Single Degree Research Articles

Seismic assessment and qualification of acceleration-sensitive nonstructural elements through shake table testing: Reliability of testing protocols and reliability-targeted safety factors

Shake table testing represents the best option for assessing and qualifying acceleration-sensitive nonstructural elements (NEs). Several testing protocols are defined in regulations and codes and implemented in the literature, but no commentaries or literature studies provide information regarding the expected reliability or recommend applicative safety factors. The study investigates the seismic reliability of shake table testing protocols for seismic assessment and qualification of acceleration-sensitive NEs. Numerical analyses are carried out considering an incremental procedure and modeling NEs as inelastic single degree of freedom (SDOF) systems, over a wide range of frequencies of interest and NE structural properties. Real floor motions recorded in instrumented reinforced concrete (RC) buildings are considered as a reference. The reliability is estimated considering several damage states and various floor motion sets. In particular, the seismic capacities associated with the real (shake table protocol) floor motions are considered as actual-demand (nominal-capacity) measures, and the demand to capacity margin is meant as the protocol overestimation of the NE capacity. In the light of the estimated protocol reliability, reliabiliy-targeted capacity safety factors are assessed, and applicative factor abaci and closed-form criteria are proposed.

Numerical roll motion control by using fins based on the linear quadratic regulator and dynamic mode decomposition

Reducing the roll motion and acceleration of a ship is a critical concern for the safety and comfort requirement in a seaway. In this paper, the uncontrolled roll motion time series is obtained under the harsh beam sea simulation for a naval vessel using a single degree of freedom nonlinear equation of motion. Then the linear quadratic controller (LQR) controller is applied by utilizing one pair of fins (port and starboard) that were positioned amidship. The amplitude and rate saturations of the fins are taken into consideration in the simulations. The LQR controller is designed based on an analytical mathematical model, with the selection of appropriate controller parameters. Then, an estimation is made based on the dynamic mode decomposition method for the ship model by taking measurements from online states as if those are derived from the experimental measurements. Finally, the ‘estimated mathematical model’ is used for the LQR controller design. The results demonstrate the successfulness of the estimation process, with only minimal degradation in performance observed.

Insights into the nonlinear dynamic characteristics of a water turbine generator set considering the coupled effects of a fractional-order broadband foundation

The analysis of the coupled shaft-foundation system (CSFS) of a water turbine generator set is an extremely complicated task owing to its structural complexity and inherent nonlinear broadband dynamic characteristics. Thus, the coupling relationships of the CSFS remain unclear. The broadband vibration of the foundation subsystem has an evident influence on the vibration of the shaft subsystem of the unit; however, for the analysis of the dynamic characteristics of the water turbine generator, an overly complicated foundation can be reasonably simplified. To this end, this paper reports the development of novel energy-equivalent broadband modeling approaches to investigate the nonlinear vibration characteristics of CSFS. First, a relatively traditional integer-order lumped parameter model of the foundation subsystem was constructed, and its parameters were determined by fitting the response spectra obtained from an accurate hydropower house model. To improve the narrow-frequency limitation of the integer-order model and account for random disturbances, a novel fractional-order broadband modeling method is proposed. The advantage of the proposed fractional-order equivalent foundation model is that it can simultaneously reveal the broadband characteristics of complex structures at low frequencies of less than 1 Hz to high frequencies of hundreds of Hz with a single degree of freedom. Finally, coupled dynamic equations for the fractional-order CSFS model were derived and solved by considering the actions of various nonlinear factors and hydraulic pulsation excitation. A comparison of the dynamic responses of the CSFS with field test data demonstrated the effectiveness and practicability of the proposed modeling approaches. The results of the integer- and fractional-order CSFS models provide insights into the abundant dynamic laws and inner mechanisms of the nonlinear coupled dynamic system. Furthermore, they provided a reliable theory for the design and stability analysis of a hydropower unit, considering the varied vibrations of the coupled foundation.

A novel tuned torsional mass damper (TTMD) for seismic protection of structures

Energy dissipators are being increasingly utilized in the seismic protection of both newly constructed and retrofitted buildings. However, their control effectiveness would decline when applied to the stiff structures with small responses, such as drifts and inter-story velocities. To more effectively dissipate the vibration energy, this paper proposes a novel energy dissipator dubbed as tuned torsional mass damper (TTMD) based on the amplification effect of inerter. In particular, the conceptual design and ideal mechanical model of the proposed TTMD are firstly elaborated. A single degree of freedom (SDOF) system is then established to derive the optimal parameters of TTMD, namely the frequency and damping ratios, based on the fixed-point theory. Subsequently, a three-story benchmark building is adopted to demonstrate the control effectiveness of TTMD in the frequency domain. For comparison, the control effectiveness of the conventional viscous damper (VD) and viscous mass damper (VMD) are also examined. Moreover, parametric studies are conducted to investigate the influences of the mass ratio, secondary mass ratio, and lead of ball screw on the control performances of TTMD, and sensitivity analyses are also performed to assess the robustness of TTMD against the structural uncertainties. Finally, case studies are performed to further illustrate the control performance and the hysteretic behaviors of TTMD in the time domain. The results show that the proposed TTMD is more effective than the conventional VD and VMD in reducing the seismic responses of building; the relative angle of TTMD can be effectively reduced by increasing either the mass ratio or the lead of ball screw. The proposed TTMD could be a promising and viable alternative to conventional dampers in the field of structural vibration control.

Finite element modeling of piezoelectric cantilever-beam energy harvester

Piezoelectric energy harvesting from mechanical vibrations has attracted considerable attention during the last decade. The homogeneous harvesters were studied experimentally or numerically by various models such as single degree of freedom (SDOF) modeling, finite element (FE) modeling as well as using analytical solutions. In this work, FE models for simulating a piezoelectric beam bimorph power harvester consisting of a laminated piezoelectric beam, a proof mass, and an electrical load (series or parallel connections) configurations are developed. The effects of the material and size of the substrate, the proof mass have been studied on the resonance frequencies and the output parameters of the piezoelectric generator (PEG). Numerical results obtained using the proposed procedure for piezoelectric bimorph power harvesters are in good agreement with the experimental data available in the literature. The proposed method can be used for modeling accurately this class of energy harvesting devices.

Mechanical Vibration Analysis of an UAV Wing Spar

This paper presents the mechanical vibration analysis of a UAV (Unmanned aerial vehicle) wing spar. Theoretical and numerical calculations are performed by considering the spar as a cantilever beam. The model is created and modal analyses are performed by using the MATLAB software. The natural frequencies and the related mode shapes are obtained. The results of theoretical calculations linear, nonlinear and random vibration of both single and multiple degree of freedom (DOF) system are graphically presented. The study aims to illustrate vibration tendencies of the wing during flight.

Numerical Studies on Seismic Response of Structural Systems Using a Response-Spectra Based Intensity Measure

This paper proposes a novel intensity measure (IM) based on the geometric mean of acceleration response spectral ordinates to assess the probabilistic performance of structures subjected to seismic loading. Instead of relying solely on the fundamental period, the proposed IM is evaluated across a fixed period range for all structural systems, which allows consideration of higher mode effects and period changes due to nonlinearity. The proposed seismic IM is evaluated using two established indices sufficiency and efficiency. Sufficiency quantifies the independence of an engineering demand parameter at a specific intensity level with ground motion characteristics such as seismic magnitude [Formula: see text] and distance from site to fault plane [Formula: see text]. It is calculated by linear regression analysis, or using gradient-based relative sufficiency measures. On the other hand, efficiency is measured as dispersion across ground motions at a given intensity level for any physical response quantity. It helps to reduce computational demand for failure probability assessment by considering a smaller number of records compared to an inefficient IM for similar confidence levels. The effectiveness of the proposed IM along with 10 other IMs is demonstrated on single degree of freedom systems with various fundamental periods by performing nonlinear time history analysis using a far-field ground motion record set. The study is also extended to five degree of freedom lumped mass stick models, 2D models (4-, 8-, and 12-story archetype steel frames), and 3D reinforced concrete shear wall building model. The results indicate that the proposed IM limits dispersion to within 10% for long-time period structures, and demonstrates improved sufficiency across different structural systems. For example, gradient of the proposed IM with respect to magnitude [Formula: see text] and site-to-source distance [Formula: see text] for a 12-story steel frame is reduced by 42.9% and 94%, respectively, compared to spectral acceleration at fundamental time period. Potential application of this research lies in efficiently conducting seismic reliability assessment and design for structural systems.

Numerical simulation of rarefied supersonic flows using a fourth-order maximum-entropy moment method with interpolative closure

Maximum-entropy moment methods allow for the modeling of gases from the continuum regime to strongly rarefied conditions. The development of approximated solutions to the entropy maximization problem has made these methods computationally affordable. In this work, we apply a fourth-order maximum-entropy moment method to the study of supersonic rarefied flows. For such conditions, we compare the maximum-entropy solutions to results obtained from the kinetic theory of gases at different Knudsen numbers. The analysis is performed for both a simplified model of a gas with a single translational degree of freedom (5-moment system) and for a typical gas with three degrees of freedom (14-moment system). The maximum-entropy method is applied to the study of the Sod shock-tube problem at various rarefaction levels, and to the simulation of two-dimensional low-collisional crossed supersonic jets. We show that, in rarefied supersonic conditions, it is important to employ accurate estimates of the wave speeds. Since analytical expressions are not presently available, we propose an approximation, valid for the 14-moment system. In these conditions, the solution of the maximum-entropy system is shown to realize large degrees of non-equilibrium and to approach the Junk subspace, yet provides a good overall accuracy and agreement with the kinetic theory. Numerical procedures for reaching second-order accurate discretizations are discussed, as well as the implementation of the 14-moment solver on Graphics Processing Units (GPUs).

A time and ensemble equivalent linearization method for nonlinear systems under combined harmonic and random excitation

An Equivalent Linearization technique, termed an Equivalent Linearization Time and Ensemble Expectation (EL-TEE) approach, is used to develop an alternative method for estimating the response of a nonlinear oscillator to a combination of deterministic harmonic and random white noise excitation. The approach is based on applying equivalent linearization and averaging over the time period of one harmonic excitation cycle. This gives a set of coupled nonlinear equations that can be solved for the response averaged over time and across the ensemble. The primary advantages of the proposed method are its computational speed, ability to return physically meaningful linearization matrices and that it can be applied to a wide variety of nonlinearities. The method is applied to three example test systems: the well-known single degree of freedom Duffing oscillator; a single degree of freedom system with a displacement constraint imposing a discontinuous nonlinearity; and a multi degree of freedom oscillator with a localized polynomial nonlinearity that has also been examined experimentally. It is shown that the response predicted matches well with Monte Carlo results from direct time integration at a fraction of the computational cost, and the method is capable of reproducing key results observed experimentally.

Development and evaluation of a light-weight flexure-based lockable joint for morphing wings

Single degree of freedom (single-DOF) morphing wings have the advantages of light-weight and multiple morphing shapes, which can enable aircraft to adapt to uncertain flight environments and various mission types. A single-DOF morphing wing with four morphing shapes designed based on the reconfigurable mechanism is introduced firstly in this paper. Then, a light-weight compliant locking mechanism (CLM) based on flexure hinges is proposed for lockable joints in the reconfigurable mechanism. The CLM has two types depending on the locking method, namely the “plug-in” compliant locking mechanism (PCLM) and the “friction” compliant locking mechanism (FCLM). The working principles of the two CLMs are described. The mathematical models are established to assess the static and dynamic characteristics of the proposed CLM, which are also verified by the finite element simulation. The influence of the flexure hinge dimensions on the working performance of the CLM is analyzed, and its dimensions are optimized considering both the locking performance and the maximum stress. Finally, a PCLM and a FCLM actuated by SMA wires are fabricated based on the optimized dimensions. The experiment is conducted to assess the locking torque of the CLM and the feasibility of the proposed CLM used for morphing wings is confirmed.

A Study on the Relationship between Response Spectrum and Seismic Fragility Using Single Degree of Freedom System

A Study on the Relationship between Response Spectrum and Seismic Fragility Using Single Degree of Freedom System

Evaluation of equivalent linearization methods of MDOF isolated structures in response spectrum analysis

In the seismic design of isolated structures, equivalent linearization of the hysteretic isolators is normally considered. There exist many equivalent linearization methods and evaluation of these methods has been widely studied. However, most of the previous studies concern a single degree of freedom system only, and the used analysis method is time history analysis. In such a case, the evaluation heavily depends on the ground motions selected. Note that the response spectrum analysis is a commonly used method for seismic design of structures. Therefore, it is more valuable to evaluate these equivalent linearization methods based on the response spectrum analysis. In this study, a multiple degree of freedom model is adopted due to the contribution of higher modes of the superstructure to the seismic responses, and the procedure of the response spectrum analysis in conjunction with the equivalent linearization method is presented in detail. Then, considering a series of parameters of isolators, a statistical study is performed to evaluate the accuracy of these equivalent linearization methods by comparing with the nonlinear time history analysis. Moreover, the effect of the damping reduction factor for the response spectrum on the accuracy of the equivalent linearization methods is discussed in terms of probability in a desirable error range. The analytical results show that the accuracy of the equivalent linearization methods is associated with the earthquake intensity. Meanwhile, for different response quantities the accuracy of each equivalent linearization method varies significantly. In addition, to estimate the seismic responses with a better accuracy in the response spectrum analysis, a suitable damping reduction factor should be considered.

202 Evaluation of Increasing Levels of Mycotoxin-Containing Corn Fines fed to Nursery Pigs on Growth Performance

Abstract The effects of feeding corn fines (screenings) containing mycotoxin levels at greater than the FDA cautionary levels were evaluated using crossbred pigs [n = 150, 90 barrows and 60 gilts; mean initial body weight (BW) = 6.42 ± 0.06 kg; n =] that were blocked by BW and sex, randomly allotted within block to 6 dietary treatments, and housed 5 pigs/pen resulting in a total of 5 replicates. The corn fines used in this study contained mycotoxin levels that were analyzed to be 20,334 ppb total fumonisin, 1,499 ppb zearalenone, and 5,075 ppb total deoxynivalenol. The corn fines were added into a corn-soybean meal basal diet at 0, 20, 40, and 60% total dietary corn fines (Diets 1-4, respectively). Diet 5 was created by adding 40 ppm of boron (as sodium tetraborate decahydrate, 11.34% B) to Diet 4. Diet 6 was created by adding 0.25% Biofix Plus with FUMzyme (DSM Nutritional Products, Parsippany, NJ) to Diet 4. Dietary treatments were fed for a total of 6 weeks; thereafter, all pigs received a common corn-soybean meal basal diet without fines for about 2 weeks. Data were analyzed by ANOVA using the GLM procedure of SAS with the pen being the experimental unit. Orthogonal polynomial contrasts were used to determine linear and quadratic effects with increasing dietary levels of corn fines in Diets 1-4 as well as preplanned single degree of freedom comparisons. Increasing fines linearly decreased ADG during week 1-6 (P = 0.03), as well as linearly decreased gain/feed ratio during week 1-6 (P = 0.04; Table 1). Comparing Diets 4 and 5 to Diet 1 during week 1-6, there was a decrease in ADG and gain/feed ratio (P < 0.05) but no effect on ADFI (P > 0.05); subsequently, the difference in Diets 4 and 5 compared with Diet 1 was no longer significant for week 1-8. Comparing Diet 6 to Diets 1 and 4 during week 1-6, pigs fed Diet 6 were able to recover 57% of the lost ADG and 30% of the lost BW gain/feed ratio that occurred when corn fines were increased from 0 to 60%. During week 6-8 (all pigs on a common diet), pigs on Diet 5 and 6 had an increase in ADG compared with Diet 1. In conclusion, as mycotoxins increased pigs exhibited negative effects on ADG and gain/feed ratio but the enzyme FUMzyme ameliorated a portion of these effects. Further, the recovery from week 6-8 from all pigs does show the importance of feeding clean corn to optimize ADG, ADFI and gain/feed ratio.

ANCHORAGE DESIGN FOR BLAST-RESISTANT WINDOWS

This paper presents a summary of experimental research on the performance of blast-resistant window anchors and the development of a design procedure for the anchors. The experimental results, obtained from forty-six window tests conducted under simulated blast loading using a shock tube are reported. Two analysis procedures that were developed for anchor design are described. The first procedure involves a two-degree-of-freedom dynamic analysis. The second procedure involves a single degree of freedom analysis that can be implemented manually. The development of both methods is presented for the anchorage design of windows subjected to blast loads.

Multi-Temporal Change of LULC and Its Impact on Carbon Storage in Jiangsu Coastal, China

Coastal is the coupling of socio-economic and fragile ecosystems area existing development and protection problems, with lots of reserve land resources (i.e., bottomland and tidal flats). Analyzing and predicting the carbon storage changes caused by land use/land cover (LULC) on the Jiangsu coast were critical for revealing the potential problems of land surface changes and sustainable development. Then, we utilized the single dynamic degree and transfer in/out contribution, exploring the characteristics of LULC change in the study area from 1980 to 2018. Using the InVEST model, PLUS-LEAS model, and PLUS-Markov chain module, we assessed the spatiotemporal of the study area at the county level to reveal the LULC change strategy and driving factor contribution, as well as the composition of LULC and carbon storage in 2036. The results show that the LULC structure in the study area significantly changed from 1980 to 2018, in which the tidal flat and high coverage grassland decreased by 552.84 km2 and 383.71 km2 while the reservoir ponds and urban residential land increased by 1210.69 km2 and 101.70 km2. The major driving factor of LULC change has shifted from a single-factor to multi-factor coupling, and the influence contribution of human activity increased by 6.73%, especially the population. The carbon storage of study areas showed a significant decrease trend during 1980–2010, followed by a slight increase during 2010–2018. High-density carbon storage was mainly distributed in Lianyungang and Nantong and presented a decreasing trend along the coastline extending inland. The dry land and reservoir ponds are the main composition of LULC types in 2036, and the carbon storage increased to 2.39 × 108 t. In addition, more than decades of LULC change will cover part or all of the land use change process and trends, especially high-covered grasslands, so we suggest a 10-year LULC change to analyze coastal areas with lots of tidal flats and bottomlands. Therefore, this study can provide reference and theoretical guidance for ecologically sustainable development and future LULC evolution in coastal cities.

Rigid-Foldable Polyhedral Origami

This paper introduces a novel origami pattern that enables the construction of polyhedral shapes from a planar sheet. The proposed polyhedral origami exhibits rigid foldability, which means that it can be folded without deforming its facets. The folding motion to a polyhedral shape can possess a single degree of freedom under the symmetric condition. A range of shapes, including pyramidal and prismatic shapes, can be created, depending on the design variables; and they can be folded into compact shapes for storage. Considering geometry, we derive mathematical conditions for the pattern design and investigate the folding process through kinematic analysis. Additionally, we conduct a parametric study of the effective volume and radius of its operational state. The proposed origami design will serve as a basic framework for developing foldable three-dimensional structures. It can have potential applications such as foldable space shields or deployable shelters made of thick materials for protection against space radiation.

Self-Directed Mobile Robot Navigation Based on Functional Firefly Algorithm (FFA)

This paper proposes an optimized mobile robot navigation strategy using a functional firefly algorithm (FFA) and choice function. This approach has two key advantages: first, the linear objective function performs efficiently with the single degree and finite-order polynomial time operation, and second, the cartesian constraint performs compactly with the chosen degree of freedom on the finite interval. This functional approach optimizes the size of operational parameters in context with key size, operation time, and a finite range of verification. The choice function achieves parameter order (size) reduction. The attraction characteristic of fireflies is represented by the choice function for optimizing the choice between low and high intensities of fireflies. In 2D and 3D environments, the proposed robot navigation performs well in an uncertain environment with static and dynamic obstacles. This efficiency includes the robot’s speed as determined by the choice function’s minimum path lengths. The collision-free path is achieved by the non-void family of non-void sets. The obtained results are optimal in terms of path length and navigational time. The proposed controller is also compared with the other existing controllers, and it is observed that the FFA gives the shortest path in less time for the same environmental condition.

Backstepping integral sliding mode control for pneumatic manipulators via adaptive extended state observers

In this paper, a nonlinear control strategy is proposed for a pneumatic manipulator based on an adaptive extended state observer and a backstepping integral sliding mode controller. A single degree of freedom dynamic model is established for the pneumatic manipulator using an Euler–Lagrange dynamic equation. The adaptive extended state observer is designed by an adaptive law to estimate uncertainties and disturbances. The backstepping integral sliding mode controller is proposed using an integral sliding mode surface based on backstepping technique. Comparative experiments verify effectiveness of the proposed nonlinear control strategy for the pneumatic manipulator.

A compatible uniaxial Bouc–Wen model for accurate estimation of residual deformation of seismically isolated structures

Bouc–Wen (BW) model is commonly used to model lead rubber bearings (LRBs) in seismically isolated buildings. However, the original BW model violates the Drucker’s or Ilyushin’s postulate of plasticity by displaying the displacement drift, force relaxation, and non-closure of hysteretic loops. These deficiencies can significantly impact the seismic performance of the isolated structures, leading to unrealistic evaluation of residual deformation concentrated in the isolation layer. To address these issues, a step-by-step amendment algorithm is proposed to develop a compatible uniaxial BW (CBW) model that conforms to the basic physical rules. The proposed algorithm involves adding a reinforcement factor to the short-path reloading branches, defining reversal and reloading points to identify reloading behavior. Furthermore, it develops an adaptive limit to distinguish between the short-path and full-path reloading branches. The proposed algorithm was validated using various short unloading–reloading scenarios. Subsequently, a simplified single degree of freedom (SDOF) model representing a seismically isolated building was defined. Incremental dynamic analysis was performed to evaluate the seismic responses of the isolated building designed with the original BW, CBW, and bilinear models. Results indicate that although the peak displacement and seismic force of the isolation layer induced by the three models produce small deviations, considerable errors in residual displacement are observed. Compared with the original BW model, the bilinear model produces unrealistic sharp yielding transition and overestimates the residual displacement. However, it can reduce displacement drift and force relaxation. By contrast, the proposed CBW with the improved algorithm can effectively correct the defects of the original BW and bilinear models. The CBW model can be used to accurately estimate the residual deformation of the seismically isolated buildings.

Investigation of energy-absorbing connections for application in mass timber structures

This study presents the results of an experimental program investigating the use of steel energy-absorbing connections (EAC) for the purpose of improving the energy dissipation capabilities of timber assemblies. The performance of the EACs is investigated both experimentally and numerically. A total of thirty-six specimens, representing nine configurations, including angle and circular hollow-steel sections, were tested under quasi-static and dynamic loading. The results of the study showed that connection configurations with well-defined plateaus were capable of dissipating a significant amount of energy and as such can be used in design for blast mitigation. Scalability of resistance based on the connection's depth was shown to be achievable experimentally. The welding configurations were shown to impact the behaviour significantly, and thus the details used in manufacturing must be identical to those assumed in design. The resistance curves of the EAC configurations investigated were reasonably predicted using Finite Element models. Analysis with single degree of freedom utilizing resistance curves obtained experimentally or from the finite element model mimicked the observed behaviour of the EACs. An example of the application of EACs in a mass timber assembly is demonstrated. This example showed that a 247 % increase in the energy absorption of the system might be obtained when compared to glulam members with idealized simply-supported boundary conditions.