Abstract A closed-form explicit solution for statistical fatigue life assessment under broad-band... more Abstract A closed-form explicit solution for statistical fatigue life assessment under broad-band stochastic loading is proposed herein. Obtained solution is valid for stationary, random and ergodic zero mean Gaussian stress process. It is based on Rice/Lalanne peak stress probability distribution function. The solution is given in terms of special Gaussian HyperGeometric function which accurately describes the transcendent error weighting function between the Rayleigh (i.e. narrow-band) and Gaussian (i.e. broad-band) contribution of the random vibration fatigue model. HyperGeometric-based solution is more accurate compared to other approximate methods based on the peak distribution from literature. Fatigue benchmark test comparison is performed in time and frequency domains with very good match-up reported.
Skyhook damping is an active vibration isolation method, which can also be used to reduce vibrati... more Skyhook damping is an active vibration isolation method, which can also be used to reduce vibration transmission between masses in lumped parameter 2 degree of freedom (dof) systems. The method is based on measuring the absolute velocity of the clean body, multiplying it by a negative gain, and feeding the result back to a force actuator reacting between the clean and the dirty body. In such a way disturbances coming onto the clean body from the dirty body can be successfully rejected in a broad frequency band. However, the method is only suitable if the feedback loop is unconditionally stable such that appropriately high feedback gains can be applied. It has been previously shown that passive 2 dof systems can be classified as so called subor supercritical based on whether the skyhook damping loop is conditionally or unconditionally stable. For subcritical systems the absolute velocity feedback loop is conditionally stable and a skyhook damping approach is consequently not appropri...
Fatigue life of plates damaged with multiple collinear cracks and subjected to cyclic tension loa... more Fatigue life of plates damaged with multiple collinear cracks and subjected to cyclic tension loading was investigated. Results of fatigue crack growth tests with a constant tensile stress range were reported for a plate with a single crack and a plate with three collinear equidistant cracks. A simulation procedure based on numerical integration of the differential equation of a crack growth model was introduced. The Mode I stress intensity factor values, KI, were calculated by a FEM program using singular elements and assuming plane stress conditions. Using the Paris law, Klesnil- Lukas and Zheng-Hirt crack growth models, the fatigue life was simulated for the test specimens. Experiments and simulations showed a higher crack growth rate for the specimen with three cracks and 40% shorter fatigue life compared to the specimen with a single crack, which is due to the interaction of multiple cracks.
The main goal in designing the wind turbine is ensuring structural safety and optimal operational... more The main goal in designing the wind turbine is ensuring structural safety and optimal operational performance. Key aspects to be addressed are: long design life, sensitivity of structure to vibration and resonance, non- deterministic wind loads with significant time variations and micro-location dependence. In order to achieve these goals, a simple dynamic lumped-mass model of a conic tubular steel wind turbine tower has been developed in this paper. The tower stiffness matrix is determined by considering the stiffness of a cantilever beam with variable cross-section, and lumped masses for each conical segment are determined in such a way that the centres of gravity of conical segments match their actual position in the structure. There is a very good agreement between the measured field data and the results obtained by the developed simple numerical model.
This paper considers using the Energy Balance Method for estimation of overhead transmission line... more This paper considers using the Energy Balance Method for estimation of overhead transmission line Aeolian vibrations. Since the damper’ s efficiency strongly depends on its position, the procedure of determining the optimum position of the damper is described. It is observed that the optimal damper position depends on the span length also and that the best results can be achieved by determining the damper position for each span inside the line section. In order to examine accuracy of the developed computational program, as well as correctness of the estimation of the data used (wind power, data on the damper's mechanical impedance, and mechanical characteristics of the conductor), numerical results generated using the developed computer program and data from field measurements (before and after the application of Stockbridge dampers) are compared. A very high correlation between these data has been observed.
Numerical simulation procedures for landing dynamics of large transport aircraft are shortly pres... more Numerical simulation procedures for landing dynamics of large transport aircraft are shortly presented. Developed numerical procedures allow for determination of dynamic response of landing aircraft for different flight and touch-down parameters. Non-linear dynamical model of landing aircraft, which serves as a basis for computational procedures, is synthesised by modelling of aircraft structural subsystems using multibody dynamics approach. Dynamical model with variable kinematical structure includes discontinuous dynamics of landing gear oleo-pneumatic shock-absorber with friction and hydraulic/thermodynamic processes. Non-linear tire contact dynamics and unilateral dynamics of nose gear elastic leg assembly is modelled as well. The longitudinal and lateral aerodynamic loads are estimated by considering aircraft various system configurations (landing gears in "up" and "down" position, different control surfaces in active/inactive modes). Mathematical model is d...
Fatigue crack growth tests with constant stress range and frequency were carried out for a plate ... more Fatigue crack growth tests with constant stress range and frequency were carried out for a plate with a single centre crack, P1, and a plate with three collinear cracks, P3, (see Fig.1). The applied average stress range and loading frequency were 80 MPa and 5 Hz, respectively, where the specimens' material was a mild structural steel. Based on experimental a-N data obtained for the two specimens, (see Fig.2), crack growth rates were calculated, (see Fig.3), and Paris' equation constants were estimated. It was observed in the experiment that in case of specimen P3 the crack tips propagated at different crack propagation rate, where the tip 1 showed the highest propagating rate. An interactive crack propagation simulation procedure for multiple propagating crack tips was introduced, using a FEM analysis to calculate stress intensity factors, KI, and numerical integration of Paris' equation. Generally, any propagating crack tip can be taken in the simulation procedure as a ...
The thin infinite plate with an embedded straight crack of a length 2a is considered. The plate i... more The thin infinite plate with an embedded straight crack of a length 2a is considered. The plate is uniaxially loaded in its plane with uniformly distributed continuous load in a direction perpendicular to the crack plane. The plate material is ductile so the small plastic zones around the crack tips are formed. Also, it is assumed that the plate material possesses a property of isotropic strain hardening. The strain hardening of the material is non-linear and it obeys the Ramberg-Osgood relation. The different stages of strain hardening of plate material are modeled by varying the parameters yy ∞ ∞ σ = σ α and n in the Ramberg-Osgood's analytical expression. So, it is assumed that the strain hardening exponent n takes the values n = 3, 5, 7, 10, 25 and ∞ . The stress intensity factor (SIF) of the cohesive stresses coh ( p K a r ) + is determined by means of Green's functions method. The crack tip and crack centre opening, or any arbitrary point at the crack surface, is deter...
U radu se razmatraju problemi cvrstoce i krutosti kucista statora hidrogeneratora horizontalne iz... more U radu se razmatraju problemi cvrstoce i krutosti kucista statora hidrogeneratora horizontalne izvedbe. Ta je analiza posebno važna i zanimljiva kod generatora ciji rotor, a onda i stator, imaju velike promjere (3 m i vise). Važno je da kuciste statora hidrogeneratora ima dovoljno veliku krutost kako pomaci pojedinih karakteristicnih tocaka statora ne bi bili preveliki i time promijenili geometriju statora, odnosno utjecali na promjenu zracnog raspora između rotora i statora. Na konstrukciju kucista statora hidrogeneratora u eksploataciji djeluje nekoliko razlicitih opterecenja. U prvom redu, kod horizontalne izvedbe rotora i statora, to je utjecaj vlastite težine samoga kucista na koje je pricvrscen statorski paket i statorski namot. To opterecenje modelira se kao jednoliko raspodijeljeno kontinuirano opterecenje q. Ovaj rad bit ce posvecen upravo analizi utjecaja toga opterecenja na velicinu unutarnjih sila i pomaka u kucistu statora. Druga vrsta opterecenja su sile magnetskog pri...
Sveucilisni udžbenik "Mehanika deformabilnih tijela", drugi dio nosi naslov "Cvrst... more Sveucilisni udžbenik "Mehanika deformabilnih tijela", drugi dio nosi naslov "Cvrstoca elemenata konstrukcija". Osim predgovora, popisa oznaka fizikalnih velicina i mjernih jedinica, popisa literature (52 reference), kazala pojmova i biljeske o autorima, sadrži jos pet poglavlja. To su: 7. Matricne metode analize konstrukcija, 8. Debelostjene cijevi i cilindricne posude, 9. Rotirajuci diskovi promjenljive i konstantne debljine. Utjecaj nejednolikog zagrijavanja diska na raspodjelu naprezanja i pomaka, 10. Savijanje tankih kružnih ploca, 11. Uvijanje i savijanje tankostjenih stapova.
The supervising and health monitoring of structures is a new field that has been of increasing im... more The supervising and health monitoring of structures is a new field that has been of increasing importance with regard to control durability, stability and safety as well as for estimating the life span of the structure. Crack growth is interesting for the proper evaluation of the reliability of structural parts. Different methods are used to record the actual situation in order to get reliable information about the on-site structure and structural elements. The experimental techniques in fracture mechanics are employed for determining the stress-intensity factors (SIFs) of the cracks in deformed structures. A procedure for the simulation of crack propagation for multiple cracks was introduced and SIFs have been calculated by using the finite-element method. The crack growth of a single crack or a periodic array of cracks initiated at the stiffeners in a stiffened panel has been investigated. The optical method of caustics is established for the application to mechanically isotropic ...
Damaging process analysis is significant for determination of reliability of mechanical component... more Damaging process analysis is significant for determination of reliability of mechanical components while the numerical simulations of crack appearances and growing will process phenomena of structural damages. In recent years, substantial advances in the understanding of the basic principles governing dynamic structural damage, coupled with the development of new, relatively easy to use verifiable computational methodologies have made it possible to utilize the concepts of fatigue and fracture analysis to a wide spectrum of very diverse applications. They are relevant to technical problems, such as accident prevention, manufacturing processes, and reliability in design. Advanced experimental and numerical analysis will provide the verification of behavior of structural elements. Numerical analysis of dynamic loading and its optimization is important even in the designing of the structure to reduce possible damages, preferably combined by the experimental verification. In electrical ...
This paper addresses the Coulomb dry friction force as a technical indicator for fast and efficie... more This paper addresses the Coulomb dry friction force as a technical indicator for fast and efficient condition-based maintenance. To estimate the value of friction force, the Bayesian analysis is used. Instead of the complex Markov Chain Monte Carlo numerical method, a closed-form analytical solution is applied. Thus, a simple and efficient procedure for friction estimation is described. Such a solution in the Bayesian context is known as the conjugate prior. The procedure presented here is verified numerically and experimentally by directly comparing the estimated value with the measured one. Two families of conjugate priors, the gamma-exponential and the normal-gamma, are compared. It is shown that the latter is suitable for friction estimation. An additional parameter, the precision parameter, was proposed as a criterion for the acceptance of estimation.
This paper presents a theoretical study on passive and active vibration isolation schemes using i... more This paper presents a theoretical study on passive and active vibration isolation schemes using inerter elements in a two degree of freedom (DOF) mechanical system. The aim of the work is to discuss basic capabilities and limitations of the vibration control systems at hand using simple and physically transparent models. Broad frequency band dynamic excitation of the source DOF is assumed. The purpose of the isolator system is to prevent vibration transmission to the receiving DOF. The frequency averaged kinetic energy of the receiving mass is used as the metric for vibration isolation quality. It is shown that the use of inerter in the passive and active vibration isolation schemes considered enhances the isolation effect.
This paper presents an optimization and numerical analysis of vibration-induced fatigue in a two ... more This paper presents an optimization and numerical analysis of vibration-induced fatigue in a two degree-of-freedom inerter-based vibration isolation system. The system is comprised of a primary, e.g. source body, and a secondary, e.g. receiving body, mutually connected through an isolator. The isolator includes a spring, a dashpot and an inerter. Inerter is a mechanical device which produces a force proportional to relative acceleration between its terminals. A broadband frequency force excitation of the primary body is imposed throughout the study. The goal of the proposed optimization is to prolong the fatigue life of the ground connecting helical spring of the secondary body. The optimization is based on minimizing separately the displacement and velocity amplitudes. Both optimization criteria are compared with regard to spring fatigue life improvement for fair benchmark comparison. The inerter-based optimized systems, in which the H 2 index of the receiving body is minimized, are also compared with the optimized systems without inerter. Notable improvements are observed in inerter-based systems due to the inclusion of an optimally tuned inerter in the isolator. The proposed analytical vibration fatigue method optimization results are compared with the finite element method results, and a very good agreement is observed. Most accurate helical spring deflection and stress correction factors are discussed and determined. Furthermore, the inerter concept is successfully implemented into finite element-based dynamic solution.
Supervising and health monitoring of structures can assess the actual state of existing structure... more Supervising and health monitoring of structures can assess the actual state of existing structures after initial loading or in the state of operation. Structural life management requires the integration of design and analysis, materials behavior and structural testing, as given for several examples. Procedure of survey of structural elements and criteria for their selection must be strongly defined as it is for the offshore gas platforms. Numerical analysis of dynamic loading is shown for the Aeolian vibrations of overhead transmission line conductors. Since the damper's efficiency strongly depends on its position, the procedure of determining the optimum position of the damper is described. The optical method of caustics is established in isotropic materials for determination of the stress intensity factors (SIFs) of the cracks in deformed structures and is advantageously improved for the application to fiberreinforced composites. A procedure for simulation of crack propagation for multiple cracks was introduced and SIFs have been calculated by using finite element method. Crack growth of a single crack or a periodical array of cracks initiated at the stiffeners in a stiffened panel has been investigated.
In this paper we consider the problem which can appear at the determination of the dynamical stab... more In this paper we consider the problem which can appear at the determination of the dynamical stability of the responses of oscillators with discontinuous or steep derivative of the restoring characteristic obtained in the frequency domain. For that purpose, a simple one degree-of-freedom system with piecewise-linear force-displacement relationship subjected to a harmonic excitation is analysed. Stability of the periodic response obtained in the frequency domain by the incremental harmonic balance method is determined by using the Floquet-Liapounov theorem. Confirmation of the results obtained in the frequency domain is done by comparing with the results obtained in the time domain by the method of piecing the exact solutions. Determination of the dynamical stability can be made more reliable by using the proposed plot of maximum modulus of the eigenvalues of the monodromy matrix in dependence of non-dimensional fre
Abstract A closed-form explicit solution for statistical fatigue life assessment under broad-band... more Abstract A closed-form explicit solution for statistical fatigue life assessment under broad-band stochastic loading is proposed herein. Obtained solution is valid for stationary, random and ergodic zero mean Gaussian stress process. It is based on Rice/Lalanne peak stress probability distribution function. The solution is given in terms of special Gaussian HyperGeometric function which accurately describes the transcendent error weighting function between the Rayleigh (i.e. narrow-band) and Gaussian (i.e. broad-band) contribution of the random vibration fatigue model. HyperGeometric-based solution is more accurate compared to other approximate methods based on the peak distribution from literature. Fatigue benchmark test comparison is performed in time and frequency domains with very good match-up reported.
Skyhook damping is an active vibration isolation method, which can also be used to reduce vibrati... more Skyhook damping is an active vibration isolation method, which can also be used to reduce vibration transmission between masses in lumped parameter 2 degree of freedom (dof) systems. The method is based on measuring the absolute velocity of the clean body, multiplying it by a negative gain, and feeding the result back to a force actuator reacting between the clean and the dirty body. In such a way disturbances coming onto the clean body from the dirty body can be successfully rejected in a broad frequency band. However, the method is only suitable if the feedback loop is unconditionally stable such that appropriately high feedback gains can be applied. It has been previously shown that passive 2 dof systems can be classified as so called subor supercritical based on whether the skyhook damping loop is conditionally or unconditionally stable. For subcritical systems the absolute velocity feedback loop is conditionally stable and a skyhook damping approach is consequently not appropri...
Fatigue life of plates damaged with multiple collinear cracks and subjected to cyclic tension loa... more Fatigue life of plates damaged with multiple collinear cracks and subjected to cyclic tension loading was investigated. Results of fatigue crack growth tests with a constant tensile stress range were reported for a plate with a single crack and a plate with three collinear equidistant cracks. A simulation procedure based on numerical integration of the differential equation of a crack growth model was introduced. The Mode I stress intensity factor values, KI, were calculated by a FEM program using singular elements and assuming plane stress conditions. Using the Paris law, Klesnil- Lukas and Zheng-Hirt crack growth models, the fatigue life was simulated for the test specimens. Experiments and simulations showed a higher crack growth rate for the specimen with three cracks and 40% shorter fatigue life compared to the specimen with a single crack, which is due to the interaction of multiple cracks.
The main goal in designing the wind turbine is ensuring structural safety and optimal operational... more The main goal in designing the wind turbine is ensuring structural safety and optimal operational performance. Key aspects to be addressed are: long design life, sensitivity of structure to vibration and resonance, non- deterministic wind loads with significant time variations and micro-location dependence. In order to achieve these goals, a simple dynamic lumped-mass model of a conic tubular steel wind turbine tower has been developed in this paper. The tower stiffness matrix is determined by considering the stiffness of a cantilever beam with variable cross-section, and lumped masses for each conical segment are determined in such a way that the centres of gravity of conical segments match their actual position in the structure. There is a very good agreement between the measured field data and the results obtained by the developed simple numerical model.
This paper considers using the Energy Balance Method for estimation of overhead transmission line... more This paper considers using the Energy Balance Method for estimation of overhead transmission line Aeolian vibrations. Since the damper’ s efficiency strongly depends on its position, the procedure of determining the optimum position of the damper is described. It is observed that the optimal damper position depends on the span length also and that the best results can be achieved by determining the damper position for each span inside the line section. In order to examine accuracy of the developed computational program, as well as correctness of the estimation of the data used (wind power, data on the damper's mechanical impedance, and mechanical characteristics of the conductor), numerical results generated using the developed computer program and data from field measurements (before and after the application of Stockbridge dampers) are compared. A very high correlation between these data has been observed.
Numerical simulation procedures for landing dynamics of large transport aircraft are shortly pres... more Numerical simulation procedures for landing dynamics of large transport aircraft are shortly presented. Developed numerical procedures allow for determination of dynamic response of landing aircraft for different flight and touch-down parameters. Non-linear dynamical model of landing aircraft, which serves as a basis for computational procedures, is synthesised by modelling of aircraft structural subsystems using multibody dynamics approach. Dynamical model with variable kinematical structure includes discontinuous dynamics of landing gear oleo-pneumatic shock-absorber with friction and hydraulic/thermodynamic processes. Non-linear tire contact dynamics and unilateral dynamics of nose gear elastic leg assembly is modelled as well. The longitudinal and lateral aerodynamic loads are estimated by considering aircraft various system configurations (landing gears in "up" and "down" position, different control surfaces in active/inactive modes). Mathematical model is d...
Fatigue crack growth tests with constant stress range and frequency were carried out for a plate ... more Fatigue crack growth tests with constant stress range and frequency were carried out for a plate with a single centre crack, P1, and a plate with three collinear cracks, P3, (see Fig.1). The applied average stress range and loading frequency were 80 MPa and 5 Hz, respectively, where the specimens' material was a mild structural steel. Based on experimental a-N data obtained for the two specimens, (see Fig.2), crack growth rates were calculated, (see Fig.3), and Paris' equation constants were estimated. It was observed in the experiment that in case of specimen P3 the crack tips propagated at different crack propagation rate, where the tip 1 showed the highest propagating rate. An interactive crack propagation simulation procedure for multiple propagating crack tips was introduced, using a FEM analysis to calculate stress intensity factors, KI, and numerical integration of Paris' equation. Generally, any propagating crack tip can be taken in the simulation procedure as a ...
The thin infinite plate with an embedded straight crack of a length 2a is considered. The plate i... more The thin infinite plate with an embedded straight crack of a length 2a is considered. The plate is uniaxially loaded in its plane with uniformly distributed continuous load in a direction perpendicular to the crack plane. The plate material is ductile so the small plastic zones around the crack tips are formed. Also, it is assumed that the plate material possesses a property of isotropic strain hardening. The strain hardening of the material is non-linear and it obeys the Ramberg-Osgood relation. The different stages of strain hardening of plate material are modeled by varying the parameters yy ∞ ∞ σ = σ α and n in the Ramberg-Osgood's analytical expression. So, it is assumed that the strain hardening exponent n takes the values n = 3, 5, 7, 10, 25 and ∞ . The stress intensity factor (SIF) of the cohesive stresses coh ( p K a r ) + is determined by means of Green's functions method. The crack tip and crack centre opening, or any arbitrary point at the crack surface, is deter...
U radu se razmatraju problemi cvrstoce i krutosti kucista statora hidrogeneratora horizontalne iz... more U radu se razmatraju problemi cvrstoce i krutosti kucista statora hidrogeneratora horizontalne izvedbe. Ta je analiza posebno važna i zanimljiva kod generatora ciji rotor, a onda i stator, imaju velike promjere (3 m i vise). Važno je da kuciste statora hidrogeneratora ima dovoljno veliku krutost kako pomaci pojedinih karakteristicnih tocaka statora ne bi bili preveliki i time promijenili geometriju statora, odnosno utjecali na promjenu zracnog raspora između rotora i statora. Na konstrukciju kucista statora hidrogeneratora u eksploataciji djeluje nekoliko razlicitih opterecenja. U prvom redu, kod horizontalne izvedbe rotora i statora, to je utjecaj vlastite težine samoga kucista na koje je pricvrscen statorski paket i statorski namot. To opterecenje modelira se kao jednoliko raspodijeljeno kontinuirano opterecenje q. Ovaj rad bit ce posvecen upravo analizi utjecaja toga opterecenja na velicinu unutarnjih sila i pomaka u kucistu statora. Druga vrsta opterecenja su sile magnetskog pri...
Sveucilisni udžbenik "Mehanika deformabilnih tijela", drugi dio nosi naslov "Cvrst... more Sveucilisni udžbenik "Mehanika deformabilnih tijela", drugi dio nosi naslov "Cvrstoca elemenata konstrukcija". Osim predgovora, popisa oznaka fizikalnih velicina i mjernih jedinica, popisa literature (52 reference), kazala pojmova i biljeske o autorima, sadrži jos pet poglavlja. To su: 7. Matricne metode analize konstrukcija, 8. Debelostjene cijevi i cilindricne posude, 9. Rotirajuci diskovi promjenljive i konstantne debljine. Utjecaj nejednolikog zagrijavanja diska na raspodjelu naprezanja i pomaka, 10. Savijanje tankih kružnih ploca, 11. Uvijanje i savijanje tankostjenih stapova.
The supervising and health monitoring of structures is a new field that has been of increasing im... more The supervising and health monitoring of structures is a new field that has been of increasing importance with regard to control durability, stability and safety as well as for estimating the life span of the structure. Crack growth is interesting for the proper evaluation of the reliability of structural parts. Different methods are used to record the actual situation in order to get reliable information about the on-site structure and structural elements. The experimental techniques in fracture mechanics are employed for determining the stress-intensity factors (SIFs) of the cracks in deformed structures. A procedure for the simulation of crack propagation for multiple cracks was introduced and SIFs have been calculated by using the finite-element method. The crack growth of a single crack or a periodic array of cracks initiated at the stiffeners in a stiffened panel has been investigated. The optical method of caustics is established for the application to mechanically isotropic ...
Damaging process analysis is significant for determination of reliability of mechanical component... more Damaging process analysis is significant for determination of reliability of mechanical components while the numerical simulations of crack appearances and growing will process phenomena of structural damages. In recent years, substantial advances in the understanding of the basic principles governing dynamic structural damage, coupled with the development of new, relatively easy to use verifiable computational methodologies have made it possible to utilize the concepts of fatigue and fracture analysis to a wide spectrum of very diverse applications. They are relevant to technical problems, such as accident prevention, manufacturing processes, and reliability in design. Advanced experimental and numerical analysis will provide the verification of behavior of structural elements. Numerical analysis of dynamic loading and its optimization is important even in the designing of the structure to reduce possible damages, preferably combined by the experimental verification. In electrical ...
This paper addresses the Coulomb dry friction force as a technical indicator for fast and efficie... more This paper addresses the Coulomb dry friction force as a technical indicator for fast and efficient condition-based maintenance. To estimate the value of friction force, the Bayesian analysis is used. Instead of the complex Markov Chain Monte Carlo numerical method, a closed-form analytical solution is applied. Thus, a simple and efficient procedure for friction estimation is described. Such a solution in the Bayesian context is known as the conjugate prior. The procedure presented here is verified numerically and experimentally by directly comparing the estimated value with the measured one. Two families of conjugate priors, the gamma-exponential and the normal-gamma, are compared. It is shown that the latter is suitable for friction estimation. An additional parameter, the precision parameter, was proposed as a criterion for the acceptance of estimation.
This paper presents a theoretical study on passive and active vibration isolation schemes using i... more This paper presents a theoretical study on passive and active vibration isolation schemes using inerter elements in a two degree of freedom (DOF) mechanical system. The aim of the work is to discuss basic capabilities and limitations of the vibration control systems at hand using simple and physically transparent models. Broad frequency band dynamic excitation of the source DOF is assumed. The purpose of the isolator system is to prevent vibration transmission to the receiving DOF. The frequency averaged kinetic energy of the receiving mass is used as the metric for vibration isolation quality. It is shown that the use of inerter in the passive and active vibration isolation schemes considered enhances the isolation effect.
This paper presents an optimization and numerical analysis of vibration-induced fatigue in a two ... more This paper presents an optimization and numerical analysis of vibration-induced fatigue in a two degree-of-freedom inerter-based vibration isolation system. The system is comprised of a primary, e.g. source body, and a secondary, e.g. receiving body, mutually connected through an isolator. The isolator includes a spring, a dashpot and an inerter. Inerter is a mechanical device which produces a force proportional to relative acceleration between its terminals. A broadband frequency force excitation of the primary body is imposed throughout the study. The goal of the proposed optimization is to prolong the fatigue life of the ground connecting helical spring of the secondary body. The optimization is based on minimizing separately the displacement and velocity amplitudes. Both optimization criteria are compared with regard to spring fatigue life improvement for fair benchmark comparison. The inerter-based optimized systems, in which the H 2 index of the receiving body is minimized, are also compared with the optimized systems without inerter. Notable improvements are observed in inerter-based systems due to the inclusion of an optimally tuned inerter in the isolator. The proposed analytical vibration fatigue method optimization results are compared with the finite element method results, and a very good agreement is observed. Most accurate helical spring deflection and stress correction factors are discussed and determined. Furthermore, the inerter concept is successfully implemented into finite element-based dynamic solution.
Supervising and health monitoring of structures can assess the actual state of existing structure... more Supervising and health monitoring of structures can assess the actual state of existing structures after initial loading or in the state of operation. Structural life management requires the integration of design and analysis, materials behavior and structural testing, as given for several examples. Procedure of survey of structural elements and criteria for their selection must be strongly defined as it is for the offshore gas platforms. Numerical analysis of dynamic loading is shown for the Aeolian vibrations of overhead transmission line conductors. Since the damper's efficiency strongly depends on its position, the procedure of determining the optimum position of the damper is described. The optical method of caustics is established in isotropic materials for determination of the stress intensity factors (SIFs) of the cracks in deformed structures and is advantageously improved for the application to fiberreinforced composites. A procedure for simulation of crack propagation for multiple cracks was introduced and SIFs have been calculated by using finite element method. Crack growth of a single crack or a periodical array of cracks initiated at the stiffeners in a stiffened panel has been investigated.
In this paper we consider the problem which can appear at the determination of the dynamical stab... more In this paper we consider the problem which can appear at the determination of the dynamical stability of the responses of oscillators with discontinuous or steep derivative of the restoring characteristic obtained in the frequency domain. For that purpose, a simple one degree-of-freedom system with piecewise-linear force-displacement relationship subjected to a harmonic excitation is analysed. Stability of the periodic response obtained in the frequency domain by the incremental harmonic balance method is determined by using the Floquet-Liapounov theorem. Confirmation of the results obtained in the frequency domain is done by comparing with the results obtained in the time domain by the method of piecing the exact solutions. Determination of the dynamical stability can be made more reliable by using the proposed plot of maximum modulus of the eigenvalues of the monodromy matrix in dependence of non-dimensional fre
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Papers by Hinko Wolf