Swept Shape Research Articles

A new control method of the joint position at the working current at electron beam welding

Experimental studies shown that the use of an electron beam sweep in order to improve the quality of formation of a welded joint allows to transform a vapor-gas channel into a stable fusion penetration cavity along the entire depth of the weld. The presence of the cavity opens up new possibilities for the control and management of electron beam welding. In this work, the authors propose a new method for monitoring the position of welded parts butt based on the working current and X-ray radiation from the fusion penetration cavity formed during longitudinal and transverse scanning of the butt by using an electron beam with an appropriate sweep shape. A mathematical model of the method is developed, which makes it possible to study the sensor characteristics is developed.

Lateral torsional buckling of steel I-beams: Effect of initial geometric imperfection

In the current study, the influence of the initial lateral (sweep) shape and the cross-sectional twist imperfection on the lateral torsional buckling (LTB) response of doubly-symmetric steel I-beams was investigated. The material imperfection (residual stress) was not considered. For this objective, standard European IPN 300 beam with different unbraced span was numerically analyzed for three imperfection cases: (i) no sweep and no twist (perfect); (ii) three different shapes of global sweep (half-sine, full-sine and full-parabola between the end supports); and (iii) the combination of three different sweeps with initial sinusoidal twist along the beam. The first comparison was done between the results of numerical analyses (FEM) and both a theoretical solution and the code lateral torsional buckling formulations (EC3 and AISC-LRFD). These results with no imperfection effects were then separately compared with three different shapes of global sweep and the presence of initial twist in these sweep shapes. Besides, the effects of the shapes of initial global sweep and the inclusion of sinusoidal twist on the critical buckling load of the beams were investigated to unveil which parameter was considerably effective on LTB response. The most compatible outcomes for the perfect beams was obtained from the AISC-LRFD formulation; however, the EC-3 formulation estimated the Pcr load conservatively. The high difference from the EC-3 formulation was predicted to directly originate from the initial imperfection reduction factor and high safety factor in its formulation. Due to no consideration of geometric imperfection in the AISC-LFRD code solution and the theoretical formulation, the need to develop a practical imperfection reduction factor for AISC-LRFD and theoretical formulation was underlined. Initial imperfections were obtained to be more influential on the buckling load, as the unbraced length of a beam approached to the elastic limit unbraced length (Nr). Mode-compatible initial imperfection shapes should be taken into account in the design and analysis stages of the I-beam to properly estimate the geometric imperfection influence on the Pcr load. Sweep and sweep.twist imperfections led to 10% and 15% decrease in the Pcr load, respectively, thus; well-estimated sweep and twist imperfections should considered in the LTB of doubly-symmetric steel I-beams.

Direct construction of a four-dimensional mesh model from a three-dimensional object with continuous rigid body movement

Abstract In the field of design and manufacturing, there are many problems with managing dynamic states of three-dimensional (3D) objects. In order to solve these problems, the four-dimensional (4D) mesh model and its modeling system have been proposed. The 4D mesh model is defined as a 4D object model that is bounded by tetrahedral cells, and can represent spatio-temporal changes of a 3D object continuously. The 4D mesh model helps to solve dynamic problems of 3D models as geometric problems. However, the construction of the 4D mesh model is limited on the time-series 3D voxel data based method. This method is memory-hogging and requires much computing time. In this research, we propose a new method of constructing the 4D mesh model that derives from the 3D mesh model with continuous rigid body movement. This method is realized by making a swept shape of a 3D mesh model in the fourth dimension and its tetrahe-dralization. Here, the rigid body movement is a screwed movement, which is a combination of translational and rotational movement.

Changes in spectrotemporal features of echolocation signals in multiple bat assemblages.

Echolocating bats face potential acoustical interference when flying and foraging near echolocating conspecifics. Quantifying changes in the signal structure of echolocation emissions between bats flying alone and within a larger group has proven difficult. Here, we use two new methodologies, an onboard radio telemetry microphone and a multiple microphone array to record the sounds of big brown bats (Eptesicus fuscus) flying alone and in small groups both in the laboratory and in the field. In a laboratory flight room, bats changed the ending frequency of their first harmonic when the conspecific with which they were paired emitted calls at a similar frequency. In the field, ending frequency and sweep shape were more variable among groups of bats flying together than among single bats compared to one another. The presence of other nearby bats did not have any effect on the timing of emissions or the interpulse intervals [Work supported by NIH, NSF, ONR, and JSPS.]

An experimental study on the reduction of motor-fan noise by modification of the blade and shroud configuration

The noise reduction (NR) of fans used for cooling electric motors is one of the key parameters in the design of a motor fan. In the authors’ previous paper, aeroacoustic analysis (which is based on unsteady computational fluid dynamics results) was performed for the baseline fan to know its sound level. To further find a better blade shape from an NR point of view, aeroacoustic analysis on various blade profiles from the NACA-63 and NACA-65 series was conducted. In this work, an experimental study on the baseline fan and three redesigned composite material fans for the low-noise fan is performed. The experimental parameters under investigation are better aerofoil-shape blade cross-section, using inlet bell-mouth entry, using composite materials, reducing the number of blades, using uneven blade spacing, making it a mixed flow fan, using backward-skewed blade design and reducing tip clearance. From the noise measurements in a semi-anechoic chamber for Fan-2, it is observed that the overall NR was 12.8 dB(A) compared with the baseline fan. It is observed that a mixed flow fan consisting of seven evenly spaced blades of NACA 65-010 aerofoil cross-section with backward swept shape and fabricated with glass and jute fibre produced the low-noise fan design at the fan operating point.

The structure of echolocation sounds used by the big brown bat Eptesicus fuscus: Some consequences for echo processing

Analysis of the sonar emissions produced by five big brown bats (Eptesicus fuscus) during detection and range-discrimination tests show that each bat has a distinctive, “personal” emission. This may help bats distinguish their own emissions from those of others and thereby prevent jamming. Emissions usually contain three harmonics and are strongly frequency swept. Modeling of the sweep shape showed it to be more nearly linear in log time than hyperbolic (linear period modulation), which is optimal for Doppler tolerance. However, logarithmic time and linear period modulation are similar in their Doppler properties, and so bats may suffer little penalty for using a slightly nonoptimal sweep shape. We suggest that bats use logarithmic time modulation rather than linear period modulation in order to simplify signal processing during approach to prey, as this type of modulation stabilizes the filtering of echoes resulting from the bat’s automatic gain control. Likewise, the use of several harmonics in the emission may simplify signal processing of Doppler-shifted echoes by reducing the number of matched filters needed for reception.