Core Geometry Research Articles

Sound Propagation of Three-Dimensional Sandwich Panels: Influence of Three-Dimensional Re-Entrant Auxetic Core

Re-entrant auxetic cellular structures (RACSs) offer various mechanical properties. Specifically, their high acoustic absorption and dissipation properties turn them into proper candidates to effectively increase the sound insulation characteristics of sandwich plates. Accordingly, this approach proposes an analytical strategy to investigate the exact effect of using three-dimensional (3D)-RACS in order to determine the sound transmission loss (STL) coefficient of a sandwich panel. Therefore, the dynamic equations of fluid–structure interaction are extracted using 3D stress distribution, and then the obtained equations are solved analytically based on the state vector method. The reliability and precision of the outcomes are checked according to previous works. The results obtained are significant because the designed sandwich model seems to improve the sound characteristics of the system based on the STL comparisons between the current approach and the single-layer plates as well as sandwich panels with other core geometries. The achievements of this study can provide novel insights into the STL of 3D-RACS sandwich systems with a complex core model.

Energy absorption of foam-filled corrugated core sandwich panels under quasi-static loading

The present paper tries to introduce the effect of foam-filled on a type of trapezoidal corrugated core and their structures derived from the related previous studies. The main purpose of this work is to present a novel geometry of trapezoidal cores, and their configurations are inspired by the earlier works. These absorbers have been proposed to raise the specific energy absorption (SEA) while declining the initial peak crushing force. Therefore, five corrugated core sandwich panels have been tested under quasi-static axial compressive load experimentally and then simulated by ABAQUS software. The accuracy of the numerical simulations is validated by comparing the numerical results with the corresponding experimental data. Besides, some other simulations have been carried out to investigate the effect of foam density, core type, and thickness in more detail. The comparison results show that the SEA rate of bi-core sandwich panels which has not been filled by foam is better than the single trapezoidal core sandwich panels, and this rate is roughly around 70%. The best performance is relevant to the pure foam core without any trapezoidal core structure and the next item is the single foam-filled corrugated core and the lowest performance among them is related to the bi-core corrugated core foam-filled.

Experimental investigation of the compressive strength of hybrid composite sandwich beams with double-corrugated sinusoidal core reinforced by graphene and polyurethane foam

In this paper, the effects of some system parameters such as nanographene, core geometry, and polyurethane foam on the compressive strength of composite sandwich beams with double corrugated lattice core subjected to flatwise-compression load are investigated experimentally. The face sheets and core of the sandwich beams are made of 10-layers bidirectional carbon fibers using the vacuum infusion process. According to the results of the flatwise-compression test, it was revealed that some factors, including height and angle of the core, the weight percentage of nanographene, and polyurethane foam, can be considered as effective parameters to enhance the compressive strength of the composite sandwich beams. Scanning electron microscopy images were utilized to observe the composition and distribution of the nanoparticles. It was observed that adding nanographene particles to the composite laminates significantly affects the mechanical properties and flexural strength of the sandwich beams. In addition, experimental results showed that the shape of the core can be an effective parameter to control the elasticity and strength of the sandwich beams, and also polyurethane foam dramatically increases the compressive strength and can postpone core failure.

A complete biomimetic iron-sulfur cubane redox series

Synthetic iron-sulfur cubanes are models for biological cofactors, which are essential to delineate oxidation states in the more complex enzymatic systems. However, a complete series of [Fe4S4]n complexes spanning all redox states accessible by 1-electron transformations of the individual iron atoms (n = 0-4+) has never been prepared, deterring the methodical comparison of structure and spectroscopic signature. Here, we demonstrate that the use of a bulky arylthiolate ligand promoting the encapsulation of alkali-metal cations in the vicinity of the cubane enables the synthesis of such a series. Characterization by EPR, 57Fe Mössbauer spectroscopy, UV-visible electronic absorption, variable-temperature X-ray diffraction analysis, and cyclic voltammetry reveals key trends for the geometry of the Fe4S4 core as well as for the Mössbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the S = 4 electronic ground state of the most reduced member of the series, [Fe4S4]0, and provide electrochemical evidence that it is accessible within 0.82 V from the [Fe4S4]2+ state, highlighting its relevance as a mimic of the nitrogenase iron protein cluster.

NIR-Absorbing Mesoporous Silica-Coated Copper Sulphide Nanostructures for Light-to-Thermal Energy Conversion.

Plasmonic nanostructures, featuring near infrared (NIR)-absorption, are rising as efficient nanosystems for in vitro photothermal (PT) studies and in vivo PT treatment of cancer diseases. Among the different materials, new plasmonic nanostructures based on Cu2−xS nanocrystals (NCs) are emerging as valuable alternatives to Au nanorods, nanostars and nanoshells, largely exploited as NIR absorbing nanoheaters. Even though Cu2−xS plasmonic properties are not linked to geometry, the role played by their size, shape and surface chemistry is expected to be fundamental for an efficient PT process. Here, Cu2−xS NCs coated with a hydrophilic mesoporous silica shell (MSS) are synthesized by solution-phase strategies, tuning the core geometry, MSS thickness and texture. Besides their loading capability, the silica shell has been widely reported to provide a more robust plasmonic core protection than organic molecular/polymeric coatings, and improved heat flow from the NC to the environment due to a reduced interfacial thermal resistance and direct electron–phonon coupling through the interface. Systematic structural and morphological analysis of the core-shell nanoparticles and an in-depth thermoplasmonic characterization by using a pump beam 808 nm laser, are carried out. The results suggest that large triangular nanoplates (NPLs) coated by a few tens of nanometers thick MSS, show good photostability under laser light irradiation and provide a temperature increase above 38 °C and a 20% PT efficiency upon short irradiation time (60 s) at 6 W/cm2 power density.

Optimizing optical properties by core geometry variation of chalcogenide tellurite based photonic crystal fiber

We propose an approach based on core geometry variation in designing photonic crystal fiber (PCF) to optimize different optical properties. To investigate those properties of the nobly designed geometrically varied core PCF, Finite element method (FEM) is adopted. The nonlinearity, scattering loss, confinement loss, dispersion profile, numerical aperture, dissemination of power in different portions and effective modal area of the designed waveguide are thoroughly analyzed. The proposed structure with circular core numerically shows unprecedented confinement loss of the order of 10−10 (2.22 × 10−10 dB/m to be precise) with nonlinearity of 51000 W−1km−1 and scattering loss of 1. 2 × 10−12 dB/km. Zero dispersion is also obtained at 1500 nm. The fiber is then used for supercontinuum generation and obtained bandwidth of about 3500 nm at – 40 dB along 2 mm of fiber length. It is anticipated that the proposed PCF could be useful in spectroscopy and biomedical imaging as well.

Thermal Management Design of Transformers for Dual Active Bridge Power Converters

A methodology for the design of compact transformers operating at high frequency is presented in this article. A particular emphasis is paid to the thermal management of the magnetic core and of the winding components. For a 7 kW dual active bridge dc–dc converter, the objective is to reduce the core volume (<80 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), improve the power efficiency (>99%) and integrate the serial inductance (8.7 μH) as being the leakage inductance of the transformer. A parametric study shows that the heating in the copper winding is very sensitive to the anisotropic thermal conduction behavior of the wire. Due to this characteristic, a pot-core configuration is prone to a higher warming compared with the E-E core geometry, as the efficiency of the winding cooling is lower. In order to take part of the self-shielding ability of pot cores, we studied new configurations in which internal thermal drains are inserted into voids specially designed to shorten the distance between the external cooled walls and the hottest points of the winding. The heating of internal components of the transformer and resulting thermo-mechanical stress peak is reduced by 40% paving the way for robust transformers with a power density that could theoretically reach up to 200 kW/dm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

ARCHER - a new Three-Dimensional method of characteristics neutron transport code for Pebble-bed HTR with coarse mesh finite difference acceleration

A new deterministic code ARCHER using Three-Dimensional (3-D) Method of Characteristics (MOC) has been developed by Institute of Nuclear and new Energy Technology (INET), Tsinghua University, aiming to obtain high-fidelity transport solution of pebble-bed High Temperature gas-cooled Reactor (HTR) with explicit pebble-bed geometry. However, 3-D MOC usually suffers from the slow convergence rate without efficient acceleration methods. In this work, the Coarse Mesh Finite Difference (CMFD) based on regular mesh is implemented to accelerate 3-D MOC calculation, which is available for the problems with cylinder and cuboid geometry. The complex geometry of reactor core with randomly stacked spherical fuel elements and irregular helium flow area, as well as the topological relationships between fine Flat Source Region (FSR) mesh for MOC and coarse CMFD mesh, are the key but challenging tasks for high-fidelity transport solution. Constructive Solid Geometry (CSG) and Boolean operation are constructed to describe problem geometry, which has the ability to deal with complex topological relationships between meshes. In addition, tree grid structure is utilized to reduce the time complexity of ray tracing and obtain the grid mapping relationship between coarse mesh and fine mesh. Spatial domain decomposition parallel based on MPI is utilized to alleviate the memory pressure and pursue high computational performance. Ray parallel is further achieved through OpenMP with shared memory. Several problems have been used to verify the geometric modeling capability and computational performance of this new 3-D MOC code for pebble-bed HTR.

Novel thermosyphon-assisted setup for determining heat exchanger thermal characteristics

To be used in the market, thermal and friction characteristics of newly launched heat exchangers must be acknowledged, usually by experimental methods. Steady-state Kays and London is considered the classical experimental technique. In this setup, one of the heat exchanger streams is usually vapor, to provide controlled known heat transfer and temperature conditions, while the other stream is subjected to different flow rates, for the determination of the equipment thermal and pressure drop behaviors. Large expensive industrial boilers are usually used, resulting in difficulties in stabilizing and controlling vapor temperatures. In the present work, a new experimental setup, based on the above-mentioned technique, is proposed for determining the heat transfer characteristics of compact heat exchangers. The boiler vapor flow is substituted by the working fluid (water in vapor state) of a two-phase thermosyphon. Being smaller and much more flexible, this technology allows for easy control of the vapor temperature, while providing uniform temperature distribution along one of the heat exchanger streams, which is difficult to obtain with the classical procedure. In the proposed apparatus, the “known side” of the heat exchanger takes the role of the condenser of the thermosyphon. Two well-known heat exchanger cores, composed by circular and square cross section channels, were used to validate the proposed arrangement, considering the ranges: 2200 < Re < 8000 and 850 < Re < 2800, respectively. The wall temperatures were tested in the range 120 °C to 220 °C with a precision of ± 0.5 °C in steady-state. In addition, the resulting Nusselt number (Nu) and the Fanning friction factor (f) data were compared with consolidate literature correlations showing an average discrepancy of 15% for both geometries and parameters. Therefore, the use of thermosyphons results in smaller, simpler and more precise test benches to be used for the evaluation of heat exchangers, as it provides the desired constant wall temperature conditions for the characterization of core geometries, substituting, with advantages, the use of large and expensive steam boilers.

Functional Behavior and Energy Absorption Characteristics of Additively Manufactured Smart Sandwich Structures

Additive manufacturing (AM) of functional parts using smart materials has attracted considerable interest in both scientific and industrial domains. The application of shape memory polymers (SMPs) opens up new possibilities in the fabrication process and makes them able to recover their initial shape after deformation. This study aims to demonstrate the synergic potentiality of the SMPs in fused filament fabrication (FFF) to manufacture 4D printed smart sandwiches and address their functional behavior. This technological solution promises lightweight and biodegradable parts, which boast exceedingly valuable performance in reusable energy absorbing applications. Several designs, materials, and process parameters including nozzle temperature, layer height, and printing speed are investigated in this work. The results show that selecting the appropriate core geometries could enhance the mechanical strength as well as the deformation capability in the sandwich structures. Likewise, the applied materials considerably affect the energy absorption characteristics. Moreover, tweaking the process parameters is found to be a useful approach for maximizing the mechanical properties and displacement in the 4D‐printed sandwiches.

External Reactor Vessel Cooling Evaluation for Severe Accident Mitigation in NPP Krško

The In-Vessel corium Retention (IVR) through the External Reactor Vessel Cooling (ERVC) is mean for maintaining the reactor vessel integrity during a severe accident, by cooling and retaining the molten material inside the reactor vessel. By doing this, significant portion of severe accident negative phenomena connected with reactor vessel failure could be avoided. In this paper, analysis of NPP Krško applicability for IVR strategy was performed. It includes overview of performed plant related analysis with emphasis on wet cavity modification, plant’s site specific walk downs, new applicable probabilistic and deterministic analysis, evaluation of new possibilities for ERVC strategy implementation regarding plant’s post-Fukushima improvements and adequacy with plant’s procedures for severe accident mitigation. Conclusion is that NPP Krško could perform in-vessel core retention by applying external reactor vessel cooling strategy with reasonable confidence in success. Per probabilistic and deterministic analysis, time window for successful ERVC strategy performance for most dominating plant damage state scenarios is 2.5 hours, when onset of core damage is observed. This action should be performed early after transition to Severe Accident Management Guidance’s (SAMG). For loss of all AC power scenario, containment flooding could be initiated before onset of core damage within related emergency procedure. To perform external reactor vessel cooling, reactor water storage tank gravity drain with addition of alternate water is needed to be injected into the containment. ERVC strategy will positively interfere with other severe accident strategies. There are no negative effects due to ERVC performance. New flooding level will not threaten equipment and instrumentation needed for long term SAMGs performance and eventually diluted containment sump borated water inventory will not cause return to criticality during eventual recirculation phase due to the lost core geometry.

Simulation of xenon transients in the VVER-1200 NPP using the KARATE code system

Xenon transients in Russian VVER reactors have been studied in great theoretical and experimental detail. On the other hand, with an upgraded reactor design (including higher power density, modified safety systems and thermohydraulics), it is essential to study the relationship between reactor perturbations, reactor core geometry and feedback effects. Recently, some measurements have been published describing the interaction between xenon oscillations and power in the core of the newly developed VVER-1200 reactor. The construction of this type of reactor is planned in Hungary, so the simulation of these experiments using a Hungarian reactor physics code system is essential.In this paper, we introduce the core of the Novovoronezh reactor, which is the first VVER-1200 reactor, and present selected measurements from the physical start-up experiments of this new unit, including several xenon transients. We simulated these transients using our upgraded KARATE code system and found that the calculated and measurement results show reasonable agreement, which demonstrates the capabilities of our code. Similar trends to our results can be observed in the calculations performed by Russian design codes.

A High-Efficiency High-Power-Density SiC-Based Portable Charger for Electric Vehicles

This paper proposes a portable 11 kW off-board charger for electric vehicles. In the ac/dc stage, a three-phase power factor correction (PFC) in Vienna topology is chosen. The loss and volume of the PFC inductance are calculated over a wide range of parameters and optimized with regard to design, winding, and core material. A three-phase LLC resonant converter operating at 1 MHz is chosen for the galvanically isolated dc/dc stage. A parametrizable loss model of the high-frequency transformer and the resonance inductor is developed to minimize volume, weight, and losses. With the help of an automated algorithm using these loss models, the inductive components are optimized in terms of winding specification, magnetic material, and core geometry, verified by finite element analysis and measurements. For the ac/dc stage, 900 V SiC devices are adopted, and 1200 V SiC devices are used in the primary and secondary sides of the dc/dc stage. A variable dc-link voltage is utilized to adjust the charging profile and to operate the LLC resonant converter at the most efficient point near the series resonance frequency. A mechatronically integrated portable air-cooled off-board charger prototype with 11 kW, three-phase 400 VAC input, and 620–850 VDC output is realized and tested. The prototype demonstrates a power density of 2.3 kW/liter (37.7 W/in³), a peak efficiency of 96%, and 95.8% efficiency over the defined battery voltage range.

Effect of Core Geometry, Orientation and Support on the Core Shift in Mould

Abstract: This paper focuses on how to improve the effect of core geometry and its orientation when core shift occurs in the mould. Core shift is the change in position of the core from its original position in the mould before the molten fluid is passed into the cavity. Core shift occurs due to the temperature difference in the mould box and the pressure induced on the side walls of the mould box. Thus, the final product will have unexpected and uncountable variations and defects which will have a huge impact on the mechanical properties which in turn will affect the performance when running an operation. Also, the design and analysis of the final product will give an estimation on the various stresses acting on the core and how it will eventually affect both the mould and the core during the casting process. The problem of core shift has been resolved and the results obtained from the correction, have made an impact on the small foundries which usually do not operate in a systematic way. Thus, the goal of minimal to absolutely zero core shift can be achieved and the new final product will have more advantages compared to the old product with defects. Keywords: Core shift, Cavity, Knuckle joint, Fork end, Sand casting, Core, Mould.

Interconnection of Few-Mode Fibers and Photonic Integrated Circuits Using Mode-Field Adapters

We propose a detailed method for the interconnection between optical fibers and waveguides of photonic integrated circuits. Appropriate modal transmission is accomplished by matching the mode field diameters from both waveguide structures. Links from one structure to another are created by an interconnecting waveguide, maintaining a fixed coupling efficiency as its size is modified to adjust to the target waveguide core. This tailored transition acts as a mode field adapter, equalizing the transmission among multiple modes and reducing the mode-dependent losses while coupling. We present an algorithm to design the mode field adapter based on matching the effective mode areas using the power overlap integral. A study case considering a polymer photonic integrated device immediately connected to a few-mode fiber is analyzed. Coupling efficiencies over 90% for every transmitted mode are achieved, showing an evident improvement compared to typical approaches only matching core sizes. Detailed comparison of the results for each transmission mode is presented. This same procedure can be used to interconnect optical waveguides with different refractive index profiles and core geometry.

Computer-Aided Formulation of Magnetic Pastes for Composition Improvement for Power Magnetics

The size of magnetic components can be reduced with novel designs, but the intricate structures are difficult to make due to the limited sets of conventional magnetic core geometries and materials. Magnetic pastes have the flexibility of forming complicated structures with a pressure-less and low-temperature molding process, and are ideal for making the novel magnetic designs. The conventional approach of developing magnetic pastes involves time-consuming experimental iterations to determine the optimal composition parameters. Instead of relying on the trial-and-error efforts, we explored a computer-aided approach to guiding the magnetic paste development by creating material&#x2019;s microstructure by discrete element method (DEM) and studying the property by finite element method (FEM). From a starting formula with two different-sized spherical powders, we improved the composition guided by DEM and FEM, and studied the magnetic permeability versus two variables: powder mixing ratio and magnetic volume fraction. The simulated permeability agreed well with the experimental data with an average error of only 10&#x0025;. With the computer-aided formulation methodology demonstrated in this work, one can develop magnetic pastes with minimum experimental efforts and explore different compositions to meet various magnetic design needs.

Synthesis and characterization of a tetradentate bispidine-based ligand and its zinc(II) complex

The efficient synthesis of a tetradentate diol-bispidine-based ligand and its metal complex with Zn(II) is here reported. The single-crystal X-ray diffraction (SC-XRD) analysis of the Zn(II) complex allowed the characterization of the coordination sphere around the cation as a distorted square pyramid and confirmed that the bispidine core was in a chair-chair (cc) conformation. This finding agreed with the theoretical analysis. The structural data demonstrated the influence of the ligand conformation on the coordination mechanism, confirming that the cc geometry of the bispidine core is a key factor to form a stable complex. Hirshfeld surface and two-dimensional fingerprint analysis showed that hydrogen bonds (O⋯H) and van der Waals interactions constituted the major contribution to the intermolecular forces, with O⋯H/H⋯O and H⋯H contacts accounting for 39.8% and 38.8% of the surface, respectively. NMR titration experiments provided information on the formation mechanism of the complex and on the species formed throughout the reaction.

Effect of Non-Covalent Interactions on the 2,4- and 3,5-Dinitrobenzoate Eu-Cd Complex Structures

Heterometallic {Eu2Cd2} complexes [Eu2(NO3)2Cd2(Phen)2(2,4-Nbz)8]n·2nMeCN (I) and [Eu2(MeCN)2Cd2(Phen)2(3,5-Nbz)10] (II) with the 2,4-dinitrobenzoate (2,4-Nbz) and 3,5-dinitrobenzoate (3,5-Nbz) anions and 1,10-phenanthroline were synthesized. The compounds obtained were characterized by X-ray single-crystal analysis, powder X-ray diffraction analysis, IR spectroscopy, and elemental analysis. Moreover, the thermal stability of the complexes was also studied. Analysis of the crystal packing showed that where 1,10-phenanthroline is combined with various isomers of dinitrobenzoate anions, different arrangements of non-covalent interactions are observed in the complex structures. In the case of the compound with the 2,4-dinitrobenzoate anion, these interactions lead to a significant distortion of the metal core geometry and formation of a polymeric structure, while the complex with the 3,5-dinitrobenzoate anion has a structure that is typical of similar systems. The absence of europium metal-centered luminescence at 270 nm wavelength was shown. For all the reported compounds, a thermal stability study was carried out that showed that the compounds decomposed with a significant thermal effect.

Tunable performance metrics for acoustic liners

In the development of automated design tools for acoustic liners customized to mitigate specific noise spectral characteristics, it is often beneficial to have a unified quantitative metric to discriminate between candidate designs. Such metrics are especially useful when optimizing the packing of 3D folded cavities into a prescribed liner volume. We devise tunable performance metrics (TPM) that account for absorption parameters such as the peak absorption and the frequency at which it occurs, the bandwidth of appreciable absorption and its lower bound among others. Metrics are tuned by varying the weight functions for these absorption parameters in order to address the specific priorities for the liner’s design. A numerical study is conducted using a procedure based on the Zwikker–Kosten Transmission Line (ZKTL) theory to demonstrate the application of TPMs for the selection of acoustic liner designs for various scenarios. When liners with complex core geometries are used to enhance acoustic performance, TPMs that also include structural parameters related to mass, volume, stiffness or strength could be utilized to provide a more comprehensive means of evaluation.

Experimental investigation of 3D-printed auxetic core sandwich structures under quasi-static and dynamic compression and bending loads

Auxiliary metamaterials designed according to the Negative Poisson’s Ratio (NPR) property are exciting structures due to their high impact strength, impact energy absorption abilities, and different damage mechanisms. These good mechanical features are suitable for aviation, automotive, and protective construction applications. These structures, whose most significant disadvantages are production difficulties, have become easier to produce with the development of 3D production technology and have been the subject of many studies in recent years. In this presented study, two conventional core geometries and three different auxetic geometries, commonly used in sandwich structures, were designed and produced with 3D printer technology. The strength and energy absorption capabilities of prototype sandwich structures investigated experimentally under bending loads with static and dynamic compression. Except for the re-entrant (RE) type core, the auxetic core foam sandwich structures demonstrate higher rigidity and load-carrying capacity than classical sinusoidal corrugated (SC) core and honeycomb (HC) core sandwich structures under both quasi-static and impact-loaded compression and three-point bending experiments. Double arrowhead (DAH) and tetrachiral (TC) auxetic cores outperformed honeycomb core in terms of specific quasi-static and impact load-bearing performance under compression by 1.5 ± 0.25 times. In three-point bending experiments under both quasi-static and impact loading conditions, the load-carrying capacity of the double arrowhead and tetrachiral auxetic cores was found to be more than 1,86 ± 0.38 times that of the honeycomb core sandwich panels.