Alexander S. Liberson

Autonomous impact damage detection and isolation prediction for aerospace structures

This paper presents a practical yet innovative impact damage identification and prognosis approach for aerospace structures that uses an optimized suite of reliable COTS sensors coupled with advanced damage detection and modeling algorithms. The presented methodology utilizes a monitoring approach based on acceleration measurements that are analyzed using advanced signal processing and dispersive wave theory models that capture frequency and orientation dependent wave propagation effects. The acceleration measurements and associated processing modules are used to provide immediate detection and isolation estimates, while an energy amplitude feature allows for assessments of damage severity after the impact. By embedding wave theory model results with the adaptive signal processing algorithms, a more accurate understanding of the time-frequency behavior of the dispersive waves produced at impact is gained. Damage localization is performed based on the comparison between the predicted and measured wave group velocities, with a genetic algorithm used to optimize the parameters of a triangulation procedure. This combination of model and feature-based algorithms allows the system to make use of limited, but readily available accelerometer data. This procedure also minimizes the learning and modeling difficulties associated with other techniques that are based solely on models or measurements. A few selected demonstrations are presented that illustrate the impact location prediction capabilities in realistic carbon fiber reinforced polymer (CFRP) composite panels

Pulse Wave Velocity Prediction and Compliance Assessment in Elastic Arterial Segments

Pressure wave velocity (PWV) is commonly used as a clinical marker of vascular elasticity. Recent studies have increased clinical interest in also analyzing the impact of heart rate, blood pressure, and left ventricular ejection time on PWV. In this article we focus on the development of a theoretical one-dimensional model and validation via direct measurement of the impact of ejection time and peak pressure on PWV using an in vitro hemodynamic simulator. A simple nonlinear traveling wave model was developed for a compliant thin-walled elastic tube filled with an incompressible fluid. This model accounts for the convective fluid phenomena, elastic vessel deformation, radial motion, and inertia of the wall. An exact analytical solution for PWV is presented which incorporates peak pressure, ejection time, ejection volume, and modulus of elasticity. To assess arterial compliance, the solution is introduced in an alternative form, explicitly determining compliance of the wall as a function of the other variables. The model predicts PWV in good agreement with the measured values with a maximum difference of 3.0%. The results indicate an inverse quadratic relationship (

Fluid structure interaction model analysis of cerebrospinal fluid circulation in patients with continuous-flow left ventricular assist devices

R^{2} = .99

Fiber optic probe and system for measurement of moisture in steam turbines

R2=.99) between ejection time and PWV, with ejection time dominating the PWV shifts (12%) over those observed with changes in peak pressure (2%). Our modeling and validation results both explain and support the emerging evidence that, both in clinical practice and clinical research, cardiac systolic function related variables should be regularly taken into account when interpreting arterial function indices, namely PWV.

Improved Blood Pressure Prediction Using Systolic Flow Correction of Pulse Wave Velocity

Pulse wave velocity (PWV) quantification commonly serves as a highly robust prognostic parameter being used in a preventative cardiovascular therapy. Being dependent on arterial elastance, it can serve as a marker of cardiovascular risk. Since it is influenced by a blood pressure (BP), the pertaining theory can lay the foundation in developing a technique for noninvasive blood pressure measurement. Previous studies have reported application of PWV, measured noninvasively, for both the estimation of arterial compliance and blood pressure, based on simplified physical or statistical models. A new theoretical model for pulse wave propagation in a compliant arterial segment is presented within the framework of pseudo-elastic deformation of biological tissue undergoing finite deformation. An essential ingredient is the dependence of results on nonlinear aspects of the model: convective fluid phenomena, hyperelastic constitutive relation, large deformation and a longitudinal pre-stress load. An exact analytical solution for PWV is presented as a function of pressure, flow and pseudo-elastic orthotropic parameters. Results from our model are compared with published in-vivo PWV measurements under diverse physiological conditions. Contributions of each of the nonlinearities are analyzed. It was found that the totally nonlinear model achieves the best match with the experimental data. To retrieve individual vascular information of a patient, the inverse problem of hemodynamics is presented, calculating local orthotropic hyperelastic properties of the arterial wall. The proposed technique can be used for non-invasive assessment of arterial elastance, and blood pressure using direct measurement of PWV, with account of hyperelastic orthotropic properties.

Fiber optic probe, and method for measuring water in steam turbine

Purpose: The current 1-dimensional fluid structure interaction model (FSI) for understanding cerebrospinal fluid (CSF) circulation requires pulsatility as a precondition and has not been applied to patients with continuous-flow left ventricular assist devices (CF-LVAD) where pulsatility is chronically reduced. Our study aims to characterize the behavior of CSF pressure and flow in patients with CF-LVADs using a computational FSI model. Methods: Utilizing the computational FSI model, CSF production in choroid plexuses of the 4 ventricles was specified as a boundary condition for the model. The other source of production from capillary ultrafiltrate spaces was accounted for by the mass conservation equation. The primary CSF absorption sites (i.e., arachnoid granulations) were treated as the outlet boundary conditions. We established a low pulse wave to represent patients with a CF-LVAD. Results: From the model, low pulse conditions resulted in a reduction in CSF pressure amplitude and velocity though the overall flow rate was unchanged. Conclusions: The existing FSI model is not a suitable representation of CSF flow in CF-LVAD patients. More studies are needed to elucidate the role of pulsatility in CSF flow and the compensatory changes in CSF production and absorption that occur in patients with CF-LVADs in whom pulsatility is diminished.

Numerical Solution for the Boussinesq Type Models with Application to Arterial Flow

Office hours are available for students to receive extra help outside of class. Unfortunately, this resource is often underutilized by students despite efforts to schedule convenient and accessible office hour times. Previous survey results from students attending a variety of courses in Mechanical Engineering at the Rochester Institute of Technology (RIT) have shown a positive correlation between low office hour attendance and the following factors: (i) high understanding of course material, (ii) procrastination and lack of time to seek help before deadlines, and (iii) low time studying materials outside of class. Interestingly, the results of this survey did not support the hypothesis that students who attended more office hours performed better.A new homework grading policy was instituted in Thermodynamics and Fluid Mechanics I in the fall and spring semesters of the 2013 academic year at RIT. Under this policy, students were required to visit office hours to receive credit for completion of assigned weekly problems. Implementation of this policy has provided quantitative information regarding participation and timing of office hour visits. This investigation will examine the effects of attendance and timing of office hour participation on metrics of performance including final class grades and theoretical understanding as measured by performance on multiple choice test questions.Results presented here suggest that the office hour grading system resulted in high participation rates across a broad range of students. Higher office hour participation rates had a positive impact on student performance in long answer exam problems and low impact on performance in multiple choice questions. While performance was a stronger function office participation at the of end of term than in week five, early semester participation rates can be used as a tool to help identify students at risk of dropping a class or receiving a poor grade.Copyright