Simple Design Method Research Articles

Online Frequency Response Measurements of Grid-Connected Systems in Presence of Grid Harmonics and Unbalance

Grid characteristics have a drastic impact on the stability and control performance of grid-connected systems. Because the grid conditions typically vary over time, online measurements are most desirable for the stability assessment, protection design, and control system optimization of the systems. Previous studies have presented methods based on Fourier techniques and broadband sequences, with which the frequency responses of the grid-connected systems, such as the grid impedance or inverter control loops, can be measured. However, online measurements under unbalanced grids with harmonic voltages have not been comprehensively considered. This letter demonstrates how the previously applied online measurement methods fail in the presence of unbalanced grid and voltage harmonics due to the spectral leakage caused by the Fourier transform. This letter also proposes a simple signal design method to avoid the leakage. Experimental results based on a high-power grid-connected system are shown to demonstrate the effectiveness of the proposed method.

Facile method for adjustable preparation of nano-Fe7S8 supported by carbon as the anode for enhanced lithium/sodium storage properties in Li/Na-ion batteries

Iron sulfide (FeSx), as an anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), has attracted special attention in recent years. In this paper, an extremely facile calcination method for the synthesized of Fe7S8@C nanocomposites with different morphologies and sizes is described. The Fe7S8@C anode provides an ultrahigh charge capacity of 1042 mAh g−1 after 100 cycles at a current density of 100 mA g−1 for LIBs and 524 mAh g−1 after 150 cycles at a current density of 200 mA g−1 for SIBs. It is impressive that the material shows super-long cycle stability with a reversible capacity of 789 mAh g−1 after 1000 cycles and 370 mAh g−1 after 500 cycles at a high current density of 1000 mA g−1 and 500 mA g−1 for LIBs and SIBs, respectively. Nanosized particles, in situ generated carbon and the porous structure of the materials are beneficial for the storage of lithium/sodium ions. Importantly, the preparation of the Fe7S8@C anode provides a very simple method for the structural design of high-performance anode materials, and may be practical in various applications such as catalysis and sensors.

A simplified design method for energy piles

This paper introduces a simplified method to investigate the influence of thermal loads on the shaft friction and tip resistance of energy piles. The method is based on the influence factors (λ and η) which are back-calculated drawing on a large number of field and model tests. Values for λ and η during heating and cooling are suggested. Moreover, a new equation is proposed to calculate total shaft friction. The equations concerning the relationship between η and temperature difference are recommended to investigate the impacts of the thermal load on the pile tip resistance. The slope of the linear equation of an end-bearing pile is 2.14 times that of a floating pile indicating that the pile tip resistance of an end-bearing pile is much more affected by the same thermal load.

Stability Analysis for Cofferdams of Pile Wall Frame Structures

Pile wall frame structures (PWFSs) are double-wall sheet-pile structures with an integrally precast framework of reinforced concrete to connect double rows of closely placed piles. An engineering test on a cofferdam of PWFSs was conducted in Binzhou, where lateral displacement along pile shaft was carefully monitored during the hydraulic filling process. A 3D finite element model (FEM) of the test was established to study the stability failure mechanism of PWFSs. Then, a design method for PWFSs was proposed through a structural stability analysis based on the limit equilibrium method, with special consideration of the cutting pile force influenced by row spacing. According to FE results, lateral pile displacements drawn from the FEM correspond well with field observations, and earth pressures applied on closely spaced piles are in line with Rankine’s theory. Results of the theoretical analysis indicate that the control slip surface lies on the bottom of a soil layer with a poorer shear strength index. The effects of framework width, pile spacing, pile length and diameter on structural stability are also evaluated. The feasibility of PWFSs has been verified by an engineering test, and the simplified design method established here is reasonable and effective for structural stability prediction.

A New Practical Approach to the Design of Industrial Axial Fans: Tube-Axial Fans With Very Low Hub-to-Tip Ratio

This paper presents a simple but complete design method to obtain arbitrary vortex design tube-axial fans starting from fixed size and rotational speed. The method couples the preliminary design method previously suggested by the authors with an original revised version of well-known blade design methods taken from the literature. The aim of this work is to verify the effectiveness of the method in obtaining high-efficiency industrial fans. To this end, the method has been applied to a 315 mm rotor-only tube-axial fan having the same size and rotational speed, and a slightly higher flow rate coefficient, as another prototype previously designed by the authors, which was demonstrated experimentally to noticeably increase the pressure coefficient of an actual 560 mm industrial fan. In contrast, no constraints are imposed on the hub-to-tip ratio and pressure coefficient. The new design features a hub-to-tip ratio equal to 0.28 and radially stacked blades with aerodynamic load distribution corresponding to a roughly constant swirl at rotor exit. The ISO-5801 experimental tests showed fan efficiency equal to 0.68, which is 6% higher than that of the previous prototype. The pressure coefficient is lower, but still 12% higher than that of the benchmark 560 mm industrial fan.

Local bulging analysis of a restraint tube in a new buckling-restrained brace

This paper describes a restraint tube local bulging study of newly developed small-type buckling-restrained braces (SBRBs). An analytical calculation model for the restraint tube stress distribution is established by the shell theory and the Fourier series. It is demonstrated that the stress concentration lies mainly in a region with a length of 2R0, which is approximately equal to the tube middle surface diameter. A simplified design method including a safety factor and recommended thickness-radius ratio is then proposed based on the analytical study. To verify the accuracy of this calculation method, four SBRB specimens with different tube thicknesses were tested under quasi-static cyclic loading. The calculation results are in reasonable agreement with the test results and can predict the local bulging occurring instant with acceptable accuracy.

ON THE OPTIMAL STRUT-AND-TIE MODELS AND DESIGN APPROACH FOR THE CABLE-PYLON ANCHORAGE ZONE

The cable-pylon anchorage zone is a typical D-region in a cable-stayed bridge, for which there has been no uniform simplified design method until now. In this paper, based on the extensive statistics of actual projects, topology optimization techniques and principle of minimum strain energy, two precise strut-and-tie models for the cable-pylon anchorage zone are proposed, which can clearly reveal the load-transmitting mechanism of the anchorage zone. Th e explicit geometric parameters of the strut-and-tie models are derived; thus, the designers can directly use these models. A simple design procedure to deploy prestressing tendons in the anchorage zone is also introduced, whose effectiveness and convenience are demonstrated by two design examples. A new design named the “one-way prestressing tendons PC cable-pylon” is also discussed regarding its application scope.

On the Optimum Noise-Gain Locus of Two-Ports

A novel result is presented concerning the locus, on the source reflection coefficient plane, of the optimum tradeoff between noise factor and available gain. Although this locus has been discussed and exploited in previous contributions, here, it is shown in a simple manner that it must be an arc of a circumference with center $C_{\mathrm{ tc}}$ and radius $\rho _{\mathrm{ tc}}$ (tangency circle). A handy transformation (a reversible, conformal one) of two-port networks is adopted to study the problem in a simplified, yet general, representation. Properties of the tangency circle are observed in this “noise-centered” representation which are preserved under the conformal transformation, thus providing two equivalent, closed-form approaches to computing $C_{\mathrm{ tc}}$ and $\rho _{\mathrm{ tc}}$ . The second method presented lends itself to being easily implemented in commercial circuit simulators, thus serving as the basis of a simple design method for single-stage low-noise amplifiers.

Numerical Study of the Geometry Effect of Notched Connections in Mass Timber Panel-Concrete Composite Floors

A mass timber panel-concrete (MTPC) composite floor system consists of a timber panel in the tensile zone, a concrete layer in the compression zone, and shear connectors between timber and concrete. The notched connections that are cut in timber and connected with concrete by the interlocking effect are often classified as the best type of connection system in terms of stiffness and load-carrying capacity. To study the effect of notch geometry to the performance of notched connections and composite beams, 2D finite element models are built in ABAQUS in this study. The concrete portion is modelled with concrete damaged plasticity model while the timber portion is modelled with Hashin’s failure criteria. The effective bending stiffness and ultimate bending capacity of the composite beam under uniformly distributed load are obtained from the finite element models and are compared with the well-known Gamma method in Eurocode 5 and strut-and-tie model. Good agreement between finite element model in the elastic range and strut-and-tie model was achieved. However, due to the assumptions made in the Gamma method, it was found that this simplified design method is not capable of describing MTPC composite floors with discrete notched connections.

Evaluation of compressive arch action of reinforced concrete beams and development of design method

This paper describes a study on the compressive arch action of reinforced concrete beams with various levels of horizontal restraints. An analytical model is proposed based on Park’s assumption, in which the tension-stiffening effect of steel reinforcement and its slip relative to beam-column joints are considered. The model is calibrated by experimental results of beam-column sub-assemblages and frames subject to column removal scenarios. The model is calibrated by experimental results of beam-column sub-assemblages and frames subjected to middle column removal scenarios. A parametric study is conducted to shed light on the effects of horizontal restraints on the axial compression force of beams and the strain of compressive reinforcement. Analytical results suggest that the compressive reinforcement may not yield under compressive arch action, and its strain varies with the axial compression force in the beam. To develop a simplified design method, the relationship between the axial compression force and the strain of compressive reinforcement is established through the theoretical axial force-bending moment interaction diagram. An explicit expression for axial compressive strain is derived from force equilibrium and compatibility and incorporated in the design method to evaluate the compressive arch action capacity and associated axial compression force of reinforced concrete beams. Comparisons with existing experimental results in the available literature and other models suggest that the design method yields reasonably accurate estimations of critical parameters related to compressive arch action.

Simplified Method for Optimal Design of Friction Damper Slip Loads by Considering Near-Field and Far-Field Ground Motions

ABSTRACT A simplified method is proposed for optimum design of friction dampers by considering the characteristics of design earthquakes. Optimum slip loads for 3, 5, 10, 15 and 20-storey RC frames with friction wall-dampers are obtained for a set of 20 near- and far-field earthquakes as well as artificial spectrum-compatible records scaled to different acceleration levels. Optimum solutions are shown to be more sensitive to Peak Ground Velocity (PGV) than Peak Ground Acceleration (PGA), especially for near-field earthquakes with high-velocity pulses. For identical PGA levels, far-field earthquakes on average result in 1.5 times lower optimum slip loads compared to near-field records, while they lead to 118% higher energy dissipation and 24% lower maximum inter-storey drifts. Empirical equations are proposed to predict optimum slip loads (as a function of number of storeys and PGA/PGV of design earthquakes) and their efficiency is demonstrated through selected examples.

Numerical investigation and design of reinforced concrete beams with non-uniform frost damage on the compression and tension sides

This paper aims to investigate the bending behaviour of a reinforced concrete (RC) beam with different non-uniform frost damages. A multi-scale poromechanical approach is developed to build a bridge between the material deterioration process and the structural mechanical performance by considering the global heat and moisture transport and rebar confinement, as well as the local phase changes and poromechanical deformation. The real-time frost damage process is first simulated and experimentally validated for different depths of exposure on both the compression and tension sides and then used for testing the residual bending behaviour. The failure modes, load-carrying capacity and strain distribution of the reinforcement are fairly consistent with the experimental results. The bearing capacity decreases with the increment of the freeze-thaw cycles (FTC) and the frost exposure depth. Reinforcing bars can restrain not only crack propagation but also frost damage. Thus, the bearing capacity of the damaged beam on the compression side drops more than that on the tension side for the same exposure depth. Finally, an indirect method for the use of the equivalent deteriorated mechanical properties is compared with the detailed real-time simulation, and a simple design method is proposed for RC beams with partial frost damage.

New results on regional observer-based stabilization for locally Lipchitz nonlinear systems

Abstract This paper describes the design of a regional observer-based controller for the locally Lipchitz nonlinear systems, which can be employed successfully to attain both monitoring and control of a wide range of systems. An observer-based control approach has been employed to attain advantages of the traditional state feedback along with the state estimation through an observer. A lot of work has been accomplished for the globally Lipchitz nonlinear systems. However, a less conservative continuity, called the generalized ellipsoidal Lipchitz condition, has been applied in this paper to consider the locally Lipchitz systems. This condition is then incorporated to attain convex routines for computing the local controller and observer gains. The focus of the present study is to investigate conditions for simultaneous design of observer and controller under locally Lipchitz nonlinearities for systems with norm-bounded disturbances that not only guarantees the stabilization and true state estimation but also robustness against external perturbations. Furthermore, the decoupling of the observer and controller design conditions has been worked out for obtainment of a simple design method. Since the resultant control approach applies to a general class of systems, it can be straightforwardly employed to the globally Lipschitz nonlinear systems as a specific case. The approach is tested via a chaotic system and simulation results are provided to validate the effectiveness of resultant control schemes for the locally Lipschitz systems.

Simplified force-based seismic design procedure for linked column frame system

Dual structural systems with structural fuse such as linked column frame system (LCF) have two main performances, including the resistance to lateral seismic loads and the proper function of structural fuse to control deformation of the other members to remain in elastic phase. The achievement of these two functions is necessary for appropriate seismic design of these systems. Undoubtedly, despite the practical complexity, displacement-based seismic design methods are generally the best method for this purpose. In contrast, conventional force-based methods are relatively simple, but it cannot easily guarantee the desired performance. In this paper, a simplified force-based seismic design method is presented for linked column frame system based on parametric studies on different structures, which are designed with displacement-based method. In addition to simplicity, the proposed method has an appropriate accuracy in terms of achieving the performance objectives. For the parametric study, 18 prototype structures with various relative lateral stiffness of moment frame and linked column system are designed with the displacement-based method. Based on the results of the structures designed with desirable performance, the criteria are proposed for the force-based design method. Based on evaluating results, the structures designed by the proposed simplified force-based method properly reached the performance objectives.

Optimal Decision-Making of Renewable Energy Systems in Buildings in the Early Design Stage

Renewable energy systems (RES) in buildings should be designed carefully, not only because of the need for an optimal design, but also to comply with related laws. Therefore, the design of RES in the buildings requires close collaboration between architects and engineers from the beginning of the design process. To support such collaboration, this study proposes a simplified design method for RES in buildings during the early design stage. By using the proposed design method, design alternatives that meet the required energy standards as suggested by law are first generated. Further designs are made to evaluate the performance and cost of the design alternatives and to find the optimal types of RES for the building. The study also uses a case study to verify the applicability of the design method to the early design stage. Although the performance and cost of the different design alternatives are similar, the implementation of each type of RES in each design alternative is different. Nonetheless, by analyzing performance patterns and the cost ratio of each type of RES in each design alternative, the study allows the most suitable type of RES to be chosen for the building.

Behaviour of square CFST beam-columns under combined sustained load and corrosion: FEA modelling and analysis

This paper presents a numerical investigation on concrete-filled steel tubular (CFST) beam-columns with square sections subjected to combined sustained load and corrosion. A general numerical method is used for the simulation of the time dependent behaviour of the core concrete, while the wall-thickness loss of the outer steel tube induced by corrosion is considered in this model simultaneously. The established finite element analysis (FEA) modelling is verified with test data and used for further investigations of the load-deformation relationship, load-transfer mechanism, stress and strain development, failure modes and ultimate states on CFST beam-columns when suffering combined sustained load and corrosion. Parametric studies are conducted to reveal the effects of key parameters, based on which simplified design method is suggested for square CFST beam-columns under combined sustained load and corrosion.

Exponentially stabilizing fuzzy controller design for a nonlinear ODE-beam cascaded system and its application to flexible air-breathing hypersonic vehicle

This paper addresses fuzzy control design for a class of nonlinear systems which are described by nonlinear ordinary differential equations (ODEs) cascaded with an Euler-Bernoulli beam (EBB) equation. Two design difficulties are involved in the control design addressed in this paper. The first one is caused by the EBB equation whose spatiotemporal dynamics is affected by the output of the nonlinear ODE subsystem through its differential equation rather than boundary conditions. A state differential transformation is introduced for the EBB equation to bring the output of the ODE subsystem in the differential equation to its boundary conditions. The second one comes from the nonlinear ODE subsystem. To overcome this difficulty, it is assumed that an exact Takagi-Sugeno (T-S) fuzzy ODE model is utilized by the sector nonlinearity approach to describe the dynamics of nonlinear ODE subsystem. Based on the T-S fuzzy model, a composite Lyapunov function is constructed to develop a fuzzy controller via the ODE state feedback and boundary feedback of transformed EBB equation to exponentially stabilize the nonlinear ODE-EBB cascaded system. The design procedure is presented in terms of bilinear matrix inequalities (BMIs). Moreover, a simple design method is also provided in terms of linear matrix inequalities (LMIs) from the obtained design procedure. Finally, numerical simulations on flight control with vibration suppression of a flexible air-breathing hypersonic vehicle are given to illustrate the effectiveness of the proposed design method.

Transverse flux permanent magnet generator design and optimization using response surface methodology applied in direct drive variable speed wind turbine system

Recently, Transverse Flux Permanent Magnet Generators (TFPMGs) have been proposed as a possible generator in direct drive variable speed wind turbines due to their unique merit. Generally, the quality of output power in these systems is lower than multi stage fixed speed systems, because of removing the gears, so it’s important to design these kinds of generators with low ripple and lowest harmful harmonics and cogging torque that is one of the most important terms in increasing the quality of output power of generator. The objective of this paper is introducing a simple design method and optimization of high power TFPMG applied in vertical axis direct drive wind turbine system by lowest possible amplitude of cogging torque and highest possible power factor, efficiency and power density. For this reason an optimum method called combined response surface methodology (RSM) and design of experiment and in order to extract the output values of generator and sensitivity analysis for design and optimization, 3D-Finite element model, was applied. This method has high accuracy and gives us a better insight of generator performance and presents back EMF, cogging torque, flux density and FFT of this TFPMG. This study can help designers in design approach of such generators.

Flux switching permanent magnet generator design and optimization using response surface methodology

Flux Switching Permanent Magnet Generators (FRPMGs) have been used increasingly in direct drive variable speed wind turbines due to their merit such as their high torque density, easy flux weakening operation and robust rotor structure. Generally, the quality of output power in direct drive systems is lower than multi stage fixed speed systems, because of removing the gears, so it’s important to design these kinds of generators with low ripple and lowest harmful harmonics and cogging torque. This aim is one of the most important terms in increasing the quality of output power of generator simultaneously with back-EMF improvement. The objective of this paper is introducing a simple design method and optimization of high power FRPMG applied in direct drive wind turbine system by lowest possible amplitude of cogging torque and highest possible power factor, efficiency and power density. For optimization reason an optimum method called combined response surface methodology (RSM) and design of experiment has been applied. Also in order to extract the output values of generator and sensitivity analysis for design, 3D-Finite element model, was used. This method has high accuracy and gives us a better insight of generator performance and presents back EMF, cogging torque, flux density and FFT of the FSPMG. This study can help in design approach of such machines.

Anomalously Perfect Reflections Based on 3‐Bit Coding Metasurfaces

AbstractHerein, a new design method to realize anomalously perfect reflections based on digital coding metasurfaces is proposed. Previous studies on perfect reflections usually rely on impedance matching, which requires complicated analyses and calculations. Based on the digital design of coding metasurfaces, a simple design method to generate anomalously perfect reflections for different reflection angles with high efficiency is presented. 3‐bit digital coding units are designed and verified to provide reflection phase responses of 0°, 45°, 90°, 133°, 176°, 221°, 269°, and 302°. Four digital coding patterns for different reflection angles are created to demonstrate the anomalously perfect reflections. Numerical simulations and experimental results have good agreements, suggesting the powerful potentials of the digital coding metasurface in controlling the electromagnetic waves.