Mechanical Projects

Development of a Dynamic Test Facility for Environmental Control Systems

Passenger cars and light trucks consume 80% of the total oil imported by U.S.A. Mobile air conditioners (MACs) increase vehicle fuel consumption and exhaust gas emissions. They operate most of the time in a transient state.

It is currently impossible to test the performance of an air conditioner during transient operation without it being associated with its intended conditioned space, the car cabin. In this research work a new smart test facility is designed, built, and verified. This facility makes it possible to test the MAC independent of the vehicle, but yet under realistic dynamic conditions.

The facility depends on simulation software that measures the conditions of the air supplied by the MAC and subsequently adjusts the conditions of the air returning to the MAC depending on the results of a thermal numerical model of the car cabin that takes into consideration sensible and latent loads, as well as passengers’ control settings. It was successful in controlling the temperature and relative humidity within ±0.9°C and ±5% of their respective intended values. The test facility is used to investigate the dynamic performance of a typical R134a MAC system. The tests include pull-down, drive cycle, and cyclic on/off tests.

The analysis focuses on the latent capacity and moisture removal due to the difficulty in measuring these variables during field tests. The results show that the most energy efficient method to pull-down the air temperature inside a hot-soaked cabin is to start with fresh air as long as the temperature in the cabin exceeds that of the ambient and then switch to recirculated air. The effect of re-evaporation is illustrated by showing the off-cycle latent capacity. Cyclic tests show that the net moisture removal rate has a minimum at around a 2 minute duty cycles.

This implies a means of controlling the coil latent heat factor by varying duty cycle. The automotive air conditioning system is numerically modeled and used in cooperation with the cabin model to conduct numerical tests. The numerical simulation results are compared to the experimental results and the error is less than 1.5 K of cabin air temperature.
Source: University of Maryland.

Life Consumption Monitoring for Electronics:

Life consumption monitoring is a method to assess product’s reliability based on its remaining life in a given life cycle environment. The life consumption monitoring process involves continuous or periodic measurement, sensing, recording, and interpretation of physical parameters associated with a system’s life cycle environment to quantify the amount of degradation.

This project explains a life consumption monitoring methodology for electronic products, which includes failure modes, mechanisms and effects analysis (FMMEA), virtual reliability assessment, monitoring product parameters, data simplification, stress and damage accumulation analysis and remaining life estimation. It presents two case studies to estimate the remaining life of identical circuit card assemblies in an automobile underhood environment using the life consumption monitoring methodology.

Failure modes, mechanisms, and effects analysis along with virtual reliability assessment is used to determine the dominant failure mechanism in the given life cycle environment. Temperature and vibration are found to be the environmental factors, which could potentially cause malfunction of the circuit card assembly through solder joint fatigue. Temperature sensor and accelerometers are used along with a data logger to monitor and record the environmental loads during the experiment.

A data simplification scheme is used to make the raw sensor data suitable for further processing. Stress and damage models are used to estimate the remaining life of the circuit card assembly based on the simplified data. Performances of the test board assemblies are monitored through resistance monitoring. The life cycle environment and results for the case studies are compared with each other. The estimated results are also compared with experimental life results.
Source: University of Maryland.

Camera Spectral Sensitivity Characterization using a Blackbody Source :

With digital cameras emerging as more effective tools for scientific research, there is increasing need for accurate and inexpensive ways to calibrate them. In particular, to date there has been no simple method to measure camera sensitivity as a function of wavelength.

For example, narrow bandwidth monochromator beams are expensive and have calibration problems, while color chart method is unreliable owing to illumination dependence. This thesis presents a novel technique for spectral sensitivity calibration of a camera (or any black-and-white cameras or color sensors) using blackbody furnace operating at 650 – 1250 °C.

Images recorded at 11 different temperatures are observed for red, green, and blue camera outputs. Using Planck ’ s Law to calculate the incident light intensities, the three color sensitivities as functions of wavelength are computed using MATLAB function that optimizes the spectral sensitivities until the blackbody measurements are closely matched. The results are in reasonable agreement with published sensitivities.
Source: University of Maryland.

Vehicle Handling, Stability and Bifurcaiton Analysis for Nonlinear Vehicle Models :

Vehicle handling, stability, and bifurcation of equilibrium conditions were studied using a state vector approach. The research provided a framework for an improved method of vehicle handling assessment that included non-linear regions of performance and transient behavior.

Vehicle models under pure lateral slip, constant velocity, and constant front steer were developed. Four-wheel, two-axle vehicle models were evolved from simpler models and were extended to include vehicle roll dynamics and lateral load transfer effects. Nonlinearities stem from tire force characteristics that include for tire force saturation. Bifurcations were studied by quasi-static variations of vehicle speed and front steer angle.

System models were expanded, assessing overall stability, including vehicle behavior outside normal operating ranges. Nonlinear models of under steering, over steering, and neutral steering vehicles were created and analyzed. Domains of attraction for stable equilibrium were discussed along with physical interpretations of results from the system analysis.
Source: University of Maryland.