velocity (Vf), fin thickness (tf), fin length (Lf) and initial fin position (yf). The optimization process aims to maximize both power (P) and stored energy per mass (Em), assigning equal importance to both criteria. The outcomes reveal a considerable rise in power with minor compromises in stored energy per mass. The incorporation of moving fins in rectangular enclosure with PCM leads to a significant power boost while preserving stored latent energy with minimal compromise. In comparison to the no-fin condition, fixed 1-fin and fixed 3-fin configurations lead to stored energy losses of 4.16 % and 11.73 %, respectively, accompanied by power increases of 20.48 % and 51.17 %, respectively. Conversely, the optimized condition for maximum power with moving fins incurs a mere 2.73 % stored energy loss but achieves a remarkable 173.92 % increase in power. The optimized design parameters for maximizing power (P) include Vf = 22.5 × 10−3 mm/s, yf = 60 mm, tf = 2 mm, and Lf = 40 mm.

Multi-objective optimization of L-shaped fins in rectangular phase change energy storage units based on genetic algorithm

Phase change energy storage technology holds immense potential in the field of energy storage, and enhancing the efficiency of energy storage systems has long been a focal point of industry attention. This study aims to optimize the design of an L-shaped fin structure to improve the melting rate of the phase change material (PCM) within a rectangular phase change energy storage unit and enhance the overall system performance. Through the utilization of numerical simulations and the response surface method (RSM), the influence of fin design parameters - specifically, the length and thickness of the main segment and the length and thickness of the branch segment - on the energy storage per unit mass (Em) and energy storage efficiency (Pt) of the energy storage unit is evaluated. The results reveal that the length of both the main and branch segments of the L-shaped fin significantly impacts the melting rate of the PCM, whereas the thickness of these segments has a comparatively lesser effect. Additionally, when the length of the main segment reaches a sufficient value, increasing the length of the branch segment effectively addresses the challenge of PCM melting difficulties at the bottom of the rectangular phase change cavity caused by natural convection. The Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) is employed for the multi-objective optimization of the L-shaped fin shape, and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) with entropy weighting is applied for decision-making to determine the optimal solution. Notably, when the weights of Em and Pt are set at 44.9 % and 55.1 % respectively, the overall performance of the energy storage unit is optimized. The Pareto-optimal decision solution exhibits a significant improvement of nearly threefold in Pt compared to the case without fins, while the reduction in Em is only 5.24 %. This design approach presents a novel perspective for determining fin parameters in phase change energy storage devices and is expected to drive advancements in phase change energy storage technology.

Mechanical meta-sheets with independently tunable Poisson’s ratio and coefficient of thermal expansion

Mechanical metamaterials with tunable Poisson’s ratio (PR) and coefficient of thermal expansion (CTE) have received great attention due to their unique responsive behaviors under mechanical and thermal stimuli useful in a wide range of applications. But, in most designs, they are often coupled to each other, limiting the range of their values to be achieved and their independent controllability. Here, we present mechanical meta-sheets whose PR and CTE can be independently modulated by using rotating rectangular units consisting of alternated bi-material beams. Design principles for these mechanical meta-sheets are provided and verified through simulations and experiments. Both isotropic and anisotropic thermal deformations can be realized and diverse reconfigurations are possible under thermo-mechanical loads for sandwich panels utilizing these meta-sheets as skins. The proposed design principle would be powerful in a broad range of applications requiring shape morphing, stress mitigation, and smart actuation under a thermo-mechanical environment.

Design and analysis of a new deployable articulated mast mechanism with two-dimensional deploying-folding motion

Abstract A traditional deployable articulated mast mechanism can only provide one-dimensional (1D) deploying-folding motion. This paper aims to investigate the design and analysis of a novel deployable articulated mast mechanism with two-dimensional (2D) deploying-folding motion. Firstly, the topological motion of deployable mast mechanisms can provide 2D deploying-folding motion is analyzed, and a potential rectangular prism linkage unit is presented to construct single degree-of-freedom (DOF) deployable mast mechanisms with 2D deploying-folding motion. Secondly, the kinematics of the new deployable mast mechanism is established based on its structural symmetry and modular features. Thirdly, the deploying dynamics of the new mechanism are built based on the Lagrange equation. Fourthly, the deployed/folded ratio, interference and singularity of the new mechanism are analyzed. Finally, a numerical example is used to illustrate the effectiveness of the theoretical analysis, and a physical prototype is developed to show the fabrication feasibility of the new deployable mechanism. Compared with the traditional counterparts with 1D deploying-folding motion, the new deployable mast mechanism has a larger deployed/folded ratio, which has a good application prospect in space missions to support solar arrays, magnetometers, cameras and antennas.

Assembly Structure Formation in Bulk and Ultrathin Films of Poly(substituted methylene) Having an Azobenzene Side Chain.

The density of the side chain introduced to a polymer main chain greatly influences the properties and functions of the polymer. This work first reports on the packing structure and properties at an interface of a poly(substituted methylene) where an azobenzene side chain is introduced at every carbon atom in the main chain (C1PAz). The structure and properties are compared with those of a conventional vinyl polymer [poly(methacrylate)] possessing an identical side-chain structure (C2PAz). The packing structure in the bulk state analyzed by X-ray measurements revealed that C1PAz adopts a highly ordered rectangular unit cell structure, whereas C2PAz shows a less ordered lamellar one. Langmuir film balance experiments indicated that both polymers with the trans-azobenzene give essentially the identical 2D side-chain occupying area on water, which agrees well with the smectic B (hexatic packing) model based on the X-ray data. Upon transfer onto a solid substrate, only C1PAz shows a conformational transformation to a spread bilayer-type layer, most probably due to conformational frustration stemming from the crowding of the side chains. This study proposes new insights into the effects of side-chain density on the self-assembly and photoreaction of azobenzene-containing polymers, which are expected to expand the possibilities of polymer design for various applications.

Numerical investigation of the mechanical properties of lattice structures inspired from polycrystalline materials

In this work, polycrystalline-like lattice structures that are inspired by the geometry of polycrystalline materials are designed. They are generated by filling periodic lattice structures into a Voronoi diagram. Then, finite element analyses of two periodic and eight polycrystalline-like lattice structures are performed to compare their mechanical properties. The numerical results show that polycrystalline-like lattice structures consisting of anisotropic rectangular X-type periodic unit cells are isotropic at the macroscale. Moreover, they have a higher specific stiffness and specific strength than periodic lattice structures under compression. Then, the energy absorption capability is investigated. Five energy absorption indicators (energy absorption, energy absorption per unit volume, specific energy absorption per unit mass, crush stress efficiency, and plateau stress) reveal that polycrystalline-like lattice structures are better energy absorption structures. Furthermore, the defect sensitivity of missing struts is discussed. The findings of this work offer a new route for designing novel lattice structures.

A single-step recursive algorithm of the convolution integral for computing non-viscous damping forces in dynamic analyses

The non-viscous damping force features the convolution integral of the velocity and the kernel function, causing the difficulty of the solutions of the system equation of motion due to the nonlocal time dependence. In accordance with the linear time-invariant system theory in signal processing, this paper presents a single-step recursive algorithm of convolution integral for efficiently computing non-viscous damping forces. The algorithm parameters are effectively identified from the discrete responses of the kernel function to the rectangular unit impulse through digital filter technologies. The proposed algorithm is compatible with the solution schemes based on existing time integration methods, which handle the nonlocal dependence using internal recursive support vectors while leaving the order of the equation of motion unchanged. The central difference method, the Newmark-ß method, and the Bathe method are employed to illustrate the use of the algorithm, proving to retain the stability characteristics of time integration methods. The single and multiple DOF examples show that the simulated results based on the compatible solution schemes compare well with those built on other existing methods, verifying high accuracy and efficiency. The proposed algorithm thus extends the application range of existing time integration methods from the viscously damped system to the non-viscously damped one, fully demonstrating its generalizability.

Investigation and Tailoring of Rotating Squares' and Rectangles' Auxetic Structure Behavior through Computational Simulations of 6082T6 Aluminum Alloy Structures.

Auxetic structures, renowned for their unique lateral expansion under longitudinal strain, have attracted significant research interest due to their extraordinary mechanical characteristics, such as enhanced toughness and shear resistance. This study provides a systematic exploration of these structures, constructed from rigid rotating square or rectangular unit cells. Incremental alterations were applied to key geometrical parameters, including the angle (θ) between connected units, the side length (a), the side width (b) of the rotating rigid unit, and the overlap distance (t). This resulted in a broad tunable range of negative Poisson's ratio values from -0.43 to -1.78. Through comprehensive three-dimensional finite-element analyses, the intricate relationships between the geometric variables and the resulting bulk Poisson's ratio of the modeled auxetic structure were elucidated. This analysis affirmed the auxetic behavior of all investigated samples, characterized by lateral expansion under tensile force. The study also revealed potential stress concentration points at interconnections between rotating units, which could impact the material's performance under high load conditions. A detailed investigation of various geometrical parameters yielded fifty unique samples, enabling in-depth observation of the impacts of geometric modifications on the overall behavior of the structures. Notably, an increase in the side width significantly enhanced the Poisson's ratio, while an increase in the overlap distance notably reduced it. The greatest observable change in the Poisson's ratio was a remarkable 202.8%, emphasizing the profound influence of geometric parameter manipulation. A cascaded forward propagation-backpropagation neural network model was deployed to determine the Poisson's ratio for auxetic structures, based on the geometric parameters and material properties of the structure. The model's architecture consisted of five layers with varying numbers of neurons. The model's validity was affirmed by comparing its predictions with FEA simulations, with the maximum error observed in the predicted Poisson's ratio being 8.62%.

Numerical simulation of fin arrangements on the melting process of PCM in a rectangular unit

Innovative fin arrangements were proposed to enhance the thermal performance of latent heat storage units. The enthalpy-porosity approach was employed to optimize the fin distribution and predict the transient melting behaviors of N-octadecane. The unit with horizontal fins of uniform length was set as the base condition for comparison. It was found that the dead space of heat transfer and melting due to natural convection was not effectively eliminated by the conventional fin set. The region persisted at the bottom of the unit until the end of the melting process. In light of these observations, the fins were repositioned and resized. Three alternative fin configurations were proposed and evaluated: angled fins, asymmetrically located fins, and stepped fins. Results illustrated that fin structures significantly influenced the heat transfer characteristics and melting behaviors of latent heat storage units. Generally, greater enhancements were attained with downward angles and downward offset distances. The downward angle −20°led to an accelerated melting rate of 18.3 % compared to the base condition. In case 9, where the fins were moved down by 12 mm, the heat transfer enhancement ratio reached 32.5 %. However, introducing inhomogeneity in the fin length had only a minimal impact on the melting process.

The Effect of Width-Mismatch of Modulated Nanowaveguides on the Thermoelectric Efficiency.

Width-modulated nanowaveguides are promising for thermoelectric efficiency enhancement because electron and phonon transport properties can be geometrically tuned for improved performance. The shape of the modulation profile drastically affects the transport properties. Optimization of the width modulation for simultaneous maximum thermoelectric transport and minimum thermal transport is challenging because of the interconnected electron and phonon transport properties. We addressed this problem by analysing the effect of each characteristic dimension of a single rectangular modulation unit on electron and phonon transport. We identified distinct behaviours for electrons and phonons. We reveal that whereas phonon thermal conductance decreases with increasing width-mismatch, the electron thermoelectric power factor shows a non-monotonic dependence. It is pointed out that optimal width-mismatch that maximizes thermoelectric efficiency is mainly determined by electron transport and should be identified by maximizing the thermoelectric power. Our work points to a new strategy of optimizing geometry-modulated metamaterials for maximum thermoelectric efficiency.

Terahertz vector beams generated by rectangular multilayer transmission metasurface

We propose a multilayer unit structure with an “H” shape to construct a vector beam metasurface generator. Based on the principle that half-wave plate can modulate and change the polarization state of linearly polarized incident waves, we have designed a metasurface composed of rectangular units, which can convert linearly polarized beams into azimuthally or radially polarized vector beams at 0.1 THz. The theoretical transmission efficiency is about 60.92 %.We also have prepared a sample of the vector beam generating metasurface by printed circuit board (PCB) technology, and tested the intensity distribution and polarization state of the transmitted beam on the self-built terahertz testbed. The vector beam metasurface realizes the miniaturization and integration characteristics of the device, which has potential applications in microscopic imaging, biophotonics, quartentum information, laser acceleration, micromachining, and other fields.

Natural convection and structural impact of rectangular PCM storage units through the modular expansion

To increase the storage capacity and air flow rate of the rectangular thermal energy storage unit (RTESU) for enhancing its application capability, three modular units with air flow rates of 60 m3/h, 120 m3/h, and 180 m3/h for heights of 150 mm, 300 mm, and 450 mm are proposed. Besides, the effect of natural convection (NC) on the charging and discharging process is examined during the modular expansion of the RTESU. The melting performance including melting duration and phase change process is numerically investigated by varying the configurations such as module configuration, non-uniform, and eccentric tube arrangements. The results show that NC has a significant impact on the charging process. It is further demonstrated that the charging process can be enhanced by about 14.58 % and 13.61 % when non-uniform and eccentric tube arrangements are implemented, respectively, as they both increase the area dominated by NC. However, the non-uniform tube arrangement for acceleration of the melting process is gradually enhanced with the increase in storage unit height compared to that of the eccentric tube arrangement. It is worth noting that the Nusselt number (Nu) is introduced for examining heat transfer performance during the melting process with different unit configurations. And the correlation between the dimensionless numbers is applied to predict the liquid fraction for different configurations. For the heat release process, the performance including air outlet temperature, heat extraction, and heat release efficiency of the modular RTESU is evaluated. It is found that the NC has a negligible effect on the discharging process, which is dominated by heat conduction. With the modular expansion, an increase in air flow rate and heat storage capacity as well as the maintenance of a higher heat release efficiency of about 84.97 % can be achieved in the RTESU.

Experimental study of high performance mercury-based triboelectric nanogenerator for low-frequency wave energy harvesting

Wave energy is acknowledged as one of the most promising renewable energy sources, effectively developing wave energy conversion technologies might contribute to solving the power shortage dilemma. However, the optimum performance frequency range of current wave energy capture devices does not match the low-frequency ocean kinetic energy. Here, a triboelectric nanogenerator based on liquid mercury (M-TENG) is presented for low-cost and high-power harvesting. The start-up performance of the M-TENG unit is analyzed at low operating frequencies, and discuss the effect of kinematic inputs, structural parameters and materials aspects on output performance. Meanwhile, the sloshing characteristics of mercury in a rectangular unit were calculated by the SST k-ω model, deriving the matching law between mercury volume and electrical output. Furthermore, 18-unit integrated M-TENG produce a peak power output of 4.57 mW, the mercury with its unique physical properties generates higher transferred charge density up to 35.84 mC/m3, sufficient to light 270 commercial LEDs at 1.00 Hz. The relatively high volumetric power density provides a realistic self-supply technological solution for renewable energy harvesting and guarantees the widespread use of milliwatt power equipment in the marine industry.

Multi-scale experimental investigation on the fluidization of Geldart B 13X zeolite particles: A comprehensive dataset for CFD validation

The fluidization of zeolite 13X in a bubbling fluidized bed was experimentally investigated. The objective is to analyze the fluidization behavior of particles in a lab-scale system with a total of 1.5 million particles, enabling accurate characterization of uncertainties. Validation datasets were generated for the fluidization process in a bench-scale rectangular unit. A comprehensive characterization of the particle properties, including size, density, coefficient of friction, coefficient of restitution, and minimum fluidization velocity, is presented using advanced diagnostic tools. Corresponding fluidized bed measurements, such as pressure drop and bed expansion, are reported under three test settings with different flow rates. The tested particles have a Sauter mean diameter of 1,345 μm and a density of 2,054 kg/m3. It is classified in Geldart group B for its vigorous bubbling and good mixing behavior. With increasing the superficial inlet velocity from 0.347 to 0.740 m/s corresponding to 1.41–3.01 Umf, where Umf = 0.2458 m/s is the minimum fluidization velocity, the particles tend to transit from bubbling flow to slug/plug flow regimes. Using high-speed imaging, bubble sizes and velocities in the pseudo-two-dimensional (2D) fluidized bed could be obtained directly. The data acquisition rate is 1200 fps, far above the quantities of interest (QoI) dominant frequency (typically below 10 Hz). The QoI obtained from this study were statistics of interface height, differential pressure, and particle velocities using particle image velocimetry. The results confirm consistency given the use of randomization and repeat in the run order as well as multiple batches of bed material. This experimental dataset can serve as a benchmark for validating numerical models and as a blind study for the multiphase flow modeling community.

Experimental and numerical investigation of a rectangular finned-tube latent heat storage unit for Carnot battery

Latent heat storage technology has a great potential in Carnot battery systems, and its thermal performance directly affects the system performance. In this paper, a rectangular phase change heat storage unit with finned-tube structure is designed and manufactured, and polyethylene wax/expanded graphite is adopted as the composite phase change material. The thermophysical properties of the polyethylene wax are characterized by experiments first, and then the heat transfer performance of the unit is investigated through varying inlet mass flow rates and inlet temperature on the test rig. Meanwhile, the detailed evolution of the phase change process is visualized and obtained by corresponding numerical simulations. Furthermore, the effects and selection principle of fin number, thickness, and material on the melting process are clarified by numerical simulations. Results shows that the influence of the inlet temperature is more significant than the mass flow rate on the melting/solidification time, however, changing the inlet temperature and mass flow rate has little effect on melting/solidifying the last 10 % of PCM. Heat conduction dominated the heat transfer process due to the high viscosity of polyethylene wax, inducing little stratification of the temperature distribution in the regions bounded by fins. The regions close to the corners and sidewalls are the primary factors delaying melting/solidification rate. Increasing fin number and thickness can effectively decrease the melting/solidification time at the expense of the heat storage capacity. Compared to selecting only high thermal conductivity fin materials, adopting fins with high thermal conductivity, low density, and low specific heat is a better approach for achieving higher heat storage capacity and shorter melting time. The present study explores candidate materials for medium-low temperature latent heat storage and potential applications of traditional finned-tube heat exchangers in medium-low temperature latent heat storage.

Reexamine the emergence and stability of the square cylinder phase in block copolymers.

Recently, a few AB-type multiblock copolymers have been successfully designed to form stable square cylinder phase based on self-consistent field theory (SCFT) calculations. The previous works only identify the stability region of the square phase but not analyzing its stability, which is closely related to the free-energy landscape. In this work, we have reexamined the stability of the square phase in $\mathrm{B_1 A_1 B_2 A_2 B_3}$ linear pentablock and $\mathrm{(B_1AB_2)_5}$ star triblock copolymers by drawing the free-energy landscape with respect to the two dimensions of a rectangular unit cell. Our results demonstrate that the square phase continuously transfers to the rectangular phase as the degree of packing frustration is gradually released. Moreover, the prolate contour lines of the free-energy landscape indicate the weak stability of the square phase in the $\mathrm{B_1 A_1 B_2 A_2 B_3}$ copolymer. In contrast, the stability of the square phase is notably improved in the $\mathrm{(B_1AB_2)_5}$ copolymer due to its enhanced concentration of bridging configurations. Our work sheds light on the understanding of the stability of the square cylinder phase in block copolymers. Accordingly, we propose some possible strategies for further designing new AB-type block copolymer systems to obtain more stable square phase.