Development of a Relationship for Air Vent Discharge in Bottom Outlets Using Numerical Simulation

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Application Of Water Cycle Algorithm For Optimal Cost Design Of Water Distribution Systems

Water distribution system (WDS) design is considered as a class of large combinatorial non-linear optimization problems having complex implicit constraints such as conservation of mass and energy equations. Due to the complexity and large feasible solution, traditional optimization techniques are not capable to tackle these kinds of problems. Recently, applications of metaheuristic algorithms, due to their efficiencies and performances, are increased dramatically. In this paper, water cycle algorithm (WCA), a recently developed population-based algorithm, coupled with hydraulic simulator, EPANET, are applied for finding the optimal cost design of WDS. The performance of the WCA is shown using well-known Balerma benchmark problem widely used in the literature. The obtained optimization results using the WCA are compared with other optimizers such as genetic algorithm, simulated annealing, and harmony search. Comparisons of obtained statistical results show the superiority of the WCA over other optimization methods in terms of convergence rate and solution quality

Flexible HVDC transmission systems small signal modelling: a case study on CIGRE Test MT-HVDC grid

Future Flexible HVDC Transmission Systems will consist of several active and passive infrastructures including DC Power Flow Controller (DC-PFC) device. The addition of the DC-PFC to the future Multi-Terminal HVDC (MT-HVDC) grids arises some key concerns such as stability, system interoperability, and possible adverse interactions. Hence, a suitable model is necessary to conduct deep frequency domain analysis. In this context, this paper proposes a linearized model for small-signal stability analysis of flexible MT-HVDC grids in state space framework that can be straightforwardly utilized in the process of control design. In this paper, a spick-and-span, systematic and step-by-step process to derive the small signal model of all flexible MT-HVDC grid components is presented such that each sub-system is modeled individually and then all are integrated together. The derived model is cross-verified by time domain simulations of a nonlinear system model in a MATLAB/SIMULINK platform for CIGRE DCS3 MT-HVDC test grid.Peer ReviewedPostprint (author's final draft

Analysis on impacts of the shunt conductances in multi-terminal HVDC grids optimal power-flow

This study deals with impacts of the shunt conductances associated with HVDC cables and VSC-HVDC stations on optimal operation of Multi-Terminal HVDC (MT-HVDC). In this study, for the first time, shunt conductances are integrated to HVDC Optimal Power-Flow (OPF) program that is executed at the Power Dispatch Center (PDC) of the MT-HVDC grid. With the objective of losses minimization, optimal reference operation points of the VSC-HVDC stations are derived. The operating points of the power converter stations are adjusted based on the calculations performed in the dispatch center. CIGRE DCS3 MT-HVDC grid, structured by CIGRE B4 working group, is taken as the test platform. Test results have revealed the optimum voltages and loss pattern change. Moreover, the findings are compared with the case of neglecting the shunt conductances.Peer ReviewedPostprint (author's final draft

Adaptation of VSC-HVDC Connected DFIG Based Offshore Wind Farm to Grid Codes: A Comparative Analysis

Lack of synchronism between VSC-HVDC (Voltage Source Converter - High Voltage Direct Current) connected offshore wind farm and onshore grid leads to immunity of wind turbines to grid contingencies. Focusing on DFIG (Doubly Fed Induction Generator) based wind farms; this paper has presented a univalent control structure based on inertial and primary frequency response in which DC link voltage is utilized as synchronization interface. Based on the presented structure, four approaches based on the communication system, frequency, voltage and combined frequency and voltage modulation are utilized and compared to inform the onshore grid status to individual wind turbines. Considering Kondurs two area power system, results have revealed that all four approaches have similar ability (with negligible error) in offering inertial and primary frequency response to improve slow network oscillations. On the other hand, voltage and combined frequency and voltage modulation approaches have the ability to satisfy Fault Ride Through (FRT) requirements thanks to superior dynamics. However, communication and frequency modulation approaches lose that ability as communication and frequency measurement delays increase respectively. It has been concluded that combined frequency and voltage modulation, as the superior approach, has advantages like minimum FRT DC voltage profile increase and deviation from operating point after the fault, the minimum imposition of electrical and mechanical stress on DFIG and preservation of prevalent control structure thanks to appropriate dissociation between slow and fast dynamics. ©2019. CBIORE-IJRED. All rights reserved Article History: Received Dec 8th 2017; Received in revised form July 16th 2018; Accepted December 15th 2018; Available online How to Cite This Article: Yazdi, S.S.H., Milimonfared, J. and Fathi, S.H. (2019). Adaptation of VSC-HVDC Connected DFIG Based Offshore Wind Farm to Grid Codes: A Comparative Analysis. Int. Journal of Renewable Energy Development, 8(1), 91-101. https://doi.org/10.14710/ijred.8.1.91-10

Impaired local dynamic stability during treadmill walking predicts future falls in patients with multiple sclerosis:A prospective cohort study

Background: Falling is a significant problem in patients with multiple sclerosis (MS) and the majority of falls occur during dynamic activities. Recently, there have been evidences focusing on falls and local stability of walking based on dynamic system theory in the elderly as well as patients with cerebral concussion. However, in patient with MS, this relationship has not been fully investigated. The aim of this study was to investigate local stability of walking as a risk factor for falling in patients with MS. Methods: Seventy patients were assessed while walking at their preferred speed on a treadmill under single and dual task conditions. A cognitive task (backward counting) was used to assess the importance of dual tasking to fall risk. Trunk kinematics were collected using a cluster marker over the level of T7 and a 7-camera motion capture system. To quantify local stability of walking, maximal finite-time Lyapunov exponent was calculated from a 12-dimensional state space reconstruction based on 3-dimensional trunk linear and angular velocity time series. Participants were classified as fallers (≥1) and non-fallers based on their prospective fall occurrence. Findings: 30 (43%) participants recorded ≥1 falls and were classified as fallers. The results of multiple logistic regression analysis revealed that short-term local dynamic stability in the single task condition (P < 0.05, odds ratio = 2.214 (1.037–4.726)) was the significant fall predictor. Interpretation: The results may indicate that the assessment of local stability of walking can identify patients who would benefit from gait retraining and fall prevention programs

The Role of Religious Attitude in Coping with Psychological Distress and Emotion Regulation Difficulties of UT Students

For downloading the full-text of this article please click here.Background and Objective: There is strong evidence to suggest that psychological distress and emotion regulation problems have adverse effects on life. Given that, finding the underlying processes seems important. Besides, since religion is a determining factor in emotion regulation and mental health, this study aimed to investigate the role of religious attitude in emotion regulation difficulties and distress. (Depression, Anxiety, stress).Method: This descriptive-correlational study used multistage cluster sampling from all students at University of Tehran in academic year of 94-95. 211 students (120 female and 91 male) were selected. They were asked to complete Religious Attitude Scale-Short Form (RAS-R), difficulties in emotion regulation questionnaire (Difficulties in Emotion Regulation Scale or DERS-16) and Depression, Anxiety, Stress Scale (DASS-21). Then, the data were analyzed with using Pearson correlation coefficient and multiple regression analysis. In this study, the ethical issues were all considered and the authors declared no conflict of interest.Results: The results show that religious attitudes negatively affect depression, anxiety and stress. Also, anxiety has negative relationships with inner spirituality, worship and religious morality. Besides, morality had predictive power for anxiety. Moreover, among the four dimensions of distress, only anxiety negatively correlated with religious attitude (morality, inner spirituality and worship) and morality had predictive power for anxiety. Furthermore, the results indicated that morality had predictive power for difficulties in emotion regulation (limited access in emotion regulation, impulse control) and the inner spirituality had predictive power for non-acceptance of emotion.Conclusion: It can be concluded that different aspects of religious attitude can both directly and indirectly play important roles in anxiety and difficulties in emotion regulation. Therefore, paying attention to religious attitude in pathology and treatment protocols of anxiety disorders is necessary.For downloading the full-text of this article please click here

Comparison of Muscle Recruitment Patterns During Sit-to-Stand and Stand-to-Sit in “Movement System Impairment” Subgroups of Low Back Pain and Healthy Women

Background: While various studies have examined motor control differences between subjects with and without low back pain (LBP), only a few have investigated the muscle recruitment pattern in classified LBP patients during functional activity. The aim of this study was to investigate the firing pattern of the main muscles involved in sit-to-stand (STD) and stand-to-sit (STS) tasks in two prevalent LBP subgroups based on movement system impairment (MSI) classification. Methods: A total of 37 women between 18 and 50 years of age voluntarily participated in this cross-sectional study. They were divided into three groups (15 healthy, 15 lumbar extension rotation syndrome (LERS), and seven lumbar flexion rotation syndrome (LFRS)). Surface electromyography was recorded bilaterally from the trunk stabilizer muscles—i.e. the internal oblique (IO), lumbar erector spine (ES), and hip mobilizer muscles—and the medial (MH) and lateral (LH) hamstring muscles during STD and STS tasks. The variations in EMG onset muscle timing and asymmetry in side-to-side muscle timing were measured. Results: The firing sequence during the STD task showed no significant difference among groups. However, in the healthy and LFR groups the trunk stabilizer muscles were activated before the hip mobilizer muscles, and in the LERS group an insignificant delay was shown in the onset of the ES activity. There was no significant difference of bilateral muscle timing during STD. In the STS task no consistent order of pattern was found even in the healthy group. The bilateral muscle timing of IO (mean difference, -427.00; P=0.021) and ES (mean difference, 1964.57; P=0.000) had significant difference in the LFRS group during STS. Conclusion: The cumulative effects of recruitment pattern impairment may contribute to continuing the cycle of lumbar movement impairments and subsequent persistence of LBP

Predicting falls among patients with multiple sclerosis:Comparison of patient-reported outcomes and performance-based measures of lower extremity functions

Background Accurate fall screening tools are needed to identify those multiple sclerosis (MS) patients at high risk of falling. The present study aimed at determining the validity of a series of performance-based measures (PBMs) of lower extremity functions and patient-reported outcomes (PROs) in predicting falls in a sample of MS patients (n = 84), who were ambulatory independent. Methods Patients were assessed using the following PBMs: timed up and go (TUG), timed 25-foot walk (T25FW), cognitive T25FW, 2-min walk (2MW), and cognitive 2MW. Moreover, a series of valid and reliable PROs were filled in by participants including the activities-specific balance confidence (ABC), 12-item multiple sclerosis walking scale (MSWS-12), fall efficacy scale international (FES-I), and modified fatigue impact scale (MFIS). The dual task cost (DTC) of 2MW and T25FW tests were calculated as a percentage of change in parameters from single to dual task conditions. Participants were classified as none-fallers and fallers (⩾1) based on their prospective fall occurrence. Results In the present study, 41(49%) participants recorded ≥ 1 fall and were classified as fallers. The results of logistic regression analysis revealed that each individual test, except DTC of 2MW and T25FW, significantly predicted future falls. However, considering the area under the curves (AUCs), PROs were more accurate compared to PBMs. In addition, the results of multiple logistic regression with the first two factors extracted from principal component analysis revealed that both factor 1 (PROs) and factor 2 (PBMs) significantly predicted falls with a greater odds ratio (OR) for factor 1 (factor 1: P = <0.0001, OR = 63.41 (6.72–597.90)) than factor 2 (P <0.05, OR = 5.03 (1.33–18.99)). Conclusions The results of this study can be used by clinicians to identify and monitor potential fallers in MS patients