Nonlinear Dynamic Modelling of a Suspension Seat for Predicting the Vertical Seat Transmissibility

Suspension seats are widely used in heavy vehicles to reduce vibration transmitted to human body and promote ride comfort. Previous studies have shown that the dynamics of the suspension seat exhibits nonlinear behaviour with changed vibration magnitudes. Despite various linear seat models developed in the past, a nonlinear model of the suspension seat capturing the nonlinear dynamic behaviour of the seat suspension and cushion has not been developed for the prediction of the seat transmissibility. This paper proposes a nonlinear lumped parameter model of the suspension seat to predict the nonlinear dynamic response of the seat. The suspension seat model comprises of a nonlinear suspension submodel integrated with a nonlinear cushion submodel. The parameters of the submodels are determined by minimizing the error between the simulated and the measured transmissibility of the suspension mechanism and the force-deflection curve of the seat cushion, respectively. The model of the complete seat is then validated using the seat transmissibility measured with inert mass under vertical vibration excitation. The results show that the proposed suspension seat model can be used to predict the seat transmissibility with various excitation magnitudes.

Car seat impact on driver’s sitting behavior and perceived discomfort during prolonged real driving on varied road types

Prolonged driving under real conditions can entail discomfort linked to driving posture, seat design features, and road properties like whole-body vibrations (WBV). This study evaluated the effect of three different seats (S1 = soft; S2 = firm; S3 = soft with suspension system) on driver’s sitting behavior and perceived discomfort on different road types in real driving conditions. Twenty-one participants drove the same 195 km itinerary alternating highway, city, country, and mountain segments. Throughout the driving sessions, Contact Pressure (CP), Contact Surface (CS), Seat Pressure Distribution Percentage (SPD%) and Repositioning Movements (RM) were recorded via two pressure mats installed on seat cushion and backrest. Moreover every 20 minutes, participants rated their whole-body and local discomfort. While the same increase in whole-body discomfort with driving time was observed for all three seats, S3 limited local perceived discomfort, especially in buttocks, thighs, neck, and upper back. The pressure profiles of the three seats were similar for CP, CS and RM on the backrest but differed on the seat cushion. The soft seats (S1 & S3) showed better pressure distribution, with lower SPD% than the firm seat (S2). All three showed highest CP and CS under the thighs. Road type also affected both CP and CS of all three seats, with significant differences appearing between early city, highway and country segments. In the light of these results, automotive manufacturers could enhance seat design for reduced driver discomfort by combining a soft seat cushion to reduce pressure peaks, a firm backrest to support the trunk, and a suspension system to minimize vibrations.

Effects of Different Seat Pressures and Rowing Cadences on Muscle Oxygenation and Physiological Parameter Responses

This study investigated the effects of rowing with different seat cushion and cadence conditions on oxyhemoglobin (O2Hb) and total hemoglobin (tHb) levels of the erector spinae (ES) as well as the effects on heart rate (HR) and ratings of perceived exertion (RPE). Thirty healthy adults completed tests under three unstable air seat cushion pressure levels (0, 80, and 140 mmHg) and three rowing cadences (slow: 18 bpm, medium: 30 bpm, and fast: 36 bpm) on a rowing machine, for a total of nine test conditions. During the exercise period, rowing on cushions set to 80 mmHg resulted in greater O2Hb and tHb changes than did rowing at 0 mmHg (p < 0.05). When rowing cadence increased, the O2Hb and tHb decreased during the exercise period, whereas HR and RPE increased (p < 0.05). During the recovery period, O2Hb and tHb on cushions set to 140 mmHg during slow rowing were higher than those at 0 mmHg during slow rowing and 140 mmHg during fast rowing (p < 0.05). Rowing on an appropriate pressure of seat cushion and using a slow cadence contribute to increasing muscle oxygenation of low back during exercise.

Changes in external ischial tuberosity width at varying trunk–thigh angles between sexes using two measurement methods

This study examined the influence of two methods and various trunk–thigh (TT) angles on external ischial tuberosity width (EITW) for 45 men and 45 women. In the experiment, the impress and seat pressure methods were applied at TT angles of 60°, 75°, 90°, and 105°. When the impress method was used, EITW remained highly consistent across the four measured TT angles with differences of 2.8 and 2.1 mm for men and women, respectively. Conversely, in the seated pressure method, EITW increased with TT angle such that differences in EITW across a full TT angle range were 11.5 and 11.7 mm for men and women, respectively. Irrespective of method, differences in EITW between genders measured approximately 12.6–13.7 mm across all TT angles. Correlation analyses revealed that hip circumference was positively related to EITW in all cases, whereas the relationship of hip width and depth with EITW varied by method and gender. Because of inherent differences in EITW between genders, these findings suggest that gender variability should be considered in seat cushion design.

OLD JAVANESE SEATING EQUIPMENT AS DEPICTED ON THE BASE RELIEF OF BOROBUDUR TEMPLE

This article describes cultural products related to sitting positions, seating equipment, and sitting accessories of the Old Javanese people as in the reliefs of the base section of the Borobudur temple. The reliefs of the Borobudur temple contain stories, meanings, and reflections of the socio-cultural conditions of the people at the time it was being built. As illustrated, the study reveals the variety of sitting positions, equipment, and accessories during the Old Javanese period. The uniqueness of their seating equipment and sitting accessories can be meaningful as the basis for product creation innovations referring to the culture of the Old Javanese people. The research is conducted by interpreting illustrations of people in their sitting positions, including the seating equipment and sitting accessories. The study is conducted by examining the reliefs at the base of Borobudur temple (kamadhatu), specifically in the karmawibangga story panel, which contains the illustrations of sitting activities, including their equipment and accessories. The proportions of the images of people and equipment on the reliefs of the Borobudur temple are perfect. Therefore, they are used to analyze the characteristics of the seating equipment and sitting accessories. The novelty of the research is the identification and study of the illustrations of the ancient people's sitting positions, seating equipment, and some related accessories depicted on the reliefs of the Borobudur temple. Currently, there are several different types of seating equipment in circulation. It is found that the equipment can be classified as personal and communal with a wide seat. The seating equipment, as classified, can be higher than the knee, at the same height as the knee, lower than the knee, and straight on the ground. It is also revealed that the accessories of the seating equipment are in the form of knee straps, backrest, seat cushion, and footstep.

Perception thresholds for whole-body vibrations on an airplane seat

The comfort during a flight on an aircraft is important for passengers. Like many other physical factors, vibrations of the airplane may negatively affect comfort. To understand the impact of vibration on comfort, it is important to know in which way the vibrations transmitted through the seat affects the perception of whole-body-vibrations. In this study, perception thresholds for vertical sinusoidal whole-body vibrations with frequencies between 20 Hz and 75 Hz were determined on a vibration platform with a typical economy class aircraft seat bench. Acceleration levels were recorded with accelerometers placed at the right rear seat rail and inside a seat cushion between the seat surface and the participant. The results show a distinct frequency dependency of the detection thresholds when measured at the seat rail. When taking the difference between the two measurement positions into account and describing the thresholds by the acceleration levels at the seat cushion, the determined perception thresholds are nearly frequency independent up to 50 Hz. This finding is in good agreement with literature data suggesting that the specific experimental setup does not play a big role in this frequency range. Differences above 50 Hz might be explained by the additional armrests in the present study.

Customer Preference of Attributes of Skema Wooden Chair Furniture

The purpose of this research was to find the preferred combination of attributes regarding wooden chair furniture. The subject of this research was Skema Furniture, a Surabaya-based furniture developer since 2016. Variables in this research were acquired through a pre-survey with twenty of Skema Furniture’s previous customers. The attributes were form, seat cushion, customization and wood finish. The form attribute had two levels: curvilinear and rectilinear. The seat cushion attribute had two levels: using a seat cushion and not using a seat cushion. The customization attribute had two levels: the ability to customize and otherwise. The wood finish attribute had two levels: natural finish and solid color finish. Conjoint analysis was used. The sample of 134 people were past consumers of Skema Furniture from the age of 25 to 54. The sample needed for this research, using the Slovin formula, with a 0.05 error tolerance, was around 100 people. The research was conducted via an online survey, due to the COVID-19 pandemic. This research concluded that the most preferred wooden chair furniture was that with a curvilinear form, without a seat cushion, able to be customized, and with a solid color finish. The variables that were most important for the consumers were wood finish and form. This study only describes the preferences of the buyer and user of the furniture chair products. The wooden chair furniture in this research is not specified to any function of a chair. Keywords: customer preference, Skema Furniture, wooden chair furniture