scholarly journals The Energy Transition’s Impact on the Accumulated Average Efficiency of Large Hydrogenerators

2021 ◽  
Author(s):  
Yannick Cyiza Karekezi ◽  
Thomas Øyvang ◽  
Jonas Kristiansen Nøland
Keyword(s):  
Load Distribution ◽  
Weighted Average ◽  
Energy Transition ◽  
Operating Efficiency ◽  
Concentrated Load ◽  
Complex Load ◽  
Economic Implications ◽  
Average Efficiency ◽  
Load Distributions ◽  
The Impact

<div><div><div><p>The energy transition is aimed to take advantage of the operational flexibility of hydropower to extend the in- tegration of intermittent renewable sources. Consequently, the hydrogenerators will have to operate in regimes far away from their designed best-point operation. In order to accurately assess the impact, this paper presents a useful approach to determine the overall operating efficiency of synchronous generators under intermittent operation. An accumulated average efficiency (AAE) model is proposed and compared against an alternative approach; the weighted average efficiency (WAE) model. It is found that the WAE approach produces unrealistic low efficiencies when the generator operates in synchronous condenser mode (SCM) for long periods. In general, the AAE supersedes the WAE for all the different load distributions that were investigated. This was further illustrated by a worked example and by constructing more complex load distributions. A load distribution dominated by SCM yields a difference as high as 33.18%, while an even distribution deviates 1.43 % in their respective efficiencies. Finally, a yearly on-site measurement of our studied 103MVA generator’s concentrated load distribution revealed a discrepancy of 0.67 %, which is a significant deviation considering what the operating regime would mean in terms of economic implications.</p></div></div></div>

scholarly journals The Energy Transition’s Impact on the Accumulated Average Efficiency of Large Hydrogenerators

2021 ◽  
Author(s):  
Yannick Cyiza Karekezi ◽  
Thomas Øyvang ◽  
Jonas Kristiansen Nøland
Keyword(s):  
Load Distribution ◽  
Weighted Average ◽  
Energy Transition ◽  
Operating Efficiency ◽  
Concentrated Load ◽  
Complex Load ◽  
Economic Implications ◽  
Average Efficiency ◽  
Load Distributions ◽  
The Impact

<div><div><div><p>The energy transition is aimed to take advantage of the operational flexibility of hydropower to extend the in- tegration of intermittent renewable sources. Consequently, the hydrogenerators will have to operate in regimes far away from their designed best-point operation. In order to accurately assess the impact, this paper presents a useful approach to determine the overall operating efficiency of synchronous generators under intermittent operation. An accumulated average efficiency (AAE) model is proposed and compared against an alternative approach; the weighted average efficiency (WAE) model. It is found that the WAE approach produces unrealistic low efficiencies when the generator operates in synchronous condenser mode (SCM) for long periods. In general, the AAE supersedes the WAE for all the different load distributions that were investigated. This was further illustrated by a worked example and by constructing more complex load distributions. A load distribution dominated by SCM yields a difference as high as 33.18%, while an even distribution deviates 1.43 % in their respective efficiencies. Finally, a yearly on-site measurement of our studied 103MVA generator’s concentrated load distribution revealed a discrepancy of 0.67 %, which is a significant deviation considering what the operating regime would mean in terms of economic implications.</p></div></div></div>

Impact of traffic demands on load distribution in congested scale-free networks

2014 ◽  
Vol 25 (10) ◽  
pp. 1450055 ◽  
Author(s):  
Hao-Ming Du ◽  
Zi-You Gao ◽  
Zhi-Hong Zhu ◽  
Jian-Feng Zheng
Keyword(s):  
Flow Pattern ◽  
Traffic Flow ◽  
Load Distribution ◽  
Link Capacity ◽  
Traffic Demand ◽  
Scale Free ◽  
Load Distributions ◽  
Congested Networks ◽  
Scale Free Networks ◽  
The Impact

Traffic demand is one of the most important factors to affect the traffic flow pattern or load distribution in congested networks. In this paper, we investigate the load distributions and relations between the load and degree of the node for different traffic demands in scale-free networks. Different kinds of load distributions are obtained under different traffic demands. Furthermore, the impact of link capacity on load distribution in congested scale-free networks is also discussed.

scholarly journals The Influence of Concentration and Temperature on the Membrane Resistance of Ion Exchange Membranes and the Levelised Cost of Hydrogen from Reverse Electrodialysis with Ammonium Bicarbonate

Membranes ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 135
Author(s):  
Yash Dharmendra Raka ◽  
Robert Bock ◽  
Håvard Karoliussen ◽  
Øivind Wilhelmsen ◽  
Odne Stokke Burheim
Keyword(s):  
Ion Exchange ◽  
Waste Heat ◽  
Ammonium Bicarbonate ◽  
Operating Efficiency ◽  
Membrane Thickness ◽  
Ion Exchange Membranes ◽  
Reverse Electrodialysis ◽  
Ohmic Resistance ◽  
Production Of Hydrogen ◽  
The Impact

The ohmic resistances of the anion and cation ion-exchange membranes (IEMs) that constitute a reverse electrodialysis system (RED) are of crucial importance for its performance. In this work, we study the influence of concentration (0.1 M, 0.5 M, 1 M and 2 M) of ammonium bicarbonate solutions on the ohmic resistances of ten commercial IEMs. We also studied the ohmic resistance at elevated temperature 313 K. Measurements have been performed with a direct two-electrode electrochemical impedance spectroscopy (EIS) method. As the ohmic resistance of the IEMs depends linearly on the membrane thickness, we measured the impedance for three different layered thicknesses, and the results were normalised. To gauge the role of the membrane resistances in the use of RED for production of hydrogen by use of waste heat, we used a thermodynamic and an economic model to study the impact of the ohmic resistance of the IEMs on hydrogen production rate, waste heat required, thermochemical conversion efficiency and the levelised cost of hydrogen. The highest performance was achieved with a stack made of FAS30 and CSO Type IEMs, producing hydrogen at 8.48× 10−7 kg mmem−2s−1 with a waste heat requirement of 344 kWh kg−1 hydrogen. This yielded an operating efficiency of 9.7% and a levelised cost of 7.80 € kgH2−1.

scholarly journals Management of Chipping Operations in Polish Forests

2020 ◽  
Vol 3 (1) ◽  
pp. 56
Author(s):  
Arkadiusz Gendek ◽  
Monika Aniszewska ◽  
Witold Zychowicz ◽  
Tadeusz Moskalik ◽  
Jan Malaťák ◽  
...  
Keyword(s):  
Fuel Consumption ◽  
Travel Distance ◽  
Operating Efficiency ◽  
Site Location ◽  
Work Shift ◽  
Work Site ◽  
The Mean ◽  
The Impact ◽  
Machine Base

The aim of the research was to verify the impact of selected parameters on the efficiency and organization of chipper operations. The paper analyzes chipping operations in Polish forests with a focus on work site location, overnight chipper location, chipper workload per site, fuel consumption, and work shift duration, as all of these factors may affect operating efficiency. The mean chipper travel distance between sites during a shift ranged from 4.74 km to 9.5 km (chippers moved on average every other day). The mean work shift duration was 12.4 h. At the end of a shift, the chippers traveled on average from 4.2 km to 6.3 km to an overnight location. At the beginning of a workday, the chippers were dispatched to sites at a distance of 2.5 km to 4.0 km. The average fuel consumption of the forwarder-mounted chippers was 16 L/h and that of the truck-mounted chipper was 7.7 L/h. It was found that the following actions have a decisive influence on the effectiveness of the operation of the chippers: determination of the size of individual tasks and the deployment of successive forest areas, indication of the proper location of the machine base, and the method of accessing the forest area.

scholarly journals Antarctic sea-ice thickness and volume estimates from ice charts between 1995 and 1998

2015 ◽  
Vol 56 (69) ◽  
pp. 383-393 ◽  
Author(s):  
E. Rachel Bernstein ◽  
Cathleen A. Geiger ◽  
Tracy L. Deliberty ◽  
Mary D. Lemcke-Stampone
Keyword(s):  
Sea Ice ◽  
Regional Scale ◽  
Weighted Average ◽  
Ice Thickness ◽  
Average Thickness ◽  
Sea Ice Thickness ◽  
Subjective Analysis ◽  
Stage Of Development ◽  
Volume Estimates ◽  
The Impact

AbstractThis work evaluates two distinct calculations of central tendency for sea-ice thickness and quantifies the impact such calculations have on ice volume for the Southern Ocean. The first calculation, area-weighted average thickness, is computed from polygonal ice features and then upscaled to regions. The second calculation, integrated thickness, is a measure of the central value of thickness categories tracked across different scales and subsequently summed to chosen regions. Both methods yield the same result from one scale to the next, but subsequent scales develop diverging solutions when distributions are strongly non-Gaussian. Data for this evaluation are sea-ice stage-of-development records from US National Ice Center ice charts from 1995 to 1998, as proxy records of ice thickness. Results show regionally integrated thickness exceeds area-weighted average thickness by as much as 60% in summer with as few as five bins in thickness distribution. Year-round, the difference between the two calculations yields volume differences consistently >10%. The largest discrepancies arise due to bimodal distributions which are common in ice charts based on current subjective-analysis protocols. We recommend that integrated distribution be used for regional-scale sea-ice thickness and volume estimates from ice charts and encourage similar testing of other large-scale thickness data archives.

scholarly journals Considerations of the Scale of Radiocarbon Offsets in the East Mediterranean, and Considering a Case for the Latest (Most Recent) Likely Date for the Santorini Eruption

Radiocarbon ◽  
2012 ◽  
Vol 54 (3-4) ◽  
pp. 449-474 ◽  
Author(s):  
Sturt W Manning ◽  
Bernd Kromer
Keyword(s):  
Time Horizon ◽  
Weighted Average ◽  
17Th Century ◽  
Data Sets ◽  
East Mediterranean ◽  
Average Value ◽  
Accuracy And Precision ◽  
Wide Range ◽  
The Impact ◽  
East Mediterranean Region

The debate over the dating of the Santorini (Thera) volcanic eruption has seen sustained efforts to criticize or challenge the radiocarbon dating of this time horizon. We consider some of the relevant areas of possible movement in the14C dating—and, in particular, any plausible mechanisms to support as late (most recent) a date as possible. First, we report and analyze data investigating the scale of apparent possible14C offsets (growing season related) in the Aegean-Anatolia-east Mediterranean region (excluding the southern Levant and especially pre-modern, pre-dam Egypt, which is a distinct case), and find no evidence for more than very small possible offsets from several cases. This topic is thus not an explanation for current differences in dating in the Aegean and at best provides only a few years of latitude. Second, we consider some aspects of the accuracy and precision of14C dating with respect to the Santorini case. While the existing data appear robust, we nonetheless speculate that examination of the frequency distribution of the14C data on short-lived samples from the volcanic destruction level at Akrotiri on Santorini (Thera) may indicate that the average value of the overall data sets is not necessarily the most appropriate14C age to use for dating this time horizon. We note the recent paper of Soter (2011), which suggests that in such a volcanic context some (small) age increment may be possible from diffuse CO2emissions (the effect is hypothetical at this stage and hasnotbeen observed in the field), and that "if short-lived samples from the same stratigraphic horizon yield a wide range of14C ages, the lower values may be the least altered by old CO2." In this context, it might be argued that a substantive “low” grouping of14C ages observable within the overall14C data sets on short-lived samples from the Thera volcanic destruction level centered about 3326–3328 BP is perhaps more representative of the contemporary atmospheric14C age (without any volcanic CO2contamination). This is a subjective argument (since, in statistical terms, the existing studies using the weighted average remain valid) that looks to support as late a date as reasonable from the14C data. The impact of employing this revised14C age is discussed. In general, a late 17th century BC date range is found (to remain) to be most likelyeven ifsuch a late-dating strategy is followed—a late 17th century BC date range is thus a robust finding from the14C evidence even allowing for various possible variation factors. However, the possibility of a mid-16th century BC date (within ∼1593–1530 cal BC) is increased when compared against previous analyses if the Santorini data are considered in isolation.

Dynamic Response of a Generic Vehicle Floor Model to Coupled Transient Loads

1996 ◽  
Author(s):  
Aaron D. Gupta
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Response Analysis ◽  
Impact Loads ◽  
Valuable Insight ◽  
Concentrated Load ◽  
Shell Elements ◽  
Transient Loads ◽  
Method Of Evaluation ◽  
The Impact

Abstract A dynamic elastic large displacement response analysis of the bottom floor of a generic vehicle hull model subjected to empirically obtained coupled blast and impact loads has been conducted using three-dimensional (3-D) shell elements in the ADINA nonlinear dynamic finite element analysis code. For the impulse-dominated problem, the impact load is a square wave step function concentrated load while the blast loads from the detonation of an explosive are a series of distributed pressure loads approximated as triangular impulse loads with linear decay and varying arrival and duration times. The 3-D numerical model has been generated using the PATRAN3 modeling code and converted to the ADINA finite element input data deck using the ADINA translator and careful inclusion of appropriate material properties as well as initial and boundary conditions. Monolithic single-layered four-noded quad shell elements were sufficient to model the bottom floor and the left- and right-horizontal and vertical sponsons as well as the lower front glacis. Although several simplifying assumptions and approximations are made during the generation of the basic floor model, material properties, and the forcing functions, the investigation gives valuable insight into the response behavior of a generic hull bottom floor to externally applied coupled blast and impact loads and provides an inexpensive nondestructive method of evaluation of the structural integrity of modern vehicles subjected to spatially varying transient loads.

Research in Different Categories of UK Universities

1997 ◽  
Vol 11 (5) ◽  
pp. 304-313
Author(s):  
W. O. George ◽  
A. N. Hill
Keyword(s):  
Weighted Average ◽  
Unit Group ◽  
Research Quality ◽  
Average Score ◽  
Social Sciences And Humanities ◽  
Peer Rating ◽  
Subject Areas ◽  
Broad Subject ◽  
The Impact

In this paper, the origins and characteristics of the 102 current UK universities are briefly traced and the outcomes of recent assessments of research quality are summarized for all universities and for the 69 subject units within which assessment was made. The quality of research in a subject unit, group of subject units or complete institution is measured by a weighted average score based on a peer rating of submitted subject units from each university and the numerical values obtained are described within the limitations of the methodology developed. The authors consider the scores in terms of the characteristics of each university and the broad subject areas, science, engineering, social sciences and humanities. They then discuss the industrial link with research in terms of recent government policy inputs, university research outcomes and the impact of market forces on universities from diminishing patterns of some income streams.

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