Timelike-Ruled and Developable Surfaces in Minkowski 3-Space E 31

In this study, the timelike-ruled and developable surfaces are constructed in Minkowski 3-space E 31 . Using the E. Study map, we demonstrate that dual forms of timelike-ruled and developable surfaces can be obtained from the coordinates and ﬁ rst derivatives of the base curve at the dual hyperbolic unit sphere. This is proposed as a novel method for obtaining timelike-ruled and developable surfaces. Some examples have also been provided.


INTRODUCTION
In spatial kinematics, the movement of an oriented line over a curve forms a ruled surface. The oriented lines are named generators (rulings), and each curve that intersects all the generators is called A directrix (or base curve). The theory of ruled surfaces is mentioned by researchers and mathematicians because of its applications in screw systems, iterative methods for displacement analysis of spatial mechanisms, and computer aided design (CAD) [1][2][3][4]. Because many researchers have already studied and determined numerous characteristics of ruled surfaces, as in [24,25], this study is limited to the Minkowski 3 space. Developable surfaces define a subset of ruled surfaces, such that every point from the same ruling shares a common tangent plane. Rulings define the principal curvature lines of zero normal curvature in addition to the Gaussian curvature, which is zero at each point on the surface. Because the inner metric of a surface locates the Gaussian curvature, all the angles and lengths on the surface remain invariant under bending. This feature is what makes ruled and developable surfaces important in manufacturing. Hence, both ruled and developable surfaces have been considered in engineering, architecture, design, etc. (see [5][6][7][8][9][10])].
A suitable method to study the motion of an oriented line in space starts from the relationship among this space, dual numbers, and dual vector calculus. Dual numbers were first introduced by W. Clifford; subsequently E. Study utilized it as an instrument for the purpose of differential line geometry and kinematics. He devoted special care to the impersonation of oriented lines by dual unit vectors and defined the mapping, which was later named after him. The E. Study map indicates that the set of all oriented lines in Euclidean 3-space E 3 is directly linked to a set of points on the dual unit sphere in the dual 3-space D 3 [1,4,7]. Thus, the differential geometry of the ruled surfaces based on the E. Study map has derived the curvature theory of the line trajectory and exposed the fundamental curvature functions which describe the shape of a ruled surface (refer to example [11][12][13]).
Kose introduced a novel method for determining developable ruled surfaces using dual-vector calculus [14]. They demonstrated that a ruled surface can be obtained from coordinates and first derivatives of the base curve. Further Yildz et al. applied this method using an orthotomic concept [15]. In the course of time, this method has been extended and presented in the dual Lorentzian 3space D 3 1 by [16][17][18][19]. However, to the best of the authors' knowledge, no literature exists regarding the fact that a timelike-ruled surface can be obtained from coordinates and the first derivatives of the base curve. Hence, this study attempts to address this need. The remainder of this paper is organized as follows: In Section 2, we present some basic concepts dealing with the dual Lorentzian 3-space D 3 1 . In Section 3, we offer a method for determining a timelike ruled surface from the coordinates and first derivatives of the base curve using a dual-vector calculus. Consequently, as a special case, we discuss the method for timelike developable ruled surfaces, and obtain a linear differential equation of the first order. We illustrate the method by providing some representative examples with their figures.

BASIC CONCEPTS
We begin with basic concepts on the theory of dual numbers, dual Lorentzian Vectors, and the E. Study map (see [1][2][3][4][5][16][17][18][19][20][21]): A directed (non-null) line L in Minkowski 3-space E 3 1 can be defined by a point p ∈ L and a normalized direction vector x of L; that is, a 2 ± 1. To obtain components for L, one forms the moment vector x* = p ×x with respect to the origin point in E 3 1 . If p is replaced by any point q p + ta, t ∈ R on L, it is implied that a* is independent of p on L. The two non-null vectors a and a* are not independent of one another. They satisfy the following condition: 〈a, a〉 ± 1, 〈a*, a〉 0.
The six components a i , a p i (i 1, 2, 3) of a and a*are called the normalized Plűcker coordinates of the line L; hence the two vectors x and x* determine the directed line L.
A dual number A is a number a + εa*, where a, a* in R and ε is a dual unit with the property that ε 2 = 0. Therefore the set joining with Lorentzian scalar product leads to what is named the dual Lorentzian 3-space D 3 If a is spacelike, we have If a is timelike, we have Therefore, A is the spacelike dual unit vector in case 〈A, A〉 = 1 and the timelike dual-unit vector in case 〈A, A〉 = −1. The hyperbolic and Lorentzian dual unit spheres are respectively.
Theorem 1 : [17-19, 22, 23]. There is a one-to-one correspondence between spacelike (resp. timelike) oriented lines at Minkowski 3-space E 3 1 and ordered pairs of vectors (a, a*) ∈ E 3 1 × E 3 1 , such that 〈A, A〉 ± 15〈a, a〉 ± 1, 〈a*, a〉 0, where a and a* are the normed Pl ücker coordinates of the line. Using Theorem 1, we obtain the following map (E. Study's map), where the dual unit spheres are shaped as a pair of conjugate hyperboloids. The ring shaped hyperboloid represents the set of spacelike lines, the common asymptotic cone represents the set of null (lightlike) lines, the oval shaped hyperboloid forms the set of timelike lines, and opposite points of each hyperboloid perform a pair of obverse vectors on a line (see Figure 1). Applying to the E. Study map, the differentiable curve on H 2 + corresponds to the timelike-ruled surface at E 3 1 . In a similar way, the dual curve at S 2 1 corresponds to the spacelike or timelikeruled surface at E 3 1 .
2.1 Timelike-Ruled Surface as a Curve at H 2 + Let y(t) be the regular curve at the Minkowski 3-space E 3 1 defined on I ⊆ R and x(t) is the timelike unit vector of the oriented line at E 3 1 . Therefore we acquire a timelike-ruled surface's parametrization M as Here y = y(t) is its directrix or base curve, and t is the motion parameter. The E. Study map is adopted to write Eq. 2 using the dual vector function as Because the spherical image x, is the timelike unit vector, the timelike dual vector X and unit magnitude, as is observed from the computation Therefore, the timelike-ruled surface is presented using the dual curve at the surface of the dual hyperbolic unit sphere. The dual arc length of X(t) ∈ H 2 + is defined by Hence, the distribution parameter is expressed as Here, and in what follows, the prime symbol denotes derivatives with respect to parameter "t." The Gaussian curvature K (t, v) is related to the distribution parameter λ(t) of the timelike-ruled surface [5] as follows: If K (t, v) equals zero everywhere, this means that λ equals zero everywhere; therefore, M is referred to as developable. At Eq. 5: (a) in case λ(t) = 0, therefore M is the timelike developable ruled surface (b) if x′ = 0, therefore M is the timelike cylindrical ruled surface.
Notably, ϑ*(t) has two values; using the minus sign resulted in the reciprocal of the timelike-ruled surface obtained using the plus sign. Therefore, in this study, we chose a lower sign. Into Eq. 2 we substitute from Eqs 13, 14 and obtain: where y 2 2 + y 2 3 ≠ 0, v ∈ R, and ϑ(t) is arbitrary.
Theorem 2 : Let y(t) be a regular curve in Minkowski 3-space E 3 1 . Therefore there exists the family of timelike-ruled surface represented by Eq. 15.To the best of our knowledge, no previous study has obtained a timelike-ruled surface using coordinates and the first derivatives of the base curve, which means that this theorem presents a novel approach to building timelike-ruled surfaces in Minkowski 3-space.
Example 1 : Let y(t) = (t, t 2 , t 2 ) be the curve at Minkowski 3-space E 3 1 . Then, the family of the timelike-ruled surface is The distribution parameter is Function ϑ(t) can control the shape of the surface. If we take ϑ(t) = t, then λ(t) 2 2 √ t, and the timelike ruled surfaces are illustrated in Figure 2. If ϑ(t) = −t, λ(t) −2 2 √ t and the surface are illustrated in Figure 3; Example 2 : Let y(t) = (t, t, 1) be the null curve at Minkowski 3space E 3 1 . Similarly, we have: (17) The distribution parameter is If we take ϑ(t) = t, then for -1 ≤ t ≤ 1 and −6 ≤ v ≤ 6, the timelikeruled surface is illustrated in Figure 4. For ϑ(t) = −t, 1 ≤ t ≤ 1 and −6 ≤ v ≤ 6, the surface is illustrated in Figure 5.
we substitute these values into Eq. 19 and solve this differential equation f t ( ) coth ϑ c, c ∈ R.