E. A. Badr

Univariate modeling and forecasting of energy consumption : the case of electricity in Lebanon

In Lebanon, electric power is becoming the main energy form relied upon in all economic sectors of the country. Also, the time series of electrical energy consumption in Lebanon is unique due to intermittent power outages and increasing demand. Given these facts, it is critical to model and forecast electrical energy consumption. The aim of this study is to investigate different univariate-modeling methodologies and try, at least, a one-step ahead forecast for monthly electric energy consumption in Lebanon. Three univariate models are used, namely, the autoregressive, the autoregressive integrated moving average (ARIMA) and a novel configuration combining an AR(1) with a highpass filter. The forecasting performance of each model is assessed using different measures. The AR(1)/highpass filter model yields the best forecast for this peculiar energy data.

Backpropagation neural networks for modeling gasoline consumption

This paper presents an artificial neural network (ANN) approach to gasoline consumption (GC) forecasting in Lebanon. In order to provide the forecasted gasoline consumption, the ANN interpolates among the GC and its determinants in a training data set. In this study, four ANN models are presented and implemented on real GC data. The first model is a univariate model based on past consumption values. The second model is a multivariate model based on GC time series and price (P). The third model is also a multivariate model based on GC and car registration (CR). Finally, the fourth model combines GC, P and CR. Forecasting performance measures, such as mean square errors and mean absolute deviations, are presented for all models.

Compensation of axle-generator errors due to wheel slip and slide

Significant errors of train axle generators (tachometers) are due to wheel slip and slide. An algorithm is designed to compensate for these errors. The algorithm identifies the wheel slip and slide by examining the variation of the processed vehicle longitudinal acceleration. Whenever wheel slip/slide is identified, then the vehicle speed is adjusted if a certain condition is met. The adjustment is a simple linear interpolation between the two speed values recorded before and after wheel slip/slide detection. In addition, a speed and acceleration observer using a Kalman filter is implemented. Experimental results using three different axle encoders aboard a freight train are provided to illustrate the performance of the proposed algorithm.

Residual stress estimation in crossbores with Bauschinger effect inclusion using FEM and strain energy density

Crossbore intersections in liquid ends of positive displacement pumps (PDPs) have regions with high stress concentration. Due to the cyclic loading that occurs in most PDPs, these stress concentration points are susceptible to fatigue cracking. In order to prolong their life, the liquid ends are often overpressurized (autofrettaged), thus inducing beneficial compressive hoop stresses in these critical regions upon removal of the autofrettage pressure. This autofrettage process drives the region of high stress concentration beyond the elastic limit and well into the elastic-plastic region. Elastic-plastic stresses and strains due to loading and unloading were analyzed in crossbore geometries, with Bauschinger effect included, using 3-D finite element analysis of the liquid end. For comparison, an analytical approach was developed, based on the strain energy density criterion first proposed by Glinka. The approach was modified to include the Bauschinger effect for precise estimation of such stresses and strains. Good correlation was observed between elastic-plastic crossbore stresses and strains predicted by the analytical approach and the finite element analysis.

Evaluation of the Autofrettage Effect on Fatigue Lives of Steel Blocks with Crossbores Using a Statistical and a Strain-Based Method

A problem of fundamental and industrial interest is the effect of autofrettage on fatigue lives and the structural integrity of engineering components. The component considered is a steel block containing crossbores, a situation found in many industrial applications such as the fluid ends of positive displacement pumps. Twenty-one steel blocks containing intersecting perpendicular crossbores were autofrettaged with pressures ranging from 79 to 172 MPa. The specimens were subsequently fatigue tested on a specially designed test facility under 53 and 69-MPa pressures. Statistical procedures based on analysis of variance were used to analyze the effect of the different autofrettage pressure levels on fatigue lives of specimens. The reverse plasticity criterion was also used to investigate the fatigue enhancement limit of the autofrettage process. Results of the statistical methodology correlated with results of the reverse plasticity criterion showed the existence of an “optimal” autofrettage pressure.

An analytical procedure for estimating residual stresses in blocks containing crossbores

Intersecting bore geometries are used in a number of industrial applications such as the fluid ends of reciprocating pumps and have regions with high stress concentration. To increase the fatigue life of a fluid end, a reduction in the operating mean stress is helpful. This can be achieved with the introduction of compressive residual stresses in these critical regions by means of proof loading or autofrettage. Accurate estimation of fluid end fatigue lives necessitates accurate evaluation of the residual stresses induced by autofrettage. In this paper, finite element models were used to obtain hoop stress to pressure ratios, at the most highly stressed plane, in blocks of different sizes and bore ratios. The hoop stress to pressure ratios were used along with Neubers rule and kinematic hardening to select an autofrettage pressure and to estimate the elastoplastic residual stresses on this plane. The suggested method estimates residual stress magnitudes close to finite element solutions, and eliminates the need for a lengthy and costly elastoplastic finite element analysis.

Econometric Modeling of Gasoline Consumption: A Cointegration Analysis

Abstract This article applies econometric models to investigate determinants of gasoline consumption (GC) in postwar Lebanon (1993–1999). The impact of gasoline price (P) and car registration (CR) on gasoline consumption is investigated through three models, namely, the static, autoregressive, and partial adjustment models. Analysis results showed the statistical significance of the price, at the 10% level, in affecting gasoline consumption and the insignificance of the car registration time series. Furthermore, given that regression models may produce spurious results, if time series are non-stationary, the GC, P, and CR were tested for order of integration using the Dickey-Fuller (DF) and the augmented Dickey-Fuller (ADF) tests. Cointegration analysis, using the Johansen and the Engle and Yoo test methods, revealed the existence of a long-run relationship between all variables. Moreover, an error correction model is developed to predict short-run dynamics. Finally, statistical performance measures, such as mean square error, mean average deviation, and mean average percentage error, are presented for all models.

An Experimental Study of a Collector and Diffuser System on a Small Demonstration Wind Turbine

A diffuser-augmented wind turbine (DAWT) has been an attractive concept of wind energy extraction since the early 1970s, due to the systems ability to increase the power generated by a regular bare turbine of the same size. However, the DAWT needs to reach a minimum augmentation ratio of 4 in order to become economically feasible. This paper investigates the possible improvement of a DAWT system by adding a collector fuselage to increase its augmentation ratio. Testing using a small experimental unit shows that adding a collector increases the power augmentation of the DAWT by more than 50%, and increases the mass flow rate through the turbine by increasing the effective upstream area of the wind that enters it. Changing the angle of the incident wind on a collector- and diffuser-augmented wind turbine (CDAWT) shows that it is possible to capture the energy in the wind up to an angle of 71°. Moreover, the CDAWT can keep extracting wind energy, without any diminution of the augmentation ratio, as wind direction varies ±45° from the turbine axes, thus eliminating the requirement for a yaw mechanism. Hence, the variant wind direction has a positive effect on the augmentation ratio.

Investigation of Pressure Stress Concentration Factors for Intersecting Elliptic Bores With Circular Bores in Blocks

Stress concentration factors due to intersecting elliptic bores as well as circular bores in blocks have been thoroughly investigated by Badr [1] and Sorem et al [2]. Results of these investigations indicated that intersecting elliptic crossbores generate lower stress concentration factors than those due to intersecting circular crossbores. In this study, we investigate stress concentration factors for crossbores in blocks (cubical and rectangular) emanating from intersecting elliptic with circular holes. Comparing these results with those generated by Badr [1] for elliptic hole intersections; it was found that crossbores due to intersecting elliptic with circular bores generate higher hoop stress concentration factors. A regression analysis was also performed to determine a relationship between the stress concentration factors, the bore ratio (a2 /a1 ) and the tilt angle θ.Copyright