Surface Effect Ship Research Articles

Analytical and experimental studies on dynamic response of a SES air cushion plenum experiencing forced oscillation

In this study, a series of experiments is conducted in which a plenum experiences forced oscillation. The oscillating system is driven by a periodic force arising from regular volumetric fluctuations analogous to fixed-height water waves entering a surface-effect ship (SES) plenum below a heave deck. An analytical study is then conducted in which a MATLAB Simulink model is created to incorporate the same parameters taken into account during the experiments. The results of both the experiments and the simulation demonstrated that as the frequency associated with the plenum volume's forced oscillations approaches the natural frequency of the mass/plenum system, the vibration magnitude of the heave deck increases as predicted. Resonance is observed in vibrations of the heave deck. The mean hover height of the heave deck increases predictably and remains high at higher frequencies when the forced oscillations' frequency approaches the natural frequency of the mass/plenum system. Higher frequency oscillations lead to air accumulation in the plenum. Since there was a significant difference between the experimentally-measured (and simulated) natural frequency and the theoretical natural frequency of a similar, but rigid-walled plenum, it appeared that the natural frequency of the heave deck above the plenum is reduced by the flexibility of the seals and water surface under a SES.

Nonlinear air dynamics of a surface effect ship in small-amplitude waves

In many existing works, the seakeeping motions and air dynamics of a surface effect ship (SES) were assumed to be linear under small-amplitude waves (wave amplitude to wave length ratio ≤ 5%) to enhance the computational efficiency. However, according to SES model test results, it was found that even in small-amplitude waves, the fluctuating air cushion pressure shows significantly nonlinear effects. To precisely reveal this distinctive feature, the origin of nonlinearity was carefully investigated and the air leakage was considered as the main source of nonlinearity based on mathematical analysis in this paper. The reason is that the variance of clearance height under seals is comparable to the clearance height at equilibrium state in small-amplitude waves, which makes the air leakage area intermittently equal to zero without any harmonic variance. Therefore, an efficient partial nonlinear numerical model for the SES dynamics was proposed by combining a linear frequency-domain hydrodynamic model based on the efficient 2.5D methods with a nonlinear time-domain air dynamic model. The nonlinear parts of numerical results from the partial nonlinear model, including the fluctuating air pressure and midship accelerations, agree well with experimental results. The results demonstrate the effectiveness of the partial nonlinear model on the SES seakeeping performance prediction, and confirm that its nonlinearity mainly originates from the air leakage.

Analysing the effectiveness of different offshore maintenance base options for floating wind farms

Abstract. With the growth of the floating wind industry, new operation and maintenance (O&M) research has emerged evaluating tow-to-port strategies (Offshore Wind Innovation Hub, 2020), but limited work has been done on analysing other logistical strategies for offshore floating wind farms. In particular, what logistical solutions are the best for farms located far offshore that cannot be reached by crew transfer vessels (CTVs)? Previous studies have looked at the use of surface effect ships (SES) and CTVs during the operation and maintenance (O&M) of bottom-fixed wind farms, but only some of them included service operation vessels (SOVs). This study analyses two strategies that could be used for floating wind farms located far from shore using ORE Catapult's in-house O&M simulation tool. One strategy comprises of having a SOV performing most of the maintenance on the wind farm, and the other strategy uses an offshore maintenance base (OMB) instead, which would be located next to the offshore substation and would accommodate three CTVs. This paper provides an overview of the tool and the inputs used to run it, including failure rates of floating wind turbine subsea components and their replacement costs. In total six types of simulations were run with two strategies, two different weather limits for CTVs and two weather datasets ERA5 and ERA-20C. The results of this study show that the operational expenditure (OPEX) costs for the strategy with an OMB are 5 %–8 % (depending on the inputs) lower than with SOV, but if capital expenditure (CAPEX) costs are included in the analysis and the net present value (NPV) is taken into account then the fixed costs associated with building the offshore maintenance base have a significant impact on selecting a preferred strategy. It was found that for the case study presented in this paper the OMB would have to share the foundation with a substation in order to be cost competitive with the SOV strategy.

Analytical and numerical investigation of the lift system stability of the air cushion vehicle fitted with closed inflated side seals

An air cushion vehicle (ACV) with inflated side seals is a promising new type of air cushion supported vessels. These vehicles combine good amphibious abilities of conventional air cushion vehicles with seakeeping and maneuverability qualities pertinent to Surface Effect Ships (SES).One of the most important design concerns for the ACV with inflated side seals is eliminating vertical resonant oscillations of the vessel. These oscillations are caused by the unstable interaction between the air cushion and the inflated side seals.In this paper two mathematical models are derived to investigate the stability of an ACV with inflated side seals. The only difference between these models is that one of them takes into account the heave degree of freedom while the other one neglects it. It turns out that the simplified approach tends to underestimate the decrement of the oscillations compared to the full model. The analytical conditions of the lift system stability are derived from the simplified model.The developed models are applied to investigate the stability of the three ACVs with inflated side seals. The difficulties associated with scaling of the stability characteristics from the model tests are discussed.

Vertical Wedge Drop Experiments as a Model for Slamming

_ A deeper comprehension of hydrodynamic slamming can be achieved by revisiting the wedge water entry problem using flexible structures. In this work, two wedge models that are identical, with the exception of different bottom thicknesses, are vertically dropped into calm water. Pressure, full-field out-of-plane deflection, strain, vertical acceleration, and vertical position are measured. Full-field deflections and strains are measured using stereoscopic-digital image correlation (S-DIC) and strain gauges. A nondimensional number, R, quantifying the relative stiffness of the structure with respect to the fluid load is revisited. An experimental parametric study on the effect of R on the nondimensional hydrodynamic pressure and the maximum strain is presented. It was found there is a sharp change in the trend of pressure and strain when R passes through a critical value. It was also discovered that the structural deformation causes a delay in the peak pressure arrival time and a reduction in the peak pressure magnitude during the wedge water entry. Introduction When high-speed planing craft operating in waves becomes airborne and reenters the water surface, a substantial impact or “slam” between the vessel bottom and the water surface will occur (Faltinsen 2005; Lloyd 1989). The bottom slamming events occur frequently and may injure the passengers, compromise the equipment onboard, or even damage the structure. Slamming is a major cause of speed reduction in small craft where slamming loads are important. Current design criteria are primarily based on empirical measurements with little regard for the fluid–structure interaction (FSI) physics of the slamming phenomenon. This study offers a first step toward better understanding of FSI in slamming for optimal structural design in the future. Since the cross sections of most surface effect ships may be approximated by a V-shaped wedge, the slamming characteristics of these sections may be examined by dropping a wedge model into water (Faltinsen 2005; Lloyd 1989). Studying the wedge water entry problem is also helpful in shedding light on the wet deck slamming of catamaran, sloshing under the chamfered roof of a partially filled tank (Faltinsen 2000), seaplane landing (Wagner 1932), water landing of spacecraft and solid rocket boosters, water landing/ditching of aircraft (Abrate 2013), and animal diving behavior (Chang et al. 2016).

Research of wing in surface effect ship configuration and development of an experimental model of increased stability

The article provides an analysis of the foundations of wing-in-surface-effect ship (WISE) development and describes the experiments conducted using the constructed three radiocontrolled and one virtual model of the WISE. The main problems identified during the experiments are de-scribed, as well as further prospects for the development of the project.

Experimental investigations on the resistance performance of a high-speed partial air cushion supported catamaran

The partial air cushion supported catamaran (PACSCAT) is a novel Surface Effect Ship (SES) and possesses distinctive resistance performance due to the presence of planing bottom. In this paper, the design of PACSCAT and air cushion system are described in detail. Model tests were carried out for Froude numbers ranging from 0.1 to 1.11, the focus is on the influence of air cushion system on resistance characteristics. Drag-reducing effect of air cushion system was proved by means of contrast tests in cuhionborne and non-cushionborne mode. Wave-making characteristics reflect that the PACSCAT would eventually enter planing regime, in which the air could just escape under the seals and the hull body could operate in a steady state. To acquire different air cushion pressure, air flow rate and leakage height were adjusted during tests. Experimental results show that the resistance performance in planing regime would decrease evidently as the increased air flow rate, however, the scheme with medium leakage height presents the best resistance performance in the hump region.

Surface Effect Ship with Four Air Cushions Part I: Dynamic Modeling and Simulation

This paper deals with dynamic modelling and numerical simulations of a Surface Effect Ship (SES) with split cushion. Traditionally, a SES is a catamaran with front and aft seals equipped with lift fans that could fill an air cushion with pressurized air to lift up to 90 % weight of the vehicle. A new SES concept is designed by UMOE Mandal AS that consists of four air chambers, each one equipped with variable vent valves, through which cushion pressures can be controlled by adjusting the air out-flow from the cushion. The new design makes it possible to actively regulate the motion of the SES in all degrees of freedom but surge. In this paper, we develop a dynamic model of the four cushion SES. Furthermore, we present a high fidelity numerical simulator that can effectively simulates the dynamics of the vessel. A companion paper (Haukeland, Hassani, and Auestad 2019) studies the performance of the control system through numerical simulation using the presented high fidelity model of SES subject to waves.

Design and verification of a sway-yaw control system for Surface Effect Ships using vent valves

For an offshore worker in the oil and gas industry, the helicopter transport is the activity associated with the highest risk. An alternative to helicopter crew transfers is to use Surface Effect Ships (SES) to transport the crew. A SES is a catamaran vessel carried in part by a pressurized air cushion. The pressure is maintained by fans and controlled using vent valves. The benefit of these vessels are the high speed to fuel consumption ratio due to decreased wave resistance. During crew transfer from the SES to the offshore installation, the position of the SES needs to be maintained within a safety region using a Dynamic Positioning (DP) system. By mounting the vent valves on the hull sides, the thrust force coming from the air exiting the vent valves can be used to act as an assistance to the DP system. This would reduce required installation power and operational cost of the DP system. Furthermore, combining the thrust from the vent valves with DP thrusters would give a DP system with a high degree of redundancy since thrust force may be generated from two different physical principles. This paper presents a sway-yaw control system for a SES to demonstrate an assisted system that is actuated purely by vent valve thrust from the pressurized cushion. The developed control system is verified using numerical simulations carried out in a high fidelity simulator.

Surface Effect Ship with Four Air Cushions Part II: Roll and Pitch Damping

This paper introduce damping of roll and pitch motion on a Surface Effect Ship (SES) in low vessel speeds. The SES consist of two side-hulls, a reinforced rubber bow and stern seal skirt system and four air cushion. The air cushions can lift up to 90 % of the total vessel mass depending on the output of the controller. The pressure in the air cushions are controlled using feedback from gyros which results in heavily reduced motions in roll and pitch. The effectiveness of the proposed system is examined through numerical simulation in a high fidelity simulator developed in a companion article (Ola M. Haukeland, Hassani, and Auestad 2019).

Vent Valve Thrust Force for Surface Effect Ships

The Surface Effect Ship (SES) holds promise as a viable and appealing alternative for transferring crew to offshore wind farms and oil platforms due to its superior seakeeping capability, high comfort and speed. A SES is a marine craft with catamaran hull, with flexible stern- and bow rubber -seal system. The air cushion is defined as the enclosed volume between the hull, seals and water plane. Centrifugal lift fans blow air into the air cushion, pressurizing the air cushion that lifts up to 90 % of the vessel weight. Modern SES are also equipped with adjustable vent valves allowing outflow air from the pressurized cushion. By mounting the vent valves on the hull sides, the thrust force coming from the air exiting the vent valves can be seen as an extra actuator on the ship. Using Vent valve to control the ship’s position requires an accurate thrust force model. This paper develops two thrust force models and investigates their performance. Both models are compared to computational Fluid Dynamic (CFD) analysis and experimental tests. Results show that both models may be used to estimate the maximum thrust, However, one holds higher promise to be used for control design.

Условия устойчивости несущего комплекса судна на воздушной подушке с гибкими скегами

Условия устойчивости несущего комплекса судна на воздушной подушке с гибкими скегами

A novel 2.5D method for solving the mixed boundary value problem of a surface effect ship

When a surface effect ship (SES) sails in waves, the unsteady velocity potential of water can be decomposed into incident potential, sidehull radiation potential, sidehull diffraction potential and radiation potential due to fluctuating air pressure. The potentials related to sidehulls satisfy Neumann boundary conditions (BC) and have been successfully addressed using the 2.5D method. In contrast, the potential related to fluctuating air pressure satisfies mixed BC consisting of homogeneous Neumann BC on the wetted surface of sidehulls and nonhomogeneous Dirichlet BC on the interface between air and water, which has never been studied using the efficient 2.5D method. In this paper, the 2.5D method is firstly proposed to solve the mixed boundary value problem (BVP), which can deal with the coupling between the fluctuating air pressure and sidehulls. By using the 2.5D method, the radiation wave and other relative hydrodynamic parameters of a SES due to the fluctuating air pressure are evaluated. The numerical results on motion response and the fluctuated air pressure of the SES show acceptable agreement with the experimental ones.

A robust neuro-based adaptive control system design for a surface effect ship with uncertain dynamics and input saturation to cargo transfer at sea

This paper is concerned with the problem of safely cargo transfer over a ramp between a cargo vessel and a lighter surface effect ship (SES). For this purpose, an adaptive neural network (NN) controller is proposed to control of ramp motions in the presence of entirely unknown dynamics and disturbances wherein the controller is subject to input saturation constraint. In this regard, we develop a novel non-affine nonlinear SES model by considering the nonlinear relationship among the air cushion pressure, the air flow into and out of the air cushion and the air cushion volume. To deal with the saturation constraint, an auxiliary system is proposed. To ensure the system stability, Lyapunov’s direct method is employed to investigate the uniformly ultimately boundedness (UUB) of all closed-loop system states. The simulation results demonstrate the effectiveness of the proposed controller in critical sea conditions, including regular and irregular waves with high frequencies and large amplitudes. A comparative analysis with model-based approaches including Proportional Integral Derivative (PID) and Linear-Quadratic Regulator (LQR) control systems are given to highlight the performance of the controller.

Multi-Domain 2.5D Method for Multiple Water Level Hydrodynamics

The mean water surface (interface) under the air cushion of a surface effect ship (SES) or an air cushion supported platform (ACSP) is generally lower than the outside water surface due to the overpressure of the air cushion. To precisely analyze the hydrodynamics under the air cushion, multiple water levels should be considered in numerical models. However, when using free surface Green’s functions as numerical methods, the water level difference cannot be taken into account, because free surface Green’s functions normally require users to set in the whole water domain a unique datum water surface that completely separates the air domain and the water domain. To overcome this difficulty, a multi-domain approach is incorporated into a 2.5D method that is based on a time domain free surface Green’s function with viscous dissipation effects in this paper. In the novel multi-domain 2.5D method, the water domain is partitioned into inner and outer domains, and the interface is located in the inner domain while the outside water surface is placed in the outer domain. In each domain there exists only one unique water level, while water levels in different domains are allowed to be different. Benefited from this characteristic, the multi-domain 2.5D method is able to precisely consider the water level difference and its influence on hydrodynamics. The newly proposed multi-domain 2.5D method is employed to predict the hydrodynamics of an SES, and it is confirmed that the multi-domain 2.5D method can give better numerical results than the single-domain one for the given case.

Roll damping of a surface effect ship with split air cushion

This paper considers linear modeling of a surface effect ship (SES) where roll motions are damped by exclusively exploiting a longitudinally split air cushion design. On a SES, the pressurized air cushions can support up to approximately 80 % of the vessels weight. By implementing a separating wall midships in the longitudinally direction, motion control of roll is possible. When the vessel is subject to wave-induced roll motions, the starboard and port air cushion pressures are controlled in anti-phase, reducing these motions significantly. The effectiveness of the scheme is demonstrated through model scale experimental testing carried out in the Towing Tank, NTNU, Trondheim.1

Assessment of URANS surface effect ship models for calm water and head waves

Surface effect ship (SES) air cushion and seal models are implemented in an URANS hydrodynamics solver. The air cushion is modeled either as a prescribed pressure patch, or as a compressible isothermal/adiabatic ideal stagnant air with fan and leakage flows. The seals are either discretized as hinged bodies or modeled as 2D planing surfaces with hydrodynamic interaction. Verification and validation studies are performed using T-Craft experimental data for calm water resistance, sinkage and trim at Froude number (Fr)=0.1–0.6; impulsive heave and pitch decay at Fr=0; and wave-induced resistance and motion predictions in head waves at Fr=0 and 0.6. The compressible air cushion model with fan and leakage flows perform better than those without the fan and leakage flows and the prescribed pressure patch model. The hinged seal model performs better than the 2D planing surface model, but is computationally expensive for time accurate simulations. Therefore, the 2D planing surface model is used for the validation studies. SES simulations on grids with 5.3M cells show grid verification intervals of 6%, which are comparable to those reported for displacement and semi-planing hull studies on similar grid sizes. On an average calm water and impulsive motion predictions compare within 8.5% of the experimental data, and wave-induced motion predictions show somewhat larger error of 13.5%. The errors levels are mostly comparable to those for displacement and semi-planing and planing hulls. The study identifies that most critical advancement needed for SES simulations is the seal modeling including fluid structure interaction.

Robust Lateral Control of a Surface Effect Ship using H∞ Mixed Sensitivity Synthesis

Abstract: This paper presents a systematic procedure to design robust controllers for lateral control of a class of Surface Effect Ship (SES) subjected to the influence of sea waves, currents, and wind loads using robust H ∞ techniques. The proposed technique will expand operational weather window for boarding the service personnel to and from offshore wind mills. The vessel under study is equipped with a boarding control system for heave and pitch compensation. The current paper focuses at controlling the sway motion by using the outgoing air flow from the boarding control system to produce lateral control forces. To this end, a mathematical model of the lateral motion is presented and by selecting suitable weighting functions to dictate the desired performance, mixed sensitivity H ∞ synthesis method is exploited to design the controller. Model tests has been performed on a scaled model. The performance of the actuators was identified, and is presented in a bode plot. The results of the tests have been used to find a suitable thrust mapping for the controllable forces from the vent valves in sway. Numerical simulations, using this mapping and excitation from realistic external forces from waves and wind, shows satisfactory performance of the control system.

Boarding control system for improved accessibility to offshore wind turbines: Full-scale testing

This paper considers the dynamic modelling and motion control of a Surface Effect Ship (SES) for safer transfer of personnel and equipment from vessel to-and-from an offshore wind-turbine. The control system designed is referred to as Boarding Control System (BCS). The performance of this system is investigated for a specific wind-farm service vessel—The Wave Craft. On a SES, the pressurized air cushion supports the majority of the weight of the vessel. The control problem considered relates to the actuation of the pressure such that wave-induced vessel motions are minimized. Results are given through simulation, model- and full-scale experimental testing.

A FEM fluid–structure interaction algorithm for analysis of the seal dynamics of a Surface-Effect Ship

This paper shows the recent work of the authors in the development of a time-domain FEM model for evaluation of the seal dynamics of a surface effect ship. The fluid solver developed for this purpose, uses a potential flow approach along with a streamline integration of the free surface. The paper focuses on the free surface-structure algorithm that has been developed to allow the simulation of the complex and highly dynamic behaviour of the seals in the interface between the air cushion, and the water.; The developed fluid-structure interaction solver is based, on one side, on an implicit iteration algorithm, communicating pressure forces and displacements of the seals at memory level and, on the other side, on an innovative wetting and drying scheme able to predict the water action on the seals. The stability of the iterative scheme is improved by means of relaxation, and the convergence is accelerated using Aitken's method.; Several validations against experimental results have been carried out to demonstrate the developed algorithm. (C) 2015 Elsevier B.V. All rights reserved.