Structural vibrations caused by a flowing fluid. Whenever a structure is exposed to a flowing fluid,…

Flow-induced vibration

Impact resistance and damage tolerance of fiber reinforced composites: A review

The use of X-ray computed tomography for design and process modeling of aerospace composites: A review

Although good progress was made by two international benchmark exercises on in-plane permeability, existing methods have not yet been standardized. This paper presents the results of a third benchmark exercise using in-plane permeability measurement, based on systems applying the radial unsaturated injection method. 19 participants using 20 systems characterized a non-crimp and a woven fabric at three different fiber volume contents, using a commercially available silicone oil as impregnating fluid. They followed a detailed characterization procedure and also completed a questionnaire on their set-up and analysis methods. Excluding outliers (2 of 20), the average coefficient of variation (cv) between the participant?s results was 32% and 44% (non-crimp and woven fabric), while the average cv for individual participants was 8% and 12%, respectively. This indicates statistically significant variations between the measurement systems. Cavity deformation was identified as a major influence, besides fluid pressure / viscosity measurement, textile variations, and data analysis.

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In-plane permeability characterization of engineering textiles based on radial flow experiments: A benchmark exercise

A review of flow-induced vibration energy harvesters

In this work, three types of 3D woven fabric (orthogonal, angle interlock, and layer-to-layer) were used to study the effect of weaving architecture on processing and mechanical properties. In orde...

The mechanical properties of 3D woven composites

Compaction and permeability characterization of fibrous reinforcements is fundamental to liquid composite molding (LCM) processes, given that these fabric properties determine the part thickness, fiber volume content and mold filling time and patterns. In this study, the permeability of three different 3D woven carbon fiber reinforcements (orthogonal, angle interlock and layer-to-layer) was studied, each having a different weave style and z-binder pattern. For all reinforcements, single-cycle and multiple cycle compaction experiments were conducted on dry and saturated samples. The orthogonal preforms were more difficult to compact to the target fiber volume fraction of 0.65, with peak stresses reaching up to 2.3 MPa. Cyclic compaction tests were conducted to highlight the importance of permanent deformation in the reinforcements, when higher fiber volume content is desired via manufacturing using an LCM process. Unsaturated in-plane radial and saturated through-thickness permeability data were obtained at several fiber volume fractions. The orthogonal and layer-to-layer fabrics exhibited greater levels of anisotropy in the plane of flow. The rate of change of in-plane permeability with increasing fiber volume content was lower compared to through-thickness values. The effect of cyclic compaction on permeability was greater in the orthogonal and angle interlock reinforcements. Micrographs of infused samples showed significant permanent deformation of the z-binder yarns, an effect that reduced permeability at high fiber volume contents.

Characterization of 3D woven reinforcements for liquid composite molding processes

Origami, the ancient Japanese art of folding paper to create esthetic sculptures, has recently emerged in the scientific literature as an innovative means to build mechanical structures with tailorable properties. Along those lines, the Kresling origami pattern has been used to design and construct bi-stable bellows with tailorable stiffness. In this work, we exploit the inter-well dynamic behavior of such bellows to develop and characterize a cluster of mechanical binary switches that can be selectively operated using a single input. This input is in the form of a harmonic resonant excitation with a pre-selected frequency and magnitude applied at the base of the switch. Using a phenomenological model of the switch, we study its nonlinear dynamic behavior and approximate its activation frequency bandwidth. We also demonstrate that multiple binary switches of different geometric characteristics can be combined to create a mechanical memory board of multiple bits placed on a single harmonically excited platform.

An origami-inspired dynamically actuated binary switch

When a bi-stable oscillator undergoes a supercritical Hopf bifurcation due to a galloping instability, intra-well limit cycle oscillations of small amplitude are born. The amplitude of these oscillations grows as the flow speed is increased to a critical speed at which the dynamic trajectories escape the potential well. The goal of this paper is to obtain a simple yet accurate analytical expression to approximate the escape speed. To this end, three different analytical approaches are implemented: (i) the method of harmonic balance, (ii) the method of multiple scales using harmonic and elliptic basis functions, and (iii) the Melnikov criterion. All methods yielded an identical expression for the escape speed with only one key difference which lies in the value of a constant that changes among the different methods. A comparison between the approximate analytical solutions and a numerical integration of the equation of motion demonstrated that the escape speed obtained via the multiple scales method using the elliptic functions and the Melnikov criterion are in excellent agreement with the numerical simulations. On the other hand, the first-order harmonic balance technique and the multiple scales using harmonic functions provide analytical estimates that significantly underestimate the actual escape speed. Using the Melnikov criterion, the influence of parametric and additive noise on the escape speed was also studied.

Potential well escape in a galloping twin-well oscillator

Small scale flow energy harvesters are designed to operate at low elevations where surface effects cause significant flow velocity variations. To harness flow energy efficiently in such environments, the harvester must be very sensitive to flow fluctuations. In particular, the rise time of the harvester to the steady-state value must be short. This Letter proposes a method to reduce the rise time of galloping flow energy harvesters by passively manipulating the flow near the trailing edge. To this end, the rear face of the square prism typically used in galloping energy harvesting is augmented with Y-shaped fins of different lengths and fork angles. The addition of the fins is shown to significantly increase the rate at which the magnitude of the normal force coefficient grows with the angle of attack. This, in turn, can reduce the rise time of the harvester by as much as 75% when compared to the finless square prism. The addition of the fins has no detrimental influence on the steady-state performance of the harvester. On the contrary, the steady-state voltage of the harvester can also be improved for some fin geometries.

Hussam Alhussein

Papers

The mechanical properties of 3D woven composites

Characterization of 3D woven reinforcements for liquid composite molding processes

An origami-inspired dynamically actuated binary switch

Potential well escape in a galloping twin-well oscillator

Improving the sensitivity of galloping energy harvesters to flow fluctuations