Structural Design Considerations Research Articles

Hollow Metallic Micromachined Needle Arrays

In this paper, fluid coupled metallic micromachined needle arrays are designed, fabricated, packaged, and characterized. The described hollow metallic needle arrays include design features such as dual structural supports and needle coupling channels. The supports and needle walls are formed by micro-electroformed metal to provide increased structural integrity. The needle coupling channels are used to fluidically interconnect the needles and allow pressure equalization and balance of fluid flow between needles. In addition, the needle coupling channels minimize the effects of restricted needle passages by providing a redistribution point for fluid flow between them. The optimum design for the needle coupling channels is investigated using an ANSYS finite element numerical model. The significance of this work includes the development of hollow, metallic micromachined needle arrays for biomedical applications, as well as, a discussion of structural, fluidic, and biological design considerations

A novel compact PMSM with magnetic bearing for artificial heart application

This paper describes a novel compact permanent-magnet synchronous motor with a configuration of axial-field slotted windings. It is designed for driving an artificial heart. Both the motor rotor and the pump impeller of the artificial heart are levitated by a magnetic bearing. Structure description, design considerations, and analyses for the motor and bearing are presented in this paper.

Structural Design Considerations in House Builders' Model: Optimization Approach

In a housing market model, the supply of housing, particularly new houses, is usually treated in a very cursory fashion, with new housing being regarded as homogeneously good and building cost function defined as a function of capital and labor costs. This paper formally recognizes heterogeneity in a housing model and introduces engineering design parameters in building cost function. Using structural engineering concepts, an engineering cost function is derived in terms of design parameters. A multiobjective compromise optimization algorithm is suggested to choose from various building cost functions. An empirical application of this method is demonstrated by solving the production function of a modular room 3.5 m × 3.5 m in area and 3.14 m in height.

Design-Construction of Umbrella-Shaped Precast Folded Plate Roofs for Pavilions

Based on a system developed in China, this article describes an umbrella-shaped precast, prestressed folded plate roof for pavilion buildings, which have been built successfully in San Pedro Sula, Honduras. The method relies on precast, prestressed flat plates and V-sections. These panels are assembled into an umbrella shape with joints formed and cast-in-place to fully integrate the structure. The author presents the design concept, structural design considerations, connections issues, panel production and erection, and joint closure. This folded plate roofing system can be used in other building applications.

Micromachined needle arrays for drug delivery or fluid extraction.

Micromachined needle arrays have been designed, fabricated, and characterized. The design includes arrays of 25 needles with fluid coupling channels and dual structural supports. Numerical modeling of fluid flow characteristics was performed, demonstrating that the needle coupling channels redistribute flow when the input or output ports are fully restricted. Micromachining technologies have been used to batch fabricate hollow metallic fluid coupled needle arrays. The significance of this work includes the development of the hollow metallic micromachined needle arrays for biomedical applications, as well as a discussion of structural, fluidic, and biological design considerations. The micromachined needle array has many advantages, including (a) reduced trauma at penetration site (small size), (b) greater freedom of patient movement (minimal penetration), (c) a practically pain-free drug delivery device (distribution of force), (d) precise control of penetration depth (needle extension length), and (e) they can be stacked and packaged into a 3-D device for fluid transfer.

Developments in aircraft interior acoustics—Recent progress and directions

Aircraft interior noise is a continuing problem for a wide range of aircraft types. High interior noise levels in general aviation aircraft make any communication difficult, significantly impact pilot endurance, and are considered important to the reemergence of this class of aircraft. For passengers in propeller-powered commuter aircraft, conversation is difficult at best and becomes oppressive on the passengers for long periods. It is also regarded as one reason for the replacement of propeller commuter aircraft by the emerging regional jet. In business jets, the passengers are often interested in conducting meetings during flights. This calls for low SPL and SIL for which the aircraft incurs both space and weight penalties. Large commercial aircraft pay a significant weight penalty for current interior noise levels considered acceptable. With the drive for more weight-efficient airframes, the challenge becomes even more difficult. This paper will overview current efforts to develop both design and noise control techniques. These range from improvements in the quantification of the noise sources, to considerations in the overall structural design, and to the use of both active and passive control tools. In addition, the emerging use of predictive and measurement tools will be discussed and applications to aircraft highlighted.

Recombination current in GaAs/AlGaAs heterostructure bipolar transistors

The dependence of the performance of GaAs/AlGaAs finger geometry HBTs on surface processing and on structural design considerations is investigated. It is found that these factors have significant effect on mesa edge leakage current and therefore on device gain. However, it is noted that the changes effected by annealing and chemical processing are unstable, and that any improvement or degradation of device performance by these means is progressively reduced on storage in air at room temperature.

Design-Construction of Precast Prestressed Concrete Floating Wave Attenuator

Precast, prestressed concrete was used imaginatively to build the first phase of a 960 ft (293 m) floating wave attenuator in Flushing Bay, New York. The precast system proved to be cost effective and efficiently constructable, while also solving the site constraints and environmental issues. The attenuator features three 16 ft (4.9 m) wide, 320 ft (97.5 m) long sections comprising 8 ft (2.4 m) wide, 40 ft (12.2 m) long precast, prestressed polystyrene-filled concrete box units transversely post-tensioned together. This article provides the conceptual system, bidding process, design criteria and structural design considerations of the project as well as highlights of the manufacture, transportation, and erection of the precast segments.

A Progressive Damage Model and Analysis Methodology for Predicting the Residual Strength of Composite Laminates

The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve efficient and economical structural designs. The purpose of the research presented in this paper is to experimentally verify the application of the damage model developed by the authors to predict progressive damage development in a toughened material system. Damage growth, stiffness degradation, and residual strength were experimentally determined for cross-ply and quasi-isotropic IM7/5260 graphite/bismaleimide laminates due to monotonic and tension-tension fatigue. The damage model, which has been implemented into a finite element code, was used to predict the stiffness loss and residual strength of unnotched and notched laminates. The model predictions were in good agreement to experimental results for several different fatigue loading histories and several different laminate stacking sequences.

Spliced Bulb-Tee Girders Bring Strength and Grace to Pueblo's Main Street Viaduct

The new $7.6 million Main Street Viaduct in Pueblo, Colorado, is a six-span precast, prestressed concrete bulb-tee girder bridge, spliced together with post-tensioning. The overall length of the structure is 807 ft (246 m) with a maximum central span of 174 ft (53 m). There are eight girder lines with girders varying in depth from 72 in. (1829 mm) at the ends to 96 in. (2438 mm) at the center, creating an attractive haunched effect. The project was constructed within the designated 12-month time frame and was under budget. This article discusses the design alternatives and structural design considerations. Production, transportation and erection of the precast concrete components are also highlighted.

Experimental Verification of a Progressive Damage Model for IM7/5260 Laminates Subjected to Tension-Tension Fatigue

The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve structurally efficient and economical designs. The purpose of this research is to experimentally verify the application of a continuum damage model to predict progressive damage development in a toughened material system. Damage due to monotonic and tension-tension fatigue was documented for IM7/5260 graphite/bismaleimide laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables to predict stiffness loss in unnotched laminates. A damage dependent finite element code predicted the stiffness loss for notched laminates with good agreement to experimental data. It was concluded that the continuum damage model can adequately predict matrix damage progression in notched and unnotched laminates as a function of loading history and laminate stacking sequence.

Precast Partnering Provides Solution for USAA Office Building and Parking Structure

Precast and prestressed concrete played a prominent role in meeting the stiff requirements of the new USAA Southeast Regional Office Building and Parking Structure in Tampa, Florida. The seven-story office building and five-level parking structure are separated into two curving volumes facing an existing man-made lake. These volumes unite to form a single south facade characterized by a large-scale grid of punched windows in a horizontally banded exterior wall. The free standing 1600-car parking structure is all-precast, employing a distinctive loadbearing ladder wall system with a pretopped double tee floor system. The authors present the architectural requirements and environmental issues, the structural design considerations and some production/erection highlights of the proiect. A key ingredient, which ensured the success of the project, was the concept of partnering ― the theme of which is carried throughout the article

Ply layup optimization and micromechanics tailoring of composite aircraft engine structures

A ply layup optimization and micromechanics tailoring capability for composites aircraft engine components is under development. The composites optimization methodology is multidisciplinary, encompassing structural, heat transfer, and aeromechanical design considerations. The methodology includes provision for handling multiple objective functions and a framework for approximation of both the response functions and its derivatives. Derivative approximations are found to be sufficiently accurate to guide the numerical search in the right direction. A micromechanics tailoring procedure to correlate the calculated and measured lamina properties at elevated temperatures is outlined. The micromechanics tailoring also provides the ability to back out effective (in situ) matrix properties as part of the composite. Several real life aircraft engine components are optimized for structural, thermal, and aeromechanical responses as design objectives and constraints.

Wisconsin Avenue Viaduct Design-Construction Highlights

The new Wisconsin Avenue Viaduct in Milwaukee, Wisconsin, is an imaginatively designed 1456 ft (443,80) long eleven-span precast, prestressed concrete arch structure. A key element in the design of this bridge is the use of curved U-shaped precast, post-tensioned arch segments that functioned as both load-carrying structural members and as self-supporting permanent forms. The deck is formed by standard AASHTO pretensioned concrete girders that frame into cast-in-place cross beams. The innovative use of precast arch segments and standard girders shortened the construction period and cost an estimated $2 million less than a similar cast-in-place concrete arch bridge. This article discusses the design challenge, design solution, aesthetics, structural design considerations, construction highlights, and cost breakdown.

Hydrocarbon production concepts for dynamic annual sea ice regions

Petroleum production from Russian seas such as the northern Timan-Pechora Basin (Pechora Sea) and the northeastern Sakhalin Island Shelf (Sea of Okhotsk) is likely to occur in the near future. Several different types of offshore structures may be needed in the Russian arctic offshore to support development activities. These structures may include: a number of production structures for offshore fields, subsea pipelines, a regional tanker terminal, and ice-breaking tankers. Dynamic first-year sea ice will be a major design consideration for offshore structures considered for use in these areas. Exxon previously performed engineering studies for petroleum development in Norton Sound off the west coast of Alaska. Norton Sound is also an area of dynamic first-year sea ice, so many of the lessons learned and much of the technology developed for that region are considered to be applicable to the Pechora Sea and the Sakhalin Shelf. Several of the concepts for production structures, pipelines, terminals, and tankers are presented along with a discussion of the related ice technology. Field and laboratory studies undertaken to collect environmental data are described along with a probabilistic load calculation procedure for structure design. More recent work by Exxon to enhance technology since the Norton Sound studies is also presented along with a discussion of recommended future work activities.

Design, fabrication and characterization of high-speed asymmetric Fabry-Perot modulators for optical interconnect applications

Free-space ‘smart-pixel’ optical interconnect architectures promise to relieve the interconnect ‘bottleneck’ in high-speed parallel computers and switching systems. One of the most promising output devices that has been advanced for use in these systems is the asymmetric Fabry-Perot modulator, or AFPM, which offers high on-off contrast, low insertion loss, and low operating voltage swing, among other advantages. In this paper we summarize our work on optimizing the AFPM for high-speed operation, including analysis of the material structure design considerations, fabrication of small (16×20 μm) devices, and high-speed electrical and optical characterization of the finished modulators. We conclude that at relatively high incident optical intensities the modulators' speed appears to be limited by transit effects to about 18 GHz, but that at lower optical intensities their frequency response outstrips that of our 20 GHz measurement apparatus — that is, these AFPMs are still capable of large signal modulation (20 dB contrast, 1.5 dB insertion loss) at low AC voltage swings (±3 V) for operating frequencies up to 20 GHz. We presume that further investigation will prove them to be RC-limited in this low-intensity regime to speeds of about 35 GHz.

Design considerations for channel-doped back-gated high electron mobility structures

We present the results of self-consistent calculations for the electronic subband structure of channel-doped, back-gated GaAs-AlGaAs heterostructures. The calculations identify the important design parameters for this system and illustrate the quantum effects occurring. We show that the doping density in the channel determines the mode of operation of the device and whether resonant effects are important. We discuss the design of velocity modulation transistors and structures with improved transconductance.

Structural design considerations for a Personnel Launch System

A vehicle capable of performing the transfer of eight people to and from the Space Station Freedom is currently in the conceptual/preliminary design stages at the NASA Langley Research Center. Structural definition of this Personnel Launch System (PLS) and the considerations leading to it are described. Issues such as cost, technology level, human factors, and maintainability are used as guidelines for the structural definition. A synergistic design technique involving aerodynamics, performance, mission, packaging, and weights and sizing analyses is utilized to evaluate the structural design. A closed-loop design is achieved when the mission requirements are met by each previously mentioned analysis for a particular vehicle weight. Although satisfactory, the structural concept presented herein is not to be treated as a final answer, but one promising solution. An examination of alternative designs and more detailed analyses can be undertaken in order to identify design inadequacies and more efficient approaches.

Stress concentration structure with front beam for pressure sensor

The beam-diaphragm structure is a new type of stress concentration structure in which the stress concentration areas are separated for positive and negative stresses. Geometric design considerations for beam-diaphragm structures have been investigated theoretically and experimentally. According to the results of finite-element analysis and experimental measurements, geometric design rules for maximum sensitivity are given. Experimental results of the dependence of the non-linearity on the beam width, W 2, are also presented.

Stochastic Wave Representation of Seismic Ground Motion. I: F‐K Spectra

The spatial variation of seismic ground motion is an important consideration for the seismic design of elongated structures supported on extended foundations or on multiple supports. The temporal and spatial variability of seismic ground motion is effectively described by the frequency‐wave number spectra, which provide information concerning the corresponding correlational characteristics of earthquake motions. Until now, the frequency‐wave number spectra have only been inferred experimentally, for specific seismic events, using data from seismograph arrays. In this work, closed‐form analytic expressions of the frequency‐wave number spectra are established. The corresponding seismic ground motion is produced by a seismic source located in an elastic half‐space and characterized by a double couple. The model used considers the propagation of three‐dimensional waves in an elastic half‐space that are generated at a seismic source and their eventual reflection at the ground surface. Analytic expressions for the frequency‐wave number spectra are then derived for the three displacement components (two horizontal ones and one vertical) at the ground surface.