Performance Of Such Structures Research Articles

Simulation and analysis of the angular response of 1D dielectric nanophotonic light-trapping structures in thin-film photovoltaics

Nanophotonics can guide the design of novel structures for light-trapping in ultra-thin photovoltaic cells. Here, we report on the systematic study of the effect of the angle of incidence of sunlight on the performance of such structures. We also conduct a parametric study of a sinusoidal grating and demonstrate that light intensity in the active region averaged over a range of input angles from 0° to 80° can be enhanced by more than 3 times compared to the bare device. Such a broadband light-trapping nanostructure can increase the total daily energy production of a fixed (non-tracking) device by over 60%, compared to a reference device with an anti-reflection coating.

Leakage failure in fibre-reinforced polymer composite tubular vessels at elevated temperature

Pressure-containing structures made from fibre-reinforced polymer composites are increasingly used in harsh environments. This is in part due to their good corrosion resistance. Assessing the performance of such structures often requires consideration of different temperature regimes. Compared to metallic structures, pressurized composite structures exhibit complex damage behaviour which commonly includes fluid leakage that is induced by micro-cracking of the polymer matrix. This is an important damage mode to consider since it not only affects the pressure capacity of unlined components but also causes reduced stiffness and, possibly, fluid ingress into the structure. Leakage behaviour, and thus the occurrence of matrix cracking, may conveniently be assessed through pressure testing. Since fluid properties vary with test temperature, an appropriate testing scheme is required to obtain truly comparable leakage thresholds. The work described in the present paper involves a permeability based testing methodology. Fibre-reinforced tubular specimens were used in this study with either an epoxy or bismaleimide matrix material, which are intended for room and elevated temperature service, respectively.

Seismic analysis of an asymmetric fixed base and base-isolated high-rack steel structure

Since, in the case of plan-eccentric, externally-braced, high-rack storage structures made of steel, damage to the central part of the structure can cause damage to the stored goods, and thus higher earthquake-induced costs, an investigation has been performed into the seismic performance of such structures. An actual structure was analysed both as a fixed base variant, and as a base-isolated variant. The extended N2 method (pushover analysis) was used, and the results obtained were compared with selected results obtained by nonlinear-dynamic analysis. The response of several different mass-asymmetric structural variants, corresponding to different occupancy levels of the structure, was analysed, and the results obtained are presented as floor plan projection envelopes of the top, relative and base displacements, as well as the storey drifts. An interesting result obtained in the research was that asymmetry can increase the damage in the supporting structure on the flexible side, and that the central part of the rack structure remains in the elastic region only when the eccentricity is small. In fact, from the seismic point of view, full occupancy is not the most critical condition, but rather lower occupancy, which could cause eccentricities ranging up to 10% or 15% of the larger floor plan dimension; this could lead to damage propagation in some of the columns. The application of base isolation has a positive effect on the management of seismic performance, even in the case of higher levels of occupancy and larger mass eccentricities. It is pointed out that an eccentricity of 5%, which is prescribed in Eurocode 8, might not be sufficient in such structural types, and that similar concerns could be present in other types of industrial structures with a similar ratio between live and dead loads.

Impact Resistance and Energy Absorption of Functionally Graded Cellular Structures

The dynamic response of functionally graded cellular structures subjected to impact of a finite mass was investigated in this paper. Compared to a cellular structure with a uniform cell size, the one with gradually changing cell sizes may improve many properties. Based on the two-dimensional random Voronoi technique, a two-dimensional topological configuration of cellular structures with a linear density-gradient in one direction was constructed by changing the cell sizes. The finite element method using ABAQUS/Explicit code was employed to investigate the energy absorption and the influence of gradient on stress wave propagation. Results show that functionally graded cellular structures studied are superior in energy absorption to the equivalent uniform cellular structures under low initial kinetic energy impacts, and the performance of such structures can be significantly improved when the density difference is enlarged. The stress levels at the impact and support ends may be reduced by introducing a gradual change of density in cellular structures when the initial impact velocity is low.

Similitude relationships for physical modelling of monopile-supported offshore wind turbines

Offshore wind turbines are considered as an important element of the future energy infrastructure. There is currently a surge in the construction of such facilities in Europe, yet there is no track record of long-term performance of these structures. Offshore wind turbines are dynamically sensitive structures because of the very nature of the structural form (tall and slender) and the different types of dynamic and cyclic loading imposed on them. Lack of data concerning long-term performance indicates a need for detailed investigation to predict the future performance of such structures. Arguably this can be best carried out through small-scale well-controlled laboratory experimental investigation. In this paper, scaling laws are derived for the design of such model tests for studying the long-term performance. Non-dimensional groups that need to be preserved are identified while carrying out these tests. The effectiveness of these chosen non-dimensional groups is investigated by carrying out controlled tests on a 1:100 scale offshore wind turbine. Typical experimental data are presented.

NUMERICAL ANALYSIS OF CONFORMAL UC-PBG STRUCTURES

In this paper, the performance of conventional Uniplanar Compact Photonic Band Gap (UC-PBG) structures is investigated under difierent bending extents. The structure under study is operated as an Artiflcial Magnetic Conductor (AMC) in which performance is mainly characterized by its resonant frequency and bandwidth. Modelling and numerical analysis have been carried out using CST Microwave Studio simulation software which is based on Finite Integration Technique (FIT). Results show that difierent bending extents afiect the AMC's performance which is specifled by a shift to higher resonant frequencies and bandwidth degradation when the degree of bending is increased. Furthermore, we point out some important simulation tips to avoid inaccurate and/or invalid results. This type of study is important to evaluate the performance of such structures for conformal applications. To the best of the authors' knowledge, such type of systematic study is being reported for the flrst time.

Modelling the fatigue behaviour of composites honeycomb materials (aluminium/aramide fibre core) using four-point bending tests

Composite Sandwich Materials are being increasingly used in high-performance structural applications because of their high stiffness and low weight characteristics. Presently, the long-term performance of such structures, especially under fatigue loading, is not enough studied. The aim of this paper is to address such fatigue behaviour by using a fatigue model verified by experimentation. The fatigue model is based on the fatigue modulus concept (degradation of stiffness) which is proposed for core-dominated behaviour and for two directions cells (L and W). Two non-linear cumulative damage models (L and W) derived from the chosen stiffness degradation equation, are examined in context with the linear Miner’s damage summation and compared with available experimental results.

Lateral Behavior of Partially Infilled Reinforced Concrete Frames with Masonry Inserts

Masonry infill walls increase the initial stiffness of reinforced concrete frames and attract more seismic shear forces on buildings thereby reducing the demand on the frame members. Sometimes window or ventilator openings have been left in the infill wall for architectural necessities. Many reinforced concrete constructions with such partial masonry infill face serious earthquake damages due to captive-column effect. In this study, an attempt was made to improve the performance of such structures by providing masonry inserts without completely closing the gap. Experimental investigations were conducted on partially infilled one-third scale reinforced concrete frames with and without masonry inserts under lateral loading. The partially filled masonry wall induced captive-column effect and leads to a severe failure of the column. On the other hand, the masonry inserts over the partial infill increased the stiffness of the structure by forming a compression strut thereby avoiding critical captive-column damage. Results demonstrated the failure with respect to strength, stiffness, ductility and hysteretic characteristics.Keywords: Reinforced concrete frame, partial infill, captive-column effect, lateral loading

Plasmonic array nanoantennas on layered substrates: modeling and radiation characteristics

In this paper, we theoretically characterize the performance of array of plasmonic core-shell nano-radiators located over layered substrates. Engineered substrates are investigated to manipulate the radiation performance of nanoantennas. A rigorous analytical approach for the problem in hand is developed by applying Green's function analysis of dipoles located above layered materials. It is illustrated that around the electric scattering resonances of the subwavelength spherical particles, each particle can be viewed as an induced electric dipole which is related to the total electric field upon that particle by a polarizability factor. Utilizing this, we can effectively study the physical performance of such structures. The accuracy of our theoretical model is validated through using a full-wave finite difference time domain (FDTD) numerical technique. It is established that by novel arraying of nano-particl and tailoring their multilayer substrates, one can successfully engineer the radiation patterns and beam angles. Several optical nanoantennas designed on layered substrates are explored. Using the FDTD the effect of finite size substrate is also explored.

Cases of Collapse of Demountable Grandstands

A significant number of accidents has occurred with demountable grandstands in the past as well as recently. The performance of such structures is the subject of this paper. First, structural details and some structural systems of actual grandstands are presented and discussed. Next, specifics of the design, erection, and inspection process are detailed. Finally, a survey of cases of collapse of demountable grandstands is presented and discussed. Ninety three cases of collapse were found between the years 1889 and 2008, in which more than 85 people died and 6,350 were injured. From these, 35 cases in which information about the causes of collapse were available were selected. An analysis of the causes showed that unexpected or excessive loads were the major contributing cause, followed by problems with the supports, connections, and bracing. Possible measures that could be adopted aimed at minimizing the risk of accidents with these structures are discussed.

Electrical properties of charging effect in Au nanoparticle memory device

AbstractSemiconductors or metal nanoparticles (NPs) using their monolayer bindings with self-assembly chemicals are an attractive topic for device researchers. Electrical performance of such structures can be investigated for a particular application, such as memory device. Currently, Au NPs has been reported to show a substantial potential in the memory applications. In this study, Au NP and gluing layer were fabricated through a new method of monolayer formation of a chemical bonding or gluing. In this study, a new NPs memory system was fabricated by using organic semiconductor, i.e., pentacene as the active layer, evaporated Au as electrode, SiO2 as the gate insulator layer on silicon wafer. In addition, Au NPs coated with binding chemicals were used as charge storage elements on an APTES (3-amino-propyltriethoxysilane) as a gluing layer. In order to investigate chemical binding of Au NP to the gate insulator layer, GPTMS (3-glycidoxy-propyltrimethoxysilane) were coated on the Au NPs. As a result of that, a layer of gold nanoparticles has been incorporated into a metal-pentacene-insulator-semiconductor (MPIS) structure. The MPIS device with the Au NP exhibited a hysteresis in its capacitance versus voltage analysis. Charge storage in the layer of nanoparticles is thought to be responsible for this effect.

Multipanel Concept for Wide-Angle Scanning of Phased Array Antennas

A method for scanning of the main beam of phased array antennas in a wide angular range is presented. The method utilizes several smaller flat antenna panels, arranged in an array of panels, each of the panels pointed in the direction of the main beam of overall antenna. The output signal of the overall antenna is summation of the signals from all antenna panels. Investigation of the array performance of such structure with respect to the distance between the panels and sidelobe level of the antenna structure is presented.

Noise analysis of correlated double sampling sc integrators with a hold capacitor

Noise performance of the correlated double sampling switched-capacitor integrators incorporating a supplementary hold capacitor is analyzed. These types of integrators rely on an extra capacitor to attenuate the amplifier low-frequency noise. Approximate expressions for the input-referred noise of the integrators are derived. It is shown that a large parasitic capacitance at the amplifier input may seriously degrade the low-frequency noise performance of such structures.

Behaviour and analysis of masonry‐infilled frames

AbstractMasonry infills are frequently used as interior partitions and exterior walls in buildings. They are usually treated as non‐structural elements, and their interaction with the bounding frame is often ignored in design. The performance of such structures during an earthquake has attracted major attention. Even though frame–infill interaction has sometimes led to undesired structural performance, recent studies have shown that a properly designed infilled frame can be superior to a bare frame in terms of stiffness, strength, and energy dissipation. A number of different analytical models have been developed to evaluate infilled structures. Nevertheless, most of the models proposed today have been validated with limited experimental data, and they have often yielded different performances when compared with recent test data. Limit analysis methods that can account for a variety of possible failure modes seem to be the most promising approach. However, these methods need to be further refined and validated in a systematic manner before they could be used in engineering practice. Sophisticated finite element models have also been developed to analyse infilled structures. While these models are general and widely applicable to different types of infilled frames, they should be used with caution because they could be easily misused and lead to unconservative results. This paper summarizes some of the recent findings and developments on the behaviour and modelling of infilled structures, and provides thoughts for future research.

Design of Wideband Thin Layer Planar Absorber

—The most important requirements of well designed planar absorbers are compact size or thin layer structure and wideband performance for a specified reflectance level. In this paper, analytical treatment of thin planar absorber structures having two layers is given. The possibility of obtaining wideband performance of such structures using magnetic and electric dispersive materials is examined. Illustrative curves are given for the cases that produce an optimized 20 dbs bandwidth absorber. Optimum frequency dependence of absorber materials that can lead to wideband performance with lowest possible reflectance levels has also been deduced.

Modal Analysis of Steel-Framed Residential Structures for Application to Seismic Design

There has been a significant worldwide increase in the use of cold-formed steel in low-rise resi dential structures as an alternative to timber. A major research project to assess the performance under lateral loading of cold-formed steel frames commenced more than 7 years ago at The University of Melbourne, Australia, in collaboration with industry and other research organizations. This paper reports key findings from an extensive experimental program. It details a particular aspect of the program that uses nondestruc tive dynamic testing to identify the basic dynamic properties of such structures. Laboratory tests, employing a shaking table, have been conducted on unclad wall panels and a model test house to study the influence of different framing connection types and to assess the influence of nonstructural components, namely, plas terboard interior lining and brick-veneer exterior cladding. The findings from these tests were verified and further extended by testing a full-scale prototype house at various stages of construction. This paper presents information concerning typical natural frequencies and mode shapes for such structures. It also details the contribution of nonstructural components to the lateral stiffness, which was found to be significant. The re sults have important implications for seismic design and performance of such structures, even in regions of low to moderate seismicity.

Experimental Performance of a Seawall Model Under Seismic Conditions

Man-made islands have recently been considered as possible new construction sites for a variety of facilities. The performance of the seawalls bounding these islands when subjected to seismic loading is an important aspect of design. To obtain data on the performance of such structures when founded on a medium dense sand seabed and supported by an armored embankment, a series of large scale centrifuge models were tested at the University of California, Davis. The concrete caisson within the seawall was found to settle, displace laterally and rotate slightly away from the backfill. However, the deformations were limited, and global failure of the structure did not occur despite base accelerations of up to 0.6 g. The model accelerations were amplified up through the substratum and caisson during relatively small events, but were strongly attenuated during the larger events. Zones containing high excess pore pressures were generally located towards the top of the sand fill forming the island, and in the seabed below the toe of the armored embankment. These zones grew progressively larger as the event magnitude increased, and accordingly the times for pore pressure dissipation to occur lengthened with increasing event magnitude.

PREDICTING THE ABSORPTION OF OPEN WEAVE TEXTILES AND MICRO-PERFORATED MEMBRANES BACKED BY AN AIR SPACE

Although theories for both membrane absorbers and micro-perforated plate absorbers have been well developed, it appears that no theory has been given for their combination, such as a glass-fibre textile or a micro-perforated membrane mounted over an airtight cavity. This paper presents a theoretical method for predicting the absorption of such a structure. The basic idea of the theory is to regard an open weave textile or a micro-perforated membrane as a parallel connection of the membrane and apertures. The predictions for both normal and random incidence have shown very good agreement with measurements. It has also been demonstrated that the absorption performance of such structures can be very high. Typically, with appropriate parameters the absorption coefficient of a glass-fibre textile or a micro-perforated membrane mounted at 100 mm from a rigid wall can exceed 0·4 over 3–4 octaves. With two layers of the material over the same total air space of 100 mm this range can extend to 4–5 octaves.

Modelling the fatigue behaviour of sandwich beams under monotonic, 2-step and block-loading regimes

FRP composite sandwich materials are being increasingly used in high-performance structural applications because of their high stiffness and low weight characteristics. At present, relatively little is known about the long-term performance of such structures, especially under multi-step loading conditions. The aim of this paper is to address such fatigue behaviour by using a fatigue model verified by experimentation. The fatigue model is based on the fatigue modulus concept (degradation of stiffness) which is proposed for core-dominated behaviour. Two non-linear cumulative damage models derived from the chosen stiffness degradation equation are examined in context with the linear Miner's damage summation and compared with available experimental data for 2-step loading. The models are then applied to examine the influence of 2-step block loading. Finally, conclusions are drawn regarding the aptness of the chosen models.

An Introduction to the Impact Behaviour of Polymer Composites Using Simplified Beam Models

The paper describes a final-year undergraduate course that has been taught at the University of Liverpool for the past three years. The main aims of the course are to introduce the student to the design of structures using multi-component (composite) materials and to the performance of such structures under impact loading. Given the complexity of generalized composite behaviour and of structural crashworthiness, a simple structural case is considered, namely, a beam subject to three-point bending. A feature of the course is that not only is linear structural response considered but also non-linear (progressive) structural collapse is covered. The course is split into four parts, namely: (i) analysis of composite laminae, (ii) analysis of laminated beams, (iii) local and global effects in sandwich beams, and (iv) post-failure and progressive collapse of sandwich beams. Static and impact loadings are considered. Comments are made on how the theories are simplified and communicated to the undergraduate students.