Structural Optimization Techniques Research Articles

Integration of a Hybrid Method into an Efficient Reliability-Based Design Optimization Technique for Large Structures

The computational burden imposed by the repetitive and lengthy nature of the structural analyses of large structures has lead researches to continuously devise efficient methods for conducting their reliability analysis in addition to powerful methods for solving the design optimization problem. The presence of a considerably large number of random variables in the reliability analyses of large structure is another issue that tends to slow down the design optimization problem. In this paper, a hybrid method that was recently presented by the first author will be integrated into a structural reliability-based design optimization technique for large structures. In this technique, modified concepts of the weighted average simulation method are used to determine the most probable point of failure in a computationally efficient manner. The most probable point of failure is then transferred into the standard normal space, where the reliability index is calculated in closed-form. The firefly algorithm will be used for solving the optimization problem. It will be shown that the integrated approach significantly reduces the computational resources required for solving the design problem. The technique will be tested on a truss bridge. The results will shed light on the efficiency of the proposed technique in solving reliability-based design optimization problems.

On The Optimal Forms Finding of Shallow Foundations Made Up of Four Foothills with Explicit Considerations of Structural Perturbations

In the absence of the exact footing form of shallow foundations, we develop a procedure to determine the optimal footing form made up of four foothills from the knowledge of the inexact footing forms. The structural perturbations that are the major cause of the inexact forms are approximated in linear elastic model whose the solution is used to formulate the evolutionary structural optimization problem. To stabilize the solution, a serial of decisions is made to minimize structural perturbations in finite element modeling, initial volume and design constraints. By using the evolutionary structural optimization technique, we examine if the material of efficient and inefficient perturbations is needed or not on the points of inexact forms. Our analysis shows that the loading forces can be transferred to structural perturbations when they are efficient and used to reinforce the design material. This transfer can modify geometric elements of footing in finite element analysis and the optimal solution. The results of the numerical experiment provide the optimal footing form of shallow foundation, the sizes of associated foothills and the form of inefficient perturbations. This approach allows to redesign the structures from the inexact forms and detects the errors of dimensioning.

On the benefits of applying topology optimization to structural design of aircraft components

To date, topology optimization has proven to be the most beneficial, yet most complex, structural optimization technique available to engineers and scientists. However, particularly in the aerospace industry, there exists little application to real-world design problems, including all the complexities required to ensure that the resulting design complies with the regulations. In this paper, a topology optimization algorithm is developed to solve aerospace design problems. Two problems are considered in this work. The first is the design of an aircraft landing gear. The final topology is compared to a design found using standard engineering practices to show the benefits of topology optimization. The second problem uses the topology optimization methodology to design an aircraft engine mount. The main goal of this paper is to demonstrate that topology optimization can be used to find minimum weight structures to aerospace design problems, using Federal Aviation Regulations to ensure that the resulting designs meet the airworthiness standards of the aviation industry.

Design of Truss Structures Through Reuse

This paper presents structural optimization techniques to design truss structures that make best use of a given stock of structural components. Still little explored, the reuse of structural components over multiple service lives has the potential to significantly reduce the environmental impact of building structures. Structural design and construction based on reuse avoids sourcing new material, it reduces superfluous waste, and requires little energy. However, designing a structure from a stock of reclaimed elements entails a change of design paradigm: in contrast to conventional design practice, the structural geometry and topology depends on element stock characteristics, e.g. available cross sections and lengths. This paper presents discrete structural optimization formulations to design truss systems from stock elements. The approach taken in this work is iterative: 1) element assignment and topology optimization are carried out, and 2) geometry optimization follows thereafter to best-fit the system geometry to the length of assigned stock elements, for instance to reduce cut-off waste. Two case studies are presented: a) a cantilever of simple layout used to explain the details of the design methodology, and b) a train station roof structure of complex layout made from elements reused from disassembled electric pylons. For these case studies, Life Cycle Assessment confirms that an up to 63% environmental impact reduction is possible when comparing structures obtained with the proposed method against weight-optimized solutions made of new elements.

An optimized harmonic probe with tailored resonant mode for multifrequency atomic force microscopy

For simultaneously measuring specimen’s surface morphology and material properties, multifrequency atomic force microscopy is often employed. In this kind of atomic force microscopy, if the probe’s higher-order resonance frequencies match the integer multiples of its fundamental frequency, the probe’s responses at such harmonic frequencies will be enhanced. Meanwhile, an enlarged effective slope during vibration at the probe’s tip results in an improved probe sensitivity. Moreover, increasing the probe’s natural frequency leads to a fast scanning speed. In this study, we propose to design cantilever probes that satisfy the aforementioned requirements via a structural optimization technique. A cantilever probe is represented by a three-layer symmetrical geometric model, and its width profile is continuously varied through the optimization procedure. Thereafter, an optimized design of probe considering the fifth harmonic is prepared by focused ion beam milling. Both simulation and experiment results show that the prepared probe agrees well with design requirements.

Long-Span Pedestrian Bridges in the USA: A Futuristic Approach

Pedestrian bridges have historically provided engineers and architects with opportunities to push the envelope in terms of engineering concepts, analysis and design techniques and technology, materials and aesthetics. The challenges they present—from spanning long distances and vibration control to the construction logistics associated with the space being bridged—have led to a plethora of iconic structures. This trend continues today, driven—in addition to the traditional impetus to innovation—by the current focus on sustainability, resilience and the availability of new computational optimization tools. This emphasis invariably results in the economic usage of materials and structural resilience, and this focus is expected to continue to influence the approach to the design of pedestrian bridges in the future. This paper presents examples of two box-girder/orthotropic pedestrian bridges designed to optimally meet the challenges posed by their respective site and functional constraints in regions of high seismicity. These bridges are under construction or have recently been completed. Also presented are conceptual studies for a pedestrian bridge at the Los Angeles International Airport (LAX), the design for which was developed using computational structural optimization techniques. Such techniques have already been successfully applied to structures in the aeronautical, automobile and mechanical industries, in which natural force flows are modeled. Two optimization techniques were utilized leading to two unique design solutions.

Vehicle crash optimization considering a roof crush test and a side impact test

The vehicle performances for the side impact test and the roof crush test are dependent on the side structure design of a vehicle. Crash optimization can be employed to enhance the performances. A meta-model-based structural optimization technique is generally utilized in the optimization process since the technique is simple to use. However, the meta-model-based optimization is not suitable for problems with many design variables such as topology and topometry optimizations. A crash optimization methodology is proposed to consider both the side impact test and the roof crush test. The equivalent static loads method is adopted for the side impact test and the enforced displacement method is adopted for the roof crush test, and the two methods are integrated. A design formulation is defined. The survival distance from the side impact test and the roof strength for the roof crush test are used for the design constraints. Crash optimization is performed for a practical large-scale structure. For conceptual design, reinforcement of the B-pillar is determined by using topometry optimization, and size and shape optimizations are employed for a detailed design to satisfy the design constraints while the mass is reduced.

A Comparison between different techniques for optimum design of steel frames subjected to blast

Abstract According to the conditions of today's world, design of resistant structures against blast loading is an important subject that requires special attention. Thus, given the benefits of optimization in engineering, development and assessment of optimization methods for optimum design of structures against blast is of great importance. In this research, the optimum design of steel frame structures against blast loading is investigated. For this purpose first an optimization methodology is proposed. In the proposed method the structural analysis is performed using nonlinear explicit finite element analysis. Based on the proposed method a framework is developed and three numerical examples are investigated using different numerical optimization techniques. Results of this study show that by using nonlinear explicit FE analysis as the structural analysis method and NLPQLP optimization technique as the optimization method, the current optimization problem can be performed effectively, because the procedure is relatively accurate and computationally inexpensive.

Structural Optimization Techniques to Design Light Weight and Low Radiated Noise Components

Structural Optimization Techniques to Design Light Weight and Low Radiated Noise Components

On the internal architecture of emergent plants

It remains a puzzling issue why and how the organs in plants living in the same natural environment evolve into a wide variety of geometric architecture. In this work, we explore, through a combination of experimental and numerical methods, the biomechanical morphogenesis of the leaves and stalks of representative emergent plants, which can stand upright and survive in harsh water environments. An interdisciplinary topology optimization method is developed here by integrating both mechanical performance and biological constraint into the bi-directional evolutionary structural optimization technique. The experimental and numerical results reveal that, through natural selection over many million years, these leaves and stalks have been optimized into distinctly different cross-sectional shapes and aerenchyma tissues with intriguing anatomic patterns and improved load-bearing performance. The internal aerenchyma is an optimal compromise between the mechanical performance and functional demands such as air exchange and nutrient transmission. We find that the optimal distribution of the internal material depends on multiple biomechanical factors such as the cross-sectional geometry, hierarchical structures, boundary condition, biological constraint, and material property. This work provides an in-depth understanding of the property–structure–performance–function interrelations of biological materials. The proposed topology optimization method and the presented biophysical insights hold promise for designing highly efficient and advanced structures (e.g., airplane wings and turbine blades) and analyzing other biological materials (e.g., bones, horns, and beaks).

Integration of cutting time into the structural optimization process: application to a spreader bar design

Nowadays, there is no doubt about the suitability and efficiency of structural optimization techniques and the improvement achieved in the design process when they are applied. However, if we look to the product design process, do we really believe that it is an unbeatable improvement? Current structural optimization methods (based on metrics such as stress, mass or compliance) have reached a high level of development, but their integration with other factors as manufacturing processes is still at an early stage of development. In many cases, those designs suggested applying only structural optimization are found to be difficult and/or expensive to manufacture. This situation is further accentuated in the case of cutting processes, where it is well-known that structural optimization significantly affects to the cutting time and commonly produces manufacturing overcost. In this sense, this paper tries to fill the gap between structural optimization and manufacturing-based design applied to the case of cutting processes. For this purpose, the authors propose a methodology that allows including those parameters that affect to the cutting time within structural optimization phase. Additionally, to obtain a fair conclusion about its performance the method is applied to a real industrial component manufactured by a cutting process as it is the Abrasive Waterjet Cutting (AWJ).

Shape optimization of streamlined decks of cable-stayed bridges considering aeroelastic and structural constraints

Structural optimization techniques have the potential to become a powerful tool in the design of long-span bridges. The search for more efficient and reliable designs involves considering shape variations in the deck cross-section, which is one of the key features of the bridge. This affects the deck aerodynamics and its mechanical properties, and consequently to the aeroelastic response of the bridge. A numerical approach pursuing to optimize a long-span bridge needs to explore changes in the deck shape, including structural and aeroelastic responses as design constraints. Therefore, the flutter response of the bridge must be computed numerically for every candidate proposed by the optimization algorithm.This work presents a novel approach to conduct the optimization of deck shape and cables size of a long-span cable-stayed bridge considering simultaneously aeroelastic and structural constraints. The design variables are the cross-section area and prestressing force of each stay, the deck plates thickness and the width and depth of a streamlined box deck. The aeroelastic constraint is evaluated based on the fully numerical procedure developed in an authors' previous work. A series of parameter variation studies, that are instrumental for the sound interpretation of the optimum designs, are also reported.

Lightweight design of an automobile hinge component using glass fiber polyamide composites

Abstract In recent years, there has been a great deal of interest in lightweight vehicle design due to regulations about reducing fuel consumption and emissions. Lightweight design of vehicle components is one of the most important research topics in vehicle design. Developing the optimum structure in the early stages of design process is very important for minimizing the vehicle weight and production costs. In this paper, an automobile hinge component has been developed using PA66 GF60 glass fiber-reinforced polyamide composite materials instead of conventional steel. The automobile hinge component has been conceived using computer aided design software. Topology optimization was made under specific loadings subject to the constraints of finite element method analysis. As a result of this study, optimum dimensions of the component have been obtained and the weight of the component has been reduced via structural topology optimization techniques while satisfying displacement and stress conditions. The results show that composite materials are an important alterative in lightweight vehicle design.

Smoothing evolutionary structural optimization for structures with displacement or natural frequency constraints

The Smoothing Evolutionary Structural Optimization (SESO) technique was extended to solve 2D elastic problems with constraint of displacements or natural frequencies. At the end of each finite element analysis, a scalar representing the sensitivity due to the removal of an element is calculated. Thus, the elements that have the lowest values are removed from the structure, while the displacements in prescribed locations are kept inside of limits stated or the first frequencies are maximized. The proposed technique proved to be adequate and efficient in the execution of shape and topological optimization.

Multidisciplinary shape optimization of ductile iron castings by considering local microstructure and material behaviour

During the casting process and solidification of ductile iron castings, a heterogeneous microstructure is formed throughout the casting. This distribution is strongly influenced by the item geometry and the process related factors, as chemical composition and local solidification conditions. Geometrical changes to the geometry of the casting thus alters the local mechanical behavior and properties, as well as the distribution of stresses and strains when the casting is subjected to load. In order to find an optimal geometry, e.g. with reduced weight and increased load-bearing capacity, this interdependency between geometry and local material behavior needs to be considered and integrated into the optimization method. In this contribution, recent developments in the multidisciplinary integration of casting process simulation, solidification and microstructure modelling, microstructure-based material characterization, finite element structural analyses with local material behavior and structural optimization techniques are presented and discussed. The effect and relevance of considering the local material behavior in shape optimization of ductile iron castings is discussed and evidenced by an industrial application. It is shown that by adopting a multidisciplinary optimization approach by integration of casting simulation and local material behavior into shape optimization, the potential of the casting process to obtain components with high performance and reliability can be enabled and utilized.

Shape optimization of solid–air porous phononic crystal slabs with widest full 3D bandgap for in-plane acoustic waves

The use of Phononic Crystals (PnCs) as smart materials in structures and microstructures is growing due to their tunable dynamical properties and to the wide range of possible applications. PnCs are periodic structures that exhibit elastic wave scattering for a certain band of frequencies (called bandgap), depending on the geometric and material properties of the fundamental unit cell of the crystal. PnCs slabs can be represented by plane-extruded structures composed of a single material with periodic perforations. Such a configuration is very interesting, especially in Micro Electro-Mechanical Systems industry, due to the easy fabrication procedure. A lot of topologies can be found in the literature for PnCs with square-symmetric unit cell that exhibit complete 2D bandgaps; however, due to the application demand, it is desirable to find the best topologies in order to guarantee full bandgaps referred to in-plane wave propagation in the complete 3D structure. In this work, by means of a novel and fast implementation of the Bidirectional Evolutionary Structural Optimization technique, shape optimization is conducted on the hole shape obtaining several topologies, also with non-square-symmetric unit cell, endowed with complete 3D full bandgaps for in-plane waves. Model order reduction technique is adopted to reduce the computational time in the wave dispersion analysis. The 3D features of the PnC unit cell endowed with the widest full bandgap are then completely analyzed, paying attention to engineering design issues.

Optimum design of steel space structures using social spider optimization algorithm with spider jump technique

In this study, recently developed swarm intelligence algorithm called Social Spider Optimization (SSO) approach and its enhanced version of SSO algorithm with spider jump techniques is used to develop a structural optimization technique for steel space structures. The improved version of SSO uses adaptive randomness probability in generating new solutions. The objective function of the design optimization problem is taken as the weight of a steel space structure. Constraints\' functions are implemented from American Institute of Steel Construction-Load Resistance factor design (AISC-LRFD) and Ad Hoc Committee report and practice which cover strength, serviceability and geometric requirements. Three steel space structures are optimized using both standard SSO and SSO with spider jump (SSO_SJ) algorithms and the results are compared with those available in the literature in order to investigate the performance of the proposed algorithms.

A new hybrid meta-heuristic algorithm for optimal design of large-scale dome structures

ABSTRACTIn this article a hybrid algorithm based on a vibrating particles system (VPS) algorithm, multi-design variable configuration (Multi-DVC) cascade optimization, and an upper bound strategy (UBS) is presented for global optimization of large-scale dome truss structures. The new algorithm is called MDVC-UVPS in which the VPS algorithm acts as the main engine of the algorithm. The VPS algorithm is one of the most recent multi-agent meta-heuristic algorithms mimicking the mechanisms of damped free vibration of single degree of freedom systems. In order to handle a large number of variables, cascade sizing optimization utilizing a series of DVCs is used. Moreover, the UBS is utilized to reduce the computational time. Various dome truss examples are studied to demonstrate the effectiveness and robustness of the proposed method, as compared to some existing structural optimization techniques. The results indicate that the MDVC-UVPS technique is a powerful search and optimization method for optimizing structural engineering problems.

System-Based Approaches for Structural Optimization of Flexible Mechanisms

This paper reviews the state-of-the-art methods to perform structural optimization of flexible mechanisms. These methods are based on a system-based approach, i.e. the formulation of the design problem incorporates the time response of the mechanism that is obtained from a dynamic simulation of the flexible multibody system. The system-based approach aims at considering as precisely as possible the effects of nonlinear dynamic loading under various operating conditions. Also, the optimization process enhances most existing studies which are limited to (quasi-) static or frequency domain loading conditions. This paper briefly introduces flexible multibody system dynamics and structural optimization techniques. Afterwards, the two main methods, named the weakly and the fully coupled methods, that couple both disciplines are presented in details and the influence of the multibody system formalism is analyzed. The advantages and drawbacks of both methods are discussed and future possible research areas are mentioned.

Design and Development of Compliant Mechanisms Using Parameterization Technique

Design and development of compliant mechanism based systems with precision motion are the need of the hour in micro-precision industry. Compliant mechanisms coupled with the proper flexure hinge can provide excellent accuracy contrary to conventional rigid body mechanism. Various design methods are proposed to design a compliant mechanism such as structural optimization technique, Pseudo Rigid Body Model, Inverse Methods and Intuitive methods. Developing a manufacturable monolithic compliant mechanism is highly challenging. In this paper we have attempted a novel approach to design a compliant mechanism with circular based contemporary flexure hinge. The initial design of flexure hinge is designed intuitively and selection of appropriate geometrical parameters of the flexure hinges is another critical task in the design process. The developed hinges are parameterised using the general screening algorithm in ANSYS Workbench to obtain precise dimensions. The initial design of flexure hinge is designed as a curved beam which have fixed centre of rotation during execution. The method is implemented to design a four bar compliant mechanism and compared with the mathematical results. Scott-Russell straight line mechanism is also developed using this approach and verified its effectiveness. Dimensions of the developed hinges are also provided in the paper to enable future researchers to implement and improve the design.