Single Spring Research Articles

Rope tension analysis based on single spring model against elevator rope

Elevators run vertically by suspension ropes, therefore each rope has to be adjusted correctly to fulfill each tension balance. That contributes to establish a long life against elevator ropes. If a groove wear of the traction sheave causes difference against other grooves, the difference induces rope tension fluctuation while changing the car position. Conventional elevator models to evaluate the rope tension have not considered the detailed winding behavior of the rope on the sheave. As the winding amount of the rope contains the rope deformation, the deformation should be considered to evaluate the rope length and the rope tension in an elevator tension model. This paper shows a simple elevator model with a single spring model against the rope. The derived model can not only calculate the appropriate winding amount against the rope spring model, but also get a faster solution even though the elevator system has a complicated roping configuration. The proposed simulation model is validated by experiments.

Two new species of Pyrgulopsis Call amp; Pilsbry, 1886 (Mollusca: Caenogastropoda: Hydrobiidae) from springs in the Rio Grande watershed in Texas.

Pyrgulopsis Call Pilsbry, 1886 is a genus of small (<5 mm) spring snails, usually endemic to single freshwater springs. Two new populations of Pyrgulopsis found in very small, isolated springs and spring runs in the mainstem Rio Grande watershed of western Texas are distinguished from congeners. Mitochondrial and nuclear sequences, morphometrics, and morphological characteristics support Pyrgulopsis rubra sp. nov. and Pyrgulopsis harrymilleri sp. nov. as distinct from other known Pyrgulopsis species, including the geographically proximate P. metcalfi.

Reducing agriculture irrigation water consumption through reshaping cropping systems across China

The disparity in unit irrigation water consumption (UIWC) of different cropping systems provides an opportunity to reduce total irrigation water consumption (TIWC) by optimizing cropping systems. However, the UIWC for diverse cropping systems has neither been systematically quantified nor been optimized at a national scale. Here, we quantify the cropping system-specific UIWC and TIWC for the major cropping systems in China during 2014-2018 and estimate the potential of TIWC reduction by optimizing the cultivated areas of 17 cropping systems in each prefecture. The TIWC is about 154.1 km3 yr−1 for Chinese cropping systems, mainly including single rice (25.8%), early-late rice (16.6%), winter wheat-summer maize (13.9%), single spring maize (12.5%) and cotton (9.4%). Optimizing cropping systems by increasing the cultivation areas of winter wheat-summer maize, spring rape, single summer maize, single spring maize and cotton, in the meantime reducing those for single winter wheat, single rice and soybean, can reduce the TIWC by 5.3% ±1.6% in China and by more than 10% in 23.9% of the prefectures, especially in the North China Plain and Southwest China. The water-saving potential is highly influenced by irrigation water availability and minimum crop production limitation. Our findings provide a novel framework to optimize cropping systems and minimize TIWC without compromising food security and economic benefit, which can accelerate realization of water-saving agriculture.

Discharge variation of multiple springs associated with a fractured aquifer

Springs are important source of fresh water for many regions of the world. Most mathematical models simulating spring discharge are linear and non-linear reservoir-based models that are simple and easy to use. They, however, suffer from oversimplification and a lack of physical processes that limit their applicability. The goal of this work is to present process-based analytical model of discharge variation of multiple springs associated with a rectangular fractured aquifer subjected to arbitrary recharge. The solution is obtained via Laplace and Fourier transformations along with the superposition principle and image well method for a constant flux point sink. Then the constant head point sink solution representing a single spring is obtained from the constant flux point sink solution. Finally, the constant head point sink solution is extended to simulate the multiple constant head sinks (or springs) utilizing the principle of superposition and matrix solution. The solution considers the vertical anisotropy of fractures, the inter-porosity flow between fractures and matrix blocks and the instantaneous gravity drainage of the water table. The results of this study are presented in the form of dimensionless discharge-time curve and dimensionless spring depletion volume-time curves. The influences of aquifer geometric and hydraulic parameters on spring discharge variation are explored. The presented model can be utilized to simulate the discharge variation of multiple springs depleting a fractured aquifer, to estimate the hydraulic parameters of the aquifer utilizing the discharge data of springs, and to evaluate the dynamic storage volume of multiple springs depleting a fractured aquifer, among other applications.

3D spring-based piezoelectric energy generator

Well-defined design and fabrication of piezoelectric energy generators are required for surrounding environment energy harvest, capable of providing sustainable, renewable energy for future life. Herein, we present a 3D piezoelectric spring in a sandwich structure mainly constituted of a flexible Al electrode, electrospun PVDF film, and a Pt electrode, where the inside commercial springs act as a 3D structural foundation. The resulting 3D piezoelectric spring exhibits its potential as a multifunctional sensor to detect strain, speed, frequency, and resistance. It is further bridged with LED/capacitor by rectifier for illumination and charging, enabling highly efficient environment energy harvest and storage. The parallel connection of three piezoelectric springs exhibits an output voltage of 7.2 V and output current of 300 nA for 21 MΩ resistance, which are three times of single piezoelectric spring, demonstrating the possibility of scale‐up. This work provides an effective strategy for 3D piezoelectric spring fabrication, and new insights for spring-based piezoelectric energy generators, devoting to energy harvesting technology.

Cultivable Winogradskyella species are genomically distinct from the sympatric abundant candidate species

Winogradskyella is a genus within the phylum Bacteroidetes with a clear marine origin. Most members of this genus have been found associated with marine animals and algae, but also with inorganic surfaces such as sand. In this study, we analyzed genomes of eleven species recently isolated from surface seawater samples from the North Sea during a single spring algae bloom. Corresponding metagenomes yielded a single Candidatus species for this genus. All species in culture, with the exception of W. ursingii, affiliated with a Winogradskyella lineage characterized by large genomes (~4.3 ± 0.4 Mb), with high complexity in their carbohydrate and protein degradation genes. Specifically, the polysaccharide utilization loci (PULs) were diverse within each individual strain, indicating large substrate versatility. Although present in the North Sea, the abundances of these strains were at, or below, the detection limit of the metagenomes. In contrast, the single species, classified as Candidatus W. atlantica, to which all North Sea MAGs belonged, affiliated with a lineage in which the cultivated representatives showed small genomes of ~3.0–3.5 Mb, with the MAGs having ~2.3 Mb. In Ca. W. atlantica, genome streamlining has apparently resulted in the loss of biosynthesis pathways for several amino acids including arginine, methionine, leucine and valine, and the PUL loci were reduced to a single one for utilizing laminarin. This as-yet uncultivated species seems to capitalize on sporadically abundant substrates that are released by algae blooms, mainly laminarin. We also suggest that this streamlined genome might be responsible for the lack of growth on plates for this Candidatus species, in contrast to growth of the less abundant but coexisting members of the genus.

Vegetation Response of a Dry Mixed Prairie to a Single Spring or Fall Burn

Climate change may make semiarid grasslands increasingly prone to wildfire. We studied fire seasonality and growing season condition effects on a semiarid grassland in Southern Alberta, Canada. Plots were hand-torched in either fall or spring. Response variables estimated included plant composition and diversity, plant height, aboveground net primary production (ANPP), and forage nitrogen quality. The experiment was replicated over three consecutive growing seasons, and each replicate was monitored for 3 yr thereafter. Drought conditions occurred during two of the six growing seasons. Fall fires appeared to be hotter than spring fires based on a greater fuel mass (standing litter) and exposed the soil surface to a longer period without the benefit of standing litter over winter. Although this grassland is resilient to fire, compared with spring-burned grasslands, the species composition, ANPP, and leaf length of grasses of fall burned communities took a longer time to recover to preburn conditions. Our results suggest that spring-burned grasslands should not be grazed for 1 year post burn to allow time for recovery of ANPP and litter. However, given that ANPP of fall-burned communities also exhibited higher nitrogen concentration that may make the forage more palatable to livestock, and that these communities were more severely impacted, it seems prudent to delay their grazing for more than 1 year to prevent overgrazing. The negative impacts of fire on ANPP may be ameliorated with above-average precipitation in June, which may be forecast during an El Niño year.

Identification and Machine Learning Prediction of Nonlinear Behavior in a Robotic Arm System

In this study, the subject of investigation was the dynamic double pendulum crank mechanism used in a robotic arm. The arm is driven by a DC motor though the crank system and connected to a fixed side with a mount that includes a single spring and damping. Robotic arms are now widely used in industry, and the requirements for accuracy are stringent. There are many factors that can cause the induction of nonlinear or asymmetric behavior and even excite chaotic motion. In this study, bifurcation diagrams were used to analyze the dynamic response, including stable symmetric orbits and periodic and chaotic motions of the system under different damping and stiffness parameters. Behavior under different parameters was analyzed and verified by phase portraits, the maximum Lyapunov exponent, and Poincaré mapping. Firstly, to distinguish instability in the system, phase portraits and Poincaré maps were used for the identification of individual images, and the maximum Lyapunov exponents were used for prediction. GoogLeNet and ResNet-50 were used for image identification, and the results were compared using a convolutional neural network (CNN). This widens the convolutional layer and expands pooling to reduce network training time and thickening of the image; this deepens the network and strengthens performance. Secondly, the maximum Lyapunov exponent was used as the key index for the indication of chaos. Gaussian process regression (GPR) and the back propagation neural network (BPNN) were used with different amounts of data to quickly predict the maximum Lyapunov exponent under different parameters. The main finding of this study was that chaotic behavior occurs in the robotic arm system and can be more efficiently identified by ResNet-50 than by GoogLeNet; this was especially true for Poincaré map diagnosis. The results of GPR and BPNN model training on the three types of data show that GPR had a smaller error value, and the GPR-21 × 21 model was similar to the BPNN-51 × 51 model in terms of error and determination coefficient, showing that GPR prediction was better than that of BPNN. The results of this study allow the formation of a highly accurate prediction and identification model system for nonlinear and chaotic motion in robotic arms.

Development of disc spring stack containment methods for vibration isolation

Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from low frequency vibrations. However, the stroke of a single disc spring is too low for most applications, and springs are stacked to increase the displacement. A method to contain the isolator stack then becomes critical for practical uses. Many challenges in developing these containment methods have been identified and can be collectively described as how to appropriately contain the stack without affecting isolation performance. In this work, three designs are considered: a retaining ring design, tube and shaft design, and zero poisson ratio sleeve design. Disc spring stacks with containment method are built, and load-deflection curves are measured and compared with standalone stacks. Under quasi-static compression testing, each containment method has minimal effect on the standalone stack load-deflection curve. However, significant differences in isolation performance are observed in vibration testing and found to depend on characteristics such as lateral stability, lateral strength, and degrees of freedom. Lastly, advantages, disadvantages, and appropriate applications for each containment method are summarized. The conclusions of this work are that containment method is an important variable in the application of disc spring isolators and robust, versatile containment designs have been demonstrated.

Crawling–jumping synergic bioinspired robots harnessing electroactive bistable actuators by adjusting mechanical responses and forces

Mechanical responses and forces are two urgently concerning factors in actuators. Actuation mechanisms inspired by natural systems are increasingly common, especially the snap-through mechanism in cascading power-induced bioinspired systems. Here, we propose an electroactive bistable actuator that can synergize the fast mechanical response and high mechanical forces. It is constructed by combining a single pretension spring (i.e., p-spring) bistable linkages as a “skeletal spine” and twinned SMA-springs (i.e., s-springs) as “skeletal muscle.” The p-spring connected to linkages plays a role in determining elastic instabilities threshold, while the coupled s-springs serve as actuation generators. The system shows a rapid and switchable snap-through between two stable states as each s-spring is individually actuated. The p-spring and the voltage exerted on s-springs are the two key parameters influencing response time (0.05 s) and mechanical forces (3.4 N). Additionally, synergic movements between crawling and jumping are enabled, which benefit from the ease of control of the exerted voltage and manual convenience in customized pretension. Our prototype can achieve a linear locomotion speed of 0.56 mm/s, a jump height of 95 mm, and a horizontal distance of 150 mm. We look forward to providing a new design paradigm in mechanical systems requiring fast dynamic properties and brilliant static capabilities.

Nitrogen requirements of first‐year small grains after alfalfa

AbstractSmall grains are commonly grown in rotation following alfalfa (Medicago sativa L.) in Utah and the Intermountain West, especially during drought years, as they require less irrigation than corn (Zea mays L.). Several studies have shown that corn following alfalfa rarely needs N fertilizer, yet few have evaluated the N needs of small grains. Objectives of this research were to determine whether N fertilizer is needed to economically optimize the yield and quality of first‐year soft white winter wheat (Triticum aestivum L.) following alfalfa and whether the response could be predicted. Fertilizer trials (four replications of up to 13 N rates) were conducted on 12 first‐year wheat sites in Utah during 2018–2019. Three sites in 2018 with spring soil nitrate concentrations ≥17 mg kg–1 required no N to improve yield. The remaining nine sites in 2019 with soil nitrate ≤13 mg kg–1 all had yield, test weight, and protein responses to fertilizer N. Economic optimum N rates for optimal yield, protein, and test weight across the nine sites in 2019 were 22 kg N ha–1 (18%) greater for split applications (fall and spring) compared with single spring N across various wheat/N price ratios. Delaying N applications until flag leaf decreased yield in 2019 provided no economic protein or test weight advantages. Results indicate that 96–147 kg N ha–1 (depending on price ratio) should be applied as a single application in the spring to first‐year soft white winter wheat following alfalfa only when spring soil nitrate is &lt;17 mg kg–1.

Stability Design of Air Vibration Isolation Device for a High Power Density Main Engine

In order to improve the alignment stability of the air vibration isolation device of a high-powered main engine, we established a mechanical model for the air vibration isolation system and analyzed the alignment deviation of the device and the vibration decoupling conditions of the system. Additionally, an optimized design method for the dual-direction support of the air vibration isolators positioned symmetrically on the main engine was proposed. The resultant design showed that when compared to the conventional inclined support of air springs for the main engines onboard ships, the dual-direction support design proposed in this paper for air vibration isolation could eliminate the adverse effect of the output torque reaction on the alignment of the main engine and decouple the system to reduce the number of peaks in the frequency response of vertical force transmission. The optimized design could effectively improve the alignment performance of the device for tilted or swinging operating conditions and maintain the good alignment stability of the device when a single vertical support air spring fails. A single vertical support air spring failure mainly affects the stability of the main engine under the reaction of the output torque, especially the air springs arranged in the corner, while the air springs arranged in the middle have no effect. The optimized design could also improve the vibration isolation performance. This is important for the design of air spring vibration isolation devices for high power density main engines.

Optimization of selective laser etching (SLE) for glass micromechanical structure fabrication.

In this work, we show how femtosecond (fs) laser-based selective glass etching (SLE) can be used to expand capabilities in fabricating 3D structures out of a single piece of glass. First, an investigation of the etching process is performed, taking into account various laser parameters and scanning strategies. These results provide critical insights into the optimization of the process allowing to increase manufacturing throughput. Afterward, various complex 3D glass structures such as microfluidic elements embedded inside the volume of glass or channel systems with integrated functional elements are produced. A single helix spring of 1 mm diameter is also made, showing the possibility to compress it by 50%. Finally, 3D structuring capabilities are used to produce an assembly-free movable ball-joint-based chain and magnet-actuated Geneva mechanism. Due to minimized friction caused by low (down to 200 nm RMS) surface roughness of SLE-produced structures, the Geneva mechanism was shown to be capable of rotating up to 2000 RPM.

Estimation of Heterosis and Combining Ability for Yield, Yield Component Using Line × Tester Methods in Maize (Zea Mays L.)

This study was initiated with the objective of estimating heterosis, combing ability of selected conventional maize genotypes, comparison between hybrids, parents, and testers. Ten maize genotypes were selected (three testers and seven lines). The crosses were done in a Line × Tester mating design to produce 21 F1 single spring hybrids during 2018. The experiment was conducted. At fall season 2019; thirty-one genotypes (21 crosses + 3 tester + 7 lines) were sown in Randomized Complete Block design (RCBD) with three replications at Gerdarash research station/College of Agricultural Engineering Sciences, Salahaddin University, Erbil. The analysis of variance confirmed that the mean squares due to genotypes were highly significant for all studied characters, the tester parent (Talar) showed maximum value for tasseling number, while the parent Mst4279 recorded the maximum value for no. of days to 50% tasseling and silking and no. of ears/plant. The hybrid 232Dss × Talar showed maximum positive heterosis for plant height and ear length. The general combining ability variance was higher than specific combining ability for the plant height, ear height, 300 grain weight (g) and tassel branch number. These characters were identified to be under the control of additive-gene. Generally, the superior maize F1 hybrid L1×T2 is recommended to be taken to large-scale multilocational trials prior to commercial cultivation in Kurdistan region.

Copepods (Crustacea: Copepoda) in the Belgian part of the North Sea: Trends, dynamics and anomalies

Copepods are a dominant component of mesozooplankton communities and are unambiguously important in marine food webs. Climate change and rising sea surface temperatures are likely to induce biogeographical range shifts and phenological changes for all zooplankton species, which include copepods. Consequently, consistent time-series are fundamental to monitor the status of plankton communities and predict future changes that can greatly affect the whole food-chain. Here, a recent time series (2014–2020) of image-based copepod abundance data from the Belgian Part of the North Sea has been explored and compared with previously collected (2009–2010) microscopy-based datasets for the same study area. The time series revealed distinct discrepancies in copepod phenology, abundances and total biomass between nearshore and offshore regions. The nearshore area was characterised by an altered copepod dynamics through time, with the occurrence of a single annual spring peak in both abundance and total biomass, and no autumn peak usually described and present in that area. Conversely, the autumn peak was clearly observed at the offshore stations, together with a distinct additional early spring peak in comparison to the nearshore and midshore regions which has not been documented before. Remarkable anomalies were detected within the time-serie of copepod for both abundance and biomass, notably in autumn of 2018 and in a lesser extend in 2014 and 2019, with values dropping to near-zero for the nearshore stations. The various heat waves during the summer periods of these years are considered potential causes for these copepod decreases, since they corresponded to the physiological thermal limit of many copepods species known to be present in the area. These heat waves events could have also favoured predators of copepods such as jellyfishes as well as enhancing the occurrence of d harmful algal blooms. Both anomalies in 2018 and 2019 actually coincided with important phytoplankton autumn blooms. The results from this copepod time-series analysis illustrates the changes affecting this essential marine trophic level and highlights the value and relevance of copepod long-term data series in the context of climate change and ecosystem management.

Nonlinear oscillations of electrically driven aniso-visco-hyperelastic dielectric elastomer minimum energy structures

In view of their unique shape morphing behaviour, dielectric elastomer-based minimum energy structures (DEMES) have received an increasing attention in the technology of electroactive soft transduction. Because several of them undergo a time-dependent motion during their operation, understanding their nonlinear dynamic behaviour is crucial to their effective design. Additionally, in the recent past, there has been a growing scientific interest in imparting anisotropy to the material behaviour of dielectric elastomers in view of ameliorating their actuation performance. Spurred with these ongoing efforts, this paper presents an analytical framework for investigating the nonlinear dynamic behaviour of aniso-visco-hyperelastic DEMES actuator with an elementary rectangular geometry. We use a rheological model comprising two Maxwell elements connected in parallel with two single spring elements for modelling the material behaviour of the DE membrane. The governing equations of motion for the underlying non-conservative system are then derived using the Euler–Lagrange equation. The proposed model is used for building insights into the attainable equilibrium states, periodicity of the response as well as the resonant behaviour of the DEMES actuator over a feasible range of anisotropy and viscosity parameters. Our results reveal that the DEMES with hyperelastic material properties exhibits a supercritical pitchfork bifurcation of equilibrium state which is further accelerated in terms of attained equilibrium angle due to membrane anisotropy. A significant enhancement in the equilibrium angle attained by the structure with the extent of membrane anisotropy parameter is observed, indicating a favourable impact of material anisotropy. Poincare maps and phase-portraits are presented for assessing the periodicity of the nonlinear oscillations. The frequency response of the actuator for a combined DC and AC load indicates an upsurge in the resonant frequency with an increase in anisotropy parameter. The underlying analytical model and the trends presented in this study can find their potential use in the design and development of the futuristic anisotropic DEMES actuators subjected to time-dependent actuation.

A Hydraulic Pump Fault Diagnosis Method Based on the Modified Ensemble Empirical Mode Decomposition and Wavelet Kernel Extreme Learning Machine Methods.

To address the problem that the faults in axial piston pumps are complex and difficult to effectively diagnose, an integrated hydraulic pump fault diagnosis method based on the modified ensemble empirical mode decomposition (MEEMD), autoregressive (AR) spectrum energy, and wavelet kernel extreme learning machine (WKELM) methods is presented in this paper. First, the non-linear and non-stationary hydraulic pump vibration signals are decomposed into several intrinsic mode function (IMF) components by the MEEMD method. Next, AR spectrum analysis is performed for each IMF component, in order to extract the AR spectrum energy of each component as fault characteristics. Then, a hydraulic pump fault diagnosis model based on WKELM is built, in order to extract the features and diagnose faults of hydraulic pump vibration signals, for which the recognition accuracy reached 100%. Finally, the fault diagnosis effect of the hydraulic pump fault diagnosis method proposed in this paper is compared with BP neural network, support vector machine (SVM), and extreme learning machine (ELM) methods. The hydraulic pump fault diagnosis method presented in this paper can diagnose faults of single slipper wear, single slipper loosing and center spring wear type with 100% accuracy, and the fault diagnosis time is only 0.002 s. The results demonstrate that the integrated hydraulic pump fault diagnosis method based on MEEMD, AR spectrum, and WKELM methods has higher fault recognition accuracy and faster speed than existing alternatives.

Finite element simulation of frontal plane adaptation using full-foot, split-toe and cam-linkage designs in prosthetic feet.

ABSTRACT Introduction People with lower-limb amputation have problems with balance, falls, residual limb symptoms, functional mobility, and the need for cognitive attention during gait. Insufficient prosthetic foot frontal plane adaptability may be partly responsible. Theoretically, prosthetic foot design should allow smooth forward motion of the body mass with minimal correction despite initial ground-foot contact geometry. The purpose of this study is to determine if a cam-linkage articulation, designed for frontal plane prosthetic foot adaptability, improves forward motion on cross-slopes compared with single (full-foot) or double (split-toe) cantilever spring designs, using finite element simulation. Materials and Methods Model construction (material data, geometry, and mesh) and simulations were performed using Ansys LS-Dyna. The cam-linkage mechanism was based on a crossed four-bar linkage mechanism to provide frictionless frontal plane rotation. The cam-linkage was placed in series with a full-foot or a split-toe prosthetic foot and either locked or unlocked during stance phase of simulated gait on level surfaces and 15-degree cross-slopes. The simulation was initiated with foot flat and a proximal mass having a forward velocity of 1 m/s. Rotations and translations were calculated for the proximal mass and mediolateral contact forces at the proximal pylon–body mass connection and were calculated to determine the theoretical effect of the frictionless cam-linkage prosthetic foot on the socket interface. Primary outcomes were lateral deviation, vertical displacement, frontal plane rotation, change in forward velocity (percentage of initial) of the body mass, and maximum and average forces at the pylon–body mass connection. Results During the stance phase of gait on the 15-degree cross-slope, with the cam-linkage locked, the split-toe reduced lateral displacement compared with the full-foot prosthetic foot by 33%. The frictionless cam-linkage decreased lateral displacement by 67% for the full-foot and 50% for the split-toe variations. Vertical displacement and forward velocity were increased by the split-toe locked variation (7.4 mm and 3%, respectively) and also increased with the cam-linkage (7.6 mm and 1.5%, respectively). Frontal plane rotation was reduced with full-foot, frictionless cam-linkage compared with other variations. The frictionless linkage reduced average mediolateral forces at the pylon–body mass connection by approximately one-third compared with a locked linkage with either a full-foot or split-toe variation. Conclusions This finite element simulation study shows that a frictionless cam-linkage with frontal plane adaptability integrated into a prosthetic foot improved mediolateral forces, displacement, and frontal plane angular rotation of the proximal pylon compared with a locked linkage during the stance phase of gait when in contact with a 15-degree cross-slope. These findings may have implications for people using lower-limb prostheses if future studies demonstrate improved gait over uneven ground, or reduced pain, skin breakdown, and the work of walking.

Damped Timber Shear Wall: Shake-Table Tests and Analytical Models

Light-timber frames, using plywood (PW), exhibit a pinched hysteresis response, and their energy absorption capacity is limited. The energy-dissipation capacity can be enhanced using energy-dissipation mechanisms. In this paper, two wood-friction-based connectors, with wood-plywood-wood (WPW) and wood-steel-wood (WSW), are utilized. Reverse-cyclic static load tests have shown that the WPW and WSW wall systems have nondegrading and stable hysteretic curves. In this paper, through shake-table tests, performance of WPW, WSW, PW, and WSW-PW coupled wall systems are investigated. As expected, the shake-table results indeed showed nondegrading hysteretic curve responses of WPW and WSW wall systems. Furthermore, a phenomenological model, where nonlinear behavior of the shear wall is reduced to a single spring element, is proposed for the wall systems. The nondegrading wall system (WPW, WSW) is modeled using the Bouc-Wen hysteretic model and the PW is modeled using the Pinching4 hysteretic model. Overall, there is good agreement between the test and analytical models. Results of the experimental test indeed show the utility of the new wall systems.

Connecting the grain-shearing, creep, and squirt flow models for wave propagation in the seabed.

The generalized creep and squirt flow models are shown to be stationary creep processes. A fractional exponent is used to develop a new generalized squirt flow model. The responses of the grain-shearing and generalized creep models are identical, although based on entirely different concepts: a single spring and time-varying damper versus a continuous distribution of parallel Maxwell elements. The random structure of marine sand is more consistent with the latter, implying absence of strain-hardening. The generalized squirt flow model has a high frequency cutoff suited to practical systems, limited by the speed with which underlying physical changes can occur.