Structural Design Optimization Research Articles

Structural optimisation design of impact resistant composite wheel with compression/injection moulding hybrid structure

Structural optimisation design of impact resistant composite wheel with compression/injection moulding hybrid structure

Origami-inspired metamaterial with compression–twist coupling effect for low-frequency vibration isolation

Through unique folding methods and material selection, origami structures enable optimum structural design within a restricted space and provide strong force support. In aerospace engineering, origami-inspired structures are used in designing satellites, probes and other space devices for lightweight, compact and adjustable design requirements. A compression-twist coupled metamaterial inspired by Kresling origami structure consisting of beams and plates is presented in this study, and the vibration response of the structure is investigated. The bandgaps of the structure along longitudinal and transverse directions are studied separately due to the application of the polarization factor. The vibrational modes of the structure are further investigated to elucidate the mechanism of bandgap generation. Parametric studies make the optimal design of bandgap in graded structures possible. Finally, experiments are carried out to verify the correctness of the structural dynamic response. This research provides a new perspective on the design of origami-inspired metamaterial structures in terms of dynamics control and bandgap tuning.

Crashworthiness analysis and optimization of a novel thin-walled multi-cell structure inspired by bamboo

The sophistication and regularity of natural materials continuously provide inspiration for mankind. Mimicking biological materials to devise advanced energy absorption structures remains grand challenges. Herein, we demonstrate a new type of thin-walled multi-cell structure, based on the shape and distribution characteristics of bamboo cross-sections. Numerical simulations of the proposed structure under quasi-static axial compression, lateral compression, and three-point bending are conducted through the finite element method. The crashworthiness of the new structure is compared with that of two other classic bamboo-inspired structures and an ordinary circular tube, and the results show that the present has superior specific energy absorption (SEA), compression efficiency, and deformation mode. Besides, our study also investigates the effects of the wall thickness of bamboo-inspired cell elements and the bio-inspired inner shell on the axial crashworthiness of the proposed structure. An optimal design of the bamboo-inspired structure was obtained by particle swarm optimization and the results reveal that, with the initial peak force (IPF)/SEA almost unchanged, the associated performance in SEA/IPF is significantly improved. Along with this guideline, it may provide a meaningful avenue towards the design of new bio-inspired energy absorption structures.

Structural Design with Self-Weight and Inertial Loading Using Simulated Annealing for Non-Gradient Topology Optimization

This paper explores implementation of self-weight and inertial loading in topology optimization (TO) employing the Simulated Annealing (SA) algorithm as a non-gradient-based technique. This method can be applied to find optimum design of structures with no need for gradient information. To enhance the convergence of the SA algorithm, a novel approach incorporating the crystallization factor is introduced. The method is applied in a benchmark problem of a cantilever beam. The study systematically examines multiple scenarios, including cases with and without self-weight effects, as well as varying point loads. Compliance values are calculated and compared to those reported in existing literature to validate the accuracy of the optimization results. The findings highlight the versatility and effectiveness of the SA-based TO methodology in addressing complex design challenges with considerable self-weight or inertial effect. This work can contribute to structural design of systems where only the objective value is available with no gradient information to use sensitivity-based algorithms.

Finite Element Analysis of the Main Structure for a New Conceptual Aircraft Passenger Vertical Seat Design

Standing cabin is a new design concept of aircraft passenger cabin whereby passengers are transported in the standing position throughout flight as opposed to current seated position. An important element of this cabin concept is the design of the vertical seat to support the passengers, which has to be in compliance with requirements of aviation regulation. In commercial aircraft applications, weight of passenger seat is a significant factor that can affect flight performance of the aircraft. Meanwhile, the seat’s structure should have adequate strength to ensure proper safety provision to passengers. Hence weight and strength are potentially two conflicting design requirements for the vertical seat, and the optimum structural design should have the best compromise with regards to these two requirements. In this study, parametric study on primary structural design of the proposed vertical seat concept is done to obtain an optimized design that satisfies the strength requirements for safety of passengers without causing high penalty to the overall aircraft weight and performance. The simulation analysis for the main structures of the vertical seat design is conducted through finite element method using ABAQUS software. From the results of the analysis, main structural parts made from aluminium alloy with diameter 90 mm and thickness 3 mm are selected for the optimum vertical seat design. This standing seat design has also been shown to have adequate strength and can satisfy the safety regulation requirement without failure. The maximum stress on the seat’s structure under 9-g forward loading is found to be 147.5 MPa, which is lower than ultimate strength of aluminium. Moreover, the seat’s weight is estimated to be 9.5 kg and the maximum deflection of its main structures under forward 9-g loading is 28.42 mm. All in all, the stress analysis results highlight that the structural strength of the optimal vertical seat design can satisfy the requirements of the governing aviation regulations to provide safety to passengers.

Design and Optimization of an Interior Permanent-Magnet Synchronous Motor for Aircraft Drive Application

The torque performance of the interior permanent-magnet synchronous motor (IPMSM) must be further improved to satisfy the growing demand of aircraft drive application. To this end, this article focuses on the design optimization of the IPMSM structure in the aircraft drive systems to improve the torque density and reduce the torque ripple. A special fractional-slot winding and ∇-type magnetic-pole rotor topology are proposed as the optimized IPMSM structure compared with the structure of an existing motor. The simulations of the original and optimized structures at different current values reveal the variance of the torque in the average and ripple, mechanical and external characteristics, efficiency and steady-state temperature. The performance of an optimized prototype is analyzed by experimental testing, and the results show that an optimized motor has a higher torque density and lower torque ripple than the original one at the same speed and rated power, but it also has a higher temperature rise. However, the temperature rise value is acceptable in the experimental testing condition, so the validity of the design optimization method for the proposed structure is verified.

Structure optimization design and magneto-mechanical characteristics analysis of amorphous alloy with oriented silicon steel composite wound core

Three-dimensional wound cores are widely used in three-phase distribution transformer due to the symmetrical magnetic circuit structure. Amorphous alloy and oriented silicon steel are two kinds of ferromagnetic materials commonly used to make distribution transformer cores, each has own advantages and disadvantages in magnetic and mechanical characteristics. The amorphous alloy and oriented silicon steel composite core can synthesize the advantages of both. In this paper, a double-layer composite wound core (DCWC) structure is proposed and the corresponding dual nonlinear electric circuit and magnetic circuit coupling model is established. A structure optimization design method for the DCWC based on the free parameter scanning method is proposed by taking the percentage of oriented silicon steel in the composite core and the structure parameters as free variables. Based on the proposed optimization design method, a DCWC is designed and the experimental prototypes are manufactured. Further, the flux density distribution, core loss and mechanical vibration displacement of the DCWC are analyzed, and the effectiveness of the proposed method is verified by comparing with the measured results.

Structural and Modal Analysis of the Unloading Robot on the Broaching Machine

In order to meet the actual production of a machining company in the low production efficiency, labor intensity, process flow complexity and other real problems, the broaching machine processing upgraded and designed a broaching machine for the production of automatic loading and unloading device. This paper analyzes the layout scheme and workflow of automatic loading and unloading, designs the overall structure of the loading and unloading device and key components, and establishes a three-dimensional model through Solidworks software, and carries out a static analysis of the limit position in the operation process by using the finite element analysis software ANSYS Workbench, and obtains the maximum deformation under the limiting conditions of 0.1129mm, and the maximum stress value of 24.236MPa. The maximum deformation is 0.1129mm and the maximum stress is 24.236MPa. Subsequently, modal analysis is carried out to extract the first 6 orders of intrinsic frequency and corresponding vibration pattern, and harmonic response analysis is carried out on the weak components on the basis of modal analysis, which verifies that the structure complies with the design requirements in terms of strength, stiffness and resonance of the whole machine, and it provides the theoretical basis for the subsequent structural improvement and optimization design.

Analysis of electromechanical coupling modal and dynamic response characteristics of permanent magnet gear transmission system considering variable load condition

In order to study the influence of electromagnetic (EM) effect and load change on the modal characteristics and dynamic response of gear transmission system driven by permanent magnet synchronous motor (PMSM), a electromechanical coupling dynamic model is established. The composite air gap permeability coefficient is introduced, and the formula of permanent magnet flux linkage under the influence of space harmonic and cogging effect is derived. The variation laws of gear meshing stiffness and bearing support stiffness under the influence of load change are simulated and analyzed. The natural frequency and vibration modal under different load, flux linkage and PI controller gain are revealed. On this basis, the influence of EM effect and load change on the resonance domain is analyzed through frequency sweep analysis and time domain simulation. Results indicate that the 1st order natural frequency and resonance amplitude will increase with the load, and the influence of PMSM EM excitation will gradually dominate. The increase of the flux linkage and speed loop controller gain Kpω will reduce the 1st order natural frequency. When Kpω =123, a new mode appears, and there is a modal transition between the new mode and mode 1 when Kpω =161. The research results can provide theoretical guidance for improving the transmission performance and structure optimization design of the permanent magnet gear transmission system.

A comparative approach for the optimal design of steel structures using biogeography-based optimization (BBO) algorithm and genetic algorithm (GA)

Structural optimization is one of the key concerns of civil engineering designers, but from a mathematical point of view, this optimization problem is highly complex and complicated due to a large number of non-linear design constraints and the iterative procedure of structural analysis. Introducing optimization algorithms such as biogeography-Based Optimization (BBO) and genetic algorithms (GA) into applications can help the user to optimize the cost of the structure to be adopted more quickly and with fewer errors in the preliminary phase of the design study. The aim of this research is to carry out a comparative approach to structure weight minimization using biogeography-Based Optimization (BBO) algorithm and genetic algorithms (GA), examining the influence of the number of populations and the number of iterations in the final results. In this study, both algorithms gave reliable results, but a comparison of the results obtained by the two methods reveals that the biogeography-Based Optimization algorithm (BBO) can be successfully used for the optimization of steel structures while ensuring verification of the strength, serviceability and stability criteria defined by Eurocode 3 (Union, 2006), as it has certain advantages in detecting the global minimum over genetic algorithms (GA). It is capable of finding solutions that are lighter, stiffer and have lower deflection than the original designs.

Simulation of Lithium-Sulfur Batteries and Optimization of Cathode Structure

Recently, the spread of the mobile devices and clean energy, the demand for high-power and high-capacity secondary batteries has been growing. However, the energy density of lithium-ion batteries (LiB) that is widely used nowadays is reaching its design limit. Instead of LiB, lithium-sulfur batteries (LiSB) are expected as one of the next-generation secondary batteries. Compared to LiB, LiSB has the advantages of higher energy density, lower cost, and easier weight saving. In LiB, the driving force is the insertion and desorption reaction of lithium ions between the cathode and anode, while in LiSB, is the complex sulfur dissolution and precipitation reaction. In LiSB, the electrolyte determines the dissolution and precipitation of sulfur, which is thought to have a significant impact on battery characteristics. Therefore, new electrolyte systems are being developed daily and techniques to elucidate the reaction mechanisms are needed. Furthermore, the effect of carbon black, a conductive material, on battery characteristics has also been considered. In this study, we investigated the optimal initial lithium ion concentration and calculation focused on the precipitation form of each carbon species for the design of optimal electrode structures.Kumaresan's one-dimensional model [1] based on porous electrode theory was used. Sulfur was used as the cathode active material and lithium metal as the anode active material. Electron and ionic potentials were calculated from the electro-neutrality condition, concentration distribution in the electrolyte was calculated from the non-stationary mass balance equation, and electrochemical reactions at the interface between active material and electrolyte were calculated using the Butler-Volmer equation. Furthermore, stepwise reactions were considered by incorporating the electrochemical reaction of sulfur and the dissolution and precipitation reactions into the concentration distribution and the interfacial reactions. The temperature in the electrode layer was assumed to be constant, and no heat loss or side reactions due to overvoltage were assumed to occur. In LiSB, sulfur dissolved in the electrolyte on the cathode surface is sequentially reduced as polysulfide ions as the discharge progresses. It then combines with lithium ions transferred from the anode and expands to about 1.8 times. Therefore, based on our previous research [2], the effect of the expansion and contraction of the electrode particles was reflected by dynamic changes in the structural properties of the electrode layer.Ionic conductivity and transport number are important parameters that affect the properties of the electrolyte. The higher the lithium ion concentration, the higher the transport number, but the lower the ionic conductivity [3]. In this study, we focused on sulfolane-based electrolyte and investigated the effect of initial lithium ion concentration on discharge capacity by incorporating the relationship between ionic conductivity and transport number into a model. As a result, the discharge capacity reached its maximum when the initial lithium ion concentration was 3.0 M. In the static state, the ionic conductivity was highest around 1.6 M, but considering the operating conditions during discharge, the concentration distribution became be more remarkable due to the low transport number, which may have resulted in excessive Li2S precipitation near the separator. As an extension to the microstructure of the electrode layer, we focused on carbon black (CB). Two types of CB (KB, MCND) were targeted. When MCND and KB were used as CB under the same conditions in the experiment, it was confirmed that the discharge characteristics of MCND were significantly better than those of KB. In LiSB, Li2S precipitation has a significant effect on discharge characteristics. Therefore, we focused on the pores of both CBs. We reconstructed the binarized structure from X-ray CT images of both CBs, hypothetically precipitated Li2S in the pores, and calculated the relative conductivity. The relative conductivity represents the transport property and is highly dependent on the structure of the electrode layer. As a calculation result, the relative conductivity of KB became significantly smaller as the porosity decreased. From the above, the transport properties in both CBs were confirmed by calculation.As described above, it was suggested that an optimum lithium ion concentration exists, and the effect of different CB structures on transport properties was qualitatively evaluated. In the future, it is necessary to confirm the validity of the optimal concentration through experiments and to quantitatively evaluate the effect of different CB.AcknowledgmentThis study was supported by JST ALCA-SPRING Grant JPMJAL1301, Japan.

INTEGRATING ENHANCED OPTIMIZATION WITH FINITE ELEMENT ANALYSIS FOR DESIGNING STEEL STRUCTURE WEIGHT UNDER MULTIPLE CONSTRAINTS

Real-world optimization problems are ubiquitous across scientific domains, and many engineering challenges can be reimagined as optimization problems with relative ease. Consequently, researchers have focused on developing optimizers to tackle these challenges. The Snake Optimizer (SO) is an effective tool for solving complex optimization problems, drawing inspiration from snake patterns. However, the original SO requires the specification of six specific parameters to operate efficiently. In response to this, enhanced snake optimizers, namely ESO1 and ESO2, were developed in this study. In contrast to the original SO, ESO1 and ESO2 rely on a single set of parameters determined through sensitivity analysis when solving mathematical functions. This streamlined approach simplifies the application of ESOs for users dealing with optimization problems. ESO1 employs a logistic map to initialize populations, while ESO2 further refines ESO1 by integrating a Lévy flight to simulate snake movements during food searches. These enhanced optimizers were compared against the standard SO and 12 other established optimization methods to assess their performance. ESO1 significantly outperforms other algorithms in 15, 16, 13, 15, 21, 16, 24, 16, 19, 18, 13, 15, and 22 out of 24 mathematical functions. Similarly, ESO2 outperforms them in 16, 17, 18, 22, 23, 23, 24, 20, 19, 20, 17, 22, and 23 functions. Moreover, ESO1 and ESO2 were applied to solve complex structural optimization problems, where they outperformed existing methods. Notably, ESO2 generated solutions that were, on average, 1.16%, 0.70%, 2.34%, 3.68%, and 6.71% lighter than those produced by SO, and 0.79%, 0.54%, 1.28%, 1.70%, and 1.60% lighter than those of ESO1 for respective problems. This study pioneers the mathematical evaluation of ESOs and their integration with the finite element method for structural weight design optimization, establishing ESO2 as an effective tool for solving engineering problems.

Cycling Reconstructed Hierarchical Nanoporous High-Entropy Oxides with Continuously Increasing Capacity for Li Storage.

High-entropy oxides (HEOs) have been showing great promise in a wide range of applications. There remains a lack of clarity regarding the influence of nanostructure and composition on their Li storage performance. Herein, a dealloying technique to synthesize hierarchical nanoporous HEOs with tunable compositions is employed. Building upon the extensively studied quinary AlFeNiCrMnOx, an additional element (Co, V, Ti, or Cu) is introduced to create senary HEOs, allowing for investigation of the impact of the added component on Li storage performance. With higher specific surface areas and oxygen vacancy concentrations, all their HEOs exhibit high Li storage performances. Remarkably, the senary HEO with the addition of V (AlNiFeCrMnVOx) achieves an impressive capacity of 730.2mAhg-1 at 2.0Ag-1, which surpasses all reported performance of HEOs. This result demonstrates the synergistic interaction of the six elements in one HEO nanostructure. Additionally, the battery cycling-induced reconstruction and cation diffusion in the HEOs is uncovered, which results in an initial capacity decrease followed by a subsequent continuous capacity increase and enhanced Li ion diffusion. The results highlight the crucial roles played by both nanoporous structure design and composition optimization in enhancing Li storage of HEOs.

(Poster Award - 1st Place) Liquid Water Permeability in a Hydrophobic Microporous Layer for the Anode Interdigitated Flow Field of a Gas-Liquid Separating Polymer Electrolyte Membrane Water Electrolyzer

A novel interdigitated flow field for polymer electrolyte membrane (PEM) water electrolyzers (polymer electrolyte electrolysis cells) composed of oxygen exhaust channels apart from liquid water feed channels has been developed for ground and space applications 1, 2). This design can separate oxygen gas and liquid water between the flow channels without buoyancy, so that it dispenses with water circulators for bubble removal in electrolyzers and external separators by natural or centrifugal buoyancy.In this electrolyzer, pressurized liquid water is injected in the in-plane direction from the water channels to the catalyst layer through a hydrophobic microporous layer (MPL) applied to the anode porous transport layer (PTL) 2). Produced oxygen gas is discharged in the through-plane direction of the MPL to the oxygen channels, taking advantage of the capillary pressure in the hydrophobic MPL 2),3). Extreme leakage of the liquid water to the oxygen channels has not been found.This study conducted liquid water permeability tests for an MPL (SIGRACET 29BC, SGL Carbon Inc.) with pressurized liquid water by weighing liquid water penetrated through the MPL-coated PTL to the PTL surface under ambient air pressure. We find gradual permeability decreases with time for different liquid water pressures 4). This permeability is a useful parameter for optimal structure designs of this electrolyzer. Similar tendencies were also observed for a hydrophobic PTL without MPL (SIGRACET 29BA, SGL Carbon Inc., substrate of the MPL-coated PTL). The same test on the hydrophobic MPL dried after the test revealed that the permeability partially recovered. The liquid water networks inside the MPL and the PTL substrate possibly lead to decreases in the permeability. This phenomenon is a critical issue for this electrolytic cell as well as PEM fuel cells, and thus discussed further.References1) Y. SONE, O.S. HERNANDEZ-MENDOZA, A. SHIMA, M. SATO, H. NAKAJIMA, H. MATSUMOTO, Water Electrolysis by the Direct Water Supply to the Solid Polymer Electrolyte through the Interdigitated Structure of the Electrode, Electrochemistry. 89 (2021) 138–140. https://doi.org/10.5796/electrochemistry.20-00145.2) H. NAKAJIMA, V. VEDIYAPPAN, H. MATSUMOTO, M. SATO, O.S. MENDOZA-HERNANDEZ, A. SHIMA, Y. SONE, Water Transport Analysis in a Polymer Electrolyte Electrolysis Cell Comprised of Gas/Liquid Separating Interdigitated Flow Fields, Electrochemistry. 90 (2022) 017002. https://doi.org/10.5796/electrochemistry.21-00097.3) H. Nakajima, S. Iwasaki, T. Kitahara, Pore network modeling of a microporous layer for polymer electrolyte fuel cells under wet conditions, J. Power Sources. 560 (2023) 232677. https://doi.org/10.1016/j.jpowsour.2023.232677.4) S. KUBOTA, H. NAKAJIMA, M. SATO, A. SHIMA, M. SAKURAI, and Y. SONE, Liquid Water Permeability Test for a Microporous Layer Applied to a Gas-Liquid Separating Polymer Electrolyte Membrane Water Electrolyzer, the 42nd Symposium of the Hydrogen Energy Systems Society of Japan (2022) 12H06.AcknowledgmentsThis study is based on results obtained from a project, JPNP21014, commissioned by the New Energy and Industrial Technology Development (NEDO).

A self-powered magnetoelectric tactile sensor for material recognition

Due to the complex working environments, robots need to sense and react to their various interactive surroundings with the help of tactile perception. Material recognition, one of the basic applications of tactile perception, can be achieved by further interpreting and representing the tactile data collected by tactile sensors. Suitable control strategies can be implemented to ensure stable and efficient operation of robots if the contacting materials are accurately recognized. Therefore, in this paper, a soft, deformable, and self-powered tactile sensor based on magnetoelectric materials is developed. Structural design, working principles, and shape optimization of this magnetoelectric tactile sensor are first described. Fabrication and assembly of the magnetoelectric tactile sensor are then introduced. The material recognition experiments including the voltage ratio ranges study, test 1 (velocity change), and test 2 (size and shape change) are performed to validate the effectiveness of the proposed magnetoelectric tactile sensor. The experimental results show that the recognition accuracy is high (around 90% for soft materials and 100% for hard materials) regardless of sizes and shapes of the contacting materials.

Machining distortion control of long beam parts based on optimal design of transition structure

Abstract. In the machining of monolithic components, machining distortion is a severe issue. The presence of initial residual stress is a major contributor to machining distortion. This paper proposes an approach to control the machining distortion of long beam parts by optimizing the workpiece structure before the start of the finishing stage, i.e. the transition structure. The first step is to establish a machining distortion analytical model for long beam parts with an identical cross-section, which is based on reasonable assumptions such as material linear elasticity and ignoring the influence of cutting heat. Then, an optimization model for the cross-section of the transition structure is developed, with the objective function defined as the minimum difference between the predicted distortion of the final part and the transition structure. Finally, a U-shaped beam is designed, followed by numerical simulation and machining experiments for verification. The theoretical maximum distortion of the optimized transition structure and the final part are −0.174 and −0.1782 mm, respectively, with a relative error of 2.9 %. The results of machining experiments and finite-element simulation demonstrate the effectiveness of the proposed model.

A Simulation and Experiment on the Optimization Design of an Air Outlet Structure for an Air-Assisted Sprayer

In response to the issues of low-velocity zones and non-uniform jet velocity distribution in the airflow field of traditional air-assisted orchard sprayers, an arc-shaped air outlet suitable for axial-flow air-assisted systems is designed. This article employs the method of CFD numerical simulation and experimental verification to compare and analyze the internal flow field of the air-assisted system and validates the reliability of the numerical simulation results through calculation error and chi-square test. The wind speed of the cross-section is measured at different distances from the outlet, and the distribution characteristics of the outflow field wind speed before and after the structural optimization of the air-assisted system are compared. The horizontal distribution of fog droplets is collected using a fog collection chamber. The experimental results show that the design of the arc-shaped outlet increases the average wind speed of the annular outlet from 14.95 m/s to 18.20 m/s and reduces the proportion of low-speed area from 20.83% to 0.71%. When the rounded corner radius of the air outlet is 50 mm, optimal parameters are attained. The maximum error between the simulated and experimental values is 9.52%. At a significance level of 0.05, the χ2 value is 0.252, indicating that the simulated values follow the distribution of the actual measurement values. On the cross-sections located at distances of 0.5, 0.75, 1, 1.25, and 1.5 m from the air outlet, the wind speed distribution with no arc-shaped air outlets exhibits a “low left and high right” type, tending to shift towards the right as a whole. Fog droplets also display a drift tendency towards the right side. The wind speed distribution with arc-shaped air outlets shows a symmetric “high in the middle and low on the sides” type. Fog droplets concentrate in the central position. The optimized air-assisted system can reduce the air field’s low-flow area, increase the airflow distribution uniformity, improve the average wind speed at the outlet, and decrease fog droplet drift. This provides a reference for the structural design of air-assisted systems in current orchard sprayers of the same type.

Schrödinger's Red Beyond 65,000Pixel-Per-Inch by Multipolar Interaction in Freeform Meta-Atom through Efficient Neural Optimizer.

Freeform nanostructures have the potential to support complex resonances and their interactions, which are crucial for achieving desired spectral responses. However, the design optimization of such structures is nontrivial and computationally intensive. Furthermore, the current "black box" design approaches for freeform nanostructures often neglect the underlying physics. Here, a hybrid data-efficient neural optimizer for resonant nanostructures by combining a reinforcement learning algorithm and Powell's local optimization technique is presented. As a case study, silicon nanostructures with a highly-saturated red color are designed and experimentally demonstrated. Specifically, color coordinates of (0.677, 0.304) in the International Commission on Illumination (CIE) chromaticity diagram- close to the ideal Schrödinger's red, with polarization independence, high reflectance (>85%), and a large viewing angle (i.e., up to ± 25°) is achieved. The remarkable performance is attributed to underlying generalized multipolar interferences within each nanostructure rather than the collective array effects. Based on that, pixel size down to ≈400nm, corresponding to a printing resolution of 65000 pixels per inch is demonstrated. Moreover, the proposed design model requires only ≈300 iterations to effectively search a thirteen-dimensional (13D) design space - an order of magnitude more efficient than the previously reported approaches. The work significantly extends the free-form optical design toolbox for high-performance flat-optical components and metadevices.

Full-scale resonant bending fatigue testing of casing joints under bending moment load

The quality and reliability of oil casings play a pivotal role in the safety and efficiency of offshore oil and gas exploration. This study conducted research on resonant bending fatigue of 9-5/8-inch casing joints and established a systematic theoretical model for resonant bending fatigue based on the Euler–Bernoulli beam equation. The relationships between parameters affected by frequency and mode shape functions were deduced and solved to analyze the influence of wall thicknesses, length and weights at both ends of the specimen on the natural frequency of the resonant bending fatigue system. A full-scale fatigue test was then designed and conducted to investigate the circumferential stress distribution, reveal the stress amplitude–frequency response characteristics of the specimen, and explore resonance response behaviors under different excitation forces. This was done to establish a method for evaluating the oil casing life and obtain fatigue life characteristic curves of the specimen. A finite element model was employed to analyze the internal stress distribution of the coupling under bending moment load, considering the influence of material properties, thread lead angle and non-linear contact on casing joints. Finally, the fatigue life algorithm was summarized and compared by integrating the stress simulation results with the material properties of the specimen, elucidating the fatigue damage evolution process of casing joints. This research provides a significant engineering reference value for structural design optimization, fatigue testing and life analysis of oil casing threaded joints.

Improved stochastic subset optimization method for structural design optimization

The Stochastic Subset Optimization (SSO) algorithm was proposed for optimal reliability problems that minimizes the probability of system failure over the admissible space for the design parameters. It is based on the simulation of samples of the design parameters from an auxiliary Probability Density Function (PDF) and exploiting the information contained in these samples to identify subregions for the optimal design parameters within the original design space. This paper presents an improved version of SSO, named iSSO to overcome the shortcomings in the SSO. In the improved version, the Voronoi tessellation is implemented to partition the design space into non-overlapping subregions using the pool of samples distributed according to the auxiliary PDF. A double-sort approach is then used to identify the subregions for the optimal design. The iSSO is presented as a generalized design optimization approach primarily tailored for the stochastic structural systems but also adaptable to deterministic systems. Several optimization problems are considered to illustrate the effectiveness and efficiency of the proposed iSSO.