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    A multiseries stochastic model for synthetic monthly flows
    (Taylor & Francis Ltd, 2022) HaktanIr, Tefaruk; Kara, Meltem Bircan; Acanal, Nese
    A new multiseries stochastic model is developed that takes n-year-long monthly stream flows observed at as many as 20 stations in a group and computes N-year-long synthetic monthly flows for up to 10 000 years. Initially, any series that exhibit trends with a 99% confidence level are detrended. The monthly flows of each observed series are transformed to standard-normal variates, and a variate is related to those of the other series of the same month, those of the previous month of all series, the lag-one moving-average component, and the random component. 2 M parameters of each series are iteratively computed by the least squares method, such that the variance of the random component determined using the observed variates and those computed by the model equals the variance given by the model. The model was applied to five groups in Anatolia. The relevant peculiarities of the observed and synthetic flows were in harmony.
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    Öğe
    A study on three different hydropower operation rules by monthly and daily time steps
    (Ice Publishing, 2021) HaktanIr, Tefaruk; Aydemir, Alper; Acanal, Nese
    Operation simulation models are developed for monthly and daily time steps for computing the hydroelectric energy and its financial benefits in an economic life by three different operation policies: steady-rate, three-shift and pumped-storage rules. The pump is operated during the night and consumes low-cost energy. The resulting computer programs, three on monthly and three on daily steps, are applied to the Yamula dam - which is a fairly large dam generating energy, located in the Inland Anatolia region of Turkey - over a period of 35 years using the gauged daily stream flows and daily pan evaporations. The results indicate that the pumped storage is more profitable than the other two rules aside from the intangible benefits of regulating the within-day fluctuations of demand for electrical energy. Another result is that both the average annual energy and the financial benefits given by the three rules computed by the monthly time steps are about 1-2% greater than those given by the daily time steps. This study is the first one comparing all these three operation schemes quantitatively in a realistic way both in monthly and daily time steps.
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    Öğe
    Computation of Maximum-Likelihood Parameters of the Generalized Logistic Distribution by Three-Step Newton-Raphson Algorithm
    (Springer, 2022) Acanal, Nese; HaktanIr, Tefaruk
    The skewness coefficient (G) of the generalized logistic (GLO) distribution is a function of its shape parameter (a) only. Both the methods of probability-weighted moments and maximum-likelihood (ML) mostly yield magnitudes for the shape parameter much different from that by the method of moments, the gap narrowing with increasing length of the sample series. The computation of ML parameters by the conventional Newton-Raphson method is problematic with no solution for a nonnegligible number of sample series. Here, the three-step Newton-Raphson algorithm, which was previously proposed for the generalized extreme values distribution, is adapted to the GLO distribution, and on many recorded annual flood peaks and annual maximum rainfalls series and through a comprehensive Monte-Carlo experiment it is shown to improve the rate of convergent solutions considerably.
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    Öğe
    Versions of the drainage area ratio method for transfer of daily or monthly stream flows
    (Emerald Group Publishing Ltd, 2023) HaktanIr, Tefaruk; Aydemir, Alper; Acanal, Nese
    By the drainage-area ratio method, the daily or monthly flows gauged at a nearby station are transferred to an ungauged section where a dam is to be built by multiplying them by the real number resulting from raising the ratio of the drainage areas of the dam section and of the station to an exponent (n). Commonly n is taken as 1. First, using the daily flows of two stations nearby the dam section on the same stream or on a neighboring stream, having a common N-year long gauging record, it is proposed that 365 linear regressions be fitted to N pairs of 365 daily flows, and relating them to the drainage area ratios, daily flows at the dam section be computed using 365 n's each belonging to a day. Next, by the same analytical model applied to the monthly flows, 12 monthly flows are transferred to the dam section. Five versions of the drainage-area ratio method, three of which with constant exponents, are investigated, and the last one with n = 1 is found to be relatively the worst.