Vertical Shocks Research Articles

Effects of seating on the discomfort caused by mechanical shocks: Measurement and prediction of SEAT values

Seat effective amplitude transmissibilities (SEAT values) quantify the influence of seats on discomfort caused by vibration. This study investigated SEAT values with vertical mechanical shocks at low, medium, and high magnitudes (0.5, 1.0, and 2.0 ms−1.75) at frequencies between 1.0 and 16 Hz. With 18 subjects sitting on a rigid seat and two foam cushions, SEAT values were measured objectively (from the transmitted vibration), measured subjectively (by the responses of subjects), and predicted (using a model of the seat-passenger system). Except with high magnitude low frequency shocks, predicted SEAT values were similar to measured SEAT values. With shocks causing subjects to rise off a cushion and subsequently impact the cushion (low frequencies around 1 g), subjective SEAT values were better estimated using predicted SEAT values than objectively measured SEAT values, because accelerometers on cushions exaggerated the impact of the falling subject. However, accelerometers on rigid seats will underestimate such impacts.

Reconstruction and Development of Tourism Potentials in the Fishermen’s District Village of Medan Belawan

Belawan Fishermen Village is a Fisherman Village on the edge of Medan City. The fisherman is the biggest livelihood in this village. A Spatial also has a lot of activities / local wisdom as well as traditions such as traditional rowing racing, drying salted fish and catching fish. The problems of the Villages are from poverty, lack of green open space, dirty and smelly environments, waste everywhere, improper laying of buildings, and inadequate water supply. The structures of buildings and building materials in these villages are also included in the inappropriate category. This design aims to make this village as a tourist village, comfortable to live and visited by tourists, and make a friendly village face with the surrounding environment, and can improve the lives of citizens. Also, it can improve the lives of citizens. Realizing the theme of tourism by taking the potential and cultural character and local wisdom which is then implemented in the form of tourism. There are several aspects of design in this design include the following:In the aspect of this village activity, there are 2 activities that are the daily activities of citizens and tourism activities.In the aspect of this village, the site has two accesses, on land in the form of decks that are 2m wide as well as ocean circulation that is connected directly to the pier deck of residents' homes.In the aspect of the building, the building in this village uses a structure that is resistant to seawater. In addition to being able to withstand vertical and lateral shocks and buffers that with PVC pipe material filled with cement. Utilities make a biofiltration system that treats waste before entering the sea considering the area of the settlement is a conservation area.

Frequency-dependence of discomfort caused by vibration and mechanical shocks

The frequency content of a mechanical shock is not confined to its fundamental frequency, so it was hypothesised that the frequency-dependence of discomfort caused by shocks with defined fundamental frequencies will differ from the frequency-dependence of sinusoidal vibration. Subjects experienced vertical vibration and vertical shocks with fundamental frequencies from 0.5 to 16 Hz and magnitudes from ±0.7 to ±9.5 ms–2. The rate of growth of discomfort with increasing magnitude of motion decreased with increasing frequency of both motions, so the frequency-dependence of discomfort varied with the magnitudes of both motions and no single frequency weighting will be ideal for all magnitudes. At the frequencies of sinusoidal vibration producing greatest discomfort (4–16 Hz), shocks produced less discomfort than vibration with same peak acceleration or unweighted vibration dose value. Frequency-weighted vibration dose values provided the best predictions of the discomfort caused by different frequencies and magnitudes of vibration and shock.Practitioner Summary: Human responses to vibration and shock vary according to the frequency content of the motion. The ideal frequency weighting depends on the magnitude of the motion. Standardised frequency-weighted vibration dose values estimate discomfort caused by vibration and shock but for motions containing very low frequencies the filtering is not optimum.

ON THE SURVIVAL OF HIGH-ALTITUDE OPEN CLUSTERS WITHIN THE MILKY WAY GALAXY TIDES

ABSTRACT It is a common assumption that high-altitude open clusters live longer compared to clusters moving close to the Galactic plane. This is because, at high altitudes, open clusters are far from the disruptive effects of in-plane substructures, such as spiral arms, molecular clouds, and the bar. However, an important aspect to consider in this scenario is that orbits of high-altitude open clusters will eventually cross the Galactic plane, where the vertical tidal field of the disk is strong. In this work, we simulate the interaction of open clusters with the tidal field of a detailed Milky Way Galactic model at different average altitudes and galactocentric radii. We find that the life expectancy of clusters decreases as the maximum orbital altitude increases and reaches a minimum at altitudes of approximately 600 pc. Clusters near the Galactic plane live longer because they do not experience strong vertical tidal shocks from the Galactic disk; then, for orbital altitudes higher than 600 pc, clusters again start to live longer due to the decrease in the number of encounters with the disk. With our study, we find that the compressive nature of the tides in the arms region and the bar play an important role in the survival of small clusters by protecting them from disruption: clusters inside the arms can live up to twice as long as those outside the arms at similar galactocentric distances.

Response of the seated human body to whole-body vertical vibration: discomfort caused by mechanical shocks

The frequency dependence of discomfort caused by vertical mechanical shocks has been investigated with 20 seated males exposed to upward and downward shocks at 13 fundamental frequencies (1–16 Hz) and 18 magnitudes (±0.12 to ±8.3 ms−2). The rate of growth of discomfort with increasing shock magnitude depended on the fundamental frequency of the shocks, so the frequency dependence of equivalent comfort contours (for both vertical acceleration and vertical force measured at the seat) varied with shock magnitude. The rate of growth of discomfort was similar for acceleration and force, upward and downward shocks, and lower and higher magnitude shocks. The frequency dependence of discomfort from shocks differs from that of sinusoidal vibrations having the same fundamental frequencies. This arises in part from the frequency content of the shock. Frequency weighting Wb in BS 6841:1987 and ISO 2631-1:1997 provided reasonable estimates of the discomfort caused by the shocks investigated in this study.Practitioner Summary: No single frequency weighting can accurately predict the discomfort caused by mechanical shocks over wide ranges of shock magnitude, but vibration dose values with frequency weighting Wb provide reasonable estimates of discomfort caused by shocks similar to those investigated in this study with peak accelerations well below 1 g.

Influence of Occupant Compliance on a Vertically Stroking Helicopter Crew Seat Suspension

This study addresses the effects of compliance of an occupant seated in an adaptive seat suspension equipped with a magnetorheological energy absorber, and exposed to intense vertical shocks. A 50th percentile male occupant, exposed to shock conditions characterized by sink rates varying from 5 to , was considered. The compliance effects were examined by comparing the response of a multiple degree-of-freedom biodynamic lumped-parameter model derived from the response of a Hybrid II anthropomorphic test dummy representing a compliant-occupant model to the response of an equivalent rigid-occupant model under the same shock conditions. An experimentally validated nonlinear mathematical model of a magnetorheological energy absorber was integrated with both the compliant and rigid models of the occupants. In addition, three different control techniques were investigated based on controlling the onset of magnetorheological-energy-absorber stroking load: constant stroking-load control, terminal trajectory control, and optimal control. The internal damping of a compliant occupant proved to be a crucial parameter in determining the biodynamic response for all control techniques. An assessment of the potential of injury was conducted based on the established injury criteria for compliant occupants to evaluate the applicability of the control techniques.

Effectiveness of Suspension Seats in Maintaining Performance Following Military High-Speed Boat Transits

The aim of this study was to investigate whether suspension seats (SS) fitted to rigid inflatable boats (RIB) could help maritime boarding teams maintain running performance during the high-risk posttransit phase. High-speed RIB transits have been reported to cause reductions in the running performance of boarding teams posttransit. In this experiment, two pairs of teams completed a 3-hr transit in either calm or rough seas (calm, 5 vs. 5; rough, 6 vs. 6) in an RIB fitted with either fixed (FS) or Suspension seats (SS). Exhaustive shuttle run distance was measured pre- and immediately posttransit. Transit heart rate and perceived exertion (RPE) were measured and deck and seat pan acceleration recorded; the latter were reported as impacts count and peak magnitude. Distance run was reduced for the FS teams following both transits (calm,-250 m,-20%, p < .07; rough, -398 m, -26%, p < .05), whereas it was unchanged for the SS teams. All transit heart rates and RPE indicated light exertion levels. Seat pan impacts were similarly reduced during the calm transit (FS, -42%; SS, -30%); however, during the rough transit, the SS was more than twice as effective (FS, -32%; SS, -71%). Peak impact magnitudes were reduced by the SS (calm, -38%; rough, -57%) and amplified by the FS (calm, +3%; rough, +28%). Suspension seats effectively maintained posttransit running performance by reducing magnitude of the vertical shocks imposed on the passengers. High-speed RIB transits followed immediately by high-intensity activity are intrinsic to contemporary maritime operations; suspension seats can maintain post-transit physical performance, thereby enhancing safety and operational effectiveness.

Magnetohydrodynamic structure of a plasmoid in fast reconnection in low-beta plasmas

Plasmoid structures in fast reconnection in low-beta plasmas are investigated by two-dimensional magnetohydrodynamic simulations. A high-resolution shock-capturing code enables us to explore a variety of shock structures: vertical slow shocks behind the plasmoid, another slow shock in the outer-region, and the shock-reflection in the front side. The Kelvin–Helmholtz-like turbulence is also found inside the plasmoid. It is concluded that these shocks are rigorous features in reconnection in low-beta plasmas, where the reconnection jet speed or the upstream Alfvén speed exceeds the sound speed.

CIRCULATION AND DISSIPATION ON HOT JUPITERS

Many global circulation models predict supersonic zonal winds and large vertical shears in the atmospheres of short-period jovian exoplanets. Using linear analysis and nonlinear local simulations, we investigate hydrodynamic dissipation mechanisms to balance the thermal acceleration of these winds. The adiabatic Richardson criterion remains a good guide to linear stability, although thermal diffusion allows some modes to violate it at very long wavelengths and very low growth rates. Nonlinearly, wind speeds saturate at Mach numbers $\approx 2$ and Richardson numbers $\lesssim 1/4$ for a broad range of plausible diffusivities and forcing strengths. Turbulence and vertical mixing, though accompanied by weak shocks, dominate the dissipation, which appears to be the outcome of a recurrent Kelvin-Helmholtz instability. An explicit shear viscosity, as well as thermal diffusivity, is added to ZEUS to capture dissipation outside of shocks. The wind speed is not monotonic nor single valued for shear viscosities larger than about $10^{-3}$ of the sound speed times the pressure scale height. Coarsening the numerical resolution can also increase the speed. Hence global simulations that are incapable of representing vertical turbulence and shocks, either because of reduced physics or because of limited resolution, may overestimate wind speeds. We recommend that such simulations include artificial dissipation terms to control the Mach and Richardson numbers and to capture mechanical dissipation as heat.

RESISTIVE MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION

Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten--Lan--van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv\'{e}nic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet--Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

Preparation of defined bulk densities for using the capillary rise method in the case of fine powders

The wetting properties of powders are important in many technological processes. Contact angles can be characterized by an effective contact angle of the particle arrangement relative to the wetting liquid, but their quantification is problematic. An exact determination depends on an accurate preparation of the test samples. A defined pre-consolidation by vertical shocks is introduced in this paper.

Effects of frequency, magnitude, damping, and direction on the discomfort of vertical whole-body mechanical shocks

The discomfort of seated subjects exposed to a wide range of vertical mechanical shocks has been studied experimentally. Shocks were produced from responses of single degree-of-freedom models with 16 fundamental frequencies (0.5–16 Hz) and four damping ratios (0.05, 0.1, 0.2 and 0.4) to half-sine force inputs. Shocks with a damping ratio of 0.4 were presented with both polarities. Each type of shock was presented at five unweighted vibration dose values (0.35–2.89 m s −1.75). The magnitude estimates of 15 subjects to all 400 shocks showed that the rate of growth in discomfort (the exponent in Stevens’ power law) decreased with increasing shock frequency from 0.5 to 4 Hz. Equivalent comfort contours showed greatest sensitivity from 4 to 12.5 Hz. At lower magnitudes, variations in discomfort with frequency were similar to weighting W b in British Standard 6841. At higher magnitudes, low frequencies were judged relatively more uncomfortable than predicted by this weighting. There were small but statistically significant differences in discomfort associated with variations in damping ratios and shock direction. It is concluded that the frequency dependence of discomfort produced by vertical shocks depends on shock magnitude, but for shocks of low and moderate discomfort, the current evaluation methods are reasonable.

兵庫県南部地震の際の船舶乗組員及び漁業関係者の異常体験に関するアンケート調査

On the 17th of January, 1995, the Southern Hyogo Great Earthquake hitted the Hanshin District and damaged it seriously. At the earthquake, many ships were sailing, anchoring, fishing and so on, and many seamen and fishermen had experienced quite abnormal shocks and/or phenomena on board. The questionnaire research was made on abnormal experiences and phenomena they had on board and their actions at that time. It showed that many of them felt severe vertical shocks as their ships stroke aground and/or serious engine troubles like explosion. And in many ships, many actions were taken to recognize and manage their safety against such emergency, and those worked relatively well eventhough some ships did not get suitable actions. On the other hand, many ships faced serious difficulty getting contact with the competent authorities concerned and had earth quake information from TV. Fishery situations were also seriously changed.

Subjective reaction to vertical mechanical shocks of various waveforms

Two laboratory studies have been conducted to assess the discomfort caused to seated male subjects by exposures to vertical whole-body mechanical shocks. The first experiment was designed to obtain judgements of the discomfort of single “up” or “down” damped sinusoidal impulses. Sixteen subjects used the method of magnitude estimation to indicate the discomfort produced by damped sine waves at nominal frequencies of 1, 4 and 16 Hz, with damping ratios of 0·125, 0·250 and 0·707 and vibration dose values ranging from 0·6 to 4·0 m s −1·75. Analysis was also conducted to determine whether the growth of discomfort with increasing magnitude was influenced by frequency, duration or direction of motion. The results suggested that a single frequency weighting and a single duration weighting is appropriate at all magnitudes. Analysis was also conducted to determine whether the discomfort depends on the frequency, duration and direction of shocks when they are presented at a constant vibration dose value using frequency weighting W b . There was no difference between the discomfort caused by “up” and “down” shocks of the same vibration dose value, but the W b frequency weighting slightly underestimated sensitivity to low-frequency shocks. The second experiment sought to compare two methods of evaluating stimuli containing between one and 16 repeated shocks. The vibration dose value [∫ o T a 4(t) dt] 1 4 and a measure of dose related to “energy”, [∫ o T a 2(t) dt] 1 2 , were employed to predict the reduction in shock magnitude required to counteract any increased discomfort with a greater number of shocks. Subjects employed the method of paired comparison. Judgements of the relative discomfort of the stimuli presented in pairs indicated that the vibration dose value provided the more accurate method of evaluating the discomfort of the shocks.

Evaluation of a new defibrillation pathway: Tongue-epigastric/tongue-apex route. II. Impedance characteristics in human subjects

An automated device for defibrillation using a vertical shock pathway (tongue-epigastric or tongue-apex) has been developed. The energy requirements for defibrillation using vertical pathways are uncertain and will be determined largely by the impedance of the pathway. The purpose of this study was to determine the impedance characteristics of vertical defibrillation pathways in human subjects. Twenty patients undergoing elective cardioversion of atrial fibrillation or atrial flutter, or both, were studied. Patients received shocks from electrodes placed in tongue-epigastric or tongue-cardiac apex positions. The tongue electrode was a 12 cm2 metal plate fixed to a standard plastic oropharyngeal airway. The epigastric or cardiac apex electrode was a 40 cm2 self-adhesive pad. The electrodes were connected to a standard damped-sinusoidal waveform defibrillator. It was found that the two vertical shock pathways had substantially higher impedance than the standard transthoracic pathway: tongue-epigastric pathway 130 +/- 11 omega (SD), tongue-apex pathway 115 +/- 12 omega, transthoracic pathway 68 +/- 11 omega (p less than 0.05). The higher impedance is probably due to the longer interelectrode distances of vertical pathways: tongue-epigastric 33 +/- 3 cm, tongue-apex 28 +/- 3 cm, transthoracic 23 +/- 3 cm (p less than 0.05). Vertical pathway shocks were successful in the cardioversion of 15 of 20 patients. Four of the five patients in whom vertical shocks were unsuccessful subsequently underwent successful cardioversion by transthoracic shocks; the transthoracic shocks achieved a higher current because of lower impedance of the transthoracic route.(ABSTRACT TRUNCATED AT 250 WORDS)