Srikanth Narasimalu | Nanyang Technological University (original) (raw)

Papers by Srikanth Narasimalu

Abundant and consistent wind resource of deep water ocean have attracted offshore wind energy ind... more Abundant and consistent wind resource of deep water ocean have attracted offshore wind energy industry to look for the possible expansions and adoption of various oil and gas floating platform technologies. This has compelled the industry to venture in to floating offshore installations for wind turbines. The floating installations lead to complex rotor motions in 6 degrees of freedom. The current study focuses on the dynamic effects of the platform pitching motion on the rotor aerodynamics for OC3 phase IV case 5.1 with modified wave height. High fidelity CFD (Computational Fluid Dynamics) software was employed along with semi empirical tool, FAST developed by NREL, USA by assuming the wind turbine as a rigid body. The hydrodynamic effects leading to the pitching motion of the turbine platform are obtained from FAST. These pitching motions are coupled with the rotating blades to study transient flow behaviors using CFD. The results are compared with the standard BEM based methods h...

2015 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 2015

In order to enhance the performance of an energy converter based on a vortex induced vibration (V... more In order to enhance the performance of an energy converter based on a vortex induced vibration (VIV) system, a model of nonlinear springs, the so-called hardening springs, is applied to widen the resonance range. A nonlinear spring is introduced by utilizing cantilever beams with additional plates to harden the structure partially. An experimental investigation is carried out to analyze the potential of hardening stiffness spring in widening the resonance range. A fluid-structure interaction (FSI) simulation is performed to validate the experimental results. A comparison to the experimental results from a similar system that utilized linear springs shows the potential of hardening springs in widening the resonance range of VIV energy converters.

1998 International Conference on Power Electronic Drives and Energy Systems for Industrial Growth, 1998. Proceedings.

... GPWiddowson, Liao Youyong ASGaunekar THKuah and N.Srikanth ASM Technology Singapore. ... For ... more ... GPWiddowson, Liao Youyong ASGaunekar THKuah and N.Srikanth ASM Technology Singapore. ... For the Y axis, the line of action of the force hm the two motors must be kept at the centre of CG to avoid any moment loading on the linear guides, as this would cause the beam to ...

Thin-Walled Structures, 2015

ABSTRACT A minimum mass design study applicable to thin circular tube is performed for various mo... more ABSTRACT A minimum mass design study applicable to thin circular tube is performed for various modes of eccentric compressive loading. Axial crushing failure mode, frequently noticeable in uniform axial compressive loading of thin circular tube, does not appear in eccentric compression. Hence, other compressive failure modes, e.g., global buckling, yield and local buckling are studied with respect to non-dimensional load and geometric shape factors for a fixed-free condition. These modes are predominant in ductile engineering alloys. A failure mode map in terms of non-dimensional load and shape-factor for a given load-eccentricity are obtained and the prescription for minimum mass is given.

Materials Letters, 2005

In the present study, elemental magnesium was reinforced with nano-size alumina particulates. Syn... more In the present study, elemental magnesium was reinforced with nano-size alumina particulates. Synthesis of materials was accomplished using the powder metallurgy route. Energy dissipation in the form of damping capacity was determined using free-free type suspended beam arrangement coupled with circle-fit approach. This technique is based on classical vibration theory, by which the geometry and material properties of the metallic specimen are related to measured resonant frequency and structural damping. Using the fact that the ratio of the vibration response to the applied force fits to a circle in the Argand plane for each resonant frequency of the test specimen, the damping factor and natural frequency is predicted accurately for the test specimen. The results revealed that an increase in the alumina content up to 0.4% volume percentage lead to an increase in the damping capacity up to 34%. Attempt is made to correlate the increase in damping with the various microstructural changes arising due to the presence of the nano-size alumina particulates in the composite sample.

2005 7th Electronic Packaging Technology Conference

ABSTRACT Wire bonding is an important method of interconnection in microelectronics. The micro we... more ABSTRACT Wire bonding is an important method of interconnection in microelectronics. The micro welding of the contact pad to the gold wire is achieved by a thermosonic wire bonding process. Ultrasonic energy is known to soften metallic materials and hence when used in the wire bond process to decrease the flow stress similar to thermal energy. But experimental results shows for some lead frame designs neck fatigue, squashed bonds and poor wire pull strength are observed for some particular leads. Detailed resonance studies shows that those leads have closeby resonance compared to the bonding frequency which causes enhanced vibration resulting in smeared and squashed ball as well as localized fatigue at both the neck and heel of the wirebond. Hence precautions during lead frame design are necessary to avoid closeby resonance motion that are in the in-plane direction along the capillary vibration direction. This can be determined apriori using finite element method

Microelectronics International, 2007

PurposeWire bonding is an important method of interconnection in microelectronics. Ultrasonic ene... more PurposeWire bonding is an important method of interconnection in microelectronics. Ultrasonic energy is known to soften metallic materials and hence when used in the wire bond process it is effective to decrease the flow stress similar to thermal energy. The paper aims to address this issue.Design/methodology/approachDetailed resonance studies show that some designs have closeby resonance compared to the bonding frequency which causes enhanced vibration resulting in such over squashed bonds. Hence, precautions in the design stage are necessary to understand the closeby resonance frequencies and corresponding mode shapes of the leadframe that are in‐plane in nature along the transducer axis that can be excited by the capillary's motion. This can be determined a priori using numerical methods such as finite element method. In this paper, one such case study has been dealt in detail to explain the overall methodology.FindingsTo minimize the effects of resonance, damping should be i...

2007 9th Electronics Packaging Technology Conference, 2007

Cu bonding has been making a wave in the IC packaging industry due to the combined efforts of wir... more Cu bonding has been making a wave in the IC packaging industry due to the combined efforts of wire, capillary and wirebonder manufacturers. The present challenge in copper bonding resides in minimizing the aluminium squeeze of the aluminium metallization of bond pads. This demands the copper ball to possess a lower yield stress for reduced energy to deform. In this

Key Engineering Materials, 2002

Key Engineering Materials22793-100KEMA

2007 32nd IEEE/CPMT International Electronic Manufacturing Technology Symposium, 2007

The integration of stacked dice into convention packaging formats provides a promising capability... more The integration of stacked dice into convention packaging formats provides a promising capability in reducing the cost, weight and size of the package while increasing the overall functionality of the system. It has been well accepted as enabling approach for smaller handheld devices such as cellular phones and digital camera. Among the various process steps in the packaging of these

Thin Solid Films, 2004

Copper wire is getting well accepted as a reliable design alternative to the gold wire in the wir... more Copper wire is getting well accepted as a reliable design alternative to the gold wire in the wire bonding process. In the present study, the shear strength results of the copper ball bond show better performance than the gold bond. Additionally, microhardness results also confirm that Cu ball bonds reveal a higher hardness of 111 VHN than that of initial Cu ball (84 VHN). The increased shear strength and hardness can be rationalized based on the strain hardening process due to application of the ultrasonic energy. Microstructural study of the deformed ball confirms the presence of subdivided grains (or cells) of a few microns in size. In addition, slip bands inside the cells are also observed.

Scripta Materialia, 2001

A new methodology of using impact-based vibration measurement of a suspended beam coupled with ci... more A new methodology of using impact-based vibration measurement of a suspended beam coupled with circle-®t approach is discussed to measure damping of SiC particulate reinforced magnesium composites. This study also focuses on the dependence of damping capability of the composite with SiC particulate size variation.

Materials Science and Engineering: A, 2006

Pure Al was reinforced with alumina particles with size ranging from micro to nano-size dimension... more Pure Al was reinforced with alumina particles with size ranging from micro to nano-size dimension. Magnesium was added to the Al matrix to enhance the wettability of alumina particles. Synthesis of materials was accomplished using the solidification route viz., disintegrated melt deposition technique. Energy dissipation in the form of damping capacity was determined using free-free type suspended beam arrangement coupled with circle-fit approach. Three samples with Al-4 wt.% Mg matrix were prepared that were reinforced by alumina particles whose size ranged from m to nm length scale (viz., 10, 0.3 m and 50 nm and with a volume percentage of 10.13, 1.47 and 0.94, respectively). Damping per unit volume percentage of alumina particles in the Al-Mg matrix increased by 58%, 30% and 3% for the alumina particles size of 50 nm, 0.3 and 10 m, respectively, with respect to the monolithic Al-Mg specimen. Such increase in damping can be rationalized in terms of microstructural changes that arise due to the presence of the alumina particles in the composite samples compared to that of unreinforced sample.

Materials Science and Engineering: A, 2004

In the present study, elemental Cu powder was mechanically milled (MMed) for 10 h to reduce the g... more In the present study, elemental Cu powder was mechanically milled (MMed) for 10 h to reduce the grain (crystalline) size in the nano-range (<100 nm). The mechanically milled powder (10 h-MMed) and elemental powder without mechanical milling (MM) (0 h-MMed) was consolidated by die-cold compaction and were further hot extruded at different temperatures to maintain a crystallite size within the nano-range. Further, the specimen was tested by a novel free-free type suspended beam arrangement, coupled with circle-fit approach to determine damping characteristics. The characterization results help to understand the effect of the nano-size grains on the overall damping capacity of the bulk samples compared to a normal micro-crystalline sample. Results show that the damping capacity of the nano-grained material increases due to the presence of process induced microstructural changes similar to the damping behavior of a micro-grain sized specimen.

Materials Research Bulletin, 2002

In the present study, a new methodology of using free±free beam method coupled with circle-®t app... more In the present study, a new methodology of using free±free beam method coupled with circle-®t approach is used to determine damping of Mg±SiC composites. This technique is based on classical vibration theory, by which the geometry and material properties of the metal matrix composites are related to resonant frequency and structural damping of the test specimen. Using the fact that the ratio of the vibration response to the applied force ®ts to a circle in the Argand plane for each resonant frequency of the test specimen, the damping factor and natural frequency is predicted accurately for the test specimen. An attempt is made to rationalize the increase in damping capability of the composites when compared against the monolithic specimen in terms of increase in dislocation density and presence of plastic zone at the particulate±matrix interface.

Journal of Composite Materials, 2004

In the present study, energy dissipation capability of magnesium containing variable amounts of n... more In the present study, energy dissipation capability of magnesium containing variable amounts of nanosize alumina (Al2O3) particle is investigated. Synthesis of materials was accomplished using a solidification processing route. Energy dissipation in the form of damping capacity was determined using a free–free type suspended beam arrangement coupled with a circle-fit approach. This technique is based on the classical vibration theory, by which the geometry and material properties of the metal matrix composites are related to resonant frequency and structural damping of the test specimen. Using the fact that the ratio of the vibration response to the applied force fits to a circle in the Argand plane for each resonant frequency of the test specimen, the damping factor and natural frequency is predicted accurately for the test specimen. The results revealed that an increase in the Al2O3 content upto 1.134 vol.% lead to an increase in the damping capacity upto 64%. Attempt is made to c...

Journal of Alloys and Compounds, 2008

A new bimetal magnesium/aluminium (Mg/Al) macrocomposite containing mm-scale Al core reinforcemen... more A new bimetal magnesium/aluminium (Mg/Al) macrocomposite containing mm-scale Al core reinforcement was fabricated via casting and hot coextrusion. Characterization revealed fairly uniform Al volume fraction along the extruded rod length attributable to mechanical interlocking between Mg shell and Al core. Major defects were absent and Mg–Al interfacial integrity was good. Thermal stability of the macrocomposite was marginally improved when compared

Journal of Alloys and Compounds, 2003

ABSTRACT

Journal of Alloys and Compounds, 2005

In the present study, the damping capacity of a metal matrix composite is predicted using a micro... more In the present study, the damping capacity of a metal matrix composite is predicted using a micro-mechanical modelling approach. The model is based on finite element analysis of an axisymmetric unit cell, which mimics a pure metallic cylinder with a stiff reinforcing spherical particulate placed at the center. The energy dissipated by the composite is numerically predicted using the unit cell by applying a harmonic load, taking into account the viscoplastic behavior of the processing induced residual plastic strain at the matrix-reinforcement interface of the composite. The model shows that the plastic zone size increases with volume fraction of Ti added which results in a proportional increase in the damping capacity of the composite. The model was validated by comparing the numerical results against an impact based suspended beam experiment conducted at low strain amplitude on Al/Ti samples with different volume fractions of Ti particulates.

Composites Science and Technology, 2003

In the present study, a new methodology of using free-free method coupled with circle-fit approac... more In the present study, a new methodology of using free-free method coupled with circle-fit approach is used to determine damping of ceramic reinforced magnesium composites. This technique is based on classical vibration theory, by which the geometry and material properties of the metal matrix composites are related to the resonant frequency and structural damping of the test specimen. Using the