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The Daguangbao (DGB) landslide was the largest landslide that was triggered by the 2008 Wenchuan earthquake with a magnitude of Ms8.0. The sliding surface of this landslide was constrained on a bedding fault 400 m below the ground surface. Seismic records show that the landslide suffered not only from strong horizontal but also vertical ground shaking that was almost equal to the horizontal component. In this study, to reveal the landslide triggering mechanism of the DGB landslide, this study ignores the steep dipping tension fracture section and the leading edge-locking section of the trailing edge of the DGB landslide, and the geological model of the large optical package landslide is generalized into a block model with the bottom controlled slip soft zone as the interface. Based on the improved Newmark method that considers vertical ground motion, the three-way seismic acceleration data and the shear strength parameter of the sliding surface being taken as a variable are used to calculate the cumulative permanent displacement of the slider. Then, by considering the cumulative permanent displacement ratio of vertical seismic acceleration or not and the cumulative permanent displacement ratio value considering the inertial force as the index, the response characteristics of the cumulative permanent displacement of the block-to-vertical ground motion and inertial forces were analyzed. The results show that both the horizontal inertial force and the vertical acceleration significantly increased the permanent displacement. The permanent displacement is 4.9 cm when considering the vertical acceleration, whereas it is only 2.0 cm without taking this into account. The contribution of vertical acceleration is significantly enlarged (87.8–90.7%) by the decreasing of the internal friction angle of the slide surface, while it is less influenced (5–27.4%) by the cohesion. Compared with the lower shear strength parameter of the sliding surface, the contributions of vertical acceleration and inertial force to the permanent displacement are more obvious when the shear strength parameter of the sliding surface is higher. When ϕ > 18°, the D/D* is greater than 1, and the maximum D/D* reaches 7. The fast accumulation event of permanent displacement is triggered in the concentration stage of the seismic energy release. In the DGB landslide area, 50% of the energy is released within 30–50 s, as indicated by the acceleration peaks recorded at the nearest seismic station, Qingping station. It is assumed that the DGB landslide may be triggered at 30–50 s due to half of the seismic energy being released during that time span. [ABSTRACT FROM AUTHOR]

This contribution investigates the vertical coupling exerted by ballasted tracks on the vertical response of bridges composed either of (i) several successive simply-supported spans with weak coupling between them due to the continuous track; or (ii) adjacent single-track decks conforming a double-track bridge, in which interaction effects are induced due to the transverse continuity of the ballast layer. To this end, 2 D and 3 D track-bridge interaction Finite Element models are implemented, which consider a three-layer discrete and explicit idealization of the track. The 2 D track-bridge interaction model is used to perform sensitivity analyses on the track parameters, which have revealed that the ballast shear mechanisms along the track may significantly affect the train-induced vibrations under resonant conditions. Then, the influence of the ballast coupling on the response of twin adjacent decks is investigated with a 3 D track-bridge interaction model. To this end, this model is updated based on the results of an experimental campaign performed on a real bridge composed of two SS spans and two single track twin adjacent decks. The numerical-experimental comparison shows an evident dynamic vertical coupling between the bridge decks and reveals the importance of including the ballasted track in the modelling process of these structures. [ABSTRACT FROM AUTHOR]

Elevated cylindrical and conical steel tanks are widely used to conserve water or chemical liquids. These important structures are required to stay protected and operative at any time. The wall angle inclination of conical tank part, as well as the presence of the vertical earthquake component, can cause damage to this structure and even lead to its failure. The purpose of this study is to examine the effect of wall angle inclination of the tank and the vertical earthquake acceleration component on the nonlinear dynamic stability of the elevated steel conical tanks under seismic excitation. The elevated steel conical tank is simulated utilizing the finite element analysis method using ANSYS software. The fluid-structure interaction is considered using a suitable interface that allows the fluid to apply hydrodynamic pressures on the structure. Three different models, namely Model –A-30°, Model –B-45°and Model –C-60° are investigated; it has been concluded that the impact of inclination of the tank wall significantly affects the nonlinear stability of the elevated steel conical tank. While considering the vertical ground acceleration, inclination plays a significant role in the design of this type of structures. Therefore, it should be appropriately included in the seismic analysis of elevated steel conical tanks to satisfy the safety of the elevated steel conical tank response under seismic loading.

Elevated cylindrical and conical steel tanks are widely used to conserve water or chemical liquids. These important structures are required to stay protected and operative at any time. The wall angle inclination of conical tank part, as well as the presence of the vertical earthquake component, can cause damage to this structure and even lead to its failure. The purpose of this study is to examine the effect of wall angle inclination of the tank and the vertical earthquake acceleration component on the nonlinear dynamic stability of the elevated steel conical tanks under seismic excitation. The elevated steel conical tank is simulated utilizing the finite element analysis method using ANSYS software. The fluid-structure interaction is considered using a suitable interface that allows the fluid to apply hydrodynamic pressures on the structure. Three different models, namely Model -A-30°, Model -B-45°and Model -C-60° are investigated; it has been concluded that the impact of inclination of the tank wall significantly affects the nonlinear stability of the elevated steel conical tank. While considering the vertical ground acceleration, inclination plays a significant role in the design of this type of structures. Therefore, it should be appropriately included in the seismic analysis of elevated steel conical tanks to satisfy the safety of the elevated steel conical tank response under seismic loading. [ABSTRACT FROM AUTHOR]

The Daguangbao (DGB) landslide was the largest landslide that was triggered by the 2008 Wenchuan earthquake with a magnitude of Ms8.0. The sliding surface of this landslide was constrained on a bedding fault 400 m below the ground surface. Seismic records show that the landslide suffered not only from strong horizontal but also vertical ground shaking that was almost equal to the horizontal component. In this study, to reveal the landslide triggering mechanism of the DGB landslide, this study ignores the steep dipping tension fracture section and the leading edge-locking section of the trailing edge of the DGB landslide, and the geological model of the large optical package landslide is generalized into a block model with the bottom controlled slip soft zone as the interface. Based on the improved Newmark method that considers vertical ground motion, the three-way seismic acceleration data and the shear strength parameter of the sliding surface being taken as a variable are used to calculate the cumulative permanent displacement of the slider. Then, by considering the cumulative permanent displacement ratio of vertical seismic acceleration or not and the cumulative permanent displacement ratio value considering the inertial force as the index, the response characteristics of the cumulative permanent displacement of the block-to-vertical ground motion and inertial forces were analyzed. The results show that both the horizontal inertial force and the vertical acceleration significantly increased the permanent displacement. The permanent displacement is 4.9 cm when considering the vertical acceleration, whereas it is only 2.0 cm without taking this into account. The contribution of vertical acceleration is significantly enlarged (87.8–90.7%) by the decreasing of the internal friction angle of the slide surface, while it is less influenced (5–27.4%) by the cohesion. Compared with the lower shear strength parameter of the sliding surface, the contributions of vertical acceleration and inertial force to the permanent displacement are more obvious when the shear strength parameter of the sliding surface is higher. When ϕ > 18°, the D/D* is greater than 1, and the maximum D/D* reaches 7. The fast accumulation event of permanent displacement is triggered in the concentration stage of the seismic energy release. In the DGB landslide area, 50% of the energy is released within 30–50 s, as indicated by the acceleration peaks recorded at the nearest seismic station, Qingping station. It is assumed that the DGB landslide may be triggered at 30–50 s due to half of the seismic energy being released during that time span.

This study addresses the modeling of different energy dissipation mechanisms for numerical prediction of the vertical acceleration demand in regular moment-resisting steel frame structures. One of the issues discussed is the consideration of viscous damping in the structural model. It is shown that well-established Rayleigh-damping may highly overestimate the damping of the vertical modes, resulting in much too low vertical acceleration response predictions. A study with different damping models provides an appropriate damping modeling strategy that leads to reasonable predictions of both horizontal and vertical frame acceleration demands. Another open question is the effect of inelastic material behavior on the vertical acceleration demand on the considered regular structures. The results of a shell model of a frame structure exposed to high intensity ground motion excitation demonstrate that inelastic material behavior has virtually no impact on the vertical acceleration demand, while structural inelasticity leaves the horizontal acceleration response significantly smaller compared to the elastic demand. This leads to the conclusion that common frame models that capture the inelastic horizontal response but behave elastic in the vertical direction are suitable for the computation of both the horizontal and vertical acceleration demand. [ABSTRACT FROM AUTHOR]

Elevated cylindrical and conical steel tanks are widely used to conserve water or chemical liquids. These important structures are required to stay protected and operative at any time. The wall angle inclination of conical tank part, as well as the presence of the vertical earthquake component, can cause damage to this structure and even lead to its failure. The purpose of this study is to examine the effect of the wall angle inclination of the tank and the vertical earthquake acceleration component on the nonlinear dynamic stability of the elevated steel conical tanks under seismic excitation. The elevated steel conical tank is simulated utilizing the finite element analysis method using ANSYS software. The fluid-structure interaction is considered using a suitable interface that allows the fluid to apply hydrodynamic pressures on the structure. Three different models, namely Model – A-30°, Model –B-45°and Model –C-60°were investigated; it has been concluded that the impact of inclination of the tank wall significantly affects the nonlinear stability of the elevated steel conical tank. While considering the vertical ground acceleration, inclination plays a significant role in the design of this type of structures. Therefore, it should be appropriately included in the seismic analysis of elevated steel conical tanks to satisfy the safety of the elevated steel conical tank response under seismic loading. [ABSTRACT FROM AUTHOR]

In recent years, the promotion of green travel and the emergence of bicycle sharing have dramatically increased the population of people traveling by bicycle in China. Bicycle sharing has become an indispensable daily means of travel for some people. Therefore, the ride comfort and safety of bicycle lanes should be paid more attention. Toward meeting the demand for smooth bicycle lanes, we propose a new method of testing the roughness of bicycle lanes based on the riding condition and explore the possibility of its realization. A riding profiler is assembled and designed, and its test repeatability is verified by repeated measurements. The riding profiler is also applied to different pavement types with various speeds for roughness testing. The results demonstrate that the speed and pavement type affect the vibration acceleration and vertical displacement during riding, and the greater the riding speed, the stronger the vibration sensation. In addition, the vibration is strongest when riding on concrete block pavement and weakest on dense asphalt pavement. On the basis of the test results, the acceleration interference is taken as an evaluation index to analyze riding comfort under different conditions. [ABSTRACT FROM AUTHOR]

This paper discusses the results of an experimental study aimed at evaluating the influence of the vertical ground motion component on the seismic performance of unreinforced brick‐masonry buildings. The research was motivated by post‐earthquake observations of significant structural damage in the vicinity of the fault, where horizontal and vertical ground motions are often strong and synchronized. Vertical accelerations can fluctuate gravity loads, which control the in‐plane lateral load capacity of masonry piers and affect the out‐of‐plane overturning stability of thin walls. Such phenomena seem not to be sufficiently explained in existing literature, while experimental evidence is undoubtedly missing. Here, the damage potential of vertical accelerations was investigated through a series of multidirectional shake‐table tests on full‐scale structures under simulated near‐source ground motions of increasing intensity. The experiments comprised three nominally identical building specimens subjected to the principal horizontal component alone, the horizontal component combined with the vertical one, and the full three‐component ground motion. The buildings included structural/nonstructural elements (e.g., gables, chimneys, and parapets) sensitive to gravity load variations due to their low axial loads. Two different sets of three‐component earthquake records were employed to assess the effects of both tectonic and induced seismicity scenarios. Overall, the vertical earthquake motion did not cause appreciable differences in the behavior of the buildings. Any influence on the strength and peak response of structural/nonstructural walls was marginal and non‐systematic. Data and observations from these experiments add substantially to our understanding of the vertical acceleration effects on masonry structures. [ABSTRACT FROM AUTHOR]

With the rapid development of intercity railway, there are many vibration-sensitive buildings such as schools, residences, hotels, etc. The track structure needs to be specially designed in accordance with different conditions to meet the requirements of vibration reduction, and the vibration source should be determined reasonably and accurately. In order to solve the inaccurate value problem of vibration source and improve the accuracy of prediction of vibration effect, in-situ test and simulation methods were adopted for the research. Firstly, field vibration data was measured on a rectangular tunnel section of an intercity railway, and the finite element analysis model was verified by the measured vibration source intensity data. Afterward, calibrated model was used to analyze the vibration source intensity data. Models of different types of tunnels and different vehicle speed were built, suggested vibration source data for intercity railway with different tunnels and speeds were proposed. [ABSTRACT FROM AUTHOR]

In the previous studies on the dynamic responses of pavement, most researchers paid attention to the stress and strain responses of pavement. With the passings of vehicles, road structures will inevitably produce vibration accelerations. Since acceleration is closely related to many physical quantities according to the definitions in physics, the acceleration of pavement can reflect pavement conditions from the side, and the relevant studies on the acceleration field of pavement under moving load are worth conducting. In this study, with the help of ABAQUS, the numerical analysis on the distribution and response of the acceleration field of pavement under moving load was carried out, and the influencing degrees of vehicle load, vehicle speed and the elastic modulus of upper layer on the acceleration response of intact pavement were also compared based on the designed orthogonal test. It was found that the three-directional accelerations of pavement present symmetrical distributions around the loaded area, and the vertical acceleration is the largest but decays rapidly with the form of quartic polynomials as far away from the loaded area. Meanwhile, the mechanical state of pavement can be evaluated by analyzing pavement accelerations. Besides, the acceleration response of the intact pavement in this study is the most sensitive to the influencing factor of vehicle speed, followed by vehicle load, and the brought effect of the elastic modulus of upper layer is the lowest in general. [ABSTRACT FROM AUTHOR]

Rotational and vertical parts of ground movement are quite often overlooked in plan or in the appraisal of structures in spite of the way that vertical movement can be twice as much as the even movement and may surpass 2g level, and rotational excitation may arrive at barely any degrees in the closeness of deficiency crack. Coupling of various parts of ground excitation may essentially enhance the seismic interest by presenting extra horizontal powers and upgraded force deflection impacts. In this paper, an overseeing condition of movement is hypothesized to figure the reaction of a Single-Degree-of-Freedom Linear Oscillator (SDOF) under a multi-part excitation. The extended condition incorporates auxiliary force deflection parts related with the joined effects of tilt and vertical excitations notwithstanding the inertial compelling terms because of the precise and translational increasing speeds. [ABSTRACT FROM AUTHOR]

The wheel with a pneumatic tire of traditional design has a significant drawback, which is to stop the movement of the vehicle with the loss of excess air pressure. The loss of excess air pressure in the pneumatic tire when driving a car at high speed can lead to a traffic accident with serious consequences. One of the technical solutions aimed at preserving wheel working ability and improving vehicle safety in case of loss of overpressure of air in a pneumatic tire is the use of internal additional supports. However, the loss of excess air pressure even in one pneumatic tire leads to a noticeable deterioration in most of the performance properties, especially when driving on roads with uneven surfaces. Intensive oscillations lead to an increase in the vibration level, reducing the performance of high-speed properties, fuel efficiency, stability and controllability of the wheeled vehicle. A new mathematical model of the springing system has been developed, which is equivalent to a vehicle suspension with high-safety wheels and allows one to substantiate the parameters of the internal additional supports and evaluate their influence on the vibrations and smooth running of the vehicle at the design stage. The model is intended for engineering calculations and differs in that internal additional supports are presented as spring-damping elements of the vehicle springing system. The results of study can be claimed by manufacturers of civil and military vehicles, wheeled armored vehicles and special machines.

Featured Application: This work proposes a severity estimation method of aircraft bumpiness in turbulence, which is fundamental to turbulent flight safety of civil aviation aircraft. Atmospheric turbulence threatens flight safety of civil aviation aircraft by inducing aircraft bumpiness. A severity estimation method of aircraft bumpiness in turbulent flight is explored according to in-situ Eddy Dissipation Rate (EDR) indicator. With the turbulence intensity derived from EDR value, a time series of longitudinal and vertical turbulence was generated according to von Karman turbulence model. In order to obtain the vertical acceleration response of aircraft, the continuous change of aerodynamic force on the assembly of wing and horizontal tail was computed by Unsteady Vortex Lattice Method (UVLM). The computing accuracy was improved by using semi-circle division and assigning the vortex rings on the mean camber surface. Furthermore, the adverse effects of control surface deflections on bumpiness severity estimation can be effectively removed by separating turbulence-induced and aircraft maneuvers-induced aerodynamic force change. After that, the variance of vertical acceleration, as the severity indicator of aircraft bumpiness, was obtained by Welch spectrum estimation. With the refined grid level, the pitching moment change due to control surface deflections can be solved accurately by UVLM. The instantaneous acceleration change obtained by UVLM approximates recorded acceleration data with better accuracy than linear transfer function model. A further test with a set of flight data on the same airway shows that compared with in-situ EDR indicator, the proposed method gives an aircraft-dependent estimation of bumpiness severity, which can not only be used to estimate in-situ bumpiness but also be applied to forecast the bumpiness severity of other different aircrafts. [ABSTRACT FROM AUTHOR]

Knowledge of body motion features and walk-induced effects is of primary importance for the vibration analysis of structures, especially low-frequency slabs and lightweight and/or slender systems, as well as for clinical applications. Structurally speaking, consolidated literature procedures are available for a wide set of constructional solutions and typologies. A basic assumption consists in the description of walking humans’ effects on structures through equivalent deterministic loads, in which the ground vertical reaction force due to pedestrians depends on their mass and motion frequency. However, a multitude of additional parameters should be taken into account and properly confirmed by dedicated laboratory studies. In this paper, the focus is on the assessment of a rapid analysis protocol in which attention is given to pedestrian input, based on a minimized sensor setup. The study of gait variability and related effects for structural purposes is based on the elaboration of single Wi-Fi sensor, body centre of mass (CoM) accelerations. A total of 50 walking configurations was experimentally investigated in laboratory or in field conditions (for more than 500 recorded gaits), with the support of an adult volunteer. Parametric gait analysis is presented considering different substructure conditions and motion configurations. Body CoM acceleration records are then used for the analysis of a concrete slab, where the attention is focused on the effects of (i) rough experimental body CoM input, or (ii) experimentally derived synthetized gait input. The effects on the structural side of rough experimental walk time histories or synthetized experimental stride signals are discussed.

The vertical tyre force is crucial to the study of the dynamics of a tractor semi-trailer. The paper presents an experimental method for determining the vertical tyre force by determining the vertical acceleration of the un-sprung mass and the vertical acceleration of the sprung mass when the tractor semi-trailer moves. The results of this study form the basis for determining the dynamic tyre force without the installing of sensors on road. [ABSTRACT FROM AUTHOR]

Atmospheric turbulence threatens flight safety of civil aviation aircraft by inducing aircraft bumpiness. A severity estimation method of aircraft bumpiness in turbulent flight is explored according to in-situ Eddy Dissipation Rate (EDR) indicator. With the turbulence intensity derived from EDR value, a time series of longitudinal and vertical turbulence was generated according to von Karman turbulence model. In order to obtain the vertical acceleration response of aircraft, the continuous change of aerodynamic force on the assembly of wing and horizontal tail was computed by Unsteady Vortex Lattice Method (UVLM). The computing accuracy was improved by using semi-circle division and assigning the vortex rings on the mean camber surface. Furthermore, the adverse effects of control surface deflections on bumpiness severity estimation can be effectively removed by separating turbulence-induced and aircraft maneuvers-induced aerodynamic force change. After that, the variance of vertical acceleration, as the severity indicator of aircraft bumpiness, was obtained by Welch spectrum estimation. With the refined grid level, the pitching moment change due to control surface deflections can be solved accurately by UVLM. The instantaneous acceleration change obtained by UVLM approximates recorded acceleration data with better accuracy than linear transfer function model. A further test with a set of flight data on the same airway shows that compared with in-situ EDR indicator, the proposed method gives an aircraft-dependent estimation of bumpiness severity, which can not only be used to estimate in-situ bumpiness but also be applied to forecast the bumpiness severity of other different aircrafts.

The scope of this study is the quantification of vertical peak floor acceleration demands at column lines and along the length of beams of elastic moment-resisting steel frames subjected to recorded ground motions. These demands correlate with the maximum strength demands on rigid nonstructural components attached to a frame structure. Since it is commonly assumed that buildings behave flexibly in the horizontal direction and rigidly in the vertical direction, the assessment of vertical acceleration demands is typically not considered in most cases. The results of this study show that vertical peak floor accelerations can be up to five times larger than the vertical peak ground acceleration, in contrast to horizontal peak floor accelerations that are only up to two times larger than the horizontal peak ground acceleration for the numerical models used in this study. The most significant amplifications estimated in the vertical direction are found at the center of the girders. Further investigations of modified steel frames indicate that the story-wise mass distribution has an influence not only on the vertical acceleration demand, but also on the horizontal component of the response, though to a lesser degree. In contrast, the response in the vertical and horizontal direction is only slightly affected by an increase in the flexural stiffness of the beams. The results of this study strongly indicate that in steel frames it can be considered highly questionable to ignore the amplification of the vertical acceleration component along the height of the structure. [ABSTRACT FROM AUTHOR]

This paper describes a shake table test on a one-storey full-scale unreinforced masonry structure, which complements an earlier testing of a two-storey structure with similar characteristics. The building specimen was meant to represent the upper floors of the end-unit of a terraced house, built with cavity walls and without any particular seismic design or detailing. In these specimens, the masonry walls were composed of two leaves: a load-bearing inner one made of calcium silicate bricks sustaining a reinforced concrete floor and an external leaf made of clay-bricks connected to the inner leaf by means of metallic ties. A pitched timber roof was supported by two triangular gable walls. Floor acceleration response histories of the previously tested two-storey specimen were used as input motions. An incremental dynamic test, with vertical and horizontal inputs, was carried out up to the explicit collapse of some bearing elements of the structure. In particular, a two-way bending out-of-plane collapse of a load-bearing wall was observed and described. [ABSTRACT FROM AUTHOR]

Highlights • Monitoring transport infrastructures is a main requisite to ensure high performance. • Using inertial sensors and GPS receiver data inside vehicles are collected in a railway. • Ride comfort evaluation method was developed and tested according to ISO2631. • Mapping the infrastructure the most critical areas can be found and georeferenced. • The method can be applied indifferently to all transportation systems. Abstract Monitoring the status of infrastructural networks along their service life is fundamental to ensure a safe and good service quality. Due to the length and extension of infrastructures, it is fundamental to develop effective and low cost approaches that can allow a continuous monitoring. In this paper, an assessment method based on the ride comfort evaluation inside vehicles according to ISO 2631 (i.e. frequency weighted acceleration) was developed and tested on an Italian railway. In particular, the frequency weighted acceleration was calculated along the whole trip between two consecutive stops. In order to identify and localize the most critical areas along the traveling path, the vertical frequency weighted acceleration was also calculated for sub-sections of fixed lengths (i.e. 10 m) and then mapped on geographic information systems (GIS). In this way, it is also possible to determine, for example considering a railway infrastructure, whether the eventual discomfort may be due to localized irregularities or due to the passage on worn switches. Once proper threshold limit values are defined, early interventions can be planned in order to restore adequate comfort and safety levels. To test the proposed procedure, it was applied to a surface metropolitan railway characterized by an automatic guide, which granted the chance of evaluating the repeatability of the present approach. During the in-situ measurements, an inertial measurement unit (IMU) integrated together with a GPS receiver was used. [ABSTRACT FROM AUTHOR]

• Seismic performance assessment of fire-fighting and medical gas distribution piping systems, accounting for the influence of the geometry and the mass of the piping layout. • Numerical simulation of the non-linear behaviour of pipe joints and suspended piping restraints. • Analysis of the interaction between local modes of the piping systems and vertical component of the seismic acceleration. • Development of fragility functions at operation-limit and life-safety performance level. The evaluation of the seismic performance of piping networks is often difficult due to several parameters involved in the process, such as complex geometry, modelling uncertainties and earthquake properties. Despite several studies have been conducted on this topic, driven by the importance of piping networks from a building serviceability standpoint, generalized guidelines to achieve defined performance criteria are still difficult to develop. The hardships in analysing the seismic response of piping networks are mainly due to their peculiar configuration, which leads to interaction between local vibration modes and the seismic acceleration. Additional issues are also caused by great variability in piping systems' design and quality. The scope of this study is to investigate several aspects of the dynamic response of different types of piping networks, considering tri-directional floor seismic input. A numerical model was developed, accounting for the non-linear behaviour of piping restraint installations and pipe joints. The numerical model was used to perform nonlinear time-history analyses aimed at assessing the seismic vulnerability in a performance-based design framework. The influence of the geometric configuration and the mass of the system was investigated by analysing the accelerations and displacements, alongside damage on pipe joints and suspended piping restraints due to earthquake. Additionally, the response obtained considering and neglecting the vertical component of the floor acceleration were compared. The results of the analysis were employed to compute fragility functions at different limit states, considering the parameters investigated. A clear influence of the geometry and the mass of the system on the seismic vulnerability is observed, while the effects of the vertical acceleration seem to be generally negligible. [ABSTRACT FROM AUTHOR]

A nine degrees of freedom suspension catamaran has been developed. The ship is so designed that the heave, pitch, and roll motions of the cabin are separable from those of the twin-hull. One brushed DC motor/generator (M/G) is employed at each of the four suspending locations to produce control force. An active skyhook control strategy utilizing proportional-only control is proposed to calculate the desired control input to reduce the cabin's local vertical velocity and thus improve ride comfort. The mechanical responses of the suspension unit and the performance of the control system are verified through a group of bench tests. The ship motion responses in regular waves are investigated through a series of towing tank experiments. It is found that the proposed control strategy had significant effectiveness on motion reduction of heave and pitch of the cabin in head waves, but a small contribution to the roll motion reduction in beam waves except in the vicinity of the cabin's natural roll frequency. In head waves, the average motion reduction ratios of the heave and pitch of the cabin both exceeded 50% at zero forward speed, which at 1.5 m/s were 39% and 71%, respectively. In beam waves, the average motion reduction ratios of the heave and roll of the cabin were 62% and −57%, respectively. • The heave, pitch, and roll motions of the cabin are separable from the twin-hull. • A proportional-only controller is designed to reduce the cabin's vertical velocity. • The control forces are exerted by four brushed DC motors. • Vertical acceleration reduction of the cabin is obtained in towing tank experiments. • Resonances in heave, pitch, and roll of the cabin are suppressed significantly. [ABSTRACT FROM AUTHOR]

In marine environments, ships are bound to be disturbed by several external factors, which can cause stochastic fluctuations and strong nonlinearity in the ship motion. Predicting ship motion is pivotal to ensuring ship safety and providing early warning of risks. This report proposes a real-time ship vertical acceleration prediction algorithm based on the long short-term memory (LSTM) and gated recurrent units (GRU) models of a recurrent neural network. The vertical acceleration time history data at the bow, middle, and stern of a large-scale ship model were obtained by performing a self-propulsion test at sea, and the original data were pre-processed by resampling and normalisation via Python. The prediction results revealed that the proposed algorithm could accurately predict the acceleration time history data of the large-scale ship model, and the root mean square error between the predicted and real values was no greater than 0.1. The optimised multivariate time series prediction program could reduce the calculation time by approximately 55% compared to that of a univariate time series prediction program, and the run time of the GRU model was better than that of the LSTM model.

Wearable sensors have recently been used to evaluate biomechanical parameters of everyday movements, but few have been located at the head level. This study investigated the relative and absolute reliability (intra- and inter-session) and concurrent validity of an inertial measurement unit (IMU) embedded in smart eyeglasses during sit-to-stand (STS) movements for the measurement of maximal acceleration of the head. Reliability and concurrent validity were investigated in nineteen young and healthy participants by comparing the acceleration values of the glasses’ IMU to an optoelectronic system. Sit-to-stand movements were performed in laboratory conditions using standardized tests. Participants wore the smart glasses and completed two testing sessions with STS movements performed at two speeds (slow and comfortable) under two different conditions (with and without a cervical collar). Both the vertical and anteroposterior acceleration values were collected and analyzed. The use of the cervical collar did not significantly influence the results obtained. The relative reliability intra- and inter-session was good to excellent (i.e., intraclass correlation coefficients were between 0.78 and 0.91) and excellent absolute reliability (i.e., standard error of the measurement lower than 10% of the average test or retest value) was observed for the glasses, especially for the vertical axis. Whatever the testing sessions in all conditions, significant correlations (p < 0.001) were found for the acceleration values recorded either in the vertical axis and in the anteroposterior axis between the glasses and the optoelectronic system. Concurrent validity between the glasses and the optoelectronic system was observed. Our observations indicate that the IMU embedded in smart glasses is accurate to measure vertical acceleration during STS movements. Further studies should investigate the use of these smart glasses to assess the STS movement in unstandardized settings (i.e., clinical and/or home) and to report vertical acceleration values in an elderly population of fallers and non-fallers.