Shock waves from underwater and air explosions are significant threats to surface and underwater vehicles and structures. Recent studies on the mechanical and thermal properties of various phase-separated elastomers indicate the possibility of applying these materials as a coating to mitigate shock-induced structural failures. To demonstrate this approach and investigate its efficacy, this paper presents a fluid-structure coupled computational model capable of predicting the dynamic response of air-backed bilayer (i.e. elastomer coating – metal substrate) structures submerged in water to hydrostatic and underwater explosion loads. The model couples a three-dimensional multiphase finite volume computational fluid dynamics model with a nonlinear finite element computational solid dynamics model using the FIVER (FInite Volume method with Exact multi-material Riemann solvers) method. The kinematic boundary condition at the fluid-structure interface is enforced using an embedded boundary method that is capable of handling large structural deformation and topological changes. The dynamic interface condition is enforced by formulating and solving local, one-dimensional fluid-solid Riemann problems, which is well-suited for transferring shock and impulsive loads. The capability of this computational model is demonstrated through a numerical investigation of hydrostatic and shock-induced collapse of aluminum tubes with polyurea coating on its inner surface. The thickness of the structure is resolved explicitly by the finite element mesh. The nonlinear material behavior of polyurea is accounted for using a hyper-viscoelastic constitutive model featuring a modified Mooney-Rivlin equation and a stress relaxation function in the form of prony series. Three numerical experiments are conducted to simulate and compare the collapse of the structure in different loading conditions, including a constant pressure, a fluid environment initially in hydrostatic equilibrium, and a two-phase fluid flow created by a near-field underwater explosion.

The interaction between a spark-generated bubble and a non-oscillating air bubble attached to a horizontal rigid plate is investigated using a low-voltage spark-discharge setup. Large numbers of fascinating and complicated interactions are given rise during two bubble coupling pulsation due to the deformation property endowed to the plate through an air bubble attached. It is found that, under the combined influence of the cavitation and the structure, some complex phenomenon likes the bubble coalescence, air bubble skirt phenomenon, bubble splitting are given rise during the two bubble interaction procedure. The coupling phenomenon between the spark generated bubble, air bubble and the structure are discussed in detailed The mainly attention are paid to the coupled response of an attached quiescent bubble under oscillating bubble, the effect of the distance parameter and volume ratio parameter on the air bubble shapes are analyzed in detail, and the mechanism behind these phenomenon are investigated. Our study can be a useful scheme in the protection of a naval structure from threats induced by an explosion bubble impact loading.

In this paper, a coupling eulerian langarian method (CEL) is used to study the interaction between a collapsing underwater explosion bubble and a steel plate. The VOF method is used to simulate the physical process of bubble growth, contraction and collapse, while the finite element method is used to calculate dynamic response of the steel plate. By establishing the three dimensional numerical model, the study reveals the interesting insights into the complex problem of interaction a underwater explosion bubble and a steel plate, including the physical process of bubble growth, contraction and collapse, the dynamic response of the steel plate, as well as the wall pressure induced by the bubble dynamic. The results indicate that the elastic-plastic plate will generate permanent deformation loaded by the water jet; owing to the deformation of the nearby structure, the bubble shows as a “hazel” in the bubble contraction phase and forms toroidal jet which leads the bubble into several toroidal bubbles in the bubble collapse phase. This paper aim at proposing an effective numerical method which can be useful for the problem of strong interaction between bubble and structure.

The explosion in the closed cabin will cause a sharp rise in cabin gas pressure, which will cause serious damage to the cabin structure. The quasi-stationary pressure, due to its long duration and large impulse, plays a major role in the destruction of the structural strength of the entire cabin. The venting holes on the transverse bulkheads can effectively guide the release of energy to other locations, reducing the damage to the cabin. In this paper, the quasi-stationary pressure generated during cabin explosion with venting is studied. According to the conservation of mass and energy, the cabin explosion model with venting is transformed into an equivalent high pressure gas release model to simulate the initial instantaneous state of cabin explosion, and it is verified by finite element calculation that the two models are equivalent in predicting quasi-stationary pressure. The entire gas flow process during the exploding with venting holes is divided into two parts: the gas flow in the cabin to the venting hole and the venting hole to the atmosphere. An approximate analytical method for predicting quasi-stationary pressure generated during cabin explosion with venting is improved by using Bernoulli equation and isentropic compression formula of ideal gas, and the results of the improved calculation method are compared with the results obtained by the numerical simulation method to verify its validity.

Maintaining the integrity of an aging offshore facility often requires the repair of corrosion. With advances in adhesive technology, epoxy adhesives (cold bond repairs) are increasingly being adopted to repair corrosion damage on offshore structures. Structural elements, protection barriers, and occupied buildings, for example a platform living quarters, designated as safety critical often must comply with project or facility performance standards that specify minimum design accidental loading (e.g., from fire, explosions, or impact). In addition to satisfying conventional structural design criteria, a corrosion repaired structure must also perform within acceptable limits when subjected to accidental loads. The present study outlines approaches to assess the performance of cold bond repairs subjected to accidental explosion loads. The living quarters considered in this study featured approximately 50 individual cold bond repairs; each arbitrarily located over the building’s external surfaces. Under accidental blast conditions, failure of a cold bond repair was deemed unacceptable due to the threat of pressure leakage into the building’s interior. As such, the study demanded an analysis capable of considering both the global response of the living quarters as well as the local response of cold bond repairs. There have been several studies conducted by researchers around the globe to evaluate the response characteristics of adhesive bonds. However, these studies are largely focused on experimental, local, and micromechanical analysis of adhesively bonded materials. Numerical analysis of adhesive bonds, for purposes of global structural system response assessments, especially in the case of accidental loading, appear to be nonexistent in available literature. Inspired by this gap, we present a case study involving an assessment of global structural performance of a living quarters building repaired with cold bond adhesives subject to loading due to accidental and rare events. In this study, the local behavior of cold bond adhesives was calibrated using numerical simulations of the ASTM tests specified by the adhesive vendor. The calibrated properties were implemented in finite element analyses used to validate cold bond seal plate repairs at various locations on the living quarters building. The study includes a discussion about the methods and approaches used to model cold bond repairs in a practical and efficient manner. The approach outlined herein provides a useful framework that can be adapted to similar assessments by a practicing engineer responsible for blast analysis of marine structures.

The response of ship equipment under non-contact underwater explosion shock loading was one of the main loadings of equipment. In order to cut down mechanical noise caused by mechanical equipment, vibration isolation measures, such as floating raft, vibration isolation, were widely used on noise mechanical equipments in acoustical stealth of ship, vibration isolation can reduce the vibration transfer to install base effectively, while the anti-shock resistance of vibration isolation and the equipment was important synchronously, as for the response of the equipment on vibration isolation, especially the actual response of the vibration isolation with piping system under shock loading. In this paper, the research on the response of vibration isolation, equipment, flexible piping and piping under underwater explosion shock loading were considered together, and the response of vibration isolation under shock load was analyzed with different piping arrangement. Found that the piping system has a significant impact on the response of the equipment under horizontal impact, but almost all equipments were assessed in experiment without considering the piping system. With the precondition of the effect of vibration isolation, a more rigid flexible pipe can be taken was benefit to the anti-shock resistance of vibration isolation.

In this paper, the numerical model was developed by using the commercial code LS/DYNA to investigate the dynamic response of sandwich panels with three PVC foam core layers subjected to non-contact underwater explosion. The simulation results showed that the structural response of the sandwich panel could be divided into four sequential regimes: (1) interaction between the shock wave and structure, (2) compression phase of sandwich core, (3) collapse of cavitation bubbles and (4) overall bending and stretching of sandwich panel under its own inertia. Main attention of present study was placed at the blast resistance improvement by tailoring the core layer gradation under the condition of same weight expense and same blast load. Using the minimization of back face deflection as the criteria for evaluating the blast resistant of panel, the panels with core gradation of high/middle/low or middle/low/high (relative densities) from the front face to back face demonstrated the optimal resistance. Moreover, the comparative studies on the blast resistance of the functionally graded sandwich panels and equivalent ungraded ones were carried out. The optimum functionally graded sandwich panel outperformed the equivalent ungraded one for relatively small charge masses. The energy absorption characteristics as well as the core compression were also discussed. It is found that the core gradation has a negligible effect on the whole energy dissipation of panel, but would significantly affect the energy distribution among sandwich panel components and the compression value of core.

Floating Production Storage and Offloading (FPSO), a significant offshore oil-gas production system, faces a variety of risks in the process of operation. Vapor cloud explosion (VCE) caused by combustible gas leakage is likely to occur on the topside of FPSO. As an initial accident, VCE has an effect on surrounding devices, leading to subsequent consequences and ampliative scale of the accident. The process, known as the domino effect, can result in severe consequences, indicating that it is necessary to analyze characteristics and impacts of the domino effect on FPSO. In this study, the most risky equipment is determined. VCE overpressure on device surfaces caused by gas leakage of this most risky equipment is calculated, and the results are used for analyzing the domino effect based on Bayesian network.

The Deepwater Horizon Mobile Offshore Drilling Unit (MODU) was one of several classes of floatable drilling machines. The explosion on April 20, 2010 led to the worst ecological disaster with regard to oil spills in the USA. The objective of this paper is to develop a logical and independent estimate of the oil flow rate into the Gulf of Mexico produced by the rupture in this rig. We employed the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite photographs [1] starting from the days immediately following the disaster to determine the size and intensity of the oil spill. From these images, we obtained the surface area of the oil spill and calculated the oil flow rate by two different methods based on contrasting luminance within the area. The first assumes a constant thickness for the total area with upper and lower bounds for the thickness. The second method separates the spill area into different patches, based on the luminance levels of each. It was found that the probability density function (PDF) of the luminance plots typically showed some natural grouping, allowing patches to be defined. Each patch maps to a specific thickness and the result of the addition of all the patches provides a more accurate average thickness of the spill. With the assumption that evaporation and other loss amounted to 40% of the spill, we obtained, as a result of this analysis procedure, a minimum flow rate of 9,300 barrels per day and a maximum of 93,000 barrels per day using the first method. A value of 51,200 barrels per day was obtained using the method based on patch separation. This latter estimate was a reasonable value obtained based on this relatively simple method but with no details presented in an Extended Abstract in OMAE2012 [4]. It is remarkably consistent with the “official US-Govt. estimates” of [2, 3].

Blast panels are integral structures in offshore topside modules to protect personnel and safety critical equipment by preventing the escalation of events due to hydrocarbon explosions. As such, blast panels are expected to retain their integrity against any blast loading and subsequent hydrocarbon fire. Most of the blast panels currently installed in offshore structures have been designed using simplified calculation approaches such as the Single Degree of Freedom (SDOF) models, as recommended by offshore design codes and industry recommended practices. In this paper, the Non-Linear Finite Element Analysis (NLFEA) technique is used to simulate the structural response of corrugated panels subjected to blast loading. Detailed numerical analyses allow identifying the limits of the SDOF approach, and exploring different design options to optimize the structural response of corrugated blast panels. The blast load profile corresponding to an explosion is one of the most important factors to consider in the structural analysis. The mechanism of hydrocarbon explosions is very complex, and the corresponding blast load profile intimately depends on the type of explosion, the congestion and the structural confinement. A sensitivity analysis is performed to investigate the influence of the blast pulse shape, and in particular to evaluate the effect of the maximum peak pressure and the exposure time. To explore the benefits of introducing higher strength steels in demanding offshore applications, pressure-impulse diagrams have been derived for different high strength steel grades. In our analysis, (ultra)high strength cut-to-length plates from hot rolled coil are proposed to optimize the design of the blast panel whilst preserving the structural performance under demanding load conditions.

Despite regulations becoming more and more stringent, significant quantities of gas are still flared around the world every year. Indeed, for safety reasons, flaring remains a usual practice in oil and gas production in cases of process upset. For instance, emergency shutdown, when the unit must be depressurized in a short period of time, most of the gas inventories are flared to limit as much as possible the potential consequences of fire and explosion within the facility. With the increase of the global demand for energy and especially in Liquefied Natural Gas (LNG), the recent development of Floating Liquefied Natural Gas unit (FLNG) has raised new challenges concerning flare stack design. Since FLNG facilities handle large flammable gas quantities the flare stack needs to be designed considering much more stringent cases. It results in an increased length of flare stack, to reduce the radiation effects on personnel and equipment. The thermal response of the flare structure needs also to be accounted for in the design, in addition to other load cases such as piping and structural weight or vessel accelerations. To accomplish the structural design of the flare stack, the engineers will have to convert the radiative heat fluxes from the flame into the resulting temperature of the structure exposed. Indeed, temperature is the parameter that can be used as a thermal load case in any finite element analysis calculation code. Current temperature mapping methodologies applied on projects are not exhaustive and are often based on a simplified approach which is now challenged by operators and certification bodies who require more detailed verifications on flare structure heating during continuous or emergency flaring. Moreover, such simplified modelling approaches tends to overestimate thermal protection to mitigate the heat radiation impact. The proposed approach described in this paper will address these points through a multidisciplinary workflow to form a flexible, simple and robust technical methodology to be applied during project execution. The proposed approach will assess heat radiation and temperature calculations in a spatial-temporal reference including the dynamic response. This transient approach is more attractive as computed temperatures will be lower than steady-state approach results which are the usual engineering practice, especially for accidental loading cases, such as emergency depressurization, where the flare release can decrease quickly.

This study aims to introduce the Artificial Neuron Network (ANN) technique, namely Bayesian Regularization Artificial Neuron Network (BRANN) to Explosion Risk Analysis (ERA) of floating offshore platform and eventually develop the ANN-based ERA procedure. In order to verify the feasibility of this developed procedure, a case study of floating offshore platform is conducted. Firstly, several dispersion simulations and explosion simulations are performed by FLACS. With those simulation results, the corresponding BRANN models are subsequently developed. Furthermore, comparison between BRANN model and widely-used RSM model is conducted. Eventually, the exceedance curve of maximum overpressure is determined. All the results illustrate the more robustness and efficiency of this developed procedure.

Over many years, onshore plants have been deployed to liquefy the gas extracted from offshore wells and regasify the liquefied gas before sending it to the consumer grid. Currently the LNG Offshore Industry crosses a new development period since LNG Offshore Floating Units are considered as good options to improve the viability of gas supply. Nevertheless this paper will introduce the main safety challenges usually identified on LNG Offshore facilities, such as the space constraints on LNG Liquefaction Offshore Floating Units and injuries to personnel due to the cryogenic properties of the LNG. Moreover, it will be demonstrated that each hazard has a particular solution which has to be carefully assessed in order to ensure that the risks linked to an installation dealing with LNG are well understood and under control at the same time that the expectations of the project are achieved and compliance with recognized international health and safety standards is respected. Gaining knowledge about the properties of hazardous substances processed and operations performed in the installations is crucial to ensure safety in LNG Industry. Therefore this paper also aims at ensuring the awareness and understanding concerning the issues that could compromise the safety in LNG installations. As previously mentioned, a great concern in the LNG Offshore Industry is related to the space constraints in the site, once in case of a gas release followed by ignition there is the probability of escalation occurrence through the whole installation, what would affect personnel, environment and assets. Despite the space constraints found on offshore installations, it is important to consider minimum safety distances among the LNG facility systems. Thus, control of major hazards is of key importance, and prevention of escalation from an initial incident is critical. Also, it is important to understand what conditions could cause physical effects such as a pool fires, rapid phase transitions and vapour cloud explosions. Since this paper details and compares the safety challenges related to LNG processes, it will be presented some examples of accidents occurred in LNG facilities. The lessons learned from previous accidents can enable the companies to justify the investment to improve the safety in the installation and develop an effective Risk Management, which provides several benefits for the LNG operations (i.e.: the fewer accidents so lower employee absence, lessened threat of legal actions against the company, better reputation and consequently, reduced costs, increased productivity and greater profit.).

Marine and offshore structures are subjected to dynamic loads during the lifetime. The values or directions of dynamic loads rapidly change in time, causing a significant rise of inertial forces in structural elements. Dynamic loads appear as result of ship’s movement at sea, wind and wave acting, machinery operation, hull vibration and sometimes even as result of collision or explosion. The corresponding dynamic forces and moments act on the ship hull provoking the appearance of stresses, often leading to buckling, plastic deformations or fatigue cracks of the structural members. To ensure the safety and reliability of structures under dynamic loading it is necessary to estimate the transient effects on the collapse behavior of plate panels. According to the Common Structural Rules (CSR) the safety of marine structures must be proved performing the hull girder ultimate strength check. As a possible tool for the ultimate strength analysis, the Finite Element Method (FEM) is widely spread among engineers. In spite of the great effectiveness, the transient Finite Element Analysis (FEA) remains very time consuming and sometimes difficult to accomplish well. Therefore, the formulation of the Idealized Structural Unit Method (ISUM) is extended for the dynamic collapse analysis of marine structures.

A hydrocarbon Vapor Cloud Explosion (VCE) is one of critical hazardous events in offshore installations. Once VCE occurs in the ocean, it results in tremendous economic loss, casualties, and environmental impact. The combustion mechanism of VCE differs from HE in particular in complex geometries (e.g. offshore oil and gas production facilities) as there exist many objects which can trigger severe turbulences. Although many research efforts have been made to develop design provisions for blast resistant structures, most of those provisions are based on high-order explosives (HE) such as TNT (TriNiTrotoluene) in a free field. Therefore, typical blast resistant structural design standards were examined to address the weaknesses of standards in this study. Existing blast wave models which provide key design load parameters were also reviewed to address limitations of each approach. Finally, essential recommendations are discussed in this paper for future studies to improve blast resistant structural design provisions with the ultimate aim of protecting our lives, assets and environment from VCE in the ocean.

Shock load caused by underwater explosion in naval battles can lead to malfunction of the equipment on-board naval vessels. It makes the ships vulnerable and they can lose the ability to accomplish their missions. This study presents a shock analysis, using the dynamic design analysis method (DDAM), of a naval ship stern ramp subjected to a non-contact underwater explosion. The objective is to evaluate the performance of the ramp subjected to a shock load, identify areas for structural improvements and recommend design changes. The DDAM in the commercial software ANSYS is used in the evaluation of the ramp. The structural response to the shock load is estimated by combined modal and response spectrum analyses. The shock load is applied in three directions (vertical, fore and aft, athwart ships) and the results show that the vertical direction is the most severe loading direction and critical to the functionality of the ramp. A parametric study is presented which shows which parameters that influence the most the structural response. The results from this study are used to suggest improvements of the ramp structure to make it more resistant to shock loads.

The potential risk of an offshore processing facility is the major important part in the oil and gas industry due to its limited space causing difficulties in evacuation. An offshore processing facility is normally exposed to flammable oil and gas in the operating phase. Especially, uncontrolled hydrocarbon leaks or ruptures of the equipment present main threats. These failures can lead to fire and explosion disaster. Some studies have proposed fire and explosion assessment methodologies and made fire and explosion assessment tools. These tools can provide risk assessments result using physical effect modelling software and following the related standards or engineering practices according to accident scenarios. Nevertheless, existing fire and explosion assessment procedures are still not comprehensive enough to applicate a specific process due to its complexity and are not clear which stage in a project is appropriate for applying it. This paper focuses only on explosion accidents and discusses the development of an explosion risk analysis procedure possible to apply at process flow diagram (PFD) level. The explosion risk analysis procedure using PFD has 6 steps; modelling of a process, scenario selection, inventory calculation, frequency calculation, consequence modelling and risk estimation. It starts at modelling of a specific process using process simulation software, HYSYS. The process modelling can be optimized by the existing methods and finally provide the PFD for the specific process. In the scenario selection step, the information required to perform a risk analysis is identified. The inventory calculation conducts to calculate the inventory of a defined segment after sizing of the equipment in the PFD. The frequency calculation consists of leak frequency and ignition probability. The leak frequency can be calculated with historical database and the ignition probability can be calculated with a specific ignition probability model. The consequence modelling is conducted by using physical effect modelling software, PHAST. It can provide the distance to specified overpressure. Finally, at the risk estimation step, the risk results are evaluated. This procedure can help to applicate a specific process easily and provide explosion risk assessment tool at PFD level. This paper conducts the case study for a liquefied natural gas floating production storage offloading (LNG-FPSO) which is one of the representative offshore processing facilities. Especially, a natural liquefaction process in a LNG-FPSO, which liquefies the processed natural gas to store in a storage tank of a LNG-FPSO, is the most important process in terms of cost and risk. In the situation the most of ongoing or prospective projects for LNG-FPSO adopt dual mixed refrigerants (DMR) liquefaction process, the representative configurations of the DMR liquefaction processes are evaluated and compared. It can help decision making through providing which configuration has an advantage in terms of explosion accidents.

The topic on performance evaluation of air-backed metallic structures subjected to close-in underwater explosion is of interest to protecting construction designers. The focus of performance includes not only the deformation/failure modes but also the energy absorption capability. This paper presented a blast experiment to investigate the blast resistance of circular solid plate. The deformation and failure modes were classified. The energy absorption of the blast-loaded plate was quantified by the response of another plate, which was arranged below the target. Particular attention was paid to discussing the effects of the charge mass and stand-off distance ( SoD ) on the blast performance. Results showed that the target plates appeared to experience petalling failure in case of contact tests and large inelastic deformation in case of noncontact. The shock waves induced by the blast explosion and the fragments teared from the target plates caused a capping or some permanent deformation on rear plates. Damages and deformations of target and rear plates were strongly correlated with the explosion intensity. As the increase of stand-off distance, the failure mode of target plates transitioned from petalling to large inelastic deformation. Experimental results presented in this paper provided valuable guidance for the following research on sandwich structures.

As large offshore drilling facility, Floating Production Storage and Offloading (FPSO) faces with the risk of oil & gas leakage and subsequent effects (e.g. fire and explosion). In order to assess FPSO gas leakage and subsequent chain effects risk scientifically, a FPSO topsides is analyzed, and Failure Model and Effect Analysis (FMEA) method is applied to find out which equipment has high Risk Priority Number (RPN). The results show that gas washing pry of FPSO in operation phase has high RPN and needs significant attention. In this paper, CFD-model of FPSO topsides is established based on computational fluid dynamics (CFD) theory. The leak rate of gas with specified hole diameter is calculated based on appropriate leak source model according to the actual operating conditions of gas washing pry. Then based on the simulation results diffusion behavior is analyzed, as well as distribution law of gas and the hazardous area of gas of gas washing pry under the leakage conditions. Furthermore, one explosion model is selected, and then damaging over-pressure of explosion on each equipment surface and the variation trend and influence scope of explosion over-pressure are derived to evaluate personnel and equipment risk. Targeted technical measures will be put forward to reduce risk.

Hydrocarbon gas explosion is one of the critical hazards resulting in huge environmental impact as well as loss of valuable assets and lives as observed from the historical disasters in the oil and gas industry. In response to these events, stronger international rules and regulations have been made to ensure safety of these structures. Hence, considerable effort has been devoted to quantify accidental design loads for flammable gas based on probabilistic approaches which requires extensive computational fluid dynamic simulations. Also, demand for 3D nonlinear dynamic finite element structural simulations has increased significantly with rapid progress in computer performance. Some of the major issues and difficulties in structural design and evaluation for probabilistic design loads are discussed in this paper. Uncertainties in explosion hazard analysis which cause large variations in probabilistic explosion responses are reviewed. Some gaps between provisions for design load estimation based on probabilistic approaches versus current structural design and analysis schemes are compared. Finally, it is concluded that there is an urgent need for reliable guidelines for risk-based structural design and simulation for probabilistic explosion design loads.