Continuum Structures Research Articles

Statistical Formulation of Background Independence in Manifestly-Covariant Quantum Gravity Theory

The notion of background independence is a distinguished feature that should characterize the conceptual foundation of any physically-acceptable theory of quantum gravity. It states that the structure of the space-time continuum described by classical General Relativity should possess an emergent character, namely, that it should arise from the quantum-dynamical gravitational field. In this paper, the above issue is addressed in the framework of manifestly-covariant quantum gravity theory. Accordingly, a statistical formulation of background independence is provided, consistent with the principle of manifest covariance. In particular, it is shown that the classical background metric tensor determining the geometric properties of space-time can be expressed consistently in terms of a suitable statistical average of the stochastic quantum gravitational field tensor. As an application, a particular realization of background independence is shown to hold for analytical Gaussian solutions of the quantum probability density function.

Topology Optimization of Continuum Structures Based on Binary Hunter-Prey Optimization Algorithm

According to BESO’s principle of binarizing continuous design variables and the excellent performance of the standard HPO algorithm in terms of solving continuous optimization problems, a discrete binary Hunter-prey optimization algorithm is introduced to construct an efficient topology optimization model. It was used to solve the problems that the BESO method of topology optimization has, such as easily falling into the local optimal value and being unable to obtain the optimal topology configuration; the metaheuristic algorithm was able to solve the topology optimization model’s low computational efficiency and could easily produce intermediate elements and unclear boundaries. Firstly, the BHPO algorithm was constructed by discrete binary processing using the s-shape transformation function. Secondly, BHPO-BESO topology optimization theory was established by combining the BHPO algorithm with BESO topology optimization. Using the sensitivity information of the objective function and the updated principle of the meta-heuristic of the BHPO algorithm, a semi-random search for the optimal topology configuration was carried out. Finally, numerical simulation experiments were conducted by using the three typical examples of the cantilever beam, simply supported beam, and clamping beam as optimization objects and the results were compared with the solution results of BESO topology optimization. The experimental results showed that compared with BESO, BHPO-BESO could find the optimal topology configuration with lower compliance and maximum stiffness, and it has higher computational efficiency, which can solve the above problems.

Robust topology optimization of continuum structures with smooth boundaries using moving morphable components

Robust topology optimization of continuum structures with smooth boundaries using moving morphable components

Pencapaian Tugas Perkembangan Remaja Ditinjau dari Kematangan Intelektual di SMP N I Sasak Ranah Pasisia Kabupaten Pasaman Barat

Based on the reality at SMPN 1 Sasak Ranah Pasisia. students who are not satisfied with their grades, and students must think about how so that students can solve these problems and understand what the teacher explained. for example learning in class students do not understand what the teacher explained, the purpose of the research is so that students understand what the teacher explains and students can solve their own problems. This research is a descriptive research. This study has a population of 123 students and a sample of 30 students. Data collection techniques in this study using Random Sampling Techniques. The data analysis technique uses manual processing of ITP results (Development Task Inventory). Based on the research conducted, the results show that the level of developmental tasks is a continuum structure of self-development from simple to complex. In general, the developmental level of elementary school children is between 1 and 4, junior high school aged children between 2 and 5, high school aged children between 3 and 6, and student age levels between 4 and 7.

Effects of climate, spatial and hydrological processes on shaping phytoplankton community structure and β-diversity in an estuary-ocean continuum (Amazon continental shelf, Brazil)

This study investigated the influence of the estuarine plume from the Maranhense Gulf on the phytoplankton community structure and β-diversity. To understand the effects of the regulation mechanisms on shaping phytoplankton community structure and β-diversity along an estuary-ocean continuum in the eastern sector of the Amazon shelf, this study considered spatiotemporal analyses of physical, chemical, and biological variables from May 2019 to June 2020. High temporal environmental heterogeneity was identified in Cumã Bay and significant spatial environmental variability in the estuary-ocean continuum. Based on the thermohaline properties, an estuarine plume was observed alongshore at a distance of approximately 60 km from the coastline. Both phytoplankton community structure and β-diversity varied in time and space. From 189 taxa, thirty-nine indicator species were selected based on their functional traits and indicator value. Skeletonema costatum was considered the best phytoplankton indicator of the estuarine water influence. Turnover was the main component responsible for boosting β-diversity at spatial and temporal scales. The present study was the first performed on an Amazon estuary-ocean continuum which applied diversity metrics (β-diversity) to generate new information about loss of taxon richness and provided important information about spatiotemporal changes in phytoplankton community and environmental heterogeneity.

Τopology Optimization under a Single Displacement Constraint Using a Strain Energy Criterion

Based on a previous concept that has been successfully applied to the sizing optimization of truss and frame structures, this work extends and improves the strain energy criterion in the topology optimization of 2D continuum structures under a single displacement constraint. To make the proposed methodology transparent to other researchers and at the same time meaningful, the numerical value of the displacement constraint was taken to be equal to that obtained through the well-known Solid Isotropic Material with Penalization (SIMP) method under the same boundary conditions and the same external forces. The proposed method is more efficient than the SIMP method while leading to topologies very close to those obtained by the latter.

Data-driven topology optimization (DDTO) for three-dimensional continuum structures

Data-driven topology optimization (DDTO) for three-dimensional continuum structures

Uncertainty-oriented multi-scale topology optimization of coupled thermo-mechanical continuum structures

Multi-scale and multi-physical field topology optimization (TO) design has attracted large of attention, especially in aerospace and mechanical engineering, for the complex loadings and increasing performance requirements. Moreover, the unavoidable uncertainties, such as environment change, load variation, manufacturing tolerance, and elastic modulus fluctuation, exist in both macro- and micro-scale under coupled thermo-mechanical environment, which poses a significant danger for the safety of topological design of multi-scale structure in practical engineering. Therefore, a 2D multi-scale reliability-based topology optimization (MSRBTO) model is constructed to account for the uncertainty behavior of multi-physical TO problems, in which mechanical and thermal loadings are considered simultaneously. In addition, the solid isotropic material with penalization method is adopted at both macro- and micro-scales. Sensitivities of the compliance and temperature constraints with respect to the macro design variables, micro design variables, and random variables are derived simultaneously. Then, a single-loop method is introduced to address the MSRBTO problem to guarantee computational efficiency. Several numerical examples are solved by the developed MSRBTO method and traditional mono-scale RBTO method. The results show that the optimized results of the MSRBTO method show better performance than the mono-scale RBTO method, and the validity and effectiveness of the proposed method are validated.

Robust reliability-based topology optimization for stress-constrained continuum structures using polynomial chaos expansion

Robust reliability-based topology optimization for stress-constrained continuum structures using polynomial chaos expansion

Robust Topology Optimization of Continuum Structures under the Hybrid Uncertainties: A Comparative Study

Due to the inevitable involvement of multisource uncertainties related to the load, material property and geometry in practical engineering designs, robust topology optimization (RTO) has recently attracted increasing attention to account for these uncertain effects. However, the majority of the existing RTO works are concerned with single source uncertainty, and very few studies have considered the multisource (hybrid) uncertainties simultaneously. To this end, a comparative study on the hybrid uncertainties (HU), i.e., material-loading, geometric-loading, material-geometric, and material-geometric-loading uncertainties, for RTO of continuum structures is presented in this paper. A truncated Karhunen-Loeve expansion is adopted for uncertainty representation and a sparse grid collocation method for uncertainty propagation of the objective function and constraints. Effects of the various HU on the compliance and robust design are comprehensively investigated and compared with the RTO models under individual component uncertainty using two continuum benchmarks. An important observation from the results is that the hybrid uncertainty model is a conservative state, and the resulting RTO designs tend towards those with loading uncertainty only.

Design and modelling of an anisotropic continuum robot end-effector for single-port access surgery suturing

Single port access surgery has brought many advantages and new challenges to the field of minimally invasive surgery. In principle, many of these challenges can be addressed through robotics. Continuum robots in particular have seen a surge in interest in recent years for their miniaturisation potential. However, many applications with these robots have been developed for contactless or low-force tasks. This paper tackles several barriers to high-force tasks with continuum robots such as suturing for Open Spina Bifida repair. A novel continuum robot end-effector is proposed. The end-effector is composed of a distal bending segment and hybrid gripper. First, the novel hybrid gripper specifically designed for continuum robots is introduced. The hybrid gripper can function both as a general surgical gripper and as a needle driver while overall keeping the required input force limited. Second, an optimisation of the continuum structure of the distal bending segment is conducted. The objective of this optimisation is to sustain high tip forces – required by the said high-force contact tasks – while keeping deformations acceptable. Third, a quasi-static model that predicts the coupled effect of bending and gripping is derived. This model predicts the deformation of the continuum structure that is induced by the gripping action itself. It could hence be used to compensate for such deformation and establish a stable grip with the otherwise flexible instruments. Finally, experiments are conducted to validate the new designs and the model. The hybrid gripper has a diameter of [Formula: see text] mm, a length of [Formula: see text] mm and can hold securely a needle with a [Formula: see text] N input force, outputting a [Formula: see text] N gripping force. The optimised bending segment is validated for Open Spina Bifida suture: it can bend freely up to 90° and it can support a [Formula: see text] N tip load up to a 35° bending angle. The bending and gripper model error varies between 1% and 14.55%, yielding useful results to predict the shape of the bending segment and potentially compensate for the disturbance created by actuating the gripper.

Explicit Tunnels and Cavities Control Using SIMP and MMA in Structural Topology Optimization

The topology of a 3D continuum structure is usually characterized by the number of independent connected component and holes in the structure, where the holes include tunnels (through holes) and cavities (interior holes). The number of these features can be measured by the topological invariants of the structure (e.g., Betti numbers and Euler characteristic). The quantitative control of structural topology is important in topology optimization design because of various considerations, including design freedom, manufacturability, structural performance, and manufacturing costs. However, effective control of the structural topology during the topology optimization process remains a challenge, particularly to control the structural tunnels. To simplify the problem, only the number of tunnels (NT) and cavities (NC) of the structure are controlled in this paper. To solve the aforementioned problems, this study calculates the characteristic information of the tunnels and cavities by introducing the tunnel loops of homology theory and fire-burning method (FBM), while proposing a method for quantitative control of the 3D structural tunnels and cavities within the framework of the solid isotropic material with penalty (SIMP) interpolation of the design variable and method of moving asymptotes (MMA) optimization algorithm. The method achieves unilateral constraints over the structural tunnels and cavities by establishing explicit relationships between the element design variables in the structural topology optimization and NT as well as NC in the structure. Numerical examples demonstrate that the proposed method can effectively control the tunnels and cavities of an optimized structure.

Kinematics analysis, motion planning and control of the continuum manipulator in minimally invasive surgery

Due to its unique dexterity, flexibility, and safety, continuum manipulator is more suitable for the detection, diagnosis, and maintenance in complex, narrow, and unstructured constrained environment. This paper presented a new cable-driven flexible endoscope robot for diagnosis and treatment, and its kinematics model, motion planning and control performance were systematically studied. First of all, the kinematics model of the proposed continuum manipulator was established by D-H method, and the workspace was analyzed based on the improved Monte Carlo method. In order to make the multi-segment continuum robot safety and quickly intervene into the target area, a motion planning method was proposed by using the ridge method under the constraints of the navigation path. In other words, the minimum distance between the beginning point, middle point and distal point of the robot and the theoretical trajectory points was taken as the optimization function, the configuration parameters of each bending segment were solved by inverse recursion to control the robot move along the pre-given navigation path. Then, the motion planning simulations of the plane path and spatial path were carried out to verify the proposed motion planning method. Finally, the experimental prototype of the proposed endoscopic robot was set up to verify the feasibility of the proposed continuum structure and the correctness of the established model, which can be used as a feedback control and navigation reference.

Nosogenic psychosomatic disorders in patients with skin diseases

Development of a clinical typology of nosogenic psychosomatic disorders in patients with skin diseases. The study was carried out in the interclinical psychosomatic department of the Clinical Center and the Clinic of Skin and Venereal Diseases named after. V.A. Rakhmanov Sechenov University in 2007 to 2022. Nine hundred and forty-two patients (253 males, 689 females, average age 37.3±12.4 years) with nosogenic psychosomatic disorders in chronic dermatoses, including ichen planus (n=143), psoriasis (n=137), atopic dermatitis (n=132), acne (n=118), rosacea (n=115), eczema n=10), seborrheic dermatitis (n=88), vitiligo (n=52), pemphigus (n=48), were studied. Index of clinical symptoms (ICS); the Dermatology Quality of Life Index (DQLI); itching severity questionnaire - Behavioral rating scores (BRS); the Hospital Anxiety and Depression Scale (HADS) and statistical methods were used. In patients with chronic dermatoses, nosogenic psychosomatic disorders were diagnosed according to ICD-10 criteria within adaptation disorders [F43.8] (n=465; 49.3%); hypochondriacal disorder [F45.2] (n=235; 24.9%); constitutionally determined and acquired (hypochondriac development) personality disorders [F60] (n=118; 12.5%); schizotypal disorder [F21] (n=65; 6.9%); recurrent depressive disorder [F33] (n=59; 6.2%). A typological model of nosogenic disorders in dermatology has been developed: hypochondriacal nosogenies in severe clinical forms of dermatosis (pemphigus, psoriasis, lichen planus, atopic dermatitis, eczema) and dysmorphic nosogenies in objectively mild, but cosmetically significant forms of dermatosis (acne, rosacea, seborrheic dermatitis, vitiligo). When analyzing socio-demographic and psychometric indicators, significant differences were revealed between the selected groups (p<0.001). In turn, the selected groups of nosogenic disorders demonstrate significant clinical heterogeneity and include various types of nosogenies that form a unique palette of the nosogenic spectrum in the structure of an extensive psychodermatological continuum. Along with the severity of the skin process, the dominant role in the formation of the clinical picture of nosogeny, including cases of paradoxical dissociation of the quality of life with the severity of dermatosis, amplification and somatization of itching, has a premorbid personality structure and somatoperceptive accentuation of the patient, as well as the presence of a comorbid mental disorder. The typology of nosogenic psychosomatic disorders in patients with skin diseases requires consideration of both the psychopathological structure of the disorders under discussion and the severity/clinical features of the skin process.

Topological design of continuum structures with global stress constraints considering self-weight loads

Topological design of continuum structures with global stress constraints considering self-weight loads

Topology Optimization of Strength-Safe Continuum Structures Considering Random Damage

Spacecraft in the aerospace field and military equipment in the military field are at risk of being impacted by external objects, which can cause local damage to the structure. The randomness of local damage is a new challenge for structural design, and it is essential to take random damage into account in the conceptual design phase for the purpose of improving structure’s resistance to external shocks. In this article, a random damaged structure is assumed to have damages of the same size and shape at random locations, and the random damage is considered as multiple damage conditions of the structure. In order to improve the randomness and comprehensiveness of the multiple damage conditions, the stacking strategy is used to generate the distribution of the damage area. Following this strategy, the topology optimization design of the random damaged structure, which is to minimize the weight of the structure with a constraint on the stress of the structure under multiple damage conditions, is formulated based on the independent continuous mapping (ICM) method. The dual sequence quadratic programming (DSQP) algorithm combined with the stress globalization method is adopted to solve the optimization problem. The numerical examples demonstrate the effectiveness and applicability of the proposed method in the topology optimization of strength-safe continuum structures.

Algorithm Research Based on the PDE Sensitivity Filter

The PDE sensitivity filter can eliminate the checkerboard patterns and numerical instability existing in the topology optimization results of continuum structures, and the essence of the PDE sensitivity filter is the Helmholtz partial differential equation with Neumann boundary conditions. To solve the large-scale PDE sensitivity filter problem, the conjugate gradient algorithm, the multigrid algorithm and the multigrid preconditioned conjugate gradient algorithm were used to solve the algebraic equations obtained by finite element analysis, and the effects of accuracy, filter radius and grid numbers on the efficiency of topology optimization were studied. The results show that, compared with the conjugate gradient algorithm and the multi-grid algorithm, the multi-grid preconditioned conjugate gradient algorithm has the least number of iterations and the shortest running time, which greatly improves the efficiency of topology optimization.

A Smooth Bidirectional Evolutionary Structural Optimization of Vibrational Structures for Natural Frequency and Dynamic Compliance

A smooth bidirectional evolutionary structural optimization (SBESO), as a bidirectional version of SESO is proposed to solve the topological optimization of vibrating continuum structures for natural frequencies and dynamic compliance under the transient load. A weighted function is introduced to regulate the mass and stiffness matrix of an element, which has the inefficient element gradually removed from the design domain as if it were undergoing damage. Aiming at maximizing the natural frequency of a structure, the frequency optimization formulation is proposed using the SBESO technique. The effects of various weight functions including constant, linear and sine functions on structural optimization are compared. With the equivalent static load (ESL) method, the dynamic stiffness optimization of a structure is formulated by the SBESO technique. Numerical examples show that compared with the classic BESO method, the SBESO method can efficiently suppress the excessive element deletion by adjusting the element deletion rate and weight function. It is also found that the proposed SBESO technique can obtain an efficient configuration and smooth boundary and demonstrate the advantages over the classic BESO technique.

Design and control of a new electrostrictive polymer based continuum actuator for endoscopic robot

Minimally Invasive Surgery (MIS) consists of the insertion of a flexible endoscope into the patient body through natural orifices. Over the past few decades, the growing interest in microelectromechanical systems (MEMS) has paved the way for ubiquitous miniaturized integrated sensors and actuators in medical endoscopy. Nowadays, recent advances in materials have opened a promising way to fulfill the surgical requirements and size constraint for the development of smart continuum structures. Among smart materials, electroactive polymers (EAPs) exhibit exceptionally large, fast, repeatable, and reversible motions while perfectly meeting the requirements of micro-integration. However the high applied voltage required for the actuation is not compatible with in vivo medical application. To overcome these issues, a multilayered concept has been proposed. In this work a relaxor ferroelectric electrostrictive polymer is studied for its large electromechanical strain. A wide range of parameters involved in the active material has led us to the development of a finite element model on Abaqus to guide the experimental development. Then, to control this smart endoscopic robot a kinematic and a dynamic models have been built. To test and validate these models a Co-simulation procedure has been developed. This procedure coupled Abaqus and Matlab-Simulink allowing testing proposed control algorithms.

Novel multi-objective topology optimization method for stiffness and stress of continuum structures

In this paper, a topology optimization method combining Bi-directional Evolutionary Structural Optimization (BESO) and Fast Non-dominated Sorting Genetic Algorithm II (NSGA-II) is proposed, which is called BESO-NSGA-II. To effectively fuse the two algorithms, a semi-random double-penalized crossover and mutation operator is developed. The proposed algorithm extends the traditional single-objective optimization to a double objective optimization problem, and investigates the influence of the stress norm parameters on the optimization results. To verify the effectiveness of the new method, several examples of 2D structural stiffness and stress optimization are given. At the same time, the optimization design of each model was repeated six times to demonstrate the ability of the new method to converge to a solution. Compared with BESO, BESO-NSGA-II can effectively realize the double objective optimization of stiffness and stress, and eliminate the stress concentration phenomenon on the premise of ensuring that the structure has greater stiffness.