Reliable Stability Assessment Research Articles

Thermoelastic effects in Bragg reflectors as a potential bottleneck for XFELs with megahertz repetition rate

Bragg reflectors are essential for beam transport in X-ray free-electron laser (XFEL) facilities. On interaction with Bragg reflectors, a part of the pulse energy will be absorbed, causing the propagation of displacement waves due to rapid thermal expansion. It is suspected that these waves may cause stability problems for XFELs operating with megahertz repetition rates. Here, we experimentally investigate the displacement of a diamond Bragg reflector induced by an optical ultra-violet laser pulse, simulating XFEL pulses with mJ pulse energy, both at room temperature and cryogenic temperatures. Our experiment shows negligible damping of the displacement waves on µs timescales, which could cause disruption for subsequent XFEL pulses. We compare our measurements to a simulation framework based on the assumptions of local thermodynamic equilibrium and classical mechanics, observing reasonable agreement. Our results show that thermoelastic effects are critical for a reliable stability assessment of Bragg reflectors, but are often overlooked.

Rock mass quality classification based on deep learning: A feasibility study for stacked autoencoders

Objective and accurate evaluation of rock mass quality classification is the prerequisite for reliable stability assessment. To develop a tool that can deliver quick and accurate evaluation of rock mass quality, a deep learning approach is developed, which uses stacked autoencoders (SAEs) with several autoencoders and a softmax net layer. Ten rock parameters of rock mass rating (RMR) system are calibrated in this model. The model is trained using 75% of the total database for training sample data. The SAEs trained model achieves a nearly 100% prediction accuracy. For comparison, other different models are also trained with the same dataset, using artificial neural network (ANN) and radial basis function (RBF). The results show that the SAEs classify all test samples correctly while the rating accuracies of ANN and RBF are 97.5% and 98.7%, repectively, which are calculated from the confusion matrix. Moreover, this model is further employed to predict the slope risk level of an abandoned quarry. The proposed approach using SAEs, or deep learning in general, is more objective and more accurate and requires less human intervention. The findings presented here shall shed light for engineers/researchers interested in analyzing rock mass classification criteria or performing field investigation.

Assessment of the Stability of Passenger Ships in Coastal Navigation in Case of Lacking Ship Geometry Data

Ships should ensure safe navigation by meeting the stability norms defined by the International Maritime Organization (IMO) and determined by national maritime administrations. The fulfillment of these norms is becoming increasingly important, especially for passenger ships used for tourist excursions. Recently, the development of maritime tourism has greatly increased the demand for these ships most of which are converted fishing vessels. The situation described in this paper pertains to Albania and most probably differs in other countries in the region and the wider area. Ships rarely have adequate technical documentation. The Albanian Register of Shipping requires the performance of stability tests, the results of which are entered in the amended stability book to ensure the vessels’ compliance with the norms following modifications undergone and guarantee safe navigation for tourists. An examination of a variety of ship design papers helped us identify various methods and methodologies for determining approximate geometric ship elements with an acceptable degree of reliability. However, their use should be limited and reliability proven by calculating parameters such as lightship VCG, number of passengers per m2, assessing the possible range and area of navigation and weather conditions (mainly wind speed and wave forces). The calculations based on stability testing and the use of highly reliable software such as MaxSurf - Integrated Naval Architecture Software, Napa - Naval Architectural Package Autoship - Systems Operation, Orca3D – Naval Architecture Software delivered fast and reliable stability assessment results and verified conformance with the norms prescribed by the Albanian Register of Shipping.

Undrained basal stability of braced circular excavations in non-homogeneous clays with linear increase of strength with depth

Braced circular excavations are commonly used as one of effective retaining structures in practice. Despite a number of studies in the past on the stability of this problem, its stability solution under the framework of lower bound limit analysis is very rare in the literature. The present study focuses on the stability analysis of braced circular excavations in non-homogeneous clays using the lower bound finite element limit analysis under axisymmetric conditions. The stability number of the problem is comprehensively investigated, and is affected by depth-radius aspect ratios of excavation, depth ratios of rigid base, and strength gradient factors. The influence of these dimensionless parameters on the predicted failure mechanisms are discussed and compared. The presented new lower bound solutions of braced circular excavations in non-homogeneous clays are useful for an accurate, convenient and reliable stability assessment of the problem in practice.

Application of particle sedimentation analysis in sterically-stabilized TiO2 particles stability assessment

Particle sedimentation analysis is an important characterization technique for making reliable stability assessment of particles in suspensions. In this work, new analytical model was derived similar to Kynch’s continuity equation where negligible compression effect and constant solid volume concentration ϕs are assumed at the compression phase. However, this new model differs as it includes new expressions for forces due to inertia and accelerated fluid eddies. The new model was also employed in analysing dynamics of particles during sedimentation thereby making it useful to assess particle stability in suspensions as well as predict particle sedimentation profiles if variation of ϕs with time can be accurately measured.Stability of monodisperse spherically shaped TiO2 particles synthesized by the well-accepted sol–gel process and sterically stabilized separately by two different commercial surfactants, Brij30 and Brij76, were assessed via an instrument called Turbiscan and it operates based on principle of multiple light scattering (MLS) technique. The instrument measures variations in particle size and position as function of time and records as backscattered (BS) or transmitted (T) light intensity which can then be converted to ϕs expressed in terms of attenuation time and height. This makes the instrument applicable in validating the newly derived analytical model.

Impact of the sample matrix composition on the signal enhancement in the capillary electrophoretic separation of poliovirus samples

The development of capillary electrophoretic applications aiming to provide reliable stability assessment of viral suspensions, to detect subviral particles from cell extracts or to study the interactions between virus particles and various biomolecules, cannot be done without a thorough understanding of the sample matrix contribution to the observed electrophoretic behaviour. The present study thoroughly investigates the effect of the sample matrix on the electrophoretic behaviour of poliovirus injected as sample plugs of 1%, 5% and 12% effective capillary length. The effect of the sample matrix for three different poliovirus batches was evaluated. Additionally, simulated samples, obtained from concentrated poliovirus suspensions of high purity and diluted with commonly used lab buffers in order to obtain samples with either high or low conductivities, were also investigated. The goal of the study was to obtain a better understanding of the effect of the sample matrix on the signal enhancement, in order to define a general approach allowing a repeatable capillary electrophoretic (CE) separation of poliovirus from complex samples. This study clearly demonstrates that the sample matrix has an important influence on the sensitivity of the CE poliovirus separations. Translation of these observations into routine practice involves several compromises and a set of rules in order to reduce day-to-day variation and to maximize sensitivity.

Determination of Interface Flow Stability Limits by Sensitivity Analysis of Transient Energy Margin

Due to the continued development and enhancement, the transient energy function method now provides accurate and reliable stability assessment. In this paper a procedure to determine stability limits in terms of interface power flow for a particular contingency is presented using analytical sensitivity of the energy margin. The proposed procedure is tested on a 17- generator equivalent of the network of the State of Iowa. Test results show that proposed procedure determines the stability limit accurately when the generation change is small or when the energy margin changes approximately linearly.