Optimal Geometric Configuration Research Articles

Effect of cavity depth on air-breathing rotating detonation engine fueled by liquid kerosene

In our recent experimental investigation, the feasibility of a liquid-kerosene-fueled air-breathing/ramjet rotating detonation engine featuring a cavity-based annular combustor has been experimentally demonstrated. Achieving stable operation and organized detonation combustion within the rotating detonation combustor presents significant challenges that demand further investigation. Thus, this study aimed to deepen our understanding of the optimal geometrical configuration of a cavity-based annular combustor operating in air-breathing mode. Numerous experiments were conducted to evaluate the impact of varying cavity depths on combustion performance under a supersonic incoming flow with a total temperature of 860 K. The findings indicate that adequate cavity depth is essential for the generation of kerosene-fueled rotating detonation waves in air-breathing mode. Notably, a kerosene–air rotating detonation wave was achieved in combustors with cavity depths ranging from 10 to 30 mm while maintaining a supersonic heated air mass flow rate of approximately 1000 g/s and a minimum equivalence ratio of 0.77. However, at a cavity depth of 10 mm, both the propagation velocity and peak pressure of the rotating detonation waves were significantly lower compared to those at 20 and 30 mm, thereby suggesting that the depth of 10 mm may require optimization. Additionally, optical observations revealed that the detonation reaction zone was located further from the combustor head as cavity depth increased. This indicates that deeper cavity depths allow for longer mixing and preheating times of the combustible mixture before detonation, thereby enhancing detonation performance. This study clarifies how cavity depth influences liquid-fueled rotating detonation and provides guidelines for designing cavity-based annular combustors in air-breathing rotating detonation engines.

Seismic performance of novel high-strength steel external assembled 3U energy dissipator

The development of easily implemented, cost-efficient, and replaceable energy dissipation devices is increasingly emphasized to improve bridge resilience. This study introduces a novel external assembled 3U energy dissipator (EA3UED) made of high-strength steel, designed to enhance the performance of precast segmental concrete bridge piers. The EA3UED, featuring three distinct U-shaped components to provide multi-directional resistance, was evaluated through comprehensive cyclic loading tests on five different specimens to assess their failure modes and practical feasibility. Finite element analysis conducted in Abaqus further assessed parameters such as ultimate bearing capacity, energy dissipation, stiffness, and ductility to identify the optimal geometric configuration. The results indicate that the EA3UED exhibits high energy dissipation, strength, stiffness, and ductility alongside cost-effective benefits. Two primary failure modes were observed: U-shape failure and bolt fractures. The validated finite element models successfully simulated the hysteretic behavior of the EA3UED. And a parametric study based on these models examined the effects of the width of U-shape and the steel grade on the device performance. These improvements demonstrate the EA3UED’s potential for integration in future bridge pier designs, improving their resilience and performance under seismic loads.

Experimental investigation of the cooling effect of topology-optimized structure on photovoltaic wall

Nowadays, photovoltaic walls have been widely used, which will generate heat behind the PV panel and cause overheating, making the lower efficiency of the PV panel and higher temperature of the exterior wall. Topology optimization structures have been explored in many fields for heat dissipation, but few are applied in heat dissipation of the PV wall systems. The purpose of this paper is to experimentally investigate the effect of topological optimized structure of the copper sheet on electricity generation efficiency of the PV panel and cooling effect of the exterior wall. The topology optimization method is used to numerically find the optimal geometric configuration of high thermal conductivity material of copper sheet on the back of the photovoltaic panel. And the topology-optimized copper sheet is fabricated by 3D printing and experimented with four different cases. The experimental results show that under natural convection, compared with the reference photovoltaic wall, the largest reduction of temperature of the photovoltaic panel (ΔTpv) and the largest output power increment rate (ΔE/E) of the photovoltaic wall with topology-optimized copper in the 5 test days are 2.7℃and 1.30 % respectively, and the largest reduction of temperature of the exterior wall (ΔTw) is 1.6℃. Under forced convection, the temperature reduction (ΔTpv) and the increment of output power (ΔE) of the photovoltaic panel and the temperature reduction of the exterior wall (ΔTw) increase significantly under wind speed of 1 m/s compared with natural convection. But when the wind speed is increased from 1.5 m/s to 2 m/s, the increment is less obvious. Therefore, the optimal wind speed in the air gap of the photovoltaic wall with topology-optimized copper is 1 ∼ 1.5 m/s. At last, based on the results of our previous study, the optimal-constructed photovoltaic wall in hot summer and cold winter area is discussed. The results of this research can provide some technical guidance for engineering application of the photovoltaic panel integrated with walls in similar climate regions.

Two-Dimensional Plasma Soft X-ray Radiation Imaging System: Optimization of Amplification Stage Based on Gas Electron Multiplier Technology.

The objective of the proposed research is to develop plasma soft X-ray (SXR) radiation imaging that includes spectral information in addition to standard SXR tomography for the purpose of studying, for example, tungsten transport and its interplay with magnetohydrodynamics (MHD) in tokamak plasmas in an ITER-relevant approach. The SXR radiation provides valuable information about both aspects, particularly when measured with high spatial and temporal resolution and when tomographic reconstructions are performed. The spectral data will facilitate the tracking of both light and high-Z impurities. This approach is pertinent to both the advancement of a detailed understanding of physics and the real-time control of plasma, thereby preventing radiative collapses. The significance of this development lies in its ability to provide three-dimensional plasma tomography, a capability that extends beyond the scope of conventional tomography. The utilization of two-dimensional imaging capabilities inherent to Gas Electron Multiplier (GEM) detectors in a toroidal view, in conjunction with the conventional poloidal tomography, allows for the acquisition of three-dimensional information, which should facilitate the study of, for instance, the interplay between impurities and MHD activities. Furthermore, this provides a valuable opportunity to investigate the azimuthal asymmetry of tokamak plasmas, a topic that has rarely been researched. The insights gained from this research could prove invaluable in understanding other toroidal magnetically confined plasmas, such as stellarators, where comprehensive three-dimensional measurements are essential. To illustrate, by attempting to gain access to anisotropic radiation triggered by magnetic reconnection or massive gas injections, such diagnostics will provide the community with enhanced experimental tools to understand runaway electrons (energy distribution and spatial localization) and magnetic reconnection (spatial localization, speed…). This work forms part of the optimization studies of a detecting unit proposed for use in such a diagnostic system, based on GEM technology. The detector is currently under development with the objective of achieving the best spatial resolution feasible with this technology (down to approximately 100 µm). The diagnostic design focuses on the monitoring of photons within the 2-15 keV range. The findings of the optimization studies conducted on the amplification stage of the detector, particularly with regard to the geometrical configuration of the GEM foils, are presented herein. The impact of hole shape and spacing in the amplifying foils on the detector parameters, including the spatial size of the avalanches and the electron gain/multiplication, has been subjected to comprehensive numerical analysis through the utilization of Degrad (v. 3.13) and Garfield++ (v. bd8abc76) software. The results obtained led to the identification of two configurations as the most optimal geometrical configurations of the amplifying foil for the three-foil GEM system for the designed detector. The first configuration comprises cylindrical holes with a diameter of 70 μm, while the second configuration comprises biconical holes with diameters of 70/50/70 μm. Both configurations had a hole spacing of 120 μm.

Investigations on the primary air entrainment and flame stability in a partially submerged combustion-based porous radiant burner

This study delves into the effects of altering the geometrical dimensions of a Self-Aspirated Porous Radiant Burner (SA-PRB) of 5 kW capacity, focusing primarily on the Mixing Tube (MT) and orifice, and their influence on air entrainment and flame stability. To simulate flow and combustion, the study utilized the RNG k-ɛ and Eddy Dissipation Models, respectively, employing a four-step reaction scheme for LPG combustion. Examining various combinations of MT dimensions, orifice sizes, and their positions within the MT, the study scrutinized flame length, heat distribution uniformity, and flashback. Both numerical simulations and experimental observations corroborated the findings, highlighting the significant impact of orifice and MT dimensions on Primary Air Entrainment (PA). Optimal geometrical configurations are identified as crucial for achieving the combustion stability in PRBs. Configurations resulting in unstable PRB operation such as non-uniform temperature distribution, flashback etc., have been discussed. Stable operation is achieved in the partially submerged combustion mode with an optimized setup featuring a 0.3 mm OD orifice positioned 30 mm from the datum, coupled with a 29 mm MTD. This configuration yields a PA of 79 % and a maximum temperature of 979 °C, and demonstrated efficacy of the proposed design in enhancing PRB performance.

Three-Dimensional Finite Element Modeling of the Singer’s Formant Cluster Optimization by Epilaryngeal Narrowing With and Without Velopharyngeal Opening

This study aimed to find the optimal geometrical configuration of the vocal tract to increase the total acoustic energy output of human voice in the frequency interval 2-3.5 kHz “singer’s formant cluster”, (SFC) for vowels [a:] and [i:] considering epilaryngeal changes and the velopharyngeal opening (VPO). The study applied 3D volume models of the vocal and nasal tract based on computer tomography (CT) images of a female speaker. The epilaryngeal narrowing (EN) increased the total sound pressure level (SPL) and SPL of the SFC by diminishing the frequency difference between acoustic resonances F3 and F4 for [a:] and between F2 and F3 for [i:]. The effect reached its maximum at the low pharynx/epilarynx cross-sectional area ratio 11.4:1 for [a:] and 25:1 for [i:]. The acoustic results obtained with the model optimization are in good agreement with the results of an internationally recognized operatic alto singer. With the EN and the VPO, the vocal tract input reactance was positive over the entire fo singing range (ca. 75-1500 Hz). The VPO increased the strength of the SFC and diminished the SPL of F1 for both vowels, but with EN the SPL decrease was compensated. The effect of EN is not linear and depends on the vowel. Both the EN and the VPO alone and together can support (singing) voice production.

Effect of Radial Neutron Reflector on the Characteristics of Nuclear Fuel Burn-Up Wave in a Fast Neutron Energy Spectrum Multiplying Medium: A Consistent Parametric Approach

Abstract The influence of radial neutron reflector on the build-up and propagation of a nuclear fuel burn-up wave in a fast multiplying medium is investigated using a consistent parametric approach. Coupled multigroup neutron diffusion equations with a burn-up evolution model are simulated on the two-dimensional cylindrical reactor geometry with azimuthal symmetry. Uranium–plutonium transmutation model is considered, and the simulation is performed by using the finite element multiphysics software package comsol. Transient characteristics of the burn-up wave are represented by two new parameters, namely, transient time (TT) and transient length (TL). TT and TL are defined as the time and distance required for the burn-up wave to attain its steady-state nature. Steady-state phases are characterized in terms of wave velocity, full width half maximum (FWHM), and full width 10% of maximum (FW10M). A sensitivity study of steady-state and transient parameters is conducted for the different values of radial reflector thickness. The potential relevance of these characterization parameters on the development of optimal geometrical configuration of radial neutron reflector in breed and burn (B&B)-based reactor design is addressed based on the sensitivity study.

An Adaptive Cooperative Localization Method for Heterogeneous Air-to-Ground Robots Based on Relative Distance Constraints in a Satellite-Denial Environment.

Cooperative localization (CL) for air-to-ground robots in a satellite-denial environment has become a current research hotspot. The traditional distance-based heterogeneous multiple-robot CL method requires at least four unmanned aerial vehicles (UAVs) with known positions. When the number of known-position UAVs in a cluster collaborative network is insufficient, the traditional distance-based CL method has a certain inapplicability. A novel adaptive CL method for air-to-ground robots based on relative distance constraints is proposed in this paper. Based on a dynamically changing number of known-position UAVs in the cluster collaborative network, the adaptive fusion estimation threshold is set. When the number of known-position UAVs in the cluster cooperative network is large, the real-time dynamic topology characteristics of multiple robots' spatial geometric configurations are considered. The optimal spatial geometric configuration between UAVs and unmanned ground vehicles (UGVs) is utilized to achieve a high-precision CL solution for UGVs. Otherwise, in the event that the number of known-position UAVs in a cluster collaborative network is insufficient, distance observation constraint information between UAVs and UGVs is retained in real time. Position observation equations for UGVs' inertial navigation system (INS) have been constructed using inertial-based high-precision relative position constraints and relative distance constraints from historical to current times. The experimental results show that the proposed method achieves adaptive fusion estimation with a dynamically changing number of known-position UAVs in the cluster collaborative network, effectively verifying the effectiveness of the proposed method.

Numerical and experimental investigation of a solar air heater duct with circular detached ribs to improve its efficiency

A solar air heater duct (SAH-duct) SAH-duct has low thermal performance due to the low heat transfer coefficient of air which is the working fluid. Proper mixing of relatively hot and cold air with respect to the hot absorber plate of the SAH-duct can enhance heat transfer. It can be achieved by placing suitable hindrances in the path of airflow like detached ribs. This study presents the numerical investigation of an asymmetrically heated 2D rectangular SAH-duct with in-line arranged circular detached ribs. In the geometrical configurations of the detached ribs; blockage ratio d/H, clearance ratio c/d, and relative longitudinal pitch ratio P/d are varied as 0.04–0.48, 0.1–1.2, and 05–50 respectively at Reynolds number Re 3000–15000 to study their effect on the thermal-hydraulic performance of the SAH-duct. Local and space-averaged thermal-fluid properties like heat transfer coefficient, and friction factor, Nusselt number, pressure coefficient, etc. are discussed through the graphical illustrations and contour plots. The various dimensions of the ribs are varied to find the optimum geometrical configuration of the detached ribs.

Energy Efficient Downsizing of Ribbed Confinements for Heat Exchange Applications

Abstract Downsizing double-pipe heat exchangers is possible by deploying ribs on the two sides of the heat exchangers. The shape of these ribs, along with two key geometric variables – pitch and height, are crucial in the selection of energy-efficient rib configurations. This is because, the enhancement in heat transfer performance comes at the cost of increased pressure drop. Thus, the goal of this three-dimensional numerical investigation is to identify favourable rib shapes and explore the effect of truncation on triangular ribs, something which is missing from existing literature. Truncation is expected to greatly affect the performance of triangular ribs, either adversely or favorably. To explore this conclusively, an unbiased and exhaustive analysis is carried out by comparing the performance of confinements with modified and regular triangular ribs, keeping plain confinements as the baseline. Furthermore, the effects of two principal design variables – rib height and rib pitch are explored for each shape. Separate results are presented for the inner and outer confinements of the double-pipe heat exchangers (pipes and annuli) to allow for the extrapolation of results for a wide range of applications employing internal flows in pipes and annuli. A phenomenological model is developed to classify the thermo-hydraulic performance of each confinement and identify optimal geometrical configuration and identify best performing design(s). Once optimal rib pitch-height combinations are identified, performance at this optimal combination is evaluated at different Reynolds numbers, spanning from 10,000 to 30,000.

OPTIMIZING THE GEOMETRICAL PARAMETERS OF 3D PRINTED NEGATIVE STIFFNESS METAMATERIAL USING TAGUCHI METHOD

The field of negative stiffness metamaterials (NSM) is a rapidly developing area within the realm of mechanical metamaterials. This work presents a novel negative stiffness metamaterial based on a bistable structure that consists of a straight beam with an elastic element shaped like a ring. Further, this work presents the findings of a Taguchi-based experiment aimed at optimizing geometrical parameters in negative stiffness metamaterial. The Taguchi method, known for its efficiency in experimental design and analysis, was employed to systematically study the effects of various factors on snapping force for a novel structure exhibiting negative stiffness. The experiment utilized L18 mixed level orthogonal array. All the test samples were fabricated using additive manufacturing technique. Signal-to-noise ratio analysis and analysis of variance were two statistical approaches that were used to comprehensively evaluate the acquired data. The results of this study provide valuable insights into the optimal geometrical configuration for maximizing snapping force of negative stiffness metamaterial.

Zn(II), Mn(III), and Co(III) complexes of Schiff base derived from 2‐hydroxy‐1‐naphthaldehyde: Synthesis, spectral surveys, single crystal structure studies, Hirshfeld surface analysis, density functional theory calculation, molecular electrostatic potential, and molecular docking evaluations

A new series of transition metal complexes of bidentate Schiff base compound derived from 2‐hydroxy‐1‐(2‐methoxyethylimino)‐naphthalene (HL) were synthesized and characterized using elemental analysis, Fourier transform infrared spectroscopy (FT‐IR), and UV–vis spectroscopies. X‐ray single crystal structures of Zn(II), Mn(III), and Co(III) complexes (1–4) have also been determined, and it was indicated that these Zn(II) and Co(III) complexes (1, 4) are in an octahedral geometry. Whereas, it was found that the Zn complex (2) is in quite a regular tetrahedral environment. Also, the Mn center in complex (3) is ligated by two azomethine nitrogen atoms, two ligand oxygen atoms, and one Cl atom of metal salt forming five coordinated tetragonal pyramid geometry around the Mn atoms. The cyclic voltammetry of the complexes specifies an irreversible redox behavior for all complexes (1–4). Next, DFT/B3LYP theoretical method was used to determine the optimal geometrical configurations and comparison between experimental and theoretical data, as well as for calculations of molecular electrostatic potential, highest‐occupied molecular orbital (HOMO)‐lowest‐unoccupied molecular orbital (LUMO) energy values of selected compounds. The study of non‐covalent interactions was done by Hirshfeld surface analysis using CrystalExplorer program. Furthermore, molecular docking inspection was carried out to study the binding affinity of the tested complexes towards protein B‐cell lymphorna (PDB ID: 4LXD). Using the results obtained from the molecular docking and the summarized interaction of the binding processes, these structures show the validity of effective inhibition against liver cancer.

Utilization of a Genetic Algorithm to Identify Optimal Geometric Shapes for a Seismic Protective Barrier

The utilization of seismic barriers for protection against the hazardous impact of natural or technogenic waves is an extremely promising emerging technology to secure buildings, structures and entire areas against earthquake-generated seismic waves, high-speed-transport-induced vibrations, etc. The current research is targeted at studying the effect of seismic-barrier shape on the reduction of seismic-wave magnitudes within the protected region. The analytical solution of Lamb’s problem was used to verify the adopted numerical approach. It was demonstrated that the addition of complementary geometric features to a simple barrier shape provides the possibility of significantly increasing the resulting seismic protection. A simple genetic algorithm was employed to evaluate the nontrivial but extremely effective geometry of the seismic barrier. The developed approach can be used in various problems requiring optimization of non-parameterizable geometric shapes. The applicability of genetic algorithms and other generative algorithms to discover optimal (or close to optimal) geometric configurations for the essentially multiscale problems of the interaction of mechanical waves with inclusions is discussed.

Increasing sensitivity of the electrostatic field mill sensor by determining its optimal configuration

The object of research is the process of measuring the strength of the electrostatic field for a low dynamic range (from 0 to 1 kV/m). This study is aimed at increasing the sensitivity of the sensor of the electrostatic field mill (EF) by determining its optimal geometric configuration, which will reduce the error of measuring the electrostatic field strength. To establish the actual value of the induced current, a computer model was built and simulation modeling of the EF sensor was carried out. On the basis of the constructed computer model, studies of the EF sensor were carried out to determine the numerical value of the induced current. As a result, it was established that the occurrence of edge effects leads to the appearance of methodological error, which occurs due to the fact that the average induced current is smaller compared to the calculated value. As a result of computer modeling of the EF sensor to determine the value of the optimal number of sectors, it was established that for the proposed design of the EF sensor, the optimal number of sectors is six. It was established that the optimal value of the distance between the sensitive plates and the shielded rotor should be in the range of 2.5–3 mm to ensure the maximum sensitivity of the EF sensor and its safe use. The determined optimal parameters of the EF geometric configuration will allow to form the necessary requirements for the construction of improved electrostatic field strength meters in a low dynamic range (from 0 to 1 kV/m). A promising direction of application of such devices in production will be the development of an additional system for monitoring the strength of the electrostatic field, which will allow to prevent the occurrence of a dangerous situation.

Optimized Design of Shell and Tube Heat Exchanger with Segmental Baffles

Heat exchangers are the apparatus which is widely used in various industries. They transmit heat among two or more fluid streams. Theoretical analysis done by Kern’s method has been done on Shell and tube heat exchanger with segmental baffle and then experimented in CFD to check Heat Transfer rate and pressure drop with varying number of baffles which is 6, 8 and 10, and by keeping all the rest of parameters constant. It is found that as the number of baffles increase heat transfer rate increases also pressure drop is increases significantly. To optimize model in next step, CFD analysis is has been done by varying baffle cut to 25%, 35% and 45% by keeping same number of baffles which found best in heat transfer rate in earlier Kern’s method. Other parameters like velocity, temperature, pressure and baffle numbers are kept constant. Results obtained from numerical solution are analysed extensively to get the effect of baffle cut on heat transfer rate and pressure drop on shell side. The pressing need of the heat exchanger industry, the tradeoff optimization between the pressure drop and the heat transfer coefficient has been studied to provide an idea to get effects of the change in two parameters, namely, baffle spacing and baffle cut simultaneously and observe how these two will affect the performance of an STHX. An attempt to find the optimum geometric configuration has been carried out with number of baffles. Increasing baffles for same length of shell and baffle cut increases from 25% to 35%, heat transfer rate increases. It is beneficial in elucidating that a higher heat transfer coefficient can be obtained for fewer baffles when coupled with the appropriate baffle cut. So selection of correct optimized shell and tube heat exchanger. The work is carried out for copper tube bundles and steel shell. So optimization of baffle cut with correct number of baffles and reduction in pressure drop studied with CFD tool.

A fast satellite selection algorithm for positioning in LEO constellation

In the near future, a much larger scale of low earth orbit (LEO) satellites will be deployed, and satellite selection is an effective way to overcome challenges to processing capability and channel limitation of receivers caused by superabundant satellites in view. However, existing algorithms do not take into account the fact that a large-scale LEO constellation satellite selection subset can be closer to the theoretical optimal configuration than the traditional brute force search and recursive algorithm computational overhead is too large for end devices. In this study, the solution of the minimum optimization problem of the GDOP (Geometric Dilution of Precision) under the condition of limited elevation angle is first analyzed to determine the optimal ratio configuration scheme of top and bottom satellites under the optimal geometric satellite positioning problem. Subsequently, a fast satellite selection algorithm is proposed, which selects a subset of satellites that meet the different numbers of observation satellites and is close to the optimal geometric configuration by geometric method. The comparative simulation shows that, in the 1586 LEO constellation system, the proposed algorithm has an average GDOP of 1.52 when the satellite subset size is 10 and 0.95 when the subset size is 30. Compared with the recursive, the Rotating Partition algorithm and the Quasi-optimal algorithm, the proposed algorithm achieves better accuracy when its size is not close to the total number of observable satellites.

Numerical analysis of a flat plate collector using different types of parallel tube geometry

To obtain improved thermal performance of flat plate solar collectors, the effect of square and rectangular riser tubes of a flat plate collector (FPC) were numerically investigated and compared with circular riser tube FPC in the present study. For this purpose, a three-dimensional numerical model for FPC collectors has been developed and simulated in CFD software ANSYS FLUENT. Transient thermal performance analysis is carried out to find out the optimum geometrical configuration of the FPC riser tube. The numerical results indicated that using the square-shaped riser tube in FPC improves the collector’s useful heat exchange rate as well as thermal efficiency as compared to the use of circular and rectangular riser tubes. There is a maximum 8.1% higher heat exchange rate of the collector with a square riser tube than a circular riser tube under the same operating conditions. The average efficiency of the collector with the circular tube is 65.95%, whereas the square tube has the highest efficiency of 70.44%. However, the pressure drops through the square and rectangular riser geometry are higher than the circular tube. By making a balance between enhanced heat exchange rate and increased pressure drop, the performance evaluation criterion was evaluated and the square-shaped riser tube having the highest value of 2.65 is better than the other configurations. The results clearly indicate that the collector’s performance is notably influenced by the shape of the riser tube, with a square shape yielding superior performance.

Optimizing graded metamaterials via genetic algorithm to control energy transmission

Optimization of functionally graded metamaterial arrays with a high dimensional and continuous geometric design space is cumbersome and could be accelerated via machine learning tools. Mechanical metamaterials can manipulate acoustic or ultrasonic waves by introducing significant dispersive and attenuative effects near their natural frequency. In this work, functionally graded structures are designed and optimized to combine the energy attenuation performance of multiple unit cells with varying frequency responses and to reduce the interlayer mismatch effects. Optimization through genetic algorithms avoids many local minima related to high dimensionality of the design space, but requires many iterations. A reduced order model (ROM) is applied, which can reproduce the transmission response traditionally calculated with FEM in a fraction of the time. Pairing GA and the ROM together, an array of 6 unit cells (with a total of 18 independent geometric design variables) is optimized to have stop bands with extended width and sharper boundaries. Symmetric functionally graded structures are determined to have optimal geometric configurations. Measured 3D printed features are projected onto the ROM solutions to quantify the effect of printing uncertainty on array performance. Repeatability error of ±20μm is determined to reduce the mean depth of the transmission stop band by a factor of 102 and introduce small shifts in center frequency and band width. Proposed methods to improve the resolution of accessible points in the ROM space, reduce sensitivity to geometric uncertainty, and add design freedom include introducing out-of-plane perforations and varying constituent materials using tunable filled resin systems.

Numerical analysis and optimization of adhesively-bonded single lap joints by adherend notching using a full factorial design of experiment

The objective of this study is to carry out experiments using the experimental design methodology to determine the optimal geometric configuration which improves the resistance of a single-lap joint with notched adherends subjected to uniaxial tensile load. On the sides of the adherends in contact with the adhesive layer, a longitudinal rectangular notch is introduced. A complete experimental design (15) of three factors at two levels: the adhesive thickness (tA), depth (dN) and extended length (LE) of the notch was used to determine their effects on strength of an adhesive joint. The response or dependent variable used was the resistance of a single lap joint (SLJ). Finite element (FE) analysis was conducted to investigate the effect of different notch parameters on the strength enhancement of the SLJs. A quadratic regression model with interaction is developed to relate the strength of an adhesive joint and the variables (tA, dN and LE). The regression model was validated using various statistical approaches. According to the ANOVA results, the model is highly significant and in good agreement with the experimental results. The quadratic regression model suggested was used for optimizing the resistance of the joint. The maximum joint strength occurs when the adhesive thickness is the smallest (left end) and when the adhesive thickness is the largest (right end) of the validated domain. The strength of SLJ increases when the notching parameters (dN and LE) increase in the validation zone. The numerical results show that to improve the resistance of an adhesive joint with notched adherend, it is necessary to minimize the thickness of the adhesive layer and to use notch with the highest depth and extension equal or greater than the overlap. The results show that using the adherend notching can significantly improve the load bearing capacity of SLJs.

Time-dependent water wave scattering by a marine structure consisting of an array of compound porous cylinders

Under the assumption of linear wave theory, a semi-analytical model is developed to address the time-dependent water wave scattering problem involving a marine structure consisting of several circular rigid vertical cylinders, each of which is surrounded by a thin cylindrical porous wall with a water region between the inner cylinder and the wall. The problem is tackled by applying the eigenfunction expansion approach. The energy dissipation relation is also derived for the system of compound cylinders. The principal focus of this work lies in locating the optimum geometrical configurations for which the wave forces acting on the structure are minimal along a given wave direction in the frequency domain. Subsequently, the time-dependent response of the structure under the impact of a Gaussian wave pulse is examined. The wavenumber at which the force acting on the inner cylinder is at its maximum is obtained for a given value of the porous-effect parameter. Moreover, the value of that corresponding wavenumber decreases as the magnitude of the porous-effect parameter increases. The model is also carefully validated numerically against results available in the existing literature.