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A full-scale field study for evaluation of simple analytical models of cross ventilation and single-sided ventilation
No full textIn this study, we evaluated several simple natural ventilation models of cross ventilation and single-sided ventilation with data measured in a full-scale field study in London. In the field study, the ventilation rate in a naturally ventilated office was measured using a tracer gas technique with CO2. Internal temperatures were measured using a vertical temperature array. The external temperature, wind speed and direction were measured at a nearby weather station. In addition, a 1:200 scale model of the urban area within 300 m of the test room was built in a wind tunnel to measure the pressure coefficients. The ventilation models were evaluated with input data from two sources. Wind data from a nearby airport and pressure coefficients from the literature were used, as is common practice. Alternatively, wind data measured at the local weather station and the pressure coefficients measured from wind tunnel experiments were used. The results showed that, regardless of the input data sources, the cross-ventilation model in general gives reasonable predictions. For single-sided ventilation, several empirical models were evaluated and poor predictions were obtained using the models. We discuss ways in which models of natural ventilation might be improved in the future
Modeling Clear-Water Scour around the High-Rise Structure Foundations (HRSF) of Offshore Wind Farms
No full textThe high-rise structure foundation (HRSF) has been used in building the Donghai offshore wind farm in Shanghai, China. So far, few published studies can be found on the local scour around an HRSF. This study presents the results of a physical modeling investigation of the clear-water scour around two typical HRSF models consisting of eight piles and 10 piles, respectively. In the study, the flume bed was covered with uniform noncohesive sediment and the incoming flow was steady. The effects of the alignment angle of the HRSF, water depth, and relative sediment size on the equilibrium scour depth were analyzed. Results showed that the maximum scour depth always occurred around the middle piles on the shoulders of the HRSF. The alignment angle of the HRSF had little influence on the final equilibrium scour depth. For permeable multipile foundations, the scour depth increased when the water depth increased within the range of the testing conditions, which indicates a similar trend between a multipile foundation and a monopile. An empirical formula is proposed for estimating the equilibrium scour depth
Closure to "simplified Procedure for Prediction of Earthquake-Induced Settlements in Partially Saturated Soils" by Abdülhakim Zeybek and Santana Phani Gopal Madabhushi
No full textStatistical finite elements for misspecified models
No full textWe present a statistical finite element method for nonlinear, time-dependent phenomena, illustrated in the context of nonlinear internal waves (solitons). We take a Bayesian approach and leverage the finite element method to cast the statistical problem as a nonlinear Gaussian state-space model, updating the solution, in receipt of data, in a filtering framework. The method is applicable to problems across science and engineering for which finite element methods are appropriate. The Korteweg-de Vries equation for solitons is presented because it reflects the necessary complexity while being suitably familiar and succinct for pedagogical purposes. We present two algorithms to implement this method, based on the extended and ensemble Kalman filters, and demonstrate effectiveness with a simulation study and a case study with experimental data. The generality of our approach is demonstrated in SI Appendix, where we present examples from additional nonlinear, time-dependent partial differential equations (Burgers equation, Kuramoto-Sivashinsky equation)
Columnar heat transport via advection induced by inertial waves
No full textInertial waves are oscillations in a rotating fluid that arise due to the restoring action of the Coriolis force. Low-frequency inertial waves are known to create columnar flow structures inrapidly rotating systems. Columnar heat transport away from the equator has been observed in some strongly forced, rapidly-rotating geodynamo simulations of the Earth's core. In this study, we investigate the mechanism governing this heat transport by performing direct numerical simulations of model problems comprising buoyant blobs under rapid rotation in a periodic box. We consider a wide range of Rossby numbers (Ro), the ratio of advection to Coriolis force, and Peclet numbers (Pe), the ratio of thermal advection to thermal diffusion. Columnar flow structures, that comprise inertial wave packets, are observed to emerge from the buoyant regions and travel towards the box boundary. We find that the columnar heat transport occurs by advection governed by the local Pe (for instance, a larger vertical elongation in the blob is observed for larger Pe at the same Ro). The magnitude of the advection velocity is determined by the balance between the buoyancy and Coriolis forces. Moreover, the direction of advection is determined by the direction of the wave-induced flow in the columns above and below the blob. Our results suggest that the local Pe could be important for the columnar heat transport in strongly forced dynamo simulations
Printed aerogels: Chemistry, processing, and applications
No full textAs an extraordinarily lightweight and porous functional nanomaterial family, aerogels have attracted considerable interest in academia and industry in recent decades. Despite the application scopes, the modest mechanical durability of aerogels makes their processing and operation challenging, in particular, for situations demanding intricate physical structures. "Bottom-up"additive manufacturing technology has the potential to address this drawback. Indeed, since the first report of 3D printed aerogels in 2015, a new interdisciplinary research area combining aerogel and printing technology has emerged to push the boundaries of structure and performance, further broadening their application scope. This review summarizes the state-of-the-art of printed aerogels and presents a comprehensive view of their developments in the past 5 years, and highlights the key near- and mid-term challenges. This journal i
Roll to roll coating of carbon nanotube films for electro thermal heating
No full textCarbon nanotube (CNT) films are gaining traction in applications such as transparent conductive films, electro-magnetic shields and thin film heaters. However, to date, few cost-effective large-area CNT coating methods have been reported. Here, we present a roll-to-roll (R2R) slot-die coating process for thin film CNT heaters. In this process, a CNT suspension is continuously coated on a PET film substrate and subsequently dried and packaged. This process allows for continuous square-meter-size CNT coating. The electrical resistance and thermal map of these samples are measured by high definition infrared (IR) thermography. Anti-/de-icing demonstrations of R2R CNT coated samples are performed inside a cold room and outdoor atmospheric icing conditions. The successful R2R coating of CNTs and anti-/de-icing demonstrations show promise for application of CNTs in large area applications, such as the de-icing of ships, for which strict regulations are put in place for vessels operating in polar waters
Digital Implementation of Deadbeat-Direct Torque and Flux Control for Permanent Magnet Synchronous Machines in the M-T Reference Frame
No full textIn the traditional deadbeat-direct torque and flux control in the M-T reference frame (DB-DTFC-MT) scheme, the stator flux is calculated with the current model, and one-step delay in the digital system is neglected, which results in poor robustness to parameter variations and a serious oscillation in both the stator flux and torque, especially in the low-speed range. In this article, the digital implementation of DB-DTFC-MT is studied. First, the DB-DTFC-MT scheme considering the one-step delay in the digital system is deduced. Second, digital stator flux observer and current observer are developed to predict the stator flux and current in the next sampling instant. By using the predicted stator flux and torque, the oscillation caused by the one-step delay is eliminated and real deadbeat control is realized. Moreover, the robustness of the system to parameter variations is qualitatively evaluated. Although the system shows some sensitivity to the permanent magnet flux, it has strong robustness to the stator resistance and inductances, especially the d-Axis inductance. Hence, a larger estimated d-Axis inductance can be used in the system for reducing the pulsation in the d-Axis current when tracking sinusoidal torque. All the proposed control designs are validated on a real-Time control platform based on dSPACE DS1103
A scalable control design for grid-forming inverters in microgrids
No full textMicrogrids are increasingly recognized as a key technology for the integration of distributed energy resources into the power network, allowing local clusters of load and distributed energy resources to operate autonomously. However, microgrid operation brings new challenges, especially in islanded operation as frequency and voltage control are no longer provided by large rotating machines. Instead, the power converters in the microgrid must coordinate to regulate the frequency and voltage and ensure stability. We consider the problem of designing controllers to achieve these objectives. Using passivity theory to derive decentralized stability conditions for the microgrid, we propose a control design method for grid-forming inverters. For the analysis we use higher-order models for the inverters and also advanced dynamic models for the lines with an arbitrarily large number of states. By satisfying the decentralized condition formulated, plug-and-play operation can be achieved with guaranteed stability, and performance can also be improved by incorporating this condition as a constraint in corresponding optimization problems formulated. In addition, our control design can improve the power sharing properties of the microgrid compared to previous non-droop approaches. Finally, realistic simulations confirm that the controller design improves the stability and performance of the power network