Design Of Adaptive Structures Research Articles

Promoting sustainability in 3D printed sand casting through adaptive sand mold structures

The use of 3D printed sand molds offers a high degree of flexibility in structural design and satisfying customer requirements. The optimization and adjustment of the structure of sand mold module with the required functionality helps to maximize the application potential of binder jet 3D printing technology. In this study, an adaptive sand mold structure design method was proposed to meet the sustainable requirements of 3D printed sand casting. Firstly, the functional modular and module clustering of the sand mold is carried out and then each module is adaptive structure design, to reduce the carbon emission and cost of the 3D printed casting process. Therefore, taking the small casting furnace cover and medium-sized cast engine block as examples, the life cycle framework of the 3D printed sand casting process is established, and the sustainable advantages of the adaptive structure method are explored through the calculation and analysis of carbon emission and cost models. The results show that the adaptive structure method reduces the carbon emissions of the two castings by 9.2% and 11.9%, respectively, and the cost of two castings by 6.7% and 11.1%, respectively. This approach provides more sustainable design ideas for 3D printed sand casting and 3D printed sand mass production.

Electronic thygmonasty model in Mimosa pudica biomimetic robot

Direct contact of random objects from the open environment to the panel surface of an electronic device may reduce the work efficiency and cause permanent damage. However, there is a possible way to solve this problem, notably by implementing an adaptive structure design inspired by plants. The Mimosa pudica plant provides several interesting information on its adaptability. Various studies have been conducted on the electrical properties of its organs explaining the phytoactuator and phytosensor cells that function within it. We combined the use of sensors, actuators, and synthetic excitable tissue as the first robot model purposed to mimic the behavior of the M. pudica plant. The Computer vision method was used to measure leaf angular movement and collected it as plant behavior data based on the mechanical stimulus experiment. The Robot structure has eight arms equipped with sensors, servo motors, and microcontrollers that are operated with two activation system models approach. The first model could imitate the stimulus process received by electronic circuits that generate action potential signals with a maximum voltage of 4.71–5.02 V and a minimum voltage of −5.33 to −3.45 V that propagated from node to node. The second model involves a trained artificial neural network model with a supervised learning pattern that provides 100% accuracy when choosing movement output based on the given combination. This robot imitates the M. pudica’s intelligent sensing capabilities and its ability to change the structure shape based on the thygmonasty experiments data which could provide an overview of how plants process information and perform hazard avoidance actions efficiently. Future applications for the technology inspired by the plant’s self-defense mechanisms are adaptive intelligent structures that can protect against harmful conditions, particle contamination, and adjusting panel structure to search for desired environmental parameters.

Design of adaptive structures through energy minimization: extension to tensegrity

This paper gives a new formulation to design adaptive structures through total energy optimization (TEO). This methodology enables the design of truss as well as tensegrity configurations that are equipped with linear actuators to counteract the effect of loading through active control. The design criterion is whole-life energy minimization which comprises an embodied part in the material and an operational part for structural adaptation during service. The embodied energy is minimized through simultaneous optimization of element sizing and actuator placement, which is formulated as a mixed-integer nonlinear programming problem. Optimization variables include element cross-sectional areas, actuator positions, element forces, and node displacements. For tensegrity configurations, the actuators are not only employed to counteract the effect of loading but also to apply appropriate prestress which is included in the optimization variables. Actuator commands during service are obtained through minimization of the operational energy that is required to control the state of the structure within required limits, which is formulated as a nonlinear programming problem. Embodied and operational energy minimization problems are nested within a univariate optimization process that minimizes the structure’s whole-life energy (embodied + operational). TEO has been applied to design a roof and a high-rise adaptive tensegrity structure. The adaptive tensegrity solutions are benchmarked with equivalent passive tensegrity as well as adaptive truss solutions, which are also designed through TEO. Results have shown that since cables can be kept in tension through active control, adaptive tensegrity structures require low prestress, which in turn reduces mass, embodied energy, and construction costs compared to passive tensegrity structures. However, while adaptive truss solutions achieve significant mass and energy savings compared to passive solutions, adaptive tensegrity solutions are not efficient configurations in whole-life energy cost terms. Since cable elements must be kept in tension, significant operational energy is required to maintain stable equilibrium for adaptation to loading. Generally, adaptive tensegrity solutions are not as efficient as their equivalent adaptive truss configurations in mass and energy cost terms.

Constrained motion design with distinct actuators and motion stabilization

AbstractThe design of adaptive structures is one method to improve sustainability of buildings. Adaptive structures are able to adapt to different loading and environmental conditions or to changing requirements by either small or large shape changes. In the latter case, also the mechanics and properties of the deformation process play a role for the structure's energy efficiency. The method of variational motion design, previously developed in the group of the authors, allows to identify deformation paths between two given geometrical configurations that are optimal with respect to a defined quality function. In a preliminary, academic setting this method assumes that every single degree of freedom is accessible to arbitrary external actuation forces that realize the optimized motion. These (nodal) forces can be recovered a posteriori. The present contribution deals with an extension of the method of motion design by the constraint that the motion is to be realized by a predefined set of actuation forces. These can be either external forces or prescribed length chances of discrete, internal actuator elements. As an additional constraint, static stability of each intermediate configuration during the motion is taken into account. It can be accomplished by enforcing a positive determinant of the stiffness matrix.

Optimal Design of Adaptive Structures vs. Optimal Adaption of Structural Design

Taking advantage of adaptivity in the field of civil engineering is an ongoing research topic. Integration of adaptive elements in the load-bearing structure is already well established in many other engineering fields. First investigations promise large material saving potentials also in the field of civil engineering, especially when it comes to high-rise buildings or wide spanned structures like roofs or bridges. In times of emission problems and shortage of materials, the potentials of adaptive civil structures open various new possibilities.In the design and optimization process of adaptive civil structures, we address the differences between classical approaches for passive systems and new practices considering adaptivity. By using a suitable actuator placement, it is possible to manipulate the displacements of the structure as well as the force distribution within the structure. Both material and energy savings can be accomplished with an integrated design of the adaptive structure taking into account the actuation, suitable combination of structural design and actuator placement. For demonstration of the differences in the design process and in the resulting optimized structure, we use a small case study on a truss structure, which is inspired by a high-rise building, and consider static loads.

Performance analysis of a small wind turbine equipped with flexible blades

Abstract Wind turbine efficiency can drop drastically away from design conditions, which is especially troublesome for small fixed-pitch, constant speed types of devices and those operating in highly variable winds. Recent advances in the design of adaptive structures gives rise to a new turbine concept, employing continuous shape morphing, allowing the turbine to adapt more effectively to variable conditions. Such morphing blades could increase energy capture, and help small wind turbines become more economically viable through increased efficiency over a wide range of wind speeds and tip-speed ratios. In this paper, we examine the practicality of a flexible or morphing bladed turbine through experimental and numerical analysis. Experiments are conducted comparing a prototype rigid bladed design to an identical flexible one, with a total of 18 data sets containing 230 data points. Experimental results show that the flexible design outperforms the rigid one, especially when experiencing unfavorable loading conditions. Maximal corrected power coefficients were increased in all cases, up to 32.6%. The operational range was also increased in most cases, to a maximum of 34.5% over the rigid bladed design. These results suggest that the flexible design could produce more power than a rigid one, especially when conditions are sub-optimal.

PD control for vibration attenuation in Hoop truss structure based on a novel piezoelectric bending actuator

With increasing of the geometry of various space structures, they easily bring low-frequency, longtime and more bending modal responses. Therefore, it is necessary to suppress effectually the vibration responses above. Adaptive structure design is a common method using the piezoelectric material. However, the conventional piezoelectric actuators hardly control effectually these responses owing to the inadequate actuated performance. This paper first introduces the design of a new dual-stack piezoelectric actuator, which has the bidirectional (can act in both push and pull directions) actuated advantage, using a pair of matching piezoelectric stacks within the actuator house. Two stacks are integrated in a mechanically opposing configuration and are electrically operated out of phase. Further, we design the piezoelectric bending actuator using two dual-stack piezoelectric actuators and a fixed device, and then a five-meter hoop truss can use it to perform the active vibration control. Here the truss is mainly applied to simulate a large hoop mesh antenna. Then, we set up the active control system based on the PD algorithm and build the simulation model by the Matlab/Simulink platform. The simulation results point out the PBA can produce enough actuated moment to suppress effectually the first-order modal response of the hoop truss. Finally, we perform three experiments including one uncontrolled case and two PD controlled cases. The two control cases mainly consider whether the driving voltages are offset or not. The experimental results of both control cases are in accordance with the better simulated analysis. The control ratios of the decay time of the first-order modal response are up to more than 30 percent in the simulations and experiments. That is, this bending actuator has good application foreground in controlling the bending modes of the spacecrafts with a larger size.

Adaptable nonlinear bimode metamaterials using rigid bars, pivots, and actuators

A large family of periodic planar non-linear bimode metamaterials are constructed from rigid bars and pivots. They are affine materials in the sense that their macroscopic deformations are only affine deformations: at large distances any deformation must be close to an affine deformation. Bimode means that the paths of all possible deformations of Bravais lattices that preserve the periodicity of the lattice lie on a two-dimensional surface in the three-dimensional space of invariants describing the deformation (excluding translations and rotations). By adding two actuators inside a single microscopic cell one can control the macroscopic deformation, which may be useful for the design of adaptive structures. The design of adaptable nonlinear affine trimode metamaterials (for which the macroscopic deformations lie within a three-dimensional region in the space of invariants) is discussed, although their realization remains an open problem. Examples are given of non-affine unimode and non-affine bimode materials. In these materials the deformation can vary from cell to cell in such a way that the macroscopic deformation is non-affine.

Adaptive lifting scheme with sparse criteria for image coding

Lifting schemes (LS) were found to be efficient tools for image coding purposes. Since LS-based decompositions depend on the choice of the prediction/update operators, many research efforts have been devoted to the design of adaptive structures. The most commonly used approaches optimize the prediction filters by minimizing the variance of the detail coefficients. In this article, we investigate techniques for optimizing sparsity criteria by focusing on the use of an l1 criterion instead of an l2 one. Since the output of a prediction filter may be used as an input for the other prediction filters, we then propose to optimize such a filter by minimizing a weighted l1 criterion related to the global rate-distortion performance. More specifically, it will be shown that the optimization of the diagonal prediction filter depends on the optimization of the other prediction filters and vice-versa. Related to this fact, we propose to jointly optimize the prediction filters by using an algorithm that alternates between the optimization of the filters and the computation of the weights. Experimental results show the benefits which can be drawn from the proposed optimization of the lifting operators.

Aircraft Roll Enhancement via Multi-Objective Optimization Using Surrogate Modeling

This research is concerned with the design of adaptive structures for achieving global multishape morphing aerodynamic configurations by using thin-walled structures. The proposed methodologies pursue two threads toward global optimization of morphing structures, by providing means of aerodynamic enhancement using efficient structural shape optimization. A heuristic approach is proposed in this work that enables morphing through a range of stable cambered airfoils to achieve aerodynamic properties for different maneuvers, with the benefit of lowpowered actuation control. This allows large changes in shape by exploiting a range of incremental nonlinear structural solutions while keeping prescribed flow improvements. Such a heuristic argument provides the basis for global shape control of three-dimensional wings and is applied to aerodynamic design to provide enhanced roll control. A hierarchical strategy is employed herein, interleaving parameterization enhancement followed by structural optimization into the aerodynamic design process, such that the design paradigm, in conjunction with global approximation techniques, is emphasized by enhanced roll while drag is minimized. This figure of merit is complemented by structural metrics and constraints to maintain product integrity.

Optimal design of adaptive structures: Part I. Remodeling for impact reception

The paper (written in two parts) is devoted to the presentation of numerical tools, based on the so-called virtual distortion method (VDM) for fast structural reanalysis and to the application of this tools for optimal design of adaptive structures exposed to impact loads. The first paper deals with fast modifications of the material distribution (coupled stiffness and mass redistribution) in dynamically loaded structures, which allows their optimal remodeling, e.g., to minimize average deflections. The VDM-based approach allows analytical sensitivity determination, which is very helpful in efficient implementation of the optimization procedure, utilized to solve the defined remodeling problem. The presented methodology is illustrated with a numerical example of truss–beam structure exposed to random impact loads.

From a shape memory alloys model implementation to a composite behavior

To obtain an unified treatment of the phase transformation materials pseudoelasticity, a model based on the two independent normal dissipative processes assumption has been developed, one for forward transformation and the other one for reverse transformation. Within the context of building a numerical tool for the optimal design of adaptive structures embedding shape memory alloys ( sma), the use of these materials as command components needs the implementation of a specific homogenization method into a structural computation to take into account anelastic constituents. The transformation field analysis is used to predict the pseudoelastic behavior of shape memory alloys reinforced composite materials. The sma composite behavior evaluated by this approach was compared to the response using a two-level micromechanical theory developed by Lu. His prediction considers an inactive elastomeric matrix and volume concentration effects of sma fibers periodically aligned are examined. Both results point to the advantage of using fibrous composites for actuators or sensors under a tensile loading.

Simultaneous Optimal Design of Structural and Control Systems via Successive LMI Optimization

This article is concerned with simultaneous optimal design of adaptive structures comprising structural and control systems. In this study, we apply the fact that the nonconvex problem is approximated by a convex one by adding a semidefinite positive function, the so-called convexifying function, to make the constraint convex. This study proposes a method of simultaneous optimization for state feedback gains and structural parameters. The system formulation is given using the descriptor form representation of the plant under the linear matrix inequality (LMI) constraint. A numerical example of a simple structure is provided to demonstrate the effectiveness of the proposed method.

W05-(12) Bio-inspired Design of Materials for Actuators and Sensors

Biological systems adapted and perfected the design and functioning of their structures during thousands of years of evolution in a changing and increasingly more complex, competitive and challenging world. It is therefore smart in itself to study, understand and adopt nature's time-tested principles and mechanisms to the design of adaptive structures and intelligent materials. Here we focus on autonomous and locally controlled responses, which do not require or the remote control by a central nervous system. We look at three kinds of mechanisms. First, the principles of touch and light sensing in plants and single-celled algae will be examined for their applicability to trigger, modify and control actuation mechanisms. Second, the study of various actuators in plants provides a wide set of alternative choices to create novel, energy-conservative actuation mechanisms in intelligent materials. Third, the comparison of biological, filament-based muscles and artificial, polymer gel-based actuators provides the means to develop and test alternative explanations of the mechanics of muscle contraction and to find the causes or conditions causing the superior speed in natural systems.

Dissections: self-assembled aggregates that spontaneously reconfigure their structures when their environment changes.

This Communication describes a new strategy for the design of adaptive structures based on reconfigurable mesoscale self-assembly. Several sets of millimeter-scale objects have been designed that can self-assemble into two different, regular aggregates at the interface between an aqueous solution and perfluorodecalin; the choice between the two aggregates is determined by the density of the aqueous phase.

Modelling and design of adaptive structures using B-spline strip models

The aim of this paper is to present a family of laminated plate/shell B-spline finite strip models based on higher order displacement fields applied to the optimal design of laminated composite plate/shell structures with embedded and/or surface bonded piezoelectric actuators and sensors. Simulated annealing, as a stochastic global optimisation technique, is used to improve the performance of composite adaptive structures subjected to behavioural functions and/or constraints, with continuous and discrete design variables. To show the applicability of the proposed optimisation models, two illustrative examples are presented and discussed.

A CRUDE METHOD OF LOOP-SHAPING ADAPTIVE STRUCTURES THROUGH OPTIMUM SPATIAL COMPENSATOR DESIGN

This work continues the development of methods for optimum spatial compensator design of adaptive structures and is based upon the use of a computationally efficient estimate of the Hankel singular values of the open-loop controllability and observability Gramians to form the design metric. Results demonstrate that when a range of transducer sizes is considered in the candidate set, the proper spatial compensator design metric is the product of a coupling cost and a de-coupling cost. This leads to designs that provide a balance between coupling to modes that are important for control and de-coupling from modes not important for control. As demonstrated on a simply supported plate structure, the optimum design resulting from the application of the approach detailed herein significantly limits coupling to all modes except those present in the performance metric. The method provides the ability to crudely loop-shape the adaptive structure, as demonstrated through modification of both the actuator-to-sensor frequency response function and the system loop gain. It is concluded that emphasis should be placed on designing spatial compensators in order to facilitate the design of controllers for adaptive structures.

Refined models for the optimal design of adaptive structures using simulated annealing

This paper deals with refined finite element models based on higher-order displacement fields applied to the mechanical and electrical behavior of laminated composite plate structures with embedded and/or surface bonded piezoelectric actuators and sensors. Simulated annealing, a stochastic global optimization technique is implemented to find the optimal location of piezoelectric actuators in order to maximize its efficiency. The same technique is also used to solve optimization problems of piezolaminated plate structures where the discrete design variables are the ply orientation angles of orthotropic layers. The implemented scheme helps to recover from the premature convergence to a local optimum, without the need of reinitiating the optimal design process, as it is the case of the gradient-based methods with continuous design variables. To show the performance of the proposed optimization methods, two illustrative and simple examples are presented and discussed.

Genetic Spatial Optimization of Active Elements on an Aeroelastic Delta Wing

This work outlines a cohesive approach for the design and implementation of a genetically optimized, active aeroelastic delta wing. Emphasis was placed on computational efficiency of model development and efficient means for optimizing sensor and actuator geometries. Reduced-order models of potential-flow aerodynamics were developed for facilitation of analysis and design of the aeroelastic system in the early design phase. Using these methods, models capturing “95% of the physics with 8% of the modeling effort” can be realized to evaluate various active and passive design considerations. The aeroelastic delta wing model was employed in determining the most effective locations and sizes for transducers required to provide flutter control. The basic design presented is based upon an analytical model of the structure. A comparison of optimization strategies led to the use of a genetic algorithm to determine the optimal transducer locations, sizes, and orientations required to provide effective flutter control based upon an open-loop performance metric. The genetic algorithm and performance metric essentially provided loop shaping through the adaptive structure design. An experimental model was then developed based upon the optimal transducer designs. Wind tunnel tests were performed to demonstrate closed-loop performance for flutter control. Results from this study indicate that a single sensor/actuator pair can be designed to extend the flutter boundary and selectively couple to only those modes required to control the response.

Concurrent design concepts for adaptive structures

For an adaptive structure there are two critical design components: temporal compensation and spatial compensation. The influence of the controller on the sensor signals characterizes the temporal compensation of the adaptive structure and the dynamic coupling of the actuator and sensor through the structure characterizes the spatial compensation. Traditionally, techniques for adaptive structure design have concentrated on one component and considered the other fixed. This work proposes a method of concurrent design for both the temporal and spatial compensation of an adaptive structure. Concurrent design concepts are realized by simultaneously executing controller optimization and spatial optimization routines. The structural acoustic control performance and robustness of an adaptive plate structure is improved significantly with concurrent design. The results show the advantages of concurrent design concepts over traditional methods and the effectiveness of the proposed approach.