221 research outputs found
Auroral Cluster: A Space Physics Mission for Multiple, Electronically Tethered Small Satellites
Auroral Cluster is a space physics mission that has been identified by the NASA Space Physics Strategic Implementation Study as a candidate for flight in the next decade. Auroral Cluster will employ multiple spacecraft outfitted with similar complements of science instruments allowing simultaneous multipoint plasma measurements in the Earth\u27s auroral regions. Co-orbiting small satellites (mass \u3c 400 kg each) that are electronically tethered to share distributed spacecraft systems represent an efficient approach for achieving the science goals of the Auroral Cluster mission. Multisatellite missions represent a new trend in gathering space science data and pose many new and difficult challenges for the space systems engineer. The results of an Auroral Cluster feasibility study, which discusses a variety of mission trade-offs, are presented. A discussion of the science background and mission goals is used to identify the technical drivers for the design of the multiple spacecraft system. A mission plan and some considerations for a Auroral Cluster satellite design are presented. Special consideration is given to the spacecraft subsystems that will allow the system to be operated as a network of electronically tethered interdependent small satellites. These subsystems include attitude determination, spatial separation knowledge and control, data storage, and intersatellite communication
Electromagnetic nondestructive inspection of aircraft structures by using a magnetic flux leakage method
Aging of aircraft structures is mostly associated with fatigue cracking, de-bonding and corrosion. Detection and characterization of the structural defects at the initiation stages makes it a great challenge for any inspection technology. This study proposes a new solution for the nondestructive evaluation problem by using a magnetic flux method for non-ferromagnetic materials and provides a new neural network tool that predicts crack profiles in three dimensions by solving the inverse problem, where available neural networks can solve it in two dimensions only.;The discontinuity resulting from a crack produces disturbance to the distribution of electrical current density in the structure and as a result the magnetic field around the crack will change. The magnitude of the disturbance is determined by the size and shape of the crack. Therefore, it is possible to evaluate the crack area by magnetic field measurements. The magnetic fields from the plate edges and the wires that carry the current are very strong compared to the magnetic field produced by the crack. A new plate, called a dummy plate, is used to minimize the effect of the magnetic fields produced by the plate edges. This study proves the effectiveness of the dummy plate and shows the measurable change in the magnetic signal around the crack.;As a result of this work, a tool is now available that can solve the nondestructive evaluation problem and the inverse problem in three dimensions and has the capability to provide an enhanced assessment tool for judgment and decision-making which will improve the safety of metallic structures and save people lives
The use of Frequency domain Electro-magnetometer for the characterization of permafrost and ice layers.
openSince the industrial revolution human activities caused a record-breaking increase in the Earth’s average temperature due to the extensive use of greenhouse gases. [1] As global temperatures increase; glaciers have undergone a significant retreat in the past few decades.[2]
The Ice Memory project aims to preserve ice cores from glaciers worldwide, as a record of Earth's past climate. It involves drilling deep into glaciers, extracting ice cores, and storing them in a dedicated facility in Antarctica.
This is to prevent the potential loss of valuable climate archives due to glacier retreat which provides future scientists with valuable information for studying historical climate patterns and understanding the role of human activity in climate change.
geophysical investigations are typically required to determine the most suitable drilling positions for ice coring. the most common technique for this purpose is the so-called GPR. (Snow cover of several meters limits the use of ERT and active seismic methods.)
While each geophysical technique has certain advantages and limitations, combining them can provide a more detailed picture of changes within rock glaciers.
In the present study, electromagnetic prospecting in the frequency domain (FDEM) was performed together with the ground penetration radar (GPR). The former is not a commonly used method for studying glacier environments as FDEM has a lower resolution in the study of glaciers with respect to the GPR. However, as we will see in this study, it is a quick and convenient method to study this type of environment, as it provides a large coverage area in a cost-efficient manner, although with a lower resolution with respect to the GPR. Combining these two techniques provide a more detailed map of the glaciers. comparing the GPR and borehole data with the inverted FDEM datasets (CMD-DUO, GF-Instruments) confirms the effectiveness and applicability of FDEM methodology for investigating glacial bodies in mountainous regions.Since the industrial revolution human activities caused a record-breaking increase in the Earth’s average temperature due to the extensive use of greenhouse gases. [1] As global temperatures increase; glaciers have undergone a significant retreat in the past few decades.[2]
The Ice Memory project aims to preserve ice cores from glaciers worldwide, as a record of Earth's past climate. It involves drilling deep into glaciers, extracting ice cores, and storing them in a dedicated facility in Antarctica.
This is to prevent the potential loss of valuable climate archives due to glacier retreat which provides future scientists with valuable information for studying historical climate patterns and understanding the role of human activity in climate change.
geophysical investigations are typically required to determine the most suitable drilling positions for ice coring. the most common technique for this purpose is the so-called GPR. (Snow cover of several meters limits the use of ERT and active seismic methods.)
While each geophysical technique has certain advantages and limitations, combining them can provide a more detailed picture of changes within rock glaciers.
In the present study, electromagnetic prospecting in the frequency domain (FDEM) was performed together with the ground penetration radar (GPR). The former is not a commonly used method for studying glacier environments as FDEM has a lower resolution in the study of glaciers with respect to the GPR. However, as we will see in this study, it is a quick and convenient method to study this type of environment, as it provides a large coverage area in a cost-efficient manner, although with a lower resolution with respect to the GPR. Combining these two techniques provide a more detailed map of the glaciers. comparing the GPR and borehole data with the inverted FDEM datasets (CMD-DUO, GF-Instruments) confirms the effectiveness and applicability of FDEM methodology for investigating glacial bodies in mountainous regions
Development and application of magnetic modelling to the design of power devices
This thesis examines the use of electromagnetic modelling techniques in the development of realistic models for a saturable core fault current limiter (FCL), which can be extended to other electromagnetic power devices. It includes the use of mathematical, analytical and FEM tools which incorporate magnetic properties of the FCL with the properties of the electrical circuit in which it is placed. Two independent models for a saturable core FCL have been developed on different platforms, validated against measured results, and compared with each other for consistency. The models were incorporated into a time-domain circuitry representation of a power distribution network to assess their performance as predictive representations of the actual device. The electromagnetic models incorporate analytic representations of the non-linear soft ferromagnetic material used in the magnetic cores of the devices obtained from sample measurements. Particular attention is paid to the effects and changes needed by the non-linear equations and data, due to the high-field applications in which they are used. The models also include an improved analytic magnetic field distribution function developed for calculating the variation of magnetic field H in magnetic cores that combines accuracy and speed of computation and offers advantages over conventional finite element calculations. Three dimensional finite element modelling was also used for developing structural improvements to the FCL, such as the effect of various design configurations on the performance of the FCL in the power circuit. A comparative study of the modelling methods employed shows the advantages of each modelling method while underlining some of the challenges faced during the model development This has provided solutions to problems which invariably arise in the modelling design of such electromagnetic devices for applications
Impedance Sensors for Fast Multiphase Flow Measurement and Imaging
Multiphase flow denotes the simultaneous flow of two or more physically distinct and immiscible substances and it can be widely found in several engineering applications, for instance, power generation, chemical engineering and crude oil extraction and processing. In many of those applications, multiphase flows determine safety and efficiency aspects of processes and plants where they occur. Therefore, the measurement and imaging of multiphase flows has received much attention in recent years, largely driven by a need of many industry branches to accurately quantify, predict and control the flow of multiphase mixtures. Moreover, multiphase flow measurements also form the basis in which models and simulations can be developed and validated. In this work, the use of electrical impedance techniques for multiphase flow measurement has been investigated. Three different impedance sensor systems to quantify and monitor multiphase flows have been developed, implemented and metrologically evaluated. The first one is a complex permittivity needle probe which can detect the phases of a multiphase flow at its probe tip by simultaneous measurement of the electrical conductivity and permittivity at up to 20 kHz repetition rate. Two-dimensional images of the phase distribution in pipe cross section can be obtained by the newly developed capacitance wire-mesh sensor. The sensor is able to discriminate fluids with different relative permittivity (dielectric constant) values in a multiphase flow and achieves frame frequencies of up to 10 000 frames per second. The third sensor introduced in this thesis is a planar array sensor which can be employed to visualize fluid distributions along the surface of objects and near-wall flows. The planar sensor can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. It can be operated by a conductivity-based as well as permittivity-based electronics at imaging speeds of up to 10 000 frames/s. All three sensor modalities have been employed in different flow applications which are discussed in this thesis. The main contribution of this research work to the field of multiphase flow measurement technology is therefore the development, characterization and application of new sensors based on electrical impedance measurement. All sensors present high-speed capability and two of them allow for imaging phase fraction distributions. The sensors are furthermore very robust and can thus easily be employed in a number of multiphase flow applications in research and industry
Development and metrological characterization of measuring instruments for low-voltage networks monitoring
This thesis collects the main results about my research and the work related to the designing of monitoring systems of LV distribution networks.
The first three chapters are introductive; the first one describes the main concepts contained in the guide for the evaluation of measurement uncertainty (also called GUM), since some of them are recalled in the next sections.
Chapter 2 provides the main notions on the smart grid concept, the new generation of distribution networks characterized by a high degree of automation, and on the main power quality problems affecting the grids. Therefore, the following standard, connected to the above topics, are presented:
(i) EN 50160.
(ii) IEEE 519.
(iii) IEC 61000-4-7.
Finally, chapter 3 presents a general description of the main sensors suitable for the LV monitoring systems for the acquisition of voltage and current waveforms, providing information on the working principles, the metrological performances and recalling the related standards (as the IEC 61869).
Chapter 4 gets to the heart of the work done in my PhD course; in fact, the two monitoring devices specifically developed to meet the needs of the future smart grids are presented: the Guardian Meter and the Network Monitoring Unit. Hence, information is provided on the purposes of each device, on their technical characteristics, on the tests conducted for the metrological characterization and on the results related to measurement performance.
It is noteworthy that the testing activity has led to the development of procedures, some of which innovative, for the metrological evaluation of monitoring devices. In fact, the last chapter collects the scientific outcomes deriving from the R&D activity, which can be the starting points for the updating of current standards related to monitoring systems and for the development of new procedures to evaluate the metrological performance of the energy meters
Observation and study of giga electron volt solar energetic particles using the Milagrito extensive air shower detector
Measurements of high energy emission from solar events can lead to an understanding of the solar energetic particle acceleration mechanism(s). Although the energy source of these mechanisms is known to reside in the solar magnetic field, the details of the acceleration process(es) have continued to elude researchers. By observing the particle emission at the upper limits of the spectrum, essential information about the location and the nature of the acceleration mechanism(s) can be obtained.
Milagrito was an extensive air shower observatory which operated as a prototype for the larger Milagro instrument. It operated from February 1997 to May 1998. Although Milagrito was originally designed as a high energy (\u3e100 GeV) water-Cherenkov gamma ray observatory, it could also be used to study solar energetic particles (SEPs). In a scaler mode, it was sensitive to muons and small showers from hadronic primary particles above ∼3 GeV. Simultaneously, Milagrito also operated in a shower mode which had increased sensitivity due to its ability to reconstruct event directions, but this mode required primary particles of higher energy. In its scaler mode, Milagrito registered a ground level enhancement associated with the 6 November 1997 SEP event and X9 solar flare. At its peak, the enhancement was 22x background RMS fluctuations. Based on comparisons to neutron monitor and satellite data, we conclude that the differential flux of energetic protons from this event followed a rigidity-power-law spectrum which became steeper above a few GeV, and that the acceleration site was at ∼2 solar radii. This altitude is relatively low in the corona, but it is well above the flare site
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