Interior Noise Reduction by Adaptive Feedback Vibration Control

The objective of this project is to investigate the possible use of adaptive digital filtering techniques in simultaneous, multiple-mode identification of the modal parameters of a vibrating structure in real-time. It is intended that the results obtained from this project will be used for state estimation needed in adaptive structural acoustics control. The work done in this project is basically an extension of the work on real-time single mode identification, which was performed successfully using a digital signal processor (DSP) at NASA, Langley. Initially, in this investigation the single mode identification work was duplicated on a different processor, namely the Texas Instruments TMS32OC40 DSP. The system identification results for the single mode case were very good. Then an algorithm for simultaneous two mode identification was developed and tested using analytical simulation. When it successfully performed the expected tasks, it was implemented in real-time on the DSP system to identify the first two modes of vibration of a cantilever aluminum beam. The results of the simultaneous two mode case were good but some problems were identified related to frequency warping and spurious mode identification. The frequency warping problem was found to be due to the bilinear transformation used in the algorithm to convert the system transfer function from the continuous-time domain to the discrete-time domain. An alternative approach was developed to rectify the problem. The spurious mode identification problem was found to be associated with high sampling rates. Noise in the signal is suspected to be the cause of this problem but further investigation will be needed to clarify the cause. For simultaneous identification of more than two modes, it was found that theoretically an adaptive digital filter can be designed to identify the required number of modes, but the algebra became very complex which made it impossible to implement in the DSP system used in this study. The on-line identification algorithm developed in this research will be useful in constructing a state estimator for feedback vibration control

Sensitivity of Space Station alpha joint robust controller to structural modal parameter variations

The photovoltaic array sun tracking control system of Space Station Freedom is described. A synthesis procedure for determining optimized values of the design variables of the control system is developed using a constrained optimization technique. The synthesis is performed to provide a given level of stability margin, to achieve the most responsive tracking performance, and to meet other design requirements. Performance of the baseline design, which is synthesized using predicted structural characteristics, is discussed and the sensitivity of the stability margin is examined for variations of the frequencies, mode shapes and damping ratios of dominant structural modes. The design provides enough robustness to tolerate a sizeable error in the predicted modal parameters. A study was made of the sensitivity of performance indicators as the modal parameters of the dominant modes vary. The design variables are resynthesized for varying modal parameters in order to achieve the most responsive tracking performance while satisfying the design requirements. This procedure of reoptimization design parameters would be useful in improving the control system performance if accurate model data are provided

Structural dynamic interaction with solar tracking control for evolutionary Space Station concepts

The sun tracking control system design of the Solar Alpha Rotary Joint (SARJ) and the interaction of the control system with the flexible structure of Space Station Freedom (SSF) evolutionary concepts are addressed. The significant components of the space station pertaining to the SARJ control are described and the tracking control system design is presented. Finite element models representing two evolutionary concepts, enhanced operations capability (EOC) and extended operations capability (XOC), are employed to evaluate the influence of low frequency flexible structure on the control system design and performance. The design variables of the control system are synthesized using a constrained optimization technique to meet design requirements, to provide a given level of control system stability margin, and to achieve the most responsive tracking performance. The resulting SARJ control system design and performance of the EOC and XOC configurations are presented and compared to those of the SSF configuration. Performance limitations caused by the low frequency of the dominant flexible mode are discussed

Underlying modal data issues for detecting damage in truss structures

Independent of the modal identification techniques employed for damage detection, use of measured modal data limits the expectations for damage location. These limitations are examined using the distribution of modal strain energy and the sensitivity of the frequency and mode shapes to structural stiffness changes. For given measured modal information of specific accuracy, this examination reveals the following: (1) damage detection is feasible for members that contribute significantly to the strain energy of the measured modes, (2) the modes which are most effective in detecting damage to certain critical members can be identified, and (3) a relationship can be drawn between the accuracy of the measured modes and frequencies and damage detection feasibility

ESTIMATING LUMBAR SPINAL LOADS DURING A GOLF SWING USING AN EMG-ASSISTED OPTIMIZATION MODEL APPROACH

This study estimated the lumbar spinal loads at L4-L5 level during a golf swing using musculoskeletal modeling techniques. Data were collected from five college golfers. Four S-VHS camcorders and two force plates were used to obtain 3-D kinetics and kinematics of the golfer’s motion and 10 surface electrodes were used to record the activity of selected lower trunk muscles. The EMG-assisted optimization model was used to estimate lower trunk muscle forces. The results demonstrate that the L4-L5 motion segment is subjected to considerable compressive (4,300 N), antero-posterior (A/P) shear (882 N), and medio-lateral (M/L) shear loads (-252 N) during a golf swing. The repetitive changing direction of the shear load during a golf swing may increase the chance of fatigue fracture of pars interarticularis. The results also suggest that a golf swing with shortened backswing and follow-through may reduce the risk of back injury

DIRECTIONAL CONTROL IN TENNIS SERVES PERFORMED BY ELITE PLAYERS

This study quantified the pre-and post-impact 3-D kinematics of the ball and racquet during the serves that landed at different locations performed by five male and four female professional tennis players. Data were collected during competition using two high-speed cameras (200 Hz). Two first serves .-one landed near the center line and the other near the side line --were analyzed for each subject. A 2 x 2 ANOVA (0 < .05) was performed for each parameter. The results indicate that the males had significantly greater post-impact ball and racquet velocities than their female counterparts. Though not statistically significant, the ball tended to travel to the left less during the toss and have lower post-impact velocity for serves that landed near the side line. Altering the toss might be one of the strategies used by players to control ball direction in the serve

TIBIO-FEMORAL JOINT FORCES DURING THE LANDING PHASE OF DIFFERENT TYPES OF VERTICAL JUMP

The purpose of this study was to compare the tibio-femoral contact forces during the landing phases of 8 different types of vertical jump (squat, countermovement, hop approach and drop jumps each with and without the use of arms). Data were collected from eight males and eight females. Two S-VHS camcorders and a force platform were used to obtain the 3-D kinematics and kinetics of the knee joint. Activities of selected muscles spanning the knee joint were monitored using surface electromyographic (EMG) techniques. The EMG-assisted optimization model was used to estimate the tibio-femoral joint forces. The peak compressive contact forces ranged from 3-5 body weight (SW) and from 2.5-3.7 SW for the males and females, respectively. These loads seldom fell within the range that is considered to be damaging to the cartilage at the knee

Digital Signal Processing

Contains an introduction and reports on fifteen research projects.National Science Foundation FellowshipU.S. Navy - Office of Naval Research (Contract N00014-81-K-0742)National Science Foundation (Grant ECS 84-07285)Sanders Associates, Inc.U.S. Air Force - Office of Scientific Research (Contract F19628-85-K-0028)AT&T Bell Laboratories Doctoral Support ProgramCanada, Bell Northern Research ScholarshipCanada, Fonds pour la Formation de Chercheurs et /'Aide a la Recherche Postgraduate FellowshipCanada, Natural Science and Engineering Research Council Postgraduate FellowshipAmoco Foundation FellowshipFannie and John Hertz Foundation Fellowshi

Synthesis and Activity of Ruthenium Alkylidene Complexes Coordinated with Phosphine and N-Heterocyclic Carbene Ligands

This paper reports the synthesis and characterization of a variety of ruthenium complexes coordinated with phosphine and N-heterocyclic carbene (NHC) ligands. These complexes include several alkylidene derivatives of the general formula (NHC)(PR_3)(Cl)_2Ru═CHR', which are highly active olefin metathesis catalysts. Although these catalysts can be prepared adequately by the reaction of bis(phosphine) ruthenium alkylidene precursors with free NHCs, we have developed an alternative route that employs NHC-alcohol or -chloroform adducts as “protected” forms of the NHC ligands. This route is advantageous because NHC adducts are easier to handle than their free carbene counterparts. We also demonstrate that sterically bulky bis(NHC) complexes can be made by reaction of the pyridine-coordinated precursor (NHC)(py)_2(Cl)_2Ru═CHPh with free NHCs or NHC adducts. Two crystal structures are presented, one of the mixed bis(NHC) derivative (H_2IMes)(IMes)(Cl)_2Ru═CHPh, and the other of (PCy_3)(Cl)(CO)Ru[η^2-(CH_2-C_6H_2Me_2)(N_2C_3H_4)(C_6H_2Me_3)], the product of ortho methyl C−H bond activation. Other side reactions encountered during the synthesis of new ruthenium alkylidene complexes include the formation of hydrido-carbonyl-chloride derivatives in the presence of primary alcohols and the deprotonation of ruthenium vinylcarbene ligands by KOBu^t. We also evaluate the olefin metathesis activity of NHC-coordinated complexes in representative RCM and ROMP reactions

Measurement of the radiative decay of polarized muons in the MEG experiment

We studied the radiative muon decay $\mu^+ \to e^+\nu\bar{\nu}\gamma$ by using for the first time an almost fully polarized muon source. We identified a large sample (~13000) of these decays in a total sample of 1.8x10^14 positive muon decays collected in the MEG experiment in the years 2009--2010 and measured the branching ratio B($\mu^+ \to e^+\nu\bar{\nu}\gamma$) = (6.03+-0.14(stat.)+-0.53(sys.))x10^-8 for E_e > 45 MeV and E_{\gamma} > 40 MeV, consistent with the Standard Model prediction. The precise measurement of this decay mode provides a basic tool for the timing calibration, a normalization channel, and a strong quality check of the complete MEG experiment in the search for $\mu^+ \to e^+\gamma$ process.Comment: 8 pages, 7 figures. Added an introduction to NLO calculation which was recently calculated. Published versio