Defects simulation

Fig. 6. Test with one segment of 6 sector transducer in pulse-echo mode on aluminium plate, (a) no defect (b) defect simulated with mercury droplet (c) defect position.

In general, ab initio studies assist in confirming the validity of the defect simulations, but provide additional details on the elecironic structure that are Inaccessible... 

Fig. 2 Distribution of healthy to defective (i.e., short) chains for the three Type I defect simulation trials. The -l-z direction is out of the plane of the page. Cyan and magenta represent healthy and defective chains, respectively...

Fig. 5 Helmholtz free energy as a funetion of LKal4/SAM distance for PTMetaD-WTE simulations at 300 K a T) pe I defect simulations, trials I-in b Type n defect simulation, energy minima highlighted in inset and c control simulation. Note that the relative energy scale is arbitrary owing to the trivial constant introduced in the estimation of the free energy fixim the MetaD bias potential...

The analysis was first performed on the trial III Type I defect simulation since Fig. 5a shows similar free energy profiles for the three trials, we deemed analysis of a single trial to be sufficient. Skipping every second frame to reduce computation time, surface-bound structures (defined as peptide/surface distances below 1.2 nm) were clustered with an RMSD cutoff value of 0.2 nm. As noted above, we used only the second half of the trajectory for the clustering analysis to eliminate the transient part of the MetaD bias potential. Among 39,696 stmctures, 78 clusters... 

Fig. 6 Top three surface-bound cluster center confomiations from a clustering analysis of the Type 1, trial III defect simulation compared to the control simulation with no chain defects. Secondary structure is indicated by peptide backbone color. Purple designates an ot-helix, magenta a turn, and cyan a random coil. Silver and pink represent healthy and defective chains, respectively...

The first thing to note is the difference in cluster distribution between the defect and the control simulations Conformations in the top three clusters of the defect simulation make up about 81 % of the total probability of surface-bound states, whereas conformations in the first cluster alone in the control simulation have a similar probability of existing on the surface of just over 78 %. As Fig. 6 shows, this is because areas of shortened alkyl chain lengths caused by depressions in the gold substrate below the SAM surface dramatically disrupt the helical structure that LKal4 normally adopts at interfaces, leading to a wide array of unfolded structures. Nearly, all secondary structure, indicated by the color of the peptide s backbone (i.e., magenta, cyan, and purple indicate turns, coils, and alpha helical residues, respectively), is lost with the addition of the surface defects. Unlike the central... 

The same analysis was performed on the Type II defect simulation for each of the three energy minima highlighted in Fig. 5b (i.e.. A, B, and C). These minima are related to the presence of the outward boundary defect (see Fig. 3) the inward boundary defect appears to have little influence on binding. Within sigma of each minimum, all structures below an RMSD cutoff of 0.2 nm were clustered. This resulted in 9,885 structures in 11 clusters for minimum A, 41,203 structures in 23 clusters for minimum B, and 14,710 structures in 9 clusters for minimum C. The central cluster conformations of the clusters with the top three weights calculated for each of the minima are shown in Fig. 7. 

Corrosion coupons. Corrosion coupons connected to cathodically protected structures are finding increasing application for performance monitoring of the CP system. Essentially these coupons, installed uncoated, represent a defect simulation on the pipeline under controlled conditions. These coupons can be connected to the pipeline via a test post outlet, facilitating a number of measurements such as potential and current flow. 

TRIFOU is a combined Finite Elements/Boundary Integral formulation code. The BIM formulation in vacuum is suitable for NDT simulation where the probe moves in the air around the test block. The FEM formulation needs more calculation time, but tetrahedral elements enable a large variety of specimens and defect geometries to be modelled. TRIFOU uses a formulation of Maxwell Equations using magnetic field vector h, where h is decomposed as h = hs + hr (hj source field, and hr reaction field). 

The measurements were earned out on rectangular slots in aluminium and mild steel inspected using two probes at several frequeneies. The size of the eoils are adapted to the dimensions of the slots which simulate rectangular defects. 

Table 2 compares between the VIGRAL results and mechanical measurements of the simulated FBH defects. The table lists the size of the reflecting surface,, its depth location, the Yd, and the standard deviation of the depth information, o>i( y ). We note an excellent agreement between the VIGRAL and the mechanical measurements both in size and depth of the defects. 

To verify the modelling of the data eolleetion process, calculations of SAT 4, in the entrance window of the XRII was compared to measurements of RNR p oj in stored data as function of tube potential. The images object was a steel cylinder 5-mm) with a glass rod 1-mm) as defect. X-ray spectra were filtered with 0.6-mm copper. Tube current and exposure time were varied so that the signal beside the object. So, was kept constant for all tube potentials. Figure 8 shows measured and simulated SNR oproj, where both point out 100 kV as the tube potential that gives a maximum. Due to overestimation of the noise in calculations the maximum in the simulated values are normalised to the maximum in the measured values. Once the model was verified it was used to calculate optimal choice of filter materials and tube potentials, see figure 9. 

Now, we can make the comparison beween the real defect signal and the simulated one which have been computed by solving the linearized direct problem. The measurements were made at 300,150,50 kHz. The flaw is a notch of 8mm length, 1mm width, and 1mm depth. Representative data (300 kHz) for the notch-shaped flaw are shown in Fig. 3. 

The weld depths penetration for gold-nickel alloy and tantalum cylinders have been well controlled by an entirely contactless ultrasound method. Nevertheless, the development of signal and image processing will allow to increase the resolution of the ultrasonic images. Moreover, in order to be able to size quite well the lacks of weld penetration, the simulation of the interaction beam-defect is presently developed in our laboratory. 

Catlow C R A and W C Mackrodt 1982. Theory of Simulation Methods for Lattice and Defect Energy Calculations in Crystals. In Lecture Notes in Physics 166 (Comput. Simul. Solids), pp. 3-20. 

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