Offset Displacement Research Articles

Mechanical Behavior of Buried HDPE Pipe Subjected to Surface Load: Constitutive Modeling and Finite Element Method Simulations

Abstract In this paper, the Sherwood–Frost constitutive model was first used to simulate the stress response and deformation process of buried high-density polyethylene (HDPE) pipe subjected to surface load, where parameters in this model were obtained by fitting the results of uniaxial tensile tests with different rates and the pipe–soil model was conducted in abaqus. Apparent stress concentration and large deformation are observed in pipe cross section and are closely related to the magnitude and location of surface load. The increments of surface load and offset displacement have opposite effects on the mechanical behavior of pipes. Additionally, the location of the maximum stress appears to shift from the top or bottom to the left and right sides of the pipe cross section with the increment of surface load, and the region of peak hoop stress will show a decreasing trend of counterclockwise rotation. Then, based on stress failure criterion, the relationship between the ultimate bearing capacity of the pipe and the offset displacement was determined, which decided by the angle between the ground and the line connecting load center and cross section center of pipe. Finally, an offset of 0.6 m is a value of interest. When the offset between the load position and the pipe exceeds 0.6 m, the ultimate bearing capacity of the pipe will increase significantly with the increase of the offset. The results of the above research could provide the reference for the safety evaluation and maintenance strategy of gas polyethylene pipe under the surface load.

Indenting a thick gel with a solid spherical inclusion

A spherical inclusion is embedded in a soft gel block. A vertical force is applied on the gel surface by means of a spherical indenter. The loading axis is not aligned with the inclusion but placed at a horizontal offset displacement from the inclusion. The measurement of indentation force and inclusion trajectory are compared to the computational results from two-dimensional (2D) Finite Element Analysis (FEA) simulations. A discernible instability emerges when the indentation reaches a critical depth, in accordance with the Southwell instability theory. The three-dimensional (3D) trajectory shows distinct features that were previously not captured by the 2D FEA simulations.

Taguchi–gray relational analysis of eccentricity and tilt of multilens module mount fabricated by injection compression molding

AbstractThis study utilizes the mold flow analysis technique of the injection compression molding (ICM) process, combined with the Taguchi–gray relational analysis (GRA), for process optimization analysis on the roundness of the lens holes and the flatness of the lens mount in a 4 × 4 planar multilens array mount. After manufacturing simulation analysis, the eccentricity and tilt information of the lens mount was further evaluated optically through spot diagram analysis upon inserting the same glass lenses. The results showed a positive correlation trend between roundness and flatness in structural deformation analysis, indicating that improving the overall flatness of the lens mount can enhance the roundness of the lens holes. In optical analysis, better improvements in the lens tilt angle were achieved through GRA. In conclusion, aiming to simultaneously improve the roundness of the lens holes and the overall flatness of the lens mount, the Taguchi–GRA method can achieve the optimization objectives. In terms of optical performance, by optimizing for roundness, it is possible not only to reduce the diameter of the light spot but also to simultaneously reduce the offset displacement of the light spot center on the screen. The method proposed in this paper can serve as an analytical model for the design and fabrication of plastic multilens mount.

Numerical and analytical investigations on tensile behavior of thick rubber bearings

Thick rubber bearings (TRBs) are used for the mitigation of subway-induced vibrations in over-track buildings. TRBs might be loaded in tension in tall buildings, thus their tensile behavior needs to be explored. This paper performs numerical and analytical investigations on the tensile properties of TRBs. First, constitutive laws describing the rubber material under tension beyond cavitation were developed via a two-phase softening model, using the UHYPER user subroutine in ABAQUS. Then, parametric FE analyses were carried out to explore the effects of the shape factors, the thickness of the steel shims and the offset displacement on the tensile properties of TRBs. The numerical results showed that decreasing the first and second shape factors reduced the tensile stiffness of bearings, although the influence of the first shape factor seems marginal, when it is larger than 10. The code specified steel shim thickness (2 mm) seemed adequate, while reducing it to 0.5 mm or 0.2 mm could lead to local buckling of the shims, especially for bearings of lower first shape factors. The reduction of the tensile stiffness and yield force due to shear displacement was quantified. Finally, an analytical model that captures the tensile behavior of the bearings under cyclic loading was proposed and validated on published experimental tests.

Fiber Optic Sensor Based on Lateral Offset Displacement for Water Quality Analysis in Agricultural Applications

Fiber Optic Sensor Based on Lateral Offset Displacement for Water Quality Analysis in Agricultural Applications

A Precise Hip Protection System with Multi-scale Fall Warning Algorithm Based on Offset Displacement.

Falls occur frequently in daily life and the damage to the body is irreversible. Therefore, it is crucial to implement timely and effective warning and protection systems for falls to minimize the damage caused by falls. Currently, the fall warning algorithm has shortcomings such as low recognition rates for falls and fall-risk movements and insufficient lead-time, the time before the subject impacts the floor, making it difficult for falling protection devices to function effectively. In this study, a multi-scale falls warning algorithm based on offset displacement is built, and a hip protection system is designed. The performance of the algorithm and the system is validated using 150 falling and 500 fall-risk actions from 10 volunteers. The results showed that the recognition accuracy for falling actions is 98.7% and the recognition accuracy for fall-risk actions is 99.4%, with an average lead-time of 402ms. The protection rate for falling movements reached 98.7%. This proposed algorithm and hip protection system have the potential to be applied in elderly communities, hospitals, and homes to reduce the damage caused by falls.Clinical Relevance- This study provides important reference for clinicians in analyzing fall behaviors to patients at risk of falls in clinical settings, offering valuable technical support for ensuring the safety of patients in danger of falling. It also contributes to further promoting the development of falling-prevention medical devices.

Reducing patch-like Errors in SAR offset tracking displacements using logarithmic transformation and a weighted NCC algorithm

ABSTRACT Pixel offset tracking (OT) algorithm is a useful tool for measuring large surface displacements by matching amplitudes in master and slave synthetic aperture radar (SAR) images. However, strong backscatters can cause homogeneous errors within a matching window (referred to as patch-like errors) in traditional OT processing, thereby misleading the interpretation of displacement events, especially over a small area. In this letter, we proposed an improved SAR OT algorithm to reduce patch-like errors. In which, a logarithmic transformation was firstly utilized to narrow the SAR amplitude range between strong and weak back scatterers. Strong backscatters causing patch-like errors were then statistically detected with an indicator of median absolute deviation. Finally, those strong backscatters were excluded from SAR OT processing using a weighted normalized cross-correlation scheme, in order to reduce the caused patch-like errors. Two real data tests over the Shuozhou and Yulin coal mining areas, China, suggest that the mean accuracy of the displacements estimated by the presented method improved about 30%, with respect to that estimated by the traditional OT algorithm. The proposed SAR OT algorithm offers a robust option to measure large displacements, especially over a small area, associated with anthropologic or geophysical activities.

A novel steel bulkhead based on the method of prefabrication and assembly and its first application to the Yuliangzhou immersed tunnel

Temporary bulkheads installed at the end of each tunnel element are indispensable for immersed tunnel elements to be watertight and float. Currently, welded steel bulkheads and cast-in-place concrete bulkheads have been applied in the installation of most immersed tunnels; however, these bulkheads have many inherent drawbacks. For example, existing cast-in-place concrete bulkheads are bulky and cannot be recycled after demolition. In addition, existing welded steel bulkheads, which cannot be fully reused, are installed and dismantled with a large number of on-site welding operations. Relying on the Yuliangzhou Immersed Tunnel in China, a novel steel bulkhead based on the method of prefabrication and assembly, namely, a piece-assembled steel bulkhead, was developed to address the abovementioned problems. The structural components of the new steel bulkhead applied to realize full recycling mainly include steel bulkhead panels, ethylene-propylene-diene-monomer (EPDM) sealing gaskets, steel bearings, and steel connecting bolts. The water tightness function of the new bulkhead was achieved through the compression deformation of the designed EPDM sealing gaskets inside the assembly seams, which were designed as multihole structures to save manufacturing material. Nonlinear finite element simulations were conducted to investigate the gasketed seam mechanical and sealant behavior. It was concluded that the control threshold value of gasketed seam compression displacement needed to satisfy the design requirement for a 250 kPa waterproof capacity could be taken as 15 mm, while that for seam offset displacement was set to 40 mm. To achieve the fast and efficient construction of the new steel bulkhead, a strategy of symmetrically installing and removing steel bulkhead panels piece by piece at one carriageway bore was proposed, and an automatic installation trolley that adjusts the bulkhead panel position in three directions was designed and developed. Finally, the on-site monitoring of the assembly seam displacements and the stress and deformation of the H-shaped steel beam verified that the new steel bulkhead was in a safe state and displayed good watertightness. This bulkhead was successfully applied in the Yuliangzhou Immersed Tunnel project, and this test application supports the use of these technologies in immersed tunnel construction.

Colosseum: Regression Test Prioritization by Delta Displacement in Test Coverage

The problem of test-case prioritization has been pursued for over three decades now and continues to be one of the active topics in software testing research. In this paper, we focus on a code-coverage based regression test-prioritization solution ( <inline-formula><tex-math notation="LaTeX">${{\sf Colosseum}}$</tex-math></inline-formula> ) that takes into account the position of changed (delta) code elements (basic-blocks) along the loop-free straight-line execution path of the regression test-cases. We propose a heuristic that logically associates each of these paths with three parameters: (i) the offset (displacement <i>a</i> ) of the first delta from the starting basic-block, (ii) the offset (displacement <i>c</i> ) of the last delta from the terminating basic block, and (iii) the average scattering (displacement <i>b</i> ) within all the intermediate basic-blocks. We hypothesize that a regression test-case path with a shorter overall displacement has a good chance of propagating the affects of the code-changes to the observable outputs in the program. <inline-formula><tex-math notation="LaTeX">${{\sf Colosseum}}$</tex-math></inline-formula> prioritizes test-cases with smaller overall displacements and executes them early in the regression test-execution cycle. The underlying intuition is that the probability of a test-case revealing a regression fault depends on the probability of the corresponding change propagation. The change in this context can potentially lead to an error. Extending this logic, delta displacement provides an approximation to failed error propagation. Evaluation on 20 open-source C projects from the Software-artifact Infrastructure Repository and GitHub (totaling: 694,512 SLOC, 280 versions, and 69,305 test-cases) against four state-of-the-art prioritizations reveals that: <inline-formula><tex-math notation="LaTeX">${{\sf Colosseum}}$</tex-math></inline-formula> outperforms the competitors with an overall 84.61% success in terms of 13 prioritization effectiveness metrics, majority of which prefer to execute top- <inline-formula><tex-math notation="LaTeX">$k\%$</tex-math></inline-formula> prioritized test-cases.

Compression Deformation Prediction of Chiral Metamaterials: A Compression–Shear Coupling Model

A category of metamaterials consisting of chiral cytosolic elements assembled periodically, in which the introduction of a rotatable annular structure gives metamaterials the ability to deform in compression–shear, has been a focus of research in recent years. In this paper, a compression–shear coupling model is developed to predict the compressive deformation behaviour of chiral metamaterials. This behaviour will be analysed by coupling the rotation of the annular node and the bending characteristics of ligament beam, which are obtained as a function of the length of ligament beam and the angle of rotation at the end of the beam. The shape function of the ligament beam under large deformation is obtained based on the elliptic integral theory; the function characterises the potential relationship between key parameters such as displacement and rotation angle at any point on the ligament beam. By simulating the deformation of cells under uniaxial compression, the reasonableness of the large deformation model of the ligament beam is verified. On this basis, a chiral cell-compression mechanical model considering the ductile deformation of the annular node is established. The compression–shear deformation of two-dimensional planar chiral metamaterials and three-dimensional cylindrical-shell chiral metamaterials was predicted; the offset displacements and torsion angles agreed with the experimental and finite element simulation results with an error of less than 10%. The developed compression–shear coupling model provides a theoretical basis for the design of chiral metamaterials, which meet the need for the precise control of shapes and properties.

Baseline correction of near-fault ground motion records based on the hilbert spectral analysis

A new automatic baseline correction method based on the Hilbert spectral analysis (HSA) is proposed to recover a relatively reasonable time history of baseline offset, permanent displacement, and stable peak ground motion displacement (PGD) from a raw near-fault ground motion record. This method can get rid of the selection of the start time of strong motion (corresponding to t1 in traditional methods) by an adaptive extraction procedure, then a stable PGD as well as an accurate permanent displacement can be obtained. For baseline offsets, there is no two-stage-segment assumption in this procedure, and the extracted time histories of these offsets include complex frequency changes, which is more consistent with the explanations of causes for baseline offsets. All causes of baseline offsets are treated as contaminants that exist in all frequency ranges in a record. Uncontaminated components can be extracted from the original record by the HSA, then information about strong motions can be retained as much as possible. The residual part is regarded as a heavily contaminated component of which the energy of the noise rivals that of the real ground motion. It is corrected based on only one time point. Finally, the corrected record is contributed by both of the uncontaminated and adjusted contaminated components. The HSA method, which depends on the energy distribution of original record in different frequency component, can obtain the baseline offset, PGD, and permanent displacement reasonably, stably, and automatically.

Neural Network Meta-Models for FPSO Motion Prediction From Environmental Data With Different Platform Loads

The current design process of mooring systems for Floating Production, Storage, and Offloading units (FPSOs) depends on the availability of the platform’s mathematical model and the accuracy of dynamic simulations. These simulations then provide the FPSO’s time series motion which is evaluated according to design constraints. This process can be time-consuming and present inaccurate results due to the mathematical model’s limitations and the overall complexity of the vessel’s dynamics. We propose a Neural Simulator, called NeuroSim, a set of data-based surrogate models with environmental data as input, each model specialized in predicting different motion statistics relevant to mooring system design: Maximum Roll, Platform Offset, and Fairlead Displacements. The surrogate models are trained by current, wind, and wave data given in 3 hours periods at a Brazilian Offshore Basin from 2003 to 2010, and the associated dynamic response of a spread-moored FPSO is obtained through time-domain simulations using the Dynasim software. Hyperparameter Optimization techniques are performed to obtain optimal Artificial Neural Network (ANN) models specialized in different platform drafts. Finally, the proposed models are shown to correctly capture platform dynamics, providing good results when compared to motion statistics obtained from Dynasim. We conclude that an ANN surrogate model can be trained directly on actual measured metocean conditions and corresponding FPSO motion statistics to provide increased accuracy and reduced computational time over traditional methods based on dynamic simulation. Moreover, the proposed architecture can be integrated into an automated learning framework: The data-based surrogate models can be continuously fine-tuned and updated with newly measured data, improving accuracy over time.

Resolving co- and early post-seismic slip variations of the 2021 MW 7.4 Maduo earthquake in east Bayan Har block with a block-wide distributed deformation mode from satellite synthetic aperture radar data

On 21 May 2021 (UTC), an <i>M</i>_W 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau. The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake, and especially in proximity to the seismic gaps on the east Kunlun fault. Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake. Range offset displacements depict clear surface ruptures with a total length of ~170 km involving two possible activated fault segments in the earthquake. Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust. The well-resolved slip variations are characterized by five major slip patches along strike and 64% of shallow slip deficit, suggesting a young seismogenic structure. Spatial–temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations, and are well explained by time-dependent afterslip models. Analysis of Global Navigation Satellite System (GNSS) velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block, but exhibits significant lateral heterogeneities, as evidenced by magnetotelluric observations. The block-wide distributed deformation of the east Bayan Har block along with the significant co- and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults, especially the Tuosuo Lake and Maqên–Maqu segments of the Kunlun fault that are known as seismic gaps.

Fast Thermal Actuators for Soft Robotics.

Thermal actuation is a common actuation method for soft robots. However, a major limitation is the relatively slow actuation speed. Here we report significant increase in the actuation speed of a bimorph thermal actuator by harnessing the snap-through instability. The actuator is made of silver nanowire/polydimethylsiloxane composite. The snap-through instability is enabled by simply applying an offset displacement to part of the actuator structure. The effects of thermal conductivity of the composite, offset displacement, and actuation frequency on the actuator speed are investigated using both experiments and finite element analysis. The actuator yields a bending speed as high as 28.7 cm-1/s, 10 times that without the snap-through instability. A fast crawling robot with locomotion speed of 1.04 body length per second and a biomimetic Venus flytrap were demonstrated to illustrate the promising potential of the fast bimorph thermal actuators for soft robotic applications.

Crashworthiness index of honeycomb sandwich structures under low-speed oblique impact

It is expected to quantitatively determine the crashworthiness of honeycomb sandwich structures in engineering. However, it is challenging due to diverse cell features, hybrid component materials, as well as varied types of impact load. In this study, two dimensionless indexes (i.e., horizontal dent offset displacement per unit depth ϕ and the ratio of horizontal to vertical energy absorption η) are proposed for sandwich structures based on the mechanical response characteristics (deformation and energy absorption) of sandwich structures under low-speed oblique impact. Unlike conventional crashworthiness indexes such as dent depth, specific energy absorption, damage area, etc., the proposed indexes take into account the influence of impact angle (θ) on the mechanical behavior of sandwich structures. Multiple sets of simulation of honeycomb sandwich structures, including conventional hexagonal honeycombs, honeycomb-filled structures and negative Poisson's ratio structures, obliquely impacted (θ varies from 15° ~ 75°) by a rigid body are performed by using the finite element method, whereby the crashworthiness index values of all the sandwich structures are obtained. The index values (ϕ and η) become smaller as the crashworthiness is enhanced (where the wall thickness of the sandwich structure is thickened from 0.02 ~ 0.1 mm). It manifests that the proposed indexes can capture the crashworthiness of sandwich structures under low-speed oblique impact reasonably well. In addition, the proposed indexes can more clearly distinguish the crashworthiness of sandwich structures of different configurations than conventional indexes. The index values (ϕ and η) show that the oblique crashworthiness of the negative Poisson's ratio structure, hexagonal honeycomb, and honeycomb-filled structure becomes stronger in order.

Fast approximation algorithm to noise components estimation in long-term GPS coordinate time series

Understanding the noise content of the Global Positioning System (GPS) coordinate time series is a prerequisite for a realistic assessment and uncertainty of unknown parameters. Variance component estimation methods [e.g., restricted maximum likelihood estimator (REML)] are used to assess the noise content of GPS coordinate time series. For large-scale data, namely over a wide range of spatial and temporal scales, the previous methods’ efficiency could significantly improve. Meanwhile, the estimation method, including repeated inversion of large matrices, has led to intensive computations and large storage requirements. By quantifying the REML estimator by decorrelation property of discrete wavelet transformation, the current research has offered FREML (fast REML) for accurate and fast approximation of noise content. For evaluating the method’s efficiency, 360 synthetic daily time series with different lengths $$N=2048$$ , 4096, and 8192 observation epochs were used. The time series composed of linear trends, periodic signals, offsets, transient displacements, gaps (up to 10%), and a combination of white, flicker, and random walk noises. The FREML algorithm’s outcomes were compared with existing software that uses a maximum likelihood approach to quantify the uncertainties (e.g., Hector). The results indicated that both methods provided equivalent results for noise components, unknown parameters (rate, offset, and transient displacement), and their uncertainties. Moreover, the FREML method reduced the computation time by a factor of 2–14 compared to Hector software, depending on the amount of data and missing epochs. For more assessment of the method, the FREML method was applied to the 36 real time series with noise models as (i) white plus flicker noise and (ii) combination of white, flicker, and random walk noises. The results demonstrated that the two methods’ outcomes were close, and the FREML method speeded up the estimation of noise and unknown parameters.

Robotic constant force grinding control based on grinding model and iterative algorithm

PurposeThe purpose of this paper is to propose a robot constant grinding force control algorithm for the impact stage and processing stage of robotic grinding.Design/methodology/approachThe robot constant grinding force control algorithm is based on a grinding model and iterative algorithm. During the impact stage, active disturbance rejection control is used to plan the robotic reference contact force, and the robot speed is adjusted according to the error between the robot’s real contact force and the robot’s reference contact force. In the processing stage, an RBF neural network is used to construct a model with the robot's position offset displacement and controlled output, and the increment of control parameters is estimated according to the RBF neural network model. The error of contact force and expected force converges gradually by iterating the control parameters online continuously.FindingsThe experimental results show that the normal force overshoot of the robot based on the grinding model and iterative algorithm is small, and the processing convergence speed is fast. The error between the normal force and the expected force is mostly within ±3 N. The normal force based on the force control algorithm is more stable than the normal force based on position control, and the surface roughness of the processed workpiece has also been improved, the Ra value compared with position control has been reduced by 24.2%.Originality/valueAs the proposed approach obtains a constant effect in the impact stage and processing stage of robot grinding and verified by the experiment, this approach can be used for robot grinding for improved machining accuracy.

Study of a fiber spectrometer based on offset fusion.

A near-infrared spectrometer based on offset fused multimode fiber (MMF) is investigated in this study. The light spectrum is recovered by analyzing the speckle images when light is passing through the MMF. In order to generate adequate speckles, a polarization maintaining fiber (PMF) and a 30 cm long MMF are fused with a vertical offset. Seven different offset displacements are implemented in the fiber fusion. The follow-up experiments show that the fiber offset fusion has a significant influence on the spectral correlation and the resolution. Larger offset fusion can excite more high-order modes in the MMF, and it greatly improves the spectrometer's performance. The simulation results also show that more modes are excited in MMF, and the increase of mode number leads to lower correlation coefficients of the neighboring spectral channels. However, large offset fusion increases the fusion and the insertion loss of the whole system, which may bring difficulties in the low-light cases. In addition, an image denoising algorithm based on dynamic threshold filtering and a spectral reconstruction algorithm originated from complete orthogonal decomposition were used to remove the speckle pattern noise and recover the spectrum. The final speckle-based spectrometer has a spectral resolution of 0.6∼0.016nm depending on the different offset fusions.

Design and experimental research of superconducting magnetic bearing for helium cold compressor

In the large-scale superfluid helium cryogenic refrigeration system, the helium cold compressor faces the complex operating conditions of low temperature, high speed and sub-atmospheric pressure. The radial type high temperature superconducting (HTS) bearing of inner rotor and outer superconducting stator has the advantages and characteristics that they are suitable for being used in the helium cold compressor. Combining with the structure and operating parameters of a successful application of centrifugal active magnetic bearings in helium cold compressor, the design of radial HTS magnetic bearings considering bearing levitation performance and rotor dynamic performance was carried out. In order to ensure the accurate measurement of the rotor load and the rotor offset displacement, a performance measurement platform for the HTS magnetic bearing is built, and accurately weighed load rings and differential measurement method are used. The measured axial levitation force is 77 N when the offset displacement is 0.1 mm. And the axial stiffness is 771 N/mm and radial stiffness is about 385.5 N/mm in the measuring range. The first bending mode critical speed of the rotor system can reach 74,108 rpm. The designed HTS magnetic bearing system can provide sufficient levitation force and support stiffness for the practical application of helium cold compressor system. The research work provides a guiding for the application of HTS magnetic bearings in helium cold compressor.

Development and control of a hybrid active mount module for precision stages.

In recent years, precision stages, which are widely used in many industrial fields, have been required to have a higher speed, larger size, and higher precision to help realize higher productivity and product quality. High-performance positioning techniques for inspection and production equipment are classified as one of the most challenging technologies. Vibration control is crucial to realize high-precision positioning technologies. In a precision system, various vibrations exist, which act as disturbances and can degrade the system performance. Minimizing the vibrations generated by the system can, thus, help improve the accuracy of system positioning. This paper proposes a hybrid active mount module for a precision stage. The developed module improves stage performance by reducing the base vibration arising from the floor, minimizing the vibration caused by the driving linear motors of the precision stage, and reducing the settling time by compensating the offset displacement due to the nonlinearity of the passive mount during stage driving. The prototype design is presented herein, and the experimental results demonstrate the potential of the developed device. The developed system is expected to effectively improve the stage performance by controlling the various causes of vibration.