Values Of Vertical Acceleration Research Articles

Multi-Body Model of Agricultural Tractor for Vibration Transmission Investigation

This article analyses vibration transmission on agricultural tractors with the excitation from the road to the driver’s seat. A multi-body model of agricultural tractors created in Adams is presented. The main parts for the investigation of vibration transmission are the tractor body, where the only suspension elements are tyres, the tractor cabin, spring-dampers suspended at the rear and bushings at the front, and the driver seat with its pneumatic spring. A series of measurements were performed, and the model was validated using vertical acceleration values on the tractor body at four different locations. The FTire model (physical FEM-based model) was chosen to describe the behaviour of tyres. The model was created using measured tyre characteristics. Measured characteristics of spring-dampers and front cabin bushings were also implemented. For comfort investigation, ride simulations on ISO 5008 rough roads were performed. The transmission of vibrations in ride simulations was examined. A modal analysis of the linearised model was performed to confirm assumptions of the contribution of suspension elements to overall vibration levels. Finally, three case studies were conducted to better understand the model’s vibration transmission properties.

Measurement and optimization of nonlinear damping systems for agricultural engineering vehicle cab

The issue of nonlinear dampness in the cab of agricultural engineering vehicles is examined by analyzing the vibration reduction system of a specific agricultural loader. Firstly, the specific loader was tested under different conditions. Then, the nonlinear vibration reduction system model of the cab–seat–human body is established by using the measured frame vibration signal as input. Finally, the multi–objective genetic algorithm is used to optimize the root mean square (RMS) value of vertical acceleration of the cab and seat. The test results show that the seat vibration is significantly greater than the acceleration of the cab floor under driving and working conditions, so the seat vibration is amplified and the seat parameter setting is unreasonable; the engine and the working device are also an important part of the cab vibration source, in addition to the uneven road surface. Comparing the RMS values of the vertical acceleration of the cab and seat, which were calculated by the model and obtained from the vehicle test, the error does not exceed 6%, indicating that the model’s accuracy meets the requirement. The vehicle experiment proves that the RMS value of the vertical acceleration of the cab and seat is reduced by 16% and 53%, respectively, after optimization. This study provides a theoretical basis for the design of the damping system for the cab of agricultural engineering vehicles.

A Clustering-Based Approach to Functional and Biomechanical Parameters Recorded with a Pair of Smart Eyeglasses in Older Adults in Order to Determine Physical Performance Groups.

Falls and frailty status are often associated with a decline in physical capacity and multifactorial assessment is highly recommended. Based on the functional and biomechanical parameters measured during clinical tests with an accelerometer integrated into smart eyeglasses, the purpose was to characterize a population of older adults through an unsupervised analysis into different physical performance groups. A total of 84 participants (25 men and 59 women) over the age of sixty-five (age: 74.17 ± 5.80 years; height: 165.70 ± 8.22 cm; body mass: 68.93 ± 13.55 kg) performed a 30 s Sit-to-Stand test, a six-minute walking test (6MWT), and a 3 m Timed Up and Go (TUG) test. The acceleration data measured from the eyeglasses were processed to obtain six parameters: the number of Sit-to-Stands, the maximal vertical acceleration values during Sit-to-Stand movements, step duration and length, and the duration of the TUG test. The total walking distance covered during the 6MWT was also retained. After supervised analyses comparison (i.e., ANOVAs), only one of the parameters (i.e., step length) differed between faller groups and no parameters differed between frail and pre-frail participants. In contrast, unsupervised analysis (i.e., clustering algorithm based on K-means) categorized the population into three distinct physical performance groups (i.e., low, intermediate, and high). All the measured parameters discriminated the low- and high-performance groups. Four of the measured parameters differentiated the three groups. In addition, the low-performance group had a higher proportion of frail participants. These results are promising for monitoring activities in older adults to prevent the decline of physical capacities.

Seakeeping criteria of a moored and articulated multibody floating platform in head seas

Within the Space@Sea project, a multi-use floating concept was proposed by following the analogy of standardization to enlarge a floating platform using a multitude of smaller structures. An operability analysis must be performed to identify its seakeeping criteria and how the criteria limit its functionality. A two-step strategy is proposed to calculate the responses of the target floating concept in head waves, where nonlinearities of the mooring lines and mechanical joints are taken into account. The weakly nonlinear time-domain procedure relies on a diffraction-radiation model in the frequency domain. The motions of floating bodies are solved in the time domain, in which nonlinear Froude-Krylov and hydrostatic forces are estimated under instantaneous incident wave surface. Multibody interactions are resolved under consideration of catenary mooring lines and hinged joints. Wave-induced motions and loads are expressed in terms of transfer function for determining the limiting criteria, including the translational and rotational motions velocities and accelerations; relative motions, velocities and accelerations between module floaters; mooring tensions; as well as hinge forces. Assessments are carried out for various sea conditions against the prescribed values, for the chosen criteria, to address safety issues due to sever platform responses. Different operational requirements for trained workers and untrained passengers of motions and accelerations are taken into consideration. Results show that rotational motions have a significant influence on the platform’s seakeeping performance. Nevertheless, the root mean square (RMS) value of vertical acceleration dominates the comfort of persons onboard, defining the final limiting criterion of the entire platform.

Improving ride comfort by optimising suspension system of an electric street sweeper

The opinion of the operators of the working machines in today’s world is much more valued than in the past. Their comfort, safety and satisfaction during the working hours can be crucial in the decision making process of buying new working machine. Therefore, in this research paper the vertical dynamics and ride comfort of an electric street sweeper would be analysed by using a multibody dynamic model. The model is created using MSC. ADAMS, based on a real electric street sweeper. In order to test the ride comfort of the existing model, a road profile is modelled, according to the standard ISO 8608. The virtual tests are conducted while the vehicle is traveling with maximum velocity of 40 km/h, achieved during transit and lower velocities which are achieved during the operating hours of the machine. An optimization of the suspension system of the real electric sweeper is made, by targeting its components location and positioning, stiffness and damping characteristics. This results in improved ride comfort and smaller root mean square (RMS) values of vertical acceleration of the driver seat. These improvements would influence on operator’s better comfort and health. Results are presented using comparative diagrams of the original and optimised model.

On applicability of von Karman’s momentum theory in predicting the water entry load of V-shaped structures with varying initial velocity

The water landing of an amphibious aircraft is a complicated problem that can lead to uncomfortable riding situation and structural damage due to large vertical accelerations and the consequent dynamic responses. The problem herein is investigated by solving unsteady incompressible Reynolds-averaged Navier–Stokes equations with a standard k−ω turbulence closure model. The theoretical solutions established by the von Karman’s momentum theory are also employed. In order to validate the relationships between the initial vertical velocity and the peak value of vertical acceleration, free fall test cases of 2D symmetric wedge oblique entry and 3D cabin section vertical entry are presented first. The other parameters at which the maximum acceleration occurs, such as time, penetration depth, velocity, are also evaluated. Hence, the quantitative relations are investigated to water landing event for amphibious aircraft. Detailed results in terms of free surface shape and pressure distribution are provided to show the slamming effects. The results show that a linear dependence of the maximal acceleration from the square of initial vertical velocity can be derived for two-dimensional wedge, three-dimensional cabin section and seaplane with V-shaped hull. Moreover, the ratio between the corresponding velocity and the initial vertical velocity tends to a constant threshold value, 5/6, derived from the theoretical solution, when increasing the initial vertical velocity in all three cases.

Comparison of Vehicle Dynamics Performance When Operating on High-speed Dedicated and Existing Railways

In order to study the parameters difference between the high-speed dedicated and the existing railway tracks, the geometric parameters and irregularity of the two kind of tracks are compared and analyzed. The nonlinear dynamic model of Electric Multiple Units (EMU) is built, and the difference of dynamics performance of vehicle running on different railway tracks is simulated and analyzed. The results show that the track spectrum overall performance of the high-speed lines is better than that of the existing lines. At the same speed, the lateral and vertical Sperling index of vehicle running on the high-speed dedicated railway tracks is better than that of the existing railway tracks. At low speed (160km/h), when the vehicle is running on the high-speed dedicated railway tracks, the maximum and rootmean square values of the frame lateral acceleration are 59.7% and 24.6% of the existing railway tracks operating conditions respectively, and the corresponding maximum and root mean square values of vertical acceleration are 49.1% and 89.8% respectively. At high speeds (350km/h), the maximum and root mean square values of lateral and vertical acceleration of the frame are 54.2%, 32.3% and 27.6%, 55.3%. With the decrease of the track curvature, the lateral wheelset force gradually increases.

Body attitude control strategy based on road level for heavy rescue vehicles

This paper proposes an attitude control strategy based on road level for heavy rescue vehicles. The strategy aims to address the problem of poor ride comfort and stability of heavy rescue vehicles in complex road conditions. Firstly, with the pressure of the suspension hydraulic cylinder chamber without a piston rod as the parameter, Takagi–Sugeno fuzzy controller classification and adaptive network-based fuzzy inference system controller classification are used to recognise the road level. Secondly, particle swarm optimisation is adopted to obtain the optimal parameters of the active suspension system of vehicle body attitude control under different road levels. Lastly, the parameters of the active suspension system are selected in accordance with the road level recognised in the driving process to improve the adaptive adjustment capability of the active suspension system at different road levels. Test results show that the root mean square values of vertical acceleration, pitch angle and roll angle of the vehicle body are reduced by 59.9%, 76.2% and 68.4%, respectively. This reduction improves the ride comfort and stability of heavy rescue vehicles in complex road conditions.

MODELING THE INFLUENCE OF THE ARTICLE DEVICE ON DYNAMIC INDICATORS OF FREIGHT WAGONS

The article investigates the dynamic performance of a freight car with an articulation device - model SAC-1 RUS. As a criterion for assessing dynamic indicators, the acceleration of the car body and the dynamic deflections of the "spring-truck" system were selected, which characterize the ride and loss of stability of the car when it goes off the rails on various irregularities of the track. When an articulated car moves along different path irregularities, the acceleration that occurs at various points along the length of the car is not the same. In compiling the system of differential equations of motion of the "spring - truck" system, the Lagrange equation of the second kind was used as the mathematical apparatus. The body acceleration and the dynamic deflections of the springs were chosen as the criteria for assessing the running properties of the cars. The first characterizes the smoothness of the carriage, and the second characterizes the stability of the wheel, i.e. wheel derailment. It is known that the magnitude of the acceleration at different points along the length of the car is not the same, since the value of the vertical acceleration of bouncing is influenced by the vertical oscillations of the body's galloping. Therefore, when solving the system of differential equations, the body accelerations were determined at two points: above the center plates of the bogies and the center plate of the device for articulating freight cars or above the wheelsets, that is, in the places where acceleration sensors are installed during full-scale tests of cars. Based on the analysis of the results obtained, it was revealed that articulated cars: exclude the possibility of relative vertical displacements of adjacent cars, with other equal dynamic parameters; lead to a noticeable deterioration in driving properties, accompanied by an increase in the value of vertical acceleration of the body. The values of accelerations and dynamic deflections of an articulated car are 6% higher than those of a four-axle freight car. The vertical acceleration of the front and rear of an articulated car is 30% greater than that of a typical car. Outside the critical speed for an articulated car, the value of vertical dynamic deflections significantly decreases in the case of an isolated irregularity with a length of 6 m or less.

Sit-To-Stand Movement Evaluated Using an Inertial Measurement Unit Embedded in Smart Glasses-A Validation Study.

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.

Experimental study on shock control of a vehicle semi-active suspension with magneto-rheological damper

During driving process, the impact from the road, such as pothole or bump can deteriorate the performance of the vehicle, and increase the driving dangerousness and health risk of drivers/passengers due to high energy and short time. The magneto-rheological (MR) intelligent suspension plays an important role in improving the ride comfort of vehicle, which can reduce the impact transmitted from the road. In consideration of different impact application induced by different driving speed, an adaptive skyhook control (ASC) based on improved Genetic Algorithm (GA) is proposed in this paper. Vibration dose value (VDV) of vertical acceleration of floor at driver’s position is selected as the object function for improved GA to obtain the optimal skyhook gain coefficients under different driving speeds. And then the adaptive law is formulated by using table lookup method. The road test for the B segment car installed with MR dampers is undertaken to verify the effectiveness of the designed controller. The experimental results demonstrate that the reduction of VDV and peak value of vertical acceleration with ASC is always more than that with traditional skyhook controller. Results indicate that the energy spectrum density amplitude of using ASC algorithm is lower than that with skyhook controller, when the driving speed is less than or equal to 30 km h−1.

Muscle torque production and kinematic properties in post-stroke patients: a pilot cross-sectional study

Stroke-related hemiplegia is an important factor influencing parameters of gait. So far, limited papers have assessed temporo- spatial capabilities and their correlations with gait parameters in the early post-stroke stage. This pilot study evaluated the temporospatial parameters of gait and assessed the maximal isometric and isokinetic torque production of the plantar flexor and dorsiflexor muscles. 15 patients with lower limb spasticity and 15 healthy controls were included. Stroke severity was assessed using the Modified Ashworth Scale and the Barthel Index. Gait cadence, gait speed, and gait cycle were assessed using inertial sensors during a Timed Up and Go test. Maximal isometric and isokinetic torque production of the ankle plantar flexor and dorsiflexor muscles were assessed using an isokinetic dynamometer device. Post-stroke patients had statistically significantly lower gait cadence than healthy participants (17%, p < 0.05). Statistically significantly lower values of vertical acceleration were also noted during a sit-to-stand movement task (42%, p < 0.05). Plantar flexion torque of the affected limb was significantly different during isometric (63%, p ≤ 0.01) and isokinetic work for 30o/s (49%, p = 0.04), 60o/s (58%, p = 0.01) and 20 °/s (53%, p = 0.01). Dorsiflexor muscles' torque production was significantly different in isometric activity (38%, p = 0.04). A statistically significant positive correlation occurred between the absolute peak torque of the dorsiflexor muscles in both static and speed phases of gait (Rs = 0.65, p = 0.04). Despite the low intensity of spasticity and early phase after stroke, differences in the muscle torque production and temporo-spatial parameters, as well as the correlations between them, were noticeable.

Video analysis of response of reinforced concrete beam to impact loading during drop test

A response of concrete and reinforced concrete structures to very rapid dynamic loading shows an increase of both tensile and compressive strength. This behaviour is also accompanied by an increase of stiffness of the structure. Described response can be numerically simulated only with adequate viscous nonlinear material model of concrete. The problem of these simulations is based not only on a necessity of a derivation of the right material model but also on viscous parameters whose values are not known in advance. The proposed article deals with experimental research of the response of the reinforced concrete beam exposed to impact loading during drop test. The beam response was measured with conventional strain gauges and accelerometers and whole experiment was recorded with 1000 frames per second by slow motion camera. Measured values of vertical acceleration were then compared with results of software analysis of slow-motion video footage. The paper contains the description of the experimental research, the comparison of conventional measurements with video analysis and the simulated response of the specimen in the software based on the finite element method using the viscous material model of concrete.

Evaluation of speed loss in bulk carriers with actual data from rough sea voyages

The evaluation of speed loss is the most important studies in the optimal ship routing. However, the mode of speed loss during rough sea voyages is complicated because of the involvement of the human factor. A speed loss analysis is conducted to improve the accuracy of evaluation of measured data extracted from actual marine conditions. First, the conventional criteria to judge the deliberate speed reduction is summarized with the conventional ship maneuvering techniques. Second, a nationwide questionnaire for marine engineers implemented for engine safety during rough sea voyages is detailed. Third, these conventional criteria are validated by analyzing the collated data on accelerations, ship motions, navigation, and engine parameters. The limiting value of vertical acceleration agrees with that obtained via practical measurements. On the contrary, the limiting values of lateral acceleration, roll motions, probabilities of deck wetness, and slamming do not agree with that obtained via measurements. The probabilities of deck wetness, slamming, and propeller racing start to increase at approximately the same instant where the deliberate speed reduction occurs. Some relations between the deck and engine parameters detailed in this paper were found to be highly correlated. Finally, the results of the analysis were used to model simpler estimations. • This study makes clear the detailed situations on the speed loss in rough sea voyages. • Related parameters are validated with the measured database for 28,000-DWT bulk carrier. • Deliberate speed reduction occurs at the starting point of deck wetness or propeller racing. • Speed loss has a boundary region at Δ V = 3–4 knots, and are correlated with pitch motion.

Experimental and numerical evaluation of wave impact stress on a composite boat hull

In this paper, a composite planing hull response is tested in a numerical environment, using real material properties obtained from hull excerpts in lab. Extreme loads are simulated in a numerical quasi static situation using register rules recommendations for pressure and vertical acceleration values. The results are compared with the experimental values recorded using full scale hull and trials in real conditions on the river, for different speed values comprised between 4 and 12 m/s

Optimal control design for reducing vertical acceleration of a motor yacht form

Ship motions and their adverse effects have always been studied with the aim of reducing motions and accelerations using whatsoever plausible ways during both the ship design process and operating lifetime. In the present work, a simulation study is carried out by taking into consideration the passengers in several locations of the selected motor yacht in an intermediate sea state with Hs = 1 m. Irregular head wave scenario at Fn = 0.25 is investigated and a controller design is implemented to ensure that the calculated RMS vertical acceleration values are decreased to tolerated levels in terms of motion sickness index. First, wave loads are obtained in the time domain by using strip theory, linear superposition technique, and the most common realization technique. Then, using a linear two-degree-of-freedom mathematical model, in which pitch and heave motions are considered together with the direct solution of convolution integrals, the uncontrolled motions and accelerations are obtained. Then, the linear matrix inequalities based on robust static output feedback controller are designed to mitigate the vertical acceleration of the ship. Finally, the results obtained with the robust static output feedback control design are presented in numerical simulation studies to demonstrate the effectiveness of the proposed control approach.

Comparative analysis of dynamic behaviour of two cablestayed footbridges made entirely of steel and GFRP composite

This paper is focused on the comparative numerical analysis of the dynamic behaviour of two cable-stayed footbridges made entirely of steel and Glass Fiber Reinforced Polymer (GFRP) composite, with similar geometrical parameters and bearing capacity. The analysis was executed using the Autodesk Robot Structural Analysis Professional software. Firstly, the determination of modal parameters of both footbridges was done. For the further finite element analysis the damping ratio of the all-GFRP footbridge was measured in situ, whereas for the all-steel footbridge was taken from data published in the literature. Then, the dynamic responses of both structures were determined based on the Footfall harmonic analysis. In this case, the numerical models of analyzed footbridges were subjected to dynamic effects of human gait with various moving frequency. The maximal values of vertical acceleration of structural vibrations were obtained. The vibration comfort criteria for both footbridges were verified. The numerical results were compared and differences in dynamic responses of analyzed footbridges were examined. The obtained results delivered some important practical data regarding the dynamic response as well as vibration comfort criteria of cable-stayed footbridges which could be used at a design stage to make a decision on the construction material solution.

Optimum design for passive suspension system of a vehicle to prevent rollover and improve ride comfort under random road excitations

The main functions of suspension system are to provide ride comfort for the passengers and vehicle handling (road holding). But, in many studies, full attention to the ride comfort leads to the determination of incorrect suspension system parameters as well as other problems such as rollover and reducing road-holding ability in the vehicle. The aim of this study is to present a method for the optimized design of the vehicle suspension system in order to improve the ride comfort, road holding, workspace and preventing rollover, considering a full vehicle model with 11-DOF. The most important feature of this study is that the prevention of rollover factor and all of suspension functions are considered simultaneously. In this research, in order to assess the ride comfort, the vertical acceleration values of seats that are caused by random road roughness are calculated by power spectral density of road in frequency domain. In the context of prevention of rollover, Fishhook manoeuvre is performed using a mathematical model for the roll motion, and then the dynamic behaviour of the variables is considered in rollover threshold. Then, the optimization problem is solved to minimize the vertical acceleration values and vehicle roll angle by considering the physical limitation and safety of the model. The results of the optimization show that the vertical acceleration, in frequency domain at the desired boundary values (as defined in ISO 2631), decreases and rollover resistance of the vehicle increases.

실습선 가야호의 선속 변화에 따른 뱃멀미 지수에 관한 연구

본 연구에서는 실습선 가야호를 대상으로 하여 파랑 중 운동성능을 평가하였다. 그리고 쾌적한 승선감을 확보하기 위하여 실제 해상에서 운항중인 선박의 선내 위치별 수직가속도 성분을 선체운동 계산 기법을 통해서 구하고, 수직가속도 스펙트럼을 이용하여 가야호의 선속변화에 따른 가속도 계산 결과를 뱃멀미 지수(MSI; Motion Sickness Incidence)의 가이드라인과 비교 검토하여 멀미의 정도를 표시하였다. MSI 계산 결과는 선속이 5 knots, 10 knots, 12 knots로 커지는 순서대로 수직가속도의 가중치가 높게 나타나며, 입사각은 <TEX>$180^{\circ}$</TEX>와 <TEX>$150^{\circ}$</TEX>에 비해 선수사파인 <TEX>$120^{\circ}$</TEX>의 경우에 수직가속도의 가중치가 높게 나타났다. In this paper, the motion performance in waves for the training ship Kaya of Pukyong National University is obtained by using a computer program based on Strip method. To guarantee the pleasant seafaring in ocean, the vertical acceleration of ship motion is calculated according to the location of the ship. The results of calculation by changes of ship speed are compared with the guideline of MSI(Motion Sickness Incidence). The degree of motion sickness is shown and discussed through the comparison between calculated vertical acceleration spectrum and MSI guideline. The computational results of MSI were as follow; when ship speed increased in the order of 5 knots, 10 knots, 12 knots and encounter angle became the bow quartering sea of <TEX>$120^{\circ}$</TEX> compared to <TEX>$180^{\circ}$</TEX> and <TEX>$150^{\circ}$</TEX>, the vertical acceleration values grew higher.

Performance Analysis of Two-stage Series-connected Inerter-spring-damper Suspension Based on Half-car Model

Based on the real analogy between the inerter-spring-damper mechanical system and the capacitor-inductor-resistor electrical system,an inerter-spring-damper(ISD) vehicle suspension system with two stages connected in series is proposed according to the principle of cascaded filter.In such a suspension system,the first stage is a conventional passive suspension,and the second stage is a parallel inerter-spring-damper.A half-car vehicle model is built to analyze performance of the suspension system under random and pulse input,and to investigate effects of the second suspension stiffness on system performance.The results indicate that in contrast to conventional suspension,the proposed suspension has a better dynamic performance,and improvements of 81%,81%,79% and 82.8% are obtained for PSD peak values of vertical acceleration of the centre of body mass,pitch acceleration of body,dynamic tire load of front and rear wheels in lower-frequency stage.The results further show that the proposed suspension can effectively suppress body resonance,better ride comfort,and improve trade-offs of the ride and handling.