Per-pixel displacement mapping using cone tracing with correct silhouette

Per-pixel displacement mapping is a texture mapping technique that adds the microrelief effect to 3D surfaces without increasing the density of their corresponding meshes. This technique relies on ray tracing algorithms to find the intersection point between the viewing ray and the microrelief stored in a 2D texture called a depth map. This intersection makes it possible to deter- mine the corresponding pixel to produce an illusion of surface displacement instead of a real one. Cone tracing is one of the per-pixel displacement map- ping techniques for real-time rendering that relies on the encoding of the empty space around each pixel of the depth map. During the preprocessing stage, this space is encoded in the form of top-opened cones and then stored in a 2D texture, and during the rendering stage, it is used to converge more quickly to the intersection point. Cone tracing technique produces satisfacto- ry results in the case of flat surfaces, but when it comes to curved surfaces, it does not support the silhouette at the edges of the 3D mesh, that is to say, the relief merges with the surface of the object, and in this case, it will not be rendered correctly. To overcome this limitation, we have presented two new cone tracing algorithms that allow taking into consideration the curvature of the 3D surface to determine the fragments belonging to the silhouette. These two algorithms are based on a quadratic approximation of the object geometry at each vertex of the 3D mesh. The main objective of this paper is to achieve a texture mapping with a realistic appearance and at a low cost so that the rendered objects will have real and complex details that are vis- ible on their entire surface and without modifying their geometry. Based on the ray-tracing algorithm, our contribution can be useful for current graphics card generation, since the programmable units and the frameworks associat- ed with the new graphics cards integrate today the technology of ray tracing.

Research on Vibration Reduction Characteristics of Continuum and Noncontinuum System on Coupling for High-Power Gear Transmission Based on Particle Damping Materials

High-power gears are widely used in various engineering fields. The gear transmission system is an extremely complex elastic system, which produces complex vibration under internal and external excitation. For the vibration and noise problems caused by transmission error, a discrete element and finite coupling method based on the particle filling rate is proposed. Firstly, the gear dynamic model was established, and the particle damper was installed in the gear to reduce the vibration of the gear. Secondly, through the coupling process, the contact force and contact position between the noncontinuous medium and the continuous medium were correctly transferred to the corresponding nodes of the finite element analysis model. Then, the equivalent displacement mapping of the contact loads’ node of the gear was realized, and the transformation of the local coordinate to the global coordinate was carried out. Finally, by combining theoretical analysis with experimental verification, the influence of the filling rate of damping particles on the vibration reduction effect of the gearbox under different working conditions was studied. The 2 mm tungsten particles were selected, and the particle damper had the best damping effect when the filling rate was 88%.

Accuracy of a Method to Monitor Root Position Using 3D Digital Crown/root Model During Orthodontic Treatments

Objectives.The objective of this retrospective clinical study was to assess the accuracy of a method of predicting post-movement root position during orthodontic treatment, using a 3D digital crown/root model (3DCRM), which was created with pre-movement records of both CBCT and dental-arch digital scans.Material & Methods.Pre-movement CBCT scans, post-movement CBCT scans, and dental-arch digital scans of five patients who had completed orthodontic treatments were used in this study with the approval of internal review board of Iwate Medical University. The 3DCRM was superimposed onto post-movement scanned dental-arch to identify the post-movement root position (test method). Post-movement CBCT (referenced as current method) served as the control used to identify the actual post-movement root position. The predicted root positions by the two methods were compared using color displacement mapping and 3D coordinate XYZ analysis.Results.Color displacement mapping showed that the average root displacement of five cases was -0.16 mm ±0.05 mm. 3D coordinate analysis revealed no significant differences between test and current methods in X and Y axis. However, the discrepancy in Z axis (especially in cases of intrusion) was greater than all other directions (mesial, distal, labial, palatal and extrusion direction) for all three tooth types examined (central incisor, lateral incisor and canine, p <0.05). A strong positive correlation between the degree of discrepancy and the distance of tooth movement was observed on the Z axis (r =0.71).Conclusions.The 3DCRM method showed promising potential to accurately predict root position during orthodontic treatments without the need for a second CBCT. However, root resorption, which affected the Z axis prediction, needs to be closely monitored using periapical radiographs to complement this method.Clinical Relevance.The 3DCRM method can be a useful tool to better evaluate root positioning during and after orthodontic treatment without the need to expose patients to an additional CBCT scan.

Reveal of Internal, Early-Load Interfacial Debonding on Cement Textile-Reinforced Sandwich Insulated Panels

Internal interfacial debonding (IID) phenomena on sandwich façade insulated panels are detected and tracked by acoustic emission (AE). The panels are made of a thin and lightweight cementitious composite skin. In the lab, the panels are tested under incremental bending simulating service loads (i.e., wind). Local (up to 150 mm wide) skin-core detachments are reported in the early loading stage (at 5% of ultimate load) and are extensively investigated in this study, since IID can detrimentally affect the long-term durability of the structural element. A sudden rise in the AE hits rate and a shift in the wave features (i.e., absolute energy, amplitude, rise time) trends indicate the debonding onset. AE source localization, validated by digital image correlation (DIC) principal strains and out-of-plane full-field displacement mapping, proves that early debonding occurs instantly and leads to the onset of cracks in the cementitious skin. At higher load levels, cracking is accompanied by local debonding phenomena, as proven by RA value increases and average frequency drops, a result that extends the state-of-the-art in the fracture assessment of concrete structures (Rilem Technical Committee 212-ACD). Point (LVDT) and full-field (AE/DIC) measurements highlight the need for a continuous and full-field monitoring methodology in order to pinpoint the debonded zones, with the DIC technique accurately reporting surface phenomena while AE offers in-volume damage tracking.