Wanbo Liu

Experimental and Analytical Estimation of Loss Factors by the Power Input Method

The Power Input Method (PIM) is used both experimentally and a nalytically to estimate the system loss factor for sandwich panels with various configurations of Constrained Layer Damping (CLD) treatments over a broad frequency range. The experimental power input method is applied to both uniformly and non -uniformly da mped structures. Results are compared with results from other experimental methods. A new analytical power input method is proposed for evaluating the loss factor of built -up structures, based on the finite element model with assigned properties of the con stituents. The new analytical power input method is evaluated by comparison with the commonly used Modal Strain Energy (MSE) method. Instead of making an approximate correction of the constant material properties, this analytical power input method directl y takes into account the frequency -dependent material properties of the viscoelastic material using the MSC/NASTRAN direct frequency response solution. Results of experimental and analytical methods are presented, compared and discussed. It is shown that: 1) all three currently available experimental methods yield consistent results, while the power input method gives damping estimation other than just at several discrete frequencies basically in the low frequency range; 2) both the analytical power input m ethod and the modal strain energy method yield consistent results with the experimental power input method. Furthermore, both experimental and analytical power input methods are used to investigate how loss factors change as the excitation position change. This shows another merit of the analytical power input method, because analytical modal methods cannot take into account the change of excitation position.

Design and Structural Analysis of the Meridian Unmanned Aircraft

This paper describes the preliminary design, structural layout, detailed sizing and manufacturing of an uninhabited air vehicle (UAV) that will primarily be used to measure changes in glacial conditions in Antarctica and Greenland. This includes a brief description of the requirements definition and preliminary configuration design. Preliminary component weight estimations are created using empirical formulas then compared to the results of structural sizing using finite element analyses. The goal of this effort is to design an aircraft capable of autonomous operation in extreme climates that can carry various sensors including radar depth sounders and magnetometers.

Predicting Damping Loss Factors for Beams and Plates with Constrained Layer Damping

Constrained layer damping (CLD) treatments, wherein a viscoelastic sheet is sandwiched between a structural sheet or plate and a covering or constraining sheet, are widely used to suppress vibration and noise. Techniques for predicting the damping loss factor for such a construction include the Ross-Ungar-Kerwin (RUK) complex modulus technique [1] (which is only applicable when the treatment completely covers the structural sheet), the Modal Strain Energy Method [2] and the Analytical Power Input Method [3].

Method for Design and Analysis of Externally Mounted Antenna Fairings in Support of Cryospheric Surveying

Snow and ice penetrating radar antenna arrays have been developed and flown on NASA DC-8 and P-3 aircraft as part of the NASA Operation Ice-Bridge program. These arrays required custom, externally-mounted fairings to house the antennas. This paper documents the method for generating project requirements, load development, and subsequent structural design and analysis. Static load and modal tests were also performed to verify the physics based simulations. Involvement in such interdisciplinary work provides the basis for large numbers of graduate and undergraduate students to gain practical experience in designing, fabricating, ground testing and flight testing aerospace structures.

Design, Build and Fly: NASA Lockheed P-3 Orion with External Antenna Fairings

A suite of snow and ice penetrating radar arrays, used for polar remote sensing, have been developed by a team of University of Kansas and DARcorporation engineers in support of the NASA Operation Ice-Bridge program. This collaborative industry/academic partnership provided design, analysis, fabrication and testing of antenna fairings for the above mentioned radar array, as well as subsequent installation and flight testing on a Lockheed P-3 Orion aircraft. This installation has since flown multiple successful missions, generating in excess of 150TB of snow and ice data. This paper discusses the effect of the antennas on the aerodynamics, and performance, as well as the structure and manufacturing of the pylons and the antenna fairings.

Estimating Particle Damping of Honeycomb Sandwich Plates Using a Fluid Analogy

Damping loss factors of honeycomb sandwich plates with different par ticle damping treatments are estimated both experimentally and analytically. Particle dampers are made by filling different glass microbubbles into honeycomb cells. Damping is experimentally estimated using two methods: the modal curve -fitting method and t he power input method. Both damping estimation methods yield consistent loss factor estimations. Then peak damping performances are analytically explained by fluid resonances in a cavity. The relationship between the peak damping values is explained by int ernal friction among particles. The internal friction of different particles is evaluated by angle of repose test and flowability test. Applicability of this fluid model of particles is discussed. This technique shows the potential for designing high level particle damping in distinct frequency bands, which is of interest for aircraft interior noise suppression. I. Introduction ARTICLE damping is a passive vibration reduction technique enabled by the use of an enclosure filled with particles made of a varie ty of materials. The energy loss is basically due to the friction and impact between the particles. Unlike other commonly used passive damping approaches (e.g., constrained layer damping and tuned mass absorber), particle damping can be used over a broad r ange of temperature and frequencies due to its intrinsic characteristics. However, the mechanism of particle damping is still not fully understood. It is already found to be closely related to many factors, including particle size, particle density, partic le shape, particle surface friction, vibrational direction, packing ratio, vibration amplitude, etc. Witt and Kinra 1 considered single and multiple layers of smooth, steel spheres in rectangular enclosures. The measured time -history of the velocity decay at the tip of the steel beam (where the damper was attached) was used to compute the change in kinetic energy per cycle (called the “specific damping capacity”) at 20 Hz. They noted that the specific damping capacity generally increased with particle size, and changed significantly with the clearance between the particles and the enclosure. Nayfeh, Verdirame and Varanasi 2

Particle Damping of Composite Honeycomb Beams by the Power Input Method

Damping loss factors are evaluated for honeycomb composite beams with differ ent configurations of particle damping . Damping effectiveness is evaluated in two ways. First, measured frequency response functions are used in a conventional, polynomial curve -fitting modal method to evaluate damping loss factors at several natural res onanc es in the low frequency range. Secondly, the power input method is applied to evaluate damping loss factors over a broad frequency range. Both damping estimation methods (modal method and power input method) yield consistent loss factor estimations. The effect of different damping configurations has been studied, showing substantial differences in loss factor. Most interestingly, loss factors as high as 0.1 9 have been measured, corroborating reports by others. Further, a simplified fluid model of t he partially -filled honeycomb cell has been found to predict the frequency band of peak damping . This technology then, shows the potential for designing high levels of damping in distinct frequency bands, which is of interest for aircraft interior noise su ppression.