Equipment repair and intervention in subsea oil and gas fields are expensive, mainly due to vesse... more Equipment repair and intervention in subsea oil and gas fields are expensive, mainly due to vessel mobilization time, retrieval, repair, and replacement costs. The loss of revenue due to downtime could also be significant and the producer could face penalties in not meeting contractual commitments. These costs are part of the life cycle cost, which must be considered at the design stage. Estimating the reliability and availability of subsea systems at an early stage of design is important in assuring the quality of the system architecture, which leads to a more reliable choice of configuration and equipment. Availability analyses should be undertaken very early in the development process, while the operational concept is still under review, and the choice of components is still to be finalized. Postponing this assessment could prove to be too costly to improve the availability and dependability. This paper presents a reliability assessment using a systems engineering framework by combining the system's requirements and reliability requirements. A Design Structure Matrix (DSM) is employed to map the system and visualize the interrelationships (dependencies) between components/subsystems. The DSM is then augmented with reliability data, including intervention times, to determine the overall system availability. It is also explained how to use the system's DSM to aid integration and interface management decisions. A case study is presented to demonstrate this procedure. It is also important to consider the hookup requirements for Remotely Operated Vehicles (ROVs). In deep-water applications, the deployment time and hookup costs for an ROV will have a major impact on the optimization of the subsea field architecture. Commonly Subsea Control Modules (SCMs) are located on the X-tree during running but can be retrieved with or without the tree. From the SDU, the cable and jumpers distribute out to the SCMs. The feasibility of the final arrangement is governed by voltage drop limitations and input voltages required at the SCMs. Reliability is a cornerstone of the offshore petroleum industry (ISO 2015, ISO 2008). Repair and intervention operations at a subsea oil and gas field are costly due to expenditure needed for vessel mobilization times, retrieval of the failed unit, and replacement. Loss of production (revenue) and intervention costs are an integral part of the life cycle cost of an SPS. The primary reliability measure for a maintained system is its availability (OREDA 2009). In other words, the availability of a system is its ability to deliver the required function and performance (OREDA 2009) for the required duration. Subsea availability depends on equipment reliability, retrievability, maintainability, as well as the performance of the maintenance crew. Reliability and
In this review, we provide a detailed coverage of multi-sensor fusion techniques that use RGB ste... more In this review, we provide a detailed coverage of multi-sensor fusion techniques that use RGB stereo images and a sparse LiDAR-projected depth map as input data to output a dense depth map prediction. We cover state-of-the-art fusion techniques which, in recent years, have been deep learning-based methods that are end-to-end trainable. We then conduct a comparative evaluation of the state-of-the-art techniques and provide a detailed analysis of their strengths and limitations as well as the applications they are best suited for.
International Journal of coastal and offshore engineering, 2017
The oil and gas pipelines are significant assets in Iran. However, these assets are subject to de... more The oil and gas pipelines are significant assets in Iran. However, these assets are subject to degradation from corrosion. Corrosion causes gradual thinning of the pipelines' wall leading to leaks or bursts. Allowing a corroding pipeline to continue operation may lead to a finite risk of exceeding the limit state of burst. Codes of practice, such as Modified ASME B31G [1] and DNV F101 [3], among others, have developed relationships to determine the bursting pressure of corroded pipelines. The purpose of this paper is to develop, test, and illustrate a simple spreadsheet-based probabilistic procedure that can be used by practicing engineers to determine the Remaining Useful Life (RUL) of a corroding pipeline, following its first inspection. Modified ASME B31G and DNV F101 equations are used to illustrate this method. As new inspection data regarding the extent of corrosion becomes available, the results can be updated and a new probability of failure can be obtained. The calculated probability of failure is then compared with the target values to determine the remaining life. The approach is equally applicable to both onshore and offshore oil and gas pipelines.
Numerical simulations of Vortex-Induced Vibrations (VIV) of a circular cylinder in cross flow wit... more Numerical simulations of Vortex-Induced Vibrations (VIV) of a circular cylinder in cross flow with a rotational degree of freedom about its axis have been carried out by means of a finite-volume method. The study is performed in two dimensions at a Reynolds number of ReD = 100, based on the free stream velocity and the diameter, D, of the cylinder. The effect of the rotational degree of freedom on the cylinder’s lift and drag forces are compared with the baseline simulation results of flow around a stationary cylinder. The introduction of a rotational degree of freedom (d.o.f) is observed to cause the lift and drag forces to change. Also, the pattern of vortex shedding behind the cylinder is found to drastically change when the cylinder is allowed to rotate.
Endoscopic endonasal surgery is a minimal invasive surgery that has been used to dissect pituitar... more Endoscopic endonasal surgery is a minimal invasive surgery that has been used to dissect pituitary gland tumour via curettes with the help of endoscope. However, this type of surgery has a high risk of failure because curettes may cause damages to blood vessels and optical nerves that lead to more complication for the patient. The aim of this study is to develop a new technique to dissect the tumour by using liquid jet. A series of experimental tests have been performed on animal tissue to study the effect of liquid pressure and nozzle diameter on dissecting and cutting the tissue. Continuous / pulsed liquid jet used with variable nozzle diameters, distances, pressures and angles. The study concluded with promising results on liquid jet to dissect hypophysis tumour and preserving fine blood vessels and optical nerve located near the pituitary gland. Index Terms-Endoscopic endonasal surgery, tumour removal, liquid jet, continuous and pulsed jet
Article History: Received: 4 Sep. 2017 Accepted: 24 Dec. 2017 The accidental release and ignition... more Article History: Received: 4 Sep. 2017 Accepted: 24 Dec. 2017 The accidental release and ignition of flammable vapours in petrochemical facilities generate overpressure and drag load which can impact the safety of installation and people. The intensity of the blast loads depends on many influencing factors including congestion, geometry, type & amount of fuel, leak size, and points of ignition among others. Given the stochastic nature of these parameters, it is obvious that the design for accidental load must be determined using a probabilistic method. This paper discusses a methodology known as “explosion exceedance diagram” and draws on recent developments in vapour cloud explosion research to determine the design accidental load (DAL). A case study demonstrates the application of the method.
The accuracy and computational efficiency of various interpolation methods for the implementation... more The accuracy and computational efficiency of various interpolation methods for the implementation of non grid-confirming boundaries is assessed. The aim of the research is to select an interpolation method that is both efficient and sufficiently accurate to be used in the simulation of vortex induced vibration of the flow around a deformable cylinder. Results are presented of an immersed boundary implementation in which the velocities near nonconfirming boundaries were interpolated in the normal direction to the walls. The flow field is solved on a Cartesian grid using a finite volume method with a staggered variable arrangement. The Strouhal number and Drag coefficient for various cases are reported. The results show a good agreement with the literature. Also, the drag coefficient and Strouhal number results for five different interpolation methods were compared it was shown that for a stationary cylinder at low Reynolds number, the interpolation method could affect the drag coeffi...
With the increasing demand for energy consumption in domestic buildings and consequent CO 2 emiss... more With the increasing demand for energy consumption in domestic buildings and consequent CO 2 emission, there is a need to provide proper products to reduce energy loss. Domestic radiators for space heating can be improved by using a Compact Latent Heat Storage (CLHS) unit mounted on the wall side surface in order to offer energy saving and peak-shaving. The unit offers the potential to save otherwise wasted energy from the back surface of the radiator to the walls in the charging mode of the energy storage system. When the heating system is turned off, the CLHS unit discharges the stored heat towards the room to provide a uniform temperature on the surface of the radiator. An aluminium foam embedded inside the bulk Phase Change Material (PCM) can modify the heat storage/retrieval rate. A PCM is selected depending on the radiator's surface temperature, which is almost equal to the hot water temperature delivered to the radiator. Different metal foam porosities are examined and compared with the PCM-only alternative (i.e. without metal foam enhancement). The results show the porous-PCM CLHS alternative provides an almost constant temperature during the discharging process equal to 54°C. However, for the PCM-only alternative, the temperature of the surface reduces continuously. Using the porous medium results in a shorter melting time, about 95% of what is needed for the PCM-only alternative. Increasing the metal foam porosity results in shorter charging/discharging time; however, since the surface temperature of the porous-PCM unit is almost constant for different metal foam porosities, a system with higher porosity (97%) is desirable.
A novel multi-dimensional combined isotropic-kinematic plasticity material model was recently dev... more A novel multi-dimensional combined isotropic-kinematic plasticity material model was recently developed by the authors for thermo-mechanical analysis of steels at elevated temperatures. In this paper, the capability of the new material model was further validated for transient loading conditions during both heating and cooling using recent experimental data. The multi-dimensional material model was adapted to a 1D J2 plasticity model and implemented as a uniaxial material model in the open source software OpenSEES for studying structural performance of stainless steel beam and frame structures in fire using finite element analysis (FEA). This paper presents the findings of the studies, with a focus on the behavioural comparisons between the carbon steel and the stainless steel structures. Using the FEA method, the studies provided results that filled the research gap in understanding the global structural fire performance of stainless steel structural systems. The significant impact of stainless steels' high material non-linearity and high thermal expansion on their structural fire performance is highlighted.
Journal of Peridynamics and Nonlocal Modeling, 2020
The concept of ‘contact stress’, as introduced by Cauchy, is a special case of a nonlocal stress ... more The concept of ‘contact stress’, as introduced by Cauchy, is a special case of a nonlocal stress tensor. In this work, the nonlocal stress tensor is derived through implementation of the bond-based formulation of peridynamics that uses an idealised model of interaction between points as bonds. The method is sufficiently general and can be implemented to study stress states in problems containing stress concentration, singularity, or discontinuities. Two case studies are presented, to study stress concentration around a circular hole in a square plate and conventionally singular stress fields in the vicinity of a sharp crack tip. The peridynamic stress tensor is compared with finite element approximations and available analytical solutions. It is shown that peridynamics is capable of capturing both shear and direct stresses and the results obtained correlate well with those obtained using analytical solutions and finite element approximations. A built-in MATLAB code is developed and ...
Systems readiness level (SRL) is a metric defined for assessing progress in the development of sy... more Systems readiness level (SRL) is a metric defined for assessing progress in the development of systems. The methodologies to estimate SRLs are built on the technology readiness level (TRL), originally developed by NASA to assess the readiness of new technologies for insertion into a system. TRL was later adopted by governmental institutions and many industries, including the American Petroleum Institute (API). The TRL of each component is mathematically combined with another metric, integration readiness level (IRL), to estimate the overall level of readiness of a system. An averaging procedure is then used to estimate the composite level of systems readiness. The present paper builds on the previous paper by Yasseri (2013) and presents case examples to demonstrate the estimation of SRL using two approaches. The objective of the present paper is to show how the TRL, IRL, and SRL are combined mathematically. The performance of the methodology is also demonstrated in a parametric stud...
A peridynamics (PD)–extended finite element method (XFEM) coupling strategy for brittle fracture ... more A peridynamics (PD)–extended finite element method (XFEM) coupling strategy for brittle fracture simulation is presented. The proposed methodology combines a small PD patch, restricted near the crack tip area, with the XFEM that captures the crack body geometry outside the domain of the localised PD grid. The feasibility and effectiveness of the proposed method on a Mode I crack opening problem is examined. The study focuses on comparisons of theJintegral values between the new coupling strategy, full PD grids and the commercial software Abaqus. It is demonstrated that the proposed approach outperforms full PD grids in terms of computational resources required to obtain a certain degree of accuracy. This finding promises significant computational savings when crack propagation problems are considered, as the efficiency of FEM and XFEM is combined with the inherent ability of PD to simulate fracture.
For the purpose of concurrent engineering, ease of fabrication, time to first oil and reduction o... more For the purpose of concurrent engineering, ease of fabrication, time to first oil and reduction of onsite special competencies, the topside of FPSO is divided into several modules. Modularization minimizes interaction between the modules by increasing interaction within the module. Interactions are interfaces which must be recognized, defined, designed, documented and tested. The term interface refers to any logical or physical relationship required to integrate the boundaries between systems, subsystems and their environment. Systems and subsystems can include hardware and software. Interface management (IM) is a process to manage interfaces efficiently. The intention is to define a process which makes IM cost-effective and efficient. The proposed process starts breaking down the total system into several subsystems or modules with minimal interaction between them. Following the system engineering V-diagram all interface requirements, their possible solution, and method of testing them are documented. The Design Structure Matrix (DSM) is used to identify an optimal number of modules as well as for the tracking interface progress during the design, fabrication and installation phases. Strategies needed to manage interfaces between various subsystems are discussed. The methodology is equally applicable to other industries that also face interface management of complex systems.
The effects of moderate intensity 'hot' or 'cold' shock in brittle solids have been extensively s... more The effects of moderate intensity 'hot' or 'cold' shock in brittle solids have been extensively studied, while much less is known about thermal shock response during large temperature variations. In this study, a combined finite elementperidynamics numerical procedure is proposed for the simulation of cracking in ceramic materials, undergoing severe thermal shock. Initially, Finite Element nonlinear heat transfer analysis is conducted. The effects of surface convection and radiation heat exchange are also included. Subsequently, the interpolated temperature field is used to formulate a varying temperature induced action for a bond-based peridynamics model. The present model, which is weakly coupled, is found to reproduce accurately previous numerical and experimental results regarding the case of a 'cold' shock. Through several numerical experiments it is established that 'cold' and 'hot' shock conditions give rise to different failure modes and that large temperature variations lead to intensified damage evolution.
Fretting fatigue occurs in engineering applications where two interacting surfaces are subjected ... more Fretting fatigue occurs in engineering applications where two interacting surfaces are subjected to fluctuating forces. The fluctuating forces occasionally act as a combined loading condition. The present paper investigates fretting fatigue behaviour of 316L stainless steel under such combined (i.e. tensile and bending) loading conditions. A new fixture was developed in order to apply bending and tensile loads simultaneously. Using this fixture, the effect of different bending-to-tension ratios was investigated. The results showed that increasing the contribution of bending load improves fretting fatigue life. On the other hand, increasing grain size decreases fretting fatigue life. Furthermore, sensitivity analysis based on Taguchi method revealed that fretting fatigue life is more sensitive to the increment of bending force contribution. The cyclic behavior of the specimens was assessed and finite element simulation was utilized to study the main contact parameters, including contact pressure, shear stress, and relative slip. Whilst confirming the experimental results, the simulation further showed that increasing the contribution of bending force reduces the concentration behavior at the contact edges.
International Journal of coastal and offshore engineering, 2018
Due to the high investment costs for deep-water subsea production systems of high-value subsea fi... more Due to the high investment costs for deep-water subsea production systems of high-value subsea fields, it is crucial to ensure a high availability to recover the investment. The problem is compounded by the cost of recovery, repair and replacement of failed equipment. Testing and reliability analyses are two pillars of reliability assurance; neither of them on their own assures the delivery of a reliable system. Possibly with more imaginative use of reliability methods, it is possible to optimise testing. It is suggested to use reliability analysis as a guide for allocating resources for testing. This paper outlines a Systems Engineering Framework to link the Client's requirements for equipment reliability, as a means of proving the desired level of performance. This framework allows a better understanding of verification settings and strategies to handle constraints (e.g. costs, expandability, repair-ability, maintainability, intervention procedures, downtime, automation etc.) and performance measures, to achieve highly reliable production systems. The bilateral links between the Client's requirements and subsea equipment performance are established using the systems engineering V-model. These links relate equipment performance to one or more of the Client's requirements, which helps establish verification and validation testing strategies to enhance reliability and reduce project risk. The proposed procedure also assists risk management efforts by feeding the results of reliability analyses, testing and project risk analysis into validation processes, the systems engineering measurement process ensures enhanced reliability. We define reliability assurance as a part of the systems engineering processes to ensure the continued function and resilience of the production system from the downhole valve to the subsea equipment, housed on the topside or at an onshore terminal, in their operating environment and condition using the "Fit-For-Service" notion.
International Journal of coastal and offshore engineering, 2018
Safety in marine operations primarily depends on forward-planning and people being aware of their... more Safety in marine operations primarily depends on forward-planning and people being aware of their surroundings and managing the presence of others in the same arena at the same time. Marine operations must contend with challenging environments and hazards that require greater domain awareness; especially when many operators from different organisations are working in the same area. Being aware of what is going on around you in a marine domain, is termed Marine Domain Awareness (MDA), which involves the perception and understanding of environmental factors, their meaning and effects, and foreseeing their likely status and impact in the near future. This paper applies Situational Awareness (SA) concepts to the safety of marine operations and proposes a model for developing an information exchange system to enhance marine operational safety. The proposed model enhances MDA and can help in developing procedures and training programs to promote domain awareness. A framework for the safe marine operation is outlined in this paper.
Equipment repair and intervention in subsea oil and gas fields are expensive, mainly due to vesse... more Equipment repair and intervention in subsea oil and gas fields are expensive, mainly due to vessel mobilization time, retrieval, repair, and replacement costs. The loss of revenue due to downtime could also be significant and the producer could face penalties in not meeting contractual commitments. These costs are part of the life cycle cost, which must be considered at the design stage. Estimating the reliability and availability of subsea systems at an early stage of design is important in assuring the quality of the system architecture, which leads to a more reliable choice of configuration and equipment. Availability analyses should be undertaken very early in the development process, while the operational concept is still under review, and the choice of components is still to be finalized. Postponing this assessment could prove to be too costly to improve the availability and dependability. This paper presents a reliability assessment using a systems engineering framework by combining the system's requirements and reliability requirements. A Design Structure Matrix (DSM) is employed to map the system and visualize the interrelationships (dependencies) between components/subsystems. The DSM is then augmented with reliability data, including intervention times, to determine the overall system availability. It is also explained how to use the system's DSM to aid integration and interface management decisions. A case study is presented to demonstrate this procedure. It is also important to consider the hookup requirements for Remotely Operated Vehicles (ROVs). In deep-water applications, the deployment time and hookup costs for an ROV will have a major impact on the optimization of the subsea field architecture. Commonly Subsea Control Modules (SCMs) are located on the X-tree during running but can be retrieved with or without the tree. From the SDU, the cable and jumpers distribute out to the SCMs. The feasibility of the final arrangement is governed by voltage drop limitations and input voltages required at the SCMs. Reliability is a cornerstone of the offshore petroleum industry (ISO 2015, ISO 2008). Repair and intervention operations at a subsea oil and gas field are costly due to expenditure needed for vessel mobilization times, retrieval of the failed unit, and replacement. Loss of production (revenue) and intervention costs are an integral part of the life cycle cost of an SPS. The primary reliability measure for a maintained system is its availability (OREDA 2009). In other words, the availability of a system is its ability to deliver the required function and performance (OREDA 2009) for the required duration. Subsea availability depends on equipment reliability, retrievability, maintainability, as well as the performance of the maintenance crew. Reliability and
In this review, we provide a detailed coverage of multi-sensor fusion techniques that use RGB ste... more In this review, we provide a detailed coverage of multi-sensor fusion techniques that use RGB stereo images and a sparse LiDAR-projected depth map as input data to output a dense depth map prediction. We cover state-of-the-art fusion techniques which, in recent years, have been deep learning-based methods that are end-to-end trainable. We then conduct a comparative evaluation of the state-of-the-art techniques and provide a detailed analysis of their strengths and limitations as well as the applications they are best suited for.
International Journal of coastal and offshore engineering, 2017
The oil and gas pipelines are significant assets in Iran. However, these assets are subject to de... more The oil and gas pipelines are significant assets in Iran. However, these assets are subject to degradation from corrosion. Corrosion causes gradual thinning of the pipelines' wall leading to leaks or bursts. Allowing a corroding pipeline to continue operation may lead to a finite risk of exceeding the limit state of burst. Codes of practice, such as Modified ASME B31G [1] and DNV F101 [3], among others, have developed relationships to determine the bursting pressure of corroded pipelines. The purpose of this paper is to develop, test, and illustrate a simple spreadsheet-based probabilistic procedure that can be used by practicing engineers to determine the Remaining Useful Life (RUL) of a corroding pipeline, following its first inspection. Modified ASME B31G and DNV F101 equations are used to illustrate this method. As new inspection data regarding the extent of corrosion becomes available, the results can be updated and a new probability of failure can be obtained. The calculated probability of failure is then compared with the target values to determine the remaining life. The approach is equally applicable to both onshore and offshore oil and gas pipelines.
Numerical simulations of Vortex-Induced Vibrations (VIV) of a circular cylinder in cross flow wit... more Numerical simulations of Vortex-Induced Vibrations (VIV) of a circular cylinder in cross flow with a rotational degree of freedom about its axis have been carried out by means of a finite-volume method. The study is performed in two dimensions at a Reynolds number of ReD = 100, based on the free stream velocity and the diameter, D, of the cylinder. The effect of the rotational degree of freedom on the cylinder’s lift and drag forces are compared with the baseline simulation results of flow around a stationary cylinder. The introduction of a rotational degree of freedom (d.o.f) is observed to cause the lift and drag forces to change. Also, the pattern of vortex shedding behind the cylinder is found to drastically change when the cylinder is allowed to rotate.
Endoscopic endonasal surgery is a minimal invasive surgery that has been used to dissect pituitar... more Endoscopic endonasal surgery is a minimal invasive surgery that has been used to dissect pituitary gland tumour via curettes with the help of endoscope. However, this type of surgery has a high risk of failure because curettes may cause damages to blood vessels and optical nerves that lead to more complication for the patient. The aim of this study is to develop a new technique to dissect the tumour by using liquid jet. A series of experimental tests have been performed on animal tissue to study the effect of liquid pressure and nozzle diameter on dissecting and cutting the tissue. Continuous / pulsed liquid jet used with variable nozzle diameters, distances, pressures and angles. The study concluded with promising results on liquid jet to dissect hypophysis tumour and preserving fine blood vessels and optical nerve located near the pituitary gland. Index Terms-Endoscopic endonasal surgery, tumour removal, liquid jet, continuous and pulsed jet
Article History: Received: 4 Sep. 2017 Accepted: 24 Dec. 2017 The accidental release and ignition... more Article History: Received: 4 Sep. 2017 Accepted: 24 Dec. 2017 The accidental release and ignition of flammable vapours in petrochemical facilities generate overpressure and drag load which can impact the safety of installation and people. The intensity of the blast loads depends on many influencing factors including congestion, geometry, type & amount of fuel, leak size, and points of ignition among others. Given the stochastic nature of these parameters, it is obvious that the design for accidental load must be determined using a probabilistic method. This paper discusses a methodology known as “explosion exceedance diagram” and draws on recent developments in vapour cloud explosion research to determine the design accidental load (DAL). A case study demonstrates the application of the method.
The accuracy and computational efficiency of various interpolation methods for the implementation... more The accuracy and computational efficiency of various interpolation methods for the implementation of non grid-confirming boundaries is assessed. The aim of the research is to select an interpolation method that is both efficient and sufficiently accurate to be used in the simulation of vortex induced vibration of the flow around a deformable cylinder. Results are presented of an immersed boundary implementation in which the velocities near nonconfirming boundaries were interpolated in the normal direction to the walls. The flow field is solved on a Cartesian grid using a finite volume method with a staggered variable arrangement. The Strouhal number and Drag coefficient for various cases are reported. The results show a good agreement with the literature. Also, the drag coefficient and Strouhal number results for five different interpolation methods were compared it was shown that for a stationary cylinder at low Reynolds number, the interpolation method could affect the drag coeffi...
With the increasing demand for energy consumption in domestic buildings and consequent CO 2 emiss... more With the increasing demand for energy consumption in domestic buildings and consequent CO 2 emission, there is a need to provide proper products to reduce energy loss. Domestic radiators for space heating can be improved by using a Compact Latent Heat Storage (CLHS) unit mounted on the wall side surface in order to offer energy saving and peak-shaving. The unit offers the potential to save otherwise wasted energy from the back surface of the radiator to the walls in the charging mode of the energy storage system. When the heating system is turned off, the CLHS unit discharges the stored heat towards the room to provide a uniform temperature on the surface of the radiator. An aluminium foam embedded inside the bulk Phase Change Material (PCM) can modify the heat storage/retrieval rate. A PCM is selected depending on the radiator's surface temperature, which is almost equal to the hot water temperature delivered to the radiator. Different metal foam porosities are examined and compared with the PCM-only alternative (i.e. without metal foam enhancement). The results show the porous-PCM CLHS alternative provides an almost constant temperature during the discharging process equal to 54°C. However, for the PCM-only alternative, the temperature of the surface reduces continuously. Using the porous medium results in a shorter melting time, about 95% of what is needed for the PCM-only alternative. Increasing the metal foam porosity results in shorter charging/discharging time; however, since the surface temperature of the porous-PCM unit is almost constant for different metal foam porosities, a system with higher porosity (97%) is desirable.
A novel multi-dimensional combined isotropic-kinematic plasticity material model was recently dev... more A novel multi-dimensional combined isotropic-kinematic plasticity material model was recently developed by the authors for thermo-mechanical analysis of steels at elevated temperatures. In this paper, the capability of the new material model was further validated for transient loading conditions during both heating and cooling using recent experimental data. The multi-dimensional material model was adapted to a 1D J2 plasticity model and implemented as a uniaxial material model in the open source software OpenSEES for studying structural performance of stainless steel beam and frame structures in fire using finite element analysis (FEA). This paper presents the findings of the studies, with a focus on the behavioural comparisons between the carbon steel and the stainless steel structures. Using the FEA method, the studies provided results that filled the research gap in understanding the global structural fire performance of stainless steel structural systems. The significant impact of stainless steels' high material non-linearity and high thermal expansion on their structural fire performance is highlighted.
Journal of Peridynamics and Nonlocal Modeling, 2020
The concept of ‘contact stress’, as introduced by Cauchy, is a special case of a nonlocal stress ... more The concept of ‘contact stress’, as introduced by Cauchy, is a special case of a nonlocal stress tensor. In this work, the nonlocal stress tensor is derived through implementation of the bond-based formulation of peridynamics that uses an idealised model of interaction between points as bonds. The method is sufficiently general and can be implemented to study stress states in problems containing stress concentration, singularity, or discontinuities. Two case studies are presented, to study stress concentration around a circular hole in a square plate and conventionally singular stress fields in the vicinity of a sharp crack tip. The peridynamic stress tensor is compared with finite element approximations and available analytical solutions. It is shown that peridynamics is capable of capturing both shear and direct stresses and the results obtained correlate well with those obtained using analytical solutions and finite element approximations. A built-in MATLAB code is developed and ...
Systems readiness level (SRL) is a metric defined for assessing progress in the development of sy... more Systems readiness level (SRL) is a metric defined for assessing progress in the development of systems. The methodologies to estimate SRLs are built on the technology readiness level (TRL), originally developed by NASA to assess the readiness of new technologies for insertion into a system. TRL was later adopted by governmental institutions and many industries, including the American Petroleum Institute (API). The TRL of each component is mathematically combined with another metric, integration readiness level (IRL), to estimate the overall level of readiness of a system. An averaging procedure is then used to estimate the composite level of systems readiness. The present paper builds on the previous paper by Yasseri (2013) and presents case examples to demonstrate the estimation of SRL using two approaches. The objective of the present paper is to show how the TRL, IRL, and SRL are combined mathematically. The performance of the methodology is also demonstrated in a parametric stud...
A peridynamics (PD)–extended finite element method (XFEM) coupling strategy for brittle fracture ... more A peridynamics (PD)–extended finite element method (XFEM) coupling strategy for brittle fracture simulation is presented. The proposed methodology combines a small PD patch, restricted near the crack tip area, with the XFEM that captures the crack body geometry outside the domain of the localised PD grid. The feasibility and effectiveness of the proposed method on a Mode I crack opening problem is examined. The study focuses on comparisons of theJintegral values between the new coupling strategy, full PD grids and the commercial software Abaqus. It is demonstrated that the proposed approach outperforms full PD grids in terms of computational resources required to obtain a certain degree of accuracy. This finding promises significant computational savings when crack propagation problems are considered, as the efficiency of FEM and XFEM is combined with the inherent ability of PD to simulate fracture.
For the purpose of concurrent engineering, ease of fabrication, time to first oil and reduction o... more For the purpose of concurrent engineering, ease of fabrication, time to first oil and reduction of onsite special competencies, the topside of FPSO is divided into several modules. Modularization minimizes interaction between the modules by increasing interaction within the module. Interactions are interfaces which must be recognized, defined, designed, documented and tested. The term interface refers to any logical or physical relationship required to integrate the boundaries between systems, subsystems and their environment. Systems and subsystems can include hardware and software. Interface management (IM) is a process to manage interfaces efficiently. The intention is to define a process which makes IM cost-effective and efficient. The proposed process starts breaking down the total system into several subsystems or modules with minimal interaction between them. Following the system engineering V-diagram all interface requirements, their possible solution, and method of testing them are documented. The Design Structure Matrix (DSM) is used to identify an optimal number of modules as well as for the tracking interface progress during the design, fabrication and installation phases. Strategies needed to manage interfaces between various subsystems are discussed. The methodology is equally applicable to other industries that also face interface management of complex systems.
The effects of moderate intensity 'hot' or 'cold' shock in brittle solids have been extensively s... more The effects of moderate intensity 'hot' or 'cold' shock in brittle solids have been extensively studied, while much less is known about thermal shock response during large temperature variations. In this study, a combined finite elementperidynamics numerical procedure is proposed for the simulation of cracking in ceramic materials, undergoing severe thermal shock. Initially, Finite Element nonlinear heat transfer analysis is conducted. The effects of surface convection and radiation heat exchange are also included. Subsequently, the interpolated temperature field is used to formulate a varying temperature induced action for a bond-based peridynamics model. The present model, which is weakly coupled, is found to reproduce accurately previous numerical and experimental results regarding the case of a 'cold' shock. Through several numerical experiments it is established that 'cold' and 'hot' shock conditions give rise to different failure modes and that large temperature variations lead to intensified damage evolution.
Fretting fatigue occurs in engineering applications where two interacting surfaces are subjected ... more Fretting fatigue occurs in engineering applications where two interacting surfaces are subjected to fluctuating forces. The fluctuating forces occasionally act as a combined loading condition. The present paper investigates fretting fatigue behaviour of 316L stainless steel under such combined (i.e. tensile and bending) loading conditions. A new fixture was developed in order to apply bending and tensile loads simultaneously. Using this fixture, the effect of different bending-to-tension ratios was investigated. The results showed that increasing the contribution of bending load improves fretting fatigue life. On the other hand, increasing grain size decreases fretting fatigue life. Furthermore, sensitivity analysis based on Taguchi method revealed that fretting fatigue life is more sensitive to the increment of bending force contribution. The cyclic behavior of the specimens was assessed and finite element simulation was utilized to study the main contact parameters, including contact pressure, shear stress, and relative slip. Whilst confirming the experimental results, the simulation further showed that increasing the contribution of bending force reduces the concentration behavior at the contact edges.
International Journal of coastal and offshore engineering, 2018
Due to the high investment costs for deep-water subsea production systems of high-value subsea fi... more Due to the high investment costs for deep-water subsea production systems of high-value subsea fields, it is crucial to ensure a high availability to recover the investment. The problem is compounded by the cost of recovery, repair and replacement of failed equipment. Testing and reliability analyses are two pillars of reliability assurance; neither of them on their own assures the delivery of a reliable system. Possibly with more imaginative use of reliability methods, it is possible to optimise testing. It is suggested to use reliability analysis as a guide for allocating resources for testing. This paper outlines a Systems Engineering Framework to link the Client's requirements for equipment reliability, as a means of proving the desired level of performance. This framework allows a better understanding of verification settings and strategies to handle constraints (e.g. costs, expandability, repair-ability, maintainability, intervention procedures, downtime, automation etc.) and performance measures, to achieve highly reliable production systems. The bilateral links between the Client's requirements and subsea equipment performance are established using the systems engineering V-model. These links relate equipment performance to one or more of the Client's requirements, which helps establish verification and validation testing strategies to enhance reliability and reduce project risk. The proposed procedure also assists risk management efforts by feeding the results of reliability analyses, testing and project risk analysis into validation processes, the systems engineering measurement process ensures enhanced reliability. We define reliability assurance as a part of the systems engineering processes to ensure the continued function and resilience of the production system from the downhole valve to the subsea equipment, housed on the topside or at an onshore terminal, in their operating environment and condition using the "Fit-For-Service" notion.
International Journal of coastal and offshore engineering, 2018
Safety in marine operations primarily depends on forward-planning and people being aware of their... more Safety in marine operations primarily depends on forward-planning and people being aware of their surroundings and managing the presence of others in the same arena at the same time. Marine operations must contend with challenging environments and hazards that require greater domain awareness; especially when many operators from different organisations are working in the same area. Being aware of what is going on around you in a marine domain, is termed Marine Domain Awareness (MDA), which involves the perception and understanding of environmental factors, their meaning and effects, and foreseeing their likely status and impact in the near future. This paper applies Situational Awareness (SA) concepts to the safety of marine operations and proposes a model for developing an information exchange system to enhance marine operational safety. The proposed model enhances MDA and can help in developing procedures and training programs to promote domain awareness. A framework for the safe marine operation is outlined in this paper.
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Papers by Hamid Bahai