Mesh System Research Articles

Optimization of mesh density to design photonic crystal fiber employing finite element method

Optimization of mesh density to design photonic crystal fiber employing finite element method (Abstract: In this work, a detailed investigation of photonic crystal fiber (PCF) with different mesh systems and degrees of freedom (DoF) is studied to optimize mesh density and computational efficiency. The variation of numerical results is analysed using the finite element method (FEM). Fused silica as a cladding material was used to design the hollow core PCF and optimised for wavelength λ=1.55 μm in the FEM analysis. Triangular mesh with growth rate (G r ) up to G r =3.95 and maximum mesh element size (m L ) ranging from m L= λ to m L= 14λ is used in the FEM study. The study shows field intensity deviation as high as ~100V/m and mode purity deviation up to 0.002%. This study proves that the optimization of mesh density is very important to propose an effective PCF and electronic devices and its effect on the deviation of the numerical outcome.

Small-Signal Stability of DC Current Flow Controller Integrated Meshed Multi-Terminal HVDC System

In this paper, the small-signal stability of a DC current flow controller (CFC) integrated meshed multi-terminal HVDC (MTDC) system is investigated with unique contributions: (1) The dynamics of a multi-line CFC, interconnected voltage- source converters (VSCs) and the DC transmission lines are considered in the small-signal modelling. (2) The switching effect of the capacitive components in the π-type DC transmission lines is identified. The comparative studies of modelling the DC transmission lines using π-type/T-type equivalent circuit are conducted. (3) The impact of the CFC on the AC side of the MTDC system is taken into account with analysis of the critical short-circuit ratio (CSCR) through root-locus analysis and participation factors. The relationship of the SCR with VSC outer-loop control and power transfer is analyzed. (4) The influence of the CFC control system/structural parameters on the small-signal stability of the entire system is investigated. The relationship of the CFC integration with the VSC outer-loop control is analyzed. The adjustment of single/multiple parameters for enhancing the system stability and a sequential parameter tuning approach for multiple parameters are explained. The effectiveness of the proposed method applied in different MTDC systems with CFC is verified. It would be useful for the configuration and parametric design of the CFC integrated meshed MTDC systems.

Influencing Factors on Power Losses in Electric Distribution Network

Line losses reduction greatly affects the performance of the electric distribution network. This paper aims to identify the influencing factors causing power losses in that network. Newton-Raphson method is used for the loss assessment and the Sensitivity analysis by approach One-Factor-At-A-Time (OAT) for the influencing factors identification. Simulation with the meshed IEEE-30 bus test system is carried out under MATLAB environment. Among the 14 parameters investigated of each line, the result shows that the consumed reactive powers by loads, the bus voltages and the linear parameters are the most influencing on the power losses in several lines. Thus, in order to optimize these losses, the solution consists of the reactive power compensation by using capacitor banks; then the placement of appropriate components in the network according to the corresponding loads; and finally, the injection of other energy sources into the bus which recorded high level losses by using the hybrid system for instance.

Прогнозирование риска тяжелого течения COVID-19 у пациентов с переломами проксимального отдела бедренной кости (Обзор литературы)

Predicting the severity of COVID-19 in patients with hip fractures is of great importance, as this category of patients is particularly vulnerable and often has additional risk factors such as older age, comorbidities, and reduced mobility. Accordingly, the risk of developing a severe form of COVID-19 in such patients is higher, which can lead to an increase in mortality and complications. The aim of the current review is to find methods for predicting the severity of the course of coronavirus infection in patients with hip fractures.The review included publications on methods for predicting the course of coronovirus infection in patients with traumatological pathology. Separately, cases with fractures of the proximal femur were considered.The search strategy included the use of the MeSH system and the keywords “hip fracture”, “coronavirus infection”, OR “COVID 19” AND “proximal femur fracture”.All citations were formatted using EndNote X6 software (Clarivate Analytics, New York, USA). Restrictions on the year of publication of articles were not applied.Key words: hip fracture, coronavirus infection, COVID 19, fracture of the proximal femur.

The effect of antibacterial agents of composite resin materials in dental caries prevention and reduction of flexural strength of the material: Systematic review and meta-analysis

Background: The present study aimed to evaluate the antibacterial agents of composite resin materials, their efficacy in caries prevention, and their impact on the mechanical properties (flexural strength) of composite resin restorative materials. Methods: In this systematic review and meta-analysis, all published articles on the effects of antibacterial properties of composite resin materials in the prevention of dental caries (between 2005 to 2020) were evaluated using valid databases, including PubMed, Google Scholar, Web of Science, ISI, Scopus, Cochrane, ProQuest, and Embase, found by searching the keywords "anti-bacterial agents," "composite resins," "dental restoration," and "dental caries" according to the MeSH system. The context of the studies was extracted and subjected to modified CONSORT. The required data were extracted and analyzed with the Comprehensive Meta-Analysis software. Results: According to the results of the random effect model, the heterogeneity of biofilm colony forming unit (CFU) average was -1.90 (CI: -1.68 to -2.13). The mean value of the control group was higher than the intervention. The heterogeneity of flexural strength (FS) average was -11.92 (CI: -8.30 to -15.55). The mean value of the control group was higher than the intervention group. The heterogeneity of thiazolyl blue tetrazolium bromide (MTT) absorbance average was -0.90 (CI: -0.65 to -1.14). The mean value of the control group was higher than the intervention group. Conclusion: The results of the present study showed that the antibacterial agents had a significant effect on the caries prevention properties of the composite resin materials; however, due to the bias related to different control groups, laboratory conditions, and mismatch between in vitro and in vivo conditions, more studies are needed in this regard.

Long term surgical outcomes of vaginal colposuspension using the Uphold Lite™ mesh system vs. vaginal vault uterosacral ligament suspension for treatment of apical prolapse

ObjectiveThe aim of this study is to compare long-term outcomes (7–10 years) between vaginal hysterectomy with uterosacral ligament suspension (VHUSLS) and sacrospinous hysteropexy with the Uphold™ Lite mesh System (SHU) for management of apical prolapse. MethodsPatients undergoing VHUSLS or SHU from 2008 to 2012 at a single tertiary referral center were included. Patients were contacted, asked to return for physical examination, and to complete the Pelvic Floor Distress Inventory (PFDI-20) questionnaire. Our primary outcome was anatomic failure defined as Stage 2 POP or higher of any compartment. The secondary outcome was subjective changes in symptoms based upon PFDI-20 responses. ResultsTwo-hundred and two women were identified to have undergone the index surgeries from 2008 to 2012. Sixty-three agreed to return for follow up symptom evaluation and examination (30 VHUSLS and 33 SHU). Baseline characteristics were similar between groups. Clinical cure was high for both groups reaching 93.4 % and 94.0 % for the VHUSLS and SHU groups, respectively (p = 0.721). Anatomical success was lower with 44.7 % and 66.7 % of patients in the VHUSLS and SHU groups, respectively, meeting criteria for success (p = 0.138). There were no mesh complications among patients returning for exams. However, two patients who were contacted and were not interested in this study reported mesh complications and need for additional surgeries. Anterior vaginal wall support was noted to be significantly better supported for SHU (Ba −2.03 ± 0.75 vs −1.42 ± 0.92, p = 0.008). There were no differences between groups for overall PFDI-20 scores postoperatively. However, SHU patients reported higher rates of stress urinary incontinence compared to VHUSLS patients. ConclusionIn women with apical prolapse, VHUSLS and SHU afford similar long-term outcomes. SHU patients reported higher rates of stress urinary incontinence.

Wound closure with a mesh and liquid tissue adhesive (Dermabond Prineo) system in pediatric spine surgery: a prospective single-center cohort study incorporating parent-reported outcome measures.

Wound healing can be challenging in children undergoing spine surgery for neurological conditions due to a high risk of cerebrospinal fluid (CSF) leakage and wound infection. In adults, use of the Dermabond Prineo (DP) skin closure system, which consists of both tissue adhesive glue and a self-adhesive mesh, for wound closure of medium-length surgical incisions has been reported. The aim of this study was to investigate the efficiency and cosmetic outcome of DP for wound closure in extra- and intradural pediatric neurological spine surgery. In this prospective cohort study, 47 children underwent 50 spine procedures using DP for wound closure between 2018 and 2022 at a single institution. Patient demographic and surgical data were collected. The primary outcome was revision surgery for wound healing disorders, while secondary outcomes were infections, minor wound healing disorders, and both physician and parental satisfaction (parent-reported outcome measures [PROMs]) at last follow-up. Among 50 spinal (45 intra- and 5 extradural) interventions, 1 patient (2%) underwent revision surgery for a cutaneous CSF fistula and pseudomeningocele. Minor wound healing disorders occurred after 16 surgeries, which did not require surgical wound revision and resolved completely. No allergic reactions to DP or surgical site infections within 30 days were observed. The parents and the medical team described wound care as significantly facilitated since wound dressing changes were not needed. Three families (6.4%) encountered difficulties in wound care, and 46 (97.9%) were satisfied with DP. The cosmetic outcome based on PROMs was excellent, with a mean score of 8 (IQR 2) on a scale from 1 to 10. At long-term follow-up, a mean of 11.3 ± 10.7 months after surgery, physicians rated the cosmetic outcome on the visual analog scale (median score 9, IQR 1) and Hollander scale (median score 6, IQR 1). The outcomes were similar among the different pathologies and age groups and did not differ in patients with and without syndromic malformations. The application of DP is simple, enables good patient comfort, facilitates both professional and parental wound care, and leads to excellent cosmetic results. DP possibly aids in the reduction of postoperative CSF leakage and infections after pediatric neurological spine surgery.

Hybrid Control Scheme for VSC Presenting Both Grid-Forming and Grid-Following Capabilities

This work proposes the Hybrid Control Converter (HCC), a new kind of VSC control. This method aims to have one single converter mimic the behavior of two individual, virtual converters working in parallel (one with grid-following and the other with grid-forming control). This way, the hybrid converter can show behavioral characteristics of both kinds of converter control at the same time. Two possible applications for the HCC are presented. The first one is related to synthetic inertia capability of wind turbines. Results show that the HCC presents superior performance when compared to conventional techniques based on grid following converters, resulting in a smaller grid frequency drop during transients. The second application shows that the HCC allows for autonomous connection of multiple distinct AC systems using a meshed DC transmission system. This enables automatic frequency support and generation and load sharing between the AC grids without requiring any specific action by the system operator.

Fast Flexible Direct Power Flow for Unbalanced and Balanced Distribution Systems

The study proposes a fast flexible direct power flow solution for radial distribution systems and a fast flexible direct weakly meshed power flow solution for weakly meshed distribution systems. The algorithm is based on the direct forward sweep power flow solution, which is an updated version of the backward/forward sweep solution. The fast flexible direct power flow uses a unique conversion matrix (CM) to rapidly determine the power flow solution. The inverted conversion matrix and its slide-modified matrix are used to solve the power flow problem in a single forward sweep step, which is a novel feature of this work. To ensure the invertibility of the conversion matrix, it is constructed to have a small condition number and a determinant of minus one, and all of its eigenvalues must be equal to that of minus one. Additionally, by modifying the conversion matrix to accommodate the loop branch using the break-point idea, a new weakly meshed conversion matrix (WMCM) is generated with the same following modification as for the radial network and employed in the fast flexible direct weakly meshed power flow (FFDWMPF) solution for the weakly meshed distribution network. The usage of a single matrix in the power flow solution and advanced direct techniques decreases the number of iterations and CPU execution time when MATLAB programming is executed. Furthermore, the proposed method is flexible enough to incorporate any changes in the radial or weakly meshed distribution system just by incorporating the changes in the CM and WMCM for any radial or weakly meshed system. Moreover, the robustness of FFDPF and FFDWMPF is evaluated under various loading scenarios on balanced radial and weakly meshed distribution networks. Finally, to validate the proposed algorithm, the proposed strategy is applied to numerous balanced and unbalanced distribution systems.

Optimal Power Flow Technique for Distribution System Considering Distributed Energy Resources (DER)

Modern electric power systems consist of large-scale, highly complex interconnected systems projected to match the intense demand growth for electrical energy. This involves the decision of generation, transmission, and distribution of resources at different time horizons. They also face challenges in incorporating new forms of generation, distributed generations, which are located close to consumer centers, and new loads such as electric vehicles. Traditionally, the nonlinear Newton–Raphson optimization method is used to support operational decisions in such systems, known as Optimal Power Flow (OPF). Although OPF is one of the most practically important and well-researched sub-fields of constrained nonlinear optimization and has a rich history of research, it faces the convergence difficulties associated with all problems represented using non-linear power flow constraints. The proposal is to present an approach in a software component in cloud Application Programming Interface (API) format, with alternative modeling of the electrical optimization problem as a non-linear objective function and representing electric network constraints modeled through both current and voltage Kirchhoff linear equations. This representation overcomes the non-linearity of the OPF problem considering Distributed Energy Resources (DER). The robustness, scalability, and availability of the method are tested on the IEEE-34 bus system with several modifications to accommodate the DER testing under conditions and in radial or meshed distribution systems under different load scenarios.

Surface structure on abandoned upland blanket peatland tracks

Temporary permissions are often granted for track use on peatlands. However, even when peatland track designs attempt to minimise environmental impacts via use of mesh systems, such linear disturbances may have persistent impacts. We evaluated the surface peatland structure of five abandoned tracks (four with a mesh surface, one unsurfaced) with varying past usage frequencies, at an upland site in northern England. Simplification of the surface nanotopography was found on all tracks compared to surrounding control areas, with increased micro-erosion patterns in rutted areas, and invasive species on some treatments. The frequency of previous usage was not found to be a significant factor controlling nano-topographic loss. Edge effects and hillslope position were influential in places, but these effects were not consistent across treatments. Nano-topographic recovery was found to be inhibited when track usage commenced within a short time frame after track construction. Mesh tracks appear to create a spatial constraint leading to poor development of plants and a reduced ability to form characteristic structures which are integral to mire function.

Interval Total Transfer Capability for Mesh HVDC Systems Based on Sum of Squares and Multi-Dimensional Holomorphic Embedding Method

Total transfer capability evaluation is an effective method to analyze the backbone transmission capability among regions. To address renewable energy uncertainties, an interval total transfer capability model based on the multi-dimensional holomorphic embedding method and sum of squares relaxation technique is proposed to solve the regional total transfer capability in meshed high voltage direct current systems. First, the multi-dimensional holomorphic embedding method is used to derive the analytical expressions of regional tie lines. Second, the interval total transfer capability model can be reformulated by two bi-level optimization models. Third, sum of squares relaxation is employed to solve the two optimization problems. Numerical results on a 40-bus European Synthetic System and the Chinese meshed high voltage direct current system validate the effectiveness of the proposed model and method.

Optimal Power Dispatch of DGs in Radial and Mesh AC Grids: A Hybrid Solution Methodology between the Salps Swarm Algorithm and Successive Approximation Power Flow Method

In this paper, we address the problem of the optimal power dispatch of Distributed Generators (DGs) in Alternating Current (AC) networks, better known as the Optimal Power Flow (OPF) problem. We used, as the objective function, the minimization of power losses (Ploss) associated with energy transport, which are subject to the set of constraints that compose AC networks in an environment of distributed generation. To validate the effectiveness of the proposed methodology in solving the OPF problem in any network topology, we employed one 10-node mesh test system and three radial text systems: 10, 33, and 69 nodes. In each test system, DGs were allowed to inject 20%, 40%, and 60% of the power supplied by the slack generator in the base case. To solve the OPF problem, we used a master–slave methodology that integrates the optimization method Salps Swarm Algorithm (SSA) and the load flow technique based on the Successive Approximation (SA) method. Moreover, for comparison purposes, we employed some of the algorithms reported in the specialized literature to solve the OPF problem (the continuous genetic algorithm, the particle swarm optimization algorithm, the black hole algorithm, the antlion optimization algorithm, and the Multi-Verse Optimizer algorithm), which were selected because of their excellent results in solving such problems. The results obtained by the proposed solution methodology demonstrate its superiority and convergence capacity in terms of minimization of Ploss in both radial and mesh systems. It provided the best reduction in minimum Ploss in short processing times and showed excellent repeatability in each test system and scenario under analysis.

Considerations concerning the power loss in a gear system

The goal of the research is to assess the power losses in a gearbox with helical gears. In addition, the effects of each component of the total power loss in a gear transmission system are investigated. The study shows the important influence of the gear meshing power loss and discuss some aspects concerning the calculus formula. Also, the coefficient of friction is computed and the efficiency of the gear meshing system and the bearing rolling pair. Results are compared to a numerical results obtained by other researchers.

Investigation of waves in the strengthened net

The movements of a reinforced net are considered. Mesh systems are used in various areas of modern technology, aviation, fishing, and construction. In recent years, much attention has been drawn to the complete equations that describe the motion of a deformable thread. In accordance with the studied task, the reinforcement of the net is carried out by adding terms in the equations of motion. In the planar case, the static behavior of the structure is investigated, and equations of motion are derived that allow the study of motion. The problem of wave propagation in deformable filament systems, taking into account a significant deviation of the filament shape from the original rectilinear one, is mathematically very difficult, since the equations of motion are a system of nonlinear differential equations in partial derivatives. To solve the problem, the method of characteristics is used. As well the method of characteristics solves the problem of the propagation of unloading waves (in the case of a load, shock waves arise). Depending on the velocity distribution at the boundary, the distribution of the strain constant on the characteristics is determined. The results are constructed by numerical integration of the integrals of the characteristics found by the method. The solution using the characteristic equations shows the occurrence of traveling waves.

Dynamic Analysis of Gear Rattling of a Certain Type of Dual-Clutch Transmission

In order to accurately explore the transmission rattling phenomenon and the influence of different factors on the dynamic characteristics of the gear rattling of the dual-clutch transmission under the condition of preselected gears, this paper establishes the gear rattling dynamics model of the transmission with the 1st gear without preselection and the preselected 4th gear, respectively; The model takes into account factors such as time-varying mesh stiffness, mesh damping, nonlinear oil film force, nonlinear backlash, and the drag torque generated by the clutch in the unengaged state. In addition, the feasibility of the dynamic model was verified by the bench test. On this basis, we took the gear meshing power and system power loss as quantitative indexes to analyze the influence of the preselected gear state and different parameters on the rattle vibration of the transmission. The results show that the pre-selected gear will not have a significant effect on the gears that have been rattled in the non-pre-selected state, and the torque fluctuation of the non-power flow shaft is aggravated by the influence of the transmission power flow branch and transmission ratio at different levels, which makes the overall rattling strength increase. In order to improve the transmission efficiency of the gear, the torque fluctuation of the input end of the system should be reduced as much as possible, and a larger lubricant viscosity can be appropriately selected, the inertia of the empty gear can be properly reduced, and the tooth clearance can be relaxed for selection.

Fault Location in Power Networks Using a Sparse Set of Digital Fault Recorders

This paper presents a robust fault location method that can be used for radial or meshed power systems. It addresses several challenges encountered in previous work such as signal attenuation by power transformers, measurement errors, the impact of Inverter Based Power Sources (IBPSs), differentiating faults from other events. This is accomplished via a KMeans clustering of DFRs and using a weighted directed tree model enabling accurate fault location. The proposed algorithm is tested on both transmission and distribution systems under different fault scenarios.

Voltage Profile improvement by optimal DG allocation using atom search optimisation in radial and mesh distribution system

Recent years have seen a considerable increase in the generation of power using renewable energy sources. This paper deals with the allocation of distributed generations (DG) in radial as well as mesh distribution network (RDSm&MDSm, respectively). The allocation of DG is been done through a meta-heuristic technique known as Atom Search Optimisation. In the paper, the power loss is reduced, along with simultaneous improvement of voltage profile of the system. The proposed algorithm has been tested on IEEE 33 & 69 radial and weakly meshed system with 5 tie lines is considered for power loss minimisation using single and multiple DGs. Two power factors are considered for the simulation 0.8 lag and 0.9 pf lag. The simulation results are carried out in MATLAB.

An ANN-based protection technique for MTDC systems with multiple configurations

A unified protection technique for different configurations of Multi-Terminal high voltage Direct Current (MTDC) systems is presented in this paper. The technique is based on using positive and negative poles’ currents of one end for each line. The spectral energy of two distinct frequency bands captured from fault currents, together with the fault current initial slope, are used to supply a feed forward Artificial Neural Network (ANN) for identifying fault zone and classifying fault type. Different configurations of MTDC systems are used to train and test the proposed ANN including radial system, meshed system without Current Limiting Reactors (CLRs), and meshed system with CLRs. Different fault types, fault locations, fault inception times, and fault resistances are used to train and test the proposed ANN. The proposed algorithm showed an excellent performance in the identification of the fault zone and the classification of the fault type for various MTDC configurations. Moreover, the algorithm does not respond to non- DC fault abnormal conditions.

Numerical study of aerodynamic roles of bridge railings by immersed boundary method

The roles of railings in determining the aerodynamic characteristics of bridge girders are investigated numerically. The Direct Forcing (DF) Immersed Boundary (IB) method is utilized to model the railings while the bridge girder is modeled by body-fitted mesh system. Two benchmark tests (flow around a circular cylinder at Re = 3900 and around an equipped bridge girder at 0 ° attack angle) are designed to validate the DF-IB method. It is shown that this method has sufficient accuracy to capture representative flow structures with fewer cells and little mesh topology change. The roles of railings are investigated at several wind attack angles up to ± 12°. Results show that railings mainly affect the upper surface of the girder section and their influence is sensitive to attack angle. For negative attack angles, only downstream railings influence the flow locally. For low positive attack angles, the separated vortex is suppressed by the railings and early reattachment is observed. When the attack angle is higher, separated flows generated from the highest horizontal bar and girder corner are mixed and transferred far from the upper surface, which results in a downstream boundary layer eruption. Thus, the upstream railing affects the flow over the entire upper surface, not just locally.