Slamming Loads Research Articles

Study on the Effect of Impact Velocity on Slamming Loads

An explicit finite element method which is combined with the Arbitrary Lagrangian-Eulerian (ALE) algorithm is applied to forecast slamming loads during the structure entries into the water. By adjusting the contact parameter, the result of slamming force is improved and this result is compared with the corresponding experimental values to verify the numerical prediction method of slamming loads. By simulating the wedge into the water at a constant speed and evenly variable speed, the effect of the impact velocity on local slamming pressure and global slamming force is studied.

Recent advances in vibro-impact dynamics and collision of ocean vessels

The treatment of ship impacts and collisions takes different approaches depending on the emphasis of each discipline. For example, dynamicists, physicist, and mathematicians are dealing with developing analytical models and mappings of vibro-impact systems. On the other hand, naval architects and ship designers are interested in developing design codes and structural assessments due to slamming loads, liquid sloshing impact loads in liquefied natural gas tanks and ship grounding accidents. The purpose of this review is to highlight the main differences of the two disciplines. It begins with a brief account of the theory of vibro-impact dynamics based on modeling and mapping of systems experiencing discontinuous changes in their state of motion due to collision. The main techniques used in modeling include power-law phenomenological modeling, Hertzian modeling, and non-smooth coordinate transformations originally developed by Zhuravlev and Ivanov. In view of their effectiveness, both Zhuravlev and Ivanov non-smooth coordinate transformations will be described and assessed for the case of ship roll dynamics experiencing impact with rigid barriers. These transformations have the advantage of converting the vibro-impact oscillator into an oscillator without barriers such that the corresponding equation of motion does not contain any impact term. One of the recent results dealing with the coefficient of restitution is that its value monotonically decreases with the impact velocity and not unique but random in nature. Slamming loads and grounding events of ocean waves acting on the bottom of high speed vessels will be assessed with reference to the ship structural damage. It will be noticed that naval architects and marine engineers are treating these problems using different approaches from those used by dynamicists. The problem of sloshing impact in liquefied natural gas cargo and related problems will be assessed based on the numerical and experimental results. It is important for vessel designers to determine the capacity of ships to resist random slamming loads, sloshing loading impact, grounding accidents and ships collisions.

Slamming Strength Assessment Analysis of Large Container Ship

The analysis of slamming effect has been mainly discussed about the local strength assessment and the global longitudinal strength assessment under slamming loads. The former is to forecast the local design pressure and access the local structural strength. To achieve the strength assessment of local structure of the ship bow, the slamming design pressure results of bow bottom and bow flare areas have been selected, so as to show the calculation results of relative velocity extreme values and design slamming pressure. And then according to the slamming loads and strength assessment, the direct strength assessments have been used to check key areas. The latter is to forecast the global vertical design moment and access the global longitudinal strength through three dimension finite model.

Risk assessment of cross structure slamming of high speed ro-pax catamaran at initial design stage

One of the urgent issues of the modern theory of the ship design, in other words the appliance of the risk theory at the initial design stage has been considered. It is shown that accidents occur due to the following main reasons: collision, contact, fire or explosion, grounding or stranding, loss of hull integrity, machinery or electrical failures. For the high speed catamarans, the slamming is the main reason which leads to the loss of vessel hull integrity. Based on the research, the author presents a general method to determine the risk value from the accidents. Also, the scientific publications on the given problem are analyzed. The article also describes the algorithm of the damage probability calculation of the cross structure of the high speed ro-pax catamarans, which is based on the probability of the cross structure slamming and on the probability that the slamming dynamic load is more than the bearing capacity of the cross structure shell plate.

Experimental investigation of violent liquid slamming pressure in large-scaled tank

Structural strength of the cargo containment systems of the very large-scale Floating Liquefied Natural Gas(FLNG) can be damaged by the sloshing-induced slamming load. Large scale sloshing experimental investigation can truly reveal the process of slamming. Due to the compressibility of liquid and gas, slamming load instantaneously increases dramatically. So, accurate measurement of impact pressure is one of key issues in experimental investigation. In order to study the measurement of impact pressure accurately, sensitively and reliably, six-degree of freedom hexapod and large-scale model tank are employed. Not only the impact pressure but also the slamming process are recorded by both membrane and pinhole piezoresisitve sensors. The procedure of liquid slamming on the vertical wall is further provided by the impact occurrence in time domain. Furthermore, the spatial correlation of impact pressure is analyzed by correlation method. The results illustrate that the pinhole sensor is more sensitive to the bubble effect, and the membrane type acts averaging effect. It is reported that the slamming load performs linear correlation both in the vertical and horizontal direction below the impact point. Therefore, it is recommended that pressure sensors should be installed with an array near the impact point in the larges-scaled model test.

Cross-Deck Slamming Load Calculation of Trimaran Based on Modified Plate Slamming Theory

Since slamming loads on connecting bridges of trimaran is very important for the structural design. In this paper, trimaran slamming load calculation method is studied. First added mass caused by typical hull section and wet-deck slamming are investigated, then wet-deck slamming peak pressure are gotten by modified flat slamming theory with considered of the effect of air cushion, the regression equation of which is given by statistical process. Finally, the time-spatial distribution of slamming pressure along the wet-deck is given. This method can provide a reference for the preliminary design and operation of trimaran.

Some analytical results for the initial phase of bottom slamming

The deformation of boat hull bottom panels during the initial phase of slamming is studied analytically using a linear elastic Euler–Bernoulli beam as a representation of the cross section of a bottom panel. The slamming pressure is modeled as a high-intensity peak followed by a lower constant pressure, traveling at constant speed along the beam. The problem is solved using a Fourier sine integral transformation in space and a Laplace–Carson integral transformation in time. Deflection and bending moment as functions of time and position for different speeds, bending stiffnesses, etc. are given. In particular the effect of slamming load traveling speed on structural response of the simplified bottom structure is investigated. It is found that rather large deflections and bending moments are encountered at certain speeds of the pressure, which suggests that bottom panels may benefit from tailoring their stiffness and mass properties such that loads are reduced. This would vary with boat particulars and operation (deadrise angle, mass, speed, sea state, etc). The importance of the high-intensity pressure peak often encountered during slamming is also studied. It is seen that for relatively slow moving slamming loads the pressure peak has little influence. However, for faster moving loads its influence can be significant.

Long-term prediction of combined wave and whipping bending moments of container ships

The purpose of this paper is to propose a practical computational procedure for the long-term distribution of combined wave and whipping bending moments (BMs) of container ships. The problem is formulated in the frequency domain using standard engineering tools for load computation: a seakeeping code for the rigid-body response and a beam finite element model for transient vibratory response. The von Karman approach with correction for pile-up effect is employed for bow flare slamming load assessment. Correlation between wave and whipping BMs is considered. The procedure is demonstrated on the example of a 9200 TEU container ship. Long-term distributions of combined BMs are computed using the standard International Association of Classification Societies scatter diagram for the North Atlantic environment and two additional scatter diagrams for common shipping routes of container ships. The speed profile required for the long-term load prediction is calculated by the seakeeping analysis respecting operability limiting criteria. Conclusions about influence of various environmental and operability parameters are drawn.

Transient hydroelastic analysis of sandwich beams subjected to slamming in water

This work deals with the transient hydroelastic analysis of a sandwich beam which represents a boat hull. The beam is subjected to slamming pressure while it enters into water with constant vertically downward velocity. A coupled hydroelastic finite element model is developed using higher order shear and normal deformation theories for the faces and the core of the beam and the velocity potential theory for the fluid. Transient responses of the beam for transverse deflection and stresses are studied. Dynamic failure analysis has been carried out to investigate the initiation and cause of the failure of the beam due to slamming load.

Stacking sequence optimisation of composite panels subjected to slamming impact loads using a genetic algorithm

Optimisation of stacking sequence for composite panels under slamming impact loads using a genetic algorithm method is studied in this paper. For this purpose, slamming load is assumed to have a uniform distribution with a triangular-pulse type of intensity function. In order to perform optimisation based on a genetic algorithm, a special code is written in MATLAB software environment. The optimiser is coupled with the commercial software ANSYS in order to analyse the composite panel under study and calculate the central deflection. After validation, different cases of stacking sequence optimisation are investigated for a variety of composite panels. The investigations include symmetric as well as asymmetric conditions of stacking sequence. Results obtained from these analyses reveal the fact that the adopted approach based on a genetic algorithm is highly capable of performing such optimisations.

Slam occurrences and loads of a high-speed wave piercer catamaran in irregular seas

In order to optimise the structural design of large lightweight high-speed catamarans, a thorough understanding of the structural loads is required. Not only is slam severity an important factor in the structural design, but also the occurrence rates of such events in realistic sea conditions is vital for long-term load estimations. The slamming behaviour of a 2.5-m hydroelastic segmented model representative of an Incat wave piercer catamaran was investigated over a range of realistic irregular sea conditions. The model was instrumented with strain gauges to record centrebow slam loads, pressure transducers, wave probes and linear variable displacement transducers. More than 2000 slam events were identified over 22 test conditions, providing an extensive database of slam events. Slam events were identified from the pressure transducer measurements and two important slam parameters investigated: occurrence rates and slam severity. The slam magnitudes were found to be scattered; numerous outliers were detected with magnitudes up to 4 times the median observed in every tested condition. Slam occurrence rates and severity are generally greater in conditions where motions are large. A slam occurrence threshold was identified by extrapolating the experimentally measured occurrence rates. For a 112-m vessel with speeds between 20 and 38 knots and with a modal wave period of 8.5 s, slams are shown not to occur at significant wave heights less than 1.5 m. The slam loads and occurrence data obtained through scale model testing can be used by high-speed catamaran ferry designers to assist the development of structural load cases and operation limits for future designs.

Composite hull structures subjected to wave-induced slamming impact

This paper presents a review of the state-of-the-art concerning composite hull structures subjected to wave-induced slamming load. Slamming is one of the critical load components that can influence the behavior of marine structures and can result in micro- or macro-level damage. Emphasis of the review is placed on fundamental issues with regard to the interaction between composite hulls and slamming events, including material characteristics, structural configurations, hydroelasticity, and the nature of wave-generated impact load. Practical aspects such as design implementation are also discussed. Recent developments in predictive approaches (e.g. multi-scale modeling) and hybrid testing methodologies are elaborated. Current research needs are identified and technical topics requiring further study are suggested.

URANS study of Delft catamaran total/added resistance, motions and slamming loads in head sea including irregular wave and uncertainty quantification for variable regular wave and geometry

A methodology is assessed for uncertainty quantification (UQ) of resistance, motions and slamming loads in variable regular wave representing a given sea state, and compared to irregular wave (benchmark) and deterministic regular wave studies. UQ is conducted over the joint distribution of wave period and height; the irregular wave inlet boundary condition is based on the wave energy spectrum; deterministic study is conducted at the most probable condition. Application to the high-speed Delft Catamaran at Fr=0.5 and sea state 6 is presented and discussed. Deterministic regular wave study shows an average error for design optimization-related quantities (expected value of resistance, motions amplitude and slamming loads) equal to 25%. Variable regular wave UQ shows an average error close to 6%, providing in addition output distributions. Extension to uncertain design through Karhunen–Loève expansion is presented and discussed; variable geometry studies show a potential reduction of 6.5% for calm water resistance and 3.9% for resistance in wave, with small variations in motions amplitudes; an increase of 6.4% in maximum slamming load is experienced by the reduced-resistance geometry, revealing a trade-off between performances and loads. UQ with metamodels reveals ordinary Kriging and polyharmonic spline as the most effective metamodels overall.

Local structural response to seakeeping and slamming loads

A common approach to investigate the response of a structural detail such as a hatch corner is to compute the seakeeping loads using a linear 3D Boundary Element Method (BEM) and transfer the seakeeping loads to a Finite Element (FE) model of the ship structure. This approach is suitable for computations of the fatigue loading of structural details near amidships because a majority of the fatigue loading will occur in mild sea-states where the loading may be assumed linear. However, the linear seakeeping model may not hold when one investigates the ultimate response of the local bow structure of a ship which is designed to remain operational in severe conditions, for example, a frigate. A linear seakeeping analysis will significantly underpredict the loading at the bow because both the impulsive slamming loads and the non-linearities in the non-impulsive wave loads will contribute significant to the structural loading.The non-linear loads require one to first derive a short-term distribution of the local structural response before the ultimate value of the response can be derived. A method to compute the short-term distribution of a structural detail is presented in this paper. The first step is to perform seakeeping analyses which includes slamming, non-linear Froude-Kryloff and hydrostatic loads. The short-term distribution of the total hydrodynamic loading at the structural detail is obtained by simulating the seakeeping response for several hours. The response of the local structure is computed for the most severe impacts found in the seakeeping simulation. The hydrodynamic loading, including the non-linear contributions, is transfer to the structural model and the structural response is computed using the FE-method. The results of the structural analyses allow one to transform the short-term distribution of the structural loading to a short-term distribution of the response of the structural detail. A designer can obtain the ultimate structural response by entering the probability at which one accepts overloading of the structure in the short-term distribution of the response of the structural detail.

Using artificial neural networks and strain gauges for the determination of static loads on a thin square fully-constrained composite marine panel subjected to a large central displacement

Current methods of estimating the behaviour of marine composite structures under pressure due to slamming as a result of high waves are based on trial and error or oversimplification. Normally under these conditions the non-linearities of these structures are often neglected and, in order to compensate, an overestimated safety factor is employed. These conservative approaches can result in heavier and overdesigned structures. In this paper, a new semi-empirical method is proposed that overcomes some of these problems. This work involved the use of an artificial neural network (ANN) combined with strain gauge data to enable real-time in-service load monitoring of large marine structural panels. Such a tool has other important applications, such as monitoring slamming or other transient hydrostatic loads that can ultimately affect fatigue life. To develop this system, a glass fibre-reinforced polymer (GFRP) composite panel was used due to its potential for providing a non-linear response to pressure or slamming loads. It was found that the ANN was able to predict normal loads applied at different locations on the panel accurately. This method is also capable of predicting loads on the marine structure in real time.

Wave slamming loads on wave-piercer catamarans operating at high-speed determined by hydro-elastic segmented model experiments

Catamaran vessels operating at high-speed can be exposed to deck diving and bow damage and one resolution of this problem is the wave-piercer design of INCAT Tasmania. Owing to the complexity of the unsteady non-linear flow in the bow area during large wave encounter model testing has been undertaken to identify the peak dynamic slam loads on the ship structure. This paper provides experimental benchmark information relating to the wave slam loads on wave-piercing catamaran ferries. Since the time frames of transient slam loadings and whipping vibration of the entire hull in its first bending mode are similar it is important that the test model replicates the whipping response and therefore needs to be a hydro-elastic model. A 2.5 m hydro-elastic segmented catamaran model has been developed based on the 112 m INCAT Tasmania wave-piercer catamaran to establish the peak wave slamming loads acting on the full-scale vessel. Towing tank tests were performed in regular seas at a maximum full-scale operating speed of 38 knots. The model was instrumented to measure the dynamic slam loads acting on the centre bow and vertical bending moments acting in the demihulls of the catamaran model as a function of wave frequency and wave height. Peak slam loads measured on the centre bow were found to approach the total weight of the model, this being a broadly similar result to the peak loads measured at full-scale. It was found that global dimensionless heave and pitch accelerations peaked in the same range of encounter frequency as did the peak slam load.

Slam induced loads on bow-flared sections with various roll angles

The two-dimensional water entry of a bow-flared section with different roll angles is studied by using an explicit finite element code. The modelling technique of the fluid–structure interaction adopts a multi-material Arbitrary Lagrangian–Eulerian formulation and a penalty coupling method. The simulated vertical slamming force and pressure histories are compared with experiments and other numerical calculations. The effects of the roll angle on the slamming load are studied through simulations for a bow-flare section with different roll angles.

A PIV-based method for estimating slamming loads during water entry of rigid bodies

Hydrodynamic impact of bodies onto the water surface is a problem of great importance in the design of off-shore and naval structures (wave energy converters, off-shore platforms, high-speed boats, etc). Classical measurement techniques, namely pressure sensors, present major drawbacks in the determination of impact loads because of their intrusive nature. In this paper, we propose a method to determine the impact loads on rigid bodies during water entry, based on high-speed particle image velocimetry. The method consists of two steps: firstly, an automated procedure is developed to determine the velocity field from high-speed images during water impact. Secondly, the unsteady pressure field is estimated from the velocity fields, using a Poisson-based solver. The method is validated on a rigid wedge slamming experiment and the results are compared with results from computational fluid dynamics simulations (performed with the software LS-Dyna) and from the literature.

Experimental investigation of the wave slam and slap coefficients for array of non-circular section of offshore platforms

The offshore platforms are generally designed with sufficient vertical clearance from the maximum predicted wave crest elevations. This vertical clearance is termed as ‘air gap’. However, due to compelling reasons of hydrocarbon processes and also due to the increase in water levels due to climatic changes or seabed subsidence due to reservoir subsidence, the lower decks may become vulnerable to wave action due to reduction in air gap. The structural elements in the lower decks may become prone to wave-induced loads caused by high wave crests. The assessment of such wave-induced loads on the lower deck and supporting structures, especially in the existing platforms, becomes very essential for the continued safe operations. In the case of wave slamming on a structure, these supporting structural members will also be prone to large loads. Circular sections are commonly used for substructures due to their hydrodynamic efficiency; however, for deck structure, it is very common to use non-circular sections for supporting superstructure loads. The non-circular sections used in the lower decks get exposed to wave-induced loads. The imposed loads could be of higher magnitude compared with the circular sections due to the flat surface of the sections. A review of the literature indicates that the previous studies focused mainly on the circular sections and not much information is available on the non-circular shapes, especially in the case of wave slam and slap. The current study was focused on the measurement of wave-induced slam and slap loads on an array of non-circular sections in a laboratory wave flume and the estimation of force coefficient based on drag-based empirical equations. The studies revealed that the slam and slap coefficients for non-circular shapes are greater than those for circular shapes.

Numerical Prediction of Symmetric Water Impact Loads on Wedge Shaped Hull Form Using CFD

Over the past two decades high-speed vessels have extended their service areas from protected waters to the open ocean where frequent and large water impacts can result in structural damage. The accurate prediction of slamming loads, and their consequences on light-weight high-speed vessels, is an essential element of efficient structural design. The aim of this work is to understand and accurately predict the behavior and local slam loads of quasi-2D wedge shaped hull forms impacting water. The computed results, using finite-volume Computational Fluid Dynamics (CFD), are validated against drop test experimental data and compared to a previously published numerical simulation using Smoothed Particle Hydrodynamics (SPH). The CFD results show good agreement with the experimental measurements.