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The chaos game optimization (CGO) algorithm is a recently developed metaheuristic inspired by chaos theory and fractal configurations. In CGO, possible optimal solutions are defined as seeds and the searching process is performed using some simple equations. In this paper, weighted chaos game optimization (WCGO) is proposed and implemented to optimize engineering structures with dynamic constraints. In this method, an inertia weight coefficient based on the minimum and maximum values ​​of the objective function is introduced to create a better balance between exploration and exploitation during the searching process. By applying the inertia weight coefficient to the seeds, their positions can be controlled accurately. To evaluate the performance of WCGO, a wide range of mathematical benchmark functions, as well as several structural design optimization problems under dynamic constraints, are computationally investigated using the new algorithm. In order to demonstrate the efficiency and robustness of WCGO, its results have been compared with those obtained by some conventional methods from the literature. Additionally, a Friedman rank test is conducted to perform a statistical study on the performance of the considered algorithms. The findings indicate that WCGO performs better than its rivals in solving these structural optimization problems with dynamic constraints.

Origami tessellations can be folded from a given planar pattern into a three-dimensional object with specific geometric properties, inspiring developments in various fields of science and engineering such as deployable structures, energy absorption devices, reconfigurable robots, and metamaterials. However, the range of existing origami patterns with functional properties such as flat-foldability is rather scant, as analytical solutions to constraint equations arising in the design process are generally highly complicated. In this paper, we tackle the challenging problem of automated design of scalene-faceted flat-foldable origami tessellations using an efficient metaheuristic algorithm. To this end, this study establishes constraint curves based on compatibility conditions for all six-fold (i.e., degree-6) vertices. Subsequently, a graphical method and a particle swarm optimization (PSO) method are adopted to produce optimal origami patterns. Moreover, mountain-valley assignments for the obtained geometric designs are determined using a computational approach based on mixed-integer linear programming. It turns out that the flat-foldable internal vertices of each C2-symmetric unit fragment (UF) exist as C2-symmetric pairs about the centroid of the UF. Furthermore, numerical experiments are carried out to examine the feasibility and compare the accuracy, computational efficiency, and global convergence of the proposed methods. The results of numerical experiments demonstrated that, in comparison with the graphical method, the proposed PSO method has not only a higher accuracy but also a significantly lower computational cost, enabling us to develop an intelligent computational platform to efficiently design scalene-faceted flat-foldable origami tessellations.

Origami has attracted tremendous attention in recent years owing to its capability of inspiring and enabling the design and development of reconfigurable structures and mechanisms for applications in various fields such as robotics and biomedical engineering. The vast majority of origami structures are folded starting from an initial two-dimensional crease pattern. However, in general, the planar configuration of such a crease pattern is in a singular state when the origami starts to fold. Such a singular state results in different motion possibilities of rigid or non-rigid folding. Thus, planar origami patterns cannot act as reliable initial configurations for further kinematic or structural analyses. To avoid the singularities of planar states and achieve reliable structural configurations during folding, we introduce a nonlinear prediction–correction method and present a spatial form-finding algorithm for four-fold origami. In this approach, first, initial nodal displacements are predicted based on the mountain-valley assignments of the given origami pattern, which are applied to vertices to form an initial spatial and defective origami model. Subsequently, corrections of nodal displacements are iteratively performed on the defective model until a satisfactory nonplanar configuration is obtained. Numerical experiments demonstrate the performance of the proposed algorithm in the form-finding of both trivial and non-trivial four-fold origami tessellations. The obtained configurations can be effectively utilized for further kinematic and structural analyses. Additionally, it has been verified that corrected and nonplanar configurations are superior to initial configurations in terms of matrix distribution and structural stiffness.

PurposeIn this paper, the authors aim to examine and comparatively evaluate a recently-developed metaheuristic called crystal structure algorithm (CryStAl) – which is inspired by the symmetries in the internal structure of crystalline solids – in solving engineering mechanics and design problems.Design/methodology/approachA total number of 20 benchmark mathematical functions are employed as test functions to evaluate the overall performance of the proposed method in handling various functions. Moreover, different classical and modern metaheuristic algorithms are selected from the optimization literature for a comparative evaluation of the performance of the proposed approach. Furthermore, five well-known mechanical design examples are utilized to examine the capability of the proposed method in dealing with challenging optimization problems.FindingsThe results of this study indicated that, in most cases, CryStAl produced more accurate outputs when compared to the other metaheuristics examined as competitors.Research limitations/implicationsThis paper can provide motivation and justification for the application of CryStAl to solve more complex problems in engineering design and mechanics, as well as in other branches of engineering.Originality/valueCryStAl is one of the newest metaheuristic algorithms, the mathematical details of which were recently introduced and published. This is the first time that this algorithm is applied to solving engineering mechanics and design problems.

Shallow parabolic arches have been commonly applied in engineering structures, whereas their structural behavior has not been fully investigated due to significant geometric nonlinearity. In general, a shallow parabolic arch has a tendency to suddenly buckle when it is subjected to a step load. An analytical study and a numerical simulation on the nonlinear in-plane buckling behavior of shallow parabolic arches with tension cables and pin-joints are presented. To establish nonlinear buckling equilibrium equations for shallow parabolic arches, motion equations are evaluated using Hamilton’s principle. Then, the law of conservation of energy is adopted for unstable equilibrium paths, to establish the criteria for the nonlinear buckling of these shallow arches. Closed-form solutions for the lower and upper nonlinear buckling loads of a shallow arch under step loads are obtained. The analytical solutions show that the modified slenderness ratio is an important parameter affecting buckling. Nonlinear buckling under step loads or static snap-through buckling with symmetry is impossible when the slenderness ratio is out of the given interval. Moreover, nonlinear buckling under step loads is sensitive to the stiffness of the tension cables. In comparison with an equivalent distributed step load, a central concentrated load is much more likely to induce nonlinear buckling.

The role of artificial intelligence (AI) in facilitating the real-time processing of data is revolutionising the future of healthcare through mobile diagnostics, remote monitoring devices, and wearable technology products. The rise in digital wearables for remote healthcare is evolving at an increasing pace towards patient-centred and personalised care with connected patients. This transformation is creating new opportunities for designers to increase patients' participation and sustain their engagement in remote healthcare. In this paper, the authors have investigated the role of gender in aesthetic design in the context of digital health wearables to enhance user engagement and interaction. The investigations were conducted through participatory design sessions and showed a constructive relationship between aesthetic preferences and understanding the influence of gender as a means of facilitating user engagement with digital health wearables. This paper presents a novel user response model that leads to suggestions for future work, including research in the areas of gender awareness in aesthetics to move beyond traditional, stereotypical, and pre-identified gendered characteristics related to femininity and masculinity. The findings conclude with a path forwards for design research to promote gender awareness in aesthetic design for the realisation of healthcare wearables of the future.

Origami structures have been widely used in various engineering fields due to their desirable properties such as geometric transformability and high specific energy absorption. Based on the Kresling origami pattern, this study proposes a type of thin-walled origami tube the structural configuration of which is found by a mixed-integer linear programming model. Using finite element analysis, a reasonable configuration of a thin-walled tube with the Kresling pattern is firstly analyzed. Then, the influences of different material properties, the rotation angle of the upper and lower sections of the tube unit, and cross-sectional shapes on the energy absorption behavior of the thin-walled tubes under axial compression are evaluated. The results show that the symmetric thin-walled tube with the Kresling pattern is a reasonable choice for energy absorption purposes. Compared with thin-walled prismatic tubes, the thin-walled tube with the Kresling pattern substantially reduces the initial peak force and the average crushing force, without significantly reducing its energy absorption capacity; moreover, it enters the plastic energy dissipation stage ahead of time, giving it a superior energy absorption performance. Besides, the material properties, rotation angle, and cross-sectional shape have considerable influences on its energy absorption performance. The results provide a basis for the application of the Kresling origami pattern in the design of thin-walled energy-absorbingstructures.

Fusion–Fission Optimization (FuFiO) is proposed as a new metaheuristic algorithm that simulates the tendency of nuclei to increase their binding energy and achieve higher levels of stability. In this algorithm, nuclei are divided into two groups, namely stable and unstable. Each nucleus can interact with other nuclei using three different types of nuclear reactions, including fusion, fission, and β-decay. These reactions establish the stabilization process of unstable nuclei through which they gradually turn into stable nuclei. A set of 120 mathematical benchmark test functions are selected to evaluate the performance of the proposed algorithm. The results of the FuFiO algorithm and its related non-parametric statistical tests are compared with those of other metaheuristic algorithms to make a valid judgment. Furthermore, as some highly-complicated problems, the test functions of two recent Competitions on Evolutionary Computation, namely CEC-2017 and CEC-2019, are solved and analyzed. The obtained results show that the FuFiO algorithm is superior to the other metaheuristic algorithms in most of the examined cases.

We have analyzed the physical mechanisms responsible for the formation of an ordered sequence of nanoclusters synthesized on a nanowire in the diffusion mode of deposition of free atoms. The result...

In many optimization problems, the main goal is to improve a single performance index in which a minimum or maximum value of this index fully reflects the quality of the response obtained from a system. However, in some cases, it is impossible to rely solely on a single index, so a multi-objective optimization problem with multiple performance indicators is considered where the values of all of them should be optimized simultaneously. The mentioned process requires a multi-objective optimization algorithm that can deal with the complexity of problems with simultaneous indexes. This paper presents the multi-objective version of a recently proposed metaheuristic algorithm called Crystal Structure Algorithm (CryStAl) which was inspired by the principles underlying the formation crystal structures. For the performance evaluation of this algorithm which is called MOCryStAl, the benchmark problems of the Completions on Evolutionary Computation (CEC) on multi-objective optimization, called CEC-09, are utilized. Some real-world engineering design problems are used to evaluate the efficiency of the proposed approach. The results demonstrate that the proposed methods can provide excellent results in dealing with the considered multi-objective problems.

Based on the Monte Carlo kinetic method, we investigated the formation mechanisms of periodical modulations arising along the length of one-dimensional structures. The evolution of initially cylindrical nanowires/slabs at temperatures lower than their respective melting temperatures can result either in breakup into single nanoclusters or in the formation of stable states with pronounced modulations of cross section. Such configurations, observed in a number of experiments, are excited at wavelengths that are below the critical value for the development of classical Rayleigh instability. We show that the modulation excited in the subcritical mode corresponds to the appearance of roughening transition on the quasi-one-dimensional surface of nanowires/slabs. Since the arise of roughening transition is possible only on certain facets of metals with a given crystal structure, the short-wavelength modulations of one-dimensional systems, as shown in our work, can be realized (i) with the proper orientation of the nanowire/slab axis providing spontaneous appearance of roughening transition on its lateral surface, (ii) by the method of activating the surface diffusion of atoms by external impact (irradiation with an electron beam or contact with a cold plasma), which stimulates roughening transition without significant heating of the nanowire. The results obtained for the cases of BCC and FCC lattices can be used in the controlled synthesis of ordered one-dimensional structures for use in optoelectronics and in ultra-large-scale integrated circuits.

Tunnels, as highly cost-demanding infrastructures which facilitate the transportation of people and goods, have been a target of terrorist attacks within the past few decades. The significance of the destructive impact of explosives on these structures has resulted in research on the development of blast-resistant design approaches. In this paper, water curtains are proposed as a blast-resistant system due to the established performance of water against explosives in free fields in previous studies as well as its capability to mitigate the potential incoming fire after an explosion. A parametric study was conducted for this purpose, considering the effects of curtain thickness, the distance of the curtain from the tunnel opening, and the amount of TNT charge. Accordingly, fifty-two finite element (FE) models were created in the FE package ABAQUS to investigate the performance of a water wall in a typical tunnel through the Eulerian approach to simulation. The water curtains had four different thicknesses and were located at three different distances from the reference point. TNT explosive charges were placed at the tunnel opening with four different masses. The thicker walls nearer to the tunnel opening were found to be more effective. However, the peak pressure reduction in all charges was in a desirable range of 53 to 80%. The parametric study also illustrated that the peak pressures were more sensitive to wall thickness rather than TNT charges mass and the wall distance from the explosives. We anticipate this preliminary study to be a starting point for the further development of the concept of water curtains for blast mitigation.

A tensegrity structure may undergo large deformations under external loads, resulting in significant impact on its mechanical properties. Therefore, the nodal flexibility analysis of tensegrity structures, that is, analyzing the sensitivity of nodal displacements to external loads and the evaluation of critical nodes, is important in the structural design of tensegrities. Here, we present a numerical method for the symmetry-adapted flexibility analysis and kinematic indeterminacy of tensegrity structures using orbits of nodes and the Moore–Penrose inverse of involved matrices. To evaluate the contribution of each node to the total kinematic indeterminacy of a tensegrity structure, the distributed kinematic indeterminacies associated with the nodes of different orbits are independently computed. A flexibility ellipsoid is introduced to visually characterize the nodal flexibility of tensegrity structures. Several examples of tensegrities with different symmetries are presented to demonstrate the efficiency of the presented method. This method can be applied to the design and analysis of tensegrity structures under external loads, where flexibility ellipsoids are expected to be full and similar and each node is expected to have proper sensitivity to the external loads along different directions.

With progressive advances in the synthesis, characterization, and commercialization of nanoparticles and nanomaterials, these modern engineered materials are becoming an ingredient of innovative structural materials for various applications in civil and construction engineering. In this research, MgO nanoparticles were systematically added to normal concrete samples in order to investigate the effect of these nanomaterials on the durability of the samples under freeze and thaw conditions. The compressive and tensile strengths as well as the permeability of concrete samples containing nanoparticles were measured and compared with the corresponding values of control samples without nanoparticles. The curing time of the concrete samples, the amount of nanoparticles, and the water-cement ratios (w/c) were the variables of the experiments. Moreover, data clustering and the Charged System Search (CSS) algorithm were utilized as the numerical analysis and optimization methods. The regression analysis before clustering and after clustering proved the process of clustering is a prerequisite of regression analysis. Furthermore, the CSS optimization method showed that the optimum amount of nano MgO is 1% of the weight of cement, which can increase the compressive strength of concrete by 9.12% more than plain samples over 34 days.

Functional origami tessellations have certain geometric or physical properties - such as flat-foldability and rigid-foldability - which make them of particular interest for a broad range of applications in science, engineering, and architecture. While some simple variations of certain functional origami tessellations can be designed trivially, a systematic symmetry-reduction scheme is proved to be productive for the computational generation of more complex, non-trivial variations. Such a scheme has been previously applied to the developable double corrugation (DDC) surface, widely known as the Miura-ori, resulting in the development of novel crystalline derivatives, the symmetry groups of which are subgroups of the parent pattern. Computational algorithms can search for and find flat-foldable solutions for a large number of derivatives of the DDC surface, but fail to find solutions for all of them. In this paper, we exploit the symmetry reduction scheme along with classical plane geometry to analytically demonstrate why some crystallographic derivatives of this pattern do not exist. To this end, by applying the local flat-foldability condition at the vertices of different orbits associated with each tessellation, we show that such patterns are never flat-foldable, regardless of the geometric specifications of their constituting quadrilateral facets. In particular, we prove that two-tile DDC surfaces composed of glide-reflected irregular quadrilaterals are intrinsically non-flat-foldable, resulted from geometric incompatibilities between the properties of certain unit cells and the local flat-foldability condition.

Traditional origami design is generally based on designers’ artistic intuition and skills, mathematical calculations, and experimentations, which can involve challenges for crease patterns with a large number of vertices. To develop novel origami structures for engineering applications, systematic and easy-to-implement approaches capable of generating diverse origami patterns are desired, without requiring extensive artistic skills and experience in origami mathematics. Here, we present a computational method for automatically assigning mountain-valley fold lines to given geometric configurations of origami structures. This method is based upon a geometric-graph-theoretic representation approach combined with a graph-theoretic cycle detection algorithm, taking the subgraphs of a given structure as inputs. Then, a mixed-integer linear programming (MILP) model is established to find flat-foldable origami patterns under given constraints on the local flat-foldability and degree of vertices, leading to the identification of crease lines associated with local minimum angles. Numerical examples are presented to demonstrate the performance of the proposed approach for a range of origami structures with degree-4 or -6 vertices represented by their corresponding subgraphs.

A kinetic Monte Carlo approach is applied to study physical mechanisms responsible for the breakup of nanowires with the diamond cubic crystal structure into a chain of nanoparticles discovered in preceding experiments on Silicon nanowires. We show that this process is based on the well-known mechanism of roughening transition, which specifically manifests itself in quasi-one-dimensional systems/nanowires with a pronounced anisotropy of the surface energy density. Depending on the temperature and orientation of the nanowire relative to its internal crystal structure, the wavelengths of substantial cross-sectional modulations exceed its initial radius by 4 to 18 times. For certain orientations, a straight nanowire at the initial stage of evolution forms a serpentine/helical structure. The scenarios of the stage of nanowire ruptures into single nanoclusters are also diverse: either each spindle-shaped region of the nanowire transforms into a separate drop (by long-wave surface perturbations), or the adjacent short-scale beads absorb each other due to the Ostwald ripening effect, which can be accompanied by the formation of long-lived many-body dumbbells. The discovered features of the dynamics of quasi-onedimensional systems expand our conceptions of the physical mechanisms involved in the breakup of nanowires (presented by Nichols and Mullins as a classical model for such instabilities) which could be useful in applications based on chains of ordered nanoparticles., Comment: 38 pages, 15 figures, 7 video

Flat-foldable origami tessellations are a rich source of inspiration in the design of transformable structures and mechanical metamaterials. Among all such tessellations, the developable double corrugation (DDC) surface, popularly known as the Miura-ori, is perhaps the most ubiquitous origami pattern in science, engineering, and architectural design. Origami artists, designers, and researchers in various fields of science and engineering have proposed a range of symmetric variations for this pattern. While designing many such derivatives is straightforward, some of them present considerable geometric or crystallographic challenges. In general, the problem of finding flat-foldable derivatives for a given origami tessellation is more challenging for less symmetric descendants. This paper studies the existence and design of the least symmetric derivative of the Miura fold pattern with minimal unit cell enlargement in the longitudinal direction. The course of this study raises a fundamental problem in the flat-foldability of quadrilateral-shaped flat sheets on fold lines through their vertices. An analytical solution to this general problem is presented along with solutions for the special cases of convex quadrilaterals. Keywords: Origami design and engineering, Symmetry, Tessellations, Flat-foldability, Conics, Cubics

Applications of aerial robots are progressively expanding into complex urban and natural environments. Despite remarkable advancements in the field, robotic rotorcraft is still drastically limited by the environment in which they operate. Obstacle detection and avoidance systems have functionality limitations and substantially add to the computational complexity of the onboard equipment of flying vehicles. Furthermore, they often cannot identify difficult-to-detect obstacles such as windows and wires. Robustness to physical contact with the environment is essential to mitigate these limitations and continue mission completion. However, many current mechanical impact protection concepts are either not sufficiently effective or too heavy and cumbersome, severely limiting the flight time and the capability of flying in constrained and narrow spaces. Therefore, novel impact protection systems are needed to enable flying robots to navigate in confined or heavily cluttered environments easily, safely, and efficiently while minimizing the performance penalty caused by the protection method. Here, we report the development of a protection system for robotic rotorcraft consisting of a free-to-spin circular protector that is able to decouple impact yawing moments from the vehicle, combined with a cyclic origami impact cushion capable of reducing the peak impact force experienced by the vehicle. Experimental results using a sensor-equipped miniature quadrotor demonstrated the impact resilience effectiveness of the Rotary Origami Protective System (Rotorigami) for a variety of collision scenarios. We anticipate this work to be a starting point for the exploitation of origami structures in the passive or active impact protection of robotic vehicles.

The Miura fold pattern, or the Miura-ori, is a flat-foldable origami tessellation which has been applied to the folding of deployable structures for various engineering and architectural applications. In recent years, researchers have proposed systematic (see, e.g., [1] or [2]), and also free-form [3], variations on the Miura pattern. This paper develops a geometric framework for the symmetric generalisation of the Miura-ori while preserving the ‘stacking while folding’ behaviour of the pattern. We present a number of novel concepts and definitions which help us apply systematic variations on the original pattern. We study the Miura crease pattern as a pmg wallpaper pattern which is one of the seventeen distinct wallpaper groups. We reduce the symmetry of the Miura-ori to obtain new patterns while preserving the flat-foldability condition at each node. We conclude that we are able to use the Miura-ori, which is a globally planar pattern in its partially folded states, to systematically design either ‘globally planar’ or ‘globally curved’ patterns, through appropriate design variations on the original pattern.

This is the peer reviewed version of the following article:Gorshkov, V.N., Sareh, P., Tereshchuk, V.V. and Soleiman‐Fallah, A. (2019), Dynamics of Anisotropic Break‐Up in Nanowires of FCC Lattice Structure. Adv. Theory Simul., 2: 1900118., which has been published in final form at https://doi.org/10.1002/adts.201900118. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions

The Miura fold pattern, or the Miura-ori, is a flat-foldable origami tessellation with a wide range of engineering applications. In particular, the Miura-ori has been applied to the folding of deployable structures for various architectural applications, e.g. folding roofs and shelters. In recent years, researchers have proposed variations on the Miura-ori which change both geometry and functionality of the pattern.

A new exhibition surveys five centuries of robotic invention

The Miura fold pattern, or the Miura-ori, is a flat-foldable origami pattern with various applications in engineering and architecture. In addition to free-form variations, scholars have proposed a number of symmetric derivatives for this classic fold pattern over recent years. In a previous work, the authors of this paper studied isomorphic variations on the Miura-ori which led to the development of an 'isomorphic family' for this fold pattern. In this paper, we study non-isomorphic variations on the Miura-ori in order to develop a 'non-isomorphic family' for this pattern. Again we start with the Miura-ori, but reduce the symmetry by migrating from the original symmetry group to its subgroups, which may also include the enlargement of its unit cell. We systematically design and classify the non-isomorphic symmetric descendants of the Miura-ori which are either globally planar, or globally curved, flat-foldable tessellations.