Beam (structure)

About: Beam (structure) is a research topic. Over the lifetime, 155735 publications have been published within this topic receiving 1420731 citations.

A microstructure-dependent Timoshenko beam model based on a modified couple stress theory

Abstract: A microstructure-dependent Timoshenko beam model is developed using a variational formulation. It is based on a modified couple stress theory and Hamilton's principle. The new model contains a material length scale parameter and can capture the size effect, unlike the classical Timoshenko beam theory. Moreover, both bending and axial deformations are considered, and the Poisson effect is incorporated in the current model, which differ from existing Timoshenko beam models. The newly developed non-classical beam model recovers the classical Timoshenko beam model when the material length scale parameter and Poisson's ratio are both set to be zero. In addition, the current Timoshenko beam model reduces to a microstructure-dependent Bernoulli–Euler beam model when the normality assumption is reinstated, which also incorporates the Poisson effect and can be further reduced to the classical Bernoulli–Euler beam model. To illustrate the new Timoshenko beam model, the static bending and free vibration problems of a simply supported beam are solved by directly applying the formulas derived. The numerical results for the static bending problem reveal that both the deflection and rotation of the simply supported beam predicted by the new model are smaller than those predicted by the classical Timoshenko beam model. Also, the differences in both the deflection and rotation predicted by the two models are very large when the beam thickness is small, but they are diminishing with the increase of the beam thickness. Similar trends are observed for the free vibration problem, where it is shown that the natural frequency predicted by the new model is higher than that by the classical model, with the difference between them being significantly large only for very thin beams. These predicted trends of the size effect in beam bending at the micron scale agree with those observed experimentally. Finally, the Poisson effect on the beam deflection, rotation and natural frequency is found to be significant, which is especially true when the classical Timoshenko beam model is used. This indicates that the assumption of Poisson's effect being negligible, which is commonly used in existing beam theories, is inadequate and should be individually verified or simply abandoned in order to obtain more accurate and reliable results.

Negative dispersion using pairs of prisms.

Abstract: We show that pairs of prisms can have negative group-velocity dispersion in the absence of any negative material dispersion. A prism arrangement is described that limits losses to Brewster-surface reflections, avoids transverse displacement of the temporally dispersed rays, permits continuous adjustment of the dispersion through zero, and yields a transmitted beam collinear with the incident beam.

Bernoulli–Euler beam model based on a modified couple stress theory

Abstract: A new model for the bending of a Bernoulli–Euler beam is developed using a modified couple stress theory. A variational formulation based on the principle of minimum total potential energy is employed. The new model contains an internal material length scale parameter and can capture the size effect, unlike the classical Bernoulli–Euler beam model. The former reduces to the latter in the absence of the material length scale parameter. As a direct application of the new model, a cantilever beam problem is solved. It is found that the bending rigidity of the cantilever beam predicted by the newly developed model is larger than that predicted by the classical beam model. The difference between the deflections predicted by the two models is very significant when the beam thickness is small, but is diminishing with the increase of the beam thickness. A comparison shows that the predicted size effect agrees fairly well with that observed experimentally.

Laser beam combining for high-power, high-radiance sources

Abstract: Beam combining of laser arrays with high efficiency and good beam quality for power and radiance (brightness) scaling is a long-standing problem in laser technology. Recently, significant progress has been made using wavelength (spectral) techniques and coherent (phased array) techniques, which has led to the demonstration of beam combining of a large semiconductor diode laser array (100 array elements) with near-diffraction-limited output (M/sup 2//spl sim/1.3) at significant power (35 W). This paper provides an overview of progress in beam combining and highlights some of the tradeoffs among beam-combining techniques.

Piezomagnetoelastic structure for broadband vibration energy harvesting

Abstract: The present invention relates to the field of energy harvesting. More particularly, embodiments of the invention relate to methods, systems, and devices for scavenging vibration- based energy from an ambient vibration source. Specific embodiments of the present invention include an energy harvesting device comprising: a) an elongated ferromagnetic cantilevered beam having a base and an opposing end; b) a plurality of piezoceramic elements operably connected to the base of the beam; c) a first support member for supporting the beam at its base; and d) two permanent magnets disposed on a second support member; wherein the base end of the beam is operably connected to the support member such that the beam is suspended lengthwise from the support member at its base and the opposing end of the beam is free and is disposed a selected distance above and between the magnets; and wherein the piezoceramic elements are operably connected in parallel to each other, such that during operation the beam is capable of scavenging vibrational energy from an external excitation source and the piezoceramic elements are capable of converting the harmonic or random vibrational energy into electrical energy. The piezo-magneto-elastic generator results in a 200% increase in the open- circuit voltage amplitude (hence promising an 800% increase in the power amplitude). The inventive piezo-magneto-elastic generator can be applied for use in piezoelectric energy harvesting, as well as in electromagnetic, electrostatic and magnetostrictive energy harvesting techniques and their hybrid combinations with similar devices.