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RISS 인기검색어
- 검색키워드
- 저자 : Alireza Vahidi (검색결과 6 건)
- 무료
- 기관 내 무료
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EQUIDIMENSIONAL LOCAL RINGS WITH FINITE COUSIN COHOMOLOGY MODULES
Vahidi, Alireza Korean Mathematical Society 2018 대한수학회논문집 Vol.33 No.4
It is shown that any equidimensional local ring which has finite Cousin cohomology modules with respect to the dimension filtration has a uniform local cohomological annihilator and is universally catenary.
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Injective dimensions of local cohomology modules
Alireza Vahidi 대한수학회 2017 대한수학회보 Vol.54 No.4
Assume that $R$ is a commutative Noetherian ring with non-zero identity, $\mathfrak{a}$ is an ideal of $R$, $X$ is an $R$--module, and $t$ is a non-negative integer. In this paper, we present upper bounds for the injective dimension of $X$ in terms of the injective dimensions of its local cohomology modules and an upper bound for the injective dimension of $\H_\mathfrak{a}^t(X)$ in terms of the injective dimensions of the modules $\H_\mathfrak{a}^i(X)$, $i\not= t$, and that of $X$. As a consequence, we observe that $R$ is Gorenstein whenever $\H^{i}_\mathfrak{a}(R)$ is of finite injective dimension for all $i$.
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INJECTIVE DIMENSIONS OF LOCAL COHOMOLOGY MODULES
Vahidi, Alireza Korean Mathematical Society 2017 대한수학회보 Vol.54 No.4
Assume that R is a commutative Noetherian ring with non-zero identity, a is an ideal of R, X is an R-module, and t is a non-negative integer. In this paper, we present upper bounds for the injective dimension of X in terms of the injective dimensions of its local cohomology modules and an upper bound for the injective dimension of $H^t_{\alpha}(X)$ in terms of the injective dimensions of the modules $H^i_{\alpha}(X)$, $i{\neq}t$, and that of X. As a consequence, we observe that R is Gorenstein whenever $H^t_{\alpha}(R)$ is of finite injective dimension for all i.
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Enhancement of Power System Dynamic Stability by Designing a New Model of the Power System
Alireza Fereidouni,Behrooz Vahidi 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.2
Low frequency oscillations (LFOs) are load angle oscillations that have a frequency between 0.1-2.0 Hz. Power system stabilizers (PSSs) are very effective controllers in improvement of the damping of LFOs. PSSs are designed by linearized models of the power system. This paper presents a new model of the power system that has the advantages of the Single Machine Infinite Bus (SMIB) system and the multi machine power system. This model is named a single machine normalbus (SMNB). The equations that describe the proposed model have been linearized and a lead PSS has been designed. Then, particle swarm optimization technique (PSO) is employed to search for optimum PSS parameters. To analysis performance of PSS that has been designed based on the proposed model, a few tests have been implemented. The results show that designed PSS has an excellent capability in enhancing extremely the dynamic stability of power systems and also maintain coordination between PSSs.
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Enhancement of Power System Dynamic Stability by Designing a New Model of the Power System
Fereidouni, Alireza,Vahidi, Behrooz The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.2
Low frequency oscillations (LFOs) are load angle oscillations that have a frequency between 0.1-2.0 Hz. Power system stabilizers (PSSs) are very effective controllers in improvement of the damping of LFOs. PSSs are designed by linearized models of the power system. This paper presents a new model of the power system that has the advantages of the Single Machine Infinite Bus (SMIB) system and the multi machine power system. This model is named a single machine normal-bus (SMNB). The equations that describe the proposed model have been linearized and a lead PSS has been designed. Then, particle swarm optimization technique (PSO) is employed to search for optimum PSS parameters. To analysis performance of PSS that has been designed based on the proposed model, a few tests have been implemented. The results show that designed PSS has an excellent capability in enhancing extremely the dynamic stability of power systems and also maintain coordination between PSSs.
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Evolutionary-base finite element model updating and damage detection using modal testing results
Mehdi Vahidi,Shahram Vahdani,Aicha Remil,Nima Jamshidi,Alireza Taghavee Kanee 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.3
This research focuses on finite element model updating and damage assessment of structures at element level based on global nondestructive test results. For this purpose, an optimization system is generated to minimize the structural dynamic parameters discrepancies between numerical and experimental models. Objective functions are selected based on the square of Euclidean norm error of vibration frequencies and modal assurance criterion of mode shapes. In order to update the finite element model and detect local damages within the structural members, modern optimization techniques is implemented according to the evolutionary algorithms to meet the global optimized solution. Using a simulated numerical example, application of genetic algorithm (GA), particle swarm (PSO) and artificial bee colony (ABC) algorithms are investigated in FE model updating and damage detection problems to consider their accuracy and convergence characteristics. Then, a hybrid multi stage optimization method is presented merging advantages of PSO and ABC methods in finding damage location and extent. The efficiency of the methods have been examined using two simulated numerical examples, a laboratory dynamic test and a high-rise building field ambient vibration test results. The implemented evolutionary updating methods show successful results in accuracy and speed considering the incomplete and noisy experimental measured data.
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