Ky Sze - Profile on Academia.edu (original) (raw)

Papers by Ky Sze

2017 IEEE International Conference on Real-time Computing and Robotics (RCAR), 2017

Design of Non-fragile H-infinity Controller for Active Vehicle Suspensions

Soft Robotics, 2017

Bioinspired robotic structures comprising soft actuation units have attracted increasing research... more Bioinspired robotic structures comprising soft actuation units have attracted increasing research interest. Taking advantage of its inherent compliance, soft robots can assure safe interaction with external environments, provided that precise and effective manipulation could be achieved. Endoscopy is a typical application. However, previous model-based control approaches often require simplified geometric assumptions on the soft manipulator, but which could be very inaccurate in the presence of unmodeled external interaction forces. In this study, we propose a generic control framework based on nonparametric and online, as well as local, training to learn the inverse model directly, without prior knowledge of the robot's structural parameters. Detailed experimental evaluation was conducted on a soft robot prototype with control redundancy, performing trajectory tracking in dynamically constrained environments. Advanced element formulation of finite element analysis is employed to initialize the control policy, hence eliminating the need for random exploration in the robot's workspace. The proposed control framework enabled a soft fluid-driven continuum robot to follow a 3D trajectory precisely, even under dynamic external disturbance. Such enhanced control accuracy and adaptability would facilitate effective endoscopic navigation in complex and changing environments.

A new assumed strain quadratic triangular C0 plate bending element

Creation of a tissue interface between bone-like construct and soft tissue-like construct

The 2nd TERMIS World Congress in conjunction with the 2009 Seoul Stem Cell Symposium, Seoul, Sout... more The 2nd TERMIS World Congress in conjunction with the 2009 Seoul Stem Cell Symposium, Seoul, South Korea, 31 August-3 September 2009.

Elimination of spurious kinematic and pressure modes in biquadratic plane element

International Journal for Numerical Methods in Engineering, 1991

This article discusses two alternative methods of formulating the recently proposed quadrilateral... more This article discusses two alternative methods of formulating the recently proposed quadrilateral plane element Qcs6, which is based on a generalized functional with multiple stress fields. The first method is derived by an extended Hu‐Washizu Principle with the presence of incompatible modes and enforcement of energy orthogonality, while the second one is established on a non‐conventional discrete local stress smoothing. Both methods can be applied to other structural element formulations with enhanced efficiency.

Finite Elements in Analysis and Design, 2002

Solid-shell elements are often equipped with two layers of nodes. Thus, the thickness (normal) st... more Solid-shell elements are often equipped with two layers of nodes. Thus, the thickness (normal) strain along the thickness direction is essentially constant. When these elements are subjected to pure bending, the shrinkage/expansion induced by the in-plane strain and the Poisson's ratio coupling in the upper and lower halves of the elements cancel each other. With a constant thickness strain, the plane strain state is resulted that leads to thickness locking. In this paper, a modified generalized laminate stiffness matrix is devised to resolve not only the thickness locking but also some abnormalities of solid-shell elements in laminate analyses. Associated with the modified matrix, a set of generalized stresses can be defined and a modified Hellinger-Reissner functional can be derived by treating the generalized stresses as the independent variables. Based on the functional, an eigenteen-node hybrid-stress solid-shell element suitable for laminate analyses is proposed via a stabilization approach. All the benchmark tests indicate that the present stabilized element is close to the reduced integration element in accuracy.

Stabilization schemes for 12-node to 21-node brick elements based on orthogonal and consistently assumed stress modes

Computer Methods in Applied Mechanics and Engineering, 1994

ABSTRACT

Microplate manipulation of human mesenchymal stem cells (hMSCs)-collagen microspheres

Poster Session - Track 1 Biomaterials, Tissue Engineering and Regenerative Medicine: P1.27The 4th... more Poster Session - Track 1 Biomaterials, Tissue Engineering and Regenerative Medicine: P1.27The 4th World Congress on Bioengineering (WACBE) 2009, Hong Kong, 26-29 July 2009. In Proceedings of the 4th WACBE, 2009, p. 6

Correcting power-law viscoelastic effects in elastic modulus measurement using depth-sensing indentation

International Journal of Solids and Structures, 2005

The standard Oliver–Pharr method for measuring the elastic modulus by depth-sensing indentation m... more The standard Oliver–Pharr method for measuring the elastic modulus by depth-sensing indentation makes use of the unloading response of the material as it is assumed that the unloading behaviour is purely elastic. However, under certain conditions, the unloading behaviour can be viscoelastic, and if the viscosity effects are not corrected, the calculated modulus can be seriously erroneous. Feng and Ngan

Multifield finite element formulation for Helmholtz problem

Plenary Lectur

Hybrid Stress Finite Element Methods for Plate and Shell Structures

Advances in Structural Engineering, 2001

This paper is a survey of the use of assumed stress hybrid finite element methods for analyzing p... more This paper is a survey of the use of assumed stress hybrid finite element methods for analyzing plate and shell structures. It describes the construction of Kirchhoff plate element by complementary energy principle, and of Reissner-Mindlin plate element by Hellinger-Reissner principle. Special hybrid stress elements are used to model joining of elements which are not coplanar. Such elements include the so-called semiLoof plate elements and 3D-solid elements tailored for analyzing thin plates and shells.

Journal of Computational Physics, 2017

To overcome the shortcomings of the weakly compressible material point method (WCMPM) for modelin... more To overcome the shortcomings of the weakly compressible material point method (WCMPM) for modeling the free surface flow problems, an incompressible material point method (iMPM) is proposed based on operator splitting technique which splits the solution of momentum equation into two steps. An intermediate velocity field is first obtained by solving the momentum equations ignoring the pressure gradient term, and then the intermediate velocity field is corrected by the pressure term to obtain a divergence-free velocity field. A level set function which represents the signed distance to free surface is used to track the free surface and apply the pressure boundary conditions. Moreover, an hourglass damping is introduced to suppress the spurious velocity modes which are caused by the discretization of the cell center velocity divergence from the grid vertexes velocities when solving pressure Poisson equations. Numerical examples including dam break, oscillation of a cubic liquid drop and a droplet impact into deep pool show that the proposed incompressible material point method is much more accurate and efficient than the weakly compressible material point method in solving free surface flow problems.

Finite Elements in Analysis and Design, 1997

There exist two three-point integration rules for triangular elements. Both rules are precise up ... more There exist two three-point integration rules for triangular elements. Both rules are precise up to the second order and used for evaluating the six-node triangles. While one of rules has its sampling stations inside the triangle, that of the other coincide with the edge nodes. Though the former is commonly employed, it will be seen in this short paper that latter is indeed more favourable in view of element accuracy.

Ha5 disturbance attenuation for uncertain mechanical systems with input delay

Analyzing the mechanical behavior of bio-filament networks via a combined finite element-Langevin dynamics (FEM-LD) approach

Session - Awards Symposia: Prager Medal Symposium in honor of George Weng: Micromechanics, Compos... more Session - Awards Symposia: Prager Medal Symposium in honor of George Weng: Micromechanics, Composites and Multifunctional Materials

Three-dimensional structural frame analysis using solid finite elements

Development of a Shear Test System for Measuring the Interfacial Strength of Osteochondral Grafts from Rabbits of Different Skeletal Maturity

HKIE Transactions, 2012

ABSTRACT

Fabrication of Multicomponent Tissue-Like Constructs-Toward Spinal Motion Segment Tissue Engineering

Global Spine Journal, 2012

Introduction Allogenic spinal motion segment transplantation demonstrated promising results in tr... more Introduction Allogenic spinal motion segment transplantation demonstrated promising results in treating late stage disk degeneration and stimulated immense interests of tissue engineering in the whole spinal motion segment from autologous cell source and safe biomaterials, solving the donor availability problem and potentially alleviating the degeneration and immunogenicity problems. Bioengineering complex tissues such as spinal motion segment is extremely challenging because it involves the integration of multiple tissues with distinct structures and composition such as lamellar annulus fibrosus (AF), gel-like nucleus pulposus (NP), cartilaginous endplate, and bony vertebra. Although attempts have been made to fabricate biphasic structures such as lamellar AF structure wrapping around a NP core, or bony block with cartilaginous structure, good methods integrating different tissue parts to form a combined unit are not available. In this study, a bioreactor-based method integrating multicomponent spinal motion segment-like tissue constructs, together with in vitro mechanical and biological stimulation, was reported, as the first step towards functional spinal motion segment tissue engineering. Materials and Methods Rabbit mesenchymal stem cells (rMSC) were used to fabricate cell-collagen constructs. Constructs were cultured separately in chondrogenic and osteogenic differentiation medium for 21 days. A layer of rMSC-collagen solution was added between chondrogenic and osteogenic units for coculture with cyclic compression to form the combined osteochondral constructs with intact interface. Afterward, an acellular cylindrical collagen gel was formed in between two such combined osteochondral constructs before circumferencing the whole construct with rMSC-collagen tubular layers. The multicomponent constructs were subjected to periodic compression and torsion simultaneously. The constructs were evaluated histologically for multicomponent structures. Cell alignment in the tubular layers was quantified using an adhoc MatLab program while collagen alignment was evaluated using scanning electron microscopy (SEM). Moreover, the interfacial strength of the osteochondral units was also evaluated using a tensile test machine. Results The combined constructs were able to be dismounted with integrity from the supporting shafts of the bioreactor after 14 days of culture. Every component of the combined constructs remained intact and can be manipulated with forceps. This method proves the feasibility to proceed to bioreactor-based functional remodelling and engineering of spinal motion segment in the future. Alignment analysis of rMSC in the tubular layers of the combined constructs demonstrated that the cell aligned along different preferred direction under torsional stimulation as compared with that from the static loading control (Fig. 1). However, SEM demonstrated no significant collagen alignment after 14 days culture for all groups. Histological results showed good integration among different components while cells were able to migrate into the acellular collagen gel at the center of the combined constructs although the source of the migrated cells was not studied yet. In addition, the osteogenic and chondrogenic phenotype in the osteochondral units were maintained while the interfacial strength of the osteochondral units was significantly higher when both the biological and the compression stimulation were present during their fabrication. Conclusion A method fabricating a multicomponent tissue construct with integrity for future functional spinal motion segment tissue engineering is demonstrated. Torsional stimulation can be used to stimulate rMSC re-orientation within a collagen tubular structure. Osteogenic differentiated and chondrogenic differentiated rMSC were able to maintain the phenotype throughout the culture period and their interface stabilized by biological and mechanical stimulation. I confirm having declared any potential conflict of interest for all authors listed on this abstract No Disclosure of Interest None declared Cheng HW, Luk KD, Cheung KM, Chan BP. In vitro generation of an osteochondral interface from mesenchymal stem cell-collagen microspheres. Biomaterials 2011;32(6):1526–1535. Au-Yeung KL, Sze KY, Sham MH, Chan BP. Development of a micromanipulator-based loading device for mechanoregulation study of human mesenchymal stem cells in three-dimensional collagen constructs. Tissue Engineering Part C Methods 2010;16(1):93–107.

2017 IEEE International Conference on Real-time Computing and Robotics (RCAR), 2017

Design of Non-fragile H-infinity Controller for Active Vehicle Suspensions

Soft Robotics, 2017

Bioinspired robotic structures comprising soft actuation units have attracted increasing research... more Bioinspired robotic structures comprising soft actuation units have attracted increasing research interest. Taking advantage of its inherent compliance, soft robots can assure safe interaction with external environments, provided that precise and effective manipulation could be achieved. Endoscopy is a typical application. However, previous model-based control approaches often require simplified geometric assumptions on the soft manipulator, but which could be very inaccurate in the presence of unmodeled external interaction forces. In this study, we propose a generic control framework based on nonparametric and online, as well as local, training to learn the inverse model directly, without prior knowledge of the robot's structural parameters. Detailed experimental evaluation was conducted on a soft robot prototype with control redundancy, performing trajectory tracking in dynamically constrained environments. Advanced element formulation of finite element analysis is employed to initialize the control policy, hence eliminating the need for random exploration in the robot's workspace. The proposed control framework enabled a soft fluid-driven continuum robot to follow a 3D trajectory precisely, even under dynamic external disturbance. Such enhanced control accuracy and adaptability would facilitate effective endoscopic navigation in complex and changing environments.

A new assumed strain quadratic triangular C0 plate bending element

Creation of a tissue interface between bone-like construct and soft tissue-like construct

The 2nd TERMIS World Congress in conjunction with the 2009 Seoul Stem Cell Symposium, Seoul, Sout... more The 2nd TERMIS World Congress in conjunction with the 2009 Seoul Stem Cell Symposium, Seoul, South Korea, 31 August-3 September 2009.

Elimination of spurious kinematic and pressure modes in biquadratic plane element

International Journal for Numerical Methods in Engineering, 1991

This article discusses two alternative methods of formulating the recently proposed quadrilateral... more This article discusses two alternative methods of formulating the recently proposed quadrilateral plane element Qcs6, which is based on a generalized functional with multiple stress fields. The first method is derived by an extended Hu‐Washizu Principle with the presence of incompatible modes and enforcement of energy orthogonality, while the second one is established on a non‐conventional discrete local stress smoothing. Both methods can be applied to other structural element formulations with enhanced efficiency.

Finite Elements in Analysis and Design, 2002

Solid-shell elements are often equipped with two layers of nodes. Thus, the thickness (normal) st... more Solid-shell elements are often equipped with two layers of nodes. Thus, the thickness (normal) strain along the thickness direction is essentially constant. When these elements are subjected to pure bending, the shrinkage/expansion induced by the in-plane strain and the Poisson's ratio coupling in the upper and lower halves of the elements cancel each other. With a constant thickness strain, the plane strain state is resulted that leads to thickness locking. In this paper, a modified generalized laminate stiffness matrix is devised to resolve not only the thickness locking but also some abnormalities of solid-shell elements in laminate analyses. Associated with the modified matrix, a set of generalized stresses can be defined and a modified Hellinger-Reissner functional can be derived by treating the generalized stresses as the independent variables. Based on the functional, an eigenteen-node hybrid-stress solid-shell element suitable for laminate analyses is proposed via a stabilization approach. All the benchmark tests indicate that the present stabilized element is close to the reduced integration element in accuracy.

Stabilization schemes for 12-node to 21-node brick elements based on orthogonal and consistently assumed stress modes

Computer Methods in Applied Mechanics and Engineering, 1994

ABSTRACT

Microplate manipulation of human mesenchymal stem cells (hMSCs)-collagen microspheres

Poster Session - Track 1 Biomaterials, Tissue Engineering and Regenerative Medicine: P1.27The 4th... more Poster Session - Track 1 Biomaterials, Tissue Engineering and Regenerative Medicine: P1.27The 4th World Congress on Bioengineering (WACBE) 2009, Hong Kong, 26-29 July 2009. In Proceedings of the 4th WACBE, 2009, p. 6

Correcting power-law viscoelastic effects in elastic modulus measurement using depth-sensing indentation

International Journal of Solids and Structures, 2005

The standard Oliver–Pharr method for measuring the elastic modulus by depth-sensing indentation m... more The standard Oliver–Pharr method for measuring the elastic modulus by depth-sensing indentation makes use of the unloading response of the material as it is assumed that the unloading behaviour is purely elastic. However, under certain conditions, the unloading behaviour can be viscoelastic, and if the viscosity effects are not corrected, the calculated modulus can be seriously erroneous. Feng and Ngan

Multifield finite element formulation for Helmholtz problem

Plenary Lectur

Hybrid Stress Finite Element Methods for Plate and Shell Structures

Advances in Structural Engineering, 2001

This paper is a survey of the use of assumed stress hybrid finite element methods for analyzing p... more This paper is a survey of the use of assumed stress hybrid finite element methods for analyzing plate and shell structures. It describes the construction of Kirchhoff plate element by complementary energy principle, and of Reissner-Mindlin plate element by Hellinger-Reissner principle. Special hybrid stress elements are used to model joining of elements which are not coplanar. Such elements include the so-called semiLoof plate elements and 3D-solid elements tailored for analyzing thin plates and shells.

Journal of Computational Physics, 2017

To overcome the shortcomings of the weakly compressible material point method (WCMPM) for modelin... more To overcome the shortcomings of the weakly compressible material point method (WCMPM) for modeling the free surface flow problems, an incompressible material point method (iMPM) is proposed based on operator splitting technique which splits the solution of momentum equation into two steps. An intermediate velocity field is first obtained by solving the momentum equations ignoring the pressure gradient term, and then the intermediate velocity field is corrected by the pressure term to obtain a divergence-free velocity field. A level set function which represents the signed distance to free surface is used to track the free surface and apply the pressure boundary conditions. Moreover, an hourglass damping is introduced to suppress the spurious velocity modes which are caused by the discretization of the cell center velocity divergence from the grid vertexes velocities when solving pressure Poisson equations. Numerical examples including dam break, oscillation of a cubic liquid drop and a droplet impact into deep pool show that the proposed incompressible material point method is much more accurate and efficient than the weakly compressible material point method in solving free surface flow problems.

Finite Elements in Analysis and Design, 1997

There exist two three-point integration rules for triangular elements. Both rules are precise up ... more There exist two three-point integration rules for triangular elements. Both rules are precise up to the second order and used for evaluating the six-node triangles. While one of rules has its sampling stations inside the triangle, that of the other coincide with the edge nodes. Though the former is commonly employed, it will be seen in this short paper that latter is indeed more favourable in view of element accuracy.

Ha5 disturbance attenuation for uncertain mechanical systems with input delay

Analyzing the mechanical behavior of bio-filament networks via a combined finite element-Langevin dynamics (FEM-LD) approach

Session - Awards Symposia: Prager Medal Symposium in honor of George Weng: Micromechanics, Compos... more Session - Awards Symposia: Prager Medal Symposium in honor of George Weng: Micromechanics, Composites and Multifunctional Materials

Three-dimensional structural frame analysis using solid finite elements

Development of a Shear Test System for Measuring the Interfacial Strength of Osteochondral Grafts from Rabbits of Different Skeletal Maturity

HKIE Transactions, 2012

ABSTRACT

Fabrication of Multicomponent Tissue-Like Constructs-Toward Spinal Motion Segment Tissue Engineering

Global Spine Journal, 2012

Introduction Allogenic spinal motion segment transplantation demonstrated promising results in tr... more Introduction Allogenic spinal motion segment transplantation demonstrated promising results in treating late stage disk degeneration and stimulated immense interests of tissue engineering in the whole spinal motion segment from autologous cell source and safe biomaterials, solving the donor availability problem and potentially alleviating the degeneration and immunogenicity problems. Bioengineering complex tissues such as spinal motion segment is extremely challenging because it involves the integration of multiple tissues with distinct structures and composition such as lamellar annulus fibrosus (AF), gel-like nucleus pulposus (NP), cartilaginous endplate, and bony vertebra. Although attempts have been made to fabricate biphasic structures such as lamellar AF structure wrapping around a NP core, or bony block with cartilaginous structure, good methods integrating different tissue parts to form a combined unit are not available. In this study, a bioreactor-based method integrating multicomponent spinal motion segment-like tissue constructs, together with in vitro mechanical and biological stimulation, was reported, as the first step towards functional spinal motion segment tissue engineering. Materials and Methods Rabbit mesenchymal stem cells (rMSC) were used to fabricate cell-collagen constructs. Constructs were cultured separately in chondrogenic and osteogenic differentiation medium for 21 days. A layer of rMSC-collagen solution was added between chondrogenic and osteogenic units for coculture with cyclic compression to form the combined osteochondral constructs with intact interface. Afterward, an acellular cylindrical collagen gel was formed in between two such combined osteochondral constructs before circumferencing the whole construct with rMSC-collagen tubular layers. The multicomponent constructs were subjected to periodic compression and torsion simultaneously. The constructs were evaluated histologically for multicomponent structures. Cell alignment in the tubular layers was quantified using an adhoc MatLab program while collagen alignment was evaluated using scanning electron microscopy (SEM). Moreover, the interfacial strength of the osteochondral units was also evaluated using a tensile test machine. Results The combined constructs were able to be dismounted with integrity from the supporting shafts of the bioreactor after 14 days of culture. Every component of the combined constructs remained intact and can be manipulated with forceps. This method proves the feasibility to proceed to bioreactor-based functional remodelling and engineering of spinal motion segment in the future. Alignment analysis of rMSC in the tubular layers of the combined constructs demonstrated that the cell aligned along different preferred direction under torsional stimulation as compared with that from the static loading control (Fig. 1). However, SEM demonstrated no significant collagen alignment after 14 days culture for all groups. Histological results showed good integration among different components while cells were able to migrate into the acellular collagen gel at the center of the combined constructs although the source of the migrated cells was not studied yet. In addition, the osteogenic and chondrogenic phenotype in the osteochondral units were maintained while the interfacial strength of the osteochondral units was significantly higher when both the biological and the compression stimulation were present during their fabrication. Conclusion A method fabricating a multicomponent tissue construct with integrity for future functional spinal motion segment tissue engineering is demonstrated. Torsional stimulation can be used to stimulate rMSC re-orientation within a collagen tubular structure. Osteogenic differentiated and chondrogenic differentiated rMSC were able to maintain the phenotype throughout the culture period and their interface stabilized by biological and mechanical stimulation. I confirm having declared any potential conflict of interest for all authors listed on this abstract No Disclosure of Interest None declared Cheng HW, Luk KD, Cheung KM, Chan BP. In vitro generation of an osteochondral interface from mesenchymal stem cell-collagen microspheres. Biomaterials 2011;32(6):1526–1535. Au-Yeung KL, Sze KY, Sham MH, Chan BP. Development of a micromanipulator-based loading device for mechanoregulation study of human mesenchymal stem cells in three-dimensional collagen constructs. Tissue Engineering Part C Methods 2010;16(1):93–107.