Alfred L. Wicks

A direct-measurement thin-film heat flux sensor array

A new thin-film heat flux array (HFA) was designed and fabricated using a series of nickel/copper differential thermocouples deposited onto a thin Kapton® polyimide film. A special bank of amplifiers was designed and built to measure the signal from the HFA. Calibrations were performed to determine the gages sensitivity and temporal response. The HFA produced signals of 42 µV (W cm−2)−1 with a measured first-order response time of 32 ms. The apparent thermal conductivity of the Kapton used was larger than what is usually reported. The design methodology, construction techniques, steady-state and transient calibrations, and a test case are all discussed.

Pose estimation of a scanning laser Doppler vibrometer with applications to the automotive industry

A scanning laser Doppler vibrometer (SLDV) is an optical in- strument that can scan an area to measure the velocity field of struc- tures. It has been widely used in the automotive industry. In some appli- cations, the pose (position and orientation) of the SLVD are required. First, this paper describes two such applications. Then it presents a non- linear regressive model for the pose determination of the SLDV with respect to a structural coordinate system. The model is derived from coordinate transformation and the scanner model. In it, the pose is ex- pressed by six independent parameters: three for the translation vector and three for the rotation matrix. The six parameters are estimated by using the least-squares technique. Statistical inferences about this model are obtained by linear approximation. To determine the pose, four or more registration (reference) points are required. For each registration point, the structural coordinates and its corresponding input voltages need to be known. The model has been implemented in a laser-based data acquisition system, which has been used for modal analysis, struc- tural dynamic modifications, and noise control.

Geometrical method for the determination of the position and orientation of a scanning laser doppler vibrometer

In this paper, a geometrical method is presented to determine the pose (position and orientation) of a Scanning Laser Doppler Vibrometer (SLDV) with respect to a structural coordinate system. Multiple registration points are used simultaneously in a least-squares sense. The structural coordinates and the corresponding scanning angles are known for each of the registration points. In the geometrical method three steps are involved in the determination of the SLDV pose. Its implementation has been tested by simulated data and experimental data. The results have shown that this method and its implementation are correct and effective.

High Speed High Dynamic Range Video

High-speed digital video is a common measurement tool used in the analysis of explosive or similarly energetic events. The dynamic range of a digital camera is limited to bit depth of the analog to digital converter and deep well capacity of the sensor. The dynamic range of an explosive event can exceed the camera’s dynamic range by many orders of magnitude, often in excess of 120 dB causing loss of data from sensor saturation. A method has been developed to utilize current off the shelf synchronized high-speed cameras to film events consisting of extremely high dynamic range events. This paper will describe the process for the design and implementation of an optimized system composed of any number of cameras, and demonstrates the capabilities of a constructed system to capture a video spanning 169 dB range (28 stops) at 79,000 pps using three and four high speed cameras.

Using multi-axis material extrusion to improve mechanical properties through surface reinforcement

ABSTRACT Due to the layer stacking inherent in traditional three-axis material extrusion (ME) additive manufacturing processes, a parts mechanical strength is limited in the print direction due to weaker interlayer bond strength. Often, this requires compromise in part design through either adding material in critical areas of the part, reducing end-use loads or forgoing ME as a manufacturing option. To address this limitation, the authors propose a multi-axis deposition technique that deposits material along a parts surface to improve mechanical performance. Specifically, the authors employ a custom 6 degree of freedom robotic arm ME system to create a surface reinforcing ‘skin’, similar to composite layup, in a single manufacturing process. In this paper, vertical tensile bars are fabricated through stacked XY layers, followed by depositing material directly onto the printed surface to evaluate the effect of the skinning approach on mechanical properties. Experimental results demonstrate that surface-reinforced interlayer bonds provide increased yield strength.

Simplified weighting function for high dynamic range video frame formation

High dynamic range imagery has matured from a laboratory demonstration to an integrated capability in consumer-level cameras. However, high dynamic range video has lagged in development despite the introduction of several different frame formation methodologies and system architectures. The most common formation methodology involves the calculation of a high dynamic range image from a series of rapidly bracketed frames at varying exposure levels, then through the use of a radiometric calibration, recombined utilizing a weighted maximum likelihood estimator. The ideal weighting scheme to minimize the error on final image formation has been investigated by several authors. A new nonrecursive, simplified weighting scheme is proposed that utilized only knowledge of the optical attenuation, integration time, and sensor gain. A method is developed to test the various weighting schemes for their resilience to error with limited available exposures over a wide range of exposure value offsets, a common scenario for multi-imager-based high dynamic range video systems.

Universal framework for unmanned system penetration testing

Multiple industries, from defense to medical, are increasing their use of unmanned systems. Today, many of these systems are rapidly designed, tested, and deployed without adequate security testing. To aid the quick turnaround, commercially available subsystems and embedded components are often used. These components may introduce security vulnerabilities particularly if the designers do not fully understand their functionality and limitations. There is a need for thorough testing of unmanned systems for security vulnerabilities, which includes all subsystems. Using a penetration testing framework would help find these vulnerabilities across different unmanned systems applications. The framework should encompass all of the commonly implemented subsystems including, but not limited to, wireless networks, CAN buses, passive and active sensors, positioning receivers, and data storage devices. Potential attacks and vulnerabilities can be identified by looking at the unique characteristics of these subsystems. The framework will clearly outline the attack vectors as they relate to each subsystem. If any vulnerabilities exist, a mitigation plan can be developed prior to the completion of the design phase. Additionally, if the vulnerabilities are known in advance of deployment, monitoring can be added to the design to alert operators of any attempted or successful attacks. This proposed framework will help evaluate security risks quickly and consistently to ensure new unmanned systems are ready for deployment. Verifying that a new unmanned system has passed a comprehensive security evaluation will ensure greater confidence in its operational effectiveness.

Design of a System to Monitor Youth Workers’ Heat Stress and Positioning Using Non-Invasive Techniques

Due to inadequate training and an undeveloped ability to recognize dangerous scenarios, youth workers can be exposed to many dangers in the agriculture and lawn care industries. With the abundance of new technologies available on the market, a project was devised to reduce the risk that youth experience heat exhaustion and equipment run-overs by employing sensor based technologies. Using aural temperature measurement techniques involving a thermistor and thermopile, an accurate estimation of core body temperature was demonstrated. The measurements performed by the devices are recorded and transmitted wirelessly over a ZigBee network using XBee radiofrequency modules. Utilizing the properties of wireless transmission, the Received Signal Strength Indication (RSSI) is used to approximate the distance between devices. With accuracy comparable to GPS methods and no necessity for line of sight to sky, RSSI supplies a more than adequate estimate for proximity distance. The temperature and RSSI values are then sent to a coordinating modem where the data is displayed for the supervisor. After testing and calibrating the device, it was found that these methods are effective for the monitoring of core body temperature and proximity of workers. The temperature sensor was able to measure temperatures with less than 0.25% error and the proximity sensor was able to estimate distance within 1.25 meters at close range.

Effects of Flow Control on Forced Response and Performance of a Transonic Compressor

The main contributor to the high-cycle fatigue of compressor blades is the response to aerodynamic forcing functions generated by an upstream row of stators or inlet guide vanes. Resonant response to engine order excitation at certain rotor speeds is especially damaging. Studies have shown that flow control by trailing edge blowing (TEB) can reduce stator wake strength and the amplitude of the downstream rotor blade vibrations generated by the unsteady stator-rotor interaction. In the present study, the effectiveness of TEB to reduce forced blade vibrations was evaluated in a modern transonic compressor rig. A row of wake generator (WG) vanes with TEB capability was installed upstream of the rotor, which was instrumented with strain gages. Data was collected with and without TEB at various rotor speeds involving resonance crossings. Using 0.8% of the compressor core flow for TEB along the full WG-span, rotor blade strain was reduced by 66% at the first torsional resonance crossing. Substantial reductions were also achieved with only partial span TEB. The results demonstrate the effectiveness of the TEB technique for reducing rotor vibrations in the complex flow environment of a closely-spaced transonic stage row. Moderate increases in stage performance were also measured.Copyright

Determination of the position and orientation of a scanning laser vibrometer for a laser-based mobility measurement system

In this paper, a geometrical method is presented to determine the pose (position and orientation) of a scanning laser vibrometer with respect to a structural coordinate system. Multiple registration points are simultaneously used to determine the pose in a least squares sense. The known information from each registration point is the structural coordinate and the corresponding scanning coordinate. Three steps are involved in the determination of the pose. The least squares method is applied to each of the three steps. The implementation of the geometrical method has been tested by simulated data and experimental data. The results have shown that this method and its implementation are correct and effective.