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Other Applications of Radiography in NDE
Published in Don E. Bray, Roderic K. Stanley, Nondestructive Evaluation, 2018
Don E. Bray, Roderic K. Stanley
Computed tomography (CT) utilizes scatter data from radiographic scans obtained at a large number of orientations of source, object and receiver. The source and detector are moved in each scan plane as shown in Fig. 32-1. Additionally, the scan planes may be rotated until a full scan global field is obtained. The scatter data are digitized and stored and the results appear as a reconstructed image. Engineering applications of computed tomography have been increasing in number in recent years, as described by Refs. 34–36, 41 and 42. A very typical application has been for low density, light element castings since the low absorption of these materials decreases the overall time requirement for obtaining the data set, Gil boy and Foster35 reported that a 30 hour scan was required to obtain global data for a reconstruction of a light alloy pump casting, using 1.5 MeV x-rays. The thickest section of this part was 100 mm. (3.94 in). More recent work reported by Ellinger41 and Johns42 give examples of CT inspections of industrial castings of automotive engine blocks and aircraft engine parts, respectively. Defects sought include thin walls as well as porosity, voids, inclusions, etc.
Finite Element Method
Published in Manoj Kumar Buragohain, Composite Structures, 2017
In the FEM, the domain or the body is divided into a finite number of elements. Certain basic field variables, for example, displacement or temperature, is identified for the physical problem. The actual variation of the field variable within the body is unknown and its determination is the first objective. However, instead of determining the continuous variation, the values of the field variable at the nodes are determined and the actual variation is approximated within each element by some simple approximating function. Also, the loads and boundary conditions are applied at the nodes. For each element, an element characteristic matrix is obtained by using certain variational principle or equilibrium condition. Now, the focus is shifted from individual elements to the entire body and the field equations are written for the body. Toward this, the element characteristic matrices are assembled to form global field equations. The nodal values of the field variable are obtained by solving these field equations from which other desired information is extracted.
Optical Switches
Published in Abdul Al-Azzawi, Fibre Optics, 2017
To rotate unclamped mirrors into the up state, magnetic actuation is implemented globally by applying an external field generated with a small electromagnet. The magnetic signal only needs to be applied momentarily. Using a global field avoids the need to fabricate individual magnetic actuators for each chip. Mirrors are fabricated with a layer of attached nickel to produce torque on the mirror hinge in response to the applied field. The nickel plate aligns with the magnetic field lines and generates a magnetostatic torque on the mirror. This lifts the mirror off the substrate and orients it near the desired vertical position, where electrostatic force can take over in setting and holding the final desired mirror position. An electrostatic field is applied mirror by mirror, either to hold the mirror down against the torque produced by the magnet or to hold the mirror in the up position against the restoring force of the elastic hinge. Since the magnetic field is applied globally, all mirrors will attempt to rotate when the field is turned on. Only the mirrors to be rotated into the up position are unclamped; all others are held down electrostatically. Similarly, mirrors clamped in the up state remain so until the electrostatic signal is removed; the magnet is no longer needed to hold the mirror up. The combination of magnetic and electrostatic actuation provides an effective means for configuring a mirror array without resorting to complex individual actuators for each mirror. Since electrostatic clamping of the mirrors requires virtually no current flow, the switch array consumes very little steady state power. Power is consumed only during transitions when the magnet is activated. The components of the switch are packed in a packaging base and lid.
A study of global magnetic helicity in self-consistent spherical dynamos
Published in Geophysical & Astrophysical Fluid Dynamics, 2022
P. Gupta, R.D. Simitev, D. MacTaggart
Since magnetic helicity is not strictly conserved in the simulations we have considered, we cannot claim that reversals are linked causally to magnetic helicity. However, what our results do suggest is that there are perhaps preferred states of global magnetic linkage for particular dynamo solutions. When the dynamo moves away from such states, it can return via a global reversal. For example, if there is a reversal of the large-scale toroidal field, this changes the global field linkage. To return to the original linkage, the poloidal field reverses, thus completing the global magnetic field reversal and returning the magnetic helicity distribution to what it was before any reversal took place. Therefore, even if magnetic helicity is not the cause of reversals in these simulations, it is a clear signature of the global poloidal-toroidal linkage, which is intimately linked to reversals. Furthermore, maps of the magnetic helicity density at the surface, which are measurable quantities in stellar observations, indicate the onset of reversals. This result is robust for dynamo solutions with different reversal mechanisms.
Evaluation of shortwave and longwave radiation models for mechanistic-empirical pavement analysis
Published in International Journal of Pavement Engineering, 2022
Shafkat Alam-Khan, Bora Cetin, Barton A. Forman, M. Emin Kutay, Stephan Durham, Charles W. Schwartz
The pavement distresses predictions for analysis case 1 (PMED models) are compared against case 2 (direct input of MERRA-2 D-SWR), case 3 (updated D-SWR and D-LWR models assuming constant vapour pressure) and case 4 (updated D-SWR and D-LWR with time-varying vapour pressure) in Figure 8. All analyses use the same global field calibration factors similar to PMED. Figure 8(a–c) shows the corresponding total rutting (TR), asphalt rutting (AR), and bottom up fatigue cracking (BUFC) values, respectively, for the four cases. Previous studies have found that TR, AR, and BUFC were the most sensitive distresses to the climate inputs (Schwartz et al. 2015b, Cetin et al. 2018). For all modified methods (cases 2, 3 and 4), the pavement distresses were significantly higher than those obtained using the unmodified method (case 1). Figure 8 shows that the TR, AR, and BUFC distresses increase between 20% and 44%, 60% and 131%, 102% and 236%, respectively as a result of the use of the updated D-SWR model (case 2). This suggests that the flexible pavement distresses may be significantly impacted when using the modified D-SWR model.
Visual Performance Models in Road Lighting: A Historical Perspective
Published in LEUKOS, 2021
These two reports, 19 and 19.2, can be considered both as a success and a failure. A success, because a scientific, causal approach is proposed, predicting the visual performance in any visual task, in terms of the lighting parameters (along with parameters specifics to the task). The visual performance is mediated by the visibility, which subsums all aspects of the stimulus. It was a nice move, which gave rise to a lot of discussions in the lighting community. On the other hand, some of the model’s parameters (such as the task difficulty) cannot be directly estimated. Moreover, the model is uneasy to implement because of the number of parameters. This issue has been addressed by later authors in road lighting through a global field factor, which subsums most of these parameters.