Effects of local vibrations on the dynamics of space truss structures

Warnaar, D. B.; Mcgowan, Paul E.

doi:10.2514/6.1987-941

Cited by 7 publications

(5 citation statements)

References 1 publication

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“…To model bending vibrations of truss members, discretized finite beam elements should be used to represent deformations between structural nodes. Due to the fact that this can make it difficult to distinguish between global and local mode shapes in the numerical modelling, an approach based on modal strain energy (MSE) has been suggested by [8], which allows for a breakdown of modal strain energy into axial, bending, torsional, and shear components. Axial strains dominate global deformation, while bending strains dominate local member deformation.…”

Section: Modal Strain Energymentioning

confidence: 99%

“…The next 18 mode shapes, only six of them are shown in Figure 2, reveal two types of vibration modes: global and local mechanisms. According to [8], a mode is considered as global if the complete structure deforms as a continuum system, while a local mode is dominated by member deformations.…”

Section: Modelling and Simulationmentioning

confidence: 99%

“…On the other hand, modes 7 and 13 display local vibrations of the threaded rod, while mode 18 demonstrates local bending of some members in the space structure bottom chord. As discussed in section 2.2, [8] suggests to differentiate between global and local modes in a space truss structure by examining the percentage of axial and bending strain energies relative to the total modal strain energy. In Figure 3, the total modal strain energies are decomposed into axial and bending contributions for the modes given in Figure 2. )…”

Section: Modelling and Simulationmentioning

confidence: 99%

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Identification of closely spaced modes in space truss structures as base for the determination of member normal forces

Abdelnour,

Zabel

2024

J. Phys.: Conf. Ser.

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Space truss structures are a type of versatile lightweight systems that are applied in different fields such as civil and aerospace engineering. For some of these systems that were built decades ago, for example as roof structures for relatively large spans, not all proofs regarding the load-bearing capacity and serviceability can be satisfied according to current codes of practice as the requirements may have changed since the initial design phase of these systems. In such cases, it may become necessary to obtain the actual stress status of the structural skeleton based on experimental investigations. From the identification of forces in many members, a general stress status can be derived, which leads to an estimation of the current status and possible reserves in the load-bearing capacity of space truss structures. One option for the identification of element forces is their identification from modal parameters of the structure. In literature, the main focus has been put so far on the identification of longitudinal forces and boundary conditions inside a single tension member/cable utilising vibration-based methods. Very good results were also reported for the identification of longitudinal forces in elements of two-dimensional truss structures of moderate complexity. Fewer studies documented in the literature concentrate on space truss structures. For these modular systems consisting of standardized elements, not only the identification of element forces based on identified modal parameters is very challenging, but also the modal identification itself. The latter is often caused by the situation that space truss structures often have numerous modes characterised by both local and global vibrations at close natural frequencies. The study presented in this contribution focuses on the identification of mode shapes and natural frequencies required as a prerequisite for a model based approach to estimate the stress state of the complete considered space truss structure. Apart from aspects with respect to the instrumentation for modal testing, specific issues within a parametric modal analysis such as the choice of model order are discussed. It is explained by means of a case study, why the minimal model order to be taken into account in the modal identification of space truss structures can become considerably higher than those commonly applied in the analysis of, for example, bridge structures, towers or floor systems. These descriptions are illustrated by the results of both numerical and experimental analyses.

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Section: Modal Strain Energymentioning

confidence: 99%

Section: Modelling and Simulationmentioning

confidence: 99%

Section: Modelling and Simulationmentioning

confidence: 99%

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Identification of closely spaced modes in space truss structures as base for the determination of member normal forces

Abdelnour,

Zabel

2024

J. Phys.: Conf. Ser.

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“…Truss structures comprise truss members such as beams that are connected to each other via the relatively stiff truss supports. Due to this design, truss structures show local and global vibration modes [16]. Global vibration modes are characterized by lateral moving or rotating truss supports, whereas local modes are dominated by the lateral vibration behavior of each beam.…”

Section: Introductionmentioning

confidence: 99%

Effect of static axial loads on the lateral vibration attenuation of a beam with piezo-elastic supports

Götz

Platz

Melz

2018

Smart Mater. Struct.

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In this paper, vibration attenuation of a beam with circular cross-section by resonantly shunted piezo-elastic supports is experimentally investigated for varying axial tensile and compressive beam loads. The beam's first mode resonance frequency, the general electromechanical coupling coefficient and static transducer capacitance are analyzed for varying axial loads. All three parameter values are obtained from transducer impedance measurements on an experimental test setup. Varying axial beam loads manipulate the beam's lateral bending stiffness and, thus, lead to a detuning of the resonance frequencies. Furthermore, they affect the general electromechanical coupling coefficient of transducer and beam, an important modal quantity for shunt-damping, whereas the static transducer capacitance is nearly unaffected. Frequency transfer functions of the beam with one piezoe-elastic support either shunted to an RL-shunt or to an RL-shunt with negative capacitance, the RLC-shunt, are compared for varying axial loads. It is shown that the beam vibration attenuation with the RLC-shunt is less influenced by varying axial beam loads and, therefore, is more robust against detuning.

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“…On the other hand, local modes exist that are dominated by the lateral vibration of each truss member. Truss structures that are subject to heavy mass loading may show adequate separation in the structural frequencies of global and local modes [7]. However, the dynamics of other truss structure designs may be affected by local modes with frequencies within the bandwidth of the global modes.…”

Section: Introductionmentioning

confidence: 99%

Lateral vibration attenuation of a beam with circular cross-section by a support with integrated piezoelectric transducers shunted to negative capacitances

Götz

Schaeffner

Platz

et al. 2016

Smart Mater. Struct.

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Undesired vibration may occur in lightweight structures due to excitation and low damping. For the purpose of lateral vibration attenuation in beam structures, piezoelectric transducers shunted to negative capacitances can be an appropriate measure. In this paper, a new concept for lateral vibration attenuation by integrated piezoelectric stack transducers in the elastic support of a beam with circular cross-section is presented. In the piezoelastic support, bending of the beam in an arbitrary direction is transformed into a significant axial deformation of three stack transducers and, thus, the beam's surface may remain free from transducers. For multimodal vibration attenuation, each piezoelectric transducer is shunted to a negative capacitance. It is shown by numerical simulation and experiment that the concept of an elastic beam support with integrated shunted piezoelectric stack transducers is capable of reducing the lateral vibration of the beam in an arbitrary direction.

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Effects of local vibrations on the dynamics of space truss structures

Cited by 7 publications

References 1 publication

Identification of closely spaced modes in space truss structures as base for the determination of member normal forces

Identification of closely spaced modes in space truss structures as base for the determination of member normal forces

Effect of static axial loads on the lateral vibration attenuation of a beam with piezo-elastic supports

Lateral vibration attenuation of a beam with circular cross-section by a support with integrated piezoelectric transducers shunted to negative capacitances

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