Surge Load Research Articles

A comparison of extreme mooring loads and response of a spar-buoy wind turbine using conditional waves

Three-hour random sea-state evaluations for ultimate limit state design of floating offshore wind installations are time-consuming and prevent the use of high-fidelity numerical methods from being implemented. In this work, three conditional waves, Most-Likely Wave (MLW), Most-Likely Response Wave (MLRW) and Conditional Random Response Wave (CRRW), are experimentally investigated as alternative means to generate statistical extreme responses in surge and mooring line loads of a spar-buoy substructure, with shorter time-series duration compared to a 3-hour JONSWAP sea-state. MLW and MLRW are found to generate the greatest mooring line loads, far greater than the statistical expected maximum from a 3-hour random sea-state. However, MLW is uncorrelated with the substructure’s linear transfer function of response, and the MLRW includes no memory effects from a random background sea, indicating possible conservatism in the associated load magnitudes. CRRW is a MLRW embedded within a random background and is found to excite a similar mooring load as the 3-hour sea-state, with memory effects included. CRRW could thus be an appropriate method of generating statistically appropriate load responses within a reduced time-series. However, nonlinear effects on the mooring are not accounted for in any of the methods and will be included in future work.

Extensive analysis of PCM-based heat sink with different fin arrangements under varying load conditions and variable aspect ratio

The present study compares a modified variable height fin heat sink with the conventional constant height fin heat sink. The two heat sinks are filled with an equal volume of PCM (n-eicosane) and a fin volume fraction of 8 %. The experiments are performed for constant loads and also different power surge conditions. The pulsed heat loads are applied for two scenarios: 1. Constant load 4 W - power surge and constant load 4 W - power surge - 1800 s no-load condition, and 2. Power surge (50 s, 100 s, and 150 s) - no-load conditions of 1800 s. During experiments, the proposed variable height fin heat sinks possess better thermal performance for all load scenarios. Further, a 3D computational model is developed using ANSYS Fluent 19 to assess not only the effect of fin arrangement for different aspect ratios but also the impact of fin shape. The enclosure aspect ratio employed for the given study ranges from 0.3 to 0.8 for both the heat sinks. Regarding the fin structure in a heat sink, four types of fin shapes are adopted: square, circular, diamond, and triangular. The contour images of temperature and the liquid fraction are shown for the charging process. For the discharging process, the time required for the heat sinks to completely solidify the PCM is discussed. From the outcomes, variable height fin heat sinks provide enhanced melting/solidification for all the aspect ratios and fin shapes considered. As the aspect ratio increases, the time difference between the heat sink for the completion of the discharging cycle is reduced. Moreover, the triangular shaped fin shows a higher enhancement percentage of 2.29 % and 1.43 % during melting and 6.25 % and 12.5 % during solidification for both the heat sinks, respectively.

Experimental hydrodynamic assessment of a cylindrical-type floating solar system exposed to waves

In this paper, an experimental investigation on the wave loads and structural motions of two semi-fixed semi-immersed horizontal cylinders type rafts in the free surface zone is conducted. The physical models are tested at the 1:4.5 scale and exposed to a range of regular and irregular waves in a wave flume at Queen's University Belfast. The physical models and experimental setup are discussed alongside an investigation of the hydrodynamic phenomena, surge forces, and dynamic responses that each structure exhibits in the coastal wave climates. Furthermore, an investigation into the wave attenuation by both models is carried out. The results show that the surge forces have a positive correlation with wave steepness for both models. Hydrodynamic phenomena such as wave runup and overtopping, radiative damping and reflected waves, constructive interference, diffraction and flow separation were identified during the experiments. A negative mean heave displacement is observed during the monochromatic sea states which could result in impact loading and submergence of the superstructure components and photovoltaic panels at full-scale. The results presented in this paper may be used to calibrate and verify numerical models that calculate the global responses and hydrodynamic forces. It may also benefit the design processes of geometrically similar floating solar technologies by providing data on surge loads, motion responses and hydrodynamic observations.

Estimating hurricane-induced vertical surge and wave loads on elevated coastal buildings based on CFD simulations and ensemble learning

This study focuses on developing Machine Learning models based on CFD simulations to estimate hurricane induced vertical wave and surge forces on elevated coastal buildings caused by regular waves. In particular, this study aims at addressing the existing gap in designing elevated coastal buildings, which stems from lack of a generalizable equation for estimating vertical hurricane wave and surge forces for a variety of building geometries and wave conditions. To this end, based on a validated Computational Fluid Dynamics (CFD) model, six key variables that affect the wave forces on buildings are considered, which include building dimensions (length and width of rectangular plan buildings) and wave characteristics. In addition, the effect of building length in relation to wave length on the resulting vertical forces is explicitly considered, while the effect of building width is considered implicitly. Subsequently, a Latin Hypercube Sampling (LHS) strategy is implemented for generating 256 random samples, each representing a unique building geometry with a rectangular plan and wave condition scenario. A pipeline is then developed for generating CFD models corresponding to each sample, which are then deployed on a high-performance computing (HPC) cluster, creating a dataset of vertical surge and wave forces. Based on the key design variables, an ensemble of Machine Learning (ML) models is developed to predict vertical wave forces. For the purpose of design and risk assessment, different force levels may be of interest. Therefore, different models were trained to predict multiple levels of forces on elevated buildings, including maximum, average, 25th, 75th, and 99th percentiles of peak forces. The developed model for each of these force levels is then investigated to identify the main building geometry and wave conditions features that affect the resulting forces, which can inform the decisions of the designers in the early-stage phases. For further assistance in the early-stage design, based on a subset of identified important features, a simple expression for each force level is provided to narrow down the design space to top performing early design candidates, while the main estimators can be used for the final design of elevated buildings. Results show that based on CFD simulations, highly accurate and generalizable predictive models with error rates of about 4% on the test set can be developed.

Comparison of different fidelity hydrodynamic-aerodynamic coupled simulation code on the 10 MW semi-submersible type floating offshore wind turbine

This study aimed to analyze and examine the precision of a middle-fidelity simulation tool by performing load analysis using CFD and middle-fidelity analysis tools. The analysis was performed on a fully coupled system including turbine, platform, and mooring system under the severe operating state. Grid sensitivity tests were performed on the turbine and floater to increase the precision of CFD results. The results showed that the mid-fidelity analysis tool had a high error rate in surge and pitch load responses due to failure in considering the current load caused by wind. Moreover, potential flow-based analysis tools can be less accurate for complex-shaped structures such as the rectangular pontoon used in this study. To determine the extent to which the viscosity effect, dependent on the wet body shape, affects the accuracy of the results, this study compared the accuracy of potential flow-based analysis tools and CFD. This study contributes to the development of research in this field by providing new insights and undiscovered results for analyzing a FOWT with an unstructured shape.

Performance Comparison of Electric Drives for Chopping/Shredding Sugarcane in Sugar Industry

A performance comparison of the conventional slip ring induction motor (SRIM) drive and the recently inducted variable frequency drive (VFD) in the sugar industry, for sugarcane preparation (chopping/ shredding of sugarcane), is carried out to assess their effectiveness and to explore better electric drives for the application. These high inertial machines demand high starting torque and mitigating means to reduce surge load due to the impact load imposed on them. Though, both the drives meet the requirement but the SRIM drives are subjected to huge slip power loss, low power factor, unequal load sharing problem for coupled motors and high drop in rpm, whereas VFDs are subjected to the problems of input current harmonics, high dV/dt stress and common-mode voltage (CMV). In this paper, along with the performance comparison a three/four-level multilevel inverter (MLI) fed open-end winding induction motor (OEWIM) drive is also proposed as an improvement over the existing ones.

Accelerated second-order hydrodynamic load calculation on semi-submersible floaters

A rapid method for calculation of second-order hydrodynamic wave loads on semi-submersible platforms is developed and validated against radiation–diffraction theory. The method is based on slender-body theory and builds on modal truncation of the quadratic transfer function (QTF). The semi-submersible floater is split into individual members and the existing theory for vertical cylindrical columns is extended to include the heave force. Further expressions for the surge, heave and pitch load on the horizontal pontoons are derived and implemented. The accuracy of the method is assessed by comparison to radiation–diffraction results using the Pinkster approximation. We find that the slender-body approximation for the column surge force is most accurate for small values of the diameter-to-draft ratio. For the three sea states considered, this error is below 10% for diameter-to-draft ratios less than 0.2.Error analysis is provided for the column heave and pitch and the pontoon loads. For all members, application of 128 modes in the QTF approximation is found sufficient to accurately represent the full slender-body QTF solution.Next, the first- and second-order loads on the full floater under different sea state conditions are compared to radiation–diffraction theory. With 128 modes, the second-order loads are obtained 2500 times faster than with conventional approaches with error levels of 22% for surge, 10% for pitch and zero error for heave. The surge error is discussed and linked to the small draft of the columns. The numerical efficiency of the method allows the consideration of second-order loads in the first stages of the design and optimisation of semi-submersible floaters.

Influence on Structural Loading of a Wave Energy Converter by Controlling Variable-Geometry Components and the Power Take-Off

AbstractOceans are harsh environments and can impose significant loads on deployed structures. A wave energy converter (WEC) should be designed to maximize the energy absorbed while ensuring the operating wave condition does not exceed the failure limits of the device itself. Therefore, the loads endured by the support structure are a design constraint for the system. Furthermore, the WEC should be adaptable to different sea states. This work uses a WEC-Sim model of a variable-geometry oscillating wave energy converter (VGOSWEC) mounted on a support structure simulated under different wave scenarios. A VGOSWEC resembles a paddle pitching about a fixed hinge perpendicular to the incoming wave fronts. The geometry of the VGOSWEC is varied by opening a series of controllable flaps on the pitching paddle when the structure experiences threshold loads. It is hypothesized that opening the flaps should result in load shedding at the base of the support structure by reducing the moments about the hinge axis. This work compares the hydrodynamic coefficients, natural periods, and response amplitude operators from completely closed to completely open configurations of the controllable flaps. This work shows that the completely open configuration can reduce the pitch and surge loads on the base of the support structure by as much as 80%. Increased loads at the structure’s natural period can be mitigated by an axial power take-off damping acting as an additional design parameter to control the loads at the WEC’s support structure.

Modeling and Analysis of Offshore Gangway under Dynamic Load

The safety transfer on the sea is threatened by wind, wave and surge loads. An offshore gangway ensures smooth and safe transfer by compensating the ship’s motion. In a mixed offshore gangway system, the transfer gangway is a huge asymmetric load on top of the stable platform, and the displacement of its center of gravity causes it to exert a large dynamic load on the stable platform. A dynamic model of the offshore gangway under dynamic load is established in this work. The Lagrange equation is used to establish the dynamic model of the transfer gangway; the equivalent center of gravity method is used to visualize its dynamic load. The dynamic of the stable platform is modeled by the virtual work principle. Finally, the accuracy of the mathematical model was verified by the joint simulation. Simulation results indicate that under the influence of dynamic load, the tractive force of the second drive support chain is 2–3 times greater than the tractive force of the first and third drive support chains. With the same excitation, the tractive force of the second drive support chain is 2.83 times higher than that under the static load.

Energy saving slot allocation-based multicast routing in cloud wireless mesh network

Many techniques of cloud computing are affected by surge load and time issues. This proposed method for virtual cloud planning utilise simple protocols in a single or multiple data centres. A new load balanced amortised multi-scheduling algorithm (LBAM) is proposed for assigning the task to cloud based on active load in the cloud environment. The proposed system calculates the multiple attribute weight for each workplace and introduces an application source that changes in application virtualisation environment. The system calculates the cloud data weight based upon the allocation of data and its consequence based on the processing efficiency of the cloud machine. This approach works effectively in most configurations, also virtual machines hold the ability to process load with high pace and efficient memory management. A detailed comparative analysis is made with the existing methods namely SLA, FPGGA and DJS algorithms. The obtained results indicated that the LBAM model is superior to compared methods under several aspects.

A Computational Method of Rotating Stall and Surge Transients in Axial Compressor

The onset of rotating stall and surge in compressors limits the operating range of aero-engines. Accurately predicting the key features during these events is critical in the engine design process. In this paper, a three-dimensional computational model for transient simulation of multi-stage axial compressors during stall is proposed. The kinetic equations describing the dynamic process of the compression system are constructed, with a 3D through-flow model for the compression part and a 1D gas collector model for the outlet part. The calculation of the source term is performed using the developed body-force model, which realizes the correlation between the deviation angle and the loss coefficient with the inlet parameters in various flow regions. Validated on a single-stage compressor and a single-rotor fan, the results show that the method is capable of capturing the stall and surge features correctly and that the three-dimensional structure of the stall cell can be captured. In addition, this model could be used for the analysis of the surge load, which is significant for the structural integrity of the compressor.

Performance Analysis of Hybrid Ultra Capacitor (HUC) based Solar Microgrid for Household Applications

Localised power generation and consumption using a solar-based hybrid micro-grid system are gaining predominance in remote locations where conventional transmission of power from far off substations work out to be uneconomical. Since the peak irradiance from the sun lasts for 4-6 hours per day, a hybrid micro-grid with batteries for storing energy is usually adopted. This study considered a typical household load of 3kW comprising resistive and inductive loads. Sudden surges will be caused by switching ON/OFF of any load, and in particular, switching ON of inductive loads (such as fans, washing machines and mixer) will further contribute to transients. These sudden changes in loads harm the cyclic life of the battery. A viable solution to overcome the above problem is to use Hybrid Ultra Capacitors (HUC) as an assistant to the Batteries. These HUC banks can take over the surge loads, whereas Batteries can focus on delivering steady power. Such a combination has the potential to enhance the battery’s life. This study discusses the performance of Hybrid Ultra Capacitor (HUC) based Hybrid Energy Storage System (HESS) in a 3kW Solar MicrogriAU: Please prod system by evaluating the electrical parameters involving experiments with different loads.

OC6 phase I: Improvements to the OpenFAST predictions of nonlinear, low-frequency responses of a floating offshore wind turbine platform

In the OC5 and OC62 projects, the authors observed a persistent underprediction of the nonlinear, low-frequency responses of an offshore wind semisubmersible with many mid-fidelity engineering models, including the OpenFAST tool developed by the National Renewable Energy Laboratory. Both the low-frequency wave excitation in surge and pitch and the resulting resonance motions were severely underpredicted. In response, we developed several modifications to the OpenFAST model from the OC5/6 projects to improve the predictions of the low-frequency wave loads and responses. All modifications are in the modeling of the viscous drag forces. Efforts were made to provide physical justifications to the changes and to limit the number of additional parameters requiring tuning, so that the modified model can be applied to other floating wind systems. With the proposed modifications, the predictions of the low-frequency surge and pitch wave loads on a fixed floater and the resonance responses of a floating structure are both significantly improved with a single set of model coefficients, which leads to good agreement with the measurements from the OC6 wave-basin experimental campaign.

Parameterized coastal fragilities and their application to aging port structures subjected to surge and wave

This study proposes a methodology for the development of parameterized fragility models for open type port structures subjected to hurricane-induced storm surge and wave loading, while also considering the potential influences of time-dependent aging and deterioration. The proposed framework uses a simulation-based strategy to propagate uncertainty in loads, geometrical configurations, material properties and capacities associated with different exposure conditions and failure modes (i.e. uplift, flexure, shear). Alternative classification-type statistical learning methods are tested to derive parameterized fragility models for each failure mode in order to evaluate limit state exceedance probability given a vector of deterministic or probabilistic parameters that define the structure and exposure conditions. Such parameterized coastal fragility models enable rapid application to a portfolio of aging port structures to explore the impact of current and future storm conditions, as illustrated via case study application for two terminals located in the Houston Ship Channel. The results reveal the dominant failure mode, spatial distribution of failure probabilities for structures within and across terminals, and influence of aging on surge and wave vulnerability of port structures.

Physical modelling of tsunami barrier and debris interaction

Tsunami events can cause vast damage to infrastructure and human lives. A self-lifting membrane barrier was proposed to limit impacts of tsunami inundation during an event while allowing permanent access to the sea. Many aspects of this novel barrier concept have not been studied yet, including its performance under debris impact. In this context, this study investigates the interaction between a self-lifting membrane barrier and tsunami-induced debris transport. Laboratory experiments in a wave flume were carried out, in which 20 ft shipping-container models were propagated by tsunami-like waves into a model membrane barrier. Varying hydrodynamic boundary conditions and amount of debris were used to study different magnitudes of surge and debris loading. The tests showed that an increased amount of debris led to decreased surge propagation upstream the barrier. Formation of a temporally stable debris dam was prevented by the dynamic character of the barrier-debris-interaction. In total, 90% of debris transport further in land was obstructed in presence of the studied membrane barrier. The self-lifting membrane barrier retains functionality under debris-loaded surge impact.

Focused wave interactions with floating structures: a blind comparative study

The paper presents results from the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI) Blind Test Series 2. Without prior access to the physical data, participants, with numerical methods ranging from low-fidelity linear models to fully non-linear Navier–Stokes (NS) solvers, simulate the interaction between focused wave events and two separate, taut-moored, floating structures: a hemispherical-bottomed cylinder and a cylinder with a moonpool. The ‘blind’ numerical predictions for heave, surge, pitch and mooring load, are compared against physical measurements. Dynamic time warping is used to quantify the predictive capability of participating methods. In general, NS solvers and hybrid methods give more accurate predictions; however, heave amplitude is predicted reasonably well by all methods; and a WEC-Sim implementation, with CFD-informed viscous terms, demonstrates comparable predictive capability to even the stronger NS solvers. Large variations in the solutions are observed (even among similar methods), highlighting a need for standardisation in the numerical modelling of WSI problems.

Hybrid Energy Storage System Based on a Novel Reduced Rating Multi-Input Converter

Batteries are assisted by supercapacitors (SC) to supply the surge power requirement of the loads, which can be much larger than the steady-state power and severely deteriorate the battery life. A novel multi-input converter (MIC) is proposed in this article for interfacing a battery–SC combination, also known as hybrid energy storage system (HESS) that reduces the required converter rating to meet the surge power needs of the load. In a conventional active HESS, individual interfacing converters are used, where generally, the SC supplies the complete surge power. Therefore, the SC converter is mostly rated for the full surge power, which leads to a costly system. In the proposed converter, the SC is connected to the load through a series-connected converter during surge loading, which reduces the required converter power rating and ensures the SC utilization over a wide voltage range. Under normal loading conditions, the battery is operated in current control mode such that the battery current does not experience a sudden rise in case of load changes, which enhances its life. The load voltage is controlled by the SC. The operation of the proposed converter is validated under normal, surge, and negative loading through experiments on a lab prototype.

Parameterized fragility models for multi-bridge classes subjected to hurricane loads

Past hurricanes in the United States have highlighted the structural vulnerability of bridges exposed to storm surge and wave loads, triggering the development of fragility models. These models are essential for estimating the likelihood of structural failures in bridges during extreme events to support risk mitigation and resilience enhancement. However, the literature still lacks fragility models that can accommodate the effects of spatial variability of surge and wave loads and bridge characteristics like superstructure type and span slope. In addition, the presence of different types of superstructure within the same bridge necessitates the development of fragility models which can handle such variations. In this light, first, this study develops fragility models for individual spans of different bridge classes (concrete girder, steel girder, slab, box girder) considering spatial variability of wave loads and variations in structural characteristics. Herein, nonlinear dynamic analyses are employed for calculating the structural response and stepwise logistic regression is used for deriving the predictive fragility models. Then, a bridge system fragility assessment framework is proposed for system reliability assessment of the entire bridge, which accounts for different types of superstructures within the bridge and partially correlated span failures. In order to demonstrate the application of the fragility models and the system fragility assessment framework for regional level risk mitigation, the performance of bridges in the Houston-Galveston region is evaluated for two storm scenarios. The results show that the system failure probability obtained using no correlated span failure assumption is close to the actual failure probability obtained using the proposed approach highlighting the effects of correlations (or the lack of) on the system fragility.

Correction to: Street-scale storm surge load impact assessment using fine-resolution numerical modelling: a case study from Nemuro, Japan

Correction to: Street-scale storm surge load impact assessment using fine-resolution numerical modelling: a case study from Nemuro, Japan

Street-scale storm surge load impact assessment using fine-resolution numerical modelling: a case study from Nemuro, Japan

Due to gradual sea level rise and changes in the climate system, coastal vulnerability to storm surge hazards is expected to increase in some areas. Studies regarding the effect of storm surge inundation on buildings and human lives, especially when it comes to relatively low-threat level events, have been few, however. In this research, storm surge load impact around coastal residential areas was quantitatively assessed, through fine-resolution numerical modelling. Meso- and street-scale simulation results for a storm surge event in Nemuro, Japan, were comprehensively validated against observations and field measurements, and the simulation results showed good accuracy for sea level, significant wave height and inundation area. A fine-resolution, street-scale coastal flood simulation was carried out with individual and grouped buildings, created with a building block model, and the results showed the significant role of buildings by realistically capturing inundation dynamics. Hydrodynamic results showed that coastal flood impact on buildings was insignificant (consistent with surveys). Lastly, the potential flood impact on people in the streets was investigated, using five human instability equations, where the most pessimistic results showed average values between 0.0 and 0.2 (max 0.6–0.7), and slightly below 0.4 for children and the elderly, respectively. These values indicated that threat levels during the Nemuro storm event were low, which corresponded with observations (no fatalities). This study framework could be applied wherever an accurate local storm surge threat estimate was required.