Platform Vibration Research Articles

Performance Optimization of Suppression Method for Platform Vibration Noise based on Vector Hydrophone

Objective: Aiming at the vibration control problem existing in the vector hydrophone under platform vibration and noise excitation, two methods, adaptive noise cancellation algorithm and vibration reduction design, are used to suppress vibration and noise. Methods: A simulation model of vibration and noise signals in the side area of the platform is established first, and the simulation model is simulated by adaptive noise cancellation method. Then noise reduction simulation is carried out by seismic mitigation and isolation method. Finally, the simulation results of the two methods are compared to check the effectiveness of the two noise suppression methods. Results: The results show that adaptive noise cancellation algorithm can effectively cancel the line spectra of platform vibration and noise, and the reduction of continuous spectra is about 10 dB; while the vibration reduction method can reduce the whole vibration and noise of the model, and the vibration and noise interference of the vector hydrophone is reduced by about 15 dB. Conclusion: The obtained results can serve as valuable reference for the performance optimization of suppression methos for vector hydrophones under platform’s vibration and noise excitation.

The Influence of Optical Alignment Error on Compression Coding Superresolution Imaging.

Superresolution (SR) imaging technology based on compression coding has always been considered as the key to break through the geometric resolution of the detector. In addition to factors such as the reconstruction algorithm and mounting platform vibrations, the impact of inherent errors in the optical system itself on the reconstruction results of SR imaging is also obvious. To address this issue, a study on the design of the SR optical system and the influence of optical alignment errors on SR imaging was conducted. The design of the SR optical system based on digital micro-mirror device (DMD) for long-wave infrared wavelength was completed, and an athermal analysis of the system was carried out. The design results showed that the SR optical system has good imaging quality in the operating temperature range. The imaging model of the DMD SR imaging optical system is established according to the designed SR optical system. We investigated the influence of various alignment errors, including decenter, tilt, lens interval error and defocus, on the imaging properties of the SR optical system. Various random combinations of alignment errors were introduced into the optical system, respectively, and the SR reconstructed image quality of the imaging system was analyzed using the inverse sensitivity method to obtain the tolerance limits when the system was assembled. Finally, the effectiveness of the method to obtain the alignment tolerance limit of the compression coding SR imaging optical system was verified through a desktop demonstration experiment.

Mitigating jacket offshore platform vibration under earthquake and ocean waves utilizing tuned inerter damper

The unwanted vibrations of offshore structures induced by wave or earthquake loads can lead to the reduction of the service life and fatigue failure of the offshore platforms. This paper introduces tuned inerter damper (TID) to a jacket offshore platform as passive control device for mitigating the excessive vibrations of platform structure induced by wave and earthquake loads. An analytical design method is proposed for jacket platforms and the influence of installation location on the modal response is investigated. The proposed design method can determine the optimal installation position and obtain the optimal design parameters by transform the original multi-degree of freedom (MDOF) system to a single DOF (SDOF) modal system. Two sets of closed-form solutions of which corresponding to wave and earthquake excitations are derived based on the {mathrm{H}}_{2} optimization criterion. Further, a practical 90 (m) high and 80 (m) deep in-water jacket offshore platform is used in numerical simulation and the wave forces are modeled using Morison’s equation. The case study finds that the optimal installation location of TID is deck level for both wave and earthquake loads. The proposed design method is validated by the numerical example and the results demonstrate that TID system can effectively mitigate the maximum, minimum, and RMS responses of jacket platforms. Besides, the TID is more effective when the jacket platform is under the action of waves and the tuning of TID according to earthquake load is more reliable when the jacket platform subjected to both wave and seismic loads.

Modeling and analysis of light detection and ranging point cloud error in vibration state of airborne platform

Airborne light detection and ranging (LiDAR) is frequently influenced by multiple positioning errors when converting laser echo signals into three-dimensional geospatial data. We focus on the error factor of airborne platform vibration, and analysis of the influence of platform instability on the output point cloud data by simulation, so as to correct it in the subsequent work. First, the influence of LiDAR attitude change on the formation of point cloud was analyzed from the airborne LiDAR geo-location equation. Then, the fluid characteristics of airborne platform in hovering state were obtained by simulation, and the vibration transfer relationship between airborne platform and LiDAR and the vibration model of LiDAR system were obtained based on the dynamic model, which was built on the flexible connection between airborne platform and LiDAR. Finally, we coupled the above vibration model with the airborne LiDAR geo-location equation and conducted a simulation to evaluate its effect on point cloud generation in a LiDAR system. The simulation results show that in the 100-m hovering state, the point cloud error caused by unmanned aerospace vehicle vibration can reach 200 and 400 mm in the horizontal and vertical directions, respectively. Moreover, due to the high vibration frequency, this error factor will also lead to the distortion of point cloud image, which will affect the subsequent point cloud data recognition.

Varying Amplitude Vibration Phase Suppression Algorithm in ISAL Imaging

Platform vibration introduces sinusoidal modulation in inverse synthetic aperture lidar (ISAL) imaging, which causes paired echoes in ISAL imaging. In this paper, a varying amplitude vibration phase suppression algorithm is proposed. Working without prior knowledge, the proposed algorithm can suppress paired echoes under the condition of varying vibration amplitude and will not introduce new phase errors. Furthermore, the method is suitable for the imaging scene without isolated points. Both the simulated and real experiment results of ISAL turntable data demonstrate the effectiveness of the proposed algorithm.

Experimental investigation of the vortex-induced motion of tension leg platform system with suppression system under current

The vortex-induced motion (VIM) of a tension leg platform (TLP) and vortex-induced vibration (VIV) of tension legs and risers occur only under the action of water flow. The VIM results in a high amplitude motion in the cross-flow (CF) direction, and the VIV leads to fatigue failure of the tension legs and risers. A three-dimensional (3D) physical model investigation was conducted on the overall dynamic response of the platform and acceleration at different positions of the tension legs in the in-line (IL) and CF directions. Different lengths of the splitter plate behind the TLP columns were observed, and the suppression effect of the VIM at six flow velocities was investigated. The experimental results indicated the obvious VIM phenomenon of the platform without the splitter plate, and multi-frequency time-varying coupling characteristics were observed when the heading angle was 45°. Furthermore, the results revealed that the VIM phenomenon of the platform was evidently suppressed, in amplitude and frequency, and the force coefficients are reduced significantly, after the splitter plates were arranged behind each column of the platform. However, the splitter plate slightly affected the VIV of the tension legs.

Near-surface atmospheric turbulence profile measuring technology based on an airship-mounted laser communication system.

Atmospheric turbulence is an important factor affecting the transmission performance of free-space optical communications (FSOC), especially in the near-surface where the atmospheric turbulence characteristics are complex and variable. In this paper, we study the real-time measurement technique of a near-surface atmospheric turbulence profile of an airship-borne laser communication system based on the principle of light intensity scintillation. Aiming at the influence of an avalanche photon diode detector system noise and environmental factors such as background light and platform vibration on the measurement results, a noise-canceling scintillation index calculation method, combined with a wavelet threshold denoising method, is proposed to improve the accuracy of atmospheric turbulence profile measurements. We build a communication distance of 12 km airship-borne laser communication experiment and carry out a real-time measurement of turbulence profile under 1 km near the ground without affecting the laser communication rate of 2.5 Gbps data transmission. The experimental results show that the atmospheric turbulence profile measured in real time follows the same trend as the theoretical simulation curve of the Hufnagel-Valley model, and the jitter of the measured values after denoising is significantly smaller than that of the measured values without denoising. The research results provide technical guidance and data support to promote the development of space laser communication and adaptive optics.

On the Problem of Position and Orientation Errors of a Large-Sized Cable-Driven Parallel Robot

This paper deals with the application of force sensors to estimate position errors of the center of mass of the mobile platform of a cable-driven parallel robot. Conditions of deformations of cables and towers of the robot are included in the numerical model and external disturbance is included too. The method for estimating the error in positioning via force sensors is sensitive to the magnitude of spatial oscillations of the mobile platform. To reduce torsional vibrations of the mobile platform around the vertical axis, a dynamic damper has been included into the system.

A Combined Stripe Noise Removal and Deblurring Recovering Method for Thermal Infrared Remote Sensing Images

Remote sensing images (RSIs) have been applied to many fields such as environmental monitoring, urban planning, and military defense. All-day thermal infrared imaging observation system can finely portray the trajectory of human activities and provide data support for United Nations sustainable development planning. However, in the process of RSIs, image quality degradation containing image blurring is caused by optical system aberration, satellite platform vibration, imaging system out-of-focus, and atmospheric turbulence. Moreover, stripe noise in the image is produced by the non-uniformity of infrared sensors. Image deblurring and destriping are classical tasks in RSIs, but the above two problems are discussed separately in almost all research. i.e., denoising after adding stripe noise on clear images or deblurring under the assumption that only random noise exists. In this paper, stripe noise and blur are jointly removed from on-orbit RSIs acquired by the thermal infrared spectrometer on the SDGSAT-1 satellite, using a method based on stripe component residuals and gradient property. According to the experimental results, the performance of the proposed method is greatly improved compared with processing these two tasks separately, which can provide a valuable reference for the study of high-resolution thermal infrared RSIs recovery.

Imaging characteristics and image restoration method for large field circular scanning system

Large field circular scanning system obtains remote sensing images by rotating scanning, which is one of the technical ways to effectively expand the field of view of geostationary orbit optical remote sensing imaging system. However, due to its special rotation scanning imaging mechanism, the on-orbit imaging process of this system is affected by the coupling of detector rotation sampling, satellite platform vibration, optical system aberration and other factors, so the image degradation characteristics are very complex. In this paper, the on-orbit imaging characteristics of large field circular scanning system are first analyzed to provide a theoretical basis for the subsequent research of image restoration method. Secondly, aiming at the problems of annular geometric distortion and spatial blur of the system image, the image restoration method is proposed based on ring block and regularization methodology. Experimental results show that under the condition of detector rotation speed ω <0.06 rad/s, the proposed method exhibited a satisfactory processing performance.

A New Cross-Platform Instrument for Microstructure Turbulence Measurements

This study developed a new cross-platform instrument for microstructure turbulence measurement (CPMTM) and evaluated its performance. The CPMTM is designed as an “all-in-one” payload that can be easily integrated with a variety of marine instrumentation platforms. The sensors in the CPMTM include two shear probes, a fast-response temperature probe, and an accelerometer for monitoring vibrations. In addition, a custom-designed flexible connection vibration-damping device is used to isolate platform vibrations. To validate the CPMTM performance, a direct comparison was carried out with a reference acoustic Doppler velocimeter in a controlled flume for four background turbulence levels. The results of the comparison show that the velocity spectra measured by the CPMTM and ADV w components are in agreement, which demonstrates the ability of the CPMTM to acquire accurate turbulence data. Furthermore, the CPMTM was integrated into the long-range Sea-Whale 2000 AUV and tested in the northern South China Sea in September 2020. The data collected by the CPMTM show that the measured shear spectrum of the noise reduction agrees well with the empirical Nasmyth spectrum. Turbulent kinetic energy dissipation rates as low as 7 × 10−10 W kg−1 can be resolved. Laboratory and field experiments illustrate that the CPMTM has an extraordinarily low noise level and is validated for turbulence measurements.

Multi-element full-duplex FSO transceiver design using optimum tiling

With ever-growing demand of high-speed mobile data and in vision of smart cities, optical wireless, a.k.a. free-space optical (FSO), communication deem to be a critical technology due to its significantly faster data transfer rate, higher security, lower costs, and reduced power usage. These beneficial effects have led to interest in exploring FSO technologies for mobile platforms such as drone-based cell tower to provide Internet services to remote areas, or even for wireless communications on the ground with jammed radio channels as in battlefields. Direct line-of-sight (LOS) is required to establish secure directional FSO communication (FSOC) links which are highly susceptible to random and erratic movements of the mobile nodes as well as the turbulence in the free-space medium. The performance of FSOC links can be improved by designing multi-element tiling of the laser-based transceivers which is capable of in-band full-duplex (IBFD) communication. In this work, we propose a genetic algorithm framework to explore optimized multi-element FSO transceiver tiling patterns to ensure maximal signal-to-interference and noise ratio (SINR) and minimize the effects of vibration of the mobile platform and atmospheric turbulence.

Vibration-Induced Noise in Extremely Low Frequency Magnetic Receiving Antennas

The extremely low frequency magnetic antennas are widely used in geophysical exploration, marine electromagnetic detection, and other applications. However, the slight vibration of the antenna platform will cause extra antenna electromagnetic noise. In this letter, the electromagnetic noise of the magnetic antenna caused by vibration is simulated under different vibration conditions first. Then, in order to evaluate the effect of vibration on magnetic antenna performance, some vibration-induced noise measurement experiments of magnetic antenna were carried on. Experiment results show that vibration-induced noise is one of the main sources of antenna electromagnetic noise, but with proper vibration isolation technology, the vibration-induced noise can be reduced to the level of ambient electromagnetic noise.

Neural network-based fuzzy vibration controller for offshore platform with random time delay

A neural network-based fuzzy controller is proposed to attenuate the irregular wave-induced vibration of a steel-jacket offshore platform. Firstly, the offshore platform is modeled as a system with time-varying control delay under random wave forces. Secondly, disturbance rejection measures are taken in designing an optimal controller containing delayed states. Thirdly, neural networks are adopted to observe and restore the controlled system, in order to learn the delayed control law using instant state. Finally, fuzzy models are constructed for reducing the complexity in data collecting and neural network training. Trained with sample data from fuzzy models, the neuro-fuzzy observation system is able to reconstruct the control system, and the generalized neural network-based controller works efficiently in different delayed cases. It achieves better vibration-attenuating performance under uncertain control delay and random waves, when compared to existed optimal control laws and fuzzy controllers without neural networks. The main contributions of this paper are: 1) obtaining a neural network-based observer in state approximation; 2) designing a neural network-based controller based on fuzzy rules to cope with random control delay.

Adaptive preload controller design and analysis for electrostatic suspension system

The electrostatic suspension control system (ESCS) is the core component of the inertial sensor in space gravitational wave detection. To adapt to the changes in orbit environment and satellite platform vibration, the test mass stable is kept in the center of the electrode cage, the ESCS requires high-precision parameters calibration and high-stability verification of the control system. This paper studied the ESCS method, an adaptive controller with variable preload was proposed, and the stability conditions of the control system are given to provide a theoretical basis for the design of the controller. The structure and working principle of the system were also introduced. The electrostatic control system model was derived, and the performance of adaptive preload controller was analyzed. Finally, a simulation was conducted under different disturbance conditions. The results show that the control method proposed in this paper can achieve stable control in difference disturbance, and the preload voltage will change with the conditions. Compared with the traditional fixed preload method, we can see that our method has significantly improved the stability margin and the control quality during the process of dynamic response. This paper provides a solid foundation for the future exploration of space gravitational waves in China and clears the optimization direction for the next step.

Multi-frame image restoration method for novel rotating synthetic aperture imaging system

The novel rotating synthetic aperture (RSA) optical imaging system is an important development direction for future high-resolution optical remote sensing satellites in geostationary orbit. However, owing to the rotating rectangular pupil, the point spread function of the RSA system has an asymmetric spatial distribution, and the images obtained using the primary mirror from different rotation angles have nonuniform blur degradation. Moreover, platform vibration and pupil rotation have coupling effects on the RSA imaging, resulting in further radiometric and geometric quality degradation. To address these problems, the image degradation characteristics are first analyzed according to the imaging mechanism. Then, combined with the theory of mutual information, an image registration method is suggested by introducing the orientation gradient information. From this, a multi-frame image restoration model is proposed based on the directional gradient prior of the RSA system image. From the perspective of interpretation and application, when the aspect ratio is less than 3, the proposed inversion restoration method can achieve a satisfactory processing performance. This work can provide engineering application reference for the future space application of RSA imaging technology.

Analysis of Vehicle Platform Vibration Based on Empirical Mode Decomposition

Vehicle platform vibration (VPV) directly affects the measurement accuracy of precise measuring instrument (PMI) fixed on it. In order to reduce the influences of VPV on measurement accuracy, it is necessary to perform vibration isolation between vehicle platform and PMI. Analysis of vibration characteristics is a prerequisite for vibration isolation. However, empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) reveal that there is obvious mode mixing phenomenon in the collected VPV signals. In this paper, a noise stretch ensemble empirical mode decomposition (NSEEMD) method is proposed to suppress mode mixing, and the specific operation process of NSEEMD is expounded. By NSEEMD, mode mixing of the collected platform vibration data is well suppressed, and the principal component of platform vibration can be obtained.

Memory-event-triggering H ∞ reliable control for networked jacket platforms against earthquakes and stochastic actuator faults

This paper deals with the problems of networked modelling and memory-event-triggering reliable control for steel jacket-type platforms in network environments. First, a networked model of the jacket platform against earthquakes and probabilistic actuator faults is established. Based on this model, a memory-based event-triggering communication scheme is introduced to account for the constrained communication resources. A distinct feature of the proposed triggering scheme is that it has great potential to identify and trigger the significantly changed data than the existing ones without ‘memory’. Then, by formulating the network-based closed-loop platform system as a stochastic delay system, some sufficient conditions are derived for co-designing the desired controller and the triggering scheme. Finally, comparative simulation results are provided to demonstrate the effectiveness and merits of the proposed triggering and control co-design method. It is shown that compared with some existing event-triggering control methods, the proposed memory-event-triggering reliable controller is effective to mitigate vibrations of the jacket platform and is potentially advantageous to save more network bandwidth and control cost.

Satellite platform vibration influence on acquisition system for intersatellite optical communications

Accurate pointing, acquisition and tracking systems are an important part of maintaining stable intersatellite optical communications links. Satellite platform vibration causes system instability and reduces the system precision during the building and maintaining satellite optical communication system. This manuscript studies the satellite platform vibration influence on acquisition system for intersatellite optical communications. Considering the scan parameters and platform vibration, an approximately analytical expression of scan lost possibility (SLP) is derived through newly models for acquisition analysis. Taken scanning restricted condition and SLP into account, vibration influence on the acquisition time of single-scan and multi-scan is also presented. And the theoretical result calculated by the proposed analytical expression is approximately to the result by Monte Carlo simulation.

A High Frequency Vibration Compensation Approach For Terahertz SAR Based on Sinusoidal Frequency Modulation Fourier Transform

In this paper, a vibration estimation method for terahertz synthetic aperture radar (THz SAR) is proposed based on the sinusoidal frequency modulation Fourier transform (SFMFT), which directly operates on the phase term of the signal. Small high frequency vibration of the platform will introduce nonlinear phase modulation in radar echoes. To improve the potential of the method for vibration with multiple vibration frequencies, SFMFT is used to extract the vibration spectrum of the platform. When the vibration amplitude exceeds a certain threshold, the phase ambiguity will occur. To improve the range of estimable vibration amplitude, a method based on the conjugate cancellation of the phase errors with sub-band decomposition is introduced to reconstruct a signal with a longer equivalent wavelength. Then the accurate phase errors caused by the platform vibration can be estimated by performing SFMFT on the composite signal. The simulations prove that the proposed method is superior to the time-frequency (TF) analysis methods and can improve the range of estimable vibration amplitude.