scholarly journals An improved method for obtaining rotational accelerations from instrumented headforms

2019 ◽  
Vol 22 (3-4) ◽  
Author(s):  
Derek Nevins ◽  
Lloyd Smith ◽  
Philip Petersen
Keyword(s):  
Angular Rate ◽  
Reference Signal ◽  
Cutoff Frequency ◽  
Angular Acceleration ◽  
Absolute Error ◽  
Tuning Parameter ◽  
Total Variation Regularization ◽  
Cutoff Frequencies ◽  
The Impact ◽  
Point Stencil

Abstract The following compares the effect of differentiation methods used to acquire angular acceleration from three types of un-helmeted headform impact tests. The differentiation methods considered were the commonly used 5-point stencil method and a total variation regularization method. Both methods were used to obtain angular acceleration by differentiating angular velocity measured by three angular rate sensors (gyroscopes), and a reference angular acceleration signal was obtained from an array of nine linear accelerometers (that do not require differentiation to obtain angular acceleration). For each impact, three injury criteria that use angular acceleration as an input were calculated from the three angular acceleration signals. The effect of the differentiation methods were considered by comparing the criteria values obtained from gyroscope data to those obtained from the reference signal. Agreement with reference values was observed to be greater for the TV method when a user-defined tuning parameter was optimized for the impact test and cutoff frequency of each condition, particularly at higher cutoff frequencies. In this case, mean absolute error of the five-point stencil ranged from 1.0 (the same) to 11.4 times larger than that associated with the TV method. When a constant tuning parameter value was used across all impacts and cutoff frequencies considered in this study, the TV method still provided a significant improvement over the 5-point stencil method, achieving mean absolute errors as low as one-tenth that observed for the five-point stencil method.

Self-Acceleration in the Parameterization of Orographic Gravity Wave Drag

2010 ◽  
Vol 67 (8) ◽  
pp. 2537-2546 ◽  
Author(s):  
John F. Scinocca ◽  
Bruce R. Sutherland
Keyword(s):  
Gravity Wave ◽  
Middle Atmosphere ◽  
Wave Train ◽  
Leading Edge ◽  
Wave Theory ◽  
Wave Drag ◽  
Tuning Parameter ◽  
Mean Flow ◽  
Propagating Waves ◽  
The Impact

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.

scholarly journals Photovoltaic Power Forecasting: Assessment of the Impact of Multiple Sources of Spatio-Temporal Data on Forecast Accuracy

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1432
Author(s):  
Xwégnon Ghislain Agoua ◽  
Robin Girard ◽  
Georges Kariniotakis
Keyword(s):  
Satellite Images ◽  
Forecast Accuracy ◽  
Absolute Error ◽  
Data Sources ◽  
Test Case ◽  
Temporal Data ◽  
Multiple Sources ◽  
Forecasting Error ◽  
Spatio Temporal ◽  
The Impact

The efficient integration of photovoltaic (PV) production in energy systems is conditioned by the capacity to anticipate its variability, that is, the capacity to provide accurate forecasts. From the classical forecasting methods in the state of the art dealing with a single power plant, the focus has moved in recent years to spatio-temporal approaches, where geographically dispersed data are used as input to improve forecasts of a site for the horizons up to 6 h ahead. These spatio-temporal approaches provide different performances according to the data sources available but the question of the impact of each source on the actual forecasting performance is still not evaluated. In this paper, we propose a flexible spatio-temporal model to generate PV production forecasts for horizons up to 6 h ahead and we use this model to evaluate the effect of different spatial and temporal data sources on the accuracy of the forecasts. The sources considered are measurements from neighboring PV plants, local meteorological stations, Numerical Weather Predictions, and satellite images. The evaluation of the performance is carried out using a real-world test case featuring a high number of 136 PV plants. The forecasting error has been evaluated for each data source using the Mean Absolute Error and Root Mean Square Error. The results show that neighboring PV plants help to achieve around 10% reduction in forecasting error for the first three hours, followed by satellite images which help to gain an additional 3% all over the horizons up to 6 h ahead. The NWP data show no improvement for horizons up to 6 h but is essential for greater horizons.

Head acceleration measurement techniques: Reliability of angular rate sensor data in helmeted impact testing

2017 ◽  
Vol 232 (2) ◽  
pp. 176-181 ◽  
Author(s):  
Bryan R Cobb ◽  
Abigail M Tyson ◽  
Steven Rowson
Keyword(s):  
Root Mean Square ◽  
Angular Rate ◽  
Angular Acceleration ◽  
Impact Testing ◽  
Sensor Data ◽  
Mean Square ◽  
Head Acceleration ◽  
Angular Rate Sensor ◽  
Impact Tests ◽  
Rate Sensor

This study sought to evaluate the suitability of angular rate sensors for quantifying angular acceleration in helmeted headform impacts. A helmeted Hybrid III headform, instrumented with a 3-2-2-2 nine accelerometer array and angular rate sensors, was impacted (n = 90) at six locations and three velocities (3.1, 4.9, and 6.4 m/s). Data were low-pass filtered using Butterworth four-pole phaseless digital filters which conform to the specifications described in the Society of Automotive Engineers J211 standard on instrumentation for impact tests. Nine accelerometer array data were filtered using channel frequency class 180, which corresponds to a −3 db cutoff frequency of 300 Hz. Angular rate sensor data were filtered using channel frequency class values ranging from 5 to 1000 Hz in increments of 5 Hz, which correspond to −3 db cutoff frequencies of 8 to 1650 Hz. Root-mean-square differences in peak angular acceleration between the two instrumentation schemes were assessed for each channel frequency class value. Filtering angular rate sensor data with channel frequency class values between 120 and 205 all produced mean differences within ±5%. The minimum root-mean-square difference of 297 rad/s2 was found when the angular rate sensor data were filtered using channel frequency class 175. This filter specification resulted in a mean difference of 28 ± 297 rad/s2 (1.8% ± 8.6%). Condition-specific differences (α=0.05) were observed for 11 of 18 test conditions. A total of 4 of those 11 conditions were within ±5%, and 10 were within ±10%. Furthermore, the nine accelerometer array and angular rate sensor methods demonstrated similar levels of repeatability. These data suggest that angular rate sensor may be an appropriate alternative to the nine accelerometer array for measuring angular head acceleration in helmeted head impact tests with impactor velocities of 3.1–6.4 m/s and impact durations of approximately 10 ms.

scholarly journals PENGARUH KRIB TERHADAP KECEPATAN ALIRAN PADA SUNGAI KRUENG ACEH

2020 ◽  
Vol 3 (4) ◽  
pp. 292-301
Author(s):  
Sari Rezeki ◽  
Eldina Fatimah ◽  
Masimin Masimin
Keyword(s):  
Absolute Error ◽  
Flow Speed ◽  
The Public ◽  
Public Facilities ◽  
Speed Distribution ◽  
Surface Water Modeling ◽  
The Impact ◽  
Downstream Area ◽  
Large Discharge ◽  
System Program

Krueng Aceh River is one of the rivers that has a large discharge crossing two administrative regions, namely Banda Aceh City and Aceh Besar District. One of the problems in Krueng Aceh river, precisely around the area of Pango fly over towards the downstream area is the high flow speed distribution at the turn of the river. The impact of the bridge pillar on the river turn results in changes in the cross section of the river endangering the public facilities in front of it. Based on this analysis, it is necessary to control and secure the river, namely by placing the Groyne. The purpose of this study is to obtain a speed distribution that occurs from placing Groyne construction. The methodology used in this study with hydrodynamic numerical modeling approach is by using the Surface Water Modeling System program (SMS 11.2). Calibrating with the parameter n = 0.025 has obtained an absolute error value of 0.039 in cross 1 and 0.051 in cross 2. Based on the analysis of 20 scenarios with 7 m and 9 m distance variations, 5-unit and 3-unit Groyne variations, and the variations in perpendicular angle and 10°, 30° (degrees) towards the downstream and the upstream area, as well as the flow speed with the same number of Groyne and distance variations, the result shows that (V7 m V9 m à 5 unit) and (V7 m V9 m à 3 unit). The simulation results show that the more the number of Groyne there are, the more negative the impact on the downstream area becomes, the more narrow the Groyne, the higher the flow speed value increases. From the 20 scenarios, we obtained a Groyne scenario that is in accordance with the field conditions, namely the Groyne scenario with a distance of 7 m, 3-unit cribs, and a Groyne placement angle of 30° towards upstream area (GUb3L7). The result of the velocity distribution observation shows that the scenario of GUb3L7 Existing (without pillars)

scholarly journals Ongoing solution reproducibility of earth system models as they progress toward exascale computing

2019 ◽  
Vol 33 (5) ◽  
pp. 784-790 ◽  
Author(s):  
Salil Mahajan ◽  
Katherine J Evans ◽  
Joseph H Kennedy ◽  
Min Xu ◽  
Mathew R Norman ◽  
...  
Keyword(s):  
Model Verification ◽  
Tuning Parameter ◽  
Infrastructure Development ◽  
Earth System ◽  
Software Environment ◽  
Software Infrastructure ◽  
Software Libraries ◽  
Model Configuration ◽  
Chaotic Nature ◽  
The Impact

We present a methodology for solution reproducibility for the Energy Exascale Earth System Model during its ongoing software infrastructure development to prepare for exascale computers. The nonlinear chaotic nature of climate system simulations precludes traditional model verification approaches since machine precision differences—resulting from code refactoring, changes in software environment, and so on—grow exponentially to a different weather state. Here, we leverage the nature of climate as a statistical description of the atmosphere in order to establish model reproducibility. We evaluate the degree to which two-sample equality of distribution tests can confidently detect the change in climate from minor tuning parameter changes on model output variables in order to establish the level of difference that indicates a new climate. To apply this (baselined test), we target a section of the model’s development cycle wherein no intentional science changes have been applied to its source code. We compare an ensemble of short simulations that were conducted using a verified model configuration against a new ensemble with the same configuration but with the latest software infrastructure (Common Infrastructure for Modeling the Earth, CIME5.0), compiler versions, and software libraries. We also compare these against ensemble simulations conducted using the original version of the software infrastructure (CIME4.0) of the earlier model configuration, but with the latest compilers and software libraries, to test the impact of new compilers and libraries in isolation from additional software infrastructure. The two-sample equality of distribution tests indicates that these ensembles indeed represent the same climate.

scholarly journals Blockage Correction and Reynolds Number Dependency of an Alpine Skier: A Comparison Between Two Closed-Section Wind Tunnels

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 19
Author(s):  
Ola Elfmark ◽  
Robert Reid ◽  
Lars Morten Bardal
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Absolute Error ◽  
Reynolds Numbers ◽  
Correction Method ◽  
Wind Tunnels ◽  
Alpine Skier ◽  
Blockage Correction ◽  
Reynolds Number Dependency ◽  
The Impact

The purpose of this study was to investigate the impact of blockage effect and Reynolds Number dependency by comparing measurements of an alpine skier in standardized positions between two wind tunnels with varying blockage ratios and speed ranges. The results indicated significant blockage effects which need to be corrected for accurate comparison between tunnels, or for generalization to performance in the field. Using an optimized blockage constant, Maskell’s blockage correction method improved the mean absolute error between the two wind tunnels from 7.7% to 2.2%. At lower Reynolds Numbers (<8 × 105, or approximately 25 m/s in this case), skier drag changed significantly with Reynolds Number, indicating the importance of testing at competition specific wind speeds. However, at Reynolds Numbers above 8 × 105, skier drag remained relatively constant for the tested positions. This may be advantageous when testing athletes from high speed sports since testing at slightly lower speeds may not only be safer, but may also allow the athlete to reliably maintain difficult positions during measurements.

scholarly journals Heave Motion Measurement by Adaptive Filter Based on Longuet-Higgins Wave Model

2017 ◽  
Vol 2017 ◽  
pp. 1-8
Author(s):  
Jiazhen Lu ◽  
Qiuwei Luo ◽  
Yanqiang Yang
Keyword(s):  
Adaptive Filter ◽  
Cutoff Frequency ◽  
Wave Model ◽  
Absolute Error ◽  
Average Error ◽  
Measurement Results ◽  
Highpass Filter ◽  
Normal Method ◽  
Heave Motion ◽  
Rough Sea

A method is proposed to obtain heave motion information based on the Longuet-Higgins wave model. The Longuet-Higgins wave model which is closer to the sea wave is introduced. Based on it, random process of the noise is analyzed and the highpass filter is designed to reduce errors. Then it is the key point in this article that an adaptive algorithm is put forward because of the complexity of the waves. The algorithm adjusts the cutoff frequency to reduce the amplitude attenuation of the filter by analyzing the wave. For the same reason the comprehensive parameter of the phase compensation can be also obtained by the algorithm. Simulation measurement results show that under the rough sea situation the maximum value of absolute error is 0.4942 m according to the normal method, the method is 0.1170 m, and the average error ratio of the rough sea test reduces to 3.89% from 12.54%, which demonstrates that the adaptive filter is more effective in measuring heave movement. A variety of simulation cases show that the adaptive filter can also improve the precision of the heave motion under different sea situations.

International arrivals forecasting for Australian airports and the impact of tourism marketing expenditure

2016 ◽  
Vol 23 (2) ◽  
pp. 403-428 ◽  
Author(s):  
Wai Hong Kan Tsui ◽  
Faruk Balli
Keyword(s):  
Mean Squared Error ◽  
Absolute Error ◽  
Percentage Error ◽  
Endogenous Factors ◽  
Tourism Marketing ◽  
Passenger Demand ◽  
Volatility Models ◽  
International Tourist ◽  
The Impact ◽  
The Empirical Analysis

An airport’s international passenger arrivals are susceptible to exogenous and endogenous factors (such as economic conditions, flight services, fluctuations and shocks). Accurate and reliable airport passenger demand forecasts are imperative for policymaking and planning by airport and airline management as well as by tourism authorities and operators. This article employs the Box–Jenkins SARIMA, SARIMAX and SARIMAX/EGARCH volatility models to forecast international passenger arrivals for the eight key Australian airports (Adelaide, Brisbane, Cairns, Darwin, Gold Coast, Melbourne, Perth and Sydney). Monthly international tourist arrivals between January 2006 and September 2012 are used for the empirical analysis. All the forecasting models are highly accurate with the lower values of mean absolute percentage error, mean absolute error and root mean squared error. The findings suggest that the international passenger arrivals of Australian airports are affected by positive and negative shocks and tourism marketing expenditure is also a significant factor influencing the majority of Australian airports’ international passenger arrivals.

A COMPARISON OF SCORING METRICS FOR PREDICTING THE NEXT NAVIGATION STEP WITH MARKOV MODEL-BASED SYSTEMS

2010 ◽  
Vol 09 (04) ◽  
pp. 547-573 ◽  
Author(s):  
JOSÉ BORGES ◽  
MARK LEVENE
Keyword(s):  
Markov Model ◽  
Prediction Accuracy ◽  
Prediction Models ◽  
Markov Models ◽  
Real Data ◽  
Absolute Error ◽  
Brier Score ◽  
Data Sets ◽  
Extensive Evaluation ◽  
The Impact

The problem of predicting the next request during a user's navigation session has been extensively studied. In this context, higher-order Markov models have been widely used to model navigation sessions and to predict the next navigation step, while prediction accuracy has been mainly evaluated with the hit and miss score. We claim that this score, although useful, is not sufficient for evaluating next link prediction models with the aim of finding a sufficient order of the model, the size of a recommendation set, and assessing the impact of unexpected events on the prediction accuracy. Herein, we make use of a variable length Markov model to compare the usefulness of three alternatives to the hit and miss score: the Mean Absolute Error, the Ignorance Score, and the Brier score. We present an extensive evaluation of the methods on real data sets and a comprehensive comparison of the scoring methods.

Kinematic Analysis on Series Combined Mechanism of Elliptic Gear and Outer Geneva

2013 ◽  
Vol 312 ◽  
pp. 42-46
Author(s):  
Shao Hua Shen ◽  
Ji Fei Cai
Keyword(s):  
Kinematic Analysis ◽  
Angular Acceleration ◽  
Factors Affecting ◽  
Combined Mechanism ◽  
The Impact

With elliptic gear as the leading mechanism of Geneva mechanism, the angular acceleration was reduced to decrease the impact of the entering and quitting of geneva. Various factors affecting the angular acceleration were analyzed, and choices of appropriate parameters for the decrease of angular acceleration was discussed.

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