Secondary Load Research Articles

Scaling characteristics of the hull girder's ultimate strength subjected to the combined hogging moment and bottom lateral pressure: An empirically modified scaling criterion

The ultimate strength of the ship hull girder under combined loads is closer to the load-carrying capacity during the actual sailing for considering the negative effect of the secondary load in some cases. Scaled models are designed to represent the prototype in ultimate strength experiments. To study the effect of the bottom lateral pressure on the scaled hull girder under combined loads thoroughly, a series of hull girders of a 10,000TEU container ship under different scale combinations of geometric length and plate thickness are analyzed. The relevant changes in the characteristics of ultimate strength and collapse behaviors caused by bottom lateral pressure are investigated. Results show that the ultimate hogging moment predicted by the traditional or the empirical scaling law proposed in the reference is significantly different from that obtained by numerical analysis when the scale ratio of the plate thickness is much smaller than the geometric scale ratio for ignoring the significant effect of the bottom lateral pressure. Correspondingly, an empirical scaling criterion is proposed to improve the accuracy of the converting process of the ultimate strength between scaled models and the full-scale prototype. Finally, the applicability of the proposed scaling criterion is verified by numerical results of a series of simplified hull girder models.

Maximal Oxygen Uptake in Breathing Exercises and Heart Rate Exercises Based on In-Depth Regression Equations

For the purpose of research, the maximum oxygen uptake of exercise training breathing and heart rate constructed based on the deep learning regression equation learn about the effects of training breathing and heart rate on VO2 max. Based on 77 healthy adults without chronic diseases (37 men and 40 women, aged 20–39 years old), who participate in two exercise tests (the first time is a direct test and the second time is a secondary quantitative load plan), in order to establish a second-level quantitative load scheme for power vehicles, the predictive equation for predicting the maximum oxygen uptake. The author researched and established a stable heart rate HRH based on gender, BMI, and second-level load; the second-level load RPE and R P E 1 are independent variables, the absolute value of the subject’s maximum oxygen uptake is the regression equation of the dependent variable. The experimental results prove that the reliability and validity of the second-level quantitative load scheme for power vehicles are better and can be used as the maximum oxygen uptake in the laboratory, directly tested with alternative submaximal solutions, and used for large-scale investigation of maximum oxygen uptake data. At the same time, since the load is submaximal, it can also be used to clinically assess the patient’s cardiorespiratory endurance.

Experimental investigations of secondary load cycle formation in wave force on a circular cylinder under steep regular waves

When a large wave interacts with a marine structure, it would lead to a high-frequency structure response, and impose great threats to marine structures. In this paper, wave forces on a vertical cylinder in regular waves with moderate to extreme steepness were measured experimentally. The secondary load cycle phenomenon in wave force time history was observed and its generation mechanism was analyzed. It is found that secondary load cycle strongly depends on wave steepness. When the wave steepness exceeds critical values, the secondary load cycle phenomenon appears in the time history of wave force, and a high frequency response accompanied this phenomenon. Further, a new critical wave steepness kA = 0.3tanh(kh) (A is wave crest height, k is wavenumber and h is water depth) is found to distinguish the secondary load cycle occurrence. Here the wave steepness threshold value is no more a constant value that was proposed before, it varies with water depth and becomes smaller with the decrease of water depth. Moreover, the secondary load cycle and the subsequent high-frequency response are divided from the wave force signal based on the empirical mode decomposition (EMD) method. The results show that the high-frequency response locates in the natural frequency region of cylinders, which is much higher than the high-order wave components. Finally, the generation mechanism of this phenomenon is explained. As a steep wave passes a cylinder, a large wave run-up would be generated on the front side of the cylinder. One part of water body of the run-up swashes down and impacts the wave surface heavily. The other part of wave run-up fills into the cavity on the lee side of the cylinder, and generates violent turbulence. Both processes are found to lead to an instant impact on the structure, and then excite structural high-frequency vibration. This instant impact expresses as secondary load cycle in wave force history. These new findings from experimental studies have provided new insights into the generation mechanism and the associated changes in wave properties during the formation of secondary load cycle.

Mechanical sensitivity analysis of strain gauge configurations in the main shaft of wind turbines

Wind turbines are reaching their remaining useful life, thus it is important to guarantee the well status of its components. A common way to check the status is to measure the loads on the Low Speed Shaft with strain gauges, but not always are bonded perfectly. In this work a sensitivity analysis of strain gauge configurations is carried out, where the influence of geometric and material parameters, and misplacement and misalignment parameters is analyzed. An analytical model for a single gauge was developed, obtaining a relation between the exerted loads and the strain measured by the strain gauge. By means of Taylor approximations the estimated loads were approached in order to have into account the influence of the uncertainty of parameters. Results shown that the sensitivities with respect to the geometric and material parameters did not depend on the secondary loads while in the sensitivities with respect to the gauge bonding parameters the cross-talk effect was present. In order to obtain realistic numerical results, a horizontal-axis NREL 5-MW wind turbine was simulated in OpenFAST with two wind-speed scenarios. The uncertainty of the estimated loads by the strain gauge configurations was calculated.

Effect of Transverse Restraint on Welding Residual Stress in V-Groove Butt Welding

When evaluating the safety of steel structures, welding residual stress is used as the secondary load and if there is any restraint, the yield stress of the base material is used for secondary load, regardless of the size of the restraint. Of late, as the yield stress of members is increasing with the increase in the use of high-strength steels, the proportion of the residual welding stress in the total load during the evaluation of the safety of structures is increasing. Therefore, it is necessary to investigate the effect of the size of the restraint on the residual welding stress, determine reasonable residual stress according to the size of the restraint, and apply the residual stress as a secondary load. To investigate the effect of constraint conditions on residual welding stress, thermoelastic–plastic analysis was performed for different member thicknesses, yield stresses, and constraint sizes. The restraint did not affect the residual stress in the direction of the weld line but did affect the residual stress in the direction perpendicular to the weld line. The restraint moved the tensile stress to the compression stress in the direction perpendicular to the weld line at the first layer of the weld and moved the compression stress to the tensile stress at the middle and final layers of the weld. The change in residual stress was the largest in the middle of the weld.

Numerical investigation of inline wave force on a truncated vertical cylinder with different cross-sections in regular head waves

The non-linear wave amplification around a truncated vertical cylinder, the high-order horizontal wave loading from non-breaking steep waves and the associated physical process are studied numerically. Considering the high-order free-surface deformation due to high-frequency wave scattering Type-1 and Type-2, and lateral edge waves, the simulations are conducted for a stationary, surface-piercing cylinder with different cross-sections subject to the short and long waves, propagating in deep water. A numerical wave tank based on the Unsteady Navier-Stokes/VOF model is established, using OpenFOAM combined with the olaFlow toolbox for wave generation and absorption. The capabilities of the present numerical model are assessed in conjunction with the ITTC (OEC) benchmark, where the numerical results are in good agreement. Overall, the results indicate the high potential of the present numerical model for accurate modeling of nonlinear wave interaction with cylindrical columns. Variation of wavelength together with the corner ratio significantly influences the magnitude of high-order harmonic wave loading. Moreover, the numerical results indicate the important contribution of the cross-section shape on the non-linear wave field surrounding each cylinder. As the geometrical presence of corner becomes apparent from circular to the square cross-section, there is a systematic increase in the mean value, 1st, 2nd and 3rd harmonics of the inline force subject to both short and long incident waves. Furthermore, interestingly the formation of slightly developed wave scattering of Type-2 at the front of the cylinder in short waves is observed for cross-sections with corner ratios of (rc/R=0.25&0). The development of a secondary load cycle is also observed which is found to be closely related to the occurrence of wave scattering Type-2 and the lateral edge waves where the important contribution from, mean value, 3rd, and 4th harmonics of the inline force are apparent.

Veterinary Clinical Education Delivery Models: A Conceptual Framework.

The sustainability of the traditional university-owned and -operated veterinary teaching hospital has been discussed for many years. Concerns around the shortage and lack of diversity of clinical faculty, financial sustainability, and suitability of secondary and tertiary case load for the development of Doctor of Veterinary Medicine students' Day One Competences are perennial issues. Consequently, many schools have been looking at alternative ways of delivering veterinary clinical education. This article provides a conceptual framework for evaluating the delivery of veterinary clinical education, providing putative advantages and disadvantages of each model for further empirical investigation. Four different models are proposed-owner, third party, embedded distributive, and fully distributive-that can broadly be defined along two dimensions: the degree of integration of the clinical enterprise with the academic enterprise and the degree of authority of the dean/head of school with respect to clinical enterprise governance and their role in budgetary, investment, and hiring decisions. The author offers a typology that may assist deans/heads of schools make strategic decisions about the mode of delivery of veterinary clinical education for their school.

Treatment of Olefin plant spent caustic by combination of Fenton-like and foam fractionation methods in a bench scale.

Spent Merox caustic (SMC) is a hazardous waste that is produced during the Merox desulfurization process in the petroleum refinery industry and should be treated before discharging to environment. In the present study, treatment of SMC was investigated by three methods including Fenton-like process, foam fractionation, and a combination of both processes. Immobilized TiO2/Fe0 on modified silica nanoparticles was used as a heterogeneous Fenton-like catalyst. The chemical and physical characteristics of the catalyst were determined using Fourier-transform infrared spectroscopy, X-ray diffraction, diffuse reflectance spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and transmission electron microscopy techniques. The treatment performance of the combined method was measured as a cost-effective method with chemical oxygen demand (COD) removal percentage. The effect of parameters including pH, gas flow rate, surfactant type and concentration of hydrogen peroxide, catalyst, and chelate were investigated. It is found that the prepared heterogeneous catalyst has high activity for the treatment of SMC. In addition, the results showed that the combined method achieved 97.6 ± 0.5% COD removal, while the measured values for Fenton or foam fractionation methods alone did not exceed 85.5 ± 1% and 47.2 ± 0.4%, respectively. The advantage of combination process over foam fractionation was the use of an advanced oxidation process in the separating column to eliminate or reduce the secondary phase contamination load. Besides, the role of the column in the effective contact of contaminants with the rising bubbles improved the degradation performance of the proposed process and reduced the consumption of hydrogen peroxide by 46% compared to the Fenton-like method.

A Family of Hybrid IPT Couplers With High Tolerance to Pad Misalignment

The transfer performance of inductive power transfer (IPT) systems is greatly affected by the inevitable magnetic pad misalignment. Practical IPT converters are expected to operate satisfactorily under considerable pad misalignments. Current design, control, and optimization of IPT circuits have achieved limited pad misalignment tolerance. In this article, a family of hybrid IPT couplers, which combine a conventional bipolar coupler and a simple series&#x2013;series topology, are proposed to achieve high tolerance to pad misalignments. The proposed hybrid IPT couplers are applicable to all IPT compensation topologies. In addition, overcurrent protection is inherently provided in the event of removal of the secondary coil and load. This article also provides the design principle of this family of hybrid couplers with different coil winding polarities to achieve a given coupling tolerance. Being a universally applicable IPT coupler with high tolerance to pad misalignment, the family of hybrid IPT couplers can be used in any IPT topology. An S-<i>LCC</i> compensation topology is used to illustrate the design of the IPT system with load-independent constant-voltage output under load and coupling variations. Finally, a 3-kW IPT prototype using a hybrid coupler and the S-<i>LCC</i> topology is built to verify the analytical findings.

Causes and control to lateral displacement of the main girder in the super-long-span cable-stayed bridge with transverse asymmetry dead load

In the densely populated large cities, to save valuable land resources and fit the plane alignment of the approach bridge at two ends of the main bridge, the long-span Rail-cum-Road cable-stayed bridge is arranged on the same deck with the lateral asymmetric layout. This makes the transverse secondary dead load of the main girder asymmetric and the mechanical characteristics different from the conventional cable-stayed bridge. In this paper, firstly, several measures to realize the ideal vertical alignment of the main girder for such cable-stayed bridges were analyzed theoretically, and the mechanical characteristics of the main girder via the measure of asymmetrical cable force were mainly explored. Then, taking the Changzhou-Taixing Yangtze River bridge as a typical example, a simplified mechanical model was proposed to calculate the lateral displacement of the main girder and was compared with the finite element model (FEM) of the whole bridge. Finally, according to the mechanical model, the control measures to lateral displacement of the main girder were discussed. The results show that the unbalanced longitudinal and lateral components corresponding to the asymmetric cable force lead to the main girder to deviate railway side and the highway side, respectively, and the corresponding variance value of lateral displacement is not significant, which greatly reduces the lateral shift effect of the main girder. Furthermore, the simplified mechanical model can effectively calculate the lateral displacement of the main girder and study the control measures for displacement. The conclusions of this study can provide a basis for further design of the same type of bridge.

Finite Element Analysis on Reinforced Concrete Beams Strengthened with CFRP

Reinforced concrete structure is widely used in building structure because of its unique physical and mechanic properties, but with the increase of service life, there will be different degrees of damage in the structures. In this paper, combined with the test beam, a model of reinforced concrete beam strengthened with CFRP is established by Using ANSYS finite element software, nonlinear finite element analysis is carried out on the whole process of yield, cracking and destruction of the test beam under secondary load, while different working states of CFRP sheets were simulated by the life and death unit. The results show that the bending performance of reinforced concrete (RC) beams strengthened with CFRP can be predicted by selecting the finite element analysis model rationally.

Application of WOA Tuned Type-2 FLC for LFC of Two Area Power System With RFB and Solar Park Considering TCPS in Interline

In this article, interval type-2 fuzzy logic controller (IT2FLC) has been proposed as secondary load frequency controller (LFC) for hybrid two area power system instead of type-1 fuzzy logic controller (T1FLC) and PID based controllers. The investigated power system integrates both conventional and renewable power resources like large scale solar parks. These large scale solar parks in addition to demand load changes increases load frequency control problems due to their continuous and severe output power variation. In order to reduce the effect of solar irradiance variation on the power system, another type-2 fuzzy logic controller has been proposed to control the output for the solar park during cloudy days instead of maximum power point trackers. As one of the best energy storage systems utilized in modern power systems, Reduction oxidation flow battery (RFB) has been integrated in the investigated power system to act as fast active power source which absorbs and discharges power during disturbances caused by generation or demand changes. Power flow controller like thyristor controlled phase shifter (TCPS) has been proposed in this paper to control tie-line power shared between generating areas during system disturbances. In order to enhance the dynamic performance for the proposed controller, meta-heuristic nature inspired optimization algorithm like whale optimization algorithm (WOA) has been proposed for proposed controller gains off line tuning. The superiority of the proposed IT2FLC controller against T1FLC controller has been investigated by simulating their performance during severe demand load changes and solar irradiance variations, while WOA enhanced the dynamic performance of the proposed controller compared to other optimization algorithms like particle swarm optimization (PSO) and grey wolf optimization (GWO).

Dynamic event-triggered protocol-based distributed secondary control for islanded microgrids

This paper proposes a distributed secondary control scheme with dynamic event-triggered protocol for multiple distributed generators (DGs) in an islanded microgrid. First of all, a dynamic event-triggered (DET) protocol is introduced for each DG unit to orchestrate the information transmission, which aims to save communication resources in the microgrid. The proposed event-triggered condition involves an internal dynamic variable, which is employed to dynamically adjust the event-triggered threshold. Then, under the schedule of the DET protocol, the distributed secondary controllers of the DGs are designed on the basis of the available information. The proposed secondary control scheme is completely distributed, which means that each DG only needs the information from itself and its neighbors, which reduces the requirements for the central controller and complex communication networks, and improves the reliability of the system. Meanwhile, it is proved that there is no Zeno behavior in the closed-loop system and the lower bound of the interevent time is enlarged due to the introduction of the dynamic event-triggered protocol. Subsequently, the similar idea is employed to deal with the distributed secondary frequency and load sharing problems. Finally, an illustrative example is utilized to verify the effectiveness of the proposed control scheme by using the MATLAB/SimPowerSystems toolbox.

Numerical analysis of in- and out-of-plane coupling effects on angle bracket connections in CLT structures

Angle bracket connections are commonly used to transfer shear loads in cross laminated timber (CLT) structures. In reality, these connections may experience multiple-direction loads simultaneously in the wind and seismic events. A two-phase numerical program was carried out to assess the coupling effect of biaxial loading on the performance of CLT wall-to-floor angle bracket connections. In phase I, a 3D finite element model of connections was developed using ABAQUS software and verified with the data from experimental tests previously carried out by the authors. In Phase II of the study, the verified model was used to simulate the performance of connections under three biaxial loads, i.e., in-plane shear and uplift, in-plane shear and out-of-plane outward shear, and in-plane shear and out-of-plane inward shear. The coupling effect on the performance of the connections was evaluated in terms of strength, stiffness, ductility, and failure modes under biaxial loads, and compared with the scenario where the connection was only loaded in in-plane shear. Results show that the application of biaxial loading may considerably decrease the in-plane shear performance of the angle bracket connections when the secondary load is more than 50% of its monoaxial resistance, while the effect of biaxial loading is limited when the secondary load is less than 25% of its monoaxial resistance.

Experimental study on flexural strengthening of reinforced concrete beams with U-shaped steel under secondary load

This study proposes a new method to strengthen reinforced concrete (RC) beams with U-shaped steel, which can achieve rapid construction and great improvement in the flexural performance of RC beams. To investigate the influence of secondary load defined as newly applied loads after strengthening on the strengthening effect, a total of nine specimens were tested under four-point bending, including a reference beam, a strengthened beam under initial load, and seven strengthened beams under secondary load. The initial loading degree, the thickness of the bottom plate, and the height of the steel box were the main variables considered in this study. Testing results showed that compared with the reference beam, the flexural performance of strengthened beams was significantly enhanced, indicating the good joint performance of the U-shaped steel and the RC beams. Among the three main variables, the initial loading degree was found to have a minimal effect on the flexural performance while the thickness of the bottom plate and the height of the steel box had considerable influence, with the latter having a more pronounced effect. Testing results also showed that most of the strengthened beams experienced flexural failures, which were reflected by steel web peeling and buckling, and concrete crushing. Moreover, a formula was derived for calculating the flexural capacity of strengthened beams under secondary load. The results from the derived formula were found to be in good agreement with those from experiments.

Concept Designing of a Solar Photovoltaic UPS System with Sunlight Tracker

This paper defines the design of UPS system with the help of sun tracking system, as a source for chargingthe battery to provide the backup power when the regular power source fails. This authentication is provided by obtaining the theoretical calculation of output power, output current and output voltage which are developed due to solar radiations. In this system, if the primary load is not in use, then the power is automatically switching over to secondary load. Basically, an UPS is electrical equipment that is used at the time of emergency. The battery bank is charged with the help of solar photovoltaic cell. This paper proposed an approach to understand the peak power point of the sun based on analysis of the open-circuit voltage of the PV panel. This project provides the power supply to a load which is uninterruptible, by automatically selecting the supply from the main source or inverter.

Machine Learning and GIS Approach for Electrical Load Assessment to Increase Distribution Networks Resilience

Currently, distribution system operators (DSOs) are asked to operate distribution grids, managing the rise of the distributed generators (DGs), the rise of the load correlated to heat pump and e-mobility, etc. Nevertheless, they are asked to minimize investments in new sensors and telecommunication links and, consequently, several nodes of the grid are still not monitored and tele-controlled. At the same time, DSOs are asked to improve the network’s resilience, looking for a reduction in the frequency and impact of power outages caused by extreme weather events. The paper presents a machine learning GIS-based approach to estimate a secondary substation’s load profiles, even in those cases where monitoring sensors are not deployed. For this purpose, a large amount of data from different sources has been collected and integrated to describe secondary substation load profiles adequately. Based on real measurements of some secondary substations (medium-voltage to low-voltage interface) given by Unareti, the DSO of Milan, and georeferenced data gathered from open-source databases, unknown secondary substations load profiles are estimated. Three types of machine learning algorithms, regression tree, boosting, and random forest, as well as geographic information system (GIS) information, such as secondary substation locations, building area, types of occupants, etc., are considered to find the most effective approach.

Development of universal algorithm of voltage circuits detecting faults of microprocessor protection and automation devices

Reliability, along with response speed, sensitivity, and selectivity, is the key requirement for relay protection (RP) devices. The reliability of modern RP digital terminals is understood as protection operation for all estimated failure modes and failure of protection equipment to operate in all other modes, in which this protection is not provided. Analysis of the secondary voltage schemes and algorithms of detecting faults in these circuits reveals several disadvantages of the implementation of blocking in case of faults in voltage circuits. All existing algorithms and blocking schemes in case of faults in voltage circuits suffer from several disadvantages. In this regard, it is relevant to develop a universal relay protection terminal, which can be used with any types of voltage transformers. The MatLAB Simulink is used to simulate the primary failure of secondary circuits for the connection schemes of the voltage transformer load on phase and electric line voltages. The authors propose the algorithm that allows us to create a typical universal RP terminal, which can be used with any type of voltage transformers. To detect the neutral conductor interruption of the «star» circuits, it is proposed to create an artificial asymmetry at the input voltage circuits of the relay protection and automation (RPA) terminal and develop a group of fault detectors that analyze the position of the offset neutral on the voltage complex plane. Using a simulation model of various types of failure of voltage transformer secondary circuits and the logic diagram of the unit that implements the proposed algorithm, the authors graphically show that the detection of a break in the neutral wire is possible due to monitoring the zero-sequence voltage spike (triggering of the pulsed dU0 fault detector) with neutral displacement to the complex plane area, which is set by the setpoints. The results obtained allow us to implement a universal scheme of blocking faults in voltage circuits. This scheme does not depend on the voltage transformer secondary load connection method and exclude the disadvantages of existing solutions discussed in the article. This algorithm allows us to develop a typical universal RPA terminal. Due to its connection scheme and functional and logical implementation, this terminal can be used with any types of voltage transformer without reprogramming. Also, the proposed algorithm fully complies with the requirements of the current regulatory and legal documents.

An Optimal Non-Integer Model Predictive Virtual Inertia Control in Inverter-Based Modern AC Power Grids-Based V2G Technology

In this study, virtual inertia control-based vehicle-to-grid (V2G) concept for the secondary load frequency control of AC islanded microgrids (MGs) is presented. Since autonomous modern power grids typically have much smaller inertia in comparison to conventional grids, a very fast and high-performance control plant is necessitated for controlling reserved power plants (e.g., batteries) to overcome any voltage and frequency instability. This issue can be solved by the short-term battery energy storage system, inverter, and proper inertia control technique. Because of the high cost of the battery energy storage system, utilization of controllable loads like electric vehicle (EV) to low-inertia modern power grids is presented for the decreasing of the needed capacity of the energy storage system. Hence, an optimal non-integer model predictive control is applied for the secondary frequency regulation in low-inertia stand-alone MGs with the V2G technology. Since the performance and accuracy of the applied non-integer controller are depended on its parameters’ value, a modified heuristic optimization algorithm is proposed for tuning the controller's parameters. In the end, the validity and feasibility of the proposed method are investigated by the model-in-the-loop experimental results.

Decentralized Robust Disturbance-Observer Based LFC of Interconnected Systems

This article develops a novel decentralized controller for multi-area secondary load frequency control (LFC) of power systems. The proposed robust-adaptive approach estimates the external disturbance input and uncertainties, which are assumed to be matched with the control input. In this regard, a disturbance-observer state-feedback controller is designed. To offer a systematic approach, controller design conditions are derived in terms of linear matrix inequality constraints. Thereby, for any given representation of the LFC area, the controller gains can be straightforwardly obtained by using numerical solvers. Moreover, in order to enhance the steady-state performance, the controller is modified through the heuristic genetic algorithm. The controller design procedure is wholly offline and can be simply implemented. The developed decentralized approach does not need the information of the other areas, which reduces the cost and the number of measuring units. It is also robust against the power fluctuations of the load and renewable energy sources. To show the superiorities of the developed controller, four scenarios are considered. These scenarios comprise the aggregation of the photovoltaic, wind turbines, and electric vehicle to the power system. OPAL-RT experiments are given to verify the transient and steady-state performance and robustness of the proposed controller.