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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.

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 two-load method is used to measure the transmission loss of thin panels in two different sized impedance tubes (3.49 cm and 10.16 cm). Samples were initially tested with a clamped boundary condition. This was followed by tests with an elastomer inserted between the tube and tested sample to adjust the boundary condition at the periphery. In all tests performed, the influence of the sample holding method could not be removed from the test. The measured transmission loss was compared to finite element simulation with good agreement for both impedance tubes. Additionally, the effect of a compliant boundary condition along the periphery of the sample was also validated via simulation.

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.

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.

Helmholtz resonators are normally an afterthought in the design of mufflers to target a very specific low frequency, usually the fundamental firing frequency of the engine. Due to space limitations in a complex muffler design, a resonator may have to be built by punching a few small holes on a thin-walled tube to create a neck passage into a small, enclosed volume outside the tube. The short neck passage created by punching a few small holes on a thin-walled tube can pose a great challenge in numerical modeling, especially when the boundary element method (BEM) is used. In this paper, a few different BEM modeling approaches are compared to one another and to the finite element method (FEM). These include the multi-domain BEM implemented in a substructure BEM framework, modeling both sides of the thin-walled tube and the details of each small hole using the Helmholtz integral equation and the hypersingular integral equation, and modeling just the mid surface of the thin-walled tube.

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.

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.

In many industries, muffler and silencer design is primarily accomplished via trial and error. Prototypes are developed and tested, or numerical simulation (finite or boundary element analysis) is used to assess the performance. While these approaches reliably determine the transmission loss, designers often do not understand why their changes improve or degrade the muffler performance. Analyses are time consuming and models cannot be changed without some effort. The intent of the current work is to demonstrate how plane wave muffler models can be used in industry. It is first demonstrated that plane wave models can reliably determine the transmission loss for complicated mufflers below the cutoff frequency. Some tips for developing dependable plane wave models are summarized. Moreover, it is shown that plane wave models used correctly help designers develop intuition and a better understanding of the effect of their design changes.

The measurement of sound absorption coefficient (SAC) of porous materials is covered by both American and international standards. However, by using the standards alone it is difficult to achieve consistently repeatable results given the large number of variables such as sample cutting and preparation, sample fit and position in the tube, and sample material variability. This paper will review the standards briefly and examine what is available in the literature to guide users in making consistently repeatable SAC measurements. The paper will also show some of the authors' results and interpret these results in light of the standards and technical literature on the subject.

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.

This paper documents an inverse visible element Rayleigh integral (VERI) approach. The VERI is a fast though approximate method for predicting sound radiation that can be used in the place of the boundary element method. This paper extends the method by applying it to the inverse problem where the VERI is used to generate the acoustic transfer matrix relating the velocity on the surface to measurement points. Given measured pressures, the inverse VERI can be used to reconstruct the vibration of a radiating surface. Results from an engine cover and diesel engine indicate that the method can be used to reliably quantify the sound power and also approximate directivity.

This paper explores the use of inverse boundary element method to identify aeroacoustic noise sources. In the proposed approach, sound pressure at a few locations out of the flow field is measured, followed by the reconstruction of acoustic particle velocity on the surface where the noise is generated. Using this reconstructed acoustic particle velocity, the acoustic response anywhere in the field, including in the flow field, can be predicted. This approach is advantageous since only a small number of measurement points are needed and can be done outside of the flow field, and a relatively fast computational time. As an example, a prediction of vortex shedding noise from a circular cylinder is presented.

The most common approach for measuring the transmission loss of a muffler is to determine the incident power by decomposition theory and the transmitted power by the plane wave approximation assuming an anechoic termination. Unfortunately, it is difficult to construct a fully anechoic termination. Thus, two alternative measurement approaches are considered, which do not require an anechoic termination: the two load method and the two-source method. Both methods are demonstrated on two muffler types: (1) a simple expansion chamber and (2) a double expansion chamber with an internal connecting tube. For both cases, the measured transmission losses were compared to those obtained from the boundary element method. The measured transmission losses compared well for both cases demonstrating that transmission losses can be determined reliably without an anechoic termination. It should be noted that the two-load method is the easier to employ for measuring transmission loss.

The two-source method was used to measure the bulk properties (complex characteristic impedance and complex wavenumber) of sound-absorbing materials, and results were compared to those obtained with the more commonly used two-cavity method. The results indicated that the two-source method is superior to the two-cavity method for materials having low absorption. Several applications using bulk properties are then presented. These include: (1) predicting the absorptive properties of an arbitrary thickness absorbing material or (2) layered material and (3) using bulk properties for a multi-domain boundary element analysis.

This paper explores the use of inverse numerical acoustics to reconstruct the surface vibration of a noise source. Inverse numerical acoustics is mainly used for source identification. This approach uses the measured sound pressure at a set of field points and the Helmholtz integral equation to reconstruct the normal surface velocity. The number of sound pressure measurements is considerably less than the number of surface vibration nodes. A brief guideline on choosing the number and location of the field points to provide an acceptable reproduction of the surface vibration is presented. The effect of adding a few measured velocities to improve the accuracy will also be discussed. Other practical considerations such as the shape of the field point mesh and effect of experimental errors on reconstruction accuracy will be presented. Examples will include a diesel engine and a transmission housing.

The population of drivers over the age of 65 has been rapidly increasing since the early 1970's and this trend is expected to continue in the future. Aging could affect visual and cognitive abilities of elderly drivers and possibly impair their ability to operate a vehicle safely. This study examined the impact of this population on traffic safety over a 20-year period. The factors of age and cohort are examined to determine their influence on the crash involvement of elderly drivers. Age factors have been shown to be decisive in crashes resulting from complex situations, whereas cohort effects play a more dominate role in less demanding circumstances.

Over the past decade crash rates of younger drivers have been increasing despite a decrease in their driver population. This study examined specific driving maneuvers whose unsuccessful undertaking results in specific types of crashes involving these drivers. Four types of crashes were identified including crashes at intersections, rear end, crashes resulting from passing maneuvers and single vehicle crashes. For all crashes a general trend of decreasing involvement with increasing age was observed indicating that inexperience is the largest single contributor to the increased crash rates of younger drivers. Increasing the level of awareness among young drivers about these issues and their likely crash involvement seems to be the only viable approach.

The environmental impact from herbicide utilization has been well documented in recent years. The reduction in weed control with out a viable alternative will likely result in decreased per acre production and thus higher unit production cost. The potential for selective herbicide application to reduce herbicide usage and yet maintain adequate weed control has generated significant interest in different forms of remote sensing of agricultural crops. This research evaluated the color co-occurrence texture analysis technique to determine its potential for utilization in crop groundcover identification. A program termed GCVIS (Ground Cover VISion) was developed to control an ATT TARGA 24 frame grabber; and generate HSI color features from the RGB format pixel data, HSI CCM matrices and the co-occurrence texture feature data.

This paper presents an analysis of axle weight data collected during the performance testing of the Broken Bridge dynamic electronic highway scale. Test results are analyzed by comparing the in-motion axle weights as measured by the Broken Bridge scale with the corresponding static values for an instrumented two-axle test vehicle and for a sample of trucks diverted from an Interstate highway. Analysis of the two-axle test truck data shows that the actual loads applied to the highway surface by the wheels of a moving vehicle vary above and below the static equivalents in a manner that is typical for a specific location and range of speeds. For a random selection of different types of trucks, the variation of dynamic from static axle weight is further affected by axle position (front, second, third, and so forth) and spacing.