Structural Dynamics

Vibrational characteristics of bilayer graphene sheets

by Rajib Chowdhury

Thin Solid Films
Volume 519, Issue 18, 1 July 2011, Pages 6026–6032

Bilayergraphenesheets (BLGSs) are currently receiving increasing attention. In this paper, the vibration... more Bilayergraphenesheets (BLGSs) are currently receiving increasing attention. In this paper, the vibration characteristics of BLGSs are investigated using analytical and atomistic finite element approaches. Various possible scenarios, namely different geometrical configuration (armchair and zigzag), boundary conditions, and aspect ratio are considered in the present study. The dynamic characteristics of BLGS studied have shown dependence on aspect ratio and the boundary conditions. The unique vibrational properties and large stiffness of BLGS identified in the present work make them suitable candidates for manufacturing nanosensors; electromechanical resonators also will aid the nanomaterials research community to design nanodevices.

Nonlinear dynamic analysis of dragonfly inspired piezoelectric unimorph actuated flapping and twisting wing

by Ranjan Ganguli

Sujoy Mukherjee & Ranjan Ganguli (2012): Nonlinear dynamic analysis of
dragonfly-inspired piezoelectric unimorph actuated flapping and twisting wing, International Journal of Smart and Nano Materials, DOI:10.1080/19475411.2011.649804

The nonlinear equations for coupled elastic flapping–twisting motion of a dragonfly-inspired smart flapping wing are... more The nonlinear equations for coupled elastic flapping–twisting motion of a dragonfly-inspired smart flapping wing are used for a flapping wing actuated from the root by a PZT unimorph in the piezofan configuration. Excitation by the piezoelectric harmonic force generates only the flap bending motion, which, in turn, induces the
elastic twist motion due to interaction between flexural and torsional vibration modes. An unsteady aerodynamic model is used to obtain the aerodynamic forces. Numerical simulations are performed using a wing whose size is the same as the dragonfly Sympetrum frequens wing. It is found that the value of average lift reaches its maximum when the smart flapping wing is excited at a frequency closer to the natural frequency in torsion. Moreover, consideration of the elastic twisting of the flapping wing leads to an increase in the lift force. It is also found that the flapping wing generates sufficient
lift to support its own weight and carry a small payload. Therefore, the piezoelectrically actuated smart flapping wing based on the geometry of a Sympetrum frequens wing and undergoing flapping–twisting motions can be considered as a potential candidate for use in micro air vehicle applications.

The calibration of carbon nanotube based bio-nano sensors

by Rajib Chowdhury

Journal of Applied Physics, 107[12] (2010), pp. 124322:1-8.

We derive the calibration constants necessary for using single-walled carbon nanotubes (SWCNTs) as nano-scale mass... more We derive the calibration constants necessary for using single-walled carbon nanotubes (SWCNTs) as nano-scale mass sensors. The carbon nanotube resonators are assumed to be either in cantilevered or in bridged configurations. Two cases, namely when the added mass can be considered as a point mass and when the added mass is distributed over a larger area are considered. Closed-form transcendental equations have been derived for the frequency shift due to the added mass. Using the energy principles, generalized nondimensional calibration constants have been derived for an explicit relationship between the added mass and the frequency shift. A molecular mechanics model based on the universal force field potential is used to validate the new results presented. The results indicate that the distributed nature of the mass to be detected has considerable effect on the performance of the sensor.

Scalar and vector time series methods for vibration based damage diagnosis in a scale aircraft skeleton structure

by Fotis Kopsaftopoulos

invited paper to Journal of Theoretical and Applied Mechanics, Vol. 49, No. 3, 2011.

Vibration based health monitoring for a lightweight truss structure: experimental assessment of several statistical time series methods

by Fotis Kopsaftopoulos

Mechanical Systems and Signal Processing (ISMA Special Issue), Vol. 24, pp. 1977-1997, 2010.

Output-Only Parametric Identification of a Scale Cable-Stayed Bridge Structure: a comparison of vector AR and stochastic subspace methods

by Fotis Kopsaftopoulos

Proceedings of the 4th International Operational Modal Analysis Conference (IOMAC), Istanbul, Turkey, 9-11 May 2011.

CONTROL OF DYNAMIC RESPONSE OF A COMPLIANT OFFSHORE STRUCTURE

by Syed Khaleeq Ahmad

Preliminary Study on Analytical Prediction Model of Local Impact Phenomena on Concrete Structures against Hard Missiles

by Imran Latif

Concrete is basic construction material used for many kind of structure. However, in the majority essential structures... more Concrete is basic construction material used for many kind of structure. However, in the majority essential structures such as nuclear plants, Power plants, Weapon Industries, weapons storage places, water retaining structures like dams, & etc., concrete structures have to be designed as self-protective structure endow with defense against any disaster or consciously engendered unpleasant incidents such as terrorist attack, war, missile attacked by war jets, and dynamic loading, dynamic local impact damage and global damage generated by kinetic missiles (steel rods, steel pipes, turbine blades, etc.). This study inquisitively is paying attention on verdict the numerical simulation on the behavior of concrete structures against local impact effect generated by hard missile. The fallout conquer from this study can be used for making design counsel and design procedures for seminal the dynamic retort of the target to foil local and global impact damage. This paper only endow with the appraisal of prior analytical model investigation connected with our study.

Application of Coordinate Resistance Functions on Predicting of Critical Impact Energy of Projectile for Perforation Phenomenon on Concrete Structure

by Imran Latif

missiles, generated both accidentally and deliberately, in various impact and blast scenarios in both civilian and... more missiles, generated both accidentally and deliberately, in various impact and blast scenarios in both civilian and military activities. In many cases, projectiles can be treated as rigid bodies when their damage and erosion are not severe. Due to the intricacy of the local impact damages, investigations are generally based on experimental data. Conclusions of the experimental observations are then used to guide engineering models. Local damages studies normally fall into three categories, i.e. empirical formulae based on data fitting, idealised analytical models based on physic laws and numerical simulations based on computational mechanics and material models. Perforation phenomenon is one of the local damage that has been investigated in the present study. It is describe as the complete passage of the projectile through the material with or without residual velocity is among the local damage threat in concrete structure. The relative of target thickness (H/d) to those critical energies are an important quantities that been explored in this study. The numerical simulation model has been developed using coordinate resistance function method for predict the perforation process. The target structures is described based on coordinate system in a mesh-less way, which impose penetration resistance on the projectile through resistance function based on dynamic cavity expansion theory. The penetration resistance on the surface of the rigid projectile is a function of the instantaneous velocity of that surface, which can be determined by the rigid body motion
of the projectile. Standard finite element method is introduced to model the rigid body motion of the projectile and is coupled with the coordinate resistance in a mesh-less target by exchanging the velocities and stresses through user-interfaces. Predictions of the critical impact energies during perforation process are compared with semi-empirical model and corresponding experimental data. Encouraging predictions are observed when the model was validated with the
existing experimental data.

Development of Empirical Prediction Formula for Penetration of Ogive Nose Hard Missile into Concrete Targets

by Imran Latif

Concrete is basic construction material used for more than enough kind of structures. However, the typical vital... more Concrete is basic construction material used for more than enough kind of structures. However, the typical vital structures have to be designed as self-protective such as nuclear plants, power plants, Weapon Industries, weapons storage places and water retaining structures, against any threats like natural disaster tragedy incident or intentionally produced horrible incidents such as dynamic loading, incident occurs in nuclear plants, terrorist attack, missile attack Tsunami, and etc. In modern science, the impact energies are crucial way to study the local impact effects on concrete structures. The way in which the kinetic energy is distributed through the concrete target is also noteworthy in determining its response, with the influence of dimensional analysis of the non dimensional numbers (Li et al., 2006). This study questioningly is paying concentration on development of empirical formula for predicting penetration depth of ogive nose hard missile in to the concrete structures, with the effects of different CRH ratios of missile (CRH = 2.0, CRH = 3.0, CRH = 4.5, CRH = 6.0) based on critical impact energies, by using curve fitting dimensional analysis of non-dimensional numbers. Argue overcome from this newly developed empirical formula is compared with other known formulae such as Modified NDRC formula, Hughes formula, ACE formula, UKAEA formula, and can be used for making design recommendations and design procedures for determining the dynamic reaction of the target to foil penetration in terms of critical impact kinetic energy. Furthermore relationships between CRH value and equation constant, which are used in prediction of penetration depth in new formula, also have been developed.

Review on Empirical Studies of Local Impact Effects of Hard Missile on Concrete Structures

by Imran Latif

Concrete is basic construction material used for any kind of structure. However, in most vital and local structures... more Concrete is basic construction material used for any kind of structure. However, in most vital and local structures such as nuclear plants, Power plants, Weapon Industries, weapons storage places, water retaining structures like dams, and also local industries, & etc., concrete structures have to be designed as defensive structures to provide protection against any accidents or knowingly generated incidents such as dynamic loading, dynamic local impact damage and global damage generated by kinetic missiles (steel rods, steel pipes, turbine blades, etc.). The impacting missile (projectile) can be classified as ‘Hard’ and ‘Soft’ in nature, depending upon the implication of its deformation with respect to the deformation of target. ‘Hard’ missile impact can generate both local impact damage and also overall dynamic global damage of concrete structure. This paper only provides the review of previous empirical studies related to our study and can be used for making design recommendation and design procedures for determining the dynamic response of the target to prevent local and impact damage.

Empirical Formula Prediction on Critical Impact Energy for Scabbing Phenomena on Concrete Structures

by Imran Latif

Background and Problem: Concrete is basic construction material used for structures. However, in case of the vital... more Background and Problem: Concrete is basic construction material used for structures. However, in case of the vital structures such as nuclear plants, power plants, weapon industries, weapons storage places, water retaining structures like dams, & etc., have to be designed as self-protective structures, which provides protection against local impact effects of hard missile against disastrous incidents or intentionally produced horrible incidents such as incident occurs in nuclear plants, terrorist attack, war, tsunami and etc. Methodology: The local impact effects can be studied by using dimensional analysis of non dimensional numbers in terms of the critical impact energies. The way in which the kinetic energy is distributed through the concrete target is also noteworthy in determining its response. In this paper, the influence of the relative target thickness (H/d) on those critical impact energies, at which scabbing occurs are explored. A dimensional analysis was conducted to identify influential non-dimensional numbers, which were subsequently employed in the development of proposed empirical formula relevant to required critical impact kinetic energy for scabbing by flat nose hard missiles. Results and Verification: The study is focused on judgment of minimum required kinetic energy for scabbing generated by flat nosed hard missile on the concrete structures. The results of proposed developed empirical formula are compared with other well established empirical and semi-empirical formulae, in order to examine the effects of (H/d) on the critical impact energy for scabbing failure. Conclusion: It is expected that the overcome from proposed developed empirical formula can be used for making design recommendations and design procedures for determining the dynamic reaction of the target to frustrate scabbing in terms of kinetic energy

Study on the Analytical Behaviour of Concrete Structure Against Local Impact of Hard Missile

by Imran Latif

Concrete is basic construction material used for almost all kind of structure. However, in the majority essential... more Concrete is basic construction material used for almost all kind of structure. However, in the majority essential structures such as nuclear plants, Power plants, Weapon Industries, weapons storage places, water retaining structures like dams, highways barriers, bridges, & etc., concrete structures have to be designed as self-protective structure which can afford any disaster or consciously engendered unpleasant incidents such as incident occurs in nuclear plants, incident in any essential industry, terrorist attack, Natural disasters like tsunami and etc missile attack, and local impact damage generated by kinetic missiles dynamic loading (steel rods, steel pipes, turbine blades, etc.). This paper inquisitively is paying attention on verdict of the recent development in formulating analytical behavior of concrete and reinforced concrete structures against local impact effect generated by hard missile with and without the influence of dimensional analysis based on dominant non-dimensional parameters, various nose shape factors at normal and certain inclined oblique angles. The paper comprises the analytical models and methods for predicting penetration, and perforation of concrete and reinforced concrete. The fallout conquer from this study can be used for making design counsel and design procedures for seminal the dynamic retort of the concrete targets to foil local impact damage.

Development of Empirical formula Prediction on Critical Impact Energy for Perforation Phenomena on Concrete Structures

by Imran Latif

Concrete is basic construction material used for most structures. However, the vital structures have to be designed as... more Concrete is basic construction material used for most structures. However, the vital structures have to be designed as self-protective such as nuclear plants, power plants, weapon industries, weapons storage places, water retaining structures, highway structures, & etc. These structures should have to be offer self shield against any natural disaster tragedy incidents and intentionally produced horrible incidents such as dynamic loading, incident occurs in nuclear plants, terrorist attack, missile attack, tsunami and etc. In modern science, the impact energies are crucial way to study the local impact effects on concrete structures together with the influence of relative target thickness (H/d). This study is focused on minimum required kinetic energy for perforation of the concrete structures generated by flat nose hard missile in terms of relative target thickness (H/d), by using curve fitting empirical study with the implementation of dimensional analysis of non-dimensional numbers. For verification, the proposed developed empirical formula was well compared with other established empirical formulae such as NDRC, UMIST and Semi Empirical formulae and it is expected that the outcome of the proposed formulae can be applied in design recommendations and design procedures for determining the dynamic reaction of the concrete target to foil perforation of flat nose hard missile.

Simulation Study on Effect of Diameter and CRH ratio of Ogive Nose Hard Missile on Required Critical Impact Energy for Penetration of Concrete Targets

by Imran Latif

Penetration is one of the elements in design consideration effects of the local impact damage phenomena. It has to be... more Penetration is one of the elements in design consideration effects of the local impact damage phenomena. It has to be investigated for designing protective concrete structures in order to resist kinetic impact by hard projectile. Kinetic energy is the dominant cause of damage in moving accidents. When hard projectile collides with concrete target, it is the kinetic energy of the projectile that makes concrete target to deform. Therefore, it is vital to study critical impact kinetic energy that causes penetration (local impact phenomena). A two dimension (2D) asymmetrical numerical simulation analysis has been conducted on ABAQUS software using dynamic explicit analysis function with constitutive model of Concrete Damaged Plasticity. The simulation was to determine the critical impact energy of ogive nose hard projectile which causes maximum penetration in to the concrete structures during local impact. It was found that the simulation results are in close relation with experimental data with less than 7% error in all cases. The limitation of Concrete damaged plasticity model is it contains no failure criteria. The effects of diameter and CRH ratio of ogive nose hard projectile on critical impact energy were also analysed. It is found that bigger diameter of ogive nose projectiles requires more critical impact energy for maximum penetration of concrete target as compared to the smaller diameter of ogive nose. For small CRH ratio of hard missile, it requires higher critical impact energy for maximum penetration of concrete target.

Ogive Nose Hard Missile Penetrating Concrete Slab Numerical Simulation Approach

by Imran Latif

Great demand exists for more efficient design to protect delicate and serious structures such as nuclear plants, Power... more Great demand exists for more efficient design to protect delicate and serious structures such as nuclear plants, Power plants, Weapon Industries, weapons storage places, water retaining structures, & etc, against impact of kinetic missiles generated both accidentally and deliberately such as dynamic loading, incident occurs in nuclear plants, terrorist attack, Natural disasters like tsunami and etc., in various impact and blast scenarios for both civilian and military activities. In many cases, projectiles can be treated as rigid bodies when their damage and erosion are not severe. Due to the intricacy of the local impact damages, investigations are generally based on experimental data. Conclusions of the experimental observations are then used to guide engineering models. Local damages studies normally fall into three categories, i.e. empirical formulae based on data fitting, idealised analytical models based on physic laws and numerical simulations based on computational mechanics and material models. In the present study, 2D asymmetrical numerical simulation have done on concrete slab against the impact of ogive nose hard missile of 26.90mm and 76.20mm diameter with CRH ratio 2.0 and 6.0 respectively, for penetration by using Concrete Damaged Plasticity Model, and ABAQUS/Explicit dynamic analysis in ABAQUS. It is found that the strains/stresses are induced in the concrete slab and a very nicely propagation of the stresses inside the concrete slab in the form of waves, which is a clear indication for vibrations of the concrete. The lack of failure criterion in concrete damaged plasticity model does not allow the removal of elements during the analyses. This means that spalling, scabbing, and perforation cannot be modelled with the Concrete Damage Plasticity Model. The penetration depth results shows that the deeper penetration requires higher critical impact kinetic energies, and comparison shows the simulation results are more accurate than other formulae predicted results.

Effective linear damping and stiffness coefficients of nonlinear systems for design spectrum based analysis

by Agathoklis Giaralis

Giaralis A and Spanos PD. (2010). Effective linear damping and stiffness coefficients of nonlinear systems for design spectrum based analysis. Soil Dynamics and Earthquake Engineering, 30: 798-810.

A stochastic approach for obtaining reliable estimates of the peak response of nonlinear systems to excitations... more A stochastic approach for obtaining reliable estimates of the peak response of nonlinear systems to excitations specified via a design seismic spectrum is proposed. This is achieved in an efficient manner without resorting to numerical integration of the governing nonlinear equations of motion. First, a numerical scheme is utilized to derive a power spectrum which is compatible in a stochastic sense with a given design spectrum. This power spectrum is then treated as the excitation spectrum to determine effective damping and stiffness coefficients corresponding to an equivalent linear system (ELS) via a statistical linearization scheme. Further, the obtained coefficients are used in conjunction with the (linear) design spectrum to estimate the peak response of the original nonlinear systems. The cases of systems with piecewise linear stiffness nonlinearity, along with bilinear hysteretic systems are considered. The seismic severity is specified by the elastic design spectrum prescribed by the European aseismic code provisions (EC8). Monte Carlo simulations pertaining to an ensemble of non-stationary EC8 design spectrum compatible accelerograms are conducted to confirm that the average peak response of the nonlinear systems compare reasonably well with that of the ELS, within the known level of accuracy furnished by the statistical linearization method. In this manner, the proposed approach yields ELS which can replace the original nonlinear systems in carrying out computationally efficient analyses in the initial stages of the aseismic design of structures under severe seismic excitations specified in terms of a design spectrum.

Time- frequency representation of earthquake accelerograms and inelastic structural response records using the adaptive chirplet decomposition and empirical mode decomposition

by Agathoklis Giaralis

Spanos PD, Giaralis A and Politis NP. (2007). Time- frequency representation of earthquake accelerograms and inelastic structural response records using the adaptive chirplet decomposition and empirical mode decomposition. Soil Dynamics and Earthquake Engineering, 27: 675- 689.

In this paper the adaptive chirplet decomposition combined with the Wigner-Ville transform and the empirical mode... more In this paper the adaptive chirplet decomposition combined with the Wigner-Ville transform and the empirical mode decomposition combined with the Hilbert transform are employed to process various nonstationary signals (strong ground motions and structural responses). The efficacy of these two adaptive techniques for capturing the temporal evolution of the frequency content of specific seismic signals is assessed. In this respect, two near- field and two far- field seismic accelerograms are analyzed. Further, a similar analysis is performed for records pertaining to the response of a 20-story steel frame benchmark building excited by one of the four accelerograms scaled by appropriate factors to simulate undamaged and severely damaged conditions for the structure. It is shown that the derived joint time- frequency representations of the response time histories capture quite effectively the influence of nonlinearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event; in this context, tracing the mean instantaneous frequency of records of critical structural responses is adopted.
The study suggests, overall, that the aforementioned techniques are quite viable tools for detecting and monitoring damage to constructed facilities exposed to seismic excitations.

Numerical treatment of seismic accelerograms and of inelastic seismic structural responses using harmonic wavelets

by Agathoklis Giaralis

Spanos PD, Giaralis A, Politis NP and Roessett JM. (2007). Numerical treatment of seismic accelerograms and of inelastic seismic structural responses using harmonic wavelets. Computer-Aided Civil and Infrastructure Engineering, 22: 254- 264.

The harmonic wavelet transform is employed to analyze various kinds of nonstationary signals common in aseismic... more The harmonic wavelet transform is employed to analyze various kinds of nonstationary signals common in aseismic design. The effectiveness of the harmonic wavelets for capturing the temporal evolution of the frequency content of strong ground motions is demonstrated. In this regard, a detailed study of important earthquake accelerograms is undertaken and smooth joint time- frequency spectra are provided for two near- field and two far- field records; inherent in this analysis is the concept of the mean instantaneous frequency. Further, as a paradigm of usefulness for aseismic structural purposes, a similar analysis is conducted for the response of a 20-story steel frame benchmark building considering as the excitation one of the four accelerograms scaled by appropriate factors to simulate undamaged and severely damaged conditions for the structure. The resulting joint time- frequency representation of the response time histories captures the influence of nonlinearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event. In this context, the potential of the harmonic wavelet transform as a detection tool for global structural damage is explored in conjunction with the concept of monitoring the mean instantaneous frequency of records of critical structural responses.

Synthesis of accelerograms compatible with the Chinese GB 50011-2001 design spectrum via harmonic wavelets: artificial and historic records

by Agathoklis Giaralis

Spanos PD, Giaralis A and Jie L. (2009). Synthesis of accelerograms compatible with the Chinese GB 50011-2001 design spectrum via harmonic wavelets: artificial and historic records. Earthquake Engineering and Engineering Vibrations, 8: 189-206.

A versatile approach is employed to generate artificial, and to modify field recorded accelerograms which satisfy the... more A versatile approach is employed to generate artificial, and to modify field recorded accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is incorporated to relate the GB 50011-2001 design spectrum to a parametrically defined evolutionary power spectrum (EPS). Special attention is focused on the definition of the frequency content of the EPS to accommodate the mathematical peculiarities of the aforementioned design spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average (ARMA) filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response spectrum is in a close agreement with the considered design spectrum. Furthermore, a harmonic wavelet based iterative scheme is incorporated to modify these artificial signals and field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event to achieve a close matching of the signals’ response spectra with the GB 50011-2001 design spectrum on an individual basis. Zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired spectrum compatible artificial and field accelerograms.