David P. Wick

Downstream evolution of proper orthogonal decomposition eigenfunctions in a lobed mixer

A two-dimensional (one space and time) scalar adaptation of the proper orthogonal decomposition was applied to streamwise velocity data obtained in a lobed mixer flowfield, using a rake of 15 single-component hot wires. Through the application of the proper orthogonal decomposition, the amount of streamwise turbulent kinetic energy contained in the various proper orthogonal modes was examined for two different downstream locations (z/h = 2.6 and 3.9). The large eddy or dominant mode was shown to have a measurable decrease in the relative streamwise component of the kinetic energy between these two downstream locations. This indicates that the large eddy, as defined by the proper orthogonal decomposition, breaks down, and the flow becomes more homogeneous. A pseudoflow visualization technique was then employed to help visualize this process.

Predictive assessment of student performance for early strategic guidance

In this study, we use well-accepted conceptual assessment instruments, initial state data such as the SAT, and our own recently developed instruments designed to measure aptitude in mathematics to develop a machine learning-based predictive model for student performance. Previous analysis found the expected strong correlation between performance in the mathematics and physics courses. The mathematics assessment instruments were designed to provide a means for suggesting corrective measures for students to take to improve performance in mathematics, and it was demonstrated that these measures also have an impact on performance in physics. With the predictive nature of the collected data and the impact of the various corrective measures on final grade established, we use these data to form a predictive model for student performance. By adaptively imputing missing data from previous years, and forming a random forest model, we are able to predict those students who are most at-risk of failing the introductory mathematics and physics courses with acceptable accuracy. This analysis contributes to an integrated evaluation of the current programs, which has led to an assessment-based initiative to offer strategic guidance to incoming students, better placing them for academic and career success in their selected STEM disciplines.

Modeling the motion of a toy car traveling on an arbitrarily shaped track

An analysis is performed on the motion of a Matchbox car racing down an arbitrarily shaped track that resides in a two-dimensional vertical plane. The role of friction, track shape, and air resistance on the car’s performance is investigated. The parameters that describe the car’s effective coefficient of friction and drag constant are experimentally extracted by consideration of its motion on a flat, horizontal track. These parameters are then employed to make predictions of the velocity on an arbitrarily shaped track containing hills and valleys and compared with measured values. A rigidly mounted shield of varying cross-sectional area is used to enhance the effects of drag. This analysis has been successfully incorporated into an advanced group project for an introductory course in classical mechanics and can be customized to accommodate a variety of levels.

Investigation of turbulent flows via pseudo flow visualization part II: Lobed mixer

Abstract Multipoint, single-component hot-wire anemometer measurements obtained with a rake of probes downstream of a lobed mixer are examined using a pseudo flow visualization (PFV) technique. PFV is a visualization procedure that manipulates data obtained from an array of probes to create a graphical representation of the instantaneous velocity components of a flow field. The indicator function was employed to identify the frequency content of each velocity-time trace, giving insight into the analysis of the visualizations. From this application, shedding frequencies of the large-scale structures were identified to range from 200–700 Hz, averaging around 550 Hz. In general, these results are comparable with streamwise velocity spectra obtained from the same flow field locations. Mean streamwise velocity and turbulence intensity profiles reveal that the turbulence intensity increases substantially at the expense of the mean shear, targeting the region of increased mixing to occur between z l a = 3.9 and 5.2 downstream of the trailing edge of the mixer. The ruffle-shaped shear layer is further warped by the secondary velocities in the region where the mean momentum flow emanates from the lobe troughs. This evolution of the shear layer continues until it collapses onto itself, resulting in a burst of turbulent energy that paves the path for turbulence-dominated mixing. The validity of these techniques was successfully verified in the more familiar and fundamental flow field of the near-field axisymmetric jet mixing layer, as described in Part I of this investigation, before they were applied to the flow field downstream of the lobed mixer.

IMPACT: Integrated mathematics and physics assessment for college transition

In this study we conduct an integrated assessment of first-year performance in introductory calculus and physics courses. We use well-accepted conceptual assessment instruments, initial state data such as the SAT, and our own recently developed instruments designed to measure aptitude in mathematics to develop a predictive model for student performance. The analyzed population was composed of undergraduate students at Clarkson University, cross-enrolled in the calculus-based introductory physics course and the introductory calculus course from 2004 to 2007. Both the mathematics and physics classes are large-enrollment, lecture-based courses. By analyzing the combined data sets, we found the expected strong correlation between performance (final grade) in the mathematics course and performance in the physics course. We analyze not only the predictive nature of the collected data, but also the impact of the various corrective measures on final grade. This analysis contributes to an integrated evaluation of the current programs which could lead to an assessment-based initiative to offer strategic guidance to incoming students, better placing them for academic and career success in their selected STEM disciplines.

Investigation of turbulent flows via pseudo flow visualization part I: Axisymmetric jet mixing layer

Abstract Hot-wire anemometer measurements obtained in the near-field axisymmetric jet mixing layer by Glauser and George [1] are examined using a pseudo flow visualization (PFV) technique. Pseudo flow visualization is a visualization procedure used to manipulate data obtained from an array of probes to create a graphical representation of the instantaneous and fluctuating velocity components of a flow field. An indicator function was employed to identify the frequency content of each velocity-time trace, giving insight into the analysis of the visualizations. From this application, the natural shedding frequency, or preferred mode , of the large-scale structures was determined and compared with the conventional streamwise and radial spectral measurements acquired by Glauser and George [1]. Furthermore, the wavelength of the preferred mode, nondimensionalized by the jet exit diameter, was determined to be approximately 2.4, a result consistent with the work of Crowe and Champagne [2]. In Part 1 the technique is developed and discussed for the fundamental and fairly well-researched mixing layer of the axisymmetric jet. Our aim is to verify the effectiveness of PFV in the context of a well-documented flow. In Part 2, this technique is then applied to an industrial flow field, namely, the mixing region of a lobed mixer

Coherent Structure Identification in a Lobed Mixer

The influence of large scale structures on the flow in a lobed mixer (a device utilized to enhance streamwise vorticity for increased mixing) is examined by a pseudo flow visualization method (v. Delville et al. 1988), and the Proper Orthogonal Decomposition (POD) (v. Lumley 1967). The pseudo flow visualization method utilizes specially designed hot wire rakes with high spatial resolution to provide the capability of plotting instantaneous velocity profiles. In this work, a rake of 15 hot wires is used to provide these profiles for a velocity ratio of 2:1, at several positions downstream of the lobed mixer. From these profiles a detailed description of the flow field is achieved. In particular, from this information, an idea of the spatial extent and shedding frequency of the large scale structures is determined. The shedding frequencies found are consistent with those found from spectral measurements. A one-dimensional version of the POD is then applied, which utilizes the measured streamwise velocity two-point correlation tensor. The pseudo flow visualization technique is then used to view the contribution from each proper orthogonal mode to the instantaneous signal and comparisons made to the full signal.Copyright

Experimenting with Electric Trains.

A simple experiment can be performed to characterize the relationship between applied voltage and velocity (steady state and transient) for an electric toy train. The results can be used by teams of students to solve a series of challenges in which they attempt to predict the performance of a particular train. Some sample challenges might include having groups predict the position of the train at a certain instant in time, predict the time the train will reach a given location, and select the applied voltage that will ensure the train will reach a certain point at a given instant. This activity is centered on a team-oriented modeling-based project conducted at Clarkson University, which was published in the American Journal of Physics.1

A Field Study to Assess the Long-Term Sampling Feasibility of Evacuated Canisters and the Development of a Mathematical Model to Analyze Potential Sampling Bias

Small, evacuated canisters (300 mL) equipped with a unique capillary flow controller were used to evaluate airborne concentrations of Stoddard solvent. The physical characteristics of the flow controller permitted the collection of air samples for a time period of 40 hours (5 consecutive work days). Long-term sampling (greater than 8 hours) is rarely performed in industrial hygiene due to limitations in current air sampling technology but may provide valuable information in characterizing worker cumulative exposures for some processes. A field study was performed to evaluate the feasibility of collecting a 40-hour area sample using the small canisters. Six canister samplers were used as area monitors to evaluate a cleaning operation for an entire workweek. For comparison, 30 diffusive badges (6 per day) were simultaneously used to monitor the same process. No statistical difference was found between the time-weighted average for the two sampling methods (p > 0.05). In addition, the canister samples integrate airborne concentrations for an entire workweek and therefore peak concentrations are not explicitly observed. Thus, an examination of peak exposures using simulated concentrations was conducted. A mathematical model was developed to determine whether a significant sampling bias was associated with long-term canister sampling when peak concentrations are present. The maximum possible bias was determined to be less than 9% for peak amplitudes having 10 times the background concentration and well below that for smaller amplitudes. Long-term sampling with the small, evacuated canisters was found to provide results comparable to sorbent sampling methods but with the added benefit of a significantly increased sampling time.

Modeling the motion of a toy train powered with a time-dependent applied voltage: Educational implementation and analysis

We describe the motion of an electric toy train engine that is powered by a time-dependent voltage and travels on a horizontal track. Effects such as friction, the electrically induced torque and electromotive force of the motor, resistance, inductance, and applied voltage are investigated to identify the impact of each on the train’s performance. The parameters that describe these effects are experimentally extracted by considering the train’s steady-state motion achieved for a constant applied voltage. An equivalent inertia parameter is obtained from transient velocity and current measurements. These parameters are employed in a numerical solution to predict the train’s velocity and current for a time-dependent applied voltage. The results are compared with measured values for several independent cases. This analysis has been successfully incorporated into an advanced group project for an introductory course in electricity and magnetism and can be adapted to accommodate students at different levels. Its...