Evolution of gas permeability for concrete materials under and after uni-axial loading

Under life-cycle service conditions, gas permeability which is usually employed to indicate the durability performance of concrete materials will be changed along with the evolution of microstructure under or after loading. This paper reports an extensive experimental research on the influence of loading condition on the evolution of gas permeability. A cyclic loading scheme under displacement control, which is employed to accelerate the evolution of its microstructure and model the loading condition under real service, is applied on cylinder specimens ϕ37u74mm dried to constant weight at 60°C. Both axial and lateral strains in the whole loading test are recorded by strain gauge to characterize the change of microstructure macroscopically. At the same time, gas permeability measurement is carried out by a well-designed tri-axial permeater at various loading levels in the planned loading history. The relationship between intrinsic gas permeability, Klinkenberg coefficient and residual strains discussed. It is found that intrinsic gas permeability will become great if the uniaxial loading level is beyond about 70% ultimate strength. Moreover, both the klinkenberg coefficient and intrinsic gas permeability are badly linked with elastic and plastic strains. However, the relationship between the Klinkenberg coefficient and intrinsic gas permeability can be approximated by a semi-empirical law, no matter under or after loading

Controller Design and Optimization for Rotor System Supported by Active Magnetic Bearings

Active Magnetic Bearings (AMBs) have been receiving increased attention in industry because of the advantages (contact-free, oil-free, etc.,) that they display in comparison with conventional bearings. They are used extensively in rotor system applications, especially in conditions where conventional bearing systems fail. Most AMBs are controlled by Proportional-Integral-Derivative (PID)-controllers. Controller design for AMB systems by means of hand tuning is time-consuming and requires expert knowledge. In order to avoid this situation and reduce the effort to tune the controller, multi-objective optimization with genetic algorithm is introduced to design and optimize the AMB controllers. In the optimization, criteria both in time and frequency domain are considered. A hierarchical fitness function evaluation procedure is used to accelerate the optimization process and to increase the probability of convergence. This evaluation procedure guides the optimizer to locate the small feasible region resulting mainly from the requirement for stability of control system. Another strategy to reduce the number of optimization parameters is developed, which is based on a sensitivity analysis of the controller parameters. This strategy reduces directly the complexity of the optimization problem and accelerates the optimization process. Controller designs for two AMB systems are considered in this thesis. Based on the introduced and presented hierarchical evaluation strategy, the controller design for the first AMB system is obtained without specific requirements related to initial solutions. The optimal controller design is applied to a test rig with a flexible rotor supported by AMBs. The results show that the introduced optimization procedure realizes the desired results of the controlled system’s behavior. The maximal speed of 15000 rpm is reached. The second AMB system is designed for a turbo-compressor. The introduced parameter reduction strategy is applied for the controller design of this AMB system. The controller design is optimized in the search space around an initial solution. Optimization results show the efficiency of the introduced strategy.Aufgrund vieler Vorteile (wie z. B. Kontaktfreiheit, Ölfreiheit) gegenüber konventionellen Lagern etablieren sich aktive Magnetlager zunehmend in der Industrie. Aktive Magnetlager werden zum großen Teil in Rotorsystemen verwendet, wo konventionelle Öllager für die Anwendung versagen. PID-Regler werden häufig für Magnetlager verwendet. Die Auslegung des Reglers wird durch manuelle Einstellung (trial and error) bestimmt und ist sehr zeitaufwendig. Zudem bedarf es spezieller Fachkenntnisse zur Einstellung. Um diese Situation zu vermeiden und den Aufwand für die Reglerauslegung zu reduzieren, wird die Mehrzieloptimierung mit Genetischen Algorithmen in der vorliegenden Arbeit zur Optimierung des Reglerentwurfs eingesetzt. In der Optimierung werden die Zielfunktionen sowohl im Zeit- wie auch im Frequenzbereich definiert. Um den Optimierungsprozess zu beschleunigen und die Wahrscheinlichkeit der Konvergenz der Optimierung zu erhöhen, wird eine hierarchische Struktur zur Bewertung der Zielfunktionen eingeführt. Dies hilft dem Optimierer bei der Lokalisierung des kleinen zulässigen Bereichs, der im Wesentlichen aus der Anforderung an die Stabilität des Magnetlagersystems resultiert. Desweitern wird eine Strategie zur Reduzierung der Optimierungsparameter entwickelt, die auf der Sensitivitätsanalyse der Reglerparameter basiert. Diese Strategie reduziert die Komplexität des Optimierungsproblems und führt zu einer Beschleunigung des Optimierungsprozesses. In der vorliegenden Arbeit wird der Reglerentwurf von zwei Magnetlagersystemen berücksichtigt. Mit Hilfe der eingeführten Strategie zur Bewertung der Zielfunktionen, werden die Reglerparameter von dem ersten Magnetlagersystem bestimmt bzw. optimiert, ohne dass irgendeine Information über die Anfangslösung erforderlich ist. Der optimale Reglerentwurf wird dann in einem Versuchstand implementiert, in dem eine elastische Welle durch zwei Magnetlager gelagert ist. Die Versuchsergebnisse zeigen, dass das gewünschte dynamische Verhalten des geregelten Magnetlagersystems durch die Optimierung erzielt wird. Die maximal zulässige Drehzahl (15000 rpm) des Versuchsstandes wird mit dem optimalen Regler ohne Probleme erreicht. Als zweites Beispiel wird der Reglerentwurf eines magnetgelagerten Rotorsystems eines Turboverdichters betrachtet. In der Reglerauslegung wird die vorgeschlagene Optimierungsstrategie mit Hilfe von Parameterreduktion verwendet. Die optimale Lösung wird lokal in der Nähe einer Anfangslösung gesucht. Die Optimierungsergebnisse zeigen die Effizienz der Optimierungsstrategie

Power generation expansion optimization model considering multi-scenario electricity demand constraints: a case study of Zhejiang Province, China

Reasonable and effective power planning contributes a lot to energy efficiency improvement, as well as the formulation of future economic and energy policies for a region. Since only a few provinces in China have nuclear power plants so far, nuclear power plants were not considered in many provincial-level power planning models. As an extremely important source of power generation in the future, the role of nuclear power plants can never be overlooked. In this paper, a comprehensive and detailed optimization model of provincial-level power generation expansion considering biomass and nuclear power plants is established from the perspective of electricity demand uncertainty. This model has been successfully applied to the case study of Zhejiang Province. The findings suggest that the nuclear power plants will contribute 9.56% of the total installed capacity, and it will become the second stable electricity source. The lowest total discounted cost is 1033.28 billion RMB and the fuel cost accounts for a large part of the total cost (about 69%). Different key performance indicators (KPI) differentiate electricity demand in scenarios that are used to test the model. Low electricity demand in the development mode of the comprehensive adjustment scenario (COML) produces the optimal power development path, as it provides the lowest discounted cost

Enhancing Water Resistance and Mechanical Properties of Cemented Soil with Graphene Oxide.

Although cemented soil as a subgrade fill material can meet certain performance requirements, it is susceptible to capillary erosion caused by groundwater. In order to eliminate the hazards caused by capillary water rise and to summarize the relevant laws of water transport properties, graphene oxide (GO) was used to improve cemented soil. This paper conducted capillary water absorption tests, unconfined compressive strength (UCS) tests, softening coefficient tests, and scanning electron microscope (SEM) tests on cemented soil using various contents of GO. The results showed that the capillary water absorption capacity and capillary water absorption rate exhibited a decreasing and then increasing trend with increasing GO content, while the UCS demonstrated an increasing and then decreasing trend. The improvement effect is most obvious when the content is 0.09%. At this content, the capillary absorption and capillary water absorption rate were reduced by 25.8% and 33.9%, respectively, and the UCS at 7d, 14d, and 28d was increased by 70.32%, 57.94%, and 61.97%, respectively. SEM testing results demonstrated that GO reduces the apparent void ratio of cemented soil by stimulating cement hydration and promoting ion exchange, thereby optimizing the microstructure and improving water resistance and mechanical properties. This research serves as a foundation for further investigating water migration and the appropriate treatment of GO-modified cemented soil subgrade

Time-variant TEC estimation with fully polarimetric GEO-SAR data

A time-variant total electron content (TEC) estimation method with fully polarimetric geosynchronous synthetic aperture radar (GEO-SAR) data is proposed based on inner aperture Faraday rotation angle estimation and an accurate TEC inversion model. With a long integration time and sensitivity to ionosphere effects, the fully polarimetric GEO-SAR data are utilised for estimation with high accuracy for both the time-variant TEC and the time interval. Superiority of the proposed method over conventional ionospheric sounding methods is verified by simulation results

Structure design, kinematics analysis, and effect evaluation of a novel ankle rehabilitation robot

This paper presents a novel ankle rehabilitation (2-CRS+PU)&R hybrid mechanism, which can meet the size requirements of different adult lower limbs based on the three-movement model of the ankle. This model is related to three types of movement modes of the ankle movement, without axis offset, which can cover the ankle joint movements. The inverse and forward position/kinematics results analysis of the mechanism is established based on the closed-loop vector method and using the optimization of particle groups algorithm. Four groups of position solutions of the mechanism are obtained. The kinematics simulation is analyzed using ADAMS software. The variations of the velocity and acceleration of all limbs are stable, without any sudden changes, which can effectively ensure the safety and comfort of the ankle model end-user. The dexterity of the mechanism is analyzed based on the transport function, and the results indicate that the mechanism has an excellent transfer performance in yielding the structure parameters. Finally, the rehabilitation evaluation is conducted according to the three types of movement modes of the ankle joint. The results show that this ankle rehabilitation mechanism can provide a superior rehabilitation function

Clinical features of febrile seizures in children with COVID-19: an observational study from a tertiary care hospital in China

BackgroundFebrile seizures are a common neurologic manifestation in children with coronavirus disease 2019 (COVID-19). Compared to seasonal respiratory viruses, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a pronounced neurological impact, with the result that febrile seizures with COVID-19 may exhibit unique clinical features.Materials and methodsWe conducted a retrospective study in a tertiary care hospital in China. We collected medical record information on febrile seizures with COVID-19, including demographic characteristics, clinical features, laboratory tests, and disease burden. Subsequently, the data were then analyzed descriptively.ResultsA total of 103 children diagnosed with febrile seizures and positive COVID-19 PCR results were included in our study. Among them, 81 (78.6%) were males and 22 (21.4%) were females. The age of onset of febrile seizures ranged from 14 to 57 months, with a mean age of 34.9 ± 6.24 months. Complex febrile seizures were observed in 34 (33%) cases. Antiseizure medications were administered to 24 (23.3%) patients. Laboratory tests showed a white blood cell count of (27.05 ± 8.20) × 103/µl, a neutrophil count of (20.09 ± 5.66) × 103/µl and a lymphocyte count of (6.44 ± 1.86) × 103/µl. A creatine kinase level was significantly elevated, with a mean value of (412.00 ± 158.96) U/L. The mean length of stay was 4.36 days. Twelve patients (11.7%) required intensive care services, but there were no deaths or patients remaining on antiseizure medications after discharge.ConclusionIn the post-epidemic era of COVID-19, pediatric clinicians should be aware of the changing clinical features of febrile seizures associated with COVID-19. The average age of onset has increased, with a higher proportion of males. Length of stay and hospitalization costs did not increase significantly. The prognosis remained favorable, although a small number of children required intensive care services during the acute phase

Parameter estimation and error calibration for multi-channel beam-steering SAR systems

Multi-channel beam-steering synthetic aperture radar (multi-channel BS-SAR) can achieve high resolution and wide-swath observations by combining beam-steering technology and azimuth multi-channel technology. Various imaging algorithms have been proposed for multi-channel BS-SAR but the associated parameter estimation and error calibration have received little attention. This paper focuses on errors in the main parameters in multi-channel BS-SAR (the derotation rate and constant Doppler centroid) and phase inconsistency errors. These errors can significantly reduce image quality by causing coarser resolution, radiometric degradation, and appearance of ghost targets. Accurate derotation rate estimation is important to remove the spectrum aliasing caused by beam steering, and spectrum reconstruction for multi-channel sampling requires an accurate estimate of the constant Doppler centroid and phase inconsistency errors. The time shift and scaling effect of the derotation error on the azimuth spectrum are analyzed in this paper. A method to estimate the derotation rate is presented, based on time shifting, and integrated with estimation of the constant Doppler centroid. Since the Doppler histories of azimuth targets are space-variant in multi-channel BS-SAR, the conventional estimation methods of phase inconsistency errors do not work, and we present a novel method based on minimum entropy to estimate and correct these errors. Simulations validate the proposed error estimation methods

A New Transcatheter Aortic Valve Replacement System for Predominant Aortic Regurgitation Implantation of the J-Valve and Early Outcome

AbstractObjectivesThis study introduces a newly designed transcatheter aortic valve system, the J-Valve system, and evaluates its application in patients with predominant aortic regurgitation without significant valve calcification. We also report the early results of one of the first series of transapical implantations of this device and aim to offer guidance on the technical aspects of the procedure.BackgroundTranscatheter aortic valve replacement (TAVR) has been widely used in high-risk patients for surgical aortic valve replacement. However, the majority of the TAVR devices were designed for aortic valve stenosis with significant valve calcification.MethodsSix patients with native aortic regurgitation without significant valve calcification (age, 61 to 83 years; mean age, 75.50 ± 8.14 years) underwent transapical implantation of the J-Valve prosthesis (JieCheng Medical Technology Co., Ltd., Suzhou, China), a self-expandable porcine valve, in the aortic position at our institution. All patients were considered to be prohibitive or high risk for surgical valve replacement (logistic EuroSCORE [European System for Cardiac Operative Risk Evaluation], 22.15% to 44.44%; mean, 29.32 ± 7.70%) after evaluation by an interdisciplinary heart team. Procedural and clinical outcomes were analyzed.ResultsImplantations were successful in all patients. During the follow-up period (from 31 days to 186 days, mean follow-up was 110.00 ± 77.944 days), only 1 patient had trivial prosthetic valve regurgitation, and none of these patients had paravalvular leak of more than mild grade. There were no major post-operative complications or mortality during the follow-up.ConclusionsOur study demonstrated the feasibility of transapical implantation of the J-Valve system in high-risk patients with predominant aortic regurgitation