Sensor set expansion for modal vibration testing

A comparison is made of the two different types of vibration testing: modal and environmental. Their application to the determination of the flight-safety characteristics of a flight vehicle is discussed. A brief history is included of the development of the equipment and techniques for modal or resonance vibration testing, which is so important before first flight. An example is given of a modal vibration test on an unusually complex aircraft structure, the Lockheed WV-2E, that shows the problems of separation of modes closely spaced in frequency and the difficulties in obtaining all of the modes, clean. The significance of mode shapes, location of mode lines, and mode-frequency ratios are discussed as to how they affect dynamic responses and flutter susceptibilities.

House of natural resources – modal vibration tests and long-term monitoring

Structural Health Monitoring relies on accurate modal identification and effective damage detection to assess structural performance and safety. However, traditional sensor placement methods struggle to balance modal identification uncertainty, which arises from limited sensor coverage and measurement noise and damage detection sensitivity, which requires sensors to be optimally positioned to capture structural stiffness variations. To address this challenge, this study proposes a multi-objective sensor placement optimization method based on the Non-Dominated Sorting Genetic Algorithm. The method introduces two key objective functions: minimizing modal identification uncertainty by leveraging Bayesian modal identification theory and information entropy and maximizing damage detection sensitivity by incorporating an entropy-based measure to quantify the uncertainty in stiffness variation estimation. By formulating the problem as Pareto-based multi-objective optimization, the method efficiently explores a trade-off between the two competing objectives and provides a diverse set of optimal sensor placement solutions. The proposed approach is validated through numerical experiments on a simply supported beam and a benchmark bridge structure, demonstrating that different optimization objectives lead to distinct sensor placement patterns. The results show that solutions prioritizing modal identification distribute sensors across the structure to improve global response estimation, while solutions favoring damage detection concentrate sensors in critical areas to enhance sensitivity. The proposed method significantly improves sensor placement strategies by offering a systematic and flexible framework for SHM applications, enabling engineers to tailor monitoring strategies based on specific structural assessment needs.

Operational modal analysis of a high-rise multi-function building with dampers by a Bayesian approach

The mechanical design of wind turbines requires a profound understanding of the dynamic behaviour. Even though highly detailed simulation models are already in use to support wind turbine design, modal testing on a real prototype is irreplaceable to identify site-specific conditions such as the stiffness of the tower foundation. Correct identification of the mode shapes of a complex mechanical structure much depends on the placement of the sensors. For operational modal analysis of a 3 MW wind turbine with a 120 m rotor on a 100 m tower developed by W2E Wind to Energy, algorithms for optimal placement of acceleration sensors are applied. The mode shapes used for the optimisation are calculated by means of a detailed flexible multibody model of the wind turbine. Among the three algorithms in this study, the genetic algorithm with weighted off-diagonal criterion yields the sensor configuration with the highest quality. The ongoing measurements on the prototype will be the basis for the development of optimised wind turbine designs.

In this study, an aeroelastic smart structure exhibiting regular vibrations induced by vortex shedding was developed. Two types of beam elements—straight and auxetic—were fabricated using additive manufacturing techniques. The structure incorporates beam elements along with a flow-disturbing geometry designed to induce galloping behavior. The damping and stiffness properties of the fabricated beams were determined experimentally. Additionally, the natural frequencies of the structure were identified through free, forced, and modal vibration tests and validated by comparing the results with numerical simulations. Piezoelectric actuators made from the same material were bonded to both beam types and used to suppress vibrations through a feedback control loop. Displacement feedback for the control system was provided by a laser displacement sensor measuring the vibrations of the aeroelastic structure. To induce continuous vibrations, an external aerodynamic load was applied using a centrifugal fan. A proportional–integral–derivative controller was then designed and implemented to control the vibrations. Vibration control experiments were conducted for both beam types, with and without control activated. Displacement of the beams and the control voltages applied to the actuators were recorded as functions of time. When examining the control experiment results, the control effort used to suppress the vibrations of the straight beam is higher compared to the auxetic beam. This is consistent with the results obtained from the mechanical properties, free vibration responses, damping factor, and natural frequency values derived from the experiments. The experimental results highlight the influence of varying beam stiffness on the effectiveness of vibration control.

Novel practical acoustic metamaterial sheets with hollow local resonators that can be processed with simple integral molding have been developed. This acoustic metamaterial is a variant of the acoustic metamaterial sheet reported by our group in 2021, which consists of two-dimensionally connected non-hollow-shaped stubs embedded with metal weights. Each hollow-shaped stub can work as a local resonator using the vibration mode of a circular membrane. This acoustic metamaterial can handle lower frequencies even with smaller and lighter stubs compared to those with the non-hollow-shaped stubs we previously reported. It has a particular advantage when used for objects with limited space and weight. It is also possible to control the resonant frequency by altering the material properties or adjusting the shape and size of the stub. It has been experimentally shown that significant sound insulation performance exceeding the mass law can be obtained around the resonant frequencies of the hollow stubs. We show the results of finite element method simulations, modal vibration testing, and transmission loss measurements.

Sensor placement for modal identification

Performing forced vibration tests on full-scale structures is the most reliable way of determining the relevant modal parameters in structural dynamics, such as modal frequencies, mode shapes, modal damping, and modal masses. This study describes the modal identification of a double-level curved cable-stayed bridge with separate deck systems for pedestrians and vehicles via forced vibration tests. The steady-state structural responses to sinusoidal excitations produced by an electrodynamic shaker are recorded under varying excitation frequencies, and the frequency response functions are established. The measured frequency response functions are curve fitted to estimate the modal parameters. The numerical simulation of frequency response function–based modal parameter identification of an elastically multi-supported continuous beam structure is carried out, and the emphasis has been placed on the evaluation of the effect of an additional shaker mass, excitation frequency step and range, multi-mode vibration, and noise on identification results. Finally, the modal parameters for the first lateral mode of a double-level curved cable-stayed bridge are identified by forced vibration experiments, and the results are compared with those from ambient vibration tests and free vibration tests. The effect of the unmeasured wind excitation on identification is discussed. It is shown that the effect of ambient vibration is minor for wind velocity of 3–5 m/s. The damping ratios identified by forced and free vibration tests are comparable, while those from ambient vibration are subject to large variations. The modal mass obtained from forced vibration tests is in good agreement with finite element prediction, which provides design basis for mass-type dampers.

This paper addresses the problem of how to select the optimal number of sensors and how to determine their placement in a given monitored area for multimedia surveillance systems. We propose to solve this problem by obtaining a novel performance metric in terms of a probability measure for accomplishing the task as a function of set of sensors and their placement. This measure is then used to find the optimal set. The same measure can be used to analyze the degradation in system 's performance with respect to the failure of various sensors. We also build a surveillance system using the optimal set of sensors obtained based on the proposed design methodology. Experimental results show the effectiveness of the proposed design methodology in selecting the optimal set of sensors and their placement.

Accurate localization is a critical task in underwater navigation. Typical localization methods use a set of acoustic sensors and beacons to estimate relative position, whose geometric configuration has a significant impact on the localization accuracy. Although there is much effort in the literature to define optimal 2D or 3D sensor placement, the optimal sensor placement in irregular and constrained 3D surfaces, such as autonomous underwater vehicles (AUVs) or other structures, is not exploited for improving localization. Additionally, most applications using AUVs employ commercial acoustic modems or compact arrays, therefore the optimization of the placement of spatially independent sensors is not a considered issue. This article tackles acoustic sensor placement optimization in irregular and constrained 3D surfaces, for inverted ultra-short baseline (USBL) approaches, to improve localization accuracy. The implemented multi-objective memetic algorithm combines an evaluation of the geometric sensor's configuration, using the Cramer-Rao Lower Bound (CRLB), with the incidence angle of the received signal. A case study is presented over a simulated homing and docking scenario to demonstrate the proposed optimization algorithm.

Process monitoring and fault diagnosis are of great importance for operation safety and efficiency of complex industrial plants. The present article proposes a novel methodology to address the sensor location problem for fault detection. Firstly, all the process situations are identified based on a fuzzy learning algorithm using measurements generated from the whole available set of sensors. Then, a fuzzy feature selection approach is used to select the optimal number of sensors that characterize accurately the set of process situations (abnormal and normal). This method optimizes the performance of the learning algorithm within a membership margin framework, and thereby, it is capable to address correlation and redundancy issues. A behavioral pattern of the process is constructed with the selected sensors and is used to associate new online observations to previously characterized process situations. The proposed strategy has been applied for fault diagnosis to a pharmaceutical synthesis carried out in a new intensified heat-exchanger reactor.

Sensitivity of inverse advection–diffusion–reaction to sensor and control: A low computational cost tool

A comprehensive modal survey test based on multi-input multi-output experimental modal analysis techniques was conducted on the CASSIOPE spacecraft. This paper describes the details of the methodology used to perform the successful experimental modal test to efficiently extract the critical modes of the spacecraft. Results from the modal test have been used to validate the analytical finite element model and to provide confidence in the structural integrity of the spacecraft design. The test was performed on the flight model of the CASSIOPE spacecraft in the final stages of integration, which included all of the payload and bus instruments and electronics boxes. The multiple-input excitation for the spacecraft was generated using two portable electrodynamic modal shakers installed on the top and bottom of the spacecraft to distribute the excitation energy and the response was measured using 81 miniature accelerometers. A digital multi-channel data acquisition system was used to record the time domain data and calculate the frequency domain spectra. Advanced modal analysis software was used to extract modal parameters from the measured data and critical modes were compared with predictions from the finite element model. Most modes identified through the experimental data compared favorably with the predictions. Nevertheless, some differences were large enough to require iterative update of the finite elelement model. The structural dynamics information from the updated finite element model was used to plan the mechanical vibration qualification test and predict the response of the spacecraft to the launch vehicle environmental loads through coupled loads analysis.

ISSN:1070-9932