Shapes

Different families of geometric shapes, derived mainly from lemniscatoids, are proposed to describe ground and excited states of leptodermous distributions of nuclear matter. The transition from one spherical or ellipsoidal nucleus to several spherical or ellipsoidal nuclei or vice versa (in the decay and entrance channels of nuclear reactions: fission, fusion, and fragmentation) is particularly investigated. The geometric characteristics of these configurations are given, allowing calculations of the system energy, dynamics of the reactions, and angular distribution of the fragments.

The effect of the structural coupling in the aeroelastic stability of a packet of low-pressure turbine vanes is studied in detail. The dynamics of a 3D sector vane is reduced to that of a simplified mass-spring model to enhance the understanding of its dynamics and to perform sensitivity studies. It is concluded that the dynamics of the simplified model retains the basic features of the finite element three-dimensional model. A linear fully coupled analysis in the frequency domain of the 3D vane sector has been conducted. It is concluded that the small structural coupling provided by the casing and the inter-stage seal is essential to explain the experimental evidences. It is shown that the use of fully coupled aero/structural methods is necessary to retain the mode interaction that takes place in this type of configurations.

Methods to represent and exchange parts consisting of Functionally Graded Material (FGM) for Solid Freeform Fabrication (SFF) with Local Composition Control (LCC) are evaluated based on their memory requirements. Data structures for representing FGM objects as heterogeneous models are described and analyzed, including a voxel-based structure, finite-element mesh-based approach, and the extension of the Radial-Edge and Cell-Tuple-Graph data structures with Material Domains representing spatially varying composition properties. The storage cost for each data structure is derived in terms of the number of instances of each of its fundamental classes required to represent an FGM object. In order to determine the optimal data structure, the storage cost associated with each data structure is calculated for several hypothetical models. Limitations of these representation schemes are discussed and directions for future research also recommended.

This paper describes the design, fabrication, experimental testing and performance optimization of the morphology of a flapping wing for use on a robot capable of aerial and aquatic modes of locomotion. The focus of the optimization studies is that of wing design for aquatic propulsion. Inspiration for the research stems from numerous avian species which use a flapping wing for the dual purpose of locomotion (propulsion) in both air and water. The main aim of this research is to determine optimal kinematic parameters for marine locomotion that maximize nondimensionalized performance measures (e.g., propulsive efficiency), derived from analysis of avian wing morphing mechanisms that balance competing demands of both aerial and aquatic movement. Optimization of the kinematic parameters enables the direct comparison between outstretched (aerial) and retracted (aquatic) wing morphologies and permits trade-off studies in the design space for future robotic vehicles. Static foils represen...

Magnetic stimulators are used for transcranial and peripheral stimulation of nerves for diagnostic, therapeutic, and research purposes. Stimulation is achieved by generating a rapidly changing magnetic field to induce a current at the nerve of interest. Effective nerve stimulation requires a current transient of about 108A/s. This current is obtained by switching the current through a thyristor or an insulated gate bipolar transistor (IGBT). Insulated gate bipolar transistors have better turn off characteristics than thyristors. Due to the large currents, fast switching, and inductive load required in magnetic stimulators, spike voltages can occur and cause device damage. Therefore, they require elaborate protection circuitry. Contemporary magnetic stimulators are large, bulky, and give a current wave that is constrained by the device characteristics rather than decided by physiology. Recent instruments using IGBTs have addressed this question. However, the IGBTs require special considerations to protect them against damage. No magnetic stimulators reported so far can stimulate at rates greater than 60 Hz (Magstim Rapid2, two linked stimulators). A novel magnetic stimulator design is presented in this paper which uses a set of stacked coils driven by independent but synchronized electronic circuits to distribute the current so that only a fraction of the required current flows through any given circuit element. The coils can be arranged in several different geometries, depending on the location and shape of the nerves to be stimulated. While such paralleling of coils and control circuits is not so important for the thyristor circuit design, in the case of the IGBT design it allows the use of smaller IGBTs and better transient control. The design of the coils and independent excitation improves the current control and the magnetic field that is generated. The result is a portable instrument with well controlled rectangular pulse shapes. This stimulator is also capable of much higher frequencies (tested up to 100 Hz) than previously reported. Experimental tests have been compared with the biophysical analysis of stimulation with this instrument. Peripheral nerve stimulation and the elicited compound muscle action potential was used to validate the instrument. The instrument has been tested for the controlled recruitment of a compound nerve at up to 100 Hz. In this paper we present a portable magnetic stimulator capable of high frequency stimulation and rectangular stimulation pulse. These features should give fresh momentum to the use of magnetic stimulation in neurological investigations and interventions. In particular, we expect that it will find wide clinical use such as in pediatric neurology, psychiatry, and neuromodulation.

This article investigates the cross-modal correspondences between musical timbre and shapes. Previously, such features as pitch, loudness, light intensity, visual size, and color characteristics have mostly been used in studies of audio-visual correspondences. Moreover, in most studies, simple stimuli e.g., simple tones have been utilized. In this experiment, 23 musical sounds varying in fundamental frequency and timbre but fixed in loudness were used. Each sound was presented once against colored shapes and once against grayscale shapes. Subjects had to select the visual equivalent of a given sound i.e., its shape, color (or grayscale) and vertical position. This scenario permitted studying the associations between normalized timbre and visual shapes as well as some of the previous findings for more complex stimuli. One hundred and nineteen subjects (31 females and 88 males) participated in the online experiment. Subjects included 36 claimed professional musicians, 47 claimed amate...

Redundant constraints are generally avoided in mechanism design because they can lead to binding or loss in expected mobility. However, in certain distributed-compliance flexure mechanism geometries, this problem is mitigated by the phenomenon of elastic averaging. Elastic averaging is a design paradigm that, in contrast with exact constraint design principles, makes deliberate and effective use of redundant constraints to improve performance and robustness. The principle of elastic averaging and its advantages are illustrated in this paper by means of a three-beam parallelogram flexure mechanism, which represents an overconstrained geometry. In a lumped-compliance configuration, this mechanism is prone to binding in the presence of nominal manufacturing and assembly errors. However, with an increasing degree of distributed-compliance, the mechanism is shown to become more tolerant to such geometric imperfections. The nonlinear elastokinematic effect in the constituent beams is show...

A method for the synthesis of four-bar mechanisms to generate closed paths through shape optimization is herein introduced. The objective function is not based on Fourier descriptors, but rather on the cyclic angular deviation (CAD) vector associated with a set of desired points on the curve. A simple method is introduced to account for the starting point shift between the desired CAD and the generated one. Following shape optimization, a simple mathematical approach is devised to properly scale, rotate, and translate the mechanism to the desired configuration. Two case studies are presented to demonstrate the effectiveness and robustness of the proposed method.

A microchannel heat sink shape optimization has been performed using response surface approximation. Three design variables related to microchannel width, depth, and fin width are selected for optimization, and thermal resistance has been taken as objective function. Design points are chosen through a three-level fractional factorial design of sampling methods. Navier–Stokes and energy equations for steady, incompressible, and laminar flow and conjugate heat transfer are solved at these design points using a finite volume solver. Solutions are carefully validated with the analytical and experimental results and the values of objective function are calculated at the specified design points. Using the numerically evaluated objective-function values, a polynomial response surface model is constructed and the optimum point is searched by sequential quadratic programming. The process of shape optimization greatly improves the thermal performance of the microchannel heat sink by decreasing thermal resistance of about 12% of the reference shape. Sensitivity of objective function to design variables has been studied to utilize the substrate material efficiently.

This work is devoted to the study of nonlinear dynamics of structures with cyclic symmetry under geometrical nonlinearity using the harmonic balance method (HBM). In order to study the influence of the nonlinearity due to large deflection of blades, a simplified model has been developed. It leads to nonlinear differential equations of the second order, linearly coupled, in which the nonlinearity appears by cubic terms. Periodic solutions in both free and forced cases are sought by the HBM coupled with an arc length continuation and stability analysis. In this study, specific attention has been paid to the evaluation of nonlinear modes and to the influence of excitation on dynamic responses. Indeed, several cases of excitation have been analyzed: punctual one and tuned or detuned low engine order. This paper shows that for a localized, or sufficiently detuned, excitation, several solutions can coexist, some of them being represented by closed curves in the frequency-amplitude domain....

An infinite number of closed-form solutions is reported for a deterministically or stochastically nonhomogeneous beam, for both natural frequencies and reliabilities, for specialized cases. These solutions may prove useful as benchmark solutions. Numerical examples are evaluated.

An infinite number of closed-form solutions is reported for a deterministically or stochastically nonhomogeneous beam, for both natural frequencies and reliabilities, for specialized cases. These solutions may prove useful as benchmark solutions. Numerical examples are evaluated.

There has been relatively little warnings research directed at systematically examining the component features comprising existing warning signs as specified in standards (ANSI Z535) and guidelines (e.g., FMC, 1985 ; Westinghouse, 1981). This research examines several elemental features found in real-world warning signs to determine their individual as well as their combined effects on people's hazard perceptions. Various colors, signal words, shapes and configurations-both individuallyand in combination-comprisingexisting warning headers as well as newly developed constituents were evaluated in a series of rating and ranking tasks. The results conf"mned several existing published recommendations (e.g., the color red is perceived to connote more hazard than other solid colors), but also showed instances where people's perceptions differed from those assumed in design standards and guidelines. Some newly-developed header configurations (e.g., having a skull icon to the right of the signal world) show promise as alternatives for signaling hazardous conditions.

Shape computation theory was developed for over 4 decades, demonstrating that designs can be described step-wise by formal rules similar to those of a mathematical system. A shape grammar is a rule-based system that generates a set of visual configurations (shapes) by capturing the interaction of spatial elements of 0, 1, 2 and 3 dimensions. Shape grammars include a calculating and a syntactic-interpretive part. The calculating part provides an algebraic framework for computations with shapes. The syntactic-interpretive part consists of productive rule statements assigning structure and meaning to shapes and their computations. This presentation includes useful teaching material for introducing shape grammars to students. Examples of spatial relationships and shape rules, Euclidean transformations and symmetry, as well as numerous derivations of designs are presented. 3D shapes from the spatial vocabulary of the Froebelian gifts are used in the examples. A version of these notes was presented in SIGRAPH2008.

— With increase in the temperature due to global warming cold air is necessary for human being. Air conditioning system for air cooling is always better option but there is high level of power consumption and to overcome such difficulty vortex flow cooling is the better option. In vortex flow due to geometry more the turbulence in the flow and which dissipates more amount of heat and to enhance the rate of heat transfer cooling water will be circulated and this is nothing but aim of present work.

Spar platforms with cylindrical shape and constant cross-section area may experience resonant heave motions in sea states with long peak periods, which are probably excessive for riser integrity due to its low damping and relatively low natural heave period. Changes to hull shape ...

In fusion laser designs, the laser pulse has a complicated temporal shape which undergoes significant change as it passes through the laser. Our damage data, however, was taken with pulses whose temporal shapes were (more or less) Gaussian. We want to determine the damage propensity of a material exposed to a pulse of arbitrary temporal shape, given data taken with Gaussian pulses of different pulse widths. To do so, we must adopt a physical model of damage. This model will contain some number of parameters that depend on material properties, geometry, and so forth. We determine the parameters of the model appropriate to each material by fitting the model to the Gaussian data for that material. The resulting normalized model is then applied, using the appropriate pulse shape, to find the damage level for a specific material subjected to a specific pulse. The model we shall assume is related to diffusion, although (as we shall see) the experimental results do not fit any simple diffusion model. Initially, we will discuss simple diffusion models. We then examine some experimental data, and then develop a modified diffusive model from that data. That modified model is then used to predict damage levels in various portions of the NIF laser design.

Nanotribology and nanomechanics studies are needed to develop a fundamental understanding of interfacial phenomena on a small scale and to study interfacial phenomena in micro-/nanoelectromechanical systems (MEMS/NEMS), magnetic storage devices, and other applications. Friction and wear of lightly loaded micro-/nanocomponents are highly dependent on surface interactions (few atomic layers). These structures are generally coated with molecularly thin films. Nanotribology and nanomechanics studies are also valuable in the fundamental understanding of interfacial phenomena in macrostructures and provide a bridge between science and engineering. An atomic force microscope (AFM) tip is used to simulate a single-asperity contact with a solid or lubricated surface. AFMs are used to study the various tribological phenomena, which include surface roughness, adhesion, friction, scratching, wear, detection of material transfer, and boundary lubrication. In situ surface characterization of local deformation of materials and thin coatings can be carried out using a tensile stage inside an AFM. Mechanical properties such as hardness, Young’s modulus of elasticity, and creep/relaxation behavior can be determined on micro- to picoscales using a depth-sensing indentation system in an AFM. Localized surface elasticity and viscoelastic mapping of near-surface regions can be obtained with nanoscale lateral resolution. Finally, an AFM can be used for nanofabrication/nanomachining.

The enhanced Hoshen-Kopelman (EHK) algorithm for the analysis of connected components in images that are unbounded in one of their dimensions is introduced. The algorithm characterizes in a single pass the shapes of all the connected components in a multiple class image by computing the spatial moments, the area, the boundary, and the bounding boxes of the connected components. The algorithm is applied to a real-time surface defect simulation and to a Landsat image analysis. The algorithm's performance is compared to the performances of related algorithms.

Experimental modal analysis was performed on RC beams with honeycombs. The mode shapes were extracted, and the eigenvectors were used in determining the mode shape equations using nonlinear regression. The equation used in the regression was the generalized solution of transverse vibration of a Bernoulli-Euler prismatic beam. By utilizing the regressed phase variable, the global flexural stiffness was evaluated. It was observed that the global stiffness dropped with increasing volumes of the honeycombs in the beam. The results were compared with values computed using the secant modulus from the load-deflection plot obtained upon loading at each load stage and the trend was similar. The local stiffness indicator was used successfully to locate the region of the honeycombs. (C) 2015 Elsevier Ltd. All rights reserved.

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http://www.sciencedirect.com/science/article/pii/S0263224115000068
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