Static Force Research Articles

The sensitivity of agricultural biogas plants to changes in energy prices in Poland

In Poland, despite ambitious plans from 15 years ago, when it was assumed that by 2020, an agricultural biogas plant would be standard in every commune, the potential of agricultural biogas has not been used due to the lack of stable legal regulations and financing programmes for the construction of the plants. The situation has now changed due to new forms of support systems, which motivated the authors to compare two agricultural biogas plants operating in the certificate system and the support system in the form of feed-in premiums. Moreover, the authors pointed to differences in the number of agricultural biogas plants and their capacity by voivodeship due to changes in legal conditions in force in two periods: from 1 January 2011, to 30 June 2016, and from 1 July 2016, to 19 January 2024. Based on the research methods used ‒ including Earnings Before Interest, Taxes Depreciation and Amortisation, the Internal Rate of Return, risk matrix and data analysis in spatial terms ‒ it was indicated that: 1. agricultural biogas plants are characterised by very high sensitivity related to the probability of risk in the case of investment costs, substrate prices and changes in energy prices; 2. financial support is important at the stage of construction of a biogas plant, which largely makes it possible to shorten the payback period and thus increase the willingness of future investors to invest in biogas plants and 3. in the periods analysed, significant differences were noted in the spatial location of biogas plants due to trends towards lower-power biogas plants, which is probably dictated by the constant and predictable premium system in the new support system.

Design and Experimental Study of a Cleaning Device for Edible Sunflower Harvesting

Existing cleaning devices for edible sunflower have a low cleaning efficiency, high cleaning loss rate, and high impurity rate; therefore, a wind-sieve-type cleaning device for edible sunflower harvesting was designed. According to the characteristics of dislodged objects, a vibrating screen for the device was designed, and the dislodged edible sunflower objects in the device were used for a mechanical analysis of the force conditions to determine the displacement of the different edible sunflower objects dislodged by the action of airflow. Using FLUENT-DEM gas–solid coupling simulation technology, the velocity of the flow field, the velocity vector, and the trajectory of the dislodged objects inside the cleaning device were analyzed, and the law of motion applied to the airflow and the dislodged objects inside the device was clarified. According to the results of the coupled simulation analysis, the key factors affecting the operation of the cleaning device were wind speed, vibration frequency, and amplitude. Based on the key factors of wind speed, vibration frequency, and amplitude, an orthogonal rotary combination test was carried out with the loss rate and impurity rate of cleaned grains as the evaluation indexes, and the test parameters were optimized to obtain the optimal combination of operating parameters of the device, which were as follows: wind speed: 30 m·s−1; vibration frequency: 8.44 Hz; and amplitude: 41.35 mm. With this combination of parameters, the seed loss rate and impurity rate reached 3.47% and 6.17%, respectively. Based on the optimal combination of operating parameters, a validation test was performed, and the results of this test were compared with the results of the test bench using this combination of parameters. The results show that the relative errors of the loss rate and impurity rate between the bench test and the simulation test were 3.45% and 3.07%, respectively, which are less than 5%, proving the reliability of the simulation analysis and the reasonableness of the design of the test bench.

Convective flow of couple stress ternary nanoliquid flow through a permeable microchannel: irreversibility analysis

ABSTRACT Ternary hybrid nanoliquid is employed in various engineering and science applications including electronic heaters, pharmaceutical, nuclear safety, and solar energy production. Hence, the current study focused on the thermal and entropy analysis of water-based ternary couple stress hybrid nanoliquid and couple stress hybrid nanoliquid flow in an oblique channel. The significance of heat flux, porous media, buoyant force, magnetic field, and convective condition on the couple stress ternary liquid has been scrutinized. The governing partial differential equations are transferred into ordinary differential equations with the help of dimensionless terms. In the next step, the ordinary differential equations were solved by utilizing the RKF-45 numerical method. The outturn elucidated that the inflated Brinkman number greatly promotes the thermal field. The flow profile declines with enhanced permeability parameters. The outcome of the scrutiny of the couple stress parameter concludes that highly reinforced by ternary fluid than hybrid couple stress nanofluid.

Heat transfer augmentation in heat sink with fin-bars inserted in cooling channel

Adding obstacles and obstructing fluid flow in cooling channel to induce whirl velocity enhances thermal performance in heat sinks. An analysis is presented of conjugate heat transfer in a heat sink with transversely inserted bars in the flow channel. The numerical study seeks to maximise the dimensionless thermal conductance subject to constant total volume. The study contrasts a standard heat sink without a bar with cooling channel inserts with one, two, three, and 4 bars. To improve the surface area for heat transfer, the extended surfaces are placed longitudinally at various points in the cooling channel. A high-density heat flux is applied at the bottom wall of the heat sink and coolant with an inlet velocity vin between 4.26 and 7.26 m/s is pumped in a forced convective laminar condition to eliminate the heat. A computational fluid dynamic (CFD) code incorporated in Ansys fluent is used to solve the mathematical models. The numerical analysis indicates that the configuration featuring 3 bars inserted at the roof of the cooling channel exhibits the highest global thermal conductance, achieving a 53 % increase over other configurations. All configurations with 3 bars inserted up, down, left and right, maintain a constant pump power of 3.5 W across a Reynolds number range of 857–1461. Bars positioned at the roof of the cooling channel experience the lowest outlet and inner wall temperatures, whereas those at the floor exhibit the highest temperatures. The optimised design meets the highest porosity limit of 0.8.

Analytical Study of Barrier-free Door Closer Guide Rail System based on Slider-Crank Mechanism

Abstract One of the most important elements of barrier-free design is the door entrance system, particularly door closers. Door closers ensure that doors are easy to operate and do not pose any physical barriers to users. However, existing electro-mechanical door closers are relatively heavy, costly and have reliability issues in cases of power outages. Purely mechanical door closers, such as cam action with guide rail and rack-and-pinion with scissors arm, offer a more affordable option due to simpler design and fewer components used. Static forces and torque with geometrical constraints of the door closer guide rail system are considered in deriving the mathematical expressions of a door closer guide rail system using similar approaches as slider-crank mechanism. The formulation considers the effects of pinion torque of a door closer, installation inputs as design parameters, door angle and efficiency. The mathematical model and experimental results show close agreement. The contribution of this paper is that it demonstrates the underlying physics of the door closer guide rail system, thereby aiding in understanding the door behaviour. Additionally, the model can predict the behaviour of the system under different operating conditions, which can be useful for design and optimization purposes. More importantly, this model can be utilised to identify the most effective strategies in reducing opening forces on doors thereby providing design insights to barrier-free application in the future.

Force Analysis Using Self-Expandable Valve Fluoroscopic Imaging: a way Through Artificial Intelligence.

This study aimed to develop a force analysis model correlating fluoroscopic images of self-expandable valves with stress distribution. For this purpose, a nonmetallic measuring device designed to apply diverse forces at specific positions on a valve stent while simultaneously measuring force magnitude was manufactured, obtaining 465 sets of fluorescent films under different force conditions, resulting in 5580 images and their corresponding force tables. Using the XrayGLM, a mechanical analysis model based on valve fluorescence images was trained. The accuracy of the image force analysis using this model was approximately 70% (50-88.3%), with a relative accuracy of 93.3% (75-100%). This confirms that fluoroscopic images of transcatheter aortic valve replacement (TAVR) valve stents contain a wealth of mechanical information, and machine learning can be used to train models to recognize the relationship between stent images and force distribution, enhancing the understanding of TAVR complications.

Study on calculation method for dynamic load distribution of thread pair of planetary roller screw mechanism

To reveal the dynamic load distribution characteristics of planetary roller screw mechanism under the high-speed operating conditions, based on the spiral surface equation and deformation coordination relationship, a static contact force calculation method of the roller-screw and roller-nut thread at the contact point is proposed, and a formula for calculating the contact angle after bearing is derived. On this basis, further considering the inertial force generated by using high-speed operation, a dynamic load distribution model for planetary roller screw mechanism thread was established. By comparing with the finite element contact model of planetary roller screw mechansim, the error is below 5%, which verifies the correctness of the model established. Finally, the influence of the parameters such as screw speed, axial load, pitch, and tooth flank angle on the distribution of dynamic load was analyzed. The results show that the inertia force causes the roller to have a tendency to move closer to the nut and away from the screw resulting in a decrease in dynamic contact force on the roller screw side and an increase in dynamic contact force on the roller nut side. The degree of uneven distribution of dynamic load is positively correlated with the screw speed and pitch, and negatively correlated with the tooth side angle. The size of axial load has a significant impact on the distribution of dynamic load.

Design and Research of the Grasping Force Feedback Mechanism of Flexible Surgical Robots.

Robot-assisted microsurgery (RAMS) is gradually becoming the preferred method for some delicate surgical procedures. However, the lack of haptic feedback reduces the safety of the surgery. Surgeons are unable to feel the grasping force between surgical instruments and the patient's tissues, which can easily lead to grasping failure or tissue damage. This paper proposes a tendon-driven grasping force feedback mechanism, consisting of a follower hand and a leader hand, to address the lack of grasping force feedback in flexible surgical robots. Considering the friction in the tendon transmission process, a grasping force estimation model is established for the follower hand. The admittance control model is designed for force/position control of the leader hand. Through experimental validation, it has been confirmed that the grasping force sensing range of the follower hand is 0.5-5N, with a sensing accuracy of 0.3N. The leader hand is capable of providing feedback forces in the range of 0-5N, with a static force accuracy of 0.1N. The designed mechanism and control strategy can provide the grasping force feedback function. Future work will focus on improving force feedback performance. This research has no clinical trials.

Thermal convection of a liquid metal under an alternating magnetic field

The objective of this work is to measure the heat transfer of a liquid metal in a cylindrical cell under the conjugate effects of a temperature difference and a Lorentz force generated by an alternating current in a coil. The experimental results are compared to recent direct numerical simulations (DNS) (Guillou et al., 2022). 25 experiments are performed for a large range of frequency f, ac intensity amplitude I0 and temperature difference between the top and bottom walls ΔT0: 15≤f≤1000Hz, 2≤I0≤67 A and 6≤ΔT0≤11 K. In these experiments, the Hartmann number Ha, the shielding parameter Sω and Rayleigh number Ra vary in the following range: 6≤Ha≤200, 1≤Sω≤70, 2.3×106≤Ra≤4.1×106. The experiments with an ac magnetic field are compared with the Rayleigh–Bénard convection (RBC) experiments under the same thermal conditions. Three rings of thermocouples allow characterizing the fluid temperature distribution during the convection. The heat flux at the bottom and top walls are also measured. We observe a very good agreement between the experimental results and the DNS results. As previously shown by numerical simulations, a master curve of Nu/Peω vs. QJ/Qc allows predicting the evolution of the heat transfer under different conditions of temperature difference and Lorentz force. Here Nu and Peω are the Nusselt number and a Péclet number based on the Lorentz force, and QJ and Qc are the total power deposited by the Joule effect and the total conduction heat flux without motion, respectively. The experiments show that Nu/Peω∼(QJ/Qc)−2/5.

A Simplified Analytical Model for Strip Buckling in the Pressure-Assisted Milling Process.

A simplified column-buckling model is developed to understand the buckling mechanism of thin-walled strips restrained by uniform lateral pressure in the milling process. The strip is simplified as two rigid columns connected by a rotation spring, resting on a smooth surface, restrained by a uniform pressure and loaded by an axial force. Two loading cases are considered, i.e., the dead load and the follower load. Analytical solutions for the post-buckling responses of the two cases are derived based on the energy method. The minimum buckling force, Maxwell force and stability conditions for the two cases are established. It is demonstrated that the application of higher uniform pressure increases the minimum buckling force for the column and thus makes the column less likely to buckle. For the same pressure level, the dead load is found to be more effective than the follower load in suppressing the buckling of the system. The effect of initial geometric imperfection is also investigated, and the imperfection amplitude and critical restraining pressure that prevent buckling are found to be linearly related. The analytical results are validated by finite element simulations. This analytical model reveals the buckling mechanism of strips under lateral pressure restraint, which cannot be explained by the conventional bifurcation buckling theory, and provides a theoretical foundation for buckling-prevention strategies during the milling process of thin-walled strips, plates and shells commonly encountered in aerospace or automotive industries.

Effectiveness of 12-Week Core Stability Training on Postural Balance in Soccer Players With Groin Pain: A Single-Blind Randomized Controlled Pilot Study.

Core stability training (CST) is effective in improving postural balance, core endurance, and self-reported outcomes in different populations. This study aimed to investigate the effect of CST in soccer players with groin pain (GP). CST would improve postural balance performance, core endurance, and self-reported outcomes in soccer players with GP. Randomized controlled trial. Level 2. Soccer players with GP who met the selection criteria were assigned randomly to a CST (CSTG, n = 10) or a control (CG, n = 10) group. The CG undertook no additional physical activity program besides their usual training. The CSTG performed a 12-week CST comprising 76 ~75 min sessions. Static (force platform) and dynamic (Y-Balance test) postural balance, core endurance (McGill trunk endurance tests), and self-reported outcomes (Copenhagen Hip and Groin Outcome Score [HAGOS]) were assessed before and immediately after the 12-week CST. Significant improvements were seen in dynamic postural balance (P = 0.04 to <0.01), HAGOS scores (P = 0.02 to <0.01), and core endurance measures (P < 0.01) in the CSTG in posttest compared with pretest session and compared with CG. Static bipedal postural balance measures showed significant improvements (eyes open, P = 0.02; eyes closed, P < 0.01) in the CSTG in posttest compared with pretest session. However, no significant differences (P > 0.05) were observed between CSTG and CG after the training period. A 12-week CST improved static (foam surface) and dynamic postural balance, core endurance measures, and HAGOS scores. The beneficial effect of CST on improving postural balance, core endurance, and self-reported outcomes in soccer players with GP suggests that this training would be an important feature of rehabilitation programs for these players. Coaches and clinicians should prioritize CST training when designing rehabilitation programs.

Transient mode-III problem of the elastic matrix with a line inclusion

The method of pull-out test has been used to identify the mechanical performance of hybrid and fiber-reinforced composite materials. This paper investigates the elastic phase preceding the pull-out of a rigid line inclusion from the polymer matrix with fixed top and bottom surfaces. The mode-III problem is investigated such that the pull-out force is applied from the out-of-plane direction and it can be either transient or static. By applying the singular integral equation technique, the semi-analytical elastic field expressions are obtained. Under the static pull-out force, the stress intensity factor (SIF) near the inclusion tip shows a monotonic increase as the length and height of the matrix increase, whereas for the transient pull-out force, the SIF displays an initial increasing and followed by a decline. The maximum SIF is obtained for (1) the matrix length is 2 to 2.5 times of the inclusion length, and (2) the matrix height is 1 to 2 times of the inclusion length. Moreover, this paper provides a solution approach that incorporates the elasticity of the inclusion, showing that there is an optimal shear stiffness that minimizes the stress singularity of system. The conclusions of this study hold significance for the design and performance evaluation of fiber-reinforced composite materials.

Ideal performance assessment of non-recirculating anaerobic fluidized bed reactors treating low to high strength organic loads with low retention time

This study investigated the ideal performance of non-recirculating Anaerobic Fluidized Bed Reactors (AnFBRs) for treating organic wastewater of varying strengths under low Hydraulic Retention Time (HRT). Four 4.58 L AnFBRs were used to treat synthetic wastewater with an Organic Loading Rate (OLR) ranging from 4.50 to 40.11 gCOD/L-d, and HRT between 1.1 and 4.4 hours. The AnFBRs achieved high removal efficiencies ranging from 83 % to 96 % at steady state, except during the organic shock load, which reduced removal performance to 12 %. Shortened HRT conditions led to a decreasing trend in reactor pH due to an incomplete anaerobic cycle. The modified Stover-Kincannon model estimated the maximum substrate utilization rate of AnFBR's to be 196.08 gCOD/L-d, with a correlation coefficient of 0.98. Under shortended HRT, microbial diversity analysis identified predominant non-filamentous bacterial families, such as Streptococcaceae and Veillonellaceae, which collaborate during biofilm development in anaerobic environments. It was suggested that the porous media provided secure attachment sites for the biomass growth and biofilm formation under shock load and high shear force conditions. While these results offer valuable insights, further studies are needed to confirm these findings and enhance the understanding of the use porous media in non-recirculating AnFBRs.

Effectiveness of freezing temperatures on dormancy release of temperate woody species.

Spring phenological change of plants in response to global warming may affect many ecological processes and functions. Chilling temperature regulates budburst date by releasing dormancy. However, whether freezing temperature (<0°C) contributes to dormancy release is still debated. Our poor understanding of the role of chilling makes estimating shifts in budburst date difficult. A two-year chilling-forcing experiment was explicitly designed to test the effects of chilling temperatures on dormancy release of 9 temperate woody species in Beijing, China. A total of 1620 twigs were first exposed to a wide range of temperatures (-10 to 10 °C) with different durations and then moved to growth chambers. Based on budburst data in experimental conditions, we examined whether freezing temperatures are effective on dormancy release. We also developed a new framework for constructing chilling functions based on the curve between chilling duration and forcing requirement (FR) of budburst. The chilling function derived from this framework was not affected by experimental forcing conditions. We demonstrated that freezing temperatures down to -10°C were effective in dormancy release. The rate of dormancy release, indicated by the rate of decay in chilling duration-FR curve, did not differ significantly between chilling temperatures in most cases, although it exhibited a maximum value at 0 or 5°C. The chilling function-associated phenological models could simulate budburst date from independent experimental and observational data with a mean RMSE of 7.07 days. The effective freezing temperatures found here are contrary to the well-known assumption of <0°C temperature generally not contributing to accumulated chilling in many previous chilling functions. A chilling function assuming that temperature below an upper-temperature threshold has the same effects on dormancy release could be adopted to calculate chilling accumulation when using experiments to develop spring phenological models based on the chilling-forcing relationship.

Exploring the thermomechanical and dynamical mode switch transition of a reversible solid oxide cell

Reversible solid oxide cells (r-SOCs) are regarded as a solution form of clean energy generation towards a green hydrogen energy transition. However, during transportation, installation, and operation, they are required to withstand dynamic conditions as they face thermal, mechanical, and vibrational effects. Assessing the interplay of the thermomechanical and dynamical impacts on r-SOC materials during the mode-switch from electrolysis to fuel cell operation is the subject of this current comprehensive study. Advanced FEM-based homogenisation techniques have been harnessed in predicting and evaluating the detailed transients during static and dynamic loading. The intricate 3D thermal profiles throughout the transient reversible dual-modus operation from a typical r-SOC study have been derived using advanced image processing. Orthotropic material properties were incorporated into a unified macroscopic scale model by deriving the complex 3D microstructure geometry characteristics of the cell materials and component layers. The comprehensive thermomechanical and pre-stressed modal analysis results showed that the static and dynamic forces in fuel cell mode are more pronounced, whereas, in electrolysis operation, the dynamical behaviour highly depends on geometrical and operating conditions. Smaller component size shows higher natural frequencies and more intense vibration, leading to higher deformation attributed to complex mode shapes and reduced flexural rigidity. These insights are essential for optimizing r-SOC design parameters, enhancing their dynamic and structural reliability throughout their dual-mode operation lifespan.

Modified Bentonite As a Dissolve-Extrusion Composite and Its Modification Mechanism.

In the geological core drilling industry, simple and low-cost drilling fluid formulations are required that are easy to apply and maintain. Currently, drilling fluid systems with simple formulations generally exhibit poor performance and do not satisfy the requirements of complex formations. The application of powder surface modification technology has been extensively investigated in several fields; however, few are the studies focusing on the modification of bentonite. Consequently, in this study, based on the surface modification technology of powders, bentonite is modified using the modifiers ZJ-1 and ZJ-2, giving it the characteristic of "one additive with multiple functions". This allows the construction of a new type of drilling fluid system with a simple formulation (water + modified bentonite), excellent performance, and easy application and maintenance. First, a new composite modification method named the dissolution and extrusion composite modification method was proposed, and the dosage of the modifier and the optimal ratio of each modifier were determined experimentally. Second, orthogonal design experiments were conducted to determine the optimal preparation conditions based on the rheological properties of the drilling fluid, dynamic plastic ratio, and filtration loss. Subsequently, the performance of the modified bentonite drilling fluid was analyzed by comparing it to that of a regular bentonite drilling fluid. Finally, the modification mechanism of bentonite was analyzed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). It was revealed that a total modifier dosage of 2% and a ratio of ZJ-1 to ZJ-2 of 1.5:0.5 afforded a modified bentonite drilling fluid with significantly enhanced performance compared to a regular bentonite drilling fluid. The modified bentonite exhibited a filtration loss of 7.5 mL, funnel viscosity of 51.5 s, static shear force of 2.5 Pa, dynamic shear force of 9.198 Pa, apparent viscosity of 29 mPa·s, and plastic viscosity of 20 mPa·s. The experimental repeatability was good, and the optimal preparation conditions for modified bentonite involved a reaction time of 10 h, a reaction temperature of 100 °C, and a mechanical pressure of 0.5 MPa. Microscopic analysis showed that the modifiers were incorporated into bentonite through intercalation and surface adsorption and that the modified bentonite can form a dense filter cake. Our study provides a new drilling fluid solution for the geological core drilling industry, effectively promoting the advancement of drilling fluid technologies.

Research on multi-vehicle formation control based on improved artificial potential field method

Multi-vehicle formation can perform various special tasks in unstructured environment. How to take into account the safety of vehicles in avoiding obstacles and the ability to maintain formation has a certain research value. In this paper, the four-circle model of vehicle is established first, and the circle radius is adjusted according to the state of vehicle, so as to describe the safety boundary of vehicle. The improved RRT algorithm is used for the whole route planning, and the discrete path points are used as vehicle guidance. Then the artificial potential field is constructed, and the formation coordination potential field is proposed, so that the vehicles can cooperate with other vehicles to keep the preset formation as far as possible when avoiding obstacles. Then the control quantity of the vehicle is calculated according to the force condition of the vehicle in the potential field by the double exponential sliding mode control method. Finally, the effectiveness of the method is verified by the simulation experiments of triangle formation and circular formation under different working conditions, and the formation error is reduced by about 20%.

Safety-Centric Precision Control of a Modified Duodenoscope Designed for Surgical Robotics

There is limited research on robotic systems designed for Endoscopic Retrograde Cholangiopancreatography (ERCP) procedures using a side-view duodenoscope. The unique structure of the duodenoscope presents challenges to safely and precisely control the distal end pose. Control methods applied can reduce potential medical risks. We have redesigned the control section of the duodenoscope to facilitate its manipulation by a robotic system. An orthogonal compensator is employed to rectify the motion planes to standard planes. A hysteresis compensator based on the Prandtl-Ishlinskii model enables precise control of the distal pose of the duodenoscope. Furthermore, we utilize a contact force prediction model to prevent excessive contact force at the distal end. The performance of the modified duodenoscope is comparable to that of the standard duodenoscope. Following orthogonal compensation, the deviation angles of the motion planes is reduced by 32% to 98%. Post-hysteresis compensation, the root mean square error (RMSE) of the output angle of the distal end is decreased from 8.347° to 4.826°. The accuracy of distal end contact force prediction was approximately ±25% under conditions of high contact force. In conclusion, the modification and control strategy we proposed can achieve relatively safe and precise control of bending section, laying the foundation for the subsequent roboticization of duodenoscope systems for ERCP procedures.

Impact of translator mass and buoy choice on a power absorption of point absorbing wave energy converter linear generator with linear generator power take off

AbstractOcean waves have the potential to contribute to future renewable electricity production. A wave energy converter (WEC) is a technology developed to absorb the energy of the wave and convert it to another form of energy. The Uppsala University WEC (UU WEC) is a point absorber with a direct drive permanent magnet synchronous linear generator power take off. Among other parameters affecting the value of absorbed power for UU WEC are the buoy size, mass of the system consisting of the buoy and translator, and available wave energy at the site of interest. This study reviews the earlier static model that considered only static forces as the buoyancy and gravity forces and neglected all dynamic forces. The static model was proposed to simplify the early‐stage design decision. Although the static model was applied to two UU WECs of different dimensions, the present study shows that the static model is not held for certain buoy and translator dimensions. As an alternative, the dynamic model which accounts for the impact of hydrodynamic forces and various translator masses is proposed. The dynamic model is based on Cummins' equation and the linear potential flow theory, and the damping force is approximated as a viscous damper with the constant damping coefficient optimizing the absorbed mechanical power under a particular sea condition. The dynamic model is applied to four fixed buoy geometries of two shapes (cylinder and cylinder with a moonpool), each of two different dimensions, but the method can be extended to other buoy shapes and dimensions. In addition, the impact of translator mass was assessed for two sites located on the west coast of Sweden and near Gran Canaria, Spain. A translator of 10–11 t promotes 16.8% higher annual average power absorption for a cylindrical buoy compared to a translator of 6 t for the same buoy. However, heavier translators up to 15 t provide only 1.1% increase in average annual absorbed power.

Stochastic force identification for uncertain structures based on matrix equilibration and improved Tikhonov regularization method

Accurate identification and estimation of stochastic forces applied to in-service engineering structures play a vital role in structural safety assessments. This study devised an effective force power spectral density (PSD) identification method to address the challenge of identifying multipoint stationary stochastic forces in uncertain structures. Initially, a probability model was employed to characterize structural uncertainties. Subsequently, an integral relationship was established between the probability density function (PDF) of the random structural parameters and that of the stochastic force PSD. By employing a point-selection technique based on the generalized F-discrepancy and a smoothing method, the uncertainty problem was transformed into a finite number of stochastic force PSD identification problems for deterministic structures. Simultaneously, based on the inverse pseudo-excitation method, a matrix equilibration approach and an improved Tikhonov regularization method were used to address the problem of large identification errors near structural natural frequencies. In comparison to the traditional weighting matrix method, the proposed method further reduces the condition number of frequency response function matrices, thereby enhancing the accuracy of force PSD identification. Finally, numerical examples were presented to validate the effectiveness of the proposed method in solving the stochastic force identification problem.