432 research outputs found
Why do woodpeckers resist head impact injury : a biomechanical investigation
No full textAuthor name used in this publication: Yubo Fan2011-2012 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishedC
Exploring power-performance-quality tradeoffs for exascale combustion simulation
No full textThe computational demand of high-performance computing (HPC) applications has brought major changes to the HPC system architecture. As a result, it is now possible to run simulations faster and get more accurate results. But behind this, power and energy are becoming critical concerns for HPC systems, e.g. Titan’s electric cost is about $9 million per year. Energy efficiency has become a critical challenge for the exascale research challenges, and U.S. Department of Energy’s (DOE) gives the goal to achieve exascale performance with a power budget of 20MW. Current research efforts have studied power and performance tradeoffs, and how to balance these, e.g., using DVFS to meet power constraints, which significantly impacts performance. However, scientific applications may not tolerate degradation in performance and other tradeoffs need to be explored to meet power budgets, e.g., involving the application in making energy-performance tradeoff decisions. In this research, we focus on studying the properties and exploring the performance and power/energy tradeoffs of Low-Mach-Number Combustion (LMC) application which is an Adaptive Mesh Refinement (AMR) algorithm. Our experimental evaluation provides an empirical evaluation of different application configurations that gives insights into the power-performance tradeoffs space for this LMC or AMR-based application workflows. The key contribution of this work is a better understanding of the running behavior of this AMR-based application and proposed a power-performance tradeoff for this application, which can be used to better schedule power budgets across HPC systems.M.S.Includes bibliographical referencesby Yubo Qi
Design of all digital phase-locked loop in serial link communication
Get PDFThe speed of wireline and wireless communication systems has been increasing aggressively over the past decade. Multi-GHz clocks are in demand more than ever. In particular, wireline inter-IC communications systems such as broadband Internet, multi-core CPU and system-on-chip have fueled the research on faster on-chip clock synthesizers. In addition, mobile products such as cell-phones and tablets have permeated the consumer market. Since these devices are battery-powered, it is necessary to minimize the battery consumption of the communication system circuitry inside to extend the battery life. As a result, low-power inter-IC communication design is another topic that is gaining interest.
In high speed links, clocking circuitry is vital, and phase-locked loop (PLL) is at the heart of every on-chip clocking circuit. The clocking circuitry needs to be robust, low-power and fast in order to fulfill the increasing demand for high data rate links. The performance of the input/output (I/O) communication channel needs to scale proportionally with the semiconductor fabrication technology (SFT). However, conventional analog PLLs are often incompatible from one technology node to the next and require entirely new designs. In recent years, with the increased performance of digital circuits, all digital PLL (ADPLL) has achieved speed performance similar to that of analog PLL. Since digital logic is more robust, portable, and power efficient, ADPLL is gaining traction in research.
This thesis presents the fundamentals and an in-depth analysis of the conventional analog PLL in Chapters 2 and 3. Then the discussion dives into ADPLL. Chapter 4 presents the building blocks and loop analysis of the ADPLL. Chapter 5 presents jitter sources and jitter analysis inside the ADPLL. Chapter 6 presents an ADPLL in model and transistor design. It has center frequency of 1.6GHz and operates from 1.2GHz to 2.0GHz. Chapter 7 concludes the thesis and discusses future work.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2017-05-01The student, Yubo Liu, accepted the attached license on 2015-04-15 at 11:45.The student, Yubo Liu, submitted this Thesis for approval on 2015-04-15 at 11:50.This Thesis was approved for publication on 2015-04-17 at 14:45.DSpace SAF Submission Ingestion Package generated from Vireo submission #7867 on 2015-07-22 at 14:24:42Made available in DSpace on 2015-07-22T22:45:19Z (GMT). No. of bitstreams: 2
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Application-Oriented Reliability Testing of Power Electronic Components and Converters
Get PDFPower electronics have been and will continue to be an enabling technology for energy production, storage, transmission, distribution, and consumption. Power electronic converters are usually the critical links in electrical energy systems, affecting system security, safety, energy efficiency, and cost-of-ownership. As a result, the reliability requirements for power electronic components and converter systems generally become more stringent, for example, in e-mobility, renewable energy generation, and power system applications. Testing is one of the vital reliability engineering tools to investigate failure mechanisms, identify weakest points, and demonstrate robustness margins. It contributes to reliability growth along the product development process and the likelihood of failure reduction in field operation. The required resources (i.e., testing time, sample size, and testing facility) and the relevance of the testing results to field operation are two crucial considerations in implementing a reliability test. This article introduces the emerging application-oriented testing concepts and facilities through several component-level and converter-level examples
Slow Down: New Interventionism
Get PDFReview of The New Interventionism 1991-1994: United Nations Experience in Cambodia, Former Yugoslavia and Somalia (James Mayall ed.
Research on gas drainage technology and equipment of high-level directional drilling in coal mine
No full textThe gas overrun at the upper corners of the goaf and return air lanes has been restricting the development of China's coal mining industry. To solve the problem of over-limit gas concentration at the upper corners, the fundamental reason is to reduce the gas concentration in the "fracture zone" of the coal roof . At present, the most commonly used methods such as high extraction roadway, buried pipe extraction, and high-level drilling in the "fracture zone" gas control of the goaf have the disadvantages of excessive cost and heavy workload, and the drilling trajectory of conventional drilling rigs cannot be accurately positioned problem. Therefore,it is proposed to use high-position roof directional long drilling technology to replace traditional high-drainage roadway for gas control, and analyze the influence of directional drilling diameter, position, depth and other parameters on gas drainage efficiency. Based on the analysis of four drilling cases of the directional drilling rig ZYWL-13000DS of China Coal Science and Industry Group Chongqing Research Institute Co., Ltd. at 33 (4) 13 working face of Shuangliu Coal Mine, from the perspective of construction effect,the directional drilling is a more reasonable construction level 5-8 times the mining height above the roof is appropriate; the construction diameter should be as large as possible when conditions permit;when the drilling depth is 20m deep into the fissure zone, the pumping capacity will increase greatly, and with the construction of the mining, pumping Capabilities tend to stabilize. Compared with the traditional high-drainage road control effect, the use of directional long drilling technology for gas drainage can reduce the cost by more than 70% and shorten the effective construction period by more than 75%. It is finally verified that the use of high-directional directional long drilling technology can replace the high-drainage roadway for "fracture zone" gas drainage
Research and practice of high-speed spiral composite drilling technology in complex and weak coal seams
No full textIn response to the difficult slag discharge and low hole formation rate encountered in the Wangpo Coal Mine, a study was conducted on high-speed spiral composite drilling technology. This study was integrated with the performance characteristics of the ZDY6000LR-type high-speed pit rig, resulting in the design of drill bits in three different specifications: Φ110/63.5 mm, Φ95/60.3 mm, and Φ88/50 mm. Additionally, the study optimized the three-wing drill pipe's feed speed, rotation speed, and airflow volume. The industrial field test, conducted on the 3206 working face of the Wangpo Coal Mine, resulted in the design of three drill bit combinations that exhibited high strength and stiffness. This design improvement led to enhanced hole integrity, elevated slag removal efficiency, and extended service life for both the drill pipe and bit. The high-speed spiral composite drilling technology, alongside the supporting equipment, effectively addresses the challenges of slag discharge and nozzle top drilling encountered during operations. It significantly improves the deep hole drilling rate, achieving a drilling depth of over 100 m with a success rate exceeding 70%. This technology provides vital support for the extraction of gas from coal seams within the mine. Notably, the Φ95/60.3 mm screw pipe and its corresponding drill bit demonstrated the optimal holeforming effect, with an average hole depth of 111.2 m and a hole formation rate of 90.9%. These findings offer valuable insights for drilling operations under similar conditions of complex and weak coal seams
Evaluation of rheology and strength development of alkali-activated slag with different silicates sources
No full textThis study provides a detailed investigation on the reproducibility of two groups of alkali-activated slag (AAS) mixtures, from both fresh properties and strength development perspectives. Three different commercial sodium silicate solutions and one lab-produced silicate activator (made of silica fume and sodium hydroxide) were used to prepare AAS pastes with the same nominal composition in each group. The reaction process of each AAS mixture was monitored by calorimetry and ultrasonic pulse velocity (UPV) measurements. Meanwhile, mini-slump and flow curve tests measured by rheometer were conducted in the first hour to characterize the evolution of fresh properties. The compressive and flexural strength of hardened AAS mortars were measured at different curing ages. The results revealed that AAS pastes prepared with three different sodium silicate solutions exhibited almost identical reaction kinetics, as well as the evolution of fresh properties and strength development. However, the reaction took place rather fast in AAS pastes made of silica fume. These mixtures showed worse rheology and less strength than the corresponding mixtures prepared with sodium silicate solutions. Furthermore, the present study also showed the feasibility of making the same AAS paste through different class commercial sodium silicate solutions.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen
Investigation on the potential application of MSWI bottom ash as substitute material in Portland cement concrete
No full textIt has been reported that due to the rapid urbanization and economic growth the municipal solid waste (MSW) would double in volume from 1.3 billion tons per year (in 2012) annually by the end of 2025, challenging environmental and public health management worldwide. Given that, most of the MSW incineration (MSWI) bottom ash (BA) are disposed in landfill currently, and technically and economically viable techniques for the reuse and recycling of MSWI BA is still at a premium. This issue would seriously challenge the environmental and public health management worldwide. In some European countries and the US, MSWI BA has been utilized as aggregate in pavement construction or as aggregate in concrete. Previous studies also proved the feasibility of using MSWI BA in concrete, either as aggregates or binder substitute materials. However, it is worth noticing that there are several significant drawbacks of using MSWI BA in concrete, including the potential risk of leaching due to the existence of heavy metals and harmful salts, the low reactivity due to high content of quartz and unburned organic matters, and the metallic aluminum-induced expansion. Therefore, in this study, a characterization of as-received MSWI BA was conducted at the beginning to find out the potential problems when used in concrete, namely the metallic aluminum content, low reactivity and unburned organics. A comprehensive pretreatment was performed subsequently to solve the problems. Specifically, both physical and chemical treatments were carried out to get rid of the metallic aluminum in BA. Afterwards, thermal treatment was conducted to enhance the reactivity of BA and remove the unburned organics. Pre-treated BA samples were characterized again to reveal the effectiveness of pretreatment. The results showed that both chemical and physical treatment were highly effective in removing metallic aluminum. Meanwhile, thermal treatment was proved to be a proper activation method which also removed the remaining organic matters through the high-temperature process.Subsequently, the investigations of the effects of pre-treated BA addition on compressive strength, reaction products and hydration heat development were conducted on cement paste level by varying the replacement material (BA with different treatment methods) and ratio. A proper method of pretreatment was proposed as well as an optimization of a maximum replacement level of BA in cement paste without detrimentally influence the performance of concrete paste was studied. Compared with nonreactive micronized sand (only works as filler) and pure cement, the addition of physically treated BA has a certain amount of contribution to the hydration process from the viewpoint of heat release. Results show that BA do have pozzolanic activity but is much lower than cement, and physically treated BA is suitable to be used as filler in concrete. Additionally, physically treated BA was further activated through thermal treatment according to the result of compressive strength test, which delivered the highest strength among all the treated BA under the same replacement ratio.Finally, to extend the application of MSWI BA in concrete, the mix design was made by blending treated BA with the highest compressive strength into concrete and make it suitable for structural application. The effects of treated BA addition on the workability and compressive strength of concrete were investigated. The addition of treated BA brought slight negative impact both in workability and strength due to the existence of nonreactive phases in BA (quartz and organics).Accordingly, this study proved the potential of BA with proper treatment to be used as a cement substitute material in concrete as well as promoted the understanding of the influence of BA on the hydration process, which also brings the possibility that BA could be widely reused in concrete system in future industry.Civil Engineering | Structural Engineering | Concrete Structure
Investigation on the attenuation trend of Acoustic Emission in reinforced concrete structures
No full textConsidered as an effective real-time monitoring tool, Acoustic Emission (AE) measurements is a promising technology for reinforced concrete (RC) structures. However, its application on real RC structures is still limited. Due to the lack of knowledge on the crack induced acoustic emission in large scale structures.The aim of this study is to explore the relationship between the fracture energy and the energy of AE signals at structural level. This serves as a basis for the quantification and localization of cracking activities at structural level.This study is based on the AE and crack propagation measurement of a series of large scale RC specimen tests. To avoid the influence of existing cracks, the first part of study focuses on the development of the first flexural crack. It was assumed that the amount of energy required for unit length of crack opening is linearly proportional to the energy of the AE signals that are generated upon the opening of this segment of the crack. These signals can only be monitored AE sensors at given locations. By then, they have travelled through the bulk concrete and possibly already existing cracks, thus their energy has attenuated due to the geometric spreading and the damping property of the material. When these effects are taken into account, the total energy of the AE signals that were obtained by the AE sensors at given location (defined as cumulative signal strength CSS) has a potential of reflecting the fracture energy of the corresponding crack. In the part of the study, this process is theoretically studied first. The theoretical result was further validated by the AE measurement obtained from experiments. Theoretical investigation is carried out based on a simplified model considering only length of the crack and the horizontal distance between crack and AE sensor. Theoretical result shows that both crack length and horizontal distance would affect CSS. However, when the horizontal distance is big enough, crack length is no longer the dominant factor, and CSS drops significantly with the increase of horizontal distance. The CSS of different sensors in a row in the experiments are used to validate this attenuation phenomenon. Exponential curve fitting is carried out to describe the attenuation of experimental results in different tests. Finally, a comparison of attenuation in percentage terms between curve fitting results and theoretical results is carried out. In the uncracked specimens, the results fit each other well. Furthermore, the effect of the existing cracks to the attenuation of the CSS is studied as well. In that case, a dramatic drop of CSS is observed compared to the uncracked structures.The study shows CSS detected by AE sensors could partly indicate the cracking behavior of RC structures. The attenuation tendency gives a guidance for sensor installation in future tests.Additional thesi
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