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Papers by Kok Ang

Research paper thumbnail of Large Floating Structure with Free-Floating, Self-Stabilizing Tanks for Hydrocarbon Storage

Research paper thumbnail of Hydrodynamic aspects of moving vehicle with sloshing tanks

MATEC Web of Conferences, 2018

Freight vehicles with partially filled liquid tanks will be affected by liquid sloshing during tr... more Freight vehicles with partially filled liquid tanks will be affected by liquid sloshing during transient motion. The sloshing induced by vehicle motion will lead to extra force on the vehicle and sometimes is a potential threat to safety. Previous studies on this problem usually use a mass-spring analogy to represent the sloshing effect of the liquid tank. Its main disadvantage is that CFD analysis or experimental study has to be performed beforehand, so that an equivalent mass-spring model can be constructed by curve fitting. In this paper, frequency domain boundary element method (BEM) and analytical solution to the sloshing problems are used to derive the modal equation and hydrodynamic parameters of the sloshing fluid. The accuracy of the results will be examined by comparison with available CFD results in the literature. The paper then evaluates the accuracy of equivalent mass-spring model and explores the possibility to approximate the sloshing effects inside cylindrical tanks...

Research paper thumbnail of Initial Design of a Double Curved Floating Bridge and Global Hydrodynamic Responses Under Environmental Conditions

Volume 9: Offshore Geotechnics; Torgeir Moan Honoring Symposium, 2017

In this paper, a floating bridge concept is proposed. This bridge concept comprises a two opposit... more In this paper, a floating bridge concept is proposed. This bridge concept comprises a two oppositely curves in plan, which enables the cancellation of the axial forces at the bridge as one arch will be under compression while the other arch is in tension due to environmental forces acting in one direction. The road deck is carried by truss structures that are kept above the water by several elliptical cylindrical pontoons. To reduce drag load, the cross sectional area facing the current is reduced as much as possible, while the buoyancy is kept the same based on the initial weight estimation. Initial design consideration and methodology of a double curved floating bridge is presented, and a numerical model is established for analyzing this concept. Hydrodynamic and structural dynamic aspects are included in the numerical model. Parametric study of the bridge structural rigidity is performed to investigate the effect to the responses. White noise, regular and irregular wave simulatio...

Research paper thumbnail of Dynamic Response Analysis of Floating Storage Tank System Considering Hydrodynamic and Mechanical Interactions

Volume 6: Ocean Space Utilization, 2018

For better utilization of ocean and coastal space, hydrocarbon products can be stored in the floa... more For better utilization of ocean and coastal space, hydrocarbon products can be stored in the floating tanks, which can be enclosed by barge system. The barge system can be moored through pile foundations. The tanks are moored through marine fenders connected to barges. In the system, hydrodynamic and mechanical interaction problems are involved. Different scenarios including two barge, three barge and four barge systems are investigated. In addition, one tank plus four barge system are also studied. Hydrodynamic interactions between different bodies are firstly studied to investigate the significance of interaction. Different barge configurations are then considered in terms of mechanical interaction significance. Tank dynamic responses with and without hydrodynamic interaction are evaluated.

Research paper thumbnail of Moving element analysis of high-speed rail system accounting for hanging sleepers

MATEC Web of Conferences, 2018

It is very common in the ballasted track system that sleepers are not well supported by the balla... more It is very common in the ballasted track system that sleepers are not well supported by the ballast materials due to the uneven settlement of the ballast under repeated train passage. These unsupported track elements are often termed as hanging sleepers and they can lead to undesirable effects due to increased dynamic response of the train-track system, especially when the speed of the train is high. In this paper, we present a computation scheme in conjunction with the moving element method for the analysis of high-speed train-track dynamics accounting for hanging sleepers. The proposed computational scheme will be first verified by comparison with available analytical results. The dynamic response of a high-speed train traveling on a ballasted track considering unsupported sleepers is next investigated. Various factors affecting the response of the high-speed rail system including the speed of the train, the number of hanging sleepers and the pattern of the hanging sleepers will b...

Research paper thumbnail of Moving element analysis of partially filled freight trains subject to abrupt braking

International Journal of Mechanical Sciences, 2018

Research paper thumbnail of Buckling of double-walled carbon nanotubes modeled by solid shell elements

Journal of Applied Physics, 2006

A solid shell element model is proposed for the elastic bifurcation buckling analysis of double-w... more A solid shell element model is proposed for the elastic bifurcation buckling analysis of double-walled carbon nanotubes (DWCNTs) under axial compression. The solid shell element allows for the effect of transverse shear deformation which becomes significant in a stocky DWCNT with relatively small radius-to-thickness ratio. The van der Waals (vdW) interaction between the adjacent walls is simulated by linear springs. Using this solid shell element model, the critical buckling strains of DWCNTs with various boundary conditions are obtained and compared with molecular dynamics results and those obtained by other existing shell and beam models. The results obtained show that the solid shell element is able to model DWCNTs rather well, with the appropriate choice of Young’s modulus, tube thickness, and spring constant for modeling the vdW forces.

Research paper thumbnail of Moving Element Analysis of High-Speed Train-Slab Track System Considering Discrete Rail Pads

International Journal of Structural Stability and Dynamics, 2020

This paper presents a study of the dynamic behavior of a coupled train-slab track system consider... more This paper presents a study of the dynamic behavior of a coupled train-slab track system considering discrete rail pads. The slab track is modeled as a three-layer Timoshenko beam. The study is carried out using the moving element method (MEM). By introducing a convected coordinate system moving at the same speed as the vehicle, the governing equations of motion of the slab track are formulated in a moving frame-of-reference. By adopting Galerkin’s method, the element stiffness, mass and damping matrices of a truncated slab track in the moving coordinate system are derived. The vehicle is modeled as a multi-body with 10 degrees of freedom. The nonlinear Hertz contact model is used to account for the wheel–rail interaction. The Newmark integration method, in conjunction with a global Newton–Raphson iteration algorithm, is employed to solve the nonlinear dynamic equations of motion of the vehicle–track coupled system. The proposed MEM model of the system is validated through compariso...

Research paper thumbnail of Optimization of Internal Line Support Positions for Plates Against Vibration∗

Mechanics of Structures and Machines, 1993

This paper presents a simple numerical method for determining optimal positions of internal line ... more This paper presents a simple numerical method for determining optimal positions of internal line supports for an arbitrarily shaped plate, so as to maximize the fundamental frequency of its transverse vibration. The vibration analysis is performed using the pb-2 Rayleigh-Ritz method. Because this method does not require discretization, since it treats the entire plate with its boundary conditions as a

Research paper thumbnail of Shear‐Flexural Buckling of Columns

Journal of Engineering Mechanics, 1990

Elastic flexural buckling formulas for columns under an end-concentrated load and axial uniformly... more Elastic flexural buckling formulas for columns under an end-concentrated load and axial uniformly distributed load (or selfweight), found in the literature or newly derived by the writers, are summarized herein. However, these formulas overestimate the critical buckling loads when the columns are short or consist of struts connected by lacing bars or batten plates, since the effect of shearing force on their deflections becomes significant. This paper investigates the stability of such columns, with a high shear flexibility factor, under a general combined end-concentrated load and axial distributed load. Stability criterion design curves, obtained from the finite element approach, are presented for a wide range of column end conditions. The influence of the shear flexibility factor on the critical loads is also examined. Moreover, some simple shear-flexural buckling formulas for columns under combined end-concentrated load and axial trapezoidal load are proposed.

Research paper thumbnail of Buckling and Postbuckling of Heavy Columns

Journal of Engineering Mechanics, 1987

The standing column is one of the most basic elements in the theory of structures. Its stability ... more The standing column is one of the most basic elements in the theory of structures. Its stability due to the combined effect of compression and nonzero density has been studied for the fixed-free and fixed-fixed situations. To complement this, accurate stability boundaries are compared with existing data, and postbuckling characteristics are found.

Research paper thumbnail of Effectiveness and optimal design of gill cells in minimizing differential deflection in circular VLFS

Engineering Structures, 2007

ABSTRACT Pontoon-type, very large floating structures (VLFS) carrying heavy loads in the central ... more ABSTRACT Pontoon-type, very large floating structures (VLFS) carrying heavy loads in the central portion will undergo a “bowl-type” deflection shape. The resulting differential deflection may cause problems for smooth operation of equipment and compromise the structural integrity of the VLFS. In order to minimize this differential deflection, it is proposed that gill cells be introduced in the VLFS at appropriate locations. Gill cells are flooded compartments in VLFS by which the buoyancy forces are eliminated at their locations. This paper examines the effectiveness of the gill cells in a pontoon-type, circular VLFS in reducing the differential deflection as well as the stress-resultants with respect to the size and location of the gill cells. The optimal design of gill cells that minimizes the differential deflection and reduces the stress-resultants is also investigated.

Research paper thumbnail of Computation of stress resultants in plate bending problems using higher-order triangular elements

Engineering Structures, 2008

Research paper thumbnail of Reducing hydroelastic responses of pontoon-type VLFS using vertical elastic mooring lines

Research paper thumbnail of Fully coupled nonlinear analysis of floating and fully submerged structures in waves

The study presented here investigates the hydrodynamic responses of coupled floating barge and su... more The study presented here investigates the hydrodynamic responses of coupled floating barge and submerged cylindrical payload system in waves under various conditions. The higher-order boundary element method is applied for the fully nonlinear time domain simulation of the model in a three-dimensional numerical wave tank. The 4th order Runge–Kutta scheme is adopted to update the free water surface boundary conditions expressed in a Lagrangian formulation. Following completion of the numerical model, it is first verified against existing numerical studies for a single barge subjected to wave action. After that, the cases of a crane vessel (both in head sea and beam sea conditions) and a fixed fully submerged cylindrical payload are considered. The hydrodynamic forces acting on the barge and payload and wave heights near the structures are then presented and explained for various simulation environments. The existing scenario will be further extended in future to consider the moving su...

Research paper thumbnail of Shape Control of Statically Indeterminate Laminated Beams with Piezoelectric Actuators

Mechanics of Advanced Materials and Structures, 2003

ABSTRACT Based on the cantilever beam solution and principles of superposition, analytical expres... more ABSTRACT Based on the cantilever beam solution and principles of superposition, analytical expressions for the displacements of statically indeterminate laminated beams with piezoelectric actuators are derived. Necessary optimality conditions determining the input voltages for shape matching are developed. The formulation allows for the effect of transverse shear deformation through the adoption of the first-order shear deformation beam theory. The effect of the thickness of the piezoelectric patch actuators is also taken into consideration for better accuracy. Optimal voltages for shape matching are obtained for beams with three different sets of boundary conditions, namely (1) beam with both ends clamped, (2) beam with one end clamped and the other end hinged, and (3) beam with one end clamped and the other end roller supported. The formulation allows for the handling of upper and lower bounds on the voltages, as in practice these voltages are constrained due to cost and material constraints. The solution procedure developed in this study can be extended to any beam with at least one clamped support, including multispan beams.

Research paper thumbnail of A pull-out model for perfectly bonded carbon nanotube in polymer composites

Journal of Mechanics of Materials and Structures, 2012

Research paper thumbnail of Negative moment behaviour of cold-formed steel deck and concrete composite slabs

Journal of Constructional Steel Research, 2001

... 2). An analytical model taking into consideration the contribution of the high strength cold-... more ... 2). An analytical model taking into consideration the contribution of the high strength cold-formedsteel deck to the negative ... shear studs were used to connect the slab to the supports that are usuallysteel I-beams. Hence, durability of the bond is not an issue in such a situation. ...

Research paper thumbnail of Soil–structure interaction effect from blast-induced horizontal and vertical ground vibration

Engineering Structures, 2004

Research paper thumbnail of Transient Thermomechanical Stresses of Functionally Graded Cylindrical Panels

AIAA Journal, 2007

ABSTRACT Three-dimensional thermomechanical analysis of functionally graded cylindrical panels su... more ABSTRACT Three-dimensional thermomechanical analysis of functionally graded cylindrical panels subjected to nonuniform mechanical and transient thermal loads is carried out in this paper. Thermal and mechanical properties are assumed as temperature-independent and continuously varying in the radial direction. Employing Laplace transform and the series solving method of ordinary differential equation(s), solutions of time-dependent temperature and thermornechanical stress in functionally graded material cylindrical panels are obtained. As an example, a functionally graded material cylindrical panel composed of molybdenum and mullite is calculated and all results are graphically presented.

Research paper thumbnail of Large Floating Structure with Free-Floating, Self-Stabilizing Tanks for Hydrocarbon Storage

Research paper thumbnail of Hydrodynamic aspects of moving vehicle with sloshing tanks

MATEC Web of Conferences, 2018

Freight vehicles with partially filled liquid tanks will be affected by liquid sloshing during tr... more Freight vehicles with partially filled liquid tanks will be affected by liquid sloshing during transient motion. The sloshing induced by vehicle motion will lead to extra force on the vehicle and sometimes is a potential threat to safety. Previous studies on this problem usually use a mass-spring analogy to represent the sloshing effect of the liquid tank. Its main disadvantage is that CFD analysis or experimental study has to be performed beforehand, so that an equivalent mass-spring model can be constructed by curve fitting. In this paper, frequency domain boundary element method (BEM) and analytical solution to the sloshing problems are used to derive the modal equation and hydrodynamic parameters of the sloshing fluid. The accuracy of the results will be examined by comparison with available CFD results in the literature. The paper then evaluates the accuracy of equivalent mass-spring model and explores the possibility to approximate the sloshing effects inside cylindrical tanks...

Research paper thumbnail of Initial Design of a Double Curved Floating Bridge and Global Hydrodynamic Responses Under Environmental Conditions

Volume 9: Offshore Geotechnics; Torgeir Moan Honoring Symposium, 2017

In this paper, a floating bridge concept is proposed. This bridge concept comprises a two opposit... more In this paper, a floating bridge concept is proposed. This bridge concept comprises a two oppositely curves in plan, which enables the cancellation of the axial forces at the bridge as one arch will be under compression while the other arch is in tension due to environmental forces acting in one direction. The road deck is carried by truss structures that are kept above the water by several elliptical cylindrical pontoons. To reduce drag load, the cross sectional area facing the current is reduced as much as possible, while the buoyancy is kept the same based on the initial weight estimation. Initial design consideration and methodology of a double curved floating bridge is presented, and a numerical model is established for analyzing this concept. Hydrodynamic and structural dynamic aspects are included in the numerical model. Parametric study of the bridge structural rigidity is performed to investigate the effect to the responses. White noise, regular and irregular wave simulatio...

Research paper thumbnail of Dynamic Response Analysis of Floating Storage Tank System Considering Hydrodynamic and Mechanical Interactions

Volume 6: Ocean Space Utilization, 2018

For better utilization of ocean and coastal space, hydrocarbon products can be stored in the floa... more For better utilization of ocean and coastal space, hydrocarbon products can be stored in the floating tanks, which can be enclosed by barge system. The barge system can be moored through pile foundations. The tanks are moored through marine fenders connected to barges. In the system, hydrodynamic and mechanical interaction problems are involved. Different scenarios including two barge, three barge and four barge systems are investigated. In addition, one tank plus four barge system are also studied. Hydrodynamic interactions between different bodies are firstly studied to investigate the significance of interaction. Different barge configurations are then considered in terms of mechanical interaction significance. Tank dynamic responses with and without hydrodynamic interaction are evaluated.

Research paper thumbnail of Moving element analysis of high-speed rail system accounting for hanging sleepers

MATEC Web of Conferences, 2018

It is very common in the ballasted track system that sleepers are not well supported by the balla... more It is very common in the ballasted track system that sleepers are not well supported by the ballast materials due to the uneven settlement of the ballast under repeated train passage. These unsupported track elements are often termed as hanging sleepers and they can lead to undesirable effects due to increased dynamic response of the train-track system, especially when the speed of the train is high. In this paper, we present a computation scheme in conjunction with the moving element method for the analysis of high-speed train-track dynamics accounting for hanging sleepers. The proposed computational scheme will be first verified by comparison with available analytical results. The dynamic response of a high-speed train traveling on a ballasted track considering unsupported sleepers is next investigated. Various factors affecting the response of the high-speed rail system including the speed of the train, the number of hanging sleepers and the pattern of the hanging sleepers will b...

Research paper thumbnail of Moving element analysis of partially filled freight trains subject to abrupt braking

International Journal of Mechanical Sciences, 2018

Research paper thumbnail of Buckling of double-walled carbon nanotubes modeled by solid shell elements

Journal of Applied Physics, 2006

A solid shell element model is proposed for the elastic bifurcation buckling analysis of double-w... more A solid shell element model is proposed for the elastic bifurcation buckling analysis of double-walled carbon nanotubes (DWCNTs) under axial compression. The solid shell element allows for the effect of transverse shear deformation which becomes significant in a stocky DWCNT with relatively small radius-to-thickness ratio. The van der Waals (vdW) interaction between the adjacent walls is simulated by linear springs. Using this solid shell element model, the critical buckling strains of DWCNTs with various boundary conditions are obtained and compared with molecular dynamics results and those obtained by other existing shell and beam models. The results obtained show that the solid shell element is able to model DWCNTs rather well, with the appropriate choice of Young’s modulus, tube thickness, and spring constant for modeling the vdW forces.

Research paper thumbnail of Moving Element Analysis of High-Speed Train-Slab Track System Considering Discrete Rail Pads

International Journal of Structural Stability and Dynamics, 2020

This paper presents a study of the dynamic behavior of a coupled train-slab track system consider... more This paper presents a study of the dynamic behavior of a coupled train-slab track system considering discrete rail pads. The slab track is modeled as a three-layer Timoshenko beam. The study is carried out using the moving element method (MEM). By introducing a convected coordinate system moving at the same speed as the vehicle, the governing equations of motion of the slab track are formulated in a moving frame-of-reference. By adopting Galerkin’s method, the element stiffness, mass and damping matrices of a truncated slab track in the moving coordinate system are derived. The vehicle is modeled as a multi-body with 10 degrees of freedom. The nonlinear Hertz contact model is used to account for the wheel–rail interaction. The Newmark integration method, in conjunction with a global Newton–Raphson iteration algorithm, is employed to solve the nonlinear dynamic equations of motion of the vehicle–track coupled system. The proposed MEM model of the system is validated through compariso...

Research paper thumbnail of Optimization of Internal Line Support Positions for Plates Against Vibration∗

Mechanics of Structures and Machines, 1993

This paper presents a simple numerical method for determining optimal positions of internal line ... more This paper presents a simple numerical method for determining optimal positions of internal line supports for an arbitrarily shaped plate, so as to maximize the fundamental frequency of its transverse vibration. The vibration analysis is performed using the pb-2 Rayleigh-Ritz method. Because this method does not require discretization, since it treats the entire plate with its boundary conditions as a

Research paper thumbnail of Shear‐Flexural Buckling of Columns

Journal of Engineering Mechanics, 1990

Elastic flexural buckling formulas for columns under an end-concentrated load and axial uniformly... more Elastic flexural buckling formulas for columns under an end-concentrated load and axial uniformly distributed load (or selfweight), found in the literature or newly derived by the writers, are summarized herein. However, these formulas overestimate the critical buckling loads when the columns are short or consist of struts connected by lacing bars or batten plates, since the effect of shearing force on their deflections becomes significant. This paper investigates the stability of such columns, with a high shear flexibility factor, under a general combined end-concentrated load and axial distributed load. Stability criterion design curves, obtained from the finite element approach, are presented for a wide range of column end conditions. The influence of the shear flexibility factor on the critical loads is also examined. Moreover, some simple shear-flexural buckling formulas for columns under combined end-concentrated load and axial trapezoidal load are proposed.

Research paper thumbnail of Buckling and Postbuckling of Heavy Columns

Journal of Engineering Mechanics, 1987

The standing column is one of the most basic elements in the theory of structures. Its stability ... more The standing column is one of the most basic elements in the theory of structures. Its stability due to the combined effect of compression and nonzero density has been studied for the fixed-free and fixed-fixed situations. To complement this, accurate stability boundaries are compared with existing data, and postbuckling characteristics are found.

Research paper thumbnail of Effectiveness and optimal design of gill cells in minimizing differential deflection in circular VLFS

Engineering Structures, 2007

ABSTRACT Pontoon-type, very large floating structures (VLFS) carrying heavy loads in the central ... more ABSTRACT Pontoon-type, very large floating structures (VLFS) carrying heavy loads in the central portion will undergo a “bowl-type” deflection shape. The resulting differential deflection may cause problems for smooth operation of equipment and compromise the structural integrity of the VLFS. In order to minimize this differential deflection, it is proposed that gill cells be introduced in the VLFS at appropriate locations. Gill cells are flooded compartments in VLFS by which the buoyancy forces are eliminated at their locations. This paper examines the effectiveness of the gill cells in a pontoon-type, circular VLFS in reducing the differential deflection as well as the stress-resultants with respect to the size and location of the gill cells. The optimal design of gill cells that minimizes the differential deflection and reduces the stress-resultants is also investigated.

Research paper thumbnail of Computation of stress resultants in plate bending problems using higher-order triangular elements

Engineering Structures, 2008

Research paper thumbnail of Reducing hydroelastic responses of pontoon-type VLFS using vertical elastic mooring lines

Research paper thumbnail of Fully coupled nonlinear analysis of floating and fully submerged structures in waves

The study presented here investigates the hydrodynamic responses of coupled floating barge and su... more The study presented here investigates the hydrodynamic responses of coupled floating barge and submerged cylindrical payload system in waves under various conditions. The higher-order boundary element method is applied for the fully nonlinear time domain simulation of the model in a three-dimensional numerical wave tank. The 4th order Runge–Kutta scheme is adopted to update the free water surface boundary conditions expressed in a Lagrangian formulation. Following completion of the numerical model, it is first verified against existing numerical studies for a single barge subjected to wave action. After that, the cases of a crane vessel (both in head sea and beam sea conditions) and a fixed fully submerged cylindrical payload are considered. The hydrodynamic forces acting on the barge and payload and wave heights near the structures are then presented and explained for various simulation environments. The existing scenario will be further extended in future to consider the moving su...

Research paper thumbnail of Shape Control of Statically Indeterminate Laminated Beams with Piezoelectric Actuators

Mechanics of Advanced Materials and Structures, 2003

ABSTRACT Based on the cantilever beam solution and principles of superposition, analytical expres... more ABSTRACT Based on the cantilever beam solution and principles of superposition, analytical expressions for the displacements of statically indeterminate laminated beams with piezoelectric actuators are derived. Necessary optimality conditions determining the input voltages for shape matching are developed. The formulation allows for the effect of transverse shear deformation through the adoption of the first-order shear deformation beam theory. The effect of the thickness of the piezoelectric patch actuators is also taken into consideration for better accuracy. Optimal voltages for shape matching are obtained for beams with three different sets of boundary conditions, namely (1) beam with both ends clamped, (2) beam with one end clamped and the other end hinged, and (3) beam with one end clamped and the other end roller supported. The formulation allows for the handling of upper and lower bounds on the voltages, as in practice these voltages are constrained due to cost and material constraints. The solution procedure developed in this study can be extended to any beam with at least one clamped support, including multispan beams.

Research paper thumbnail of A pull-out model for perfectly bonded carbon nanotube in polymer composites

Journal of Mechanics of Materials and Structures, 2012

Research paper thumbnail of Negative moment behaviour of cold-formed steel deck and concrete composite slabs

Journal of Constructional Steel Research, 2001

... 2). An analytical model taking into consideration the contribution of the high strength cold-... more ... 2). An analytical model taking into consideration the contribution of the high strength cold-formedsteel deck to the negative ... shear studs were used to connect the slab to the supports that are usuallysteel I-beams. Hence, durability of the bond is not an issue in such a situation. ...

Research paper thumbnail of Soil–structure interaction effect from blast-induced horizontal and vertical ground vibration

Engineering Structures, 2004

Research paper thumbnail of Transient Thermomechanical Stresses of Functionally Graded Cylindrical Panels

AIAA Journal, 2007

ABSTRACT Three-dimensional thermomechanical analysis of functionally graded cylindrical panels su... more ABSTRACT Three-dimensional thermomechanical analysis of functionally graded cylindrical panels subjected to nonuniform mechanical and transient thermal loads is carried out in this paper. Thermal and mechanical properties are assumed as temperature-independent and continuously varying in the radial direction. Employing Laplace transform and the series solving method of ordinary differential equation(s), solutions of time-dependent temperature and thermornechanical stress in functionally graded material cylindrical panels are obtained. As an example, a functionally graded material cylindrical panel composed of molybdenum and mullite is calculated and all results are graphically presented.