Number Of Structural Modes Research Articles

Morphological analysis of a novel scissor-type deployable cable dome structure

A novel deployable scissor-type strut cable dome structure was proposed, which can improve the lateral stiffness of the traditional cable structure and achieve the characteristics of fast unfolding and closing during construction. However, the geometric stability and optimal initial prestressing theory of traditional cable dome structures cannot be applied to the new structure. Based on the equilibrium matrix theory, the geometric stability analysis was conducted and the number of self-stress modes, mechanism displacement modes, and feasible prestress modes was calculated. Then, the formula for the initial prestress distribution of the structure was derived based on the node equilibrium equation. Furthermore, the geometric stability and initial prestress distribution of the structure with different rise-to-span ratios, number of circumferential struts, and hoop cables were studied. Finally, the dynamic properties of the structure are explored by finite element simulation. The analysis results show that the structure has excellent structural stability. The rise-to-span ratios, the number of circumferential struts, and hoop cables are the important factors affecting the geometric stability and the initial prestress distribution. The rise-to-span ratios have no effect on the number of structural modes, while the number of circumferential struts and cables will cause significant changes in the number of self-stress modes. The internal force of the structural members decreases with the rise-to-span ratio and the number of circumferential struts increases, and the number of circumferential struts has the greatest influence on its internal force. The structural natural frequency exhibits a dense distribution, which indicates that the structure has good stiffness. In summary, the research has provided an idea for the application of the deployable scissor-type strut cable dome structure as a new structural system in the field of structural engineering.

Multifidelity flutter prediction using regression cokriging with adaptive sampling

This work presents a flutter prediction approach that uses regression cokriging metamodels of generalized aerodynamic influence coefficients with adaptive sampling based on propagated model uncertainty along the flutter boundary. The use of regression cokriging models is compared to cokriging and regression cokriging with reinterpolation, as well as their single-fidelity counterparts. Comparisons to direct quantity-of-interest-based metamodeling are also shown. Several infill criteria based on the propagated flutter speed uncertainty are demonstrated on common flutter test cases. The value of adaptive sampling, multiple fidelity levels, and metamodeling of intermediate quantities is investigated by quantifying average cost and error metrics for the cases. Scalability with the number of structural modes is also investigated to gauge how the approach might fare for more conventional aircraft. Overall, the main benefits seen in this work stem from modeling intermediate quantities, with direct modeling costing six to eight times as much for multifidelity approaches, and three to five times as much for the single-fidelity comparators. In addition, using multiple fidelities was more accurate and required fewer infill points for convergence, leading to a cost savings of roughly 25% to 70%, depending on the case.

A comparative study of nonlinear aeroelastic models for high aspect ratio wings

Linear and nonlinear aeroelastic analyses and results for a cantilevered beam subjected to an unsteady subsonic airflow are presented as a model of a high aspect ratio wing. A third-order nonlinear beam model is used as the structural model. This model includes nonlinear inertial and damping terms as well as nonlinear stiffness terms. To model aerodynamic loads a Wagner model based on a state-space model along with 2D and 3D Peters’ aerodynamic models are used and the results are compared. The Galerkin method is used to transform partial differential equations to ordinary differential equations. For aeroelastic analysis of a high aspect ratio wing, using a state-space Wagner model reduces the number of degrees of freedom. The distribution of the lift and inflow derived using 2D and 3D Peters aerodynamic models are compared and the range of aspect ratios has been determined for which a 2D aerodynamic model is sufficient. There is a good agreement between the flutter speed obtained in this study and those reported in the literature. Beside nonlinear stiffness terms, the effects of nonlinear inertial and damping terms may be significant for flow velocities above the flutter speed. As the flow velocity increases further the oscillations lose their periodicity and become chaotic. Using the different number of structural modes, the convergence of the results is shown.

Nonlinear structure-extended cavity interaction simulation using a new version of harmonic balance method

This study addresses the nonlinear structure-extended cavity interaction simulation using a new version of the multilevel residue harmonic balance method. This method has only been adopted once to solve a nonlinear beam problem. This is the first study to use this method to solve a nonlinear structural acoustic problem. This study has two focuses: 1) the new version of the multilevel residue harmonic balance method can generate the higher-level nonlinear solutions ignored in the previous version and 2) the effect of the extended cavity, which has not been considered in previous studies, is examined. The cavity length of a panel-cavity system is sometimes longer than the panel length. However, many studies have adopted a model in which the cavity length is equal to the panel length. The effects of excitation magnitude, cavity depth, damping and number of structural modes on sound and vibration responses are investigated for various panel cases. In the simulations, the present harmonic balance solutions agree reasonably well with those obtained from the classical harmonic balance method. There are two important findings. First, the nonlinearity of a structural acoustic system highly depends on the cavity size. If the cavity size is smaller, the nonlinearity is higher. A large cavity volume implies a low stiffness or small acoustic pressure transmitted from the source panel to the nonlinear panel. In other words, the additional volume in an extended cavity affects the nonlinearity, sound and vibration responses of a structural acoustic system. Second, if an acoustic resonance couples with a structural resonance, nonlinearity is amplified and thus the insertion loss is adversely affected.

Improved Stochastic Subspace System Identification for Structural Health Monitoring

Structural health monitoring acquires structural information through numerous sensor measurements. Vibrational measurement data render the dynamic characteristics of structures to be extracted, in particular of the modal properties such as natural frequencies, damping, and mode shapes. The stochastic subspace system identification has been recognized as a power tool which can present a structure in the modal coordinates. To obtain qualitative identified data, this tool needs to spend computational expense on a large set of measurements. In study, a stochastic system identification framework is proposed to improve the efficiency and quality of the conventional stochastic subspace system identification. This framework includes 1) measured signal processing, 2) efficient space projection, 3) system order selection, and 4) modal property derivation. The measured signal processing employs the singular spectrum analysis algorithm to lower the noise components as well as to present a data set in a reduced dimension. The subspace is subsequently derived from the data set presented in a delayed coordinate. With the proposed order selection criteria, the number of structural modes is determined, resulting in the modal properties. This system identification framework is applied to a real-world bridge for exploring the feasibility in real-time applications. The results show that this improved system identification method significantly decreases computational time, while qualitative modal parameters are still attained.

How Many Vibration Response Sensors for Damage Detection & Localization on a Structural Topology? An Experimental Exploratory Study

The number of vibration response sensors required for structural damage detection andprecise localization on a continuous structural topology is investigated. For damage detection thestate–of–the–art of vibration based methods need a required number of sensors q that may be “low”compared to the number of structural modes m, that is q << m. Yet, the opposite is generally suggestedfor precise damage localization, that is q > m. In this study the hypothesis that a “low” numberof vibration response sensors, q << m, may, under certain conditions, suffice for precise damage localization,is postulated. This hypothesis is “proven” experimentally by demonstrating that preciselocalization is indeed possible using a single vibration response sensor and an advanced StructuralHealth Monitoring methodology on a laboratory 3D truss structure.

Orthogonal contributor number for the measurement of sound power

Orthogonal contributors to a global error represent a very efficient design method in terms of both sensing and control of noise radiation. In practice the price of a sensing system will be determined by the number of errors it must resolve. Therefore predicting the most efficient way of measuring radiation power is an important problem. Recently work has compared sensing the number of vibration modes to the number of orthogonal contributors to radiated power. The required number of vibration modes was based on the proximity of the structural mode resonance frequency and the excitation frequency. While ultimately this technique will result in a valid estimate of radiated power, it is shown here that the number of structural modes can be minimized by first considering orthogonal radiators based on structural mode amplitudes. Two disturbance cases are considered: a point force and an even disturbance coupling to each structural mode. Also, under these conditions the practicality of estimating the number of orthogonal radiators when it is assumed that each contributor is equal in amplitude is examined. Finally in an attempt to optimism the number of signals to be sensed, a variable error margin for the estimate of power, based on the ratio of the sound power at each frequency to the maximum peak in the considered frequency range is proposed and analyzed.

Mathematical Model for Design of Mass Dampers for Wind Excited Structures

A state space linear mathematical model oriented to the design of passive and active mass dampers for tall buildings and bridges subjected to the wind action is presented in this paper. The model accounts for an arbitrary number of passive and/or active damping devices positioned at arbitrary points of the structure, as well as for an arbitrary number of structural modes of vibration. The aerodynamic terms of the stiffness and damping matrices are considered following a linearized quasisteady approach. A general discussion on the application of \iH\d2/H\d∞ control techniques to the synthesis of the active mass dampers control law is carried out. For the tuning of the mechanical parameters of passive devices, the problem is reformulated in terms of a decentralized static output feedback control law design problem.

Point mobility techniques for the in situ estimation of modal densities of coupled cylindrical shells

This paper discusses the utilization of the experimentally measured value of the point mobility (transfer function of velocity on force at the excitation point) to estimate the modal density (number of structural modes per unit frequency) of cylindrical piping systems. The technique allows for a rapid in situ estimate of the modal density, has applications in statistical energy analysis and is especially suited at frequencies below the ring frequency where theoretical estimates do not account for the grouping of structural modes that occurs. Provided that feedback due to exciter-structure interaction is minimized, experimental results suggest that the conventional two-channel technique, using a dual-channel signal analyzer, gives reliable results. The three-channel technique, as discussed by Brown 7, serves as an important test to establish the presence, or otherwise, of any feedback in a proposed experimental set-up.