Search Results

In noise and vibration control, damping treatments are applied on panel surfaces to dissipate the energy of flexural vibrations. Presence of damping treatment on the surface of a panel also plays an important role in the resulting vibro-acoustic characteristics of the composite system. The focus of this study is to explore possibilities of reducing the weight of damping treatments by means of perforation without sacrificing performance. The power injection concept from Statistical Energy Analysis (SEA) is used in conjunction with Finite Element Analysis (FEA) to predict the effect of perforated unconstrained layer treatments on flat rectangular panels. Normalized radiated sound power of the treated panels are calculated to assess the effect of varying percentage of perforation on structural-acoustic coupling.

In this study, a simplified approach to modeling the dynamics of damping treatments in FEA (Finite Element)/ SEA (Statistical Energy) models is presented. The basic idea is to represent multi-layered composite structures with an equivalent layer. The properties of the equivalent layer are obtained by using the RKU (Ross, Kerwin and Ungar) method. The procedure presented here does not require any special pre-processing of the finite element input file and it does not increase the number of active degrees of freedom in the model, thereby making it possible to include the effect of these treatments in large system/subsystem level models. The equivalent properties obtained from RKU analysis can also be used in the SEA system models. In this study, both unconstrained and constrained layer damping treatments applied to simple structures (e.g., flat panels) as well as production vehicle components are examined.

In this paper an algorithm is developed for combining finite element analysis and boundary element techniques in order to compute the noise radiated from a panel subjected to boundary layer loading. The excitation is presented in terms of the auto and cross power spectral densities of the fluctuating wall pressure. The structural finite element model for the panel is divided into a number of sub-panels. A uniform fluctuating pressure is applied as excitation on each sub-panel separately. The corresponding vibration is computed, and is utilized as excitation for an acoustic boundary element analysis. The acoustic response is computed at any data recovery point of interest. The relationships between the acoustic response and the pressure excitation applied at each particular sub-panel constitute a set of transfer functions.

Stability and structural integrity are extremely important in the design of a vehicle. Structural foams, when used to fill body cavities and joints, can greatly improve the stiffness of the vehicle, and provide additional acoustical and structural benefits. This study involves modal testing and finite element analysis on a sports utility vehicle to understand the effect of structural foam on modal behavior. The modal analysis studies are performed on this vehicle to investigate the dynamic characteristics, joint stiffness and overall body behavior. A design of experiments (DOE) study was performed to understand how the foam's density and placement in the body influences vehicle stiffness. Prior to the design of experiments, a design sensitivity analysis (DSA) was done to identify the sensitive joints in the body structure and to minimize the number of design variables in the DOE study.

Vibration and sound radiation characteristics of bead-stiffened panels are investigated. Rectangular panels with different bead configurations are considered. The attention is focused on various design parameters, such as orientation, depth, and periodicity, and their effects on equivalent bending stiffness, modal density, radiation efficiency and sound transmission. A combined FEA-SEA approach is used to determine the response characteristics of panels across a broad frequency range. The details of the beads are represented in fine-meshed FEA models. Based on predicted surface velocities, Rayleigh integral is evaluated numerically to calculate the sound pressure, sound power and then the radiation efficiency of beaded panels. Analytical results are confirmed by comparing them with experimental measurements. In the experiments, the modal densities of the panels are inferred from averaged mechanical conductance.

Automatic thermal control (ATC) was investigated for implementation into a spacesuit to provide thermal neutrality to the astronaut through a range of activity levels. Two different control concepts were evaluated and compared for their ability to maintain subject thermal comfort. Six test subjects, who were involved in a series of three tests, walked on a treadmill following specific metabolic profiles while wearing the Mark III spacesuit in ambient environmental conditions. Results show that individual subject comfort was effectively provided by both algorithms over a broad range of metabolic activity. ATC appears to be highly effective in providing efficient, “hands-off” thermal regulation requiring minimal instrumentation. Final selection of an algorithm to be implemented in an advanced spacesuit system will require testing in dynamic thermal environments and consideration of technology for advancement in instrumentation and controller performance.

A transient model of the Minimum Consumables Portable Life Support System (MPLSS) Advanced Space Suit design has been developed and implemented using MAT-LAB/Simulink. The purpose of the model is to help with sizing and evaluation of the MPLSS design and aid development of an automatic thermal comfort control strategy. The MPLSS model is described, a basic thermal comfort control strategy implemented, and the thermal characteristics of the MPLSS Advanced Space Suit are investigated.

This paper will describe the ISS TransHab’s architectural design being proposed as a habitation module for the International Space Station. TransHab is a space inflatable habitation module that originally was designed to support a crew of six as a transit habitat (TransHab) to and from Mars. As an evolution of TransHab, it has transformed into the proposed alternative habitat module for the International Space Station (ISS). A team of architects and engineers at the Johnson Space Center has been designing and testing this concept to make it a reality.

Traditionally, vehicle emission testing has used non-intelligent analyzers to meet government-regulated standards. Typically, these instruments would provide a 0 to 5-volt signal to a central test cell computer which would then handle all calibrations including analyzer linearization, zero and span corrections, stability checks, time delays, and sample readings. Modern gas analyzers now contain intelligence within each individual analyzer; this has caused the calibration methods to change dramatically. New methods were developed in the bench control system to take advantage of the intelligence of the analyzers by creating a distributed control architecture. The zeroing, spanning, and linearization methods are quite different from the previous protocols. The results, however, will provide more accurate reading to be used in calculating vehicle emissions.

The use of composite materials in the automotive industry has become increasingly widespread. With this increase in use, techniques for non-destructive testing (NDT) have become more and more important. Various optical NDT inspective methods such as holography, moiré techniques, and shearography have been used for material testing. Among these methods, shearography appears to be most practical. Shearography has a simple optical setup due to its “self-referencing” system, and it is relatively insensitive against rigid-body motions. Measurements of displacement derivatives, and thus strain directly, rather than the displacement itself is achieved through this method. Therefore shearography detects defects in objects by correlating anomalies of strain which are usually easier than correlating the anomalies of the displacement itself, as in holography. To date shearography has shown potential as a NDT tool for identifying defects in small structures.

A process to achieve vehicle system level NVH objectives using CAE simulation tools is discussed. Issues of modeling methodology, already covered adequately in the literature, are less emphasized so that the paper can focus on the application of a process that encompasses objective setting, design synthesis, and performance achievement using simulation predictions. A reference simulation model establishes correlation levels and modeling methods that are applied to future predictions. The new model, called a “Digital Mule”, is an early new product “design intent” simulation used to arrive at subsystem goals to meet the vehicle level NVH objectives. Subsystem goals are established at discrete noise paths where structure borne noise enters the body subsystem. The process also includes setting limits on the excitation sources, such as suspension and powertrain.

It is often necessary to measure three-axis displacement of a deforming or moving part in static or dynamic impact tests. A point moving in the three-dimensional space can be monitored and measured using three string-pots or other distance measuring devices with a methodology developed here. A numerical algorithm along with required equations are shown and discussed. The algorithm was applied as an example to static seat pull test and compared to results from film analysis. The application with string pots is useful especially when the point of concern gets hidden or blocked by other parts disabling the photogrammetry technology.

Effective helmet performance is a critical component to achieving safe and efficient missions along the entire timeline; from launch and entry events to operations in a micro-gravity environment to exploration of a planetary surface, the helmet system is the capstone of the pressurized space suit assembly. Each phase of a mission requires uncompromising protection in the form of a robust pressure vessel and adequate protection from impact, both interior and exterior, all while remaining relatively comfortable and providing excellent visual interaction with the environment. Historically there have been large voids between these critical characteristics with the primary focus concerning the pressure vessel first and impact protection and crew comfort second. ILC Dover, NASA-JSC, Gentex Corporation, and Hamilton Sundstrand formed an Integrated Product Team (IPT) and conducted a NASA funded study to research and evaluate new concepts in helmet design.