Won Man Park

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Mechanical seals, such as labyrinth seals, are typically installed at the turbine outlets to prevent oil leakage. However, these seals undergo deformation because of the vibrations of the rotor, even during normal turbine operating conditions, which may cause an increase in oil leakage. In this study, the oil leakage performance of three labyrinth...

Owing to pipe thinning, fatigue damage, and aging, pipes, valves, and devices installed in the primary and secondary systems of nuclear power plants may leak high-temperature/high-pressure reactor coolant. Thus, a system must be developed to determine if the leakage is exceeding the operating limit of the nuclear power plant, thereby mitigating any...

The rupturing of steam generator tubes leads to serious accidents in nuclear power plants. It causes radioactive materials to leak into the secondary system and release outside the reactor containment region. Therefore, it is important to model a technique to determine whether the natural circulation within a reactor coolant system (RCS) can cause...

A correction to this paper has been published: https://doi.org/10.1007/s12541-021-00543-9

Various treatment devices or tables have been developed for generating axial rotation of the lumbar spine during spinal mobilization. However, the effects of the design of such treatment devices on the axial rotation of the lumbar spine have not been thoroughly investigated. In this study, the influences of the location of the treatment table rotat...

Extragraft bone formation is crucial for obtaining a successful outcome after spinal fusion surgery. However, the cause of bone formation is not well investigated. In this study, it was hypothesised that extragraft bone formation is generated by mechanical stimuli. A preoperative plan for anterior cervical discectomy and fusion was applied to the f...

Computational models and inverse dynamic optimization methods are used to predict in-vivo spinal loading. Spinal force is conventionally predicted using the constant loading path method, which is based on the concept that the physiological directions of the spine loads follow the same path of the spinal curve. However, the global convergence optimi...

Although the clinical importance of extragraft bone formation (ExGBF) and bridging (ExGBB) has been reported, few studies have investigated the biomechanical influences of ExGBF on the motion segment. In this study, ExGBF was simulated at the C5-C6 motion segment after anterior cervical discectomy and fusion using a developed finite element model a...

Spent fuel pools are used as temporary storage for spent fuel assemblies in nuclear power plants and are filled with coolant which removes the decaying heat from spent fuel assemblies. Sloshing of the coolant can occur if an earthquake occurs in the area. It may produce additional forces on the pool or inner structure and cause overflow of the cool...

Predicting the sloshing motion of a coolant during a seismic assessment of a rectangular spent fuel pool is of critical concern. Linear theory, which provides a simple analytical method, has been used to predict the sloshing motion in rectangular pools and tanks. However, this theory is not suitable for the high-frequency excitation problem. In thi...

For automobile comfort engineering, lateral support is one of the most important factors. To analyze lateral support of a vehicle seat, it is essential to understand a driver’s upper body motion when various contexts. The purpose of this study is that developing the measurement method of driver’s lateral motion when in-vehicle condition. A verifica...

The X-ray-based reconstruction methods using anterior-posterior (AP) and lateral (LAT) images assumes that the angle between the AP and LAT images is perpendicular. However, it is difficult to maintain the perfect perpendicular angle between the AP and LAT images when taking those two images sequentially in real situations. In this study, the robus...

In short-track speed skating, the three-dimensional kinematics of the lower extremities during the whole skating cycle have not been studied. Kinematic parameters of the lower extremities during skating are presented as joint angles versus time. However, the angle-time presentation is not sufficient to describe the relationship between multi-joint...

In order to clearly understand the injury mechanism of the Lateral ankle sprain (LAS), we purposed to evaluate the ligament strains in the human ankle joint during the real accidental events of LAS. Three different accidental ankle sprain cases were selected based on their reported motions, which are rarely captured under laboratory settings. The l...

Myelopathy in the cervical spine due to cervical ossification of the posterior longitudinal ligament could be induced by static compression and/or dynamic factors. It has been suggested that dynamic factors need to be considered when planning and performing the decompression surgery on patients with the ossification of the posterior longitudinal li...

Post-operative C5 palsies are among the most common complications seen after cervical surgery for ossification of the posterior longitudinal ligament (OPLL). Although C5 palsy is a well-known complication of cervical spine surgery, its pathogenesis is poorly understood and depends on many other factors. In this study, a finite element model of the...

A golf-related ACL injury can be linked with excessive golf play or practice because such over-use by repetitive golf swing motions can increase damage accumulation to the ACL bundles. In this study, joint angular rotations, forces, and moments, as well as the forces and strains on the ACL of the target-side knee joint, were investigated for ten pr...

The development of heterotopic ossification (HO) is considered one of the major complications following cervical total disc replacement (TDR). Even though previous studies have identified clinical and biomechanical conditions that may stimulate HO, the mechanism of HO formation has not been fully elucidated. The objective of this study is to invest...

Clinically, spinal cord injuries (SCIs) are radiographically evaluated and diagnosed from plain radiographs, computed tomography (CT) or magnetic resonance imaging, although the von-Mises stress and maximum principal strain are directly associated with neurological damages in the spinal cord from a biomechanical viewpoint. In this study, we develop...

Ossification of the posterior longitudinal ligament is a common cause of the cervical myelopathy due to compression of the spinal cord. Patients with ossification of the posterior longitudinal ligament usually require the decompression surgery, and there is a need to better understand the optimal surgical extent with which sufficient decompression...

Study design: A biomechanical comparison among the intact C2-C7 segments, the C5-C6 segments implanted with fusion cage and three different artificial disc replacements (ADR) by finite element (FE) model creation reflecting the entire cervical spine below C2. Objective: To analyze the biomechanical changes in subaxial cervical spine after ADR an...

Spinal fusion surgery is a widely used surgical procedure for sagittal realignment. Clinical studies have reported that spinal fusion may cause proximal junctional kyphosis and failure with disc failure, vertebral fracture, and/or failure at the implant-bone interface. However, the biomechanical injury mechanisms of proximal junctional kyphosis and...

Dynesys® is one of the pedicle-based dynamic lumbar stabilization systems and good clinical outcome has been reported. However, the cylindrical spacer between the heads of the screws undergoes deformation during assembly of the system. The pre-strain probably change the angle of instrumented spine with time and oblique-shaped spacer may reduce the...

Degeneration of the intervertebral discs and facet joints is considered a source of pain in the cervical spine. In this study, we developed finite element models of cervical spines that were healthy or had various extents of degeneration and investigated changes in biomechanical behaviors of the cervical spine, such as range of motion (ROM), intrad...

Accurate measurement of the center of rotation of the knee joint is indispensable for prediction of joint kinematics and kinetics in musculoskeletal models. However, no study has yet identified the knee center of rotations during several daily activities before and after high tibial osteotomy surgery, which is one surgical option for treating knee...

Ligatures are used with many types of interspinous process devices to prevent instability in flexion movement by wrapping around upper and lower spinous processes. In this study, the effects of the pre-tension by tightening the ligature on the spinous process fracture were investigated using a finite element method. Five different interspinous proc...

Traction therapy is one of the most common conservative treatments for low back pain. However, the effects of traction therapy on lumbar spine biomechanics are not well known. We investigated biomechanical effects of two-step traction therapy, which consists of global axial traction and local decompression, on the lumbar spine using a validated thr...

Finite element (FE) model studies have made important contributions to our understanding of functional biomechanics of the lumbar spine. However, if a model is used to answer clinical and biomechanical questions over a certain population, their inherently large inter-subject variability has to be considered. Current FE model studies, however, gener...

A protocol to choose the graft diameter attachment point of each bundle has not yet been determined since they are usually dependent on a surgeon's preference. Therefore, the influence of bundle diameters and attachment points on the kinematics of the knee joint needs to be quantitatively analyzed. A three-dimensional knee model was reconstructed w...

Knowledge of in vivo human lumbar loading is critical for understanding the lumbar function and for improving surgical treatments of lumbar pathology. Although numerous experimental measurements and computational simulations have been reported, non-invasive determination of in vivo spinal disc loads is still a challenge in biomedical engineering. T...

Although the conventional total knee arthoplasty (TKA) planning used 2D or 3D images of the patient’s lower extremity to determine bone alignment, it was shown that good bone alignment does not always guarantee successful results due to unbalanced joint contact forces and soft tissue tension. Thus, the joint contact force balance and soft tissue te...

The effects of intervertebral disc (IVD) degeneration on biomechanics of the lumbar spine were analyzed. Finite element models of the lumbar spine with various degrees of IVD degeneration at the L4-L5 functional spinal unit (FSU) were developed and validated. With progression of degeneration, intersegmental rotation at the degenerated FSU decreased...

The placement of artificial disks can alter the center of rotation and kinematic pattern; therefore, forces in the spine during the motion will be affected as a result. The relationship between the location of joint center of artificial disks and forces in the spinal components is not investigated. A musculoskeletal model of the spine was developed...

Background context: Lumbar degenerative spondylolisthesis (DS), typically characterized by the forward slippage of the superior vertebra of a lumbar motion segment, is a common spinal pathological condition in elderly individuals. Significant deformation and volume changes of the spinal canal can occur because of the vertebral slippage, but few da...

Unbalanced contact force on the tibial component has been considered a factor leading to loosening of the implant and increased wear of the bearing surface in total knee arthroplasty. Because it has been reported that good alignment cannot guarantee successful clinical outcomes, the soft tissue balance should be checked together with the alignment....

The consideration of biomechanical alterations due to intervertebral disc (IVD) degeneration is crucial for the accurate analysis of spine biomechanics. In this study, finite element (FE) models of the L4-L5 motion segment with full coverage of the degeneration grades from healthy IVD to severe degeneration were developed. The effects of IVD degene...

It may be assumed that the stability is affected when some ligaments are injured or loosened, and this joint instability causes sacroiliac joint pain. Several physical examinations have been used to diagnose sacroiliac pain and to isolate the source of the pain. However, more quantitative and objective information may be necessary to identify unsta...

Objective: Although some studies have reported on the kinematics of the lumbar segments with degenerative spondylolisthesis (DS), few data have been reported on the in vivo 6 degree-of-freedom kinematics of different anatomical structures of the diseased levels under physiological loading conditions. This research is to study the in vivo motion ch...

The most common reason for occupational low back pain is the overload on the spine [1]. Determination of the load on the spine is critical for preventing low back pain, understanding injury mechanism and developing treatment techniques and surgical implants. However, due to the limitations in technology, only few in-vivo measurements were performed...

Evaluation of the loads on lumbar intervertebral discs (IVD) is critically important since it is closely related to spine biomechanics, pathology and prosthesis design. Non-invasive estimation of the loads in the discs remains a challenge. In this study, we proposed a new technique to estimate in vivo loads in the IVD using a subject-specific finit...

Determination of physiological loads in human lumbar spine is critical for understanding the mechanisms of lumbar diseases and for designing surgical treatments. Computational models have been used widely to estimate the physiological loads of the spine during simulated functional activities. However, various assumptions on physiological factors su...

In experimental and clinical research, it is difficult to directly measure responses in the human body, such as contact pressure and stress in a joint, but finite element analysis (FEA) enables the examination of in vivo responses by contact analysis. Hence, FEA is useful for pre-operative planning prior to orthopaedic surgeries, in order to gain i...

Three-dimensional patient-specific bone models have been used in computer-aided planning and biomechanical analysis of orthopaedic surgeries. Reconstruction methods using X-ray images have been developed recently. However, these reconstruction methods have limited ability to generate femur models with severe rotational deformities. In this study, a...

Evaluation of the forces on the lumbar intervertebral discs (IVDs) is critically important since it closely relates to biomechanics, pathology, prosthesis design and tissue engineering. It remains a big challenge to noninvasively predict the in vivo forces on the IVD. Using our previously established dual fluoroscopic imaging system (DFIS) [1], mot...

A biomechanical comparison between the intact C2-C7 segments and the C5-C6 segments implanted with two different constrained types (fixed and mobile core) of artificial disc replacement (ADR) using a three-dimensional nonlinear finite element (FE) model. To analyze the biomechanical changes in subaxial cervical spine after ADR and the differences b...

When using continuous passive motion (CPM) devices, appropriate setting of the device and positioning of the patient are necessary to obtain maximum range of motion (ROM). In this study, the ROMs in both the knee joint and CPM device during CPM treatment were measured using a motion analysis system for three different CPM devices. Additionally, the...

Posterior cruciate ligament injuries commonly occur during sports activities or motor vehicle accidents. However, there is no previous comparison study of single bundle reconstruction, double bundle reconstruction, and double bundle augmentation with respect to biomechanical characteristics such as stability and ligament stress. A three-dimensional...

During computer navigated total knee arthroplasty, pin holes are drilled in the femur and tibia to allow the placement of navigation trackers, and fractures associated with these pin holes have recently been reported. We hypothesized that an increase in stress around the pin holes is one of the most relevant factors contributing to the fracture. In...

Estimation of in-vivo joint contact forces and muscle forces during walking is important in order to protect the knee joint from injury or provide adequate rehabilitation and exercise protocols [1]. Assessment of muscle forces can help to understand the neuro-muscular coordination related on neurological problems [2]. Accurate quantification of joi...

Breakage of screws has been one of the most common complications in spinal fixation systems. However, no studies have examined the breakage risk of pedicle screw fixation systems that use flexible rods, even though flexible rods are currently being used for dynamic stabilization. In this study, the risk of breakage of screws for the rods with vario...

There are several surgical techniques currently employed to treat thoracolumbar burst fractures, including anterior fixation, posterior fixation, or combined anterior-posterior fixation. Biomechanical analysis of the various types of surgical techniques is therefore critical to enable selection of the appropriate surgical method for successful spin...

The hip joint diseases have various kinds of origination, and they have multifarious forms according to the originations. One of the major concerns to plan the surgical operation for the hip diseases is the alternation of biomechanical environment, such as joint force and contact pressure. In this study, we analyzed the biomechanical effects of sur...

We have analyzed the biomechanical characteristics of cervical spine after total disc replacement using finite element analysis. A finite element model of C2-C7 spinal motion segment was developed and validated by other experimental studies. Two types of artificial discs, semi-constraint and un-constraint, were inserted at C6-C7 segments. Inferior...

With recent advances in data communications and robotic engineering, surgical robots have evolved into telerobotic surgical platforms that permit surgeons to operate on patients from remote locations using robotic instruments. Even so, telesurgical systems need to be improved by considering haptic sense or force feedback. In this study, a laborator...

Total knee arthroplasty(TKA) using computer-assisted navigation has been increased in order to improve the accuracy of femoral and tibial components implantation. Recently, a few clinical studies have reported on the femoral stress fracture after TKA using computer-assisted navigation. The purpose of this study is to investigate the stress concentr...

The artificial discs have recently used to preserve the motion of the treated segment in lumbar spine surgery. However, there have been lack of biomechanical information of the artificial discs to explain current clinical controversies such as long-term results of implant wear and excessive facet contact forces. In this study, we investigated the b...

Spinal fixation is a common surgical method to stabilize the unstable spines using internal devices. However, excessive intervertebral motions and stresses of adjacent segments are produced. The potential use of dynamic stabilization as a novel approach to spinal fixation is currently being investigated. In this study, the virtual biomechanical tes...

To evaluate the biomechanical results according to various anterior spinal fixation methodology in the treatment of thoracolumbar spine fracture.

Finite element models of the thoracolumbar spine with various techniques used in spinal fractures were developed to investigate the effects of fixation techniques on spinal stiffness.

Finite element contact analyses of dysplastic hip joints were performed based on CT and MR images as a surgical planning tool of the shelf operation. The 3-D cartilage thickness was approximated using MRI, and the joint contact force was calculated from a 3-D expansion of the Ninomiya's method. After surgical planning, the anatomical parameters inc...

In spite of the importance of nuclear power as one of major electric energies in Korea, the nuclear safety has become the most serious social issue in the operation of the nuclear power plant. In this paper, a virtual work simulation program was developed to predict exposure dose during radiation work in radwaste storage. The work simulation progra...

Since the safety of nuclear power plant has been becoming a big social issue the exposure dose of radiation for workers has been one of the important factors concerning the safety problem. The existing calculation methods of radiation dose used in the planning of radiation work assume that dose rate does not depend on the location within a work spa...

In this study, a simulation program based on virtual environment concerning radiation work at nuclear power plants was developed. VRML and Java Applet were used to develop this simulation program. Radiation exposure levels were predicted through radiation work in a virtual reality environment, and high dose danger zones were visually represented by...