Engineering topics

Zhu, Yong

Publications and source records attributed to Zhu, Yong.

7 records

NASA NTRS2016

A Piezoelectric Shear Stress Sensor

In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces and it showed high sensitivity to shear stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, shear stress, floating element, electromechanical symmetry

Kim, Taeyang↗

NASA NTRS2015

Shear Stress Sensing with Elastic Microfence Structures

In this work, elastic microfences were generated for the purpose of measuring shear forces acting on a wind tunnel model. The microfences were fabricated in a two part process involving laser ablation patterning to generate a template in a polymer film followed by soft lithography with a two-part silicone. Incorporation of a fluorescent dye was demonstrated as a method to enhance contrast between the sensing elements and the substrate. Sensing elements consisted of multiple microfences prepared at different orientations to enable determination of both shear force and directionality. Microfence arrays were integrated into an optical microscope with sub-micrometer resolution. Initial experiments were conducted on a flat plate wind tunnel model. Both image stabilization algorithms and digital image correlation were utilized to determine the amount of fence deflection as a result of airflow. Initial free jet experiments indicated that the microfences could be readily displaced and this displacement was recorded through the microscope.

Cisotto, Alexxandra↗

NASA NTRS2000

Factors Controlling Upper-Troposphere Water Vapor

The seasonal changes of the upper-tropospheric humidity are studied with the water vapor data from the Microwave Limb Sounder on the National Aeronautics and Space Administration's Upper Atmosphere Research Satellite and the winds and vertical velocity data obtained from the European Centre for Medium-Range Weather Forecasts. Using the same algorithm for vertical transport as that used for horizontal transport (by Zhu and Newell), the authors find that the moisture in the tropical upper troposphere may be increased mainly by intensified local convection in a small portion, less than 10%, of the whole area between 40 degrees S and 40 degrees N. The contribution of large-scale background circulations and divergence of horizontal transport is relatively small in these regions. These dynamic processes cannot be revealed by the traditional analyses of moisture fluxes. The negative response suggested by Lindzen, with enhanced convection in the Tropics being accompanied by subsidence drying in the subtropics, also exists, but the latter does not apparently dominate in the moisture budget.

Zhu, Yong↗

NASA NTRS1999

SONEX: NASA SASS Ozone and Nitrogen Oxide Experiment

This final report follows closely on our 1998 Annual Progress Report which was forwarded to NASA on November 19, 1998. Rather than reiterate the material therein we note here the continuation of the various items covered. SONEX has proN,Ided a number of opportunities to learn more about the fine-scale structure of the atmosphere. Coupled with the MOZAIC work on layers we can synthesize a new 3-D view of the fine scales that influence atmospheric chemistry. As a side issue we are also relating the features to clear air turbulence which would be, we think, a useful connection for commercial aviation.

Newell, Reginald E.↗

NASA NTRS1999

Observations of Convective and Dynamical Instabilities in Tropopause Folds and their Contribution to Stratosphere-Troposphere Exchange

SONEX has provided a number of opportunities to learn more about the fine-scale structure of the atmosphere. Coupled with the MOZAIC work on layers we can synthesize a new 3-D view of the fine scales that influence atmospheric chemistry. As a side issue we are also relating the features to clear air turbulence which would be, we think, a useful connection for commercial aviation.

Newell, Reginald E.↗

NASA NTRS1997

Atmospheric Layers Measured from the NASA DC-8 During PEM-West B and Comparison with PEM-West A

The Pacific Exploratory Mission-West B (PEM-West B) explored atmospheric layer structure using measurements of O3, H2O, CO, and CH4 from the NASA DC-8 fast-response instruments. The mission took place in February-March 1994 over the western Pacific, mainly in the northern hemisphere. Results were compared with similar measurements made during the Pacific Exploratory Mission-West A (PEM-West A) in September-October 1991. PEM-West B sampled 94 vertical profiles, with an average atmospheric depth per profile of 6.4 km, and this sampling yielded 254 discrete layers. PEM-West A sampled 105 profiles, also with a 6.4 km average depth, yielding 538 layers. Both missions revealed that layers containing high ozone and low water vapor were the most abundant, and low ozone and high water vapor layers were the next most abundant. Lidar images and potential vorticity cross sections showed the former associated with subsidence from the stratosphere in middle latitudes, spreading into the tropics. The latter was associated with convection from the boundary layer. The partition among different types of layers only changed slightly in the two missions, although PEM-West B had half as many layers. Compared to PEM-West A, PEM-West B showed only one-third the number of layers associated with polluted continental air. However, PEM-West B revealed significantly more layers showing characteristics of descended clean marine air. In some cases these layers originated from the southern hemisphere. For ozone- and water-vapor-rich layers, the ozone deviation amplitude was higher in low latitudes and lower in high latitudes in PEM-West B. The mean thickness of layers increased from about 450 m in PEM-West A to 680 in in PEM-West B. Layers also existed in the Intertropical Convergence Zone. CO2 measurements had sufficient vertical resolution to show layer structure as well.

Wu, Zhongxiang↗

NASA NTRS1992

Tropospheric rivers? A pilot study

Computations of daily global tropospheric water vapor flux values show the presence of a filamentary structure. The filaments, here called rivers, have lengths many times their widths and persist for many days while being translated through the atmosphere. They are present in data analyzed for both 1981 and 1991. The water vapor flux maxima coincide quite closely to reflectivity features (averaged from wavelengths of 380 and 360 nm) as revealed by the Total Ozone Mapping Spectrometer (TOMS). It is suggested that the filamentary structure may also be present in other trace constituents.

Newell, Reginald E.↗