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Recent Advances in Sensing Techniques, Structural Dynamics and Control

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (31 December 2019) | Viewed by 54074

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Special Issue Editors

Prof. Dr. Yun Lai Zhou

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Guest Editor

State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Interests: structural health monitoring; damage identification; bridge optimization; model updating; fracture mechanics
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Linya Liu

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Engineering Research Center of Railway Environment Vibration and Noise, Ministry of Education, East China Jiaotong University, Nanchang, China
Interests: static and dynamic structural analysis; vibration mitigation; noise control; rail system components, including floating track slabs
Special Issues, Collections and Topics in MDPI journals

Dr. Francisco Javier Cara Cañas

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Laboratory of Statistics, ETS Ingenieros Industriales, Universidad Politécnica de Madrid, Spain
Interests: analysis of modal operations; EM algorithms
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Structural dynamics and control serve as hotspots for both research and engineering fields including mechanical engineering, civil engineering, and aerospace engineering, since they can manipulate and optimize structural dynamics characteristics, which extends the service lifecycle. Various structures such as vehicles, bridges, and tall buildings have made our daily lives more convenient, while the dynamic control for such structures requires attention and effort. System identification; model updating; and dampers such as the tuned mass damper (TMD), the active mass damper (AMD), and so on have undergone prosperous developments with the advances of sensing techniques such as accurate fiber brag grating (FBG) sensors for large scale structures. The structural dynamics and control of long-span bridges, large infrastructures, and so on still require more studies and new findings in both theory and engineering applications.

This Special Issue aims to explore the advances in structural dynamics and control via the advanced sensing techniques, especially those for real engineering applications such as vibration mitigation in bridges. This certainly includes studies from multidisciplinary fields, and therefore studies related to advances in sensing techniques, structural dynamics, and control from distinct fields such as aerospace engineering, civil engineering, mechanical engineering, and so on are all welcomed.

This Special Issue seeks to publish high-quality investigations regarding advances in sensing techniques, structural dynamics, and control, as well as summaries recalling the latest developments. Original, high-quality contributions that have not been publishing anywhere else are the target of this Special Issue.

Potential topics include but are not limited to the following:

Advanced sensing systems;
Embedded sensing system;
Long-term condition monitoring;
Machine learning in data processing;
Big data processing and management;
Structural vibration control;
Vibration mitigation;
System identification;
Model updating;
Flexible structural dynamics control;
Tuned mass damper (TMD), active mass damper (AMD), magneto-rheological (MR) damper;
Advances in numerical methods.

Dr. Yun Lai Zhou
Prof. Linya Liu
Dr. Francisco Javier Cara Cañas
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Keywords

sensing technique
data processing
structural dynamics
structural dynamic control
vibration mitigation
machine learning

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Published Papers (14 papers)

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22 pages, 8310 KiB

Open AccessArticle

A Rail Fastener Tightness Detection Approach Using Multi-source Visual Sensor

by Qiang Han, Shengchun Wang, Yue Fang, Le Wang, Xinyu Du, Hailang Li, QiXin He and Qibo Feng

Sensors 2020, 20(5), 1367; https://doi.org/10.3390/s20051367 - 2 Mar 2020

Cited by 30 | Viewed by 4907

Abstract

At present, the method of two-dimensional image recognition is mainly used to detect the abnormal fastener in the rail-track inspection system. However, the too-tight-or-too-loose fastener condition may cause the clip of the fastener to break or loose due to the high frequency vibration shock, which is difficult to detect from the two-dimensional image. In this practical application background, 3D visual detection technology provides a feasible solution. In this paper, we propose a fundamental multi-source visual data detection method, as well as an accurate and robust fastener location and nut or bolt segmentation algorithm. By combining two-dimensional intensity information and three-dimensional depth information generated by the projection of line structural light, the locating of nut or bolt position and accurate perception of height information can be realized in the dynamic running environment of railway. The experimental results show that the static measurement accuracy in the vertical direction using the structural light vision sensor is 0.1 mm under the laboratory condition, and the dynamic measurement accuracy is 0.5 mm under the dynamic train running environment. We use dynamic template matching algorithm to locate fasteners from 2D intensity map, which achieves 99.4% accuracy, then use the watershed algorithm to segment the nut and bolt from the corresponding depth image of located fastener. Finally, the 3D shape of the nut and bolt is analyzed to determine whether the nut or bolt height meets the local statistical threshold requirements, so as to detect the hidden danger of railway transportation caused by too loose or too tight fasteners. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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19 pages, 6757 KiB

Open AccessArticle

Identification of Temperature-Induced Deformation for HSR Slab Track Using Track Geometry Measurement Data

by Zai-Wei Li, Xiao-Zhou Liu and Yue-Lei He

Sensors 2019, 19(24), 5446; https://doi.org/10.3390/s19245446 - 10 Dec 2019

Cited by 25 | Viewed by 3409

Abstract

Slab track is widely used in many newly built high-speed rail (HSR) lines as it offers many advantages over ballasted tracks. However, in actual operation, slab tracks are subjected to operational and environmental factors, and structural damages are frequently reported. One of the most critical problems is temperature-induced slab-warping deformation (SWD) which can jeopardize the safety of train operation. This paper proposes an automatic slab deformation detection method in light of the track geometry measurement data, which are collected by high-speed track geometry car (HSTGC). The characteristic of track vertical irregularity is first analyzed in both time and frequency domain, and the feature of slab-warping phenomenon is observed. To quantify the severity of SWD, a slab-warping index (SWI) is established based on warping-sensitive feature extraction using discrete wavelet transform (DWT). The performance of the proposed algorithm is verified against visual inspection recorded on four sections of China HSR line, which are constructed with the China Railway Track System II (CRTSII) slab track. The results show that among the 24,806 slabs being assessed, over 94% of the slabs with warping deformation can be successfully identified by the proposed detection method. This study is expected to provide guidance for efficiently detecting and locating slab track defects, taking advantage of the massive track inspection data. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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20 pages, 4599 KiB

Open AccessArticle

Structural Damage Diagnosis-Oriented Impulse Response Function Estimation under Seismic Excitations

by Jian-Fu Lin, Junfang Wang, Li-Xin Wang and Siu-seong Law

Sensors 2019, 19(24), 5413; https://doi.org/10.3390/s19245413 - 9 Dec 2019

Cited by 11 | Viewed by 3610

Abstract

Impulse response function (IRF) is an ideal structural damage index for the identification of structural damage associated with changes in modal properties. However, IRFs from multiple excitations applied at different degrees-of-freedoms jointly contribute to the dynamic response, and their estimation is often underdetermined. Although some efforts have been devoted to the estimation of IRF for a structure under single excitation, the case under multiple excitations has not been fully investigated yet. The estimation of IRF under multiple excitations is generally an ill-conditioned inverse problem such that an incorrect or non-feasible solution is common, preventing its application to damage detection. This work explores this problem by introducing dimensionality reduction transformation matrices relating two sets of IRFs of a structure with discussions on the performance of the non-unique transformation matrices. Then, the extraction of IRF via wavelet-based and Tikhonov regularization-based methods are compared. Finally, a numerical study with a truss structure is conducted to validate the estimation of the IRFs and to demonstrate their applicability for damage detection under seismic excitations. Both the damage locations and severity are accurately identified, indicating the proposed methodology can enable the IRFs estimation under multiple excitations for successful damage detection. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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17 pages, 3660 KiB

Open AccessArticle

Grouting Quality Evaluation in Post-Tensioning Tendon Ducts Using Wavelet Packet Transform and Bayes Classifier

by Xiang-Tao Sun, Dan Li, Wen-Yu He, Zuo-Cai Wang and Wei-Xin Ren

Sensors 2019, 19(24), 5372; https://doi.org/10.3390/s19245372 - 5 Dec 2019

Cited by 8 | Viewed by 3348

Abstract

The grouting quality of tendon ducts is very important for post-tensioning technology in order to protect the prestressing reinforcement from environmental corrosion and to make a smooth stress distribution. Unfortunately, various grouting defects occur in practice, and there is no efficient method to evaluate grouting compactness yet. In this study, a method based on wavelet packet transform (WPT) and Bayes classifier was proposed to evaluate grouting conditions using stress waves generated and received by piezoelectric transducers. Six typical grouting conditions with both partial grouting and cavity defects of different dimensions were experimentally investigated. The WPT was applied to explore the energy of received stress waves at multi-scales. After that, the Bayes classifier was employed to identify the grouting conditions, by taking the traditionally used total energy and the proposed energy vector of WPT components as input, respectively. The experimental results demonstrated that the Bayes classifier input with the energy vector could identify different grouting conditions more accurately. The proposed method has the potential to be applied at key spots of post-tensioning tendon ducts in practice. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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15 pages, 7597 KiB

Open AccessArticle

A SAFT Method for the Detection of Void Defect inside a Ballastless Track Structure Using Ultrasonic Array Sensors

by Wen-Fa Zhu, Xing-Jie Chen, Zai-Wei Li, Xiang-Zhen Meng, Guo-Peng Fan, Wei Shao and Hai-Yan Zhang

Sensors 2019, 19(21), 4677; https://doi.org/10.3390/s19214677 - 28 Oct 2019

Cited by 35 | Viewed by 4784

Abstract

High-precision ultrasound imaging of void defects is critical for the performance and safety assessment of ballastless track structures. The sound propagation velocity of each layer in the ballastless track structure is quite different. However, the traditional concrete Synthetic Aperture Focusing Technique (SAFT) ultrasound imaging method is based on the assumption that the concrete has a single constant shear wave velocity. Thus, it is not a suitable method for the ultrasonic imaging of multilayer structures. In this paper, a Multilayer SAFT high-precision ultrasound imaging method is proposed. It is based on the ray-tracing technique and uses the Fermat principle to find the refraction point that minimizes the delay of the acoustic wave propagation path at the interface of the discrete layers. Then, the acoustic wave propagation path is segmented by the position of the refraction point, and the propagation delay of the ultrasonic wave is obtained segment by segment. Thus, the propagation delay of the ultrasonic wave is obtained one by one, so that the propagation delay of the ultrasonic wave in the multilayer structure can be accurately obtained. Finally, the focused image is obtained according to the SAFT imaging algorithm. The finite element simulation and experimental results show that the Multilayer SAFT imaging method can accurately track the propagation path of the ultrasonic wave in ballastless track structures, as well as accurately calculate the propagation delay of the ultrasonic wave and the lengths of void defects. The high accuracy of the Multilayer SAFT imaging represents a significant improvement compared to traditional SAFT imaging. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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23 pages, 12738 KiB

Open AccessArticle

Mono-Component Feature Extraction for Condition Assessment in Civil Structures Using Empirical Wavelet Transform

by Yun-Xia Xia and Yun-Lai Zhou

Sensors 2019, 19(19), 4280; https://doi.org/10.3390/s19194280 - 2 Oct 2019

Cited by 10 | Viewed by 3164

Abstract

This paper proposes a methodology to process and interpret the complex signals acquired from the health monitoring of civil structures via scale-space empirical wavelet transform (EWT). The FREEVIB method, a widely used instantaneous modal parameters identification method, determines the structural characteristics from the individual components separated by EWT first. The scale-space EWT turns the detecting of the frequency boundaries into the scale-space representation of the Fourier spectrum. As well, to find meaningful modes becomes a clustering problem on the length of minima scale-space curves. The Otsu’s algorithm is employed to determine the threshold for the clustering analysis. To retain the time-varying features, the EWT-extracted mono-components are analyzed by the FREEVIB method to obtain the instantaneous modal parameters and the linearity characteristics of the structures. Both simulated and real SHM signals from civil structures are used to validate the effectiveness of the present method. The results demonstrate that the proposed methodology is capable of separating the signal components, even those closely spaced ones in frequency domain, with high accuracy, and extracting the structural features reliably. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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18 pages, 9788 KiB

Open AccessArticle

Multidimensional Vibration Suppression Method with Piezoelectric Control for Wind Tunnel Models

by Mengde Zhou, Wei Liu, Linlin Tang, Zhuang Yao, Zhengquan Wen, Bing Liang and Zhenyuan Jia

Sensors 2019, 19(18), 3998; https://doi.org/10.3390/s19183998 - 16 Sep 2019

Cited by 11 | Viewed by 3293

Abstract

In wind tunnel tests, the low-frequency and large-amplitude vibration of the cantilever sting result in poor test data in pitch plane and yaw plane, more seriously, even threatens the safety of wind tunnel tests. To ensure the test data quality, a multidimensional vibration suppression method is proposed to withstand the vibration from any direction, which is based on a system with stackable piezoelectric actuators and velocity feedback employing accelerometers. Firstly, the motion equation of the cantilever sting system is obtained by Hamilton’s principle with the assumed mode method. Then, the multidimensional active control mechanism is qualitatively analyzed and a negative velocity feedback control algorithm combined with a root mean square (RMS) evaluation method is introduced to realize active mass and active damping effect, meanwhile, a weight modification method is performed to determine the sequence number of the stacked piezoelectric actuators and the weight of control voltages in real time. Finally, a multidimensional vibration suppression system was established and verification experiments were carried out in lab and a transonic wind tunnel. The results of lab experiments indicate that the damping ratio of the system is improved more than 4.3 times and the spectrum analyses show reductions of more than 23 dB. In addition, wind tunnel test results have shown that for the working conditions (α = −4~10° with γ = 0° or α = −4~10° with γ = 45°) respectively at 0.6 Ma and 0.7 Ma, the remainder vibration is less than 1.53 g, which proves that the multidimensional vibration suppression method has the ability to resist vibration from any direction to ensure the smooth process of wind tunnel tests. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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20 pages, 7150 KiB

Open AccessArticle

Experimental and Numerical Investigation on the Ultimate Vertical Bearing Capacity of U-Shaped Girder with Damaged Web

by Jingfeng Zhang, Yuan Jing, Pandao Li, Wanshui Han, Nan Zhang and Yunlai Zhou

Sensors 2019, 19(17), 3735; https://doi.org/10.3390/s19173735 - 29 Aug 2019

Cited by 10 | Viewed by 3620

Abstract

U-shaped girder has been extensively used for its excellent adaptability in the urban railway transit system. As an open thin-walled structure, significant difference of working mechanism exists between U-shaped girder and conventional section girder (e.g., T section or box section). The thin-walled web plays significant role in the flexural performance of U type girder particularly. Moreover, severe collision may occur between the moving train and the girder, and subsequently results in the decrease of the structural bearing capacity. In this paper, a full-scale test was carried out to examine the ultimate bearing capacity and the failure mechanism of the U-shaped girder, and a refined numerical model was developed to simulate the damage evolution and the failure process. It was shown that the flexural failure occurred on the U-shaped girder under vertical loads. In addition, the ultimate bearing capacity of the structure under different web damage conditions (e.g., web damaged region or damaged range) was studied by applying the displacement based lateral load on the flange of the U-shaped girder to simulate the damage caused by accidental train collision. The numerical results have shown that the damaged web greatly affects the ultimate bearing capacity of U-shaped girder, more severe bearing capacity descending occurs around the middle span rather than the beam ends. The damaged range (length) of the web has less influence on the falling amplitude of bearing capacity. It can be concluded that the major reason accounting for the bearing capacity decrease is that the original section is weakened by the web damage, and consequently results in the buckling of the damaged web and lead to the total failure of the structure. It is recommended that the lateral resistant design for the web should be taken into consideration to ensure the operation safety of the urban railway transportation. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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22 pages, 7885 KiB

Open AccessArticle

Piezoelectric Shunt Stiffness in Rhombic Piezoelectric Stack Transducer with Hybrid Negative-Impedance Shunts: Theoretical Modeling and Stability Analysis

by Leiying He, Wenguang Zheng, Chenxue Zhao and Chuanyu Wu

Sensors 2019, 19(15), 3387; https://doi.org/10.3390/s19153387 - 1 Aug 2019

Cited by 4 | Viewed by 3174

Abstract

Negative-capacitance shunted piezoelectric polymer was investigated in depth due to its considerable damping effect. This paper discusses the novel controlled stiffness performance from a rhombic piezoelectric stack transducer with three hybrid negative-impedance shunts, namely, negative capacitance in series with resistance, negative capacitance in parallel with resistance, and negative inductance/negative capacitance (NINC) in series with resistance. An analytical framework for establishing the model of the coupled system is presented. Piezoelectric shunt stiffness (PSS) and piezoelectric shunt damping (PSD) are proposed to analyze the stiffness and damping performances of the hybrid shunts. Theoretical analysis proves that the PSS can produce both positive and negative stiffness by changing the negative capacitance and adjustable resistance. The Routh–Hurwitz criterion and the root locus method are utilized to judge the stability of the three hybrid shunts. The results point out that the negative capacitance should be selected carefully to sustain the stability and to achieve the negative stiffness effect of the transducer. Furthermore, negative capacitance in parallel with resistance has a considerably better stiffness bandwidth and damping performance than the other two shunts. This study demonstrates a novel electrically controlled stiffness method for vibration control engineering. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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14 pages, 6967 KiB

Open AccessArticle

Structural Health Monitoring of Underground Structures in Reclamation Area Using Fiber Bragg Grating Sensors

by Zhen Liu, Pengzhen Liu, Cuiying Zhou, Yuncong Huang and Lihai Zhang

Sensors 2019, 19(13), 2849; https://doi.org/10.3390/s19132849 - 27 Jun 2019

Cited by 20 | Viewed by 3309

Abstract

The long-term structural performance of underground structures in reclamation areas is very sensitive to the vibrations caused by vehicles passing above the structures and environmental factors (e.g., tide levels, rainfall and temperature). In the present study, an integrated remote real-time structural health monitoring system using fiber Bragg grating sensors was developed to assess the structural performance of underground structures. Using a composite road box-type structure project in a reclamation area in Southern China as a case study, the developed real-time system was implemented to investigate the effects of changes in tide levels, rainfall, temperature and vehicle induced vibrations on crack propagation in the structure. The results show that the change in tide levels has little influence on the change in crack width in the structure, whereas variations in temperature could significantly influence the crack width with an average Pearson correlation of around 0.8. In addition, the crack width generally decreases with an increase in rainfall. Furthermore, a relatively low frequency (<25 Hz) induced by the traffic could result in a relatively larger crack width. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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23 pages, 7297 KiB

Open AccessArticle

Experimental Study on Damage Detection in ECC-Concrete Composite Beams Using Piezoelectric Transducers

by Fengjiang Qin, Zhigang Zhang, Bo Xie and Rui Sun

Sensors 2019, 19(12), 2799; https://doi.org/10.3390/s19122799 - 22 Jun 2019

Cited by 8 | Viewed by 3353

Abstract

The use of engineered cementitious composite (ECC) has attracted extensive attention in recent years because of the highly enhanced ductility owing to its unique strain-hardening behavior. In this paper, an electromechanical impedance-based technique is used to monitor the structural damage of RC beams strengthened with an ECC layer at the tensile zone. To achieve this purpose, three specimens are tested under bending loads to evaluate the proposed damage detection methodology. Five externally bonded PZT transducers are uniformly distributed at the surface of the ECC layer of the beams to measure the output conductance signatures in a healthy state and in different damage scenarios induced by different load levels. Test results showed that discrepancies exist between the signals measured in the intact state and each damage state, which can be used to evaluate the structural integrity changes. To assess the damage of ECC-concrete composite beams quantitatively, the statistical scalar index-root mean square deviation (RMSD) is used as the index, which can be calculated from the variations of conductance measurements of PZT sensors. The damage index values of the uniformly distributed PZT sensors provided cogent evidence of damage and revealed the evolution of structural damage. The crack patterns of beams at different damage levels are compared with the damage index values, and it shows the damage location can be derived from the measured conductance signatures of an array of PZT transducers. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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23 pages, 6861 KiB

Open AccessArticle

Hybrid Data Fusion DBN for Intelligent Fault Diagnosis of Vehicle Reducers

by Tianfan Zhang, Zhe Li, Zhenghong Deng and Bin Hu

Sensors 2019, 19(11), 2504; https://doi.org/10.3390/s19112504 - 31 May 2019

Cited by 25 | Viewed by 4436

Abstract

Given its importance, fault diagnosis has attracted considerable attention in the literature, and several machine learning methods have been proposed to discover the characteristics of different aspects in fault diagnosis. In this paper, we propose a Hybrid Deep Belief Network (HDBN) learning model that integrates data in different ways for intelligent fault diagnosis in motor drive systems, such as a vehicle drive system. In particular, we propose three data fusion methods: data union, data join, and data hybrid, based on detailed data fusion research. Additionally, the significance of the fusion is explained from the energy perspective of the signal. In particular, the appropriate fusion methods and data structures suitable for model training requirements can help improve the accuracy of fault diagnosis. Moreover, mixed-precision training is used as a special fusion method to further improve the performance of the model. Experiments with the datasets obtained from the simulation platform demonstrate the superiority of our proposed model over the state-of-the-art methods. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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18 pages, 4427 KiB

Open AccessArticle

An Improved Step-Type Liquid Level Sensing System for Bridge Structural Dynamic Deflection Monitoring

by Xijun Ye, Zhuo Sun, Xu Cai and Liu Mei

Sensors 2019, 19(9), 2155; https://doi.org/10.3390/s19092155 - 9 May 2019

Cited by 8 | Viewed by 3127

Abstract

Real-time and accurate monitoring of dynamic deflection is of great significance for health monitoring and condition assessment of bridge structures. This paper proposes an improved step-type liquid level sensing system (LLSS) for dynamic deflection monitoring. Layout of straight-line-type pipeline is replaced by step-type pipeline in this improved deflection monitoring system, which can remove the interference of the inclination angle on the measurement accuracy and is applicable for dynamic deflection monitoring. Fluid dynamics are first analyzed to demonstrate that measurement accuracy is interfered with by the fluid velocity induced by structural vibration, and ANSYS-FLOTRAN is applied for analyzing the influence range caused by the turbulent flow. Finally, a step-type LLSS model is designed and experimented with to verify the influence of the three key parameters (initial displacement excitation, step height, and distance from the measurement point to the elbow) on the measurement accuracy, and the reasonable placement scheme for the measurement point is determined. The results show that the measurement accuracy mainly depends on the turbulent flow caused by step height. The measurement error gets smaller after about 1.0 m distance from the elbow. To ensure that the measurement error is less than 6%, the distance between the measurement point and the elbow should be larger than 1.0 m. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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18 pages, 4398 KiB

Open AccessTechnical Note

Non-Contact Measurement of Blade Vibration in an Axial Compressor

by Radoslaw Przysowa and Peter Russhard

Sensors 2020, 20(1), 68; https://doi.org/10.3390/s20010068 - 21 Dec 2019

Cited by 17 | Viewed by 5740

Abstract

Complex blade responses such as a rotating stall or simultaneous resonances are common in modern engines and their observation can be a challenge even for state-of-the-art tip-timing systems and trained operators. This paper analyses forced vibrations of axial compressor blades, measured during the bench tests of the SO-3 turbojet. In relation to earlier studies conducted in Poland with a small number of sensors, a multichannel tip-timing system let us observe simultaneous responses or higher-order modes. To find possible symptoms of a failure, blade responses in a healthy and unhealthy engine configuration with an inlet blocker were studied. The used analysis methods covered all-blade spectrum and the circumferential fitting of blade deflections to the harmonic oscillator model. The Pearson coefficient of correlation between the measured and predicted tip deflection is calculated to evaluate fitting results. It helps to avoid common operator mistakes and misinterpreting the results. The proposed modal solver can track the vibration frequency and adjust the engine order on the fly. That way, synchronous and asynchronous vibrations are observed and analysed together with an extended variant of least squares. This approach saves a lot of work related to configuring the conventional tip-timing solver. Full article

(This article belongs to the Special Issue Recent Advances in Sensing Techniques, Structural Dynamics and Control)

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