Do Sanh
Hanoi University
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Featured researches published by Do Sanh.
Vietnam Journal of Mechanics | 2012
Do Sanh; Do Dang Khoa
In this paper the method of transmission matrix is applied for investigatingxa0planar mechanisms [5-7]. As is known, in many engineering problems, for example,xa0in the problem of synthesis and analysis of motion, the following problem is more andxa0more interested. There is an object (a particle or body) connected with a frame ofxa0reference, which moves with respect to another frame. It is necessary to define thexa0configuration (the position, velocity, acceleration) of the object under consideration inxa0the latter frame. There are two types of the frame of reference. A frame that is fixed inxa0time named inertia frame or global frame of reference and the frame attached to eachxa0body of the system- the body frame of reference. The problem is stated now as follows:xa0Determine the configuration in global frame of a particle fixed in any body of the system. In this paper a method is constructed for solving such a problem by means of transmissionxa0matrices. The obtained results are illustrated by examples.
Vietnam Journal of Mechanics | 2012
Do Sanh; Do Dang Khoa
In the present paper it is introduced the method for determining the reactions of mechanical constraints (holonomic and nonholonomic constraints). As is known, for studying dynamical characters of a mechanical system it is necessary to determine the constraint reactions acting on the system. Up to now, the reactions are calculated through Lagranges multipliers. By such a way the reactions are determined only indirectly. In the [3, 4], two methods of determining directly the reactions are discussed. However, for applying these methods, it is necessary to compute the inverse matrix of the matrix of inertia. This thing in general is not convenient, specially when the matrix of inertial is of large size and dense. In the present paper it is represented the method for determining the constraint reactions, by which it is possible to avoid inertia the computation of the inverse matrix of the matrix of inertia is avoided. For this in the paper it is used the middle variables by which we obtain a closed set of algebraic equations for directly determining reactions.
Vietnam Journal of Mechanics | 2012
Do Sanh; Dinh Van Phong; Do Dang Khoa; Phan Dang Phong
In the paper, it is introduced a method to det ermine joint reaction forces, constraint forces and internal forces at the cross section of linkages. Based on the principle of compatibility and the ideality of constraints, the methodology is presented to analyze and determine reaction forces in planar mechanisms.
Vietnam Journal of Mechanics | 2012
Do Sanh; Do Dang Khoa
In the paper it is introduced a method of determining internal forces at any cross section of the links of mechanisms. As known, so far it is used the method of DAlembert, which consists of two steps, the determination of the acceleration states of links and the establishment of the equilibrium equations for the set of forces including the forces of inertia and the internal forces at the cross section. A. I. Lurie proposed a method of analytical mechanics for this problem. Its concept is to make a new system called the released one by cutting the link at a cross section under consideration and adding some coordinates. Only one condition putting restriction on the released system is the additional coordinates must equal zero. Under this restriction the new created system is coincided to the original one. This restriction is equivalent to put the mechanical constraints, whose reaction forces are the components of internal forces at the cross section under consideration. It is necessary emphasize that the Luries method is convenient only for opened loops, but is not applied for closed ones. Moreover, the Lagranges multiplier equations applied by A. I. Lurie are unsuitable. In this paper it is presented the generalized Luries method, which is applied for the opened and closed loops by using the Principle of Compatibility.
Vietnam Journal of Mechanics | 2012
Do Sanh; Do Dang Khoa
In the paper [2] the method of transmission matrix applying for the case ofxa0a loop with turning pairs investigated. In the present paper the kinematics of a loopxa0connected by composite joints, i.e. the one of revolute-translational joints are discussedxa0now. By means of proposed method the planar motion of rigid bodies is presented by axa0point of general view. Especially, the introduced method allows to apply effectively universal software, for example,xa0MATCAD, MAPLE, ... for investigating complex mechanical systems.
Vietnam Journal of Mechanics | 2002
Do Sanh
In the present paper a form of equations of motion of a constrained mechanical system is constructed. These equations only contain a minimum number of accelerations. In the other words, such equations are written in independent accelerations while the configuration of the system is described by dependent coordinates. It is important that the equations obtained are applied conveniently for. the mechanisms in which the use of independent generalized coordinates is not suitable.
Vietnam Journal of Mechanics | 2000
Do Sanh
The Chaplyghins systems play an important role in engineering. There exist some methods for establishing these systems. Lt is necessary to pay attention to the Chaplyghins equations which are written by means of the Lagrangian function in independent variables. By this, the mentioned equations are a closed set of second order differential equations. The application of the Lagrangian function for writing equations of motion is an advantageous point of the Chaplyghins method. However, the algorithm of establishing these equations is complicated enough, especially for the large systems.
Archive | 2000
Nguyen Nhat Le; Dinh Van Phong; Do Sanh
The dynamics of complex mechanical system is becoming increasingly important. Detailed descriptions are needed for physical processes occurring in machines, robots and other multibody systems, see [11], [14], [15]. Accuracy must be maintained as computational volume increases. Many mechanical systems are controlled by programs. The controlling quantities are reaction forces corresponding to constraints. Numerical errors in computations may lead to violation of these constraints; the level of violation depends on the complexity of the system and the nature of the constraints.
Vietnam Journal of Mechanics | 1998
Do Sanh
In the paper the method for constructing programmed motion is represented. The requirements for the programmed motion are treated as ideal constraints in analytical mechanics. The programmed motions expressed in Lagrange coordinates and in quasi coordinates are investigated. By applying the form of equations of motion of a constrained mechanical system [7], a schema for calculating programmed motions has been established. By this schema the errors of realizing programmed motions have been reduced and controlled. For illustration of the method some examples have been investigated.
Vietnam Journal of Mechanics | 1997
Do Sanh
In the paper it is given a new form of equations of motion of nonholonomic mechanical systems. The obtained equations are written in a matrix form and in order to establish them it is unnecessary to calculate the inverse matrix of the matrix of inertia. It is important that it is possible to obtain the relation between the error of realizing constraints and that of computing the solution of equations of motion of the system under consideration.