Search Results

The insertion loss of louvered terminations positioned at the end of a rectangular duct is determined using acoustic finite element analysis. Insertion loss was determined by taking the difference between the sound power with and without the louvers at the termination. Analyses were conducted in the plane wave regime and the acoustic source was anechoic eliminating any reflections from the source. The effect of different louver configurations on insertion loss was examined. Parameters investigated included louver length, angle, and spacing between louvers. Based on the analyses, equations were developed for the insertion loss of unlined louvers.

3D printing is a revolutionary manufacturing method that allows the productions of engineering parts almost directly from modeling software on a computer. With 3D printing technology, future manufacturing could become vastly efficient. However, it has been reported that the 3D printed parts exhibit anisotropic behaviors in microstructure and mechanical properties, that is, depending on the positions (infill orientations) that the parts are placed on a printer platform, the properties of resultant parts can vary greatly. So far, studies on anisotropic behaviors of 3D printed parts have been mostly limited to the static properties (modulus of elasticity, failure strength, etc.); there is a lack on the understanding of mechanical responses of 3D printed parts under dynamic conditions. In the present study, the anisotropic behaviors of 3D printed parts are investigated from the dynamic aspect.

Traditional manufacturing processes such as injection or compression molding are often enclosed and pressurized systems that produce homogenous products. In contrast, 3D printing is exposed to the environment at ambient (or reduced) temperature and atmospheric pressure. Furthermore, the printing process itself is mostly “layered manufacturing”, i.e., it forms a three-dimensional part by laying down successive layers of materials. Those characteristics inevitably lead to an inconsistent microstructure of 3D printed products and thus cause anisotropic mechanical properties. In this paper, the anisotropic behaviors of 3D printed parts were investigated by using both laboratory coupon specimens (bending specimens) and complex engineering structures (A-pillar). Results show that the orientation of the infills of 3D printed parts can significantly influence their mechanical properties.

Literature has shown that 3D printed composites may have highly anisotropic mechanical properties due to variation in microstructure as a result of filament deposition process. Laminate composite theory, which is already used for composite products, has been proposed as an effective method for quantifying these mechanical characteristics. Continuous fiber composites traditionally have the best mechanical properties but can difficult or costly to manufacture, especially when attempting to use additive manufacturing methods. Traditionally, continuous fiber composites used specialized equipment such as vacuum enclaves or labor heavy hand layering techniques. An attractive alternative to these costly techniques is modifying discontinuous fiber additive manufacturing methods into utilizing continuous fibers. Currently there exist commercial systems that utilize finite-deposition (FD) techniques that insert a continuous fiber braid into certain layers of the composite product.

The sound attenuation performance of microperforated panels (MPP) with adjoining air cavity is demonstrated. First of all, simulated results are shown based upon Maa's work investigating the parameters which impact MPP performance [1]. It is shown that the most important parameter is the depth of the adjoining cavity. Following this, an experimental study was undertaken to compare the performance of an MPP to that of standard foam. Following this, two strategies to improve the MPP performance are implemented. These include partitioning the air cavity and having a cavity with varying depth. Both strategies show a marked improvement in MPP attenuation.

The theory of patch (or panel) contribution analysis is first reviewed and then applied to a motorcycle engine on a test stand. The approach is used to predict the sound pressure in the far field and the contribution from different engine components to the sound pressure at a point. First, the engine is divided into a number of patches. The transfer functions between the sound pressure in the field and the volume velocity of each patch were determined by taking advantage of vibro-acoustic reciprocity. An inexpensive monopole source is placed at the receiver point and the sound pressure is measured at the center of each patch. With the engine idling, a p-u probe was used to measure particle velocity and sound intensity simultaneously on each patch. The contribution from each patch to the target point is the multiplication of the transfer function and the volume velocity, which can be calculated from particle velocity or sound intensity. There were two target points considered.

This paper considers two questions: how does one know when a boundary element mesh is reliable, and what are the advantages and potential pitfalls of various methods for sound radiation prediction. To answer the first question, a mesh checking method is used. With this method velocity boundary conditions are calculated on the nodes of the mesh using a point source or sources placed inside the mesh. A boundary element program is then used to calculate the sound power due to these boundary conditions. The result is compared to the known sound power of the point source or sources. This method has been used to determine the maximum frequency of a mesh, how many CHIEF points to use, etc. The second question is answered by comparing the results of several numerical methods to experimental results for a running diesel engine. The methods examined include the direct and indirect boundary element methods and the Rayleigh integral.

In this paper, the transmission loss (TL) of mufflers with a built-in catalytic converter (CC) and/or a diesel particulate filter (DPF) is predicted using the boundary element method (BEM) by either modeling the CC or DPF as a block of bulk-reacting material or by using the “element-to-element four-pole connection” between two BEM substructures. The four-pole parameters of the CC or DPF can be obtained by a measurement procedure that involves using the two-source method on a test rig with a pair of transition cones followed by a few 1-D four-pole matrix inverse operations to extract the parameters. A 3-D BEM based optimization may be further applied to fine-tune the extracted four-pole parameters. To use the bulk-reacting material modeling in BEM, the four-pole parameters will have to be converted into an equivalent set of bulk-reacting material properties. Test cases including a muffler with a series connection of CC and DPF are presented in this paper.

The design and development of new biologically inspired technologies based on intelligent materials that are capable of sensing the levels of target biomolecules and, if needed, trigger appropriate countermeasures to regulate biological processes and rhythms of the astronauts is being undertaken in our laboratories. This is accomplished by coupling biologically inspired sensors that monitor the levels of the target biomolecules with intelligent polymeric materials that can regulate the release of a countermeasure. The technology developed here integrates sensors and artificial muscle material into a self-regulating device that can perform with minimal crew intervention. Further, it takes advantage of microfabrication technology to construct lightweight and robust responsive delivery systems. These “intelligent” devices address the need for the control and regulation of biological processes and rhythms under spaceflight conditions.

Transfer path analysis is commonly used to determine input forces indirectly utilizing measured responses and transfer functions. Though it is recommended that the source should be detached from the vibrating structure when measuring transfer functions, engineers and technicians frequently have a difficult time in doing so in practice. Recently, a substitute for inverse force determination via transfer path analysis has been suggested. The indirectly determined forces are termed blocked forces and are usable so long as the source and machine are not detached from one another. Blocked forces have the added advantage of being valid even if the machine structure is modified. In this research, a typical automotive engine cover is considered as a receiver structure and is bolted to a plastic source plate excited by an electromagnetic shaker.

Finite element modeling has been used extensively nowadays for predicting the noise and vibration performance of whole engines or subsystems. However, the elastomeric components on the engines or subsystems are often omitted in the FE models due to some known difficulties. One of these is the lack of the material properties at higher frequencies. The elastomer is known to have frequency-dependent viscoelasticity, i.e., the dynamic modulus increases monotonically with frequency and the damping exhibits a peak. These properties can be easily measured using conventional dynamic mechanical experiments but only in the lower range of frequencies. The present paper describes a method for characterizing the viscoelastic properties at higher frequencies using fractional calculus. The viscoelastic constitutive equations based on fractional derivatives are discussed. The method is then used to predict the high frequency properties of an elastomer.

The paper presents work on testing of inflatable wings for unmanned aerial vehicles (UAVs). Inflatable wing history and recent research is discussed. Design and construction of inflatable wings is then covered, along with ground and flight testing. Discussions include predictions and correlations of the forces required to warp (twist) the wings to a particular shape and the aerodynamic forces generated by that shape change. The focus is on characterizing the deformation of the wings and development of a model to accurately predict deformation. Relations between wing stiffness and internal pressure and the impact of external loads are presented. Mechanical manipulation of the wing shape on a test vehicle is shown to be an effective means of roll control. Possible benefits to aerodynamic efficiency are also discussed.

Helmholtz resonators are often used in the design of vehicle mufflers to target tonal noise at a few specific low frequencies generated by the engine. Due to the uncertainty of temperature variations and different engine speeds, multiple resonators may have to be built in series to cover a narrow band of frequencies. Double-tuned Helmholtz resonators (DTHR) normally consist of two chambers connected in series. Openings or necks are created by punching small slots into a thin-walled tube which provide a natural neck passage to the enclosing volume of the Helmholtz resonator. In this paper, numerical analyses using both the boundary element (BEM) and the finite element (FEM) methods are performed and simulation results are compared against one another. A typical real-world muffler configuration commonly used in passenger vehicles is used in a case study.

The Air Force has sponsored a program at the University of Kentucky which will lead to a better understanding of the thermal and fluid instabilities during blowdown of supercritical fluids at cryogenic temperatures. An integral part of that program is the design and construction of a hydrogen test facility. This paper describes the design specifications and construction of that hydrogen test facility. This facility will be capable of providing supercritical hydrogen at 30 bars and 35 K at a maximum flow rate of 0.1 kg/s for 90 seconds. Also presented here is an extension of this facility to accommodate the use of supercritical helium.

Bench tests are an important step to developing mufflers that perform adequately with acceptable pressure drop. Though the transmission loss of a muffler without flow is relatively simple to obtain using the two-load method, the presence of mean flow modifies the muffler behavior. The development of an insertion loss test rig is detailed. A blower produces the flow, and a silencer quiets the flow. Acoustic excitation is provided by a loudspeaker cluster right before the test muffler. The measurement platform allows for the measurement of flow-induced noise in the muffler. Also, the insertion loss of the muffler can be determined, and this capability was validated by comparison to a one-dimensional plane wave model.

The high temperature and high neutron flux environment of a thermionic space power reactor presents a challenge in the design of the sheath insulator within a thermionic fuel element. The present alumina insulator design is suspect to degradation due to the neutron flux. The alumina insulator also requires a barrier coating to isolate it from the liquid alkali metal coolant. Although the alumina sheath development is progressing, the alumina insulator remains a potential point of significant performance loss in the thermionic fuel element. The recent successes in depositing polycrystalline diamond film onto cylindrical refractory metal substrates has led to the consideration of diamond as a potentially ideal sheath insulator. Investigations have been conducted into the durability of diamond thin film under exposure to simulated thermionic reactor conditions.

Additive manufacturing is slowly changing how components are developed and manufactured. As the technology develops over time, it is anticipated that industry will 3D print sound absorbers in production. Configurations may be considered that would be difficult to manufacture in another way. For exploratory purposes, several designs were 3D printed and positioned in an impedance tube for testing. Though the absorbers developed are based on well-established strategies, the absorbers considered are either difficult to manufacture by another means or take advantage of the unique features of 3D printed parts. The samples measured include long perforations, lightweight panels, and Helmholtz resonators with spiral wound necks. Selected results are compared with acoustic finite element analysis.

Microperforated panel (MPP) absorbers are rugged, non-combustible, and do not deteriorate over time. That being the case, they are especially suitable for long term use in harsh environments. However, the acoustic performance is modified when contaminated by dust, dirt, or fluids (i.e. oil, water). This paper examines that effect experimentally and correlates the absorption performance with Maa's theory for micro-perforated panels. Transfer impedance and absorption coefficient are measured for different levels of aluminum oxide and carbon dust accumulation. The amount of dust contamination is quantified by measuring the luminance difference between clean and dirty panels with a light meter. The porosity and hole diameter in Maa's equation are modified to account for dust obstruction. The effect of coating the MPP with oil, water, and other appropriate viscous fluids was also measured. This effect was simulated by modifying the viscous factor in Maa's equation.

Discontinuous or short-fiber composites are traditionally less expensive and are normally less difficult to manufacture than continuous fiber composites, while still retaining some of the benefits of reinforcing fibers. Similarly to continuous fibers, the volume ratio influences the mechanical properties of the composite. In addition the ratio of the length and diameter of the reinforcing fibers also plays a significant role. This ratio (also known as the aspect ratio) adds another variable to the anisotropic properties of lamina plies where now not only the content of fibers but also the dimensions of the fibers themselves play a role. Short fiber reinforced composites are already used in additive manufacturing techniques; however, the amount of carbon fiber and the length of the discontinuous strands in the filaments are normally not stated or vary greatly.

Engine exterior cover seals are typically made of elastomeric materials and used to seal the interfaces. The design of engine/transmission seals has been traditionally considered from the sealibility aspects. Recently, there have been additional demands that these seals be designed to reduce the vibration transmitted from engine/transmission and to attenuate the radiated noise. To accomplish this goal, the frequency-dependent viscoelastic properties of the seals will have to be considered. This article examines the frequency-dependent viscoelastic properties of some common elastomeric seals. The impacts of these materials on an engine valve cover noise and vibration are particularly investigated. Some design strategies are also discussed to optimize the viscoelastic effects of the elastomeric seals.