Search

Predicting the dynamic responses of planing hulls in real sea conditions is important for identifying how basic design factors influence their seakeeping performance. Hence, there is a pressing need to provide high-fidelity models for predicting the motions of these hulls in random waves, representing actual seas. In this article, a computational-based model for solving viscous fluid flow around the vessel is built to address this problem. Three different planing hulls, denoted as C, C1, and C2, each distinguished by the number of steps incorporated on their bottom surfaces (1 and 2 indicating the respective step count, with case C being the stepless hull), are modeled in a Computational Fluid Dynamics (CFD) tank, allowing for analysis of the effects of steps on dynamic responses of a planing surface operating in random waves. CFD data is compared against those collected in towing tank tests, revealing a satisfactory level of accuracy. Extreme value and gamma distributions are shown to give probabilities of maxima/minima of displacements and vertical acceleration at the center of gravity (CG) for all three hulls. It is shown that the stepless boat may be exposed to lower vertical acceleration at an early planing speed, but at higher planing speeds, a double-stepped design mitigates the vertical acceleration. Nevertheless, the double-stepped hull would experience more significant extreme heave responses across all speeds and may be exposed to less significant extreme pitch responses during the ride at the highest speed compared to the stepless and one-stepped hulls. The skewness of heave and pitch is evaluated, and it is found that the heave response tends to skew toward positive values (upward). This skewness becomes more noticeable with increasing speed but remains insensitive to wave steepness. Additionally, the pitch response at lower planing speeds shows a partial skew towards negative values (bow-down), but eventually, they may also be partially skewed towards

In recent years OpenFOAM studies have focused on pure wave modelling and wave-structure interaction. Considering that there is a lack of transparency concerning effects of different motion modelling settings in OpenFOAM, this paper presents the influence of different numerical setups on the accurate modelling of wave-induced motions. This is achieved by applying the interFoam solver included in OpenFOAM-v2206 with the waves2Foam toolbox. The optimal numerical setup is studied with a two-dimensional box-like ship idealisation heaving in varying wave lengths while the wave steepness remains constant. Different numerical setups are considered for accurate wave modelling, the modelling of wave excitation forces for the case of a static structure, and heave motion modelling. Finally, the optimal setup that is found is applied for a 3D ship case in head waves with heave and pitch coupling. As far as practically possible, the results are validated against experimental data. It is shown that strict requirements for mesh density and time step for accurate wave modelling result in accurate excitation force and motion results. Reflections from the relaxation zones and different mesh density layers cause inaccuracies. It is concluded that simple numerical cases are suitable for studying optimal numerical setups for more complex simulation cases.

This paper investigates the maneuvering characteristics of a planing hull free to move in heave and pitch directions undergoing a steady drift test. Results assess and compare predictions from Computational Fluid Dynamics (CFD) Detached Eddy Simulation (DES) and a 2D + t strip theory models against available experimental data from Katayama et al. (2005). At high yaw angles and high Froude numbers of predictions from both models marginally deviate from the experimental longitudinal force measurements. Whereas strip theory confronts difficulties in predicting dynamic trim angle and CG rise-up when either Froude number or yaw angle increases and hence nonlinear hydrodynamics prevail, CFD generally agrees well with experimental data. The CFD model is seen to result in numerical ventilation in zero-drift cases, leading to lower pressure and a localized reduction in the skin friction coefficient. These phenomena are hypothesized to contribute to the under-prediction of trim angle and longitudinal force in zero-drift scenarios. Strip theory provides less reliable results in terms of predicting the sway forces at larger yaw angles, the yaw moment at low Froude numbers and sway forces and associated maximum pressures near the stagnation line. This model cannot capture the asymmetric pressure distribution that emerges on the bottom of the hull at large speed and yaw angles, which is likely to be one of the reasons for errors in predicting the side force. Detached Eddy Simulations demonstrate the strong asymmetric vorticity field formation on the exposed side of the hull at nonzero drift angle. This means that added masses used in the 2D + t model can cause large errors in equilibrium predictions.

Theoretical models for the prediction of decay rate and dispersion process of gravity waves traveling into an integrated ice cover expanded over a long way are introduced. The term “wet beam” is chosen to refer to these models as they are developed by incorporating water-based damping and added mass forces. Presented wet beam models differ from each other according to the rheological behavior considered for the ice cover. Two-parameter viscoelastic solid models accommodating Kelvin–Voigt (KV) and Maxwell mechanisms along with a one-parameter elastic solid model are used to describe the rheological behavior of the ice layer. Quantitative comparison between the landfast ice field data and model predictions suggests that wet beam models, adopted with both KV and Maxwell mechanisms, predict the decay rate more accurately compared to a dry beam model. Furthermore, the wet beam models, adopted with both KV and Maxwell mechanisms, are found to construct decay rates of disintegrated ice fields, though they are built for a continuous ice field. Finally, it is found that wet beam models can accurately construct decay rate curves of freshwater ice, though they cannot predict the dispersion process of waves accurately. To overcome this limitation, three-parameter solid models, termed standard linear solid (SLS) mechanisms, are suggested to be used to re-formulate the dispersion relationship of wet beam models, which were seen to construct decay rates and dispersion curves of freshwater ice with an acceptable level of accuracy. Overall, the two-parameter wet beam dispersion relationships presented in this research are observed to predict decay rates and dispersion process of waves traveling into actual ice covers, though three-parameter wet beam models were seen to reconstruct the those of freshwater ice formed in a wave flume. The wet beam models presented in this research can be implemented in spectral models on a large geophysical scale.

The wake waves generated by the steady movement of a planing hull are analyzed by means of towing tank tests. Two sets of waves, including divergent and transverse waves, are identified and then analyzed. The wave period of the divergent waves is seen to decrease by the increase in speed of the vessel. These waves are seen to damp temporally. The mechanisms that lead to damping of the divergent wave were found to depend on the wave orbital Reynolds number in semi-planing regime, though that of in-planing regime is a function of the Reynolds number of the boat. The wake angle is seen to decrease with the increase in Froude number, the rate of which becomes relatively large in-planing regime. Transverse waves are captured through measurements, and it is shown that while their period is longer than those of the divergent waves, they are not noticeably damped. Throughout the spectral analysis, it is demonstrated that divergent waves reach a higher level of nonlinearity by the increase in Froude number and, hence, the wave energy is distributed over a boarder range of frequency. The height of the transverse wave is observed to become lower by the increase in speed, but as the towing speed increases, the probability density function curves of surface elevation deviate more and more from the Gaussian distribution.

A computational fluid–solid dynamic model is employed to simulate the interaction between water waves and a consolidated ice cover. The model solves the Navier–Stokes equations for the ocean-wave flow around a solid body, and the solid behavior is formalized by the Maxwell viscoelastic model. Model predictions are compared against experimental flume tests of waves interacting with viscoelastic plates. The decay rate and wave dispersion predicted by the model are shown to be in good agreement with experimental results. Furthermore, the model is scaled, by simulating the wave interaction with an actual sea ice cover formed in the ocean. The scaled decay and dispersion results are found to be still valid in full scale. It is shown that the decay rate of waves in a viscoelastic cover is proportional to the quadratic of wave frequency in long waves, whilst biquadrate for short waves. The former is likely to be a viscoelastic effect, and the latter is likely to be related to the energy damping caused by the fluid motion. Overall, the modeling approach and results of the present paper are expected to provide new insights into wave–ice interactions and help researchers to dynamically simulate similar fluid–structure interactions with high fidelity.

This paper presents CFD (Computational Fluid Dynamics) simulations of the performance of a planing hull in a calm-water condition, aiming to evaluate similarities and differences between results of different CFDmodels. The key differences between thesemodels are the ways they use to compute the turbulent flow and simulate themotion of the vessel. The planingmotion of a vessel on water leads to a strong turbulent fluid flowmotion, and themovement of the vessel fromits initial position can be relatively significant, which makes the simulation of the problem challenging. Two different frameworks including k-" and DES (Detached Eddy Simulation) methods are employed to model the turbulence behavior of the fluid motion of the air–water flow around the boat. Vertical motions of the rigid solid body in the fluid domain, which eventually converge to steady linear and angular displacements, are numerically modeled by using two approaches, including morphing and overset techniques. All simulations are performed with a similar mesh structure which allows us to evaluate the differences between results of the applied mesh motions in terms of computation of turbulent air–water flow around the vessel. Through quantitative comparisons, themorphing technique has been seen to result in smaller errors in the prediction of the running trim angle at high speeds. Numerical observations suggest that a DES model can modify the accuracy of the morphing mesh simulations in the prediction of the trim angle, especially at high-speeds. The DES model has been seen to increase the accuracy of the model in the computation of the resistance of the vessel in a high-speed operation, as well. This better level of accuracy in the prediction of resistance is a result of the calculation of the turbulent eddies emerging in the water flow in the downstream zone, which are not captured when a k-" framework is employed. The morphing approach itself can also increase the accuracy of the resistance prediction., QC 20220314

The current paper presents a simple mathematical model for replication of the transient acceleration motion of displacement hulls in calm water under the action of a propulsion system. Different empirical methods are coupled, and an operational speed problem is solved in the time domain. The resistance of the ship is calculated by using the Holtrop method. The values of thrust force, torque and propeller efficiency are computed by using B-Series empirical equations. The acceleration motion of the vessel, which is triggered as the engine starts to work, is simulated by solving a set of first-order differential equations, which are discretised in the time domain. It is shown that different propellers can lead to different transient and steady behaviours of the vessel. Finally, using a genetic algorithm library, it is demonstrated that the method can be helpful and be easily linked to the design process. Moreover, an optimisation study is performed, showing that, the developed method provides an efficient propeller, under the action of which ship reaches the maximum possible speed in the earliest possible time with the highest efficiency for the propeller. The current method can be useful in the mathematical reproduction of the ship-propeller-engine, which needed to be modified in future., QC 20220331

The launch of lifeboats is commonly completed through freefall dropping from a considerable height, where the lifeboat is released from an inclined skid so that it can obtain a forward speed after being launched. The drop is followed by a water entry process that can induce high impact forces on the hull, which gives a significant risk of structural damages. Ascertaining the water entry impact is therefore a key step of lifeboat design; however, conventional methods have linear assumptions and assess the water impact following a quasi-static manner, which causes these methods to be not fully accurate and ignore some important details. To address this gap, this work developed a model based on Computational Fluid Dynamics to holistically simulate and analyse the process. An overset mesh technique was incorporated to reproduce the entire series of drop, water entry and resurfacing, in which the pressure distribution on the whole hull was obtained and recorded with a sampling frequency of 1000 Hz to ensure the peak impacts can be captured. Full-scale measurements were used to confirm the accuracy of the present computational model. Subsequently, a systematic series of simulations were performed to investigate how the water entry process is influenced by the inclined angle and height at which the lifeboat is dropped. The results show that a higher dropping angle can reduce the pressure impacts, but the dropping angle also dictates the lifeboat's motion pattern during the water entry. It was demonstrated that the best dropping angle is around 70° for the investigated case, since an either too low or too high dropping angle would cause the lifeboat to appear in an undesirable after-launch status. This indicates the great importance to assess the optimal dropping angle for every potential freefall lifeboat launch, and the present work proved an effective approach to perform the task., QC 20220314

Roll motion of a planing hull can be easily triggered at high speeds, causing a significant change in hydrodynamic pressure pattern, which can threaten the stability of the vessel. Modeling and investigating roll motion of a planing vessel may require a strong coupling between motions in vertical and transverse planes. In the present paper, we have used a mathematical model to analyze the roll of a planing hull by coupling surge, heave, pitch, and roll motions using 2D+T theory to study the effects of roll-induced vertical motions on roll coefficients and response. Mathematically computed forces and moments as well as roll dynamic response of the vessel are seen to be in fair quantitative agreement with experimentally measured values of previously published data. Using the 2D+T method, it has been shown that to model the roll of a planing hull at high speeds, we need to consider the effects of heave, pitch, and surge motions. Through our mathematical modeling, it is found that freedom in vertical motions increases time-dependent roll damping and added mass coefficients, especially at early planing speeds. The results of dynamic response simulations suggest that freedom in the vertical plane can decrease the roll response., QC 20211213

The aim of this review is to provide insights into the upstream processing of microalgae, and to highlight the advantages of each step. This review discusses the most important steps of the upstream processing in microalgae research such as cultivation modes, photobioreactors design, preparation of culture medium, control of environmental factors, supply of microalgae seeds and monitoring of microalgal growth. An extensive list of bioreactors and their working volumes used, elemental composition of some well-known formulated cultivation media, different types of wastewater used for microalgal cultivation and environmental variables studied in microalgae research has been compiled in this review from the vast literature. This review also highlights existing challenges and knowledge gaps in upstream processing of microalgae and future research needs are suggested.

The aim of this review is to provide insights into the upstream processing of microalgae, and to highlight the advantages of each step. This review discusses the most important steps of the upstream processing in microalgae research such as cultivation modes, photobioreactors design, preparation of culture medium, control of environmental factors, supply of microalgae seeds and monitoring of microalgal growth. An extensive list of bioreactors and their working volumes used, elemental composition of some well-known formulated cultivation media, different types of wastewater used for microalgal cultivation and environmental variables studied in microalgae research has been compiled in this review from the vast literature. This review also highlights existing challenges and knowledge gaps in upstream processing of microalgae and future research needs are suggested.

The emergence of smart sensors has had a significant impact on the utility industry. In particular, it has made the planning and implementation of demand-side management (DSM) programmes easier. Nevertheless, for various reasons, some users may not implement smart meters for load monitoring. This paper addresses such cases, particularly large-scale industrial users, which, despite heavy electrical loads coming from many different processes, implement only simple energy measuring equipment for billing purposes. This necessitates the utilisation of novel methodologies for load disaggregation, often referred to as nonintrusive load monitoring (NILM). The availability of such tools can create multifold benefits for industrial park management, utility service providers, regulators, and policymakers. Here, we introduce an optimisation algorithm for nonintrusive load disaggregation that is low-cost, speedy, and acceptably accurate. As a case study, we used real network data of three industrial sectors: food processing, stonecutting, and glassmaking. For all cases, the optimisation framework developed a desegregated profile and estimated the load with an error of less than 5%. For non-workdays, given the higher uncertainty for the continuity of different processes, the estimation error was higher but still in an acceptable range of around 3.63–15.09% with an average of 8.10%.

In the current paper, we have developed a method, based on 2D+T theory, to model the performance of doubled-stepped planing hulls in asymmetric conditions. We have performed Computational Fluid Dynamics (CFD) simulations to evaluate the difference between the results of the 2D+T method and CFD. We have validated 2D+T and CFD simulations. The quantitative comparison between the results of both methods shows they predict almost similar heeling moment, resistance and trim angle for a doubled-stepped planing hull. Results of non-stepped and doubled-stepped planing hulls are compared against each other, demonstrating that an increase in heel angle has less influence on the performance of the doubled-stepped planing hull. The heeling moment of a double-stepped planing hull is found to be smaller than a heeling moment of a non-stepped planing hull at early planing speeds, but, by the increase in speed, heeling moment of doubled-stepped planing hulls becomes slightly larger., QC 20220321

Laboratory measurements are performed to find the performance in calm water of a planing hull with two swept steps. Furthermore, a mathematical model, based on the 2D+T theory, is adapted to provide a fast and accurate simulation for performance prediction of this craft. The trim angle of the vessel is seen to reach to two peaks, one in pre-planing and on in the early planing speed, then converges to a small value around 2 degrees. A small wetted area is seen to appear near the chine of the middle body of the vessel at early planing speed. Laboratory measurements and mathematical computations are seen to be in good agreement, especially at very high-speeds. Overall, the mathematical model is found to be a useful tool for performance prediction of boats with swept steps, which can have different, but better performance in comparison with stepless and boats with transverse steps., QC 20220321

Reducing vertical motions of high-speed planing hulls in rough water is one of the most important factors that help a boat to becomemore operable, andwill benefit the structure of the boat and the crew on board. In the recent decade, stepped planing hulls have been investigated with emphasis on their better performance in calm water than that of nonstepped planing hulls. However, there are still doubts about their performance in rough water. In this study, we investigate this problem by providing numerical simulations for motions of a double-stepped and a non-stepped planing hull in a vertical plane when they encounter head waves. The problem will be solved using the finite volume method and volume of fluidmethod. To this end, anumerical computational fluid dynamics code (STARCCM1) has been used. Accuracy of the numerical simulations is evaluated by comparing their outcome with available experimental data. The dynamic response of the investigated hulls has been numerically modeled for two different wave lengths, one of which is smaller than the boat length and the other which is larger than the boat length. Using the numerical simulations, heave and pitch motions as well as vertical acceleration are found. It has been found that at wave lengths larger than the boat length, heave amplitude decreases by 10-40%when twosteps are added to the bottom of a vessel. It has also been observed that pitch of a planing hull is reduced by 18-32% in the presence of the two steps on its bottom. Finally, it has been observed that forwave lengths larger than the boat length, the maximum vertical acceleration decreases by a gravitational acceleration of about .2-.7., QC 20220316

Stepped planing hulls have the potential to reach high-speeds in the sea. The step on the bottom of these vessels influence the pressure distribution and thus stability of the vessel, especially in transverse plane. Understanding the behavior of these vessels in a non-zero heel condition is fundamental in the early stage design. In the current paper, numerical simulation of the viscous flow field around a heeled one-stepped planing hull is performed to evaluate influences of the asymmetric planing on the performance of the vessel. The numerical model is validated in two steps. At the first step, performance of a heeled stepless planing hull operating in calm water is simulated using the numerical model, and the computed data are compared against experimental data. At the second step, the numerical model is used to compute resisatnce anad running attitudes of a one-stepped planing hull in symmetric condition, and the obtained results are compared against experimental measurements. Numerically computed results are in good quantitative agreement with laboratory measurements, showing that the numerical model has reasonable accuracy. On the whole, it has been found that a heeled condition manages a one-stepped vessel to settle at a smaller trim angle. But, unlike stepless boats, large heel angles have less effects on the trim angle at high-speeds since significant negative pressure is caused behind the step by the air, triggering negative pitching moment. It is shown that the resistance of a one-stepped planing hull is increased up to 25% at most of speeds and heel angles when the vessel advances in asymmetric condition. Moreover, this study shows that, the heeling moment of a one-stepped vessel decreases as the speed increases. The extent of reduction in the heeling moment gets more significant by the increase in heel angle at high-speeds, and, as a result, the heeling moment required to keep the vessel at large heel angle is observed to converge to the heeling moment c, QC 20220315

Categorized as one of high-speed marine vehicles, stepped planing hulls have the potential to reach relatively high speed in the sea by decreasing wetted surface. There were and still are some challenges in modeling of these vessels and design of ideal situation of steps. In the current study, a numerical-based method has been used to provide understanding about the effect of step height and its location on hydrodynamic characteristics of double-stepped planing plates. At the first step, one-stepped planing plate is numerically simulated. Results are compared against exiting numerical data, suggesting that results of the current numerical simulation are similar to results of previous numerical simulations. Then, double-stepped planing plates are modeled and pressure distribution, wetted length, free surface elevation and drag over lift ratio are computed. It is seen that, ventilation length behind the step and pressure coefficient are increased when step height of one- and a double-stepped planing plates are increased. It has been shown that, unlike an one-stepped planing plate, drag coefficient of a double-stepped planing plate can be increased when the step height is increased. The effects of the location of the second step on the performance of the planing plate have been explored, showing that this position plays a critical role on hydrodynamic forces. It is demonstrated that when the smallest possible lift force is produced by the middle-body, the plate shows the best performance (highest lift over drag ratio)., QC 20220318

The unsteady planing motion in waves is a complicated problem, that can lead to uncomfortable riding situation and structural damages due to large wave-induced dynamic responses and vertical accelerations. In the current research, this problem is investigated using different approaches, including towing tank tests, Computational Fluid Dynamics (CFD), and the 2D + t model. Results obtained from all three approaches are compared against each other in details. The spectral analysis shows that all motions can be nonlinear, but CFD and 2D + t model may predict weaker nonlinear behaviour at higher speed, especially for the case of vertical accelerations corresponding to longer waves. Interestingly, the vertical acceleration found by 2D + t model is seen to be under-predicted at moderate and long wavelengths and to be over-predicted at short waves. The values of sectional forces found by 2D + t model were compared against CFD results, showing that, while the 2D + t model computes smaller sectional forces, it can also compute negative sectional forces near the bow of the vessel at short waves when the boat exits the water. The emergence of negative sectional forces is likely to be the reason why the 2D + t model over-predicts the vertical acceleration in short waves., QC 20220317

Numerical simulations are performed to study the interaction between propeller and hull for two planing vessels: a hard-chine and a tunnelled craft. The numerical model used for reproduction of the problem is validated by comparing the obtained results against published data, showing that a morphing technique is more reliable compared to an overset one. It is demonstrated that propellers strongly affect the performance of a vessel by increasing trim angle and decreasing resistance, which are caused by a noticeable pressure reduction occurring near propellers. These changes are more significant for the case of a tunnelled hull since hydrodynamic pressure acting on the bottom of this vessel is larger compared to a hard-chine craft. While resistance of hulls is seen to be influenced by variation in the position of the propellers at early-planing mode, trim angle is seen to be insensitive to the position of propellers at all speeds., QC 20220324