Structural Design Properties Research Articles

Vibroacoustic design optimization of curved composite shells

The need to simultaneously optimize the structural design properties, and attain a satisfactory vibroacoustic performance for composite structures, has been a challenging task for modern structural engineers. This work is aimed at developing a statistical energy analysis (SEA) based numerical scheme for computing the optimal design parameters of each individual layer of layered curved shells having arbitrary complexities and layering. The main novelty of the work focuses on the computation of SEA properties for curved composite shells and derive the sensitivities of the acoustic transmission coefficient, expressed through the computed SEA properties, with respect to the structural design characteristics to be optimized. A wave finite element approach is employed to calculate the wave propagation constants of the curved shell. The calculated wave constants are then applied to compute the vibroacoustic properties for the curved shell using a SEA approach. Sensitivity analyses are conducted on the vibroacoustic properties to estimate their response to changes in the structural properties. Gradient vector is then formulated and hence the Hessian matrix, which is employed to formulate a Newton-like optimisation algorithm for optimizing the properties of the layered composite shell. The developed scheme is applied to a sandwich shell; optimal design parameters of [Formula: see text] and [Formula: see text] are obtained for the facesheet and the core of the shell whose base parameters are [Formula: see text] and [Formula: see text], respectively. This simultaneously optimizes the structure with maximum stiffness and minimum mass and attains a satisfactory dynamic performance for acoustic transmission through the sandwich shell. The principal advantage of the scheme is the ability to accurately model composite panels of arbitrary curvature at a rational computational time.

Surface plasmons in metamaterial heterostructures

ABSTRACT The extensive research of layered materials has revealed that it is possible to obtain a new degree of freedom for tuning the dispersion properties. Based on this concept, researchers have investigated the hyperbolic metamaterials. Recently, several kinds of photonic crystals have been proposed as classical counterparts of the layered materials. However, observation of nanostructured metamaterials from the perspective of the metamaterial structural design properties has remained difficult until now. Thus, we consider the propagation of surface plasmon polaritons (SPPs) at the boundary of geometrically different metamaterials. Herein, we consider two-layered and multilayered composites. All the heterostructures under consideration are made of the alternating graphene and dielectric sheets. We analytically estimate dispersion properties, absorption and propagation lengths of SPPs. The variation of graphene dielectric functions is described by the Drude model. On top of all, we analytically identify the key factors influencing propagation length along with the absorption enhancement highly desirable in terahertz photoconductive antennas and consider analytical variations aiming to tune the dispersion relations.

Characterisation of Reinforced Body Centered Cubic, Octahedral-Type and Octet Truss Lattice Structures

Developments in additive manufacturing have encouraged a dramatic increase in the production and integration of the space-filling unit cells known as lattice structures. As designers begin to leverage the useful benefits provided by lattice structures, and these structures are used more frequently in industrial designs of parts, there is a need to characterise the properties that different lattice structures possess to aid the design process. The functional requirements of a specimen will often change during the design stage and this means that a designer will always wish to select the most applicable lattice structure for the optimal result. To date, there is no repository of lattice structure design properties from which a designer can choose a structure that best suits the design requirements. This article aims to propose a methodology for testing the capabilities of lattice structures and building a database of unit cell type design properties through compression and 3-point bending tests. The samples were created with PA2200 manufactured through the selective laser sintering process on an EOS P396. The lattice structure specimens were parameterised in terms of overall specimen unit cell size and strut diameter. Through regression analysis, particular benefits of lattice structures were noted: Reinforced Body Centered Cubic (RBCC) performed best in bending, Octet Truss performed best in compression and Octahedral performed worst in both tests but resisted much greater deformation. Additionally, though increases in strut diameter or number of unit cells per sample increased both Young’s Modulus and Ultimate Compressive Strength, it was strut diameter increases that had a factor of 10 greater of an effect. To complete a repository, it is desirable to increase the number of stages per design parameter and test over a greater range of values - to fully model the shape of the output curve.Scientific Topics: Design Methodology, Design of Lattice Structures, Designing for Additive Manufacturing, Designing for Multifunctional Optimisation of Lattice Structures

Dynamic non-linear energy absorbers based on properly stretched in-plane elastomer structures

Traditionally, elastomers are considered to be one of the best material candidates for the design of energy absorbing devices, due to their remarkable visco-elastic and extensibility material properties. This capability can be further enhanced by the design of appropriate Dielectric Elastomer Generators (DEGs). The present paper proceeds to another alternative direction, which consists of the design of appropriate elastomer structures with enhanced energy absorption capabilities, are attributed more to the appropriate non-linear design of the elastomer structure itself, than to the hyperelastic material properties of the elastomer members. For this reason, a simple chi-shaped in-plane elastic structure is considered, comprising one proof mass with four elastomer members attached to it, placed in a chi-shaped configuration, and being properly stretched. A systematic analysis is carried out, with respect to the variation of two basic structure design properties on the dynamic behavior: the orientation angle of the members and their initial pre-stress. The obtained results show that the variation of just these two basic parameters of the structure may lead to a quite rich and interesting non-linear dynamic behavior. More specifically, the traditional always-in-tension concept leads to a linear dynamic system response, even though the elastomer members are considered to have been made of a non-linear hyper-elastic material. Alternatively, a new partially-loose-member operating concept is analyzed. This concept suggests that some individual elastomer members be allowed to become loose for some period of the operating cycle, (but not all of them simultaneously), strongly enhancing the broadband energy absorbing capability of the structure itself.

Proposed AASHTO Structural Design Properties for Corrugated Polypropylene Storm Sewer Pipe

Corrugated polypropylene storm sewer pipe has been available on the U.S. market since 2007. The manufacturing process and structural design are similar to the more widely used high-density polyethylene (HDPE) pipe; however, polypropylene has advantages over HDPE in applications that require higher bending resistance and operating temperatures and greater longitudinal beam strength and stress crack resistance. In 2011, ASTM and AASHTO both adopted specifications for corrugated polypropylene pipe materials and products for use in nonpressure surface and subsurface drainage applications. These standards included some requirements for polypropylene material properties related to structural design, such as the minimum initial modulus and long-term creep modulus, but not all parameters required by AASHTO for the structural design of thermoplastic pipe were addressed. This paper presents the test methods and sampling conventions required to arrive at such structural design properties, as well as test results for four candidate poly propylene resins commercially available in the United States. The paper also uses these test results as the basis for proposed structural design properties for polypropylene storm sewer pipe for adoption into the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications.

Time-Periodic Stability of a Flapping Insect Wing Structure in Hover

The wings of insectlike flapping-wing micro air vehicles experience time-periodic inertial stiffnesses during flapping motion. By modeling the wing structure as a thin beam, a linear time-periodic assumed-modes analysis is developed. The equations of motion of a flapping wing undergoing out-of-plane bending and torsion are derived. The homogeneous assumed-modes equations are nondimensionalized. It is shown that the nondimensional strain stiffness varies with the ratio of the wing's nonrotating natural frequencies to the flapping frequency, whereas the nondimensional, time-periodic inertial stiffnesses vary with the amplitudes of flapping and feathering motion. The parametric stability of a representative wing is assessed by applying Floquet analysis to the nondimensional equations of motion, and a scalable stability diagram is presented. Parametric instabilities of the wing structure, caused by time-periodic stiffnesses, are characterized and plotted in the time domain. The effects of important structural design properties on parametric stability are examined.

EXPERIMENTAL PROCEDURE AND ELASTIC RESPONSE CHARACTERISTICS OF SHAKING TABLE TEST

A shaking table test on a full-scale steel building was conducted at the E-Defense to evaluate structural and functional performance of the building under design-level ground motions and the safety margin against collapse under exceedingly large ground motions. The specimen is a 4-story moment resisting frame designed and constructed according to the current Japanese code. This paper presents the outline of the experimental plan including the design of a specimen and shaking table test results under elastic range. The elastic response characteristics regarding stiffness, restoring force and damping of the specimen are examined comparing with structural design properties.

Structural design properties of concrete for a bridge in Alberta

In this investigation, the structural design properties of concrete were characterized. Compressive, tensile, and flexural strengths were measured at different ages. In addition, modulus of elasticity, Poisson's ratio, creep, shrinkage, and various other properties were measured. Laboratory results were compared with several structural codes used by engineers for bridge and structural design. The results serve as a reminder that assumed code values can be significantly in error and must be used only in the absence of better data.Key words: concrete, creep, shrinkage, modulus of elasticity, strength, design.

Modeling development effort in object-oriented systems using design properties

In the context of software cost estimation, system size is widely taken as a main driver of system development effort. However, other structural design properties, such as coupling, cohesion, and complexity, have been suggested as additional cost factors. Using effort data from an object-oriented development project, we empirically investigate the relationship between class size and the development effort for a class and what additional impact structural properties such as class coupling have on effort. The paper proposes a practical, repeatable, and accurate analysis procedure to investigate relationships between structural properties and development effort. Results indicate that fairly accurate predictions of class effort can be made based on simple measures of the class interface size alone (mean MREs below 30 percent). Effort predictions at the system level are even more accurate as, using Bootstrapping, the estimated 95 percent confidence interval for MREs is 3 to 23 percent. But, more sophisticated coupling and cohesion measures do not help to improve these predictions to a degree that would be practically significant. However, the use of hybrid models combining Poisson regression and CART regression trees clearly improves the accuracy of the models as compared to using Poisson regression alone.

Integrating scenario-based and measurement-based software product assessment

The software industry needs means to evaluate software products and compare development and implementation technologies in the context of actual projects. Solutions need to be cost-effective but also technically sound. This paper presents a methodology to combine two software product evaluation techniques: measurement of structural design properties, and evaluation of change scenarios. The goal is to use these two approaches together so that they can address each other's limitations. In a case study in the context of the European aerospace industry, this combined methodology was used to assess the impact of choice of programming language and distribution technology on the maintainability of resulting systems. It encompasses the comparison of C++ and Java, as well as distribution/communication technologies such as IPC via sockets, and CORBA implementation. Lessons learned in terms of benefits and limitations are presented. The study shows the usefulness of the approach presented but it is also clear that it needs to be used in combination with other means of evaluation and with a critical mind, as for any engineering solution.

Structural design properties of a profiled, thermally strengthened, flat glass

Structural design properties of a profiled, thermally strengthened, flat glass