BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI Publicat de

Universitatea Tehnică „Gheorghe Asachi” din Iaşi Tomul LVI (LX), Fasc. 1, 2010

SecŃia TEXTILE. PIELĂRIE

THEORETICAL ELEMENTS OF 3D TEXTILE SURFACE REPRESENTATION

BY

RALUCA MARIA AILENI*, DANIELA FĂRÎMĂ* and MIHAI CIOCOIU**

Abstract. This paper presents aspects of 3D modelling of textile surface. 3D modelling of textile surface is useful for simulations of the behaviour of textile materials in various aspects like product decoration (curtains, tablecloths) or as outerwear product.

3D modelling parameters must be known length, width, thickness and mass density of the textile surface.

Key words: 3D modelling, textile simulation, forces, constraints.

1. Introduction

In the last twenty years, there appeared a variety of techniques to

address a virtual simulation of textile surface using variants of the finite element method. A detailed study of the early concerns in this area can be found in Ng and Grimsdale [3]. A year later, Gibson and Mirtich [4] presented a general study in computer graphics techniques for deformable model.

The first simulation of a textile surface was done in 1986 by Weil [5], who used a geometrical technique, which involves a curve made by a cable attached inextensible ends, to mimic static drapery material suspended in two points.

Concerns in this area have resulted in the definition of discrete and continuous modelling techniques, static and dynamic simulation of textile surfaces used in products for decorations or items of clothing. Simulation of dynamic behaviour requires the knowledge of textile surface forces acting on the textile surface and internal knowledge of the nature of collisions that take place.

3 techniques are used in the 3D modelling of textile surfaces: − Continuous modelling − the fabric is modelled as an elastic surface

and is done by finite element simulation [1]. − Discrete modelling − the fabric is considered as a mechanism of

thread.

94 Raluca Maria Aileni, Daniela Fărîmă and Mihai Ciocoiu

− Dynamic modelling − the fabric is modelled as a moving body, on which internal and external forces act (see Fig.1).

Fig. 1 − Discrete modelling.

2. Aspects of the Textile Surface Modelling The cloth is flexible and due to drape it has a complex configuration.

Generally, surface textiles - fabric, is made up of structures of warp and weft threads, woven together to form different structures. Overall surface properties of textiles are affected by many factors, such as constituent yarn properties, model weaving, yarn geometry structures and the interactions between threads. As a result, the overall properties of the fabrics are extremely complex, observing the non-linearity, anisotropy and hysteresis.

The material properties of drapery fabric can be measured using Kawabata evaluation system, as shown in Fig.2.

Fig. 2 − Material properties of fabrics.

To capture highlight the complex behaviour that occurs in the textile material, modelling shall be made at a scale of resolution in the visible interactions between threads [2].

Discrete modelling technique is based on the theory of elastic springs (Fig. 3). Discrete model (model based on particles) has the potential to be defined by several parameters, such as the amount of particles, constant elastic traction (horizontal and vertical direction), bending (in vertical or horizontal),

Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 1, 2010 95

and shear, damping constants, friction and stiffness.

Fig. 3 − Mass and springs model. Textile surface can be modelled as a set of particles joined together by

elastic springs (lengths of wires). Rigid yarns and interlooping points define the surface properties of the textile virtual model, as illustrated in Fig.4.

Fig. 4 – Modelling of the textile surface.

For virtual textile surface modelling when stretching, bending or shear, they are using 3 types of springs:

− for stretching springs are used to define a mesh of the polygonal surface, whereby the textile surface is represented;

− for bending (waving) springs used bows made by the union of 2 nodes which have arcs (links) common

− for shear springs use bows made by interconnecting nodes belonging to a polygonal mesh in the surface but are not adjacent.

3. Aspects of Dynamic Simulation of Textile Surface

Using different parameter settings, it is possible to simulate different

types of textile surfaces. A known problem is the effect of super elasticity discrete models, small elastic constant produces unreal behaviour of textile surface (due to excessive extension) [2]. To accurately simulate the textile surface, the model starts to define the area of textiles as a polygonal surface mesh composed of several (small sized rectangular areas), obtained through the mesh surface. Fig. 5 shows the aspect of the discrete model.

96 Raluca Maria Aileni, Daniela Fărîmă and Mihai Ciocoiu

Fig. 5 − Discrete modelling.

Using the same density and mass for the textile fabric different parameters regarding stretching, bending and shear are obtained by modelling the virtual 3 different surface aspects of textile material (see Figs. 6 and 7).

Fig. 6 − Textile surface simulation – increasing stiffness.

Fig. 7 − Textile surface modelling with mass & springs. Positioning constraint points (nails).

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Simulation and visualization of the textile surface has a complex effect: − Geometric definition of product parts and objects that will interact

with the product (egg human body); − Optical laws simulation (rendering); − Laws of dynamic simulation (forces, acceleration, speed, energy); − Interaction with ambient environment (collision detection and response).

Simulation is mainly concentrated textile surface interactions between different parts of the textile surface and other objects.

− Definition of constraint points (pins). If the first two problems are classical 3D problems, the last two require

new solutions: − Textile material behaviour in simulation − simulation of the textile

fabric relates to the mechanical model adopted to approximate the behaviour of surface elements. A parametric model can be selected in order to facilitate simulation of different materials (cotton, wool, silk ...).

− Handling constraints − constraints concern the limits of movement of the product, such as those caused by the seams of the parts.

− Collision detection: to detect collisions between the product and other bodies (human or objects around) but also between different parts of the product (auto collision).

− Physical answer: any collision requires a response to be interpreted and to simulate the effects of friction and resistance.

A simulation of textile surface should be effective and reflect the true reality. Unfortunately, computational simulation of high complexity is very difficult to achieve both goals: the systems are tailored to favour one of the two. Systems capable of real-time animation can produce great results, but uninteresting for textile, because results are not reliable and can be used to predict how you will look and behave in the real world clothing today.

High fidelity simulation of the textile surface requires hours to produce a few seconds of animation.

4. Conclusions

The benefits of modelling and virtual simulation of textile surface are: − checking the correspondence between product characteristics and

destination of its use; − Time economy running, choosing suitable textile material, achieving

optimal physical prototype; − Economy of raw materials and materials; − High productivity of personnel responsible for physical realization of

prototypes; − Rapid response to market requirements Modelling and simulation of 3D textile surface material is an important

98 Raluca Maria Aileni, Daniela Fărîmă and Mihai Ciocoiu

step in the design of products for items for interior decoration and clothing products, and hardware and software last generation.

Received: September 30, 2009 “Gheorghe Asachi” Technical University of Iaşi,

*Department of Knitting and Ready - Made Clothing e-mail: dfarima@tex.tuiasi.ro

**Department of Technology and Design of Textile Products e-mail: mciocoiu@tex.tuiasi.ro

R E F E R E N C E S 1. Xiaolin Man, Colby C. Swan, Salam Rahmatalla, A Clothing Modeling Framework

for Uniform and Armor System Design. 2006. 2. Terzopoulos D., Platt J., Barr A., Fleischer K., Elastically Deformable Models. ACM

SIGGRAPH Computer Graphics, 1987. 3. Ng H.N., Grimsdale R., Computer Graphics Techniques for Modeling Cloth. (1996). 4. Gibson S., Mirtich B., A Survey of Deformable Modeling in Computer Graphics.

Technical Report TR-9719, MERL, 1997. 5. Weil J., The Synthesis of Cloth Objects. Computer Graphics, 1986.

ELEMENTELE TEORETICE ALE REPREZENTĂRII ÎN 3D A SUPRAFEłELOR TEXTILE

(Rezumat)

Lucrarea prezintă aspecte privind modelarea 3D a unei suprafeŃe textile.

Modelarea 3D a suprafeŃei textile este utilă pentru simularea virtuală a comportamentului materialului textil în diverse ipostaze: produs pentru decoraŃiuni interioare (draperii, feŃe de masă) sau ca produs de îmbrăcaminte exterioară.

Pentru modelarea 3D trebuie cunoscuŃi parametrii de lungime, lăŃime, grosime şi densitatea de masă a suprafeŃei textile.