## Introduction

In the component builder approach, cross-sections are defined as an assembly of simple structural components that can be connected. Table 1 lists the various components that can defined and the various manner in which they can be connected to each other. This approach allows the definition of realistic sections.

 Group Component Component Structural components Wall Core Connectors Wall Connector Adhesive
##### Figure 1. Walls and Cores.

The fundamental “building blocks” of the component builder approach are the structural components. The cross-section then becomes an assembly of interconnected structural components. Figure 1 illustrates the basic structural components: the wall and the core. To illustrate the approach, the case of a rotorcraft blade cross-section is described succinctly.

Rotorcraft blades are manufactured through a complex process.

1. A number of structural components are manufactured independently through different curing operations.
2. These structural components are assembled through secondary bonding operations.

To improve the ability to model realistic rotorcraft blades, the configuration of the blade’s cross-section is defined in a manner that mimics the manufacturing process. Two interrelated concepts are involved.

1. The rotor blade cross-section is viewed as an assembly of independently defined structural components, such as front end, inner-wrap, nose weight, core, etc. The geometry and material properties of each component are defined independently and each component is meshed separately.
2. The various structural components are then assembled via a “mortar algorithm” to form the complete model of the cross-section. Because the various components of the cross-section are defined and meshed separately, a special technique is needed to connect the incompatible meshes of the various structural components. The mortar algorithm imposes the continuity of the displacement field across the boundary between the two structural components in an integral sense. The mortar algorithm is the computational equivalent of the adhesive used in secondary bonding operations.
##### Figure 2. A number of walls and cores are connected by wall connectors and adhesives to form a rotor blade section.

The upper portion of fig. 2 illustrates the first step of the process. The front portion, spar, and aft portion the blade’s cross-section are defined and meshed separately. For practical reasons, the top and bottom portions of the front and spar components are defined separately. Although the meshes of the top and bottom portions are compatible, the mortar algorithm is used to connected these top and bottom components. The top and bottom components of the aft portion of the cross-section are also defined and mesh separately.

Once the various components of the cross-section have been defined and meshed, they must be connected to form the final configuration of the blade’s cross-section. The lower portion of fig. 2 shows the assembled configuration of the cross-section. The mortar algorithm was used the connect the front portion of the section to the spar and the aft portions of the section to the same spar. The top and bottom portions of the aft components are connected at the trailing edge.