Main Frequency Research Articles

Wireless Dynamic Light Scattering Sensors Detect Microvascular Changes Associated With Ageing and Diabetes.

This paper presents clinical results of wireless portable dynamic light scattering sensors that implement laser Doppler flowmetry signal processing. It has been verified that the technology can detect microvascular changes associated with diabetes and ageing in volunteers. Studies were conducted primarily on wrist skin. Wavelet continuous spectrum calculation was used to analyse the obtained time series of blood perfusion recordings with respect to the main physiological frequency ranges of vasomotions. In patients with type 2 diabetes, the area under the continuous wavelet spectrum in the endothelial, neurogenic, myogenic, and cardio frequency ranges showed significant diagnostic value for the identification of microvascular changes. Aside from spectral analysis, autocorrelation parameters were also calculated for microcirculatory blood flow oscillations. The groups of elderly volunteers and patients with type 2 diabetes, in comparison with the control group of younger healthy volunteers, showed a statistically significant decrease of the normalised autocorrelation function in time scales up to 10s. A set of identified parameters was used to test machine learning algorithms to classify the studied groups of young controls, elderly controls, and diabetic patients. Our conclusion describes and discusses the classification metrics that were found to be most effective.

Investigation on the behavior of flow and aerodynamic noise generated around the tandem seal-vibrissa-shaped cylinder

Through comparing with the tandem circular and elliptic cylinders with the same characteristic dimensions, the behavior of flow and flow-induced noise generated around the tandem seal-vibrissa-shaped cylinder is studied based on delayed detached-eddy simulation model and acoustic analogy approach. The co-shedding pattern of flow developed around the tandem cylindrical-like bars is investigated. The spatial modes, mode energy, and mode coefficients of turbulent flow around the geometries are analyzed through spectral proper orthogonal decomposition. Results show that the lift fluctuations of downstream bar are stronger than those of upstream bar, and more aerodynamic noise is radiated from the downstream bar than from the upstream bar. The alternative arrangement of nodal and saddle planes of seal-vibrissa-shaped cylinder introduces three-dimensional flow separations and suppresses the shear layer interactions, inhibiting the regular vortex shedding of Kármán vortex street occurring in the tandem cylinder wake. The reversed vortex shedding generated by two adjacent saddle surfaces in the wake of seal-vibrissa-shaped cylinder balances the lateral force and mitigates the lift fluctuations greatly, thereafter reduces the aerodynamic noise generated by wall pressure fluctuations introduced by unsteady fluctuating forces exerting on the surfaces of geometries. Compared to the tandem circular and elliptic cylinders, the good noise reduction effect with sound pressure level reduced at main frequency range has been achieved from the tandem seal-vibrissa-shaped cylinder. The calculated spectra and amplitude levels of aerodynamic noise agree well with the experimental measurements from the anechoic wind tunnel, verifying the accuracy of the numerical simulations.

Experimental research on a novel dynamic composite distortion simulator

Large-scale dynamic distortion vortexes are generated in advanced complex inlet systems, which can cause serious dynamic distortion flows and influence the performance of engines. Thus, this paper proposes a novel dynamic distortion simulator design method, which uses a column to produce a large-scale streamwise vortex and a rotating valve to enhance the dynamic characteristics, to simulate the complex distortion flow field. Experimental studies were conducted in this paper. The results show that circumferential total pressure and swirl distortion were generated regardless of the valve position. The range of the distortion region decreased significantly when the valve changed from fully closed to fully opened. When the valve rotated continuously, the dynamic total pressure and swirl distortion were generated behind the simulator. At the section, three diameters away from the simulator, the comprehensive distortion index was 7.69%, and the turbulence intensity was 46.4%. The main frequency of the distortion flow field was the same as the switching frequency of the inner channel in the column.

Safety speed threshold of high-speed train running on bridges under seismic excitation of different soil types

This study investigates the safety speed threshold of high-speed train running on bridges under seismic excitation of different soil types. In this paper, a train-track-bridge shaking table scale model test was conducted, and the train-track-bridge spatial coupling dynamics model was established. The reliability of the numerical model was verified by the tests. Afterward, the effects of transverse seismic excitation of different soil types on the train’s running safety were investigated, and the train’s safety speed thresholds were obtained. The results indicated that the dynamic response of the train-track-bridge system and the train’s running safety indices have an obvious increasing trend with the increase of peak ground acceleration and train’s running speed, and there are significant differences in the impact of different soil types. For the train-track-bridge system and the selected seismic records in this paper, the speed thresholds under different seismic fortification intensities were obtained based on the evaluation indices for the running safety of train. Among the four soil types, the safety speed threshold of soil type IV is lowest. The main frequency of soil type IV record is closer to that of the CRH380A train, resulting in severe rolling vibration of the train, and the offload factor has exceeded the limit when the speed is 50 km/h under the Loma seismic records with 8-degree seismic precautionary intensity.

Numerical Study on Cavitating Flow-Induced Pressure Fluctuations in a Gerotor Pump

Using the RNG k-ε turbulence model and a full cavitation model, this study numerically simulated cavitating flow-induced pressure fluctuations in a gerotor pump and analyzed the relationship between cavitating flow and pressure fluctuations. The results demonstrate that, as the inlet pressure decreases, the cavitation phenomenon in the gerotor pump intensifies, and the cavitation range in the rotor increases. Some of the vapor even spreads into the oil inlet groove, leading to high vapor content in the chamber that is in contact with the oil inlet groove. The pressure fluctuation characteristics of the flow field in the pump exhibit evident periodic changes. Under different cavitation conditions, the pressure fluctuation amplitude at the monitoring point decreases with increasing inlet pressure, whereas the main frequency of pressure fluctuation remains unaffected by cavitation conditions. The pressure fluctuation amplitude is the strongest at point O1 of demarcation between the low-pressure and high-pressure zones in the chamber, and the volume between the oil inlet groove and the oil outlet groove serves as the main vibration source in the rotor pump. To ensure the stable and efficient operation of the gerotor pump, it is recommended to operate it at a larger NPSH.

Broadband surface wave attenuation in porous soil by elastic metasurfaces

To mitigate surface waves in ambient vibration, a novel broadband elastic metasurface is proposed by periodically burying the layered in-filled pipes below the ground surface. The present metasurface is a simple structure and can be easily implemented. In contrast to the existing studies of metasurfaces in single-phase elastic soil, the coupling of elastic metasurfaces with saturated porous soil is investigated within the framework of Biot's theory. Note that Biot's poroelasticity can capture the complexity of soils in the presence of fluids. Both dispersion and transmission analysis are comprehensively conducted. The present investigation shows that the elastic metasurfaces are suitable for a wide range of fluid-saturated porous soil, and a significant surface wave attenuation is observed within the attenuation zone of elastic metasurfaces. In addition, the burying depth is the key point of the design of elastic metasurfaces. Specifically, the surface wave attenuation zone (SWAZ) will vanish when the depth is larger than three times the periodic constant. Besides, the SWAZ will be widened by stacking the layers of elastic metasurfaces. Three layers is enough for the metasurface to attenuate more than 80 % surface wave energy. Due to the similar dynamic characteristics of elastic metasurface in the fluid-saturated porous half-space compared to dry half-space, single-phased soil can be used to simplify the analysis of saturated soil with ideal fluids. To widen the scope of application in elastic metasurfaces, the feasibility of ambient vibration mitigation by elastic metasurfaces is experimentally and numerically verified. The experimental results confirm an obvious wave attenuation within the SWAZ, and the average insertion loss (IL︸) is 9.8 dB. Last but not least, the performance of elastic metasurfaces to mitigate ground-borne vibration induced by trains is numerically studied in time domain. Elastic metasurfaces outperform traditional trenches within the main frequency range, and IL︸ is increased by 3.9–7 dB. Thanks to the excellent wave attenuation performance and subwavelength thickness, these novel elastic metasurfaces are expected to open new avenues in ambient vibration mitigation in the costal area of saturated soil.

Fused deposition modeling for 1 × 2 array of double ridge horn antenna

AbstractIn this letter, fused deposition modeling (FDM) was used to create a 1 × 2 array of the double ridge horn antenna (DRHA). The material used for FDM was acrylonitrile butadiene styrene. The DRHA was designed using an electromagnetic simulator and printed using FDM as well as the inner surface of the DRHA was painted with silver conducting paint. Two printed DRHA were connected together as a 1 × 2 array via a power divider. The main operating frequency of the array antenna was focussed on the range from 3 to 7 GHz. The 1 × 2 array DRHA is capable of better than −10 dB return loss, greater than 10 dBi gain, and a minimum half‐power bandwidth of 27.5°.

Continuous Wavelet Transformation to Quantify small-scale Cycles of Petrophysical Properties; a New Approach Applied in a Potential Disposal Repository of Nuclear Waste, SW Hungary

Continuous Wavelet Transformation (CWT) was applied to study the small-scale repetitive oscillations of porosity distribution patterns in a 5 m silty-claystone core sample of the Boda Claystone Formation. We handled the fluctuations in voxel porosity averages over unequal depth distributions as signals over uneven time intervals. The strength of wavelet analysis lies in the ability to study the fluctuation of a signal in detail, i.e., the wavelet transforms permit automatic localization of the cyclic attributes' sequences both in time (the depth domain) and according to their frequency (the frequency domain). Thereupon, three main frequency branches (cycles) were discerned: small scale (5, 6.67, and 11 cm), intermediate scale (20, 30 cm), and large scale (66.67 cm). Depending on the CWT coefficients magnitude plot, we were able to detect the developments of porosity oscillation according to the depth variable. Thus, small-scale cycles were seen throughout the core sample., the intermediate-scale cycles were strong in the upper parts of the core sample and dwindled toward greater depths, and the large cycle was predominant in the lower part of the core sample. The cross-correlation of the wavelet coefficients of porosity and rock-forming components allows a detailed study of the inter-dependence of such parameters as their relationship changes over time. The distinct peaks at zero lag indicates that the measured wavelet coefficient series were contemporaneously correlated; their strong positive correlations suggest that both examined series respond similarly and simultaneously to other exogenous factors. The results emphasize that cyclical porosity fluctuations at all scales would concern three main factors; sediment deposition, diagenetic processes, and structural deformation (i.e., convolute laminations).

Numerical Study on the Flow and Structural Characteristics of a Large High Head Prototype Pump-Turbine under Different Operating Conditions

During the operation of pumped storage power stations, complex operating conditions can lead to different internal flow characteristics, which can cause different vibration characteristics or even damage to the structural components of the pump-turbine units. The time–frequency characteristics of the structural components’ response are of great significance for the safe operation of the unit. In this study, a three-dimensional flow field and structural field model of a large high head prototype pump-turbine is built in order to study the flow and the flow-induced dynamic response characteristics in different turbine operating conditions. The analyzed results show that the maximum deformation occurs at the inner head cover, and the maximum value of stress is located at the fillets on the outlet side of the stay vanes. Under the 50% load condition, the vortices in the runner caused by changes in the opening of the guide vanes result in the main response frequency of 4 fn of the stationary components. The research results can provide references for the structural optimization design of other pump-turbine units.

VIBRATION ANALYSIS OF A TWIN-SCREW COMPRESSOR AS A POTENTIAL SOURCE FOR PIEZOELECTRIC ENERGY HARVESTING

The paper presents the vibration spectra of a twin-screw compressor driven at various functioning regimes. The tests are performed to assess the potential of this rotary bladed machine as energy harvesting source. It is sought to determine the optimum spots on the compressor skid where piezoelectric harvesters can be placed, meeting the operational conditions. Like most of the industrial machinery, compressors exhibit inherent vibrations and heating during operation. The pulsatory effects of the compressed air trapped between the compressor’s male and female rotors inside the compressor also give birth to harmonics. It is important to evaluate the temperatures as well since piezoelectric harvesters should preferably operate close to room temperature so as not to deteriorate the material and avoid thermal hysteresis, which can ultimately lead to the loss of piezoelectric properties. The study herein involves acquiring vibrational data and representing it graphically as vibration spectra. An analytical model is also presented for calculating the main frequencies of the compressor, validated by the experimental data measurements. We also present laboratory tests with the piezoelectric harvester tuned near the male rotor’s frequency for achieving resonance conditions. The male rotor frequency was the most stable, with the highest amplitudes and of convenient value (~83 Hz) for the tip mass required for decreasing the piezoelectric cantilever’s resonant frequency from ~210 Hz.

Multi-sensor gearbox fault diagnosis using generalized minimum entropy deconvolution and main frequency center extraction

Accurate diagnosis of gearbox faults is vital to maintain the stability and dependability of rotating machinery. In practical engineering scenarios, the installation of multiple sensors is often necessary to monitor numerous variables and gather extensive information. To effectively utilize the fault information from multiple sensors and improve fault diagnosis performance, this paper presents a gearbox fault diagnosis method using generalized minimum entropy deconvolution (GMED) and main frequency center extraction (MFCE). Firstly, the introduced GMED enhances the fault signals from multiple sensors through the maximization of standardized moments, offering advantages such as stability, wide applicability, and minimal parameter tuning requirements. Subsequently, the proposed MFCE is employed to extract features. MFCE selects main spectral lines and derives a novel feature metric named main frequency center. This not only further reduces the influence of interfering components, but also requires the extraction of only 2 n features (where n is the number of sensors) to achieve a high fault recognition rate, while remaining compatible with multiple classical classifiers. Finally, the effectiveness and robustness of the proposed method are demonstrated through experimental results on two gearbox fault datasets.

Fluid-induced vibration analysis of centrifugal pump including rotor system based on Computational Fluid Dynamics and Computational Structural Dynamics coupling approach

The flow-induced vibration of centrifugal pump under the effect of stator-rotor interaction are studied by Computational Fluid Dynamics method and Computational Structural Dynamics method based on the principle of one-way decomposition fluid-structure interaction. Firstly, the unsteady flow characteristics in centrifugal pump are studied by adopting the Computational Fluid Dynamics method, the numerical model of the whole flow field of the centrifugal pump is established, and the pulsating pressure characteristics of volute and impeller in the centrifugal pump are analyzed. The accuracy of the flow field modeling method and calculation method in this paper is verified by external characteristic test. Secondly, the vibration characteristic test of centrifugal pump is carried out, and the structural dynamic model and boundary conditions of centrifugal pump are verified and corrected in the modal test. Finally, the flow-induced excitation calculated by the flow field is simultaneously applied to the structural dynamics model of the centrifugal pump according to different transmission ways, and the flow-induced vibration of the whole centrifugal pump including the rotor system is calculated and analyzed by the Computational Structural Dynamics method in conjunction with rotor dynamics. Compared with the vibration test results, the validity of the flow-induced vibration calculation method of centrifugal pump in this paper is verified. The results show that under the influence of stator-rotor interaction effect, the blade passing frequency and shaft frequency are the main characteristic frequencies of pressure pulsation and dynamic response in the centrifugal pump.

Vibration Response of Soil under Low-Frequency Vibration Using the Discrete Element Method

The vibration response of soil is a key property in the field of agricultural soil tillage. Vibration components of tillage machinery are generally used to reduce tillage resistance and improve work efficiency, and the pressure variation under low-frequency vibration will affect the fragmentation and dispersion of farmland soil. However, the gradient of pressure variation, frequency domain response, and effective transmission range is unclear. A new method based on the DEM (discrete element method) is presented to study the vibration response and pressure transmission under low-frequency vibration. Bench test results have shown that peak pressure positively correlates with the vibration frequency and attenuates rapidly at a vibration distance of 100 to 250 mm. The resulting data were also selected to determine the simulation model’s parameters. Amplitude, vibration frequency, and soil depth were used as test factors in single-factor simulation tests, and their effects on the peak pressure, frequency domain response, and effective transmission distance were analyzed. The results showed a positive relationship between the peak pressure and the test factors. The peak pressure increased with a maximum gradient of 19.02 kPa/mm at a vibration distance of 50 mm. The amplitude, vibration frequency, and soil depth positively correlated with the dominant frequency amplitude. The main frequency was independent of amplitude and soil depth. At a vibration distance of 250 mm, the dominant frequency was approximately twice the vibration frequency at 7–11 Hz and approximately equal to the vibration frequency at 13–15 Hz. Multiple exponential functions were used to fit the peak pressure attenuation function, obtaining an effective transmission distance range of 347.15 to 550.37 mm for the 5 kPa cut-off pressure. For a soil depth of 300 mm, the vertical shear wave diffusion angle was greater than the horizontal shear wave diffusion angle. This study clarifies the vibration response of soil under low-frequency vibration, which helps to design vibration-type, soil-engaging components of tillage machinery and match vibration parameters for energy-saving and resistance reduction purposes in soil tillage.

Comparative analysis of the long-term surgical treatment results of noninvasive thymus gland tumors

The study compared the long-term results of thymectomy from traditional open thoracic/sternotomic and endovideosurgical access in 98 patients with thymus tumors. All patients were divided into two groups depending on the thymectomies performed from various surgical approaches. The control group consisted of 34 patients in whom surgical interventions were performed via the traditional open access, and the main group consisted of 29 patients in whom surgical interventions were performed via the endovideosurgical access. Both groups were comparable by sex, age, concomitant pathology, presence, and severity of clinical signs of myasthenia gravis, tumor size, morphological structure, and progression stage according to the classifications by Masaoka-Koga (1997) and TNM-8 2017. According to the frequency of tumor recurrence and regression of myasthenic disorders within 3 years after surgery, no significant differences were found between the groups (2 (5.9%) and 0, p = 0.27;
 9 (69.2%) and 10 (71.4%), p = 0.52, respectively). Moreover, no significantly significant differences were found in the long-term survival (so-called KaplanMeier survival function) between the two groups. The annual, 3-, 5- and 10-year survival rates in the control group were 100%, 90.3% 2%, 87% 4%, and 87% 4%, and in the video-assisted thymectomy group, the survival rates were 100%, 100%, 100%, and 92.3% 3%, respectively (p = 0.71). In general, the long-term results of endovideosurgical thymectomy with small tumors and the absence of invasion into neighboring anatomical structures do not differ from those of traditional open surgical interventions in terms of the main oncological indicators, namely, long-term survival and frequency of tumor recurrence. The obtained results are consistent with world literature data, according to which the most significant prognostic factor of long-term survival is the stage of tumor progression by TNM. The average 5-year survival rates following radical thymectomy were 90%, 90%, 60%, and 25%, respectively, for TNM stages I, II, III, and IV.

Unveiling the Potential of Cavitation Erosion-Induced Heavy Crude Oil Upgrading

The application of ultrasonic waves in the processing of hydrocarbons is a new promising technology that has developed rapidly in recent years. However, the acoustic-induced cavitation erosion phenomenon is poorly studied. In this paper, a comparison study of cavitation erosion was carried out in water and oils with different viscosities produced from Ashal’cha and North Komsomol using an ultrasonic reactor operating at an industrial frequency of 20 kHz. The acoustic spectra obtained from hydrophones during the ultrasonic treatment of fluids can be characterized by using subharmonics of the main frequency and a continuous white noise level. Moreover, the cavitation erosion of aluminum foil under various ultrasound irradiation times and power levels was thoroughly investigated. It has been found that the process of ultrasonic cavitation has a less erosive impact on metal foil in oil due to its high viscosity. In addition, the formation of microflows in the oil phase, which also intensify the erosion process, is hindered. Cavitation erosion in the Ashal’cha oil sample exhibited a higher intensity compared to that in the North Komsomol oil sample. It was found that upon increasing ultrasound intensity in the case of the viscous (Ashal’cha) oil sample, cavitation stability was disrupted. In turn, this led to a reduction in the collapse energy of the cavitation bubbles. The results we obtained enable the assessment of cavitation erosion in crude oil and could be used to improve methodologies for monitoring and optimizing cavitation processes in crude oil.

Analysis of IGBT Pseudodesaturation Effect Caused by Stray Parameters in DC Circuit Breaker

As a highly integrated high-voltage power electronic equipment in the power grid, the DC circuit breaker (DCCB) has misjudged overcurrent protection caused by the IGBT pseudo desaturation effect (PDE) in DC short-circuit fault. To analyze the reasons for the effect, this paper established a wide-band equivalent circuit model of a hybrid high-voltage DCCB at the initial stage of DC fault. And revealed the mechanism of PDE: the stray inductance of series-connected solid-state switches, the junction capacitance of metal oxide varistors (MOVs), and the parasitic capacitance to the ground of DCCB form multiple resonant circuits. The external disturbance is converted into the interference of DCCB port through these stray parameters, and the interference would exceed the IGBT desaturation detection threshold. Furthermore, an equivalent experimental circuit that reproduces the electromagnetic interference of DCCB at the DC fault transient process was proposed, and the correctness of the mechanism analysis was verified by the scaled prototype of DCCB, the main resonance frequency error is less than 15%. Finally, the frequency domain and time domain characteristics of electromagnetic interference on the IGBT desaturation detection monitoring ports in 200kV DCCB at the initial stage of DC fault were analyzed. Based on these characteristics, a scheme of adding a delay time to the overcurrent protection criterion to avoid electromagnetic interference was proposed, which is adopted by an industrial project.

Evaluation of quantitative ultrasonic C-scan testing for refill friction stir spot welding joints based on time-frequency analysis

This paper focuses on a comparative study of different ultrasonic feature-based C-scan testing imaging methods for characterizing refill friction stir spot welding (RFSSW) joints, and accurately identifying and measuring the nugget boundary. The aim is to explore a suitable method for nugget characterization and automatic size analysis. The research indicates that the frequency-domain C-scan imaging method outperforms the time-domain C-scan imaging method in accurately characterizing the nugget. Furthermore, the C-scan imaging method based on the feature value of the base material zone (BMZ) echo signal performs better than the method based on the nugget echo signal. The tested nugget sizes obtained by using the –6 dB drop-off method to identify the boundaries in the C-scan images are generally larger than the metallographic measurement values. A novel method is proposed in this paper, using the difference in main frequency amplitude values between the BMZ and the nugget as the feature value for the C-scan testing image, and employing the Hough circle transformation for an automatic extraction of joint size. This method achieves improved nugget characterization and higher accuracy in size analysis.

Machine learning predictive model for motor moise by expanding dataset using electromagnetic force characteristics

To understand the variations of electric vehicle motor noise, the electromagnetic force change due to the tilting and the eccentricity between the rotor and the stator on the noise should be studied. However, it takes enormous computation time to consider all the various conditions, so machine learning (ML) model that can reduce the analysis time of electromagnetic force and noise was developed. The developed ML model showed very high accuracy prediction performance with an R2 value higher than 0.99 even for data that was not used at all for training. The speed increase was more than 100 times of FE analysis. The authors doubt that the high accuracy of the developed model implies the potential for electromagnetic force data structure to be much simpler than it appears. Therefore, various analyzes were conducted on the force and uneven magnetic pull. The change in the temporal-spatial main frequency component was not large, and only the change in the side order was meaningful. It was confirmed that to create a predictive model using a smaller dataset for not only the UMP but also all the individual teeth force is possible. This new way of creating a training dataset for an ML model helps to increase the training efficiency. Based on the generated prediction model, it can be used to identify changes in noise characteristics in major rotational orders and derive suitable improvements.

Experimental investigation on the hydro-acoustic characteristics of tandem cylinders with equal diameters

The investigation of the hydro-acoustic characteristics of tandem cylinders has a great importance because they occur in a variety of maritime applications that include submarines, offshore structures and seabed pipelines systems. Better understanding of the noise generation mechanism of tandem cylinders provides great contribution to reduce noise levels for many engineering applications. In this study, the hydro-acoustic characteristics of tandem cylinders with same diameter were experimentally investigated for five different distance ratios at Reynolds number of 1.6 × 104. The diameter of the front and rear cylinders used in hydro-acoustic experiments is 0.02 m. It is observed that the main peak spectrum becomes narrower as the distance ratio increases. The width of the main peak spectrum also decreases as the flow regime transition from the reattachment regime to the separation regime. An increase in the distance ratio is found to correspond to an increase in the main peak frequency. The maximum sound pressure level is observed to attain its peak value at the critical distance ratio of 3.0. Notably, the maximum sound pressure level exhibits a substantial increase of approximately 6 dB as the distance ratio increases from 1.5 to 3.0, followed by a subsequent decrease of approximately 1 dB between the distance ratios of 3.0 and 6.0.

Identification of Vibration Modes in Floating Offshore Wind Turbines

Compared to onshore turbines, floating offshore wind turbines (FOWTs) take advantage of the increased availability of offshore wind while causing less environmental impact. However, the strong winds, waves, and currents to which they are subjected trigger oscillations that can cause significant damage to the entire structural system and reduce its useful life. To reduce these loads, active tower damping techniques such as filter banks can be used. These filters must be carefully tuned to block specific vibration frequencies. Therefore, it is essential to analyze the nature of the oscillations in the FOWT and to understand how the frequencies vary in time. This topic is usually approached from a point of view very focused on a specific turbine. What is proposed here is a general method, which can be applied to any type of wind turbine, to automatically study the relationship between vibration frequencies and the degrees of freedom (DOF) of the turbine, which facilitates the design of structural control. Each frequency is associated with the DOF of the FOWT that produces it. This methodology has been successfully validated in simulation experiments with the NREL 5 MW ITI Barge FOWT. Under the wind conditions of the experiments, the main frequency found is 0.605 Hz. This frequency coincides with the 3P theoretical frequency of the FOWT. This proposal may help to design structural control systems able to damp these vibration frequencies with accuracy and efficiency.