Mismatch Equations Research Articles

Relationship between Learning Environment Design and Musculoskeletal Disorders in Learners

Introduction: Students spend most of their day at school sitting in their classroom furniture which is not quite the right size for students. This can be uncomfortable and even lead to back pain, leg cramps, and other problems. Method: Students’ body size for good posture while sitting, include popliteal to floor height, elbow to seat height, thigh thickness, sitting height, buttock to popliteal length, buttock to knee length, elbow to elbow breadth, the width of bitrochanter, subscapular height, and sitting shoulder height, and one standing is stature. Similarly, dimensions of chair-with-table, like seat height, the upper edge of the backrest, seat width, seat depth, table length, table width, table height, backrest height, and footrest currently used in the classroom were taken. The study compared students' anthropometry data with the furniture dimension data to obtain a match or mismatch between them with the help of standard mismatch equations. Results: The study reported that the mean body measurements of males are larger than females except for the width of bitrochanter. Seat width, seat depth, backrest height, and the upper edge of the backrest showed high mismatch percentages in students when patronising chairs. Table length reported high mismatch percentages among students. Conclusion: Using the users’ body sizes for furniture design will reduce musculoskeletal disorders and improve users’ sitting position. The recommended dimensions in furniture design will ergonomically fit students’ anthropometric measurements.

A generic power flow formulation for flexible modeling and fast solving for large-scale unbalanced networks

This paper proposes a new three-phase power flow formulation for fast solving and systematic modeling based on generic formulation and modular approach. In this method, each component of the system is modeled independently as a subsystem while extra-equations are added to establish the connection between components. The augmented system equations are solved using Newton-like method and KLU sparse matrix solver. The mismatch equations are formulated with dynamic parameters to avoid the repetitive symbolic factorizations required after each change in nonzero pattern of the Jacobian matrix. Compared to conventional solution methods, the proposed solution is faster and offers greater modeling flexibility, which makes it more efficient for simulating complex and large-scale networks. The IEEE standard 34-bus and 8500-bus are used as test systems to evaluate the numerical performance, the convergence characteristics, and the accuracy of the results. The comparison with the traditional power flow methods shows significant reduction of resolution time without compromising on solution accuracy.

Unified load flow calculation for flexible interconnected AC-MTDC distribution system considering control strategy switching with high penetration of DGs

A new unified algorithm is proposed in this paper to solve the power flow problem of AC distribution systems incorporating voltage-sourced converter (VSC) based multi-terminal direct current (MTDC) grids. In this method, the VSC modulation indices, mode changes, power losses as well as MTDC control strategy switching are all considered. Active power mismatch equations of VSC boundary buses in AC side have been modified to eliminate VSC power injection items. Various VSC control strategies are demonstrated in both active power function of DC boundary buses and reactive power function of AC boundary buses. In this way, only few modifications are required for existing AC load flow to incorporate the MTDC models. Moreover, the change of VSC operation mode and the switch of MTDC control strategies can be easily realized. The power flow calculation of AC and DC subgrids is solved simultaneously by Newton-Raphson (NR) method using a modified Jacobian matrix. Two case studies have been presented to demonstrate that the proposed algorithm is fast, flexible and effective in solving power flow of AC-MTDC distribution systems with various control strategies and can easily accommodate any changes in VSC control modes with high convergence performance.

Application of mismatch equations in dynamic seating designs

Anthropometry is critical for product and workplace design. Highly prevalent, office work is associated with sedentarism and physical discomfort due to prolonged sitting. Dynamic seating (alternating across sitting, perching, and standing) has been suggested as an alternative to overcome those problems. The current study tested a large sample of anthropometric data for mismatch levels against national and international office furniture standards using dynamic seating as a framework with traditional and perching mismatch equations, applied to three recommended dynamic seating components. Dimensions present in the standards used did not match the majority of the sample. For sitting, seat width and depth individually presented the lowest levels of match, as well as under cumulative fit of all office furniture dimensions. However, these were alleviated when incorporating adjustability. Perching was shown to be generally impeded given commercially-available chair height options. Limitations in state-of-the-art perching equations are discussed, and two new models are proposed as design alternatives. Further research should focus on testing the criteria presented in this research through discomfort and objective measures.

Developing a Multi-Criteria Decision Making approach to compare types of classroom furniture considering mismatches for anthropometric measures of university students.

The mismatch between students' anthropometric measures and school furniture dimensions have been investigated in many countries. In Iran, collegians spend at least a quarter of the day hours at university in the sitting position, so it is essential to evaluate furniture mismatch among university students. In Iranian universities, the use of chairs with an attached table is widespread, while the study of mismatches in these chairs among the collegian community is rare. This study was aimed to compare and rank different classroom furniture types based on the mismatch between collegians' anthropometric measures and the dimensions of classroom furniture among Industrial Engineering students by developing a Multi-Criteria Decision Making approach in an integrated Methodology. The sample consisted of 111 participants (71 males, 40 females). Ten anthropometric measures were gathered, together with eight furniture dimensions for four types of chairs. Mismatch analyses were carried out using mismatch equations, and the Simple Additive Weighting method was used as a base method to solve the decision-making problem. The results indicated that Underneath Desk Height and Seat to Desk Clearance showed the highest levels of the match, while Seat Width presents the highest levels of low mismatch. According to the results, Type 1 and Type 3 were the best current classroom furniture. The Sensitivity Analysis was performed in two ways: changing the weights of criteria in nine scenarios and comparing the results with five other MCDM methods. The proposed MCDM approach can be used widely in furniture procurement processes and educational environments.

Power Flow Calculation Methods for Power Systems with Novel Structure UPFC

Latest unified power flow controller (UPFC) projects adopt novel device structures to meet the requirements of practical applications. Developing power flow calculation methods for these new UPFC structures is of great significance for the design and operation of related projects. To address this issue, this paper deduces an equivalent model of the general structure UPFC, and presents the modified power mismatch equations and Jacobian matrix of the system. Then, three power flow calculation methods suitable for the novel structure UPFC are proposed based on the Newton–Raphson algorithm. The main difference between the three methods is the processing method of UPFC equivalent power injections and the Jacobian matrix. The characteristics of these methods are compared by case studies. Results demonstrate the effectiveness of the three methods for different UPFC structures, and it is found that the improved method, which considers the impact of the Jacobian matrix modifications in UPFC equivalent power injections, can realize power flow calculation in existing calculation programs, and improve the convergence characteristics.

A New and Efficient Nonlinear Solver for Load Flow Problems

Load Flow (LF) analysis is a fundamental and significant issue in electric power systems. Because of the nonlinearity of the power mismatch equations, the accuracy of the nonlinear solvers is important. In this study, a novel and efficient nonlinear solver is proposed with active applications to LF problems. The formulation of the Proposed Method (PM) and its workflow and mathematical modeling for its application in LF problems have been discussed. The performance of the PM has been validated on the IEEE 14-bus and 30-bus test systems against several existing methods. The simulation results show that the PM exhibits higher order accuracy, faster convergence characteristics, smaller number of iterations, and lesser computation times in comparison with the other benchmark methods.

Data-Driven Design Solution of a Mismatch Problem between the Specifications of the Multi-Function Console in a Jangbogo Class Submarine and the Anthropometric Dimensions of South Koreans Users

The naval multi-function console provides various types of information to the operator. It is equipment that is key for submarine navigation, and fatal human errors can occur due to the mismatch between the console specifications and the operator’s body size. This study proposes a method for deriving console specifications suitable for the body size of Korean users. The seat height, seat width, seat depth, upper edge of backrest, and worktable height were selected as the target design variables. Using six anthropometric dimensions, a mismatch equation for each target design variable was developed. Anthropometric measures of 2027 Korean males were obtained, and the optimal specifications of the console were derived via an algorithmic approach. As a result, the match rate, considering all the target design variables, was improved from 2.57% to 76.96%. In previous studies and standards, the optimal console specifications were suggested based on the anthropometric data of a specific percentile of users, and it was impossible to quantitatively confirm the suitability of the console design for the target users. However, the method used in this study calculated the match rate using the mismatch equation devised for comfortable use of the console and a large amount of anthropometric data that represented the user population, and therefore the improvement effect of the recommended specification can be directly identified when compared to the current specifications. Moreover, the methodology and results of this study could be used for deciding the specifications of multi-function consoles in several fields, including nuclear power plants or disaster situation rooms.

Steady State Energy Flow Analysis for Energy Internet Planning

The planning and design of energy Internet is an important work. The basis of this work is energy flow analysis of the design network. In this paper, the energy flow analysis model of typical gas-electricity interconnection system is established. The mismatch equations and iterative algorithm for energy flow solution are given. The effectiveness of the algorithm is verified by a typical gas-electric interconnection example.

Power flow modelling to UHVDC line and its hierarchical connection mode

At one converter station, compared with the high-voltage direct current (HVDC) line, the conversion units of the ultra HVDC (UHVDC) line are doubled and controlled independently, possibly yielding the unbalanced operation modes, separate settings to the DC variables of the positive and negative poles, and different equivalent powers and mismatch equations (MEs). Under the hierarchical connection mode (HCM), the inverters connect two AC voltages. Hence, the operation modes are not the same as the UHVDC line, and the parameters of the inverters at the high and low terminals are to be set independently. In this study, the power flow model of the UHVDC line is newly proposed. Considering the unbalanced modes and the HCM, the DC variables, the equivalent powers of the converters, and the MEs are decided. The elements of the extended Jacobian matrix are defined. The initial values and specified values are derived. The modified IEEE RTS system and a provincial system in the eastern China are applied to validate the feasibility and accuracy of the proposed models. The research provides the basis for the operation and economic dispatch of the AC/UHVDC systems.

Modeling of Step Voltage Regulators in Multiphase Load Flow Solution of Distribution Systems Using Newton's Method and Augmented Nodal Analysis

The increasing complexity of distribution systems requires general, efficient, and large-scale capable methods. This paper proposes a new technique to find the tap positions of step voltage regulators in multiphase load flow solvers in a direct and efficient manner. This is achieved by applying Newton method to the system of equations obtained by using the concept of augmented matrix formulation and adding the constraint equations. This approach allows employing the regulator equations directly. The regulators are modeled by taking into account the line drop compensator circuit with its settings, i.e., the desired voltage level, bandwidth, and R′ and X′ settings, which represent the scaled impedance parameters of the distribution feeder between the regulator and the load center at which the voltage is controlled. The limits of the regulators such as minimum and maximum tap positions are also accounted for. The proposed technique represents a voltage regulator with transformer equations using an augmented matrix formulation. The mismatch equations are developed using the desired voltage setting in constraint equations with transformation ratio of the transformer being the unknown variable. The Jacobian matrix, which is constructed using the augmented matrix formulation, is expanded to hold the constraint equations of voltage regulators. The proposed new method is tested on a variety of test circuits including the large-scale IEEE 8500 Node Test Feeder, and the minimum number of iterations reported in the literature is achieved as presented in this paper.

Unified Power Flow Algorithm Based on the NR Method for Hybrid AC/DC Grids Incorporating VSCs

This paper proposes a unified power flow algorithm based on the Newton–Raphson (NR) method to obtain a feasible solution for hybrid AC/DC grids incorporating voltage source converters (VSCs). The power flow model of hybrid AC/DC grids is composed of an AC grid model, a VSC station model, and a DC grid model. Detailed converter losses are involved in VSC station modeling. In the DC grid model, a unified dc control expression is applied to adapt to different control methods. To obtain sparse Jacobian matrix, the mismatch equations and unknown variables are classified into three categories corresponding to AC, VSC, and DC models. Then the proposed algorithm achieved quadratic convergence with the NR method. Once the solution is infeasible (variable out-of-limit) or diverging, the constrained load flow (CLF) method is applied automatically to achieve a feasible solution by revising the references of ac/dc grids. Simulations were carried out for the hybrid AC/DC test system composed of two AC grids and two DC grids. The results under different DC voltage control modes show that the proposed algorithm is able to obtain a feasible solution with high accuracy and convergence speed.

Interior point-based slack-bus free-power flow solution for balanced islanded microgrids

The power flow study is an exigency for planning, operation, and optimization of future smart microgrids. In this paper, an interior point-based power flow solution for balanced microgrids operating in islanded mode is presented. In the proposed method, the power flow problem is set up as a constrained interior-point optimization problem in which nonlinear power mismatch equations are iteratively solved without defining a slack bus. Unlike conventional power flow problems, the unknown frequency of the microgrid and droop equations for distributed generation units are also taken into account. Moreover, fixed, voltage-dependent, and frequency-dependent distributed loads are also considered. The computational efficiency of the proposed method is verified using two tools and tested with various case studies. The proposed method has a good convergence pattern and execution time for all types of distributed generation units and loads in islanded networks that are arbitrarily complex. Copyright © 2015 John Wiley & Sons, Ltd.

MODELO SIMPLIFICADO DE COMPENSADOR ESTÁTICO DE POTENCIA REACTIVA EN EL FLUJO DE CARGAS CON INYECCIÓN DE CORRIENTE

This paper describe Newton-Raphson current injection power flow model of a Static Var Compensator (SVC) to reduce the complexities of the computer load flow program codes of a network containing this device. This model is based on power mismatch approach. The SVC controlled buses in the network are converted to PV buses with zero active power generation at the required voltage magnitudes. The power mismatch equations for these connected buses are included and updated in NR current injection load flow algorithm. While, the load buses are represented by current mismatch equations. Moreover, the parameters of SVC can be calculated using an iterative process and the final value is updated after the convergence is achieved. The developed SVC model enhances the reusability of load flow program by avoiding modifications in the Jacobian matrix. This model is considered the simplest and the best representation of shunt control devices. The feasibility of the SVC model has been validated on the WSCC 9-bus and IEEE 57-bus transmission systems.

An Approximate Power Flow for Distribution Systems

Power flow calculation is the most used procedure in electrical power systems. Generally, most of optimization problems in electric power systems need a steady state analysis to evaluate the objective function. Especially, those optimization problems that make use of artificial intelligence techniques, where, due to the high number of iterations, the power flow calculation has a crucial role. In these cases, the method used for solving the power flow must be fast and accurate at the same time. This paper presents an approximate power flow solution method to solve distribution systems. The proposed method is based on current mismatch equations. The system of obtained equations cannot be presented as a set of linear complex equations. So, a simplification is introduced in this paper in order to express the system by a set of linear complex equations instead of a double set of linear real equations. Regarding the topology of the network, the proposed method is valid for both radial and mesh distribution systems. Finally, so as to demonstrate the validity and the effectiveness of the proposed method, a set of test distribution systems obtained from the technical literature have been used to test it.

Analysis of the most relevant anthropometric dimensions for school furniture selection based on a study with students from one Chilean region

Most of the worldwide standards used for furniture selection suggest the use of the Stature of the school children, assuming that all the other anthropometric characteristics will also be appropriate. However, it is important to consider that students' growth differ with age. The aim of this study is to determine if Popliteal Height can be used as a better, or more adequate, measure for classroom furniture selection when comparing with Stature. This study involved a representative group of 3046 students from the Valparaíso Region, in Chile. Regarding the methodology, eight anthropometric measures were gathered, as well as six furniture dimensions from the Chilean standard. After assigning the level of school furniture using Stature and Popliteal Height to each of the students, six mismatch equations were applied. The results show that when using Popliteal Height, higher levels of match were obtained for the two more important furniture dimensions. Additionally, it also presents a better cumulative fit than Stature. In conclusion, it seems that Popliteal Height can be the most accurate anthropometric measure for classroom furniture selection purposes.

A simple implementation of power mismatch STATCOM model into current injection Newton–Raphson power-flow method

This paper presents a simple implementation of Static Shunt Compensator (STATCOM) into Newton–Raphson current injection load flow method. The controlled STATCOM bus in the network is represented by voltage-controlled bus with zero active power generation at the required voltage magnitudes. The power mismatch equation of the connected STATCOM bus is included in Newton–Raphson current injection load flow algorithm, while the other PQ buses are represented by current mismatch equations. Moreover, the parameters of STATCOM can be calculated during iterative process and the final value will be updated after the convergence is achieved. This representation of generator buses reduces the number of required equations with respect to the classical and improved versions of the current injection methods. In addition of that the developed model reduces the complexities of the computer program codes and enhances the reusability by avoiding modifications in the Jacobian matrix. The performance of the developed STATCOM model has been tested using standard IEEE systems.

Optimal Particle Swarm Based Placement and Sizing of Static Synchronous Series Compensator to Maximize Social Welfare

Social welfare maximization in a double-sided auction market is performed by implementing an aggregation-based particle swarm optimization (CAPSO) algorithm for optimal placement and sizing of one Static Synchronous Series Compensator (SSSC) device. Dallied simulation results (without/with line flow constraints and without/with SSSC) are generated to demonstrate the impact of SSSC on the congestion levels of the modified IEEE 14-bus test system. The proposed CAPSO algorithm employs conventional quadratic smooth and augmented quadratic nonsmooth generator cost curves with sine components to improve the accurate of the model by incorporating the valve loading effects. CAPSO also employs quadratic smooth consumer benefit functions. The proposed approach relies on particle swarm optimization to capture the near-optimal GenCos and DisCos, as well as the location and rating of SSSC while the Newton based load flow solution minimizes the mismatch equations. Simulation results of the proposed CAPSO algorithm are compared to solutions obtained by sequential quadratic programming (SQP) and a recently implemented Fuzzy based genetic algorithm (Fuzzy-GA). The main contributions are inclusion of customer benefit in the congestion management objective function, consideration of nonsmooth generator characteristics and the utilization of a coordinated aggregation-based PSO for locating/sizing of SSSC.

Simplified Newton–Raphson power-flow solution method

This paper presents a simplified version of the well-known Newton–Raphson power-flow solution method, which is based on the current balance principle to formulate a set of nonlinear equations. Although there exist several powerful power flow solvers based on the standard Newton–Raphson (NR) method, their corresponding problem formulation is not simple due to the need for calculation of derivatives in their Jacobian matrix. The proposed method employs nonlinear current mismatch equations instead of the commonly-used power mismatches to simplify overall equation complexity. Derivation of Jacobian matrix’s updating formulae is illustrated in comparison with those of the standard Newton–Raphson method. To demonstrate its use, a simple 3-bus power system was selected as a numerical example. The effectiveness of the proposed method was examined by computer simulations through five test systems: (1) 5-bus test system, (2) 6-bus test system, (3) 24-bus IEEE test system, (4) 30-bus IEEE test system and (5) 57-bus IEEE test system. Its convergence and calculation time were observed carefully and compared with solutions obtained by the standard NR power flow method. The results show that the proposed NR method spends less execution time than the standard method does with similar convergence characteristics.

Investigation of residual stress effects in an alloy reinforced ceramic/metal composite

This study aims at investigating the thermal expansion behavior and internal residual strains in metal reinforced ceramic matrix composites (CMCs). A variety of Al 2 O 3 /A356 CMCs composites with an interpenetrating network structure and varying metal content, ranging from 10 to 40 vol.%, were produced using the pressure infiltration technique of Squeeze casting. Values of coefficients of thermal expansion (CTEs) were found to vary significantly with temperature, indicating an influence of the flow characteristics of the metal. Comparisons are made with well known methods for predicting CTEs values of metal/ceramic composites. The overall strain was found to increase with temperature and scaled proportionally with the metal content of the composite. Comparisons were also made with non-infiltrated porous ceramic preforms and a pure metallic sample. The uniform heating and cooling curves for the composite samples were found to exhibit hysterisis. Residual stress analysis and failure simulation were performed based on thermomechanics and the finite element method (FEM). This analysis is often utilized for the analysis of stress distribution or deformation of a structure. High angle X-ray and CTEs mismatch equation analysis were utilized to analyze the residual stresses at the ceramic/metal interface of the Al 2 O 3 /A356 composites. The relationship of residual stresses and the contact area of the ceramic/metal interface are also discussed.