Corrosion can lead to reduction of structural stiffness and strength. This paper investigates the... more Corrosion can lead to reduction of structural stiffness and strength. This paper investigates the influence of a reduction in the thickness of the plates as a result of general corrosion on sandwich panel buckling load and onset of plasticity. The results are compared to the stiffened panel of the same in-plane and bending stiffness. Current guidelines for corrosion protection threat these two structures equally. Load-shortening curves are obtained with the finite element method, with the kinematics being represented using two approaches: (1) equivalent single-layer with first-order shear deformation theory, and (2) a three-dimensional model of the actual geometry of the structure, modeled using shell and connector elements. The former is also used to identify the influence of corrosion on the stiffness coefficients and, consequently, the buckling load, also via analytical equation. The decrease of the buckling load is found higher in sandwich panel than in stiffened panel. The redu...
Although machine learning (ML) is increasingly employed recently for mechanistic problems, the bl... more Although machine learning (ML) is increasingly employed recently for mechanistic problems, the black-box nature of conventional ML architectures lacks the physical knowledge to infer unforeseen input conditions. This implies both severe overfitting during a dearth of training data and inadequate physical interpretability, which motivates us to propose a new kinematically consistent, physics-based ML model. In particular, we attempt to perform physically interpretable learning of inverse problems in wave propagation without suffering overfitting restrictions. Towards this goal, we employ long short-term memory (LSTM) networks endowed with a physical, hyperparameter-driven regularizer, performing penalty-based enforcement of the characteristic geometries. Since these characteristics are the kinematical invariances of wave propagation phenomena, maintaining their structure provides kinematical consistency to the network. Even with modest training data, the kinematically consistent netw...
Optimization of complex systems requires robust and computationally efficient global search algor... more Optimization of complex systems requires robust and computationally efficient global search algorithms. Constraints make this a very difficult task, significantly slowing down an algorithm, and can even prevent finding the true Pareto front. This study continues the development of a recently proposed repair approach that exploits infeasible designs to increase computational efficiency of a prominent genetic algorithm, and to find a wider spread of the Pareto front. This paper proposes adaptive and automatized discovery of sensitivity of constraints to variables, i.e. the link, which needed direct designer’s input in the previous version of the repair approach. This is achieved by using machine learning in the form of artificial neural networks (ANN). A surrogate model is afterwards utilized in optimization based on ANN. The proposed approach is used for the recently proposed constraint handling implemented into NSGA-II optimization algorithm. The proposed framework is compared with ...
<p>... more <p>Rapid sea level rise due to an ice sheet collapse has the potential to be extremely damaging to coastal communities and infrastructure, and conventional coastal protection techniques (dykes, levees, etc) can be quite expensive. In the past we have proposed that society might employ artificial sills and pinning points at critical marine ice streams in Antarctica to slow the rate of sea level rise at the source (Wolovick and Moore, 2018). However, thick earthen sills are likely to be extremely expensive and difficult to construct. If the goal of the intervention is only to block warm water from reaching the grounding line, then an alternate intervention consisting of thin flexible buoyant curtains anchored to the seabed might be employed instead. Flexible curtains are likely to be cheaper, more robust against iceberg collisions, and easier to remove in the event of unforeseen side effects. Here, we use a simple ice flow model to evaluate the effectiveness of such an intervention at three important Greenlandic outlet glaciers, and we make crude estimates of the forces on the curtain and of the likely cost of construction. We find that the single most important factor controlling the effectiveness of a thin water-blocking intervention (defined as either slowing glacier retreat or causing readvance) is the exposure of the glacier to deep warm water at the time of barrier construction. This means that, for Jakobshavn Isbrae, which has a deep (~1000 m) central trough extending well over 100 km inland, a water-blocking intervention is likely to be effective far into the future, and also that the preventable retreat (in comparison to a no-intervention scenario) is quite large. For Helheim and Kangerdlugssuaq, however, the central trough rises rapidly just a few tens of kilometers inland of the present-day calving front, removing the vulnerability to deep warm water after a relatively small retreat. This means both that the intervention must be begun relatively soon if it is to have an effect at those glaciers, and that the preventable retreat is smaller. With respect to the forces acting on the curtain, we find that the static tensile load on the curtain rises quadratically with the height above the seabed, and linearly with respect to the density contrast between the inner waters and the outer waters. Since the natural sills at the fjord mouths are roughly three times deeper at Helheim and Kangerdlugssuaq than they are at Jakobshavn, curtains at the former would need to be roughly an order of magnitude stronger than curtains at the latter. We estimate that this translates into roughly five times greater cost (per unit barrier length) at the two East Greenland glaciers than at Jakobshavn. Therefore, based on both cost and effectiveness, we find that this type of intervention is more favored for Jakobshavn than it is for Helheim and Kangerdlugssuuaq.</p>
Journal of Offshore Mechanics and Arctic Engineering
Present paper gives an overview of the factors that affect the strength and structural design of ... more Present paper gives an overview of the factors that affect the strength and structural design of advanced thin-walled marine structures with reduced plate thickness or alternative topologies to those used today in marine industry. Due to production-induced initial deformations and resulting geometrical non-linearity, the classical division between primary, secondary and tertiary responses becomes strongly coupled. Volume-averaged, non-linear response of structural element can be used to define the structural stress strain relation that enables analysis at the next, larger, length scale. This, today's standard homogenization process needs to be complemented with localization, where the stresses are assessed at the details, such as welds for fatigue analysis. Due to this, the production-induced initial distortions need to be considered with high accuracy. Another key question is the length-scale interaction in terms of continuum description. Non-classical continuum mechanics are n...
This paper investigates theoretically the differences in load-carrying behaviour between web-core... more This paper investigates theoretically the differences in load-carrying behaviour between web-core sandwich plate, stiffened plate and isotropic plate. Buckling and post-buckling is studied. The study is carried out using two approaches, both solved with the finite element method. The first is a three-dimensional model of the plates. The second approach is the equivalent single-layer theory approach. First-order shear deformation theory is used. The second approach allows plates to the viewed through ABD- and DQ stiffness coefficients. Plates are axially loaded in the web plate/stiffener direction. Simply supported boundary condition is considered with loaded edges kept straight and unloaded edges free to move in-plane. The results show that the buckling load of sandwich plate is 42% to 65% higher than the stiffened plates. The reason is that sand-wich plate is a symmetrical structure where coupling between in-plane and out-of-plane displacements does not exist (B-matrix is equal to zero). Furthermore, breadth-to-thickness ratio (representing local plate slender-ness) is about two times lower in sandwich plate than in stiffened plate which prevents local buckling. On the other hand, buckling load of sandwich plate can be improved by increasing the transverse shear stiffness, e.g. by filling the voids in the core. For the same structural weight, post-buckling stiffness of stiffened plate is somewhat lower than in sandwich, also owing to the B-matrix. Isotropic plate of the same bending stiffness as sandwich plate has higher post-buckling stiffness due to larger in-plane stiffness (A-matrix) or structural weight.
Recently, various novel steel sandwich structures have been proposed as they promise increased en... more Recently, various novel steel sandwich structures have been proposed as they promise increased energy absorbing capabilities during impact or collision. The amount of energy absorbed during impact depends on the sandwich core geometry. Therefore, in this study, two different sandwich core geometries (X- and Y-core) are optimized for crashworthiness. An evolutionary-based optimization algorithm is used for the optimization. Impact simulations including fracture are carried out with the non-linear finite element solver. The resulting optimized core geometries are compared with initial designs from literature to identify the potential gains in crashworthiness. Optimized sandwich panels are able to absorb more impact energy than the initial designs, even without the weight penalty. Their collapse mechanism is studied in more detail.
A homogenization method for geometric nonlinear analysis of sandwich structures with initial imperfections
A homogenization method for geometric nonlinear analysis of structural core sandwich panels is pr... more A homogenization method for geometric nonlinear analysis of structural core sandwich panels is pro- posed. The method provides high computational performance based on an efficient separation of scales. In the macroscale, the sandwich panel is discretized with an equivalent single layer of shell elements. The macroscale shell stiffness matrix is nonlinear, obtained from the analysis of a representative volume el- ement. Prescribed displacement boundary conditions are applied to the representative unit based on the strain definitions of the first-order shear deformation theory. Changes in local wavelength in the post- buckling are considered in the analyses. Manufacturing-induced imperfections are introduced to local and global scales. The method allows for description of buckling in these two scales and is shown to hold good accuracy with respect to equivalent 3D FEM models. Examples include web-core and corrugated- core sandwich panels. The method can be extended to any periodic structure of complex local topology. It can be easily implemented to commercial FE packages.
Corrosion can lead to reduction of structural stiffness and strength. This paper investigates the... more Corrosion can lead to reduction of structural stiffness and strength. This paper investigates the influence of a reduction in the thickness of the plates as a result of general corrosion on sandwich panel buckling load and onset of plasticity. The results are compared to the stiffened panel of the same in-plane and bending stiffness. Current guidelines for corrosion protection threat these two structures equally. Load-shortening curves are obtained with the finite element method, with the kinematics being represented using two approaches: (1) equivalent single-layer with first-order shear deformation theory, and (2) a three-dimensional model of the actual geometry of the structure, modeled using shell and connector elements. The former is also used to identify the influence of corrosion on the stiffness coefficients and, consequently, the buckling load, also via analytical equation. The decrease of the buckling load is found higher in sandwich panel than in stiffened panel. The redu...
Although machine learning (ML) is increasingly employed recently for mechanistic problems, the bl... more Although machine learning (ML) is increasingly employed recently for mechanistic problems, the black-box nature of conventional ML architectures lacks the physical knowledge to infer unforeseen input conditions. This implies both severe overfitting during a dearth of training data and inadequate physical interpretability, which motivates us to propose a new kinematically consistent, physics-based ML model. In particular, we attempt to perform physically interpretable learning of inverse problems in wave propagation without suffering overfitting restrictions. Towards this goal, we employ long short-term memory (LSTM) networks endowed with a physical, hyperparameter-driven regularizer, performing penalty-based enforcement of the characteristic geometries. Since these characteristics are the kinematical invariances of wave propagation phenomena, maintaining their structure provides kinematical consistency to the network. Even with modest training data, the kinematically consistent netw...
Optimization of complex systems requires robust and computationally efficient global search algor... more Optimization of complex systems requires robust and computationally efficient global search algorithms. Constraints make this a very difficult task, significantly slowing down an algorithm, and can even prevent finding the true Pareto front. This study continues the development of a recently proposed repair approach that exploits infeasible designs to increase computational efficiency of a prominent genetic algorithm, and to find a wider spread of the Pareto front. This paper proposes adaptive and automatized discovery of sensitivity of constraints to variables, i.e. the link, which needed direct designer’s input in the previous version of the repair approach. This is achieved by using machine learning in the form of artificial neural networks (ANN). A surrogate model is afterwards utilized in optimization based on ANN. The proposed approach is used for the recently proposed constraint handling implemented into NSGA-II optimization algorithm. The proposed framework is compared with ...
<p>... more <p>Rapid sea level rise due to an ice sheet collapse has the potential to be extremely damaging to coastal communities and infrastructure, and conventional coastal protection techniques (dykes, levees, etc) can be quite expensive. In the past we have proposed that society might employ artificial sills and pinning points at critical marine ice streams in Antarctica to slow the rate of sea level rise at the source (Wolovick and Moore, 2018). However, thick earthen sills are likely to be extremely expensive and difficult to construct. If the goal of the intervention is only to block warm water from reaching the grounding line, then an alternate intervention consisting of thin flexible buoyant curtains anchored to the seabed might be employed instead. Flexible curtains are likely to be cheaper, more robust against iceberg collisions, and easier to remove in the event of unforeseen side effects. Here, we use a simple ice flow model to evaluate the effectiveness of such an intervention at three important Greenlandic outlet glaciers, and we make crude estimates of the forces on the curtain and of the likely cost of construction. We find that the single most important factor controlling the effectiveness of a thin water-blocking intervention (defined as either slowing glacier retreat or causing readvance) is the exposure of the glacier to deep warm water at the time of barrier construction. This means that, for Jakobshavn Isbrae, which has a deep (~1000 m) central trough extending well over 100 km inland, a water-blocking intervention is likely to be effective far into the future, and also that the preventable retreat (in comparison to a no-intervention scenario) is quite large. For Helheim and Kangerdlugssuaq, however, the central trough rises rapidly just a few tens of kilometers inland of the present-day calving front, removing the vulnerability to deep warm water after a relatively small retreat. This means both that the intervention must be begun relatively soon if it is to have an effect at those glaciers, and that the preventable retreat is smaller. With respect to the forces acting on the curtain, we find that the static tensile load on the curtain rises quadratically with the height above the seabed, and linearly with respect to the density contrast between the inner waters and the outer waters. Since the natural sills at the fjord mouths are roughly three times deeper at Helheim and Kangerdlugssuaq than they are at Jakobshavn, curtains at the former would need to be roughly an order of magnitude stronger than curtains at the latter. We estimate that this translates into roughly five times greater cost (per unit barrier length) at the two East Greenland glaciers than at Jakobshavn. Therefore, based on both cost and effectiveness, we find that this type of intervention is more favored for Jakobshavn than it is for Helheim and Kangerdlugssuuaq.</p>
Journal of Offshore Mechanics and Arctic Engineering
Present paper gives an overview of the factors that affect the strength and structural design of ... more Present paper gives an overview of the factors that affect the strength and structural design of advanced thin-walled marine structures with reduced plate thickness or alternative topologies to those used today in marine industry. Due to production-induced initial deformations and resulting geometrical non-linearity, the classical division between primary, secondary and tertiary responses becomes strongly coupled. Volume-averaged, non-linear response of structural element can be used to define the structural stress strain relation that enables analysis at the next, larger, length scale. This, today's standard homogenization process needs to be complemented with localization, where the stresses are assessed at the details, such as welds for fatigue analysis. Due to this, the production-induced initial distortions need to be considered with high accuracy. Another key question is the length-scale interaction in terms of continuum description. Non-classical continuum mechanics are n...
This paper investigates theoretically the differences in load-carrying behaviour between web-core... more This paper investigates theoretically the differences in load-carrying behaviour between web-core sandwich plate, stiffened plate and isotropic plate. Buckling and post-buckling is studied. The study is carried out using two approaches, both solved with the finite element method. The first is a three-dimensional model of the plates. The second approach is the equivalent single-layer theory approach. First-order shear deformation theory is used. The second approach allows plates to the viewed through ABD- and DQ stiffness coefficients. Plates are axially loaded in the web plate/stiffener direction. Simply supported boundary condition is considered with loaded edges kept straight and unloaded edges free to move in-plane. The results show that the buckling load of sandwich plate is 42% to 65% higher than the stiffened plates. The reason is that sand-wich plate is a symmetrical structure where coupling between in-plane and out-of-plane displacements does not exist (B-matrix is equal to zero). Furthermore, breadth-to-thickness ratio (representing local plate slender-ness) is about two times lower in sandwich plate than in stiffened plate which prevents local buckling. On the other hand, buckling load of sandwich plate can be improved by increasing the transverse shear stiffness, e.g. by filling the voids in the core. For the same structural weight, post-buckling stiffness of stiffened plate is somewhat lower than in sandwich, also owing to the B-matrix. Isotropic plate of the same bending stiffness as sandwich plate has higher post-buckling stiffness due to larger in-plane stiffness (A-matrix) or structural weight.
Recently, various novel steel sandwich structures have been proposed as they promise increased en... more Recently, various novel steel sandwich structures have been proposed as they promise increased energy absorbing capabilities during impact or collision. The amount of energy absorbed during impact depends on the sandwich core geometry. Therefore, in this study, two different sandwich core geometries (X- and Y-core) are optimized for crashworthiness. An evolutionary-based optimization algorithm is used for the optimization. Impact simulations including fracture are carried out with the non-linear finite element solver. The resulting optimized core geometries are compared with initial designs from literature to identify the potential gains in crashworthiness. Optimized sandwich panels are able to absorb more impact energy than the initial designs, even without the weight penalty. Their collapse mechanism is studied in more detail.
A homogenization method for geometric nonlinear analysis of sandwich structures with initial imperfections
A homogenization method for geometric nonlinear analysis of structural core sandwich panels is pr... more A homogenization method for geometric nonlinear analysis of structural core sandwich panels is pro- posed. The method provides high computational performance based on an efficient separation of scales. In the macroscale, the sandwich panel is discretized with an equivalent single layer of shell elements. The macroscale shell stiffness matrix is nonlinear, obtained from the analysis of a representative volume el- ement. Prescribed displacement boundary conditions are applied to the representative unit based on the strain definitions of the first-order shear deformation theory. Changes in local wavelength in the post- buckling are considered in the analyses. Manufacturing-induced imperfections are introduced to local and global scales. The method allows for description of buckling in these two scales and is shown to hold good accuracy with respect to equivalent 3D FEM models. Examples include web-core and corrugated- core sandwich panels. The method can be extended to any periodic structure of complex local topology. It can be easily implemented to commercial FE packages.
Uploads
Papers by Jasmin Jelovica