Input Force Research Articles

Investigating the Effect of Viscous Yield Dampers on Concrete Structure Performance

Viscous dampers are one of the most effective devices in the energy consumption of the buildings. The passive hybrid system progressive applications cause each of the dampers to compensate for the weakness of the other system, thus increasing the efficiency of passive control of the structure. Speed-based viscous dampers will adjust the amount of depreciation force based on the acceleration and velocity entering the system. On the other hand, displacement-based surge dampers adjust the amount of depreciation force based on the displacement required. Therefore, considering the different performances of these two dampers, the effect of using both of them in one structure can be investigated. In this study, by combining these two dampers, the seismic behavior of concrete structures has been evaluated. To study them, 5- and 10-story structures have been designed using FE method and have been subjected to earthquake records. Historical analysis shows that the use of hybrid dampers reduces the amount of seismic input force to the structure and also the amount of floor drift is reduced due to the use of dampers and also the capacity of structures for these structures is increased. The results of the study show that the presence of dampers in the structure increases energy absorption and improves performance in the structure.

Influence of magnetohydrodynamics and heat transfer on the reverse roll coating of a Jeffrey fluid: A theoretical study

The purpose of this article is to provide a mathematical model of magnetohydrodynamic (MHD) non-isothermal flow of an incompressible Jeffrey fluid as it goes through a minimal gap between the two counter rotating rolls. The dimensionless forms of governing equations are obtained by using appropriate dimensionless parameters. The LAT (lubrication approximation theory) is utilized to simplify the dimensionless form of governing equations. Analytical solutions for the velocity, pressure gradient, flow rate, Nusselt number and temperature distribution are presented. How the Jeffrey parameters, MHD and velocities ratio influence on the flow patterns and heat transfer rate are explored. Outcomes of some significant engineering quantities such as flow rate, power input, pressure distribution and roll separation force are obtained numerically in tabular form and some are displayed graphically. We found that the MHD parameter served as a controlling parameter for different engineering quantities like velocity, temperature, flow rate, and coating thickness. Moreover, the coating thickness on the web decreases by increasing the values of velocities ratio.

Hydrodynamic forces in marine-fouled floating aquaculture cages: Physical modelling under irregular waves

Marine fouling is a major concern in marine aquaculture industry. It changes the flow field around the cage, reduces water exchange across the nets and affects the current/wave-induced forces acting on the structure. The current/wave forces induced to marine-fouled planar net panels were studied by previous researchers. The current paper reports the results of a series of small-scale physical model tests conducted to study the wave forces induced to marine-fouled 3D aquaculture net cages. Using load cells fixed on the mooring lines, the time series of the forces generated by irregular waves propagating through the clean and fouled fish cage models were recorded. The artificial fouling was representative of hydroids, an important fouling organism in the aquaculture industry. Time and frequency domain analysis were performed on the in-line (surge) and cross-line (sway) wave force data.The experimental results showed that the surge force amplitudes increased up to around 160% and by the fouling. The sway force showed up to around 50% decrease by the fouling. The probability distribution of the force response to irregular waves was not significantly affected by the fouling. The force transfer functions from the time and frequency analysis were in reasonable agreements. The fouling, interestingly, increased the linearity of the wave-force interactions and provided stronger associations between the input forcing and the output response.

InsertionNet - A Scalable Solution for Insertion

Complicated assembly processes can be described as a sequence of two main activities: grasping and insertion. While general grasping solutions are common in industry, insertion is still only applicable to small subsets of problems, mainly ones involving simple shapes in fixed locations and in which the variations are not taken into consideration. Recently, RL approaches with prior knowledge (e.g., LfD or residual policy) have been adopted. However, these approaches might be problematic in contact-rich tasks since interaction might endanger the robot and its equipment. In this letter, we tackled this challenge by formulating the problem as a regression problem. By combining visual and force inputs, we demonstrate that our method can scale to 16 different insertion tasks in less than 10 minutes. The resulting policies are robust to changes in the socket position, orientation or peg color, as well as to small differences in peg shape. Finally, we demonstrate an end-to-end solution for 2 complex assembly tasks with multi-insertion objectives when the assembly board is randomly placed on a table.

Development of Bridge and Lever Type Compact Compliant Mechanism for Micro Positioning Systems

Nowadays, for precision positioning applications (Micro-Electro-Mechanical Systems, Nano/Micro positioning devices), compliant mechanisms are extensively used over traditional mechanisms. Compliant mechanisms are joint less mechanism having merits as no wear and friction, no backlash and no lubrication. In this paper, a newly developed flexure hinge based bridge and lever type compact compliant mechanism has been proposed for the precision linear displacement applications. This mechanism can be used in the portable cameras for image stabilization, lens shutters, alignment and levelling devices, etc. The key performance parameters for developing the compliant mechanism are the input displacement/force, output displacement and amplification ratio. For designing compact amplified compliant mechanism (CACM), Pseudo-Rigid-Body-Model (PRBM) method is used. The finite element analysis of developed micro-displacement amplifier compliant mechanisms carried out by using ANSYS workbench. The analyses and experimentation is performed for the input displacement, output displacement and amplification ratio of mechanism. An input force range considered for analysis is in between 1 N to 50 N. All the results from analytical, simulation and experimentation are compared. The error in output displacement is observed up to 6% and the geometric amplification ratio for the mechanism is observed up to 6.5.

Robot Grasping System and Grasp Stability Prediction Based on Flexible Tactile Sensor Array

As an essential perceptual device, the tactile sensor can efficiently improve robot intelligence by providing contact force perception to develop algorithms based on contact force feedback. However, current tactile grasping technology lacks high-performance sensors and high-precision grasping prediction models, which limits its broad application. Herein, an intelligent robot grasping system that combines a highly sensitive tactile sensor array was constructed. A dataset that can reflect the grasping contact force of various objects was set up by multiple grasping operation feedback from a tactile sensor array. The stability state of each grasping operation was also recorded. On this basis, grasp stability prediction models with good performance in grasp state judgment were proposed. By feeding training data into different machine learning algorithms and comparing the judgment results, the best grasp prediction model for different scenes can be obtained. The model was validated to be efficient, and the judgment accuracy was over 98% in grasp stability prediction with limited training data. Further, experiments prove that the real-time contact force input based on the feedback of the tactile sensor array can periodically control robots to realize stable grasping according to the real-time grasping state of the prediction model.

Impact of Lateral Flow on Surface Water and Energy Budgets Over the Southern Great Plains—A Modeling Study

AbstractAs the horizontal grid spacing decreases, treatment of hydrologic processes in land surface models (LSMs), such as the lateral flow of surface and subsurface flow, need to be explicitly represented. Unlike previous studies that mainly focused on the mountainous regions, in this study, the offline Weather Research and Forecasting (WRF)‐Hydro model is employed to study the impact of lateral flow on soil moisture and energy fluxes over the relatively flat southern Great Plains (SGP). The vast amount of measurements over the SGP provide a unique opportunity to assess the model behavior. In addition, newly developed land surface properties and input forcing are ingested into the model, in an attempt to reduce uncertainties associated with the initial and boundary forcing and help to identify model deficiencies. Our results show that the more realistic inputs (parameters, soil types, forcing) lead to larger underestimation of latent heat flux and dry bias, indicating the existence of model structural uncertainty (embedded errors) in WRF‐Hydro that need to be characterized to inform future model development efforts. Including lateral flow processes partly mitigates the model deficiencies in representing hydrologic processes and alleviates the dry bias. In particular, both surface and subsurface lateral flow increase soil moisture mainly over the lower elevations, except that subsurface flow also affects soil moisture over steeper terrains. Additional simulations are performed to assess the effect of routing resolution on model results. When LSM resolution is high, noticeable differences in soil moisture are produced between different routing resolutions especially over steep terrain. Whereas when LSM resolution is coarse, differences between routing resolutions become negligible, especially over flat terrain.

Smoothing Transforms for Dynamical Systems with Non-smooth Input

Many control systems incorporate input from actuators. The actuators can be represented as force or displacement input. When an actuator is modeled as a displacement input, there are many practical applications for which the displacement is not smooth and its time derivative, i.e. the velocity, is not continuous everywhere. Numerical study for such displacement input becomes tedious since the state variables experience a finite jump at the time of acceleration singularity. Although the acceleration singularity can be avoided if the actuator dynamics is modeled by a force input, such an approach increases the order of the overall system. To preserve the simplicity of the displacement input of the actuators, we propose transforms of state variables so that only the velocity of the displacement input appears explicitly in the equations of the dynamical system. In short, we introduce transforms that reduce the order of time derivatives of the input. This approach simplifies the numerical solutions for non-smooth displacement input. Moreover, when the transform is applied to a parametrically excited pendulum, the stabilizing effect of the parametric excitation is shown explicitly.

Harmonic-Balance-Based parameter estimation of nonlinear structures in the presence of Multi-Harmonic response and force

Testing nonlinear structures to characterise their internal nonlinear forces is challenging. Often nonlinear structures are excited by harmonic forces and yield a multi-harmonic response. In many systems, particularly ones with strong nonlinearities, the effect of higher harmonics in the force and responses cannot be ignored. Even if the intended excitation is a single frequency sinusoidal force, the interaction of the shaker and the nonlinear structure can lead to harmonics in the applied force. The effects of these higher harmonics of the input force on nonlinear model identification in structural dynamics are often neglected. The objective of this study is to introduce an identification method, motivated by the alternating frequency/time approach using harmonic balance (AFTHB), which is able to consider both multi-harmonic forces and multi-harmonic responses of the system. The proposed AFTHB method can include all significant harmonics by selecting an appropriate time step and sampling frequency to guarantee the accuracy of the results. An analytical harmonic-balance-based (AHB) approach is also considered for comparison. However, the inclusion of all significant harmonics of the response in the analytical expansion of the nonlinear functions is often cumbersome. Furthermore, the AFTHB method can easily cope with complex nonlinearities such as Coulomb friction and with multi-degree of freedom nonlinear systems. Including the effect of higher harmonics in the identification process reduces the approximation error due to truncation and very accurate approximation of the balanced equations of each harmonic is obtained. The proposed identification method requires prior knowledge or an appropriate estimation of the type of system nonlinearities. However, the method of model selection may be used for a set of candidate models, and avoiding a dictionary of arbitrary candidate basis functions significantly reduces the computational costs. This paper highlights the important features of the AFTHB method to ensure accurate estimation using four simulated and two experimental examples. The effects of the number of harmonics considered, the modelling error, measurement noise and the frequency range on the quality of the estimated model are demonstrated.

Development of a Fiber Bragg Grating-Enabled Clamping Force Sensor Integrated on a Grasper for Laparoscopic Surgery

This paper presents a clamping force sensor based on fiber Bragg grating (FBG) to provide interaction force feedback for laparoscopic surgery. The proposed sensor mainly consists of a force-sensitive clamping flexure and a tightly suspended optical fiber with an FBG inscribed. The force-sensitive clamping flexure utilizes a bridge-type structure with an excellent load-bearing capacity and anti-interference ability to linearly convert the vertical force or displacement input exerted on the grasping surface into translational deformation along the flexure central line. The FBG fiber is arranged along the flexure central axis to sense the vertical force-induced horizontal strain. This two-point pasting configuration can achieve a uniform fiber strain distribution and an enhanced sensitivity. This assembly arrangement produces a linear relationship between the applied vertical force and the force-induced horizontal strain value sensed by the FBG. The force sensitivity remains the constant and it less affected by the grasping positions due to the high stiffness and deformation conversion, overcoming the difficulty that the traditional clamping force sensor designs are sensitive to the grasping position due to the variable grasping positions and areas on the soft tissues during clamping. The finite element method (FEM)-based simulation has been utilized for design optimization and performance investigation to guide the sensor design. The simulation sensitivity values have been determined as a close value of 52pm/N regarding the three different grasping positions at middle, left and right parts. The optimized sensor design has been integrated into a manual surgical grasper and achieve experimental sensitivity values of 56.2pm/N, 51.1pm/N and 47.5pm/N for the three different loading positions within [0, 10N]. Both dynamic loading experiments and clamping experiments on ex-vivo tissues and in-vivo animal for tissue resection were implemented to validate the effectiveness of the proposed design.

High-resolution assessment of solar radiation and energy potential in China

Global solar radiation (Rs) is a key parameter for determining the energy yields of solar photovoltaic (PV) systems. However, long-term Rs data are not available in most regions of China, impeding the management and development of PV systems. In this study, a novel model for estimating Rs was developed and coupled with a PV power model and inverse distance weighting model to generate high-resolution Rs and PV power data over China. A large network of observations was used to provide forcing inputs (daily observations from 1961 to 2018, from 2123 meteorological stations). The spatiotemporal patterns of Rs and PV power in China were further quantified. The results indicate that the newly developed Rs model accurately represents the decadal variability of Rs in China during 1961–2018. Annual potential PV power exhibited a significantly decreasing trend from 1961 to 2018, with a significant decrease from 1961 to 1991 (−0.35 ± 0.06 kWh m−2 yr−1, p < 0.01) and non-significant decrease from 1992 to 2018 (−0.14 ± 0.12 kWh m−2 yr−1, p > 0.05). Owing to air quality improvements in the future, the potential PV power may increase over China, leading to large economic benefits. Western China is favored for its abundant PV power, whereas central and eastern China are the least favorable for PV power generation. Thus, the western part of China, with its excellent geographical potential, is an optimal location for the installation of solar PV power plants. Our findings provide practical information to solar energy industries, and can help in energy structure transitions, meeting the energy demand and contributing to carbon neutrality.

Experimental and Theoretical Studies to Characterize Structural Behavior of Dry-Stone Corbelled Arches under Support Disturbances

ABSTRACT Complex dry stack stone corbel-vaulted structures are commonly constructed as assemblages of several corbelled sub-systems. While there is enough architectural documentation, limited studies explore their structural stability or factors affecting it considering that they are rather susceptible to support disturbances. A systematic study of the influence of geometry (global level), interactions between adjacent units (intermediate level) and material strength parameters, particularly joint friction (local level) on their stability is warranted. A series of static experiments are conducted on a 1:3 scaled model of an existing corbelled vault to various support movements replicating lateral actions caused by seismic or differential support movements, with non-contact measurements based on photogrammetry. Sensitivity to joint roughness and moisture conditions is also examined. Failure mechanisms categorized as overturning, joint sliding, or a combination of overturning and sliding, provide an insight on the redundancies available in complex-vaulted systems, and the interplay between one mechanism over another. The possibility of estimating collapse displacement or rotation using graphical methods in predominant overturning or the combination failure mechanism is discussed. In predominant sliding failure mechanism, a simple method to assess safety is explained with the use of the friction cone concept when subjected to known input forces.

High‐Linearity, Response‐Range Adjustable Force Sensors Based on a Yarn/Film/Spacer Triboelectric Device Design

AbstractIn this study, a novel triboelectric device is developed that consists of a silicone‐coated conductive yarn and a PET film as active substances, and an elastic spacer as a force controller. The silicone‐coated yarn is prepared by applying a thermally curable silicone to conductive yarns using a simple but continuous method. The device made of 20 cm long yarn can generate peak voltage as high as 225 V and current outputs of 2.4 µA. The elastic spacer functions to maintain the yarn and PET film in a separate state when no force is loaded and to adjust the response threshold and detection range by changing the spacer area. In comparison to the triboelectric force‐sensors reported previously, this yarn/film device shows a much larger detection range (24–380 N) and higher flexibility in tuning the detection range. The output voltage‐input force curves of the devices have an R2 value above 0.91, indicating the good linearity between the input force and voltage output. Moreover, a theoretical model is developed to elucidate the influence of the spacer area on the detection range and sensitivity. Such a yarn/film/spacer sensor design may be useful for the development of low‐cost force sensors for various applications.

Modeling and analysis of vibratory feeder system based on robust stick–slip motion

This study presents model and analysis of a robust one-dimensional stick–slip transportation of an object, on dry contact with an oscillating platform suspended by nonlinear leaf spring. The oscillating platform is designed and modeled such that the elastic spring constant is direction dependent. A recursive analytical solution algorithm is proposed to solve nonlinear system dynamics. The system and the input force parameters are both investigated with goal to optimize the average velocity of the object. Both experimental and analytical results showed that the stick–slip motion is highly nonlinear and sensitive to the system and input force parameters. Moreover, the simulations showed that it is feasible to design a platform with robust sets of parameters (natural frequencies) and further use the input force parameters (amplitude and driving frequency) to tune for desired average velocity, under given dry friction conditions.

Force Reconstruction at Mechanical Interfaces Using a Modal Filtering Decomposition Approach

Traditional approaches to analyzing nonlinear systems often involve assuming a specific model form and model order for the nonlinearity. These nonlinearities in a system could instead be modeled as a nonlinear force applied to an underlying linear system. Force reconstruction methods can be used to recreate this nonlinear force from measured data, allowing the system change to be quantified. A modal based force reconstruction technique has proven capable of recreating force inputs at unmeasured locations and has been successfully applied to nonlinear intermittent external contact forces in previous studies. To extend these findings, a two-beam system was designed such that intermittent contact occurs near the joint locations, resulting in correlated forces. Previous work with this methodology has not addressed correlated loading conditions, so this work extends these techniques to the localization of correlated forces beyond measured points. The methodology is first demonstrated using analytical case studies, then performed experimentally. Acceleration responses are obtained from a sparse measurement grid which does not include the contact points, so the forces are reconstructed at unmeasured locations. Estimates of the nonlinear contact forces are calculated using the force reconstruction process, which are then compared to the measured force values. Cases are presented which address intermittent contact, loosening of preloaded connections, and the reconstruction of multiple connections simultaneously. Reconstructing correlated forces beyond measured points allows for the ability to locate and estimate forces without needing to assume the locations of these forces prior to acquiring data, extending the range of applications for these techniques.

Multi-criteria, time dependent sensitivity analysis of an event-oriented, physically-based, distributed sediment and runoff model

Runoff and sediment yield predictions using rainfall-runoff modeling systems play a significant role in developing sustainable rangeland and water resource management strategies. To characterize the behavior and predictive uncertainty of the KINEROS2 physically-based distributed hydrologic model, we assessed model parameters importance at the event-scale for small nested semi-arid subwatersheds in southeastern Arizona using the Variogram Analysis of Response Surfaces (VARS) methodology. A two-pronged approach using time-aggregate and time-variant parameter importance analysis was adopted to improve understanding of the control and behavior of models. The time-aggregate analysis looks at several signature responses, including runoff volume, sediment yield, peak runoff, runoff duration, time to peak, lag time, and recession duration, to investigate the influence of parameter and input on the model predictions. The time-variant analysis looks at the dynamical influence of parameters on the simulation of flow and sediment rates at every simulation time step using the different forcing inputs. This investigation was able to address Simpson’s paradox-type issues where the analysis across the different objective functions and full data set vs. its subsets (i.e., different events and/or time steps) could yield inconsistent and potentially misleading results. The results indicated the uncertainties in the flow responses are primarily due to the saturated hydraulic conductivity, the Manning’s coefficient, the soil capillary coefficient, and the cohesion in sediment and flow-related responses. The level of influence of K2 parameters depends on the type of the model response surface, the rainfall, and the watershed size.

A dynamic force reconstruction method based on modified Kalman filter using acceleration responses under multi-source uncertain samples

A novel method for dynamic force reconstruction is developed in this paper to identify the time history of uncertain force for the linear time-invariant system, which combines the modified Kalman filter and non-probabilistic uncertainty analysis. For the force reconstruction issue, some acceleration responses are regarded as the observation information. The optimal estimation of the system state vector and unknown input force vector are deduced recursively on the basis of minimum variance unbiased estimate, along with the covariance matrices updating of force reconstruction error and state estimation error under the framework of modified Kalman filter. Considering multi-source uncertainties in inherent characteristics and external environment, the multidimensional interval model, which is transformed by the principal component analysis (PCA) method, is involved to envelope experiential samples of uncertain parameters. To enhance the accuracy and efficiency of uncertainty propagation, the Chebyshev orthogonal polynomial is adopted to approximate the unknown force and to obtain the force interval boundaries. Eventually, the validity and feasibility of the proposed methodology are clarified by three numerical examples: a spring-oscillator, a plane truss and an equivalent rudder structure. The results indicate that the proposed method can be utilized to reconstruct the uncertain force interval with the interference of system uncertainties and measurement noise.

Optimization of Underbody Blast Energy-Attenuating Seat Mechanisms Using Modified MADYMO Human Body Models.

Though energy attenuating (EA) seats for air and spacecraft applications have existed for decades, they have not yet been fully characterized for their energy attenuation capability or resulting effect on occupant protection in vertical underbody blast. EA seats utilize stroking mechanisms to absorb energy and reduce the vertical forces imparted on the occupant's pelvis and lower spine. Using dynamic rigid-body modeling, a virtual tool to determine optimal force and deflection limits was developed to reduce pelvis and lower spine injuries in underbody blast events using a generic seat model. The tool consists of a mathematical dynamic model (MADYMO)-modified human body model (HBM), basic EA seat model, and an optimizing sequence using modefrontier software. This optimizing tool may be shared with EA seat manufacturers and applied to military seat development efforts for EA mechanisms for a given occupant and designated blast severity. To optimally tune the EA seat response, the MADYMO human body model was first updated to improve its fidelity in kinematic response data for high rate vertical accelerative loading relative to experimental data from laboratory simulated underbody blast tests using postmortem human surrogates (PMHS). Subsequently, using available injury criteria for underbody blast, the optimization tool demonstrated the ability to identify successful EA mechanism critical design value configurations to reduce forces and accelerations in the pelvis and lower spine HBM to presumed noninjurious levels. This tool could be tailored by varying input pulses, force and deflection limits, and occupant size to evaluate EA mechanism designs.

Tuneable material properties of Organosolv lignin biocomposites in response to heat and shear forces

Lignin as a renewable biomacromolecule is considered as a sustainable feedstock for the generation of bioplastics and bioplastic composites. However, during thermoplastic processing, high temperature and mechanical forces are known to promote destructive bond-cleavage in a vast majority of macromolecules due to overheating and internal friction between molecular constituents. This study demonstrates that several material properties (e.g. thermal stability, mechanical properties) of biocomposites with a high Organosolv lignin content (≥50w%) can be tuned by carefully selecting thermal and mechanical energy input during compounding. Organosolv lignin obtained from ensiled grass was shown to undergo in-situ coupling reactions at temperatures below the main degradation point (<200 °C) resulting in an up to 6-fold increase in molecular weight (Mw). The results from Fourier Transform Infrared (FTIR) spectroscopy suggested the formation of ester bonds, which was ascribed to direct esterification reactions, which occur due to energy transfer in the melt phase. When subjecting the extracted lignin to prolonged compounding times, it was shown that higher coupling degrees resulted in a lignin biocomposite with increased stiffness and ultimate tensile stress of about 1800% and 40%, respectively. Temperature was shown to have the highest effect on coupling reactions, whereas the energy transfer by mechanical forces during compounding was lower and followed a non-linear behaviour. In tensile stress–strain curves, biocomposites with high energy input revealed a distinct yield point (16 MPa). Ultra-micro-hardness tests confirmed that the biocomposite became significantly stiffer in response to shear and thermal forces with a reduction in indentation creep Cit of 2.0% to a value of up to 8.5%. Organosolv lignin biocomposites obtained at higher specific energy input (EIN) through thermal energy input and shear forces showed an increased dynamic stiffness Cdyn up to 100%, which was observed by multiple step tests (MST).

General uncertainty analysis and synthesis for a precision boomed centrifuge

The general precision uncertainty of a centrifuge is suggested here to determine whether a precision centrifuge is suitable to calibrate inertial sensors. The possible centrifuge errors that affect the accuracy of the specific input forces are analyzed with three kinds of centrifuge errors identified: displacement error, angular rate error, and attitude error. Taking an accelerometer’s calibration on a centrifuge as an example, the specific force components for the three axes of a tested accelerometer are acquired using a homogeneous transformation algorithm. The impact of the uncertainty for each kind of error source on the specific force is calculated, and their contributions to the general uncertainty of the centrifuge are acquired. Through simulation, by limitation of the tolerances towards the centrifuge errors, the general uncertainty of a precision centrifuge is designed to satisfy the requirements of the pre-design in 6×10−6. And the influence of the general uncertainty on calibration accuracy of error model coefficients of accelerometer is calculated, mostly on C op . The influence of the error which accounts for a large part of the general uncertainty on the calibration accuracy is mainly studied. Simulation results show with the increase of the general uncertainty of centrifuge, its influence on the calibration accuracy of error model coefficient is greater. And when the general uncertainty is constant, the influence of the general uncertainty on the calibration accuracy can be reduced by increasing the input specific force.