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1

Adaptive sliding mode formation control of multiple underwater robots

Das B., Subudhi B., Pati B. B.

Archives of Control Sciences

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2014

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Vol. 24, no. 4

515--543

EN

This paper proposes a new adaptive sliding mode control scheme for achieving coordinated motion control of a group of autonomous underwater vehicles with variable added mass. The control law considers the communication constraints in the acoustic medium. A common reference frame for velocity is assigned to a virtual leader dynamically. The performances of the proposed adaptive SMC were compared with that of a passivity based controller. To save the time and traveling distance for reaching the FRP by the follower AUVs, a sliding mode controller is proposed in this paper that drives the state trajectory of the AUV into a switching surface in the state space. It is observed from the obtained results that the proposed SMC provides improved performance in terms of accurately tracking the desired trajectory within less time compared to the passivity based controller. A communication consensus is designed ensuring the transfer of information among the AUVs so that they move collectively as a group. The stability of the overall closed-loop systems are analysed using Lyapunov theory and simulation results confirmed the robustness and efficiency of proposed controller.

2

Assessment of Ergonomic and Occupational Health-Related Problems Among Female Prawn Seed Collectors of Sunderbans, West Bengal, India

Das B., Ghosh T., Gangopadhyay S.

International Journal of Occupational Safety and Ergonomics

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2012

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Vol. 18, No. 4

531--540

EN

Sixty female prawn seed collectors and 60 female control subjects from Sajenakhali and Sandeshkhali blocks of Sunderbans, West Bengal, India, were randomly selected to evaluate and compare musculoskeletal disorders and physiological stress. The control group was engaged in domestic work involving minimum handintensive activities. The modified Nordic musculoskeletal questionnaire and rapid entire body assessmentwere used. Most subjects suffered from discomfort in different body parts, especially in the lower back (98%), knees (88%), shoulders (75%), ankles (70%) and feet (67%). This study reveals that female prawn seed collectors suffer from significant physiological load and extreme physiological stress due to prolonged working hours in a standing posture and excessive work pressure. Consequently, all these factors affect female prawn seed collectors’ health and work performance.

3

Eigenvalue approach to two dimensional problem of generalized thermoelasticity for a half - space with body-force

Lahiri A., Das B.

International Journal of Applied Mechanics and Engineering

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2012

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Vol. 17, no. 2

419-437

EN

The theory of generalized thermoelasticity is applied to a two-dimensional problem for a half-space under the action of body forces. The surface is stress free with thermal shock. Double integral transforms (Laplace transform for time variable and Fourier transform for space variable) are used and the resulting equations are written in the form of a vector-matrix differential equation. The solution of the vector-matrix differential equation in the transformed domain are obtained by eigenvalue approach. The inversion of the Laplace transform is carried out numerically by the Bellman method and computations are done by Mathematica software. Finally, numerical computations of the temperature distribution, displacement and stress components are made and represented graphically.

4

Eigenvalue approach to coupled thermoelasticity with temperature dependent modulus of elasticity in an isotropic elastic medium with a cylindrical hole

Lahiri A., Das B.

International Journal of Applied Mechanics and Engineering

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2011

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Vol. 16, no. 2

411-423

EN

The fundamental equations of coupled thermoelasticity in an isotropic elastic medium with a cylindrical cavity under the dependence of the modulus of elasticity on the reference temperature have been written in the form of a vector-matrix differential equation and solved by the eigenvalue approach. The normal mode analysis is used to obtain the expressions for stresses and temperature when the lateral surface of the cylinder is kept at ambient temperature. Finally, numerical computations of the stresses and temperature have been made and presented graphically. Comparisons are made with the results obtained in the case of temperature independent modulus of elasticity.

5

An Ergonomics Study on Posture-Related Discomfort and Occupational-Related Disorders Among Stonecutters of West Bengal, India

Gangopadhyay S., Das B., Das T., Ghoshal G., Ghosh T.

International Journal of Occupational Safety and Ergonomics

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2010

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Vol. 16, No. 1

69--79

EN

Stonecutting and setting are important tasks in a construction site. A field study was conducted to assess occupational-related disorders and to conduct ergonomics assessment among stonecutters. The study focused on (a) the duration of work per day, (b) the working environment and working activities and (c) the feeling of discomfort in different parts of the body. A detailed posture analysis was performed with the Ovako working posture analysis system (OWAS). It was observed that stonecutters worked continuously in awkward postures during stonecutting and setting. Consequently, they suffered from discomfort in different parts of their body, specifically in the lower back, knees and shoulders, which mainly prevented them from continuing their work. This study also revealed that stonecutters had to work in congested work areas with a poor level of illumination. The noise level and dust particles emitted during stonecutting activities could affect stonecutters.

6

Eigenvalue approach to study the effect of rotation in three dimensional problem of generalized thermoelasticity

Lahiri A., Das B., Datta B.

International Journal of Applied Mechanics and Engineering

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2010

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Vol. 15, no. 1

99-120

EN

This paper deals with the thermoelastic interactions due to heat source in a homogeneous isotropic and unbounded rotating elastic medium in the context of generalized thermoelasticity. Integral transform techniques are adopted, namely: the Laplace transform for the time variable and the exponential Fourier transform for two of the space variables to the basic equations of the generalized thermoelasticity and finally the resulting equations are written in the form of a vector-matrix differential equation which is then solved by the eigenvalue approach. Exact expressions for the temperature distribution, thermal stresses and displacement components are obtained in the Laplace-double Fourier transform domain. A numerical approach is implemented for the inversion of the Laplace transform and double Fourier transforms in order to obtain the solution in physical domain. Finally, numerical computations of the stresses and temperature have been made and presented graphically.

7

Eigenvalue approach to generalized thermoelastic interactions in an unbounded body with circular cylindrical hole without energy dissipation

Lahiri A., Das B.

International Journal of Applied Mechanics and Engineering

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2008

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Vol. 13, no. 4

939-953

EN

The fundamental equations of the problems of generalized thermoelasticity based on the Green and Naghdi theory have been written in the form of a vector- matrix differential equation in the Laplace transform domain and solved by the eigenvalue approach. Two problems arising in the study of wave propagation in infinite medium studied in details by examining of the nature of the solution in space time domain for different conditions of the boundary. Finally, numerical computations of the stresses and temperature have been made and presented graphically.

8

Moisture transmission through textiles. Part II: Evaluation methods and mathematical modelling

Das B., Das A., Kothari V. K., Fanguiero R., Araújo M.

Autex Research Journal

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2007

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Vol. 7, no. 3

194--216

EN

The moisture transmission behaviour of a clothing assembly plays a very important role in influencing its efficiency with respect to thermophysiological body comfort. This paper is in two parts. Part I deals with the processes involved in moisture transmission and the factors at play. Part II is concerned with selecting the measurement techniques which are of great importance in determining fabric factors that influence comfort. The instruments and methods used for testing purposes should adequately simulate the exact conditions for which the fabric will be used, in order to determine the effectiveness of that fabric for a particular wearing situation and environmental condition. The testing methods used and the apparatus developed by different researchers for determining moisture transmission through textiles by different mechanisms are discussed in this paper. Moreover, this part of the paper deals with the mathematical models of liquid and vapour transport through textile materials developed by several scientists in order to understand the exact phenomena involved and to predict the factors affecting the transmission under a particular condition.

9

Moisture transmission through textiles. Part I: Processes involved in moisture transmission and the factors at play

Das B., Das A., Kothari V. K., Fanguiero R., Araújo M.

Autex Research Journal

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2007

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Vol. 7, no. 2

100--110

EN

Moisture transmission through textiles has a great influence on the thermo-physiological comfort of the human body which is maintained by perspiring both in vapour and liquid form. The clothing to be worn should allow this perspiration to be transferred to the atmosphere in order to maintaining the thermal balance of the body. Diffusion, absorption-desorption and convection of vapour perspiration along with wetting and wicking of liquid perspiration play a significant role in maintaining thermo-physiological comfort. The scientific understanding of the processes involved in moisture transmission through textiles and the factors affecting these processes are important to designing fabrics and clothing assemblies with efficient moisture transfer in different environment and workload conditions. This paper is in two parts.Part I focuses on the moisture transmission through textile materials and it discusses the processes involved in moisture transmission and the key influencing factors at play to maintaining comfort. It is underlined that the processes which play the major role in moisture transmission in a particular situation are dependant on the moisture content of the fabric, the type of material used, the perspiration rate and the atmospheric conditions, such as humidity, temperature and wind speed. Part II is concerned with the selection of the measurement techniques which are of great importance in determining fabric factors that influence comfort. The instruments and methods used for testing purposes should adequately simulate the exact conditions for which the fabric will be used, in order to determine the effectiveness of that fabric for a particular wearing situation and environmental condition. The testing methods used and the apparatus developed by different researchers for determining moisture transmission through textiles by different mechanisms are discussed in this paper. Moreover, this part of the paper deals with the mathematical models of liquid and vapour transport through textile materials developed by several scientists in order to understand the exact phenomena involved and to predict the factors affecting the transmission under a particular condition. When designing the comfort of a clothing product for a particular application, the requirements may result from needs concerning the application, the individual wearer and the environmental conditions.

10

An Ergonomic Study on Posture-Related Discomfort Among Preadolescent Agricultural Workers of West Bengal, India

Gangopadhyay S., Das B., Das T., Ghoshal G.

International Journal of Occupational Safety and Ergonomics

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2005

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Vol. 11, No. 3

315--322

EN

In India, particularly in West Bengal, preadolescents are primarily associated with agricultural work in rural areas. Owing to poor socio-economic conditions, they are compelled to carry out a considerable number of manual, rigorous tasks in agricultural fields. The main aim of this study was to investigate postures adopted by preadolescent agricultural workers during individual agricultural activities and to analyze the causes of discomfort related to those postures. Fifty male and 50 female preadolescent agricultural workers were randomly selected and a detailed posture analysis was performed with the Ovako Working Posture Analysis System (OWAS). It was observed that those workers worked continuously in awkward postures during certain agricultural activities. Consequently they suffered from discomfort in different parts of their body. Even though they were very young, they were likely to suffer from serious musculoskeletal disorders in the future.

11

Isometric Pull-Push Strengths in Workspace. 2, Analysis of Spatial Factors

Das B., Wang Y.

International Journal of Occupational Safety and Ergonomics

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2004

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Vol. 10, No. 1

59--64

EN

The effect of reach levels, horizontal angles and vertical angles on isometric pull and push strengths of males and females in standing and seated positions was determined. The effect of reach levels on strength varied as a consequence of force direction, working position and gender. Reach level has a significant effect on women's pull strength in the seated position and on push strength in the standing position. The strength value was significantly greater in the extreme reach than in maximum or normal reach. Vertical angle ö had a significant effect on strength consistently in all cases. Strength values increased significantly with the increase of ö angles from 0º to 45º to 90º. The horizontal angle è had a significant influence only on the pull strength of standing and seated men and standing women (not seated woman). The maximum strength was significantly greater at è = 90º.

12

Isometric Pull-Push Strengths in Workspace. 1, Strength Profiles

Das B., Wang Y.

International Journal of Occupational Safety and Ergonomics

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2004

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Vol. 10, No. 1

43--58

EN

The isometric pull and push strength profiles of males and females were determined in seated and standing positions in the workspace. The strongest pull strength location was at extreme reach vertically above the shoulder for both males and females. The greatest pull strength of 400 Newtons (N) for males was recorded in the seated and standing positions. Females. pull strengths in the seated and standing positions were 222 and 244 N, respectively. The strongest push strength was always at the maximum reach at the overhead location. Males. maximum push strength was 227 N in the seated position and 251 N in the standing position. Females’ maximum push strength was 96 N in the seated position and 140 N in the standing position. On the average the strength in the standing position was 79% of the seated position. The push strength was 71% of the pull strength and females were 56% as strong as males.

13

Isometric Pull and Push Strengths of Paraplegics in the Workspace: 1. Strength Measurement Profiles

Das B., Black N. L.

International Journal of Occupational Safety and Ergonomics

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2000

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Vol. 6, No. 1

47--65

EN

The isometric strength profiles of male and female paraplegics were determined for pull and push strengths in the normal, maximum, and extreme working reach envelopes. A computerized isometric strength measurement system was designed and constructed for the purpose. The strongest pull location was at extreme reach vertically above the shoulder and the strength values for males and females were 473 and 318 newtons (N), respectively. The strongest push location was at maximum reach, at vertical ($) angle of 45° and at horizontal (6) angle of 45° for males and at 0° for women and the strength values were 235 and 172 N, respectively. The nature of the strength profiles was found to be similar for both the sexes. The pull and push strengths of the female were 77 and 68% that of the male, respectively.

14

Isometric Pull and Push Strengths of Paraplegics in the Workspace: 2. Statistical Analysis of Spatial Factors

Das B., Black N. L.

International Journal of Occupational Safety and Ergonomics

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2000

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Vol. 6, No. 1

67-80

EN

The effect of reach levels, horizontal angles, and vertical angles on isometric pull and push strengths of male and female was determined. Highly significant increases in men’s push strength were found between extreme to maximum reaches, and from extreme to normal reaches. However, for women’s push strength, a significant increase was found only between extreme to maximum reach. Significant or highly significant increases were found in men’s and women’s pull strength between the horizontal angle (0) sagittal through the active shoulder (90°) and other angles (0, 45, and 135°). However, for men’s push strength, highly significant increases were found between the horizontal angle 45° from the frontal plane, and other angles. For women’s push strength, significant or highly significant increases were found between the horizontal angles 0° and angles of 90 and 135°. For men’s and women’s pull strength, significant or highly significant increases were found between the vertical angle (), 90°, and other angles (-20, 0, and 45°). Similar increases were found for women’s push strength between the 45° angle and other angles. In the design of a workstation for paraplegics that requires pull and push forces, consideration must be given to the spatial factors.

15

Evaluation of Low Back Pain Risks in a Beef Skinning Operation

Das B., Sengupta A. K.

International Journal of Occupational Safety and Ergonomics

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2000

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Vol. 6, No. 3

347--361

EN

The low back pain risks in a beef skinning operation at a high stand kill floor workstation was evaluated. The increases in compressive forces at lower back (L5/S1) between normal slump (back angle 25°, measured in the sagittal plane) and severe (45°) and between normal slump and very severe (70°) bent back postures were 387 N or 28% and 616 N or 45%, respectively. The high spine load coupled with high level of repetition can have a high probability of fatigue failure in the spine structural members. Non-neutral back posture for a large portion of the total work time can be a low back pain risk factor. The videotape analysis showed that the times involved during the task performance for the bent back (more than 25°) and severe bent back (more than 45°) were 48.4 and 33.5% of the total cycle time, respectively. The upper limit from OWAS (Ovako Working Posture Analysis System) for bent back posture is 30% of the total cycle time. The bent and twisted back posture (both more than 25°) time was 10.4% compared to OWAS limit of 5%. This indicated that actions are needed in the near future to alleviate the risk of low back pain. Ergonomics redesign of the workstation was recommended for the operation.

16

Participative Versus Assigned Production Standard Setting in a Repetitive Industrial Task: A Strategy for Improving Worker Productivity

Das B., Shikdar A. A.

International Journal of Occupational Safety and Ergonomics

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1999

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Vol. 5, No. 3

417--430

EN

The participative standard with feedback condition was superior to the assigned difficult (140% of normal) standard with feedback condition in terms of worker productivity. The percentage increase in worker productivity with the participative standard and feedback condition was 46%, whereas the increase in the assigned difficult standard with feedback was 23%, compared to the control group (no standard, no feedback). Worker productivity also improved significantly as a result of assigning a normal (100%) production standard with feedback, compared to the control group, and the increase was 12%. The participative standard with feedback condition emerges as the optimum strategy for improving worker productivity in a repetitive industrial production task.