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Mathematical Analysis of Moment of Inertia of Human Arm at Fixed Position

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Mathematical Analysis of Moment of Inertia of Human Arm at Fixed Position Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II WCECS 2017, October 25-27, 2017, San Francisco, USA Mathematical Analysis of Moment of Inertia of Human Arm at Fixed Position M. C. Agarana, IAENG Member, O.O. Ajayi, T.A. Anake and S.A. Bishop Abstract— Knowledge of moment of inertia and potential the arrangement of focuses that are all at a similar distance r energy of human arm is necessary to optimize its usage and from a given point, however in three-dimensional space. performance. In this paper, human arm is modelled as This distance r is the radius known as the centre of the ball, geometric shapes. The potential energy and the moment of and the given point is the focal point of the scientific ball. inertial of different segments of the arm were analysed in order The longest straight line through the ball, associating two to predict the inertial properties of the human arm in a fixed points of the sphere, goes through the middle and its length position. is in this manner double the radius; it is a diameter of the Index Terms— Fixed Position, Moment of Inertia, Human ball.[2] Arm. Mathematical Analysis. The moment of inertia, also known as the rotational inertia, of a rigid body, such as human arm, is a tensor that I. INTRODUCTION determines the torque needed for a desired angular acceleration about a rotational axis[2,3,4,5].It relies on upon HE exploration and utilization of space is meaningless the body's mass distribution and the axis picked, with bigger T without man. Man utilizes his parts, including the arm, moments requiring more torque to change the body's to perform support, supply, protect, and operational rotation[5,6]. It is a quantity expressing a body's tendency to undertakings in the weightless condition of space [1]. The resist angular acceleration, which is the sum of the products inertia property of human body, all in all, and human arm of the mass of each particle in the body with the square of its specifically is important to accomplish the ideal outline for distance from the axis of rotation.[6] For bodies constrained such a unit [1]. A circle is a flawlessly round geometrical to rotate in a plane, it is sufficient to consider their moment question in three-dimensional space that is the surface of a of inertia about an axis perpendicular to the completely round ball[2]. Like a circle, which geometrically plane[6,7,8,9,10]. This study is concerned with the analysis is a question in two-dimensional space, a circle is of the Mathematical model of human arm at rest based on a characterized scientifically as the arrangement of focuses simulated mass and the anthropometric data of the that are all at a similar distance, r, from a given point, individual person’s arm. This paper did not consider the however in three-dimensional space. This r is the range of following: the ball, and the given point is the focal point of the (i) The variation of the inertia properties during a change of scientific ball. The longest straight line through the ball, body position or a change of body. interfacing two purposes of the circle, goes through the (ii) The variation of the inertia properties while the body is middle and its length is in this manner double the radius; it subjected to external forces which displace tissue from the is a width of the ball.[2] rest position A frustum of a cone (truncated cone) is a strong like a (iii) The asymmetrical location of internal organs of the chamber, with the exception of that the roundabout end body. planes are not of equivalent sizes. Besides, both end planes' Within these limitations, the analysis of the mathematical centre focuses are situated straightforwardly over each other model of an individual arm at a fixed position is carried out [2]. A frustum might be shaped from a correct round cone to predict its inertia properties by removing the tip of the cone with a slice opposite to the stature, framing a lower base and an upper base that are roundabout and parallel [2]. A. Assumptions: A sphere is an impeccably round geometrical object in (i)The human arm as part of the body can be represented by three-dimensional space that is the surface of a totally round a set of rigid bodies of simple geometric shape and uniform ball, comparable to a circular object in two dimensions). density. Like a circle, which geometrically is an object in two- (ii)The different segments of the human arm move about dimensional space, a sphere is characterized numerically as fixed pivot points when body changes position. The first assumption is an analytical determination of the inertial properties of the human body using a Mathematical Manuscript received July 1, 2017; revised July 30, 2017. This work was supported in full by Covenant University. model. M.C. Agarana is with the Department of Mathematics, Covenant The second assumption is made to simplify the University,Nigeria,+2348023214236,michael.agarana@covenantu configuration of the model. niversity.edu.ng With the given assumptions, human arm is modelled as O.O. Ajayi is with the Department of Mechanical Engineering, geometric shapes - frustum and spheres Covenant University, Nigeria S. Bishop is with the Department of Mathematics, Covenant University,Nigeria ISBN: 978-988-14048-4-8 WCECS 2017 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online) Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II WCECS 2017, October 25-27, 2017, San Francisco, USA II. MODEL FORMULATION A. Notations r radius of small circle The mathematical model is made up of three simple geometric solids numbered as indicated in Fig.1. Each solid R radius of big circle represents a segment of the arm. The segments are: SL Surface length (1) Upper arm (2) Forearm FC Fist circumference (3) Hand AAC Axillary arm circumference Both the upper arm and forearm are represented by solid frustums, of different sizes, while the hand is represented by EC Elbow circumference a sphere. WC Wrist circumference UAL= Upper arm length FL= Fore arm length h2 = height of small cone h = height of big cone 1 B. Hand The third part of the human arm, the hand, is modelled as a solid sphere as shown in figure 2. The dimension and properties of the hand are: FC R (1) Fig.1 Right Circular Cone and its Frustum 2 Rr (2) SL 2 R (3) C. Upper Arm: The upper arm is modelled as a frustum of a right circular cone. The cross section is a circle when the cutting plane is parallel to the X-Y plane. The dimensions and properties of the upper arm are: AC R (4) 2 Fig.2 Model of human arm and Schematic of the Model EC RR= (5) 2 SL=UAL (6) D. Forearm The forearm modelled as frustum of a solid right circular cone. The cross section is a circle when the cutting plane is parallel to the X-Y plane. The dimensions and properties of the forearm are EC R (7) 2 Fig. 3 Solid Sphere r WC (8) SL FL (9) ISBN: 978-988-14048-4-8 WCECS 2017 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online) Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II WCECS 2017, October 25-27, 2017, San Francisco, USA III. PROPERTIES OF A FRUSTUM OF A RIGHT Mf M m (23) CIRCULAR CONE Rr33 hh (24) The right circular cone in Fig. 5 and frustum of a right 3(R r ) 3( R r ) circular cone in Fig. 6 are related by h =Rr33 (25) h h12 h (10) 3(Rr ) hhh1 (11) Equation (25) can be written after simplification as: R r R r This implies M R2 h (26) hR f h = (12) 3 1 Rr hr IV. MOMENT OF INERTIA OF FRUSTUM OF A RIGHT h2 = (13) Rr CIRCULAR CONE The centroid of the frustum is given by: A Frustum of height h, has moment of inertia about the axis 22 XX, determined by the difference of the moment of inertia h R23 Rr r of then large and small cone about the axis. The moment of x = 22 (14) 4 R Rr r inertia of the frustum is given by: Let I I M x22 I M( x h ) (27) r XX cc1 1 bb 2 2 (15) where R 2 2 3Mh112 1 (16) IRcc (28) 20 4 x (17) 2 3Mh222 h Irbb (29) Substituting equations (14). (15) and (16) into (17) gives 20 4 xh11 0.25 (30) 1 2 3 2 (18) xh22 0.25 (31) 4 MRf M (32) ()Rr A. Mass of the Frustum Mr 2 The mass of the big cone and the small cone are given m f (33) respectively as follows: ()Rr 2 M R h1 (19) After rearranging by using equations (12),(13), (14), (15), 3 (32) and (33), equation (27) becomes: 2 m r h2 (20) 32 3 3Rh2 3 4 2 IMxx f 1 (1 3 6 ) (34) 20 10 where is the density of the cones Substituting equations (12) and (13) into Equations (19) and From equation (34), it is clear that the major parameters (20) gives: influencing the moment of inertia of frustum of a right circular cone are: The mass of the frustum (Mf), the big R3 circumference of the frustum (R), the small circumference Mh (21) of the frustum (r) and the height of the frustum (h).
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